The genetic basis of a plant-insect coevolutionary key innovation

Linking plant genes to arthropod community dynamics: current progress and future challenges

Plant genetic variation can play a key role in shaping ecological communities. Prior work investigated the effects of coarse-grain variation among plant genotypes on their diverse arthropod communities. Several recent studies, however, have leveraged the boom of genomic resources to study how genome-wide plant variation influences associated communities. These studies have demonstrated that the effects of plant genomic variation are not just detectable but can be important drivers of arthropod communities in natural ecosystems. Field common gardens and lab-based mesocosm experiments are also revealing candidate genes that have large effects on arthropod communities. While we highlight these exciting results, we also discuss key challenges to address in future research. We argue that a major hurdle lies in the integration of genomic tools with hierarchical models of species communities (HMSCs). HMSCs are generative models that provide the opportunity to not only better understand the processes underlying community change but to also predict community dynamics. We also advocate for future research to apply models of genomic prediction to explore the genetic architecture of arthropod community phenotypes. We hypothesize that this genetic architecture will follow an exponential distribution, where a few genes of large effect, but also many genes of small effect, contribute to variation in arthropod communities. The next generation of studies linking plant genes to community dynamics will require interdisciplinary collaborations to build truly predictive models of plant genetic and arthropod community change.

Defensive Compounds Involved in the Invasiveness of Tithonia diversifolia

Tithonia diversifolia (Hemsl.) A. Gray forms high-density impenetrable monospecific stands as an invasive plant species. Its life history traits, such as high adaptability with high genetic variation under different environmental conditions, and high growth and reproductive capacity, may contribute to its success in invading and increasing its population in the introduced ranges. Evidence has accumulated in the literature for the activity of compounds involved in the invasive characteristics of Tithonia diversifolia against natural enemies such as herbivorous insects and mammals, pathogenic nematodes, fungi, and viruses, and of allelochemicals against neighboring competitive plant species. Tagitinin A, tagitinin C, 1β-methoxydiversifolin, phytol, phytol acetate, α-pinene, bicyclo[3.1.0]hexane,4-methylene-1-(1-methylethyl), hispidulin, dihydro-p-coumaric acid, and methyl linoleate are toxic to herbivorous insects, and tagitinin C and 5-O-(E)-caffeoylquinic acid are harmful to herbivorous mammals. Tirotundin has nematocidal activity. α-Pinene, camphor, eucalyptol, and α-terpineol have fungicidal activity. Tagitinin A, tagitinin C, and 1β-methoxydiversifolin-3-O-methyl ether have antiviral activity. Tagitinin A, tagitinin C, 1β-methoxydiversifolin, and hispidulin act as allelochemicals that inhibit the growth of neighboring competing plant species. The ability to outcompete natural enemies and competing plant species is one of the essential factors for infestation and increase in the population and distribution of Tithonia diversifolia in new habitats. Therefore, these compounds may be involved in the invasive characteristics of Tithonia diversifolia. This is the first review article focusing on the compounds involved in the invasive characteristics of Tithonia diversifolia.

The Salient Aroma Hypothesis: host plant specialization is linked with plant volatile availability in Lepidoptera

Host plant use in Lepidoptera has been a primary focus in studies of ecological specialization, and multiple factors are likely to be involved in shaping the evolution of diet breadth. Here, we first describe the Salient Aroma Hypothesis, suggesting that the availability of chemical information, particularly host-associated aromas, plays a critical role in shaping dietary specialization. According to the Salient Aroma Hypothesis, herbivores active during periods when chemical information is abundant, particularly during the daytime hours when plant aromas are hypothesized to be more prevalent, are more likely to evolve specialized diets. First, with meta-analysis, we show that plants release more diverse and abundant volatile compounds during daylight hours, increasing the availability of chemical information. We found that diurnal Lepidoptera tend to have specialized diets, while nocturnal species are more generalized, consistent with the prediction of the Salient Aroma Hypothesis. We further observed that morphological differences in the antennae of female Lepidoptera are correlated with variation in diet breadth and diel activity patterns, indirectly supporting the Salient Aroma Hypothesis. While multiple factors influence host plant specialization, the Salient Aroma Hypothesis offers a useful framework linking chemical information availability (e.g. plant volatiles) and ecological specialization.

Why Do Some Lineages Radiate While Others Do Not? Perspectives for Future Research on Adaptive Radiations

Understanding the processes that drive phenotypic diversification and underpin speciation is key to elucidating how biodiversity has evolved. Although these processes have been studied across a wide array of clades, adaptive radiations (ARs), which are systems with multiple closely related species and broad phenotypic diversity, have been particularly fruitful for teasing apart the factors that drive and constrain diversification. As such, ARs have become popular candidate study systems for determining the extent to which ecological features, including aspects of organisms and the environment, and inter- and intraspecific interactions, led to evolutionary diversification. Despite substantial past empirical and theoretical work, understanding mechanistically how ARs evolve remains a major challenge. Here, we highlight a number of understudied components of the environment and of lineages themselves, which may help further our understanding of speciation and AR. We also outline some substantial remaining challenges to achieving a detailed understanding of adaptation, speciation, and the role of ecology in these processes. These major challenges include identifying factors that have a causative impact in promoting or constraining ARs, gaining a more holistic understanding of features of organisms and their environment that interact resulting in adaptation and speciation, and understanding whether the role of these organismal and environmental features varies throughout the radiation process. We conclude by providing perspectives on how future investigations into the AR process can overcome these challenges, allowing us to glean mechanistic insights into adaptation and speciation.

A classic key innovation constrains oral jaw functional diversification in fishes

Modifications to the pharyngeal jaws-a prey processing system located posterior to the mouth cavity-are widely considered a key innovation that enhanced diversification within several prominent fish clades. Seen in cichlids, damselfishes, wrasses, and a few other lineages, these musculoskeletal alterations are believed to increase the evolutionary independence and, thus, the diversification of the oral and pharyngeal jaw systems. To test this classic hypothesis, we conducted comparative phylogenetic analyses to assess the effect of the pharyngeal novelty on the diversification of feeding morphology and kinematics across a taxonomically diverse sample of spiny-rayed fishes. We quantified movements of the oral jaws and other craniofacial structures from 689 suction-feeding strikes using high-speed videos collected from 228 species with and without the pharyngeal jaw novelty. Contradicting long-held predictions, we find significantly greater disparity across all traits and faster rates of oral jaw functional evolution in fishes without the specialized prey processing system. The modified pharyngeal jaw is undoubtedly a functional innovation as it enhances the strength of the prey processing system, facilitating exceptional transition rates to feeding on hard and tough prey. However, it also restricts the diversification of the feeding system, revealing that the impact of pharyngognathy is more nuanced than previously thought. In light of these and other recent findings, a reinterpretation of the macroevolutionary consequences of the pharyngeal jaw novelty is needed.

Common misconceptions of speciation

Speciation is a complex process that can unfold in many different ways. Speciation researchers sometimes simplify core principles in their writing in a way that implies misconceptions about the speciation process. While we think that these misconceptions are usually inadvertently implied (and not actively believed) by the researchers, they nonetheless risk warping how external readers understand speciation. Here we highlight six misconceptions of speciation that are especially widespread. First, species are implied to be clearly and consistently defined entities in nature, whereas in reality species boundaries are often fuzzy and semipermeable. Second, speciation is often implied to be 'good', which is two-fold problematic because it implies both that evolution has a goal and that speciation universally increases the chances of lineage persistence. Third, species-poor clades with species-rich sister clades are considered 'primitive' or 'basal', falsely implying a ladder of progress. Fourth, the evolution of species is assumed to be strictly tree-like, but genomic findings show widespread hybridization more consistent with network-like evolution. Fifth, a lack of association between a trait and elevated speciation rates in macroevolutionary studies is often interpreted as evidence against its relevance in speciation-even if microevolutionary case studies show that it is relevant. Sixth, obvious trait differences between species are sometimes too readily assumed to be (i) barriers to reproduction, (ii) a stepping-stone to inevitable speciation, or (iii) reflective of the species' whole divergence history. In conclusion, we call for caution, particularly when communicating science, because miscommunication of these ideas provides fertile ground for misconceptions to spread.

