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Although savanna woody encroachment has become a global phenomenon, relatively little is known about its effects on multiple dimensions and levels of savanna biodiversity.

Using a combination of field surveys, a species‐level phylogeny, and functional metrics drawn from a morphological dataset, we evaluated how the progressive increase in tree cover in a fire‐suppressed savanna landscape affects the taxonomic, functional, and phylogenetic diversity of neotropical ant communities, at both the alpha and beta levels. Ants were sampled along an extensive tree cover gradient, ranging from open savannas to forests established in former savanna areas.

Variation in tree cover had a significant influence on all facets of diversity at the beta level, whereas at the alpha level tree cover variation affected the taxonomic and functional but not the phylogenetic diversity of the ant communities.

In general, ant community responses to variation in tree cover were largely non‐linear as differences in taxonomic alpha diversity and in the taxonomic, functional, and phylogenetic composition of the sampled communities were often much stronger at the savanna/forest transition than at any other part of the gradient. This indicates that savanna ant communities switch rapidly to an alternative state once the savanna turns into forest.

Ant communities in the newly formed forest areas lacked many of the species typical of the savanna habitats, suggesting that the maintenance of a fire suppression policy is likely to result in a decrease in ant diversity and in the homogenisation of the ant fauna at the landscape scale.

 

Social parasites exploit the brood care behavior of their hosts to raise their own offspring. Social parasites are common among eusocial Hymenoptera and exhibit a wide range of distinct life history traits in ants, bees, and wasps. In ants, obligate inquiline social parasites are workerless (or nearly-so) species that engage in lifelong interactions with their hosts, taking advantage of the existing host worker forces to reproduce and exploit host colonies’ resources. Inquiline social parasites are phylogenetically diverse with approximately 100 known species that evolved at least 40 times independently in ants. Importantly, ant inquilines tend to be closely related to their hosts, an observation referred to as ‘Emery’s Rule’. Polygyny, the presence of multiple egg-laying queens, was repeatedly suggested to be associated with the origin of inquiline social parasitism, either by providing the opportunity for reproductive cheating, thereby facilitating the origin of social parasite species, and/or by making polygynous species more vulnerable to social parasitism via the acceptance of additional egg-laying queens in their colonies. Although the association between host polygyny and the evolution of social parasitism has been repeatedly discussed in the literature, it has not been statistically tested in a phylogenetic framework across the ants. Here, we conduct a meta-analysis of ant social structure and social parasitism, testing for an association between polygyny and inquiline social parasitism with a phylogenetic correction for independent evolutionary events. We find an imperfect but significant over-representation of polygynous species among hosts of inquiline social parasites, suggesting that while polygyny is not required for the maintenance of inquiline social parasitism, it (or factors associated with it) may favor the origin of socially parasitic behavior. Our results are consistent with an intra-specific origin model for the evolution of inquiline social parasites by sympatric speciation but cannot exclude the alternative, inter-specific allopatric speciation model. The diversity of social parasite behaviors and host colony structures further supports the notion that inquiline social parasites evolved in parallel across unrelated ant genera in the formicoid clade via independent evolutionary pathways.

 

Insect societies vary greatly in their social structure, mating biology, and life history. Polygyny, the presence of multiple reproductive queens in a single colony, and polyandry, multiple mating by females, both increase the genetic variability in colonies of eusocial organisms, resulting in potential reproductive conflicts. The co-occurrence of polygyny and polyandry in a single species is rarely observed across eusocial insects, and these traits have been found to be negatively correlated in ants.Acromyrmexleaf-cutting ants are well-suited for investigating the evolution of complex mating strategies because both polygyny and polyandry co-occur in this genus. We used microsatellite markers and parentage inference in five South AmericanAcromyrmexspecies to study how different selective pressures influence the evolution of polygyny and polyandry. We show thatAcromyrmexspecies exhibit independent variation in mating biology and social structure, and polygyny and polyandry are not necessarily negatively correlated within genera. One species,Acromyrmex lobicornis, displays a significantly lower mating frequency compared to others, while another species,A. lundii, appears to have reverted to obligate monogyny. These variations appear to have a small impact on average intra-colonial relatedness, although the biological significance of such a small effect size is unclear. All species show significant reproductive skew between patrilines, but there was no significant difference in reproductive skew between any of the sampled species. We find that the evolution of social structure and mating biology appear to follow independent evolutionary trajectories in different species. Finally, we discuss the evolutionary implications that mating biology and social structure have on life history evolution inAcromyrmexleaf-cutting ants.

