Evolutionary history of the little fire ant Wasmannia auropunctata before global invasion: inferring dispersal patterns, niche requirements and past and present distribution within its native range

Considering climate change impact on the global potential geographical distribution of the invasive Argentine ant and little fire ant

The Argentine ant (Linepithema humile) and the little fire ant (Wasmannia auropunctata) are among the top 100 invasive alien species globally, causing significant ecological and economic harm. Therefore, it is crucial to study their potential geographic distribution worldwide. This study aimed to predict their global distribution under current and future climate conditions. We used distribution data from various sources, including CABI, GBIF, and PIAKey, and key climate variables selected from 19 environmental factors to model their potential geographic distribution using MaxEnt. The AUC values were 0.925 and 0.937 for L. humile and W. auropunctata, respectively, indicating good predictive performance. Suitable areas for L. humile were mainly in southern North America, northern South America, Europe, central Asia, southern Oceania, and parts of Africa, while W. auropunctata suitable areas were mostly in southern North America, most of South America, a small part of Europe, southern Asia, central Africa, and some parts of Oceania. Under climate change scenario, suitable areas for L. humile increased, while highly suitable areas for W. auropunctata decreased. The top four countries with the largest areas of overlapping suitable habitat under current climate were Brazil, China, Australia, and Argentina, while under future SSP585 climate scenario, the top four countries were Brazil, China, Indonesia, and Argentina. Some countries, such as Estonia and Finland, will see an overlapping adaptation area under climate change. In conclusion, this study provides insight into controlling the spread and harm of L. humile and W. auropunctata.

A Regional Approach Shows Differences Among Invasive Ants Solenopsis geminata and Wasmannia auropunctata (Hymenoptera: Formicidae) Within Its Native Range of Distribution

Worldwide, two of the most harmful invasive ants typical of disturbed sites are Solenopsis geminata (Fabricius) and Wasmannia auropunctata (Roger). Both are natives of the Neotropics and are widely distributed all over the tropics. Within its original geographic range, there are few data on its abundance and potential damage to natural ecosystems. In this study, we recorded their abundance and relationships to diversity and richness of soil ant communities in two localities with different amount of forested area (López Mateos, LM 77% and Venustiano Carranza, VC 27%), at Los Tuxtlas reserve. In each locality, four land use systems (LUS) were sampled: tropical rain forests, agroforestry plantations, annual crops, and pastures. Data were gathered from 360 ant samples obtained from litter squares, pitfall traps, and soil monoliths in 40 sampling points (20 per locality, and five per LUS). Solenopsis geminata was more abundant in LM than in VC; the opposite trend was observed for W. auropunctata. In LM, S. geminata was more abundant in crops than in the other LUS, whereas W. auropunctata tended to have higher abundances in less managed sites of both localities. Abundance and species richness of ant communities were higher in LM than in VC. At regional and local levels, we found negative relationships between the abundance of S. geminata and species richness; the inverse pattern was found for W. auropunctata. We conclude that at Los Tuxtlas, W. auropunctata can be considered as a typical dominant native species, whereas S. geminata is the common exotic invasive ant.

North-south and climate-landscape-associated pattern of population structure for the Atlantic Forest White Morpho butterflies

Atlantic Forest White Morpho butterflies, currently classified as Morpho epistrophus and M. iphitus, are endemic to the Atlantic Forest, where they are widely distributed throughout heterogeneous environmental conditions. Studies with endemic butterflies allow to elucidate questions on both patterns of diversity distribution and current and past processes acting on insect groups in this biodiversity hotspot. In the present study, we characterized one mtDNA marker (COI sequences) and developed 11 polymorphic loci of microsatellite for 22 sampling locations distributed throughout the entire Atlantic Forest domain. We investigated both the taxonomic limits of taxa classified as White Morpho and the structure and distribution of the genetic diversity throughout their populations. Genetic markers and distribution data failed to identify species diversification, population structure, or isolation among subpopulations attributed to different taxa proposed for the White Morpho, suggesting that the current distinction between two species is unreasonable. The Bayesian coalescent tree based on COI sequences also failed to recover monophyletic clades for the putative species, and pointed instead to a north-south oriented pattern of genetic structure, with the northern clade coalescing later than the southern clade. Northern samples also showed more intragroup structure than southern samples based on mtDNA data. Clustering tests based on microsatellites indicated the existence of three genetic clusters, with turnover between the states of Paraná and São Paulo. The north-south pattern found for the White Morpho populations is showed for the first time to a endemic AF insect and coincides with the two different bioclimatic domains previously described for vertebrates and plants. Population structure observed for these butterflies is related to climate- and landscape-associated variables, mainly precipitation and elevation.

