Secondary sympatry caused by range expansion informs on the dynamics of microendemism in a biodiversity hotspot

Analysis of intrinsic evolutionary factors leading to microendemic distributions in New Caledonian leaf beetles

Microendemicity, or the condition of some species having local ranges, is a relatively common pattern in nature. However, the factors that lead to this pattern are still largely unknown. Most studies addressing this issue tend to focus on extrinsic factors associated with microendemic distributions, such as environmental conditions, hypothesising a posteriori about underlying potential speciation mechanisms, linked or not to these conditions. Here, we use a multi-faceted approach mostly focusing on intrinsic factors instead, namely diversification dynamics and speciation modes in two endemic sibling genera of leaf beetles with microendemic distributions, Taophila and Tricholapita, in a microendemicity hotspot, New Caledonia. Results suggest that the diversification rate in this lineage slowed down through most of the Neogene and consistently with a protracted speciation model possibly combined with several ecological and environmental factors potentially adding rate-slowing effects through time. In turn, species accumulated following successive allopatric speciation cycles, possibly powered by marked geological and climatic changes in the region in the last 25 million years, with daughter species ranges uncorrelated with the time of speciation. In this case, microendemicity seems to reflect a mature state for the system, rather than a temporary condition for recent species, as suggested for many microendemic organisms.

The fifth family of the true crickets (Insecta: Orthoptera: Ensifera: Grylloidea), Oecanthidae defin. nov.: phylogenetic relationships and divergence times

Crickets are frequently used as a model in several areas of science, including acoustic communication, behaviour and neurobiology. However, only a few of these studies are placed in an evolutionary framework due to the limited number of phylogenetic hypotheses for true crickets. We present a phylogenetic hypothesis for a newly defined family of crickets, Oecanthidae defin. nov., sister-group of Gryllidae defin. nov. The phylogenetic analyses are based on molecular and morphological data under likelihood and parsimony criteria and molecular data for divergence-times estimation (Bayesian inference). We used 107 terminals from all biogeographic regions and six fossils for the time calibration of the tree. All analyses resulted in Oecanthidae with four subfamilies: Euscyrtinae, Oecanthinae defin. nov., Podoscirtinae defin. nov. and Tafaliscinae defin. nov. Based on our results, we revise the definition and internal classifications of the subfamilies, supertribes and tribes. A new tribe, Phyllogryllini trib. nov. is described. We also update their diagnoses, list the genera of the tribes and list their apomorphies. We provide an identification key for all suprageneric taxa of Oecanthidae, plus all genera of Tafaliscinae. Finally, we discuss the phylogenetic relationships of Oecanthidae, their divergence times, habitat diversity and the importance of ovipositor variation in this clade.

Speciation across the Tree of Life

Much of what we know about speciation comes from detailed studies of well-known model systems. Although there have been several important syntheses on speciation, few (if any) have explicitly compared speciation among major groups across the Tree of Life. Here, we synthesize and compare what is known about key aspects of speciation across taxa, including bacteria, protists, fungi, plants, and major animal groups. We focus on three main questions. Is allopatric speciation predominant across groups? How common is ecological divergence of sister species (a requirement for ecological speciation), and on what niche axes do species diverge in each group? What are the reproductive isolating barriers in each group? Our review suggests the following patterns. (i) Based on our survey and projected species numbers, the most frequent speciation process across the Tree of Life may be co-speciation between endosymbiotic bacteria and their insect hosts. (ii) Allopatric speciation appears to be present in all major groups, and may be the most common mode in both animals and plants, based on non-overlapping ranges of sister species. (iii) Full sympatry of sister species is also widespread, and may be more common in fungi than allopatry. (iv) Full sympatry of sister species is more common in some marine animals than in terrestrial and freshwater ones. (v) Ecological divergence of sister species is widespread in all groups, including ~70% of surveyed species pairs of plants and insects. (vi) Major axes of ecological divergence involve species interactions (e.g. host-switching) and habitat divergence. (vii) Prezygotic isolation appears to be generally more widespread and important than postzygotic isolation. (viii) Rates of diversification (and presumably speciation) are strikingly different across groups, with the fastest rates in plants, and successively slower rates in animals, fungi, and protists, with the slowest rates in prokaryotes. Overall, our study represents an initial step towards understanding general patterns in speciation across all organisms.