Patterns of genetic variation and local adaptation of a native herbivore to a lethal invasive plant

Understanding the evolutionary processes that influence fitness is critical to predicting species' responses to selection. Interactions among evolutionary processes including gene flow, drift and the strength of selection can lead to either local adaptation or maladaptation, especially in heterogenous landscapes. Populations experiencing novel environments or resources are ideal for understanding the mechanisms underlying adaptation or maladaptation, specifically in locally co-evolved interactions. We used the interaction between a native herbivore that oviposits on a patchily distributed introduced plant that in turn causes significant mortality to the larvae to test for signatures of local adaptation in areas where the two co-occurred. We used whole-genome sequencing to explore population structure, patterns of gene flow and signatures of local adaptation. We found signatures of local adaptation in response to the introduced plant in the absence of strong population structure with no genetic differentiation and low genetic variation. Additionally, we found localized allele frequency differences within a single population between habitats with and without the lethal plant, highlighting the effects of strong selection. Finally, we identified that selection was acting on larval ability to feed on the plant rather than on females' ability to avoid oviposition, thus uncovering the specific ontogenetic target of selection. Our work highlights the potential for adaptation to occur in a fine-grained landscape in the presence of gene flow and low genetic variation.

Oviposition strategies in Pieridae butterflies and the role of an egg-killing plant trait therein

Most herbivorous insects are host-plant specialists that evolved detoxification mechanisms to overcome their host plant's toxins. In the evolutionary arms-races between Pieridae butterflies and Brassicaceae plants, some plant species have evolved another defence against the pierids: egg-killing. Underneath the eggs, leaves develop a so-called hypersensitive response (HR)-like cell death. Whether some butterflies have evolved oviposition strategies to counter-adapt against egg-killing remains to be studied. In this study, we assessed the oviposition site location of Pieridae butterflies on their natural host plants. We described the plant tissue on which we located the eggs of the most common Pieridae in the Netherlands: Gonepteryx rhamni, Anthocharis cardamines, Pieris rapae, P. napi, P. brassicae and P. mannii. Additionally, we assessed expression of HR-like cell death in response to the deposited butterfly eggs. We found that both A. cardamines and G. rhamni mainly oviposited on the floral stem and the branch, respectively, and oviposited on host plants from lineages not expected to kill pierid eggs. Accordingly, no HR-like cell death was seen. All Pieris eggs found were located on leaves of their host, the only tissue found to express HR-like cell death. Furthermore, each Pieris species was found to at least occasionally oviposit on Brassica nigra. This was the only plant species in this survey that expressed HR-like cell death in response to the eggs of P. rapae, P. napi and P. brassicae. Our observations demonstrate that HR-like cell death remains an effective defence strategy against these Pieris species and as such did not find evidence for the hypothesized counterstrategies. Surveying certain key species and disentangling the micro-evolution of oviposition strategies within a species would allow us to further investigate potential counter-adaptations that evolved against HR-like cell death. This study provides the basis for further investigation of potential counter-adaptations to egg-killing defences.

De Novo Genome Assembly and Annotation of Leptosia nina Provide New Insights into the Evolutionary Dynamics of Genes Involved in Host-Plant Adaptation of Pierinae Butterflies

In interactions between plants and herbivorous insects, the traits enabling phytophagous insects to overcome chemical defenses of their host plants have evolved multiple times. A prominent example of such adaptive key innovations in herbivorous insects is nitrile specifier proteins (NSPs) that enabled Pierinae butterflies to colonize Brassicales host plants that have a glucosinolate-myrosinase defense system. Although the evolutionary aspects of NSP-encoding genes have been studied in some Pierinae taxa (especially among Pieris butterflies), the ancestral evolutionary state of NSPs is unclear due to the limited genomic information available for species within Pierinae. Here, we generate a high-quality genome assembly and annotation of Leptosia nina, a member of a small tribe, Leptosiaini. L. nina uses as its main host Capparaceae plants, one of the ancestral hosts within Pierinae. By using ∼90-fold coverage of Oxford Nanopore long reads and Illumina short reads for subsequent polishing and error correction, we constructed a final genome assembly that consisted of 286 contigs with a total of 225.8 Mb and an N50 of 10.7 Mb. Genome annotation with transcriptome hints predicted 16,574 genes and covered 98.3% of BUSCO genes. A typical NSP gene is composed of three tandem domains found in Pierinae butterflies; unexpectedly, we found a new NSP-like gene in Pierinae composed of only two tandem domains. This newly found NSP-like gene in L. nina provides important insights into the evolutionary dynamics of domain and gene duplication events relating to host-plant adaptation in Pierinae butterflies.

Nitrile biosynthesis in nature: how and why?

Covering: up to the end of 2023Natural nitriles comprise a small set of secondary metabolites which however show intriguing chemical and functional diversity. Various patterns of nitrile biosynthesis can be seen in animals, plants, and microorganisms with the characteristics of both evolutionary divergence and convergence. These specialized compounds play important roles in nitrogen metabolism, chemical defense against herbivores, predators and pathogens, and inter- and/or intraspecies communications. Here we review the naturally occurring nitrile-forming pathways from a biochemical perspective and discuss the biological and ecological functions conferred by diversified nitrile biosyntheses in different organisms. Elucidation of the mechanisms and evolutionary trajectories of nitrile biosynthesis underpins better understandings of nitrile-related biology, chemistry, and ecology and will ultimately benefit the development of desirable nitrile-forming biocatalysts for practical applications.

Comprehensive phylogeny of Pieridae butterflies reveals strong correlation between diversification and temperature

Temperature is thought to be a key factor influencing global species richness patterns. We investigate the link between temperature and diversification in the butterfly family Pieridae by combining next generation DNA sequences and published molecular data with fine-grained distribution data. We sampled nearly 600 pierid butterfly species to infer the most comprehensive molecular phylogeny of the family and curated a distribution dataset of more than 800,000 occurrences. We found strong evidence that species in environments with more stable daily temperatures or cooler maximum temperatures in the warm seasons have higher speciation rates. Furthermore, speciation and extinction rates decreased in tandem with global temperatures through geological time, resulting in a constant net diversification.

Host genetics and larval host plant modulate microbiome structure and evolution underlying the intimate insect-microbe-plant interactions in Parnassius species on the Qinghai-Tibet Plateau

Insects harbor a remarkable diversity of gut microbiomes critical for host survival, health, and fitness, but the mechanism of this structured symbiotic community remains poorly known, especially for the insect group consisting of many closely related species that inhabit the Qinghai-Tibet Plateau. Here, we firstly analyzed population-level 16S rRNA microbial dataset, comprising 11 Parnassius species covering 5 subgenera, from 14 populations mostly sampled in mountainous regions across northwestern-to-southeastern China, and meanwhile clarified the relative importance of multiple factors on gut microbial community structure and evolution. Our findings indicated that both host genetics and larval host plant modulated gut microbial diversity and community structure. Moreover, the effect analysis of host genetics and larval diet on gut microbiomes showed that host genetics played a critical role in governing the gut microbial beta diversity and the symbiotic community structure, while larval host plant remarkably influenced the functional evolution of gut microbiomes. These findings of the intimate insect-microbe-plant interactions jointly provide some new insights into the correlation among the host genetic background, larval host plant, the structure and evolution of gut microbiome, as well as the mechanisms of high-altitude adaptation in closely related species of this alpine butterfly group.

