Multiple introgression events during the diversification history of the edible Mexican grasshopper genus Sphenarium (Orthoptera: Pyrgomorphidae).

Speciation with gene flow often leads to ambiguous phylogenetic reconstructions, reticulate patterns of relatedness and conflicting nuclear versus mitochondrial (mt) lineages. Here we employed a fragment of the COI mtDNA gene and nuclear genome-wide data (3RAD) to assess the diversification history of Sphenarium, an orthopteran genus of great economic importance in Mexico that is presumed to have experienced hybridisation events in some of its species. We carried out separate phylogenetic analyses to evaluate the existence of mito-nuclear discordance in the species relationships, and also assessed the genomic diversity and population genomic structure and investigated the existence of interspecific introgression and species limits of the taxa involved based on the nuclear dataset. The species delineation analyses discriminated all the currently recognised species, but also supported the existence of four undescribed species. The mt and nuclear topologies had four discordant species relationships that can be explained by mt introgression, where the mt haplotypes of S. purpurascens appear to have replaced those of S. purpurascens A and B, S. variabile and S. zapotecum. Moreover, our analyses supported the existence of nuclear introgression events between four species pairs that are distributed in the Sierra Madre del Sur province in southeast Mexico, with three of them occurring in the Tehuantepec Isthmus region. Our study highlights the relevance of genomic data to address the relative importance of allopatric isolation versus gene flow in speciation.

Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity.

Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.

Sex-related differences in aging rate are associated with sex chromosome system in amphibians.

Sex-related differences in mortality are widespread in the animal kingdom. Although studies have shown that sex determination systems might drive lifespan evolution, sex chromosome influence on aging rates have not been investigated so far, likely due to an apparent lack of demographic data from clades including both XY (with heterogametic males) and ZW (heterogametic females) systems. Taking advantage of a unique collection of capture-recapture datasets in amphibians, a vertebrate group where XY and ZW systems have repeatedly evolved over the past 200 million years, we examined whether sex heterogamy can predict sex differences in aging rates and lifespans. We showed that the strength and direction of sex differences in aging rates (and not lifespan) differ between XY and ZW systems. Sex-specific variation in aging rates was moderate within each system, but aging rates tended to be consistently higher in the heterogametic sex. This led to small but detectable effects of sex chromosome system on sex differences in aging rates in our models. Although preliminary, our results suggest that exposed recessive deleterious mutations on the X/Z chromosome (the "unguarded X/Z effect") or repeat-rich Y/W chromosome (the "toxic Y/W effect") could accelerate aging in the heterogametic sex in some vertebrate clades.

Demographic consequences of dispersal-related trait shift in two recently diverged taxa of montane grasshoppers.

Although the pervasiveness of intraspecific wing-size polymorphism and transitions to flightlessness have long captivated biologists, the demographic outcomes of shifts in dispersal ability are not yet well understood and have been seldom studied at early stages of diversification. Here, we use genomic data to infer the consequences of dispersal-related trait variation in the taxonomically controversial short-winged (Chorthippus corsicus corsicus) and long-winged (Chorthippus corsicus pascuorum) Corsican grasshoppers. Our analyses revealed lack of contemporary hybridization between sympatric long- and short-winged forms and phylogenomic reconstructions supported their taxonomic distinctiveness, rejecting the hypothesis of intraspecific wing polymorphism. Statistical evaluation of alternative models of speciation strongly supported a scenario of Pleistocene divergence (<1.5 Ma) with ancestral gene flow. According to neutral expectations from differences in dispersal capacity, historical effective migration rates from the long- to the short-winged taxon were threefold higher than in the opposite direction. Although populations of the two taxa present a marked genetic structure and have experienced parallel demographic histories, our coalescent-based analyses suggest that reduced dispersal has fueled diversification in the short-winged C. c. corsicus. Collectively, our study illustrates how dispersal reduction can speed up geographical diversification and increase the opportunity for allopatric speciation in topographically complex landscapes.

Phylogenomics of the Mesoamerican alligator-lizard genera Abronia and Mesaspis (Anguidae: Gerrhonotinae) reveals multiple independent clades of arboreal and terrestrial species.

Abronia and Mesaspis are two of the five anguid lizard genera in the subfamily Gerrhonotinae. Their members are restricted to Mesoamerica, and most have allopatric distributions. Species of Abronia are primarily arboreal and occur in cloud and seasonally dry pine-oak forests, whereas those of Mesaspis are terrestrial and inhabit mesic microhabitats of montane forests. Recent molecular studies suggest that although these genera together form a monophyletic group, neither genus is monophyletic. Here we performed a phylogenetic study of Abronia and Mesaspis based on the most comprehensive taxonomic sampling of these genera to date and double digest restriction site-associated (ddRADseq) data. Our reconstructed phylogeny differed considerably from all previously published topologies, consistently recovering multiple independent clades of arboreal and terrestrial species and Abronia and Mesaspis as non-monophyletic. Geography, rather than current taxonomy, provides the best explanation of their phylogenetic relationships. Our analyses consistently recovered two main clades, distributed on the highlands of Middle America east and west of the Isthmus of Tehuantepec, respectively, and each composed of subclades of Abronia and Mesaspis. In the former main clade, members of the subgenus Auriculabronia formed the sister taxon to the Mesaspis moreletii complex, whereas the main clade west of the Isthmus was composed of two clades with a subclade of Abronia and another of Mesaspis each (one clade on the Atlantic versant of the main mountain ranges of eastern Mexico and another one on the Sierra Madre del Sur exclusive of its Atlantic versant) and a third clade with species of the subgenera Abronia and Scopaeabronia. We discuss the taxonomic implications of our results for the classification of the examined taxa and list the morphological characters that diagnose the recovered clades. This study highlights the utility of ddRADseq data to reconstruct the evolutionary history of supraspecific vertebrate taxa.

Late Pleistocene genetic diversification and demographic expansion in the widely distributed neotropical ant Neoponera villosa (Ponerinae).

Phylogeographic studies of continent-wide distributed species are key to understand population dynamics processes that occurred at large geographical scales. Here, we examined two mitochondrial (mt) DNA sequence (COI, Cyt b) and eight nuclear microsatellites markers to investigate the cohesiveness, genetic diversity and demographic history of Neoponera villosa (Fabricius), a ponerine ant species widely distributed along most part of the Neotropics and southern Nearctic. The reconstructed phylogeny and mt variation supported the cohesiveness of the examined populations of N