Supercolonial structure of invasive populations of the tawny crazy ant Nylanderia fulva in the US

BACKGROUND

Social insects are among the most serious invasive pests in the world, particularly successful at monopolizing environmental resources to outcompete native species and achieve ecological dominance. The invasive success of some social insects is enhanced by their unicolonial structure, under which the presence of numerous queens and the lack of aggression against non-nestmates allow high worker densities, colony growth, and survival while eliminating intra-specific competition. In this study, we investigated the population genetics, colony structure and levels of aggression in the tawny crazy ant, Nylanderia fulva, which was recently introduced into the United States from South America.

RESULTS

We found that this species experienced a genetic bottleneck during its invasion lowering its genetic diversity by 60%. Our results show that the introduction of N. fulva is associated with a shift in colony structure. This species exhibits a multicolonial organization in its native range, with colonies clearly separated from one another, whereas it displays a unicolonial system with no clear boundaries among nests in its invasive range. We uncovered an absence of genetic differentiation among populations across the entire invasive range, and a lack of aggressive behaviors towards conspecifics from different nests, even ones separated by several hundreds of kilometers.

CONCLUSIONS

Overall, these results suggest that across its entire invasive range in the U.S.A., this species forms a single supercolony spreading more than 2000 km. In each invasive nest, we found several, up to hundreds, of reproductive queens, each being mated with a single male. The many reproductive queens per nests, together with the free movement of individuals between nests, leads to a relatedness coefficient among nestmate workers close to zero in introduced populations, calling into question the stability of this unicolonial system in which indirect fitness benefits to workers is apparently absent.

Southern expansion of the invasive ant Wasmannia auropunctata within its native range and its relation with clonality and human activity

The little fire ant Wasmannia auropunctata, native to the Neotropics, has become a serious pest worldwide over the past 100 years. It was originally distributed from Mexico to northern Argentina and new evidence suggests a recent southern range expansion during the last 60 years reaching central Argentina. This supercolonial ant species has a polymorphic reproductive system. Some populations, mostly found in undisturbed natural environments, are characterised by a classical sexual haplodiploid reproductive system. In other populations, which mainly occur in human-modified habitats, diploid queens and haploid males are produced clonally while workers are produced sexually. Here we studied the association between the recent southern range expansion of W. auropunctata in relation to human activity and clonality. We carried out an extensive survey within the southern limit of the species’ native distribution and characterised the type of habitat where populations were found. Moreover, we genetically determined the type of reproductive system in 35 populations by genotyping at 12 microsatellite loci a total of 191 reproductive individuals (i.e. queens and/or males). Clonality was the most common reproductive system, occurring in 31 out of 35 populations analysed. All the populations found in the recently colonised area in central Argentina were clonal and established in human-modified habitats, suggesting that clonality together with human activity might have facilitated the southwards expansion of W. auropunctata.

Combining niche shift and population genetic analyses predicts rapid phenotypic evolution during invasion

The rapid evolution of non-native species can facilitate invasion success, but recent reviews indicate that such microevolution rarely yields expansion of the climatic niche in the introduced habitats. However, because some invasions originate from a geographically restricted portion of the native species range and its climatic niche, it is possible that the frequency, direction, and magnitude of phenotypic evolution during invasion have been underestimated. We explored the utility of niche shift analyses in the red seaweed Gracilaria vermiculophylla, which expanded its range from the northeastern coastline of Japan to North America, Europe, and northwestern Africa within the last 100 years. A genetically informed climatic niche shift analysis indicates that native source populations occur in colder and highly seasonal habitats, while most non-native populations typically occur in warmer, less seasonal habitats. This climatic niche expansion predicts that non-native populations evolved greater tolerance for elevated heat conditions relative to native source populations. We assayed 935 field-collected and 325 common-garden thalli from 40 locations, and as predicted, non-native populations had greater tolerance for ecologically relevant extreme heat (40°C) than did Japanese source populations. Non-native populations also had greater tolerance for cold and low-salinity stresses relative to source populations. The importance of local adaptation to warm temperatures during invasion was reinforced by evolution of parallel clines: Populations from warmer, lower-latitude estuaries had greater heat tolerance than did populations from colder, higher-latitude estuaries in both Japan and eastern North America. We conclude that rapid evolution plays an important role in facilitating the invasion success of this and perhaps other non-native marine species. Genetically informed ecological niche analyses readily generate clear predictions of phenotypic shifts during invasions and may help to resolve debate over the frequency of niche conservatism versus rapid adaptation during invasion.