Evolution of communication signals and information during species radiation

Communicating species identity is a key component of many animal signals. However, whether selection for species recognition systematically increases signal diversity during clade radiation remains debated. Here we show that in woodpecker drumming, a rhythmic signal used during mating and territorial defense, the amount of species identity information encoded remained stable during woodpeckers’ radiation. Acoustic analyses and evolutionary reconstructions show interchange among six main drumming types despite strong phylogenetic contingencies, suggesting evolutionary tinkering of drumming structure within a constrained acoustic space. Playback experiments and quantification of species discriminability demonstrate sufficient signal differentiation to support species recognition in local communities. Finally, we only find character displacement in the rare cases where sympatric species are also closely related. Overall, our results illustrate how historical contingencies and ecological interactions can promote conservatism in signals during a clade radiation without impairing the effectiveness of information transfer relevant to inter-specific discrimination.

Animal signals often encode information on the emitter’s species identity. Using woodpecker drumming as a model, here the authors show that limited signal divergence during a clade radiation does not impair species discrimination, as long as the signals are adapted to local ecological requirements.

Pseudolebinthus lunipterus sp. nov.: a striking deaf and mute new cricket from Malawi (Orthoptera, Gryllidae, Eneopterinae)

This article presents an intriguing new cricket species of the tribe Xenogryllini discovered in Northern Malawi. This is the first case of mute and deaf species in the subfamily Eneopterinae; it shows no stridulatory apparatus on short male forewings and no tympana on either side of fore tibiae in both sexes. We introduce the new species and its complete mitogenome and assess phylogenetic relationships based on molecular data obtained from next-generation sequencing genome skimming method. Phylogenetic analyses place the new species within the genus Pseudolebinthus in Xenogryllini, as the sister species of Pseudolebinthus gorochovi Robillard. We describe Pseudolebinthus lunipterus sp. nov., provide illustrations of main morphology, male and female genitalia, photographs of living specimens and information about habitat and update the identification key for species of genus Pseudolebinthus. We discuss the differences between the new species and related taxa and the striking loss of acoustic communication in this cricket.

Diversity and evolution of New Caledonian endemic Taophila subgenus Lapita (Coleoptera: Chrysomelidae: Eumolpinae)

New Caledonia is an important biodiversity hotspot, where numerous plant and animal groups show high levels of species diversity and endemicity, while facing multiple threats to their habitats. Leaf beetles in the subfamily Eumolpinae illustrate this pattern, with species estimates higher than the number of described taxa and distribution ranges that are often consistent with microendemicity. In this study, we increase the knowledge of this group by focusing on the Taophila subgenus Lapita, known from three species but here expanded to eleven with eight new species: T. atlantis sp. nov., T. hermes sp. nov., T. kronos sp. nov., T. oceanica sp. nov., T. olympica sp. nov., T. ouranos sp. nov., T. riberai sp. nov., and T. tridentata sp. nov. Additionally, we infer the evolutionary history of the group using mtDNA markers (COI and rrnS). This phylogeny and the species distribution help hypothesize a model of evolution for this lineage in the context of historical climatic and geological changes of New Caledonia.

Distribution and relative age of endemism across islands worldwide

Islands have remarkable levels of endemism and contribute greatly to global biodiversity. Establishing the age of island endemics is important to gain insights into the processes that have shaped the biodiversity patterns of island biota. We investigated the relative age of monocots across islands worldwide, using different measures of phylogenetic endemism tested against null models. We compiled a species occurrence dataset across 4,306 islands, and identified 142 sites with neo-, paleo-, mixed and super-endemism. These sites were distributed across the world, although they tended to be more common at low latitudes. The most frequent types of endemism were mixed and super-endemism, which suggests that present-day island biodiversity has frequently been shaped by processes that took place at different points in times. We also identified the environmental factors that contributed most to different types of endemism; we found that latitude, habitat availability and climate stability had a significant impact on the persistence of ancient taxa and on recent diversification events. The islands identified here are irreplaceable both for the uniqueness and the evolutionary history of their flora, and because they are a source of "option values" and evolutionary potential. Therefore, our findings will help guide biodiversity conservation on a global scale.