Specificity and breadth of plant specialized metabolite-microbe interactions

Plant specialized metabolites shape plant interactions with the environment including plant-microbe interactions. While we often group compounds into generic classes, it is the precise structure of a compound that creates a specific role in plant-microbe or-pathogen interactions. Critically, the structure guides definitive targets in individual interactions, yet single compounds are not limited to singular mechanistic targets allowing them to influence interactions across broad ranges of attackers, from bacteria to fungi to animals. Further, the direction of the effect can be altered by counter evolution within the interacting organism leading to single compounds being both beneficial and detrimental. Thus, the benefit of a single compound to a host needs to be assessed by measuring the net benefit across all interactions while in each specific interaction. Factoring this complexity for single compounds in plant-microbe interactions with the massive expansion in our identification of specialized metabolite pathways means that we need systematic studies to classify the full breadth of activities. Only with this full biological knowledge we can develop mechanistic, ecological, and evolutionary models to understand how plant specialized metabolites fully influence plant-microbe and plant-biotic interactions more broadly.

A semiochemical view of the ecology of the seed beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae, Bruchinae)

The dried bean beetle, Acanthoscelides obtectus, is an economically important pest of stored legumes worldwide. Tracking the human-aided dispersion of its primary hosts, the Phaseolus vulgaris beans, it is now widespread in most bean-growing areas of the tropics and subtropics. In temperate regions where it can only occasionally overwinter in the field, A. obtectus proliferates in granaries, having multiple generations a year. Despite its negative impact on food production, no sensitive detection or monitoring tools exist, and the reduction of local populations still relies primarily on inorganic insecticides as fumigating agents. However, in the quest to produce more nutritious food more sustainably and healthily, the development of environmentally benign crop protection methods is vital against A. obtectus. For this, knowledge of the biology and chemistry of both the host plant and its herbivore will underpin the development of, among others, chemical ecology-based approaches to form an essential part of the toolkit of integrated bruchid management. We review the semiochemistry of the mate- and host-finding behaviour of A. obtectus and provide new information about the effect of seed chemistry on the sensory and behavioural ecology of host acceptance and larval development.

Evolution of realized niche breadth diversity driven by community dynamics

Why many herbivorous insects are host plant specialists, with non-negligible exceptions, is a conundrum of evolutionary biology, especially because the host plants are not necessarily optimal larval diets. Here, I present a novel model of host plant preference evolution of two insect species. Because habitat preference evolution is contingent upon demographic dynamics, I integrate the evolutionary framework with the modern coexistence theory. The results show that the two insect species can evolve into a habitat specialist and generalist, when they experience both negative and positive frequency-dependent community dynamics. This happens because the joint action of positive and negative frequency dependence creates multiple (up to nine) eco-evolutionary equilibria. Furthermore, initial condition dependence due to positive frequency dependence allows specialization to poor habitats. Thus, evolved habitat preferences do not necessarily correlate with the performances. The model provides explanations for counterintuitive empirical patterns and mechanistic interpretations for phenomenological models of niche breadth evolution.

The Adaptation Front Equation Explains Innovation-Driven Taxonomic Turnovers and Living Fossilization

AbstractEvolutionary taxonomic turnovers are often associated with innovations beneficial in various ecological niches. Such innovations can repeatedly occur in species occupying optimum niches for a focal species group, resulting in their repeated diversifications and species flows from optimum to suboptimum niches, at the expense of less innovated ones. By combining species packing theory and adaptive dynamics theory, we develop an equation that allows analytical prediction for such innovation-driven species flows over a niche space of arbitrary dimension under a unimodal carrying capacity distribution. The developed equation and simulated evolution show that central niches (with the highest carrying capacities) tend to attain the fastest innovation speeds to become biodiversity sources. Species that diverge from the central niches outcompete the indigenous species in peripheral niches. The outcompeted species become extinct or evolve directionally toward far more peripheral niches. Because of this globally acting process over niches, species occupying the most peripheral niches are the least innovated and have deep divergence times from their closest relatives, and thus they correspond to living fossils. The extension of this analysis for multiple geographic regions shows that living fossils are also expected in geographically peripheral regions for the focal species group.

Innate functions of natural products: A promising path for the identification of novel therapeutics

In the course of evolution, living organisms have become well equipped with diverse natural products that serve important functions, including defence from biotic and abiotic stress, growth regulation, reproduction, metabolism, and epigenetic regulation. It seems to be the organism's ecological niche that influences the natural product's structural and functional diversity. Indeed, natural products constitute the nuts and bolts of molecular co-evolution and ecological relationships among different life forms. Since natural products in the form of specialized secondary metabolites exhibit biological functions via interactions with specific target proteins, they can provide a simultaneous glimpse of both new therapeutics and therapeutic targets in humans as well. In this review, we have discussed the innate role of natural products in the ecosystem and how this intrinsic role provides a futuristic opportunity to identify new drugs and therapeutic targets rapidly.

Synthesis and Biological Activity of Sulfamate-Adamantane Derivatives as Glucosinolate Sulfatase Inhibitors

The glucosinolate-myrosinase system, exclusively found in the Brassicaceae family, is a main defense strategy against insect resistance. The efficient detoxification activity of glucosinolate sulfatases (GSSs) has successfully supported the feeding of Plutella xylostella on cruciferous plants. With the activity of GSSs hampered in P. xylostella, the toxic isothiocyanates produced from glucosinolates severely impair larval growth and adult reproduction. Therefore, inhibitors of GSSs have been suggested as an alternative approach to controlling P. xylostella. Herein, we synthesized eight adamantyl-possessing sulfamate derivatives as novel inhibitors of GSSs. Adam-20-S exhibited the most potent GSS inhibitory activity, with an IC50 value of 9.04 mg/L. The suppression of GSSs by Adam-20-S impaired glucosinolate metabolism to produce more toxic isothiocyanates in P. xylostella. Consequently, the growth and development of P. xylostella were significantly hindered when feeding on the host plant. Our study may help facilitate the development of a comprehensive pest management strategy that combines insect detoxification enzyme inhibitors with plant chemical defenses.

Roles of insect odorant binding proteins in communication and xenobiotic adaptation

Odorant binding proteins (OBPs) are small water-soluble proteins mainly associated with olfaction, facilitating the transport of odorant molecules to their relevant receptors in the sensillum lymph. While traditionally considered essential for olfaction, recent research has revealed that OBPs are engaged in a diverse range of physiological functions in modulating chemical communication and defense. Over the past 10 years, emerging evidence suggests that OBPs play vital roles in purifying the perireceptor space from unwanted xenobiotics including plant volatiles and pesticides, potentially facilitating xenobiotic adaptation, such as host location, adaptation, and pesticide resistance. This multifunctionality can be attributed, in part, to their structural variability and effectiveness in transporting, sequestering, and concealing numerous hydrophobic molecules. Here, we firstly overviewed the classification and structural properties of OBPs in diverse insect orders. Subsequently, we discussed the myriad of functional roles of insect OBPs in communication and their adaptation to xenobiotics. By synthesizing the current knowledge in this field, our review paper contributes to a comprehensive understanding of the significance of insect OBPs in chemical ecology, xenobiotic adaptation, paving the way for future research in this fascinating area of study.