A tale of swinger insects: Signatures of past sexuality between divergent lineages of a parthenogenetic weevil revealed by ribosomal intraindividual variation

Naupactus cervinus (Boheman) (Curculionidae, Naupactini) is a parthenogenetic weevil native to the Paranaense Forest which displays high levels of genetic variation. Two divergent clades were identified, one ranging in forest areas (Forest clade), and the other in open vegetation areas (Grassland clade). Both of them have individuals with high levels of heterozygosity in ribosomal sequences. Investigation of intraindividual variation in ITS1 sequences through cloning and posterior sequencing suggested that mating between both groups most likely occurred in the Paranaense Forest after a secondary contact, which led to fixed heterozygotes as a consequence of parthenogenesis. Otherwise, sexual segregation would have disrupted multilocus genotypes. Only a small number of heterozygous genotypes of all the possible combinations are found in nature. We propose the occurrence of a hybrid zone in the Paranaense Forest. The fact that it is one of the most important biodiversity hotspots of the world, together with its key role for investigating evolutionary processes, makes it worthy of conservation. This is the first genetic evidence of bisexuality in N. cervinus.

Barcoding the butterflies of southern South America: Species delimitation efficacy, cryptic diversity and geographic patterns of divergence

Because the tropical regions of America harbor the highest concentration of butterfly species, its fauna has attracted considerable attention. Much less is known about the butterflies of southern South America, particularly Argentina, where over 1,200 species occur. To advance understanding of this fauna, we assembled a DNA barcode reference library for 417 butterfly species of Argentina, focusing on the Atlantic Forest, a biodiversity hotspot. We tested the efficacy of this library for specimen identification, used it to assess the frequency of cryptic species, and examined geographic patterns of genetic variation, making this study the first large-scale genetic assessment of the butterflies of southern South America. The average sequence divergence to the nearest neighbor (i.e. minimum interspecific distance) was 6.91%, ten times larger than the mean distance to the furthest conspecific (0.69%), with a clear barcode gap present in all but four of the species represented by two or more specimens. As a consequence, the DNA barcode library was extremely effective in the discrimination of these species, allowing a correct identification in more than 95% of the cases. Singletons (i.e. species represented by a single sequence) were also distinguishable in the gene trees since they all had unique DNA barcodes, divergent from those of the closest non-conspecific. The clustering algorithms implemented recognized from 416 to 444 barcode clusters, suggesting that the actual diversity of butterflies in Argentina is 3%-9% higher than currently recognized. Furthermore, our survey added three new records of butterflies for the country (Eurema agave, Mithras hannelore, Melanis hillapana). In summary, this study not only supported the utility of DNA barcoding for the identification of the butterfly species of Argentina, but also highlighted several cases of both deep intraspecific and shallow interspecific divergence that should be studied in more detail.

The roles of barriers, refugia, and chromosomal clines underlying diversification in Atlantic Forest social wasps

Phylogeographic studies have sought to explain the genetic imprints of historical climatic changes and geographic barriers within the Brazilian Atlantic Forest (AF) biota, and consequently two processes of diversification (refugia and barriers) have been proposed. Additionally, there is evidence that eustatic changes influenced the biogeographic history of the AF. Here we evaluate these contrasting diversification processes using two AF social wasp species – the mid-montane Synoeca cyanea and the lowland Synoeca aff. septentrionalis. We analyzed several sources of data including multilocus DNA sequence, climatic niche models and chromosomal features. We find support for idiosyncratic phylogeographic patterns between these wasps, involving different levels of population structure and genetic diversity, contrary suitable climatic conditions during the last glaciation, and contrasting historical movements along the AF. Our data indicate that neotectonics and refugia played distinct roles in shaping the genetic structure of these wasps. However, we argue that eustatic changes influenced the demographic expansion but not population structure in AF biota. Notably, these wasps exhibited chromosomal clines, involving chromosome number and decreasing of GC content, latitudinally oriented along the AF. Together, these results reinforce the need to consider individual organismal histories and indicate that barriers and refugia are significant factors in understanding AF evolution.