Ten false ideas about New Caledonia biogeography

The biogeographical paradigm of New Caledonia has recently changed. Although this island is now considered by many as oceanic, its study is still often impeded by some old misconceptions concerning either regional geology or phylogenetic analysis of evolution and biogeography. I discuss ten points that I feel are especially detrimental, to help focus on the real debate and the real questions: (1) its geological history cannot be understood from the basement only; (2) the island submergence was not due simply to sea-level variation; (3) Zealandia/Tasmantis is not a lost continent; (4) short-distance dispersal is not equivalent to permanence on land; (5) long-distance dispersal is not the sole event opposing vicariance, but short-distance dispersal as well; (6) the occurrence of relicts does not prove biota permanence; (7) a major fault system was not observed in New Caledonia; (8) terranes are not rafts; (9) forest climatic refuges do not necessarily equate to centres of endemism or centres of diversity; and (10) New Caledonia is not only a sink but also a source. Study of New Caledonia will need to focus on old and non-relict clades and there is a need to improve the local fossil record.

Outstanding micro-endemism in New Caledonia: More than one out of ten animal species have a very restricted distribution range

New Caledonia is a biodiversity hotspot, with an extremely high number of endemic species with narrow distribution ranges that are at high risk of extinction due to open-cast nickel mining, invasive species and seasonal man-induced fires. Mentions of micro-endemism permeate the literature on the biota of this archipelago. However, so far there has been no research comparing distribution range in different animal groups. The aim of this study is to examine the implication of different sampling effort variables in order to distinguish micro-endemicity from data deficiency, and evaluate the distribution range, frequency, and extent to which micro-endemism is common to several groups of organisms. We compiled a dataset derived from publications in Zoologia Neocaledonica, comprising 1,149 species, of which 86% are endemic to New Caledonia. We found that the sampling effort variables that were best correlated with distribution range were the number of sampling dates and the number of collectors per species. The median value of sampling dates was used to establish a cut-off point for defining adequately sampled species. We showed that, although only 52% of species were sampled adequately enough to determine their distribution range, the number of species with a very narrow distribution range was still high. Among endemics from New Caledonia, 12% (116 species) have ranges ≤5.2km2 and 3.9% (38 species) have ranges between 23 and 100 km2. Surprisingly, a similar trend was observed in non-endemic species: 22% occurred in areas ≤ 5.2 km2, and 8% in areas 23-100 km2, suggesting that environmental dissimilarity may play an important role in the distribution of these species. Micro-endemic species were predominant in 18 out of 20 orders. These results will contribute to a re-assessment of the IUCN red list of species in this archipelago, indicating that at least 116 species are probably critically endangered.

Updating the Phylogenetic Dating of New Caledonian Biodiversity with a Meta-analysis of the Available Evidence

For a long time, New Caledonia was considered a continental island, a fragment of Gondwana harbouring old clades that originated by vicariance and so were thought to be locally ancient. Recent molecular phylogenetic studies dating diversification and geological data indicating important events of submergence during the Paleocene and Eocene (until 37 Ma) brought evidence to dismiss this old hypothesis. In spite of this, some authors still insist on the idea of a local permanence of a Gondwanan biota, justifying this assumption through a complex scenario of survival by hopping to and from nearby and now-vanished islands. Based on a comprehensive review of the literature, we found 40 studies dating regional clades of diverse organisms and we used them to test the hypothesis that New Caledonian and inclusive Pacific island clades are older than 37 Ma. The results of this meta-analysis provide strong evidence for refuting the hypothesis of a Gondwanan refuge with a biota that originated by vicariance. Only a few inclusive Pacific clades (6 out of 40) were older than the oldest existing island. We suggest that these clades could have extinct members either on vanished islands or nearby continents, emphasizing the role of dispersal and extinction in shaping the present-day biota.