Many species of eusocial insects have colonies with multiple queens (polygyny), or queens mating with multiple males (polyandry). Both behaviors generate potentially beneficial genetic diversity in ant colonies as well as reproductive conflict. The co-occurrence of both polygyny and polyandry in a single species is only known from few ant species. Leaf-cutting ants have both multi-queen colonies and multiply mated queens, providing a well-suited system for studying the co-evolutionary dynamics between mating behavior and genetic diversity in colonies of eusocial insects. We used microsatellite markers to infer the socio-reproductive behavior in five South American leaf-cutter ant species. We found that variation in genetic diversity in colonies was directly associated with the mating frequencies of queens, but not with the number of queens in a colony. We suggest that multi-queen nesting and mating frequency evolve independently of one another, indicating that behavioral and ecological factors other than genetic diversity contribute to the evolution of complex mating behaviors in leaf-cutting ants.

 

Supergenes, regions of the genome with suppressed recombination between sets of functional mutations, contribute to the evolution of complex phenotypes in diverse systems. Excluding sex chromosomes, most supergenes discovered so far appear to be young, being found in one species or a few closely related species. Here, we investigate how a chromosome harbouring an ancient supergene has evolved over about 30 million years (Ma). TheFormicasupergene underlies variation in colony queen number in at least five species. We expand previous analyses of sequence divergence on this chromosome to encompass about 90 species spanning theFormicaphylogeny. Within the nonrecombining region, the geneknockoutcontains 22 single nucleotide polymorphisms (SNPs) that are consistently differentiated between two alternative supergene haplotypes in divergent EuropeanFormicaspecies, and we show that these same SNPs are present in mostFormicaclades. In these clades, including an early diverging NearcticFormicaclade, individuals with alternative genotypes atknockoutalso have higher differentiation in other portions of this chromosome. We identify hotspots of SNPs along this chromosome that are present in multipleFormicaclades to detect genes that may have contributed to the emergence and maintenance of the genetic polymorphism. Finally, we infer three gene duplications on one haplotype, based on apparent heterozygosity within these genes in the genomes of haploid males. This study strengthens the evidence that this supergene originated early in the evolution ofFormicaand that just a few loci in this large region of suppressed recombination retain strongly differentiated alleles across contemporaryFormicalineages.

 

The ant genus Formicoxenus is notable for the fact that all its species are xenobiotic and live inside or in close association with the nests of other ant species. Here, we report the occurrence of a colony of Formicoxenus quebecensis and its host, Myrmica alaskensis from the eastern side of the Door peninsula in Wisconsin. Both species are new records for the state, and F. quebecensis was previously known only from boreal habitats much farther north in Canada. We also provide some observations on this colony’s nest demography, morphology, and feeding behavior and discuss the ant community of this biogeographically interesting location. 

 

Studying the historical biogeography and life history transitions from eusocial colony life to social parasitism contributes to our understanding of the evolutionary mechanisms generating biodiversity in eusocial insects. The ants in the genus Myrmecia are a well-suited system for testing evolutionary hypotheses about how their species diversity was assembled through time because the genus is endemic to Australia with the single exception of the species M. apicalis inhabiting the Pacific Island of New Caledonia, and because at least one social parasite species exists in the genus. However, the evolutionary mechanisms underlying the disjunct biogeographic distribution of M. apicalis and the life history transition(s) to social parasitism remain unexplored. To study the biogeographic origin of the isolated, oceanic species M. apicalis and to reveal the origin and evolution of social parasitism in the genus, we reconstructed a comprehensive phylogeny of the ant subfamily Myrmeciinae. We utilized Ultra Conserved Elements (UCEs) as molecular markers to generate a molecular genetic dataset consisting of 2,287 loci per taxon on average for 66 out of the 93 known Myrmecia species as well as for the sister lineage Nothomyrmecia macrops and selected outgroups. Our time-calibrated phylogeny inferred that: (i) stem Myrmeciinae originated during the Paleocene ~ 58 Ma ago; (ii) the current disjunct biogeographic distribution of M. apicalis was driven by long-distance dispersal from Australia to New Caledonia during the Miocene ~ 14 Ma ago; (iii) the single social parasite species, M. inquilina, evolved directly from one of the two known host species, M. nigriceps, in sympatry via the intraspecific route of social parasite evolution; and (iv) 5 of the 9 previously established taxonomic species groups are non-monophyletic. We suggest minor changes to reconcile the molecular phylogenetic results with the taxonomic classification. Our study enhances our understanding of the evolution and biogeography of Australian bulldog ants, contributes to our knowledge about the evolution of social parasitism in ants, and provides a solid phylogenetic foundation for future inquiries into the biology, taxonomy, and classification of Myrmeciinae. 