Convergent resistance to GABA receptor neurotoxins through plant-insect coevolution

The molecular mechanisms of coevolution between plants and insects remain elusive. GABA receptors are targets of many neurotoxic terpenoids, which represent the most diverse array of natural products known. Over deep evolutionary time, as plant terpene synthases diversified in plants, so did plant terpenoid defence repertoires. Here we show that herbivorous insects and their predators evolved convergent amino acid changing substitutions in duplicated copies of the Resistance to dieldrin (Rdl) gene that encodes the GABA receptor, and that the evolution of duplicated Rdl and terpenoid-resistant GABA receptors is associated with the diversification of moths and butterflies. These same substitutions also evolved in pests exposed to synthetic insecticides that target the GABA receptor. We used in vivo genome editing in Drosophila melanogaster to evaluate the fitness effects of each putative resistance mutation and found that pleiotropy both facilitates and constrains the evolution of GABA receptor resistance. The same genetic changes that confer resistance to terpenoids across 300 Myr of insect evolution have re-evolved in response to synthetic analogues over one human lifespan.

Evolution of chemosensory and detoxification gene families across herbivorous Drosophilidae

Herbivorous insects are exceptionally diverse, accounting for a quarter of all known eukaryotic species, but the genomic basis of adaptations that enabled this dietary transition remains poorly understood. Many studies have suggested that expansions and contractions of chemosensory and detoxification gene families-genes directly mediating interactions with plant chemical defenses-underlie successful plant colonization. However, this hypothesis has been challenging to test because the origins of herbivory in many insect lineages are ancient (>150 million years ago (mya)), obscuring genomic evolutionary patterns. Here, we characterized chemosensory and detoxification gene family evolution across Scaptomyza, a genus nested within Drosophila that includes a recently derived (<15 mya) herbivore lineage of mustard (Brassicales) specialists and carnation (Caryophyllaceae) specialists, and several nonherbivorous species. Comparative genomic analyses revealed that herbivorous Scaptomyza has among the smallest chemosensory and detoxification gene repertoires across 12 drosophilid species surveyed. Rates of gene turnover averaged across the herbivore clade were significantly higher than background rates in over half of the surveyed gene families. However, gene turnover was more limited along the ancestral herbivore branch, with only gustatory receptors and odorant-binding proteins experiencing strong losses. The genes most significantly impacted by gene loss, duplication, or changes in selective constraint were those involved in detecting compounds associated with feeding on living plants (bitter or electrophilic phytotoxins) or their ancestral diet (fermenting plant volatiles). These results provide insight into the molecular and evolutionary mechanisms of plant-feeding adaptations and highlight gene candidates that have also been linked to other dietary transitions in Drosophila.

Cycad phylogeny predicts host plant use of Eumaeus butterflies

Eumaeus butterflies are obligate herbivores of Zamia, the most diverse neotropical genus of cycads. Eumaeus-Zamia interactions have been characterized mainly for species distributed in North and Central America. However, larval host plant use by the southern Eumaeus clade remains largely unknown, precluding a comprehensive study of co-evolution between the genera. Here, we combine fieldwork with museum and literature surveys to expand herbivory records for Eumaeus from 21 to 38 Zamia species. We inferred a time-calibrated phylogeny of Eumaeus to test for distinct macroevolutionary scenarios of larval host plant conservatism and co-evolution. We found a remarkable coincidence between Eumaeus and Zamia diversification, with the butterfly stem group diverging at the same time as the most recent radiation of Zamia in the Miocene. Cophylogenetic reconciliation analyses show a strong cophylogenetic signal between cycads and their butterfly herbivores. Bipartite model-based approaches indicate that this is because closely related Zamia species are used by the same Eumaeus species, suggesting larval host plant resource tracking by the butterfly herbivores. Our results highlight a case of tight evolution between Eumaeus butterflies and cycads, pointing to the generality of correlated evolution and phylogenetic tracking in plant-herbivore interactions across seed plants.

Polyhydroxy Acids as Fabaceous Plant Components Induce Oviposition of the Common Grass Yellow Butterfly, Eurema Mandarina

The common grass yellow butterfly, Eurema mandarina is a Fabaceae-feeding species, the females of which readily oviposit on Albizia julibrissin and Lespedeza cuneata in mainland Japan. We previously demonstrated that the methanolic leaf extracts of these plants, and their highly polar aqueous fractions strongly elicit female oviposition. Furthermore, the three subfractions obtained by ion-exchange chromatographic separation of the aqueous fraction have been found to be less effective alone, but synergistically stimulate female oviposition when combined. This indicates that female butterflies respond to multiple compounds with different acidity. We have previously identified d-pinitol from the neutral/amphoteric subfractions and glycine betaine from the basic subfractions as oviposition stimulants of E. mandarina. The present study aimed to identify active compounds in the remaining acidic subfractions of A. julibrissin and L. cuneata leaf extracts. GC-MS analyses of trimethylsilyl-derivatized samples revealed the presence of six compounds in the acidic subfractions. In bioassays using these authentic chemicals, erythronic acid (EA) and threonic acid (TA) were moderately active in eliciting oviposition responses in E. mandarina, with their d-isomers showing slightly higher activity than their l-isomers. Female responsiveness differed between d-EA and l-TA, the major isomers of these compounds in plants, with the response to d-EA reaching a plateau at concentrations above 0.005% and that to l-TA peaking at a concentration of 0.01%. The natural concentrations of d-EA and l-TA in fresh A. julibrissin and L. cuneata leaves were sufficient to stimulate oviposition. Furthermore, mixing 0.001% d-EA or 0.001% l-TA, to which females are mostly unresponsive, with 0.1% d-pinitol resulted in a synergistic enhancement of the oviposition response. These findings demonstrate that E. mandarina females utilize both polyhydroxy acids, EA and TA, as chemical cues for oviposition.

Assessment of the Molecular Responses of an Ancient Angiosperm against Atypical Insect Oviposition: The Case of Hass Avocados and the Tephritid Fly Anastrepha ludens

Anastrepha spp. (Diptera: Tephritidae) infestations cause significant economic losses in commercial fruit production worldwide. However, some plants quickly counteract the insertion of eggs by females by generating neoplasia and hindering eclosion, as is the case for Persea americana Mill., cv. Hass (Hass avocados). We followed a combined transcriptomics/metabolomics approach to identify the molecular mechanisms triggered by Hass avocados to detect and react to the oviposition of the pestiferous Anastrepha ludens (Loew). We evaluated two conditions: fruit damaged using a sterile pin (pin) and fruit oviposited by A. ludens females (ovi). We evaluated both of the conditions in a time course experiment covering five sampling points: without treatment (day 0), 20 min after the treatment (day 1), and days 3, 6, and 9 after the treatment. We identified 288 differentially expressed genes related to the treatments. Oviposition (and possibly bacteria on the eggs' surface) induces a plant hypersensitive response (HR), triggering a chitin receptor, producing an oxidative burst, and synthesizing phytoalexins. We also observed a process of cell wall modification and polyphenols biosynthesis, which could lead to polymerization in the neoplastic tissue surrounding the eggs.

Spatio-Temporal Evolutionary Patterns of the Pieridae Butterflies (Lepidoptera: Papilionoidea) Inferred from Mitogenomic Data

Pieridae is one of the largest and almost cosmopolitan groups of butterflies, which plays an important role in natural ecosystems; however, to date, its phylogeny and evolutionary history have not been fully resolved. In this study, we obtained the complete or nearly complete mitochondrial genomes of 100 pierid taxa (six newly sequenced, sixty extracted from the whole-genome data, and thirty-four directly available from GenBank). At the same time, for the first time, we conducted comparative mitogenomic and phylogenetic analyses based on these mitogenomic data, to further clarify their spatio-temporal evolutionary patterns. Comparative mitogenomic analysis showed that, except for cox2, the GC content of each of the 13 protein-coding genes (PCGs) in the rapidly diverging subfamily Pierinae was higher than in its sister group Coliadinae. Moreover, the dN/dS values of nine genes (atp6, atp8, cox1, cox3, cob, nad1, nad3, nad5, and nad6) in Pierinae were also relatively higher than those in its sister group, Coliadinae. Phylogenetic analysis showed that all the resultant phylogenetic trees were generally in agreement with those of previous studies. The Pierinae family contained six clades in total with the relationship of (Leptosiaini + (((Nepheroniini + Arthocharidini) + Teracolini) + (Pierini + Elodini))). The Pieridae originated in the Palearctic region approximately 72.3 million years ago in the late Cretaceous, and the subfamily Pierinae diverged from this family around 57.9 million years ago in the Oriental region, shortly after the K-Pg mass extinction event; in addition, the spatio-temporal evolutionary patterns of Pierinae were closely correlated with geological events and environmental changes, as well as the host plant coevolutionary scenario in Earth's history. However, some incongruencies were observed between our results and those of previous studies in terms of shallow phylogenies for a few taxa, and should be further investigated.

Testing hypotheses of a coevolutionary key innovation reveals a complex suite of traits involved in defusing the mustard oil bomb

Coevolutionary interactions are responsible for much of the Earth's biodiversity, with key innovations driving speciation bursts on both sides of the interaction. One persistent question is whether macroevolutionary traits identified as key innovations accurately predict functional performance and selection dynamics within species, as this necessitates characterizing their function, investigating their fitness consequences, and exploring the selection dynamics acting upon them. Here, we used CRISPR-Cas9 mediating nonhomologous end joining (NHEJ) in the butterfly species Pieris brassicae to knock out and directly assess the function and fitness impacts of nitrile specifier protein (NSP) and major allergen (MA). These are two closely related genes that facilitate glucosinolate (GSL) detoxification capacity, which is a key innovation in mustard feeding Pierinae butterflies. We find NSP and MA are both required for survival on plants containing GSLs, with expression differences arising in response to variable GSL profiles, concordant with detoxification performance. Importantly, this concordance was only observed when using natural host plants, likely reflecting the complexity of how these enzymes interact with natural plant variation in GSLs and myrosinases. Finally, signatures of positive selection for NSP and MA were detected across Pieris species, consistent with these genes' importance in recent coevolutionary interactions. Thus, the war between these butterflies and their host plants involves more than the mere presence of chemical defenses and detoxification mechanisms, as their regulation and activation represent key components of complex interactions. We find that inclusion of these dynamics, in ecologically relevant assays, is necessary for coevolutionary insights in this system and likely others.

Considerations on the Systematics of Neotropical Pierina, with the Description of Two New Species of Phulia Herrich-Schäffer from the Peruvian Andes (Lepidoptera: Pieridae, Pierinae, Pierini)

A comparative analysis of high-Andean Pierina was carried out, including a total of 25 species. Based on morphological evidence, with an emphasis on venation and genitalia and molecular data, using three genetic markers, we confirm the recent subjective synonymy of the generic names Tatochila Butler, 1870, Piercolias, Staudinger, 1894, Hypsochila Ureta, 1955, Infraphulia Field, 1958, Pierphulia Field, 1958, and Theochila Field, 1958 with Phulia Herrich-Schäffer, 1867. Two new species are described, namely Phulia stoddardi Pyrcz & Cerdeña n. sp., from the Andes of Central Peru, which occurs at an unusually high altitude of close to 5000 m a.s.l. in dry puna habitat, and Phulia phantasma Lamas, Willmott & Boyer n. sp., from dry montane forests in northern Peru and southern Ecuador. An overview of high-elevation butterflies is presented, with some discussion on adaptations to this environment.

Novel host unmasks heritable variation in plant preference within an insect population

Introductions of novel plant species can disturb the historical resource environment of herbivorous insects, resulting in strong selection to either adopt or exclude the novel host. However, an adaptive response depends on heritable genetic variation for preference or performance within the targeted herbivore population, and it is unclear how heritability of host-use preference may differ between novel and historical hosts. Pieris macdunnoughii butterflies in the Rocky Mountains lay eggs on the nonnative mustard Thlaspi arvense, which is lethal to their offspring. Heritability analyses revealed considerable sex-linked additive genetic variation in host preference within a population of this butterfly. This was contrary to general predictions about the genetic basis of preference variation, which are hypothesized to be sex linked between populations but autosomal within populations. Evidence of sex linkage disappeared when butterflies were tested on methanol-based chemical extracts, suggesting these chemicals in isolation may not be the primary driver of female choice among available host plants. Although unexpected, evidence for within-population sex-linked genetic variation in preference for T. arvense over native hosts indicates that persistent maladaptive oviposition on this lethal plant must be maintained by alternative evolutionary dynamics such as migration- or drift-selection balance or pleiotropic constraints.

Additive genetic effects in interacting species jointly determine the outcome of caterpillar herbivory

Plant-insect interactions are common and important in basic and applied biology. Trait and genetic variation can affect the outcome and evolution of these interactions, but the relative contributions of plant and insect genetic variation and how these interact remain unclear and are rarely subject to assessment in the same experimental context. Here, we address this knowledge gap using a recent host-range expansion onto alfalfa by the Melissa blue butterfly. Common garden rearing experiments and genomic data show that caterpillar performance depends on plant and insect genetic variation, with insect genetics contributing to performance earlier in development and plant genetics later. Our models of performance based on caterpillar genetics retained predictive power when applied to a second common garden. Much of the plant genetic effect could be explained by heritable variation in plant phytochemicals, especially saponins, peptides, and phosphatidyl cholines, providing a possible mechanistic understanding of variation in the species interaction. We find evidence of polygenic, mostly additive effects within and between species, with consistent effects of plant genotype on growth and development across multiple butterfly species. Our results inform theories of plant-insect coevolution and the evolution of diet breadth in herbivorous insects and other host-specific parasites.

Family dinner: Transcriptional plasticity of five Noctuidae (Lepidoptera) feeding on three host plant species

Polyphagous insects often show specialization in feeding on different host plants in terms of survival and growth and, therefore, can be considered minor or major pests of particular hosts. Whether polyphagous insects employ a common transcriptional response to cope with defenses from diverse host plants is under-studied. We focused on patterns of transcriptional plasticity in polyphagous moths (Noctuidae), of which many species are notorious pests, in relation to herbivore performance on different host plants. We compared the transcriptional plasticity of five polyphagous moth species feeding and developing on three different host plant species. Using a comparative phylogenetic framework, we evaluated if successful herbivory, as measured by larval performance, is determined by a shared or lineage-specific transcriptional response. The upregulated transcriptional activity, or gene expression pattern, of larvae feeding on the different host plants and artificial control diet was highly plastic and moth species-specific. Specialization, defined as high herbivore success for specific host plants, was not generally linked to a lower number of induced genes. Moths that were more distantly related and showing high herbivore success for certain host plants showed shared expression of multiple homologous genes, indicating convergence. We further observed specific transcriptional responses within phylogenetic lineages. These expression patterns for specific host plant species are likely caused by shared evolutionary histories, for example, symplesiomorphic patterns, and could therefore not be associated with herbivore success alone. Multiple gene families, with roles in plant digestion and detoxification, were widely expressed in response to host plant feeding but again showed highly moth species-specific. Consequently, high herbivore success for specific host plants is also driven by species-specific transcriptional plasticity. Thus, potential pest moths display a complex and species-specific transcriptional plasticity.

Geographic isolation drives speciation in Nearctic aphids

Across herbivorous insect clades, species richness and host-use diversity tend to positively covary. This could be because host-use divergence drives speciation, or because it raises the ecological limits on species richness. To evaluate these hypotheses, we performed phylogenetic path model analyses of the species diversity of Nearctic aphids. Here, we show that variation in the species richness of aphid clades is caused mainly by host-use divergence, whereas variation in speciation rates is caused more by divergence in non-host-related niche variables. Aphid speciation is affected by both the evolution of host and non-host-related niche components, but the former is largely caused by the latter. Thus, our analyses suggest that host-use divergence can both raise the ecological limits on species richness and drive speciation, although in the latter case, host-use divergence tends to be a step along the causal path leading from non-host-related niche evolution to speciation.

Using phylogenetic path modelling, geographic isolation is revealed to be the main driver of Nearctic aphid speciation, with subsequent host-use divergence raising the limits on clade species richness.

β-Cyanoalanine synthase protects mites against Arabidopsis defenses

Glucosinolates are antiherbivory chemical defense compounds in Arabidopsis (Arabidopsis thaliana). Specialist herbivores that feed on brassicaceous plants have evolved various mechanisms aimed at preventing the formation of toxic isothiocyanates. In contrast, generalist herbivores typically detoxify isothiocyanates through glutathione conjugation upon exposure. Here, we examined the response of an extreme generalist herbivore, the two-spotted spider mite Tetranychus urticae (Koch), to indole glucosinolates. Tetranychus urticae is a composite generalist whose individual populations have a restricted host range but have an ability to rapidly adapt to initially unfavorable plant hosts. Through comparative transcriptomic analysis of mite populations that have differential susceptibilities to Arabidopsis defenses, we identified β-cyanoalanine synthase of T. urticae (TuCAS), which encodes an enzyme with dual cysteine and β-cyanoalanine synthase activities. We combined Arabidopsis genetics, chemical complementation and mite reverse genetics to show that TuCAS is required for mite adaptation to Arabidopsis through its β-cyanoalanine synthase activity. Consistent with the β-cyanoalanine synthase role in detoxification of hydrogen cyanide (HCN), we discovered that upon mite herbivory, Arabidopsis plants release HCN. We further demonstrated that indole glucosinolates are sufficient for cyanide formation. Overall, our study uncovered Arabidopsis defenses that rely on indole glucosinolate-dependent cyanide for protection against mite herbivory. In response, Arabidopsis-adapted mites utilize the β-cyanoalanine synthase activity of TuCAS to counter cyanide toxicity, highlighting the mite's ability to activate resistant traits that enable this extreme polyphagous herbivore to exploit cyanogenic host plants.

Ehrlich and Raven escape and radiate coevolution hypothesis at different levels of organization: Past and future perspectives

The classic paper by Ehrlich and Raven on coevolution will soon be 60 years old. Although they were not the first to develop the idea of coevolution, their thought-provoking paper certainly popularized this idea and inspired several generations of scientists interested in coevolution. Here, we describe some of their main contributions, quantitatively measure the impact of their seminal paper on different fields of research, and discuss how ideas related to their original paper might push the study of coevolution forward. To guide our discussion, we explore their original hypothesis into three research fields that are associated with distinct scales/levels of organization: (1) the genetic mechanisms underlying coevolutionary interactions; (2) the potential association between coevolutionary diversification and the organization of ecological networks; and (3) the micro- and macroevolutionary mechanisms and expected patterns under their hypothesis. By doing so, we discuss potentially overlooked aspects and future directions for the study of coevolutionary dynamics and diversification.

Microevolution of Pieris butterfly genes involved in host-plant adaptation along a host-plant community cline

Herbivorous insects have evolved counteradaptations to overcome the chemical defenses of their host plants. Several of these counteradaptations have been elucidated at the molecular level, in particular for insects specialized on cruciferous host plants. While the importance of these counteradaptations for host plant colonization is well established, little is known about their microevolutionary dynamics in the field. In particular, it is not known whether and how host plant diversity shapes diversity in insect counteradaptations. In this study, we examine patterns of host plant use and insect counteradaptation in three Pieris butterfly species across Japan. The larvae of these butterflies express nitrile-specifier protein (NSP) and its paralog major allergen (MA) in their gut to overcome the highly diversified glucosinolate-myrosinase defense system of their cruciferous host plants. Pieris napi and Pieris melete colonize wild Brassicaceae whereas Pieris rapae typically uses cultivated Brassica as a host, regardless of the local composition of wild crucifers. As expected, NSP and MA diversity was independent of the local composition of wild Brassicaceae in P. rapae. In contrast, NSP diversity correlated with local host plant diversity in both species that preferred wild Brassicaceae. P. melete and P. napi both revealed two distinct major NSP alleles, which shaped diversity among local populations, albeit with different evolutionary trajectories. In comparison, MA showed no indication for local adaptation. Altogether, MA appeared to be evolutionary more conserved than NSP, suggesting that both genes play different roles in diverting host plant chemical defense.

Evidence for tissue-specific defense-offense interactions between milkweed and its community of specialized herbivores

Coevolution between plants and herbivores often involves escalation of defense-offense strategies, but attack by multiple herbivores may obscure the match of plant defense to any one attacker. As herbivores often specialize on distinct plant parts, we hypothesized that defense-offense interactions in coevolved systems may become physiologically and evolutionarily compartmentalized between plant tissues. We report that roots, leaves, flower buds and seeds of the tropical milkweed (Asclepias curassavica) show increasing concentrations of cardenolide toxins acropetally, with latex showing the highest concentration. In vitro assays of the physiological target of cardenolides, the Na⁺ /K⁺ -ATPase (hereafter 'sodium pump'), of three specialized milkweed herbivores (root-feeding Tetraopes tetrophthalmus, leaf-feeding Danaus plexippus, and seed-feeding Oncopeltus fasciatus) show that they are proportionally tolerant to the cardenolide concentrations of the tissues they eat. Indeed, molecular substitutions in the insects' sodium pumps predicted their tolerance to toxins from their target tissues. Nonetheless, the relative inhibition of the sodium pumps of these specialists by the concentration vs. composition (inhibition controlled for concentration, what we term 'potency') of cardenolides from their target vs. non-target plant tissues revealed different degrees of insect adaptation to tissue-specific toxins. In addition, a trade-off between toxin concentration and potency emerged across plant tissues, potentially reflecting coevolutionary history or plant physiological constraints. Our findings suggest that tissue-specific coevolutionary dynamics may be proceeding between the plant and its specialized community of herbivores. This novel finding may be common in nature, contributing to ways in which coevolution proceeds in multi-species communities.

Genetic analysis reveals three novel QTLs underpinning a butterfly egg-induced hypersensitive response-like cell death in Brassica rapa

BACKGROUND

Cabbage white butterflies (Pieris spp.) can be severe pests of Brassica crops such as Chinese cabbage, Pak choi (Brassica rapa) or cabbages (B. oleracea). Eggs of Pieris spp. can induce a hypersensitive response-like (HR-like) cell death which reduces egg survival in the wild black mustard (B. nigra). Unravelling the genetic basis of this egg-killing trait in Brassica crops could improve crop resistance to herbivory, reducing major crop losses and pesticides use. Here we investigated the genetic architecture of a HR-like cell death induced by P. brassicae eggs in B. rapa.

RESULTS

A germplasm screening of 56 B. rapa accessions, representing the genetic and geographical diversity of a B. rapa core collection, showed phenotypic variation for cell death. An image-based phenotyping protocol was developed to accurately measure size of HR-like cell death and was then used to identify two accessions that consistently showed weak (R-o-18) or strong cell death response (L58). Screening of 160 RILs derived from these two accessions resulted in three novel QTLs for Pieris brassicae-induced cell death on chromosomes A02 (Pbc1), A03 (Pbc2), and A06 (Pbc3). The three QTLs Pbc1-3 contain cell surface receptors, intracellular receptors and other genes involved in plant immunity processes, such as ROS accumulation and cell death formation. Synteny analysis with A. thaliana suggested that Pbc1 and Pbc2 are novel QTLs associated with this trait, while Pbc3 also contains an ortholog of LecRK-I.1, a gene of A. thaliana previously associated with cell death induced by a P. brassicae egg extract.

CONCLUSIONS

This study provides the first genomic regions associated with the Pieris egg-induced HR-like cell death in a Brassica crop species. It is a step closer towards unravelling the genetic basis of an egg-killing crop resistance trait, paving the way for breeders to further fine-map and validate candidate genes.

Effects of Light Quality on Colonization of Tomato Roots by AMF and Implications for Growth and Defense

Beneficial soil microbes can enhance plant growth and defense, but the extent to which this occurs depends on the availability of resources, such as water and nutrients. However, relatively little is known about the role of light quality, which is altered during shading, resulting a low red: far-red ratio (R:FR) of light. We examined how low R:FR light influences arbuscular mycorrhizal fungus (AMF)-mediated changes in plant growth and defense using Solanum lycopersicum (tomato) and the insect herbivore Chrysodeixis chalcites. We also examined effects on third trophic level interactions with the parasitoid Cotesia marginiventris. Under low R:FR light, non-mycorrhizal plants activated the shade avoidance syndrome (SAS), resulting in enhanced biomass production. However, mycorrhizal inoculation decreased stem elongation in shaded plants, thus counteracting the plant’s SAS response to shading. Unexpectedly, activation of SAS under low R:FR light did not increase plant susceptibility to the herbivore in either non-mycorrhizal or mycorrhizal plants. AMF did not significantly affect survival or growth of caterpillars and parasitoids but suppressed herbivore-induced expression of jasmonic acid-signaled defenses genes under low R:FR light. These results highlight the context-dependency of AMF effects on plant growth and defense and the potentially adverse effects of AMF under shading.

Evolution of Olfactory Receptors Tuned to Mustard Oils in Herbivorous Drosophilidae

The diversity of herbivorous insects is attributed to their propensity to specialize on toxic plants. In an evolutionary twist, toxins betray the identity of their bearers when herbivores coopt them as cues for host-plant finding, but the evolutionary mechanisms underlying this phenomenon are poorly understood. We focused on Scaptomyza flava, an herbivorous drosophilid specialized on isothiocyanate (ITC)-producing (Brassicales) plants, and identified Or67b paralogs that were triplicated as mustard-specific herbivory evolved. Using in vivo heterologous systems for the expression of olfactory receptors, we found that S. flava Or67bs, but not the homologs from microbe-feeding relatives, responded selectively to ITCs, each paralog detecting different ITC subsets. Consistent with this, S. flava was attracted to ITCs, as was Drosophila melanogaster expressing S. flava Or67b3 in the homologous Or67b olfactory circuit. ITCs were likely coopted as olfactory attractants through gene duplication and functional specialization (neofunctionalization and subfunctionalization) in S. flava, a recently derived herbivore.

Expanding the Menu: Are Polyphagy and Gene Family Expansions Linked across Lepidoptera?

Evolutionary expansions and contractions of gene families are often correlated with key innovations and/or ecological characteristics. In butterflies and moths (Lepidoptera), expansions of gene families involved in detoxification of plant specialized metabolites are hypothesized to facilitate a polyphagous feeding style. However, analyses supporting this hypothesis are mostly based on a limited number of lepidopteran species. We applied a phylogenomics approach, using 37 lepidopteran genomes, to analyze if gene family evolution (gene gain and loss) is associated with the evolution of polyphagy. Specifically, we compared gene counts and evolutionary gene gain and loss rates of gene families involved in adaptations with plant feeding. We correlated gene evolution to host plant family range (phylogenetic diversity) and specialized metabolite content of plant families (functional metabolite diversity). We found a higher rate for gene loss than gene gain in Lepidoptera, a potential consequence of genomic rearrangements and deletions after (potentially small-scale) duplication events. Gene family expansions and contractions varied across lepidopteran families, and were associated to host plant use and specialization levels. Within the family Noctuidae, a higher expansion rate for gene families involved in detoxification can be related to the large number of polyphagous species. However, gene family expansions are observed in both polyphagous and monophagous lepidopteran species and thus seem to be species-specific in the taxa sampled. Nevertheless, a significant positive correlation of gene counts of the carboxyl- and choline esterase and glutathione-S-transferase detoxification gene families with the level of polyphagy was identified across Lepidoptera.

The scent chemistry of butterflies

Butterflies use structurally highly diverse volatile compounds for communication, in addition to visual signals. These compounds originate from plants or a formed de novo especially by male butterflies that possess specific scent organs.

Concordant phylogeographic responses to large-scale coastal disturbance in intertidal macroalgae and their epibiota

Major ecological disturbance events can provide opportunities to assess multispecies responses to upheaval. In particular, catastrophic disturbances that regionally extirpate habitat-forming species can potentially influence the genetic diversity of large numbers of codistributed taxa. However, due to the rarity of such disturbance events over ecological timeframes, the genetic dynamics of multispecies recolonization processes have remained little understood. Here, we use single nucleotide polymorphism (SNP) data from multiple coastal species to track the dynamics of cocolonization events in response to ancient earthquake disturbance in southern New Zealand. Specifically, we use a comparative phylogeographic approach to understand the extent to which epifauna (with varying ecological associations with their macroalgal hosts) share comparable spatial and temporal recolonization patterns. Our study reveals concordant disturbance-related phylogeographic breaks in two intertidal macroalgal species along with two associated epibiotic species (a chiton and an isopod). By contrast, two codistributed species, one of which is an epibiotic amphipod and the other a subtidal macroalga, show few, if any, genetic effects of palaeoseismic coastal uplift. Phylogeographic model selection reveals similar post-uplift recolonization routes for the epibiotic chiton and isopod and their macroalgal hosts. Additionally, codemographic analyses support synchronous population expansions of these four phylogeographically similar taxa. Our findings indicate that coastal paleoseismic activity has driven concordant impacts on multiple codistributed species, with concerted recolonization events probably facilitated by macroalgal rafting. These results highlight that high-resolution comparative genomic data can help reconstruct concerted multispecies responses to recent ecological disturbance.

Tissue-specific gene expression shows a cynipid wasp repurposes oak host gene networks to create a complex and novel parasite-specific organ

Every organism on Earth depends on interactions with other organisms to survive. In each of these interactions, an organism must utilize the limited toolbox of genes and proteins it possesses to successfully manipulate or cooperate with another species, but it can also co-opt the genome machinery of its partner to expand its available tools. Insect-induced plant galls are an extreme example of this, wherein an insect hijacks the plant's genome to direct the initiation and development of galls consisting of plant tissue. However, previous transcriptomic studies have not evaluated individual tissues within a gall to determine the full extent to which a galling insect manipulates its host plant. Here we demonstrate that the cynipid wasp Dryocosmus quercuspalustris creates a complex parasite-specific organ from red oak tissue via massive changes in host gene expression. Our results show that the gall wasp is not merely modifying oak leaf tissue but creating extensive changes in gene expression between galled and ungalled tissue (differential expression in 28% of genes) and distinct gall tissue types (20% of genes). The outer gall tissue shows increases in various plant defence systems, which is consistent with its predicted functional role of protecting the wasp larva. The inner larval capsule shows suppression of large parts of the plant innate immune system and evidence for the wasp utilizing the plant's RNA interference mechanisms, which may be a potential mechanism for the wasp's control on gall growth.

Phylogenetic reconstruction of ancestral ecological networks through time for pierid butterflies and their host plants

The study of herbivorous insects underpins much of the theory that concerns the evolution of species interactions. In particular, Pieridae butterflies and their host plants have served as a model system for studying evolutionary arms races. To learn more about the coevolution of these two clades, we reconstructed ancestral ecological networks using stochastic mappings that were generated by a phylogenetic model of host-repertoire evolution. We then measured if, when, and how two ecologically important structural features of the ancestral networks (modularity and nestedness) evolved over time. Our study shows that as pierids gained new hosts and formed new modules, a subset of them retained or recolonised the ancestral host(s), preserving connectivity to the original modules. Together, host-range expansions and recolonisations promoted a phase transition in network structure. Our results demonstrate the power of combining network analysis with Bayesian inference of host-repertoire evolution to understand changes in complex species interactions over time.

Every breath you take: assessing metabolic costs of toxin resistance in garter snakes (Thamnophis)

Trait specialization often comes at the expense of original trait function, potentially causing evolutionary tradeoffs that may render specialist populations vulnerable to extinction. However, many specialized adaptations evolve repeatedly, suggesting selection favors specialization in specific environments. Some garter snake (Thamnophis) populations possess specialized mutations in voltage-gated sodium channels that allow them to consume Pacific newts (Taricha) defended by a highly potent neurotoxin (tetrodotoxin). These mutations, however, also decrease protein and muscle function, suggesting garter snakes may suffer evolutionary tradeoffs. We measured a key physiological process, standard metabolic rate (SMR), to investigate whether specialized adaptations in toxin-resistant garter snakes affect baseline energy expenditure. In snakes, skeletal muscles influence metabolism and power ventilation, so inefficiencies of sodium channels in these muscles might impact whole-animal energy expenditure. Further, because sodium channels are membrane-bound proteins, inefficiencies of channel kinetics and performance might be exacerbated at suboptimal temperatures. We measured SMR in 2 species, Thamnophis atratus and Thamnophis sirtalis, that independently evolved tetrodotoxin resistance through unique mutations, providing replicate experiments with distinct underlying genetics and potential physiological costs. Despite our expectations, neither resistance phenotype nor sodium channel genotype affected metabolism and resistant snakes did not perform worse under suboptimal body temperature. Instead, T. atratus and T. sirtalis show nearly identical rates of mass-adjusted energy expenditure at both temperatures, despite differing eco-morphologies, life histories, and distant phylogenetic positions. These findings suggest SMR may be a conserved feature of Thamnophis, and that any organismal tradeoffs may be compensated to retain whole-animal function.

The evolution of coevolution in the study of species interactions

The study of reciprocal adaptation in interacting species has been an active and inspiring area of evolutionary research for nearly 60 years. Perhaps owing to its great natural history and potential consequences spanning population divergence to species diversification, coevolution continues to capture the imagination of biologists. Here we trace developments following Ehrlich and Raven's classic paper, with a particular focus on the modern influence of two studies by Dr. May Berenbaum in the 1980s. This series of classic work presented a compelling example exhibiting the macroevolutionary patterns predicted by Ehrlich and Raven and also formalized a microevolutionary approach to measuring selection, functional traits, and understanding reciprocal adaptation between plants and their herbivores. Following this breakthrough was a wave of research focusing on diversifying macroevolutionary patterns, mechanistic chemical ecology, and natural selection on populations within and across community types. Accordingly, we breakdown coevolutionary theory into specific hypotheses at different scales: reciprocal adaptation between populations within a community, differential coevolution among communities, lineage divergence, and phylogenetic patterns. We highlight progress as well as persistent gaps, especially the link between reciprocal adaptation and diversification.

Metabolic and biotransformation effects on dietary glucosinolates, their bioavailability, catabolism and biological effects in different organisms

Glucosinolate-producing plants have long been recognized for both their distinctive benefits to human nutrition and their resistance traits against pathogens and herbivores. Despite the accumulation of glucosinolates (GLS) in plants is associated with their resistance to various biotic and abiotic stresses, the defensive and biological activities of GLS are commonly conveyed by their metabolic products. In view of this, metabolism is considered the driving factor upon the interactions of GLS-producing plants with other organisms, also influenced by plant and plant attacking or digesting organism characteristics. Several microbial pathogens and insects have evolved the capacity to detoxify GLS-hydrolysis products or inhibit their formation via different means, highlighting the relevance of their metabolic abilities for the plants' defense system activation and target organism detoxification. Strikingly, some bacteria, fungi and insects can likewise produce their own myrosinase (MYR)-like enzymes in one of the most important adaptation strategies against the GLS-MYR plant defense system. Knowledge of GLS metabolic pathways in herbivores and pathogens can impact plant protection efforts and may be harnessed upon for genetically modified plants that are more resistant to predators. In humans, the interest in the implementation of GLS in diets for the prevention of chronic diseases has grown substantially. However, the efficiency of such approaches is dependent on GLS bioavailability and metabolism, which largely involves the human gut microbiome. Among GLS-hydrolytic products, isothiocyanates (ITC) have shown exceptional properties as chemical plant defense agents against herbivores and pathogens, along with their health-promoting benefits in humans, at least if consumed in reasonable amounts. Deciphering GLS metabolic pathways provides critical information for catalyzing all types of GLS towards the generation of ITCs as the biologically most active metabolites. This review provides an overview on contrasting metabolic pathways in plants, bacteria, fungi, insects and humans towards GLS activation or detoxification. Further, suggestions for the preparation of GLS containing plants with improved health benefits are presented.

Why are there not more herbivorous insect species?

Insect species richness is estimated to exceed three million species, of which roughly half is herbivorous. Despite the vast number of species and varied life histories, the proportion of herbivorous species among plant-consuming organisms is lower than it could be due to constraints that impose limits to their diversification. These include ecological factors, such as vague interspecific competition; anatomical and physiological limits, such as neural limits and inability of handling a wide range of plant allelochemicals; phylogenetic constraints, like niche conservatism; and most importantly, a low level of concerted genetic variation necessary to a phyletic conversion. It is suggested that diversification ultimately depends on what we call the intrinsic trend of diversification of the insect genome. In support of the above, we survey the major types of host-specificity, the mechanisms and constraints of host specialization, possible pathways of speciation, and hypotheses concerning insect diversification.

Insect egg-killing: a new front on the evolutionary arms-race between brassicaceous plants and pierid butterflies

Evolutionary arms-races between plants and insect herbivores have long been proposed to generate key innovations such as plant toxins and detoxification mechanisms that can drive diversification of the interacting species. A novel front-line of plant defence is the killing of herbivorous insect eggs. We test whether an egg-killing plant trait has an evolutionary basis in such a plant-insect arms-race. Within the crucifer family (Brassicaceae), some species express a hypersensitive response (HR)-like necrosis underneath butterfly eggs (Pieridae) that leads to eggs desiccating or falling off the plant. We studied the phylogenetic distribution of this trait, its egg-killing effect on and elicitation by butterflies, by screening 31 Brassicales species, and nine Pieridae species. We show a clade-specific induction of strong, egg-killing HR-like necrosis mainly in species of the Brassiceae tribe including Brassica crops and close relatives. The necrosis is strongly elicited by pierid butterflies that are specialists of crucifers. Furthermore, HR-like necrosis is linked to PR1 defence gene expression, accumulation of reactive oxygen species and cell death, eventually leading to egg-killing. Our findings suggest that the plants' egg-killing trait is a new front on the evolutionary arms-race between Brassicaceae and pierid butterflies beyond the well-studied plant toxins that have evolved against their caterpillars.