Old Lineage on an Old Island: Pixibinthus, a New Cricket Genus Endemic to New Caledonia Shed Light on Gryllid Diversification in a Hotspot of Biodiversity

Few studies have focused on the early colonization of New Caledonia by insects, after the re-emergence of the main island, 37 Myr ago. Here we investigate the mode and tempo of evolution of a new endemic cricket genus, Pixibinthus, recently discovered in southern New Caledonia. First we formally describe this new monotypic genus found exclusively in the open shrubby vegetation on metalliferous soils, named 'maquis minier', unique to New Caledonia. We then reconstruct a dated molecular phylogeny based on five mitochondrial and four nuclear loci in order to establish relationships of Pixibinthus within Eneopterinae crickets. Pixibinthus is recovered as the sister clade of the endemic genus Agnotecous, mostly rainforest-dwellers. Dating results show that the island colonization by their common ancestor occurred around 34.7 Myr, shortly after New Caledonia re-emergence. Pixibinthus and Agnotecous are then one of the oldest insect lineages documented so far for New Caledonia. This discovery highlights for the first time two clear-cut ecological specializations between sister clades, as Agnotecous is mainly found in rainforests with 19 species, whereas Pixibinthus is found in open habitats with a single documented species. The preference of Pixibinthus for open habitats and of Agnotecous for forest habitats nicely fits an acoustic specialization, either explained by differences in body size or in acoustic properties of their respective habitats. We hypothesize that landscape dynamics, linked to major past climatic events and recent change in fire regimes are possible causes for both present-day low diversity and rarity in genus Pixibinthus. The unique evolutionary history of this old New Caledonian lineage stresses the importance to increase our knowledge on the faunal biodiversity of 'maquis minier', in order to better understand the origin and past dynamics of New Caledonian biota.

Predicting Where a Radiation Will Occur: Acoustic and Molecular Surveys Reveal Overlooked Diversity in Indian Ocean Island Crickets (Mogoplistinae: Ornebius)

Recent theory suggests that the geographic location of island radiations (local accumulation of species diversity due to cladogenesis) can be predicted based on island area and isolation. Crickets are a suitable group for testing these predictions, as they show both the ability to reach some of the most isolated islands in the world, and to speciate at small spatial scales. Despite substantial song variation between closely related species in many island cricket lineages worldwide, to date this characteristic has not received attention in the western Indian Ocean islands; existing species descriptions are based on morphology alone. Here we use a combination of acoustics and DNA sequencing to survey these islands for Ornebius crickets. We uncover a small but previously unknown radiation in the Mascarenes, constituting a three-fold increase in the Ornebius species diversity of this archipelago (from two to six species). A further new species is detected in the Comoros. Although double archipelago colonisation is the best explanation for species diversity in the Seychelles, in situ cladogenesis is the best explanation for the six species in the Mascarenes and two species of the Comoros. Whether the radiation of Mascarene Ornebius results from intra- or purely inter- island speciation cannot be determined on the basis of the phylogenetic data alone. However, the existence of genetic, song and ecological divergence at the intra-island scale is suggestive of an intra-island speciation scenario in which ecological and mating traits diverge hand-in-hand. Our results suggest that the geographic location of Ornebius radiations is partially but not fully explained by island area and isolation. A notable anomaly is Madagascar, where our surveys are consistent with existing accounts in finding no Ornebius species present. Possible explanations are discussed, invoking ecological differences between species and differences in environmental history between islands.

Spider Web DNA: A New Spin on Noninvasive Genetics of Predator and Prey

Noninvasive genetic sampling enables biomonitoring without the need to directly observe or disturb target organisms. This paper describes a novel and promising source of noninvasive spider and insect DNA from spider webs. Using black widow spiders (Latrodectus spp.) fed with house crickets (Acheta domesticus), we successfully extracted, amplified, and sequenced mitochondrial DNA from spider web samples that identified both spider and prey to species. Detectability of spider DNA did not differ between assays with amplicon sizes from 135 to 497 base pairs. Spider and prey DNA remained detectable at least 88 days after living organisms were no longer present on the web. Spider web DNA as a proof-of-concept may open doors to other practical applications in conservation research, pest management, biogeography studies, and biodiversity assessments.