Aim One of the most consistent global biogeographic patterns is the latitudinal diversity gradient where species richness peaks within the equatorial tropics and decreases towards the poles. Here, we explore the global biogeography of socially parasitic ant species, which comprises the most diverse group of social parasites in the Hymenoptera. We test the biogeographic hypothesis that ant social parasites are distributed along an inverse latitudinal diversity gradient (iLDG) by peaking in diversity outside of the equatorial tropics, which would contrast with the biogeographic pattern observed in free-living, non-parasitic ant species. Location Global. Taxon Ants (Hymenoptera: Formicidae). Methods We assembled a comprehensive biogeographic dataset consisting of 6001 geographic distribution records for all 371 taxonomically described socially parasitic ant species. We used phylogenetic and taxonomic studies to estimate the number of independent evolutionary origins of ant social parasitism to directly compare species richness with the number of species representing independent evolutionary origins of social parasitism across a latitudinal gradient. In addition, we compared ant social parasite diversity across biogeographic regions using rarefaction to account for different sampling efforts. Finally, we tested for a correlation between latitude and the proportion of ant social parasite species within regional ant faunae. Results The geographic distribution records and the inferred 91 independent evolutionary origins of socially parasitic life histories in ants show that both species richness and the number of species representing independent evolutionary origins of social parasitism peak in the northern hemisphere outside of the equatorial tropics. Based on rarefaction curves, northern latitude regions harbour the most ant social parasite species, but the diversity of independent evolutionary origins is not significantly different between northern and southern hemispheres. The proportion of ant social parasite species within regional faunae is tightly correlated with latitude only in the northern hemisphere. Main conclusions The iLDG of ant social parasites contrasts with the biogeographic pattern observed in free-living, non-parasitic ant species and appears to be driven by large species radiations as well as by the presence of specialized life histories exclusive to the northern hemisphere. 

Abstract The prevalent mode of reproduction among ants is arrhenotokous parthenogenesis where unfertilized eggs give rise to haploid males and fertilized eggs develop into diploid females. Some ant species are capable of thelytokous parthenogenesis, a type of asexual reproduction where females develop from unfertilized diploid eggs. Thelytoky is well-documented in more than 20 ant species. Cytogenetic data are available for six species demonstrating that some thelytokous ant species are capable of producing males occasionally as well as maintaining their chromosome numbers and proper chromosome pairings. Mycocepurus smithii is a thelytokous fungus-growing ant species that inhabits large parts of Central and South America. Cytogenetic data are unavailable for M. smithii and male individuals were never documented for this species, although the presence of males is expected because genetic recombination was observed in a few sexually reproducing populations in Brazil and haploid sperm was documented from the spermathecae of M. smithii queens. This study aims at comparatively studying asexual and sexual populations of M. smithii using classical and molecular cytogenetic methods to test whether karyotype configuration is modified according to the mode of reproduction in M. smithii . Moreover, we report the discovery of M. smithii males from a sexually reproducing population in the Brazilian state Pará, diagnose the male of M. smithii , and morphologically characterize their spermatozoa. Karyotypic variation was observed within the asexual population (2n = 9, 10, or 11), whereas the chromosome number was fixed in the sexual population (2n = 14, n = 7). Identical karyotypes were maintained within individual M. smithii colonies and karyotype variation was only observed between colonies. In asexual individuals, the karyomorphs showed a decay of homologous chromosome pairs, especially in individuals with the karyomorph 2n = 11, which is potentially caused by relaxed natural selection on proper chromosome pairing. In contrast, females in the sexual population showed proper homologous chromosome pairings. In individuals of both asexual and sexual populations, we find that heterochromatin was localized in centromeric regions and on the short arms of the chromosomes, GC-rich regions were associated with heterochromatic regions, and 18S rDNA genes were located on the largest chromosome pair. This comparative cytogenetic analysis contributes to our understanding about the cytological mechanisms associated with thelytokous parthenogenesis in ants and suggests the decay of chromosome structure in the absence of meiosis and genetic recombination. 

Temnothorax (Myrmicinae, Crematogastrini) is one of the most diverse Holarctic ant genera, and new taxonomic advancements are still frequent worldwide. The Mediterranean region, a global biodiversity hotspot characterized by a complex geographic history, is home to a substantial portion of its described diversity. Sicily is the region’s largest island and, as ongoing investigations are revealing, it is inhabited by a long-overlooked but highly diverse ant fauna that combines multiple biogeographic influences. We combined qualitative and quantitative morphology of multiple castes with phylogenomic analysis based on ultra-conserved elements (UCEs) to describe four species of Temnothorax endemic to Sicily and the neighboring Maltese Islands (Sicilian Channel). Three of these species, T. marae Alicata, Schifani & Prebus sp. nov., T. poldii Alicata, Schifani & Prebus sp. nov. and T. vivianoi Schifani, Alicata & Prebus sp. nov., are new to science, while a redescription clarifies the identity of T. lagrecai (Baroni Urbani, 1964). These descriptions highlight the current difficulties of delimiting monophyletic Temnothorax species groups based on morphological characters. The intra-insular endemicity patterns we revealed highlight the importance of Mediterranean paleogeography to contemporary ant diversity and distribution in the region.