The geography and ecology of plant speciation: range overlap and niche divergence in sister species

A goal of evolutionary biology is to understand the roles of geography and ecology in speciation. The recent shared ancestry of sister species can leave a major imprint on their geographical and ecological attributes, possibly revealing processes involved in speciation. We examined how ecological similarity, range overlap and range asymmetry are related to time since divergence of 71 sister species pairs in the California Floristic Province (CFP). We found that plants exhibit strikingly different age-range correlation patterns from those found for animals; the latter broadly support allopatric speciation as the primary mode of speciation. By contrast, plant sisters in the CFP were sympatric in 80% of cases and range sizes of sisters differed by a mean of 10-fold. Range overlap and range asymmetry were greatest in younger sisters. These results suggest that speciation mechanisms broadly grouped under 'budding' speciation, in which a larger ranged progenitor gives rise to a smaller ranged derivative species, are probably common. The ecological and reproductive similarity of sisters was significantly greater than that of sister-non-sister congeners for every trait assessed. However, shifts in at least one trait were present in 93% of the sister pairs; habitat and soil shifts were especially common. Ecological divergence did not increase with range overlap contrary to expectations under character displacement in sympatry. Our results suggest that vicariant speciation is more ubiquitous in animals than plants, perhaps owing to the sensitivity of plants to fine-scale environmental heterogeneity. Despite high levels of range overlap, ecological shifts in the process of budding speciation may result in low rates of fine-scale spatial co-occurrence. These results have implications for ecological studies of trait evolution and community assembly; despite high levels of sympatry, sister taxa and potentially other close relatives, may be missing from local communities.

Climate and soil type together explain the distribution of microendemic species in a biodiversity hotspot

The grasshopper genus Caledonula, endemic to New Caledonia, was studied to understand the evolution of species distributions in relation to climate and soil types. Based on a comprehensive sampling of 80 locations throughout the island, the genus was represented by five species, four of which are new to science, of which three are described here. All the species have limited distributions in New Caledonia. Bioclimatic niche modelling shows that all the species were found in association with a wet climate and reduced seasonality, explaining their restriction to the southern half of the island. The results suggest that the genus was ancestrally constrained by seasonality. A molecular phylogeny was reconstructed using two mitochondrial and two nuclear markers. The partially resolved tree showed monophyly of the species found on metalliferous soils, and molecular dating indicated a rather recent origin for the genus. Adaptation to metalliferous soils is suggested by both morphological changes and radiation on these soils. The genus Caledonula is therefore a good model to understand the origin of microendemism in the context of recent and mixed influences of climate and soil type.

Biodiversity sampling using a global acoustic approach: contrasting sites with microendemics in New Caledonia

New Caledonia is a Pacific island with a unique biodiversity showing an extreme microendemism. Many species distributions observed on this island are extremely restricted, localized to mountains or rivers making biodiversity evaluation and conservation a difficult task. A rapid biodiversity assessment method based on acoustics was recently proposed. This method could help to document the unique spatial structure observed in New Caledonia. Here, this method was applied in an attempt to reveal differences among three mountain sites (Mandjélia, Koghis and Aoupinié) with similar ecological features and species richness level, but with high beta diversity according to different microendemic assemblages. In each site, several local acoustic communities were sampled with audio recorders. An automatic acoustic sampling was run on these three sites for a period of 82 successive days. Acoustic properties of animal communities were analysed without any species identification. A frequency spectral complexity index (NP) was used as an estimate of the level of acoustic activity and a frequency spectral dissimilarity index (D_f) assessed acoustic differences between pairs of recordings. As expected, the index NP did not reveal significant differences in the acoustic activity level between the three sites. However, the acoustic variability estimated by the index D_f, could first be explained by changes in the acoustic communities along the 24-hour cycle and second by acoustic dissimilarities between the three sites. The results support the hypothesis that global acoustic analyses can detect acoustic differences between sites with similar species richness and similar ecological context, but with different species assemblages. This study also demonstrates that global acoustic methods applied at broad spatial and temporal scales could help to assess local biodiversity in the challenging context of microendemism. The method could be deployed over large areas, and could help to compare different sites and determine conservation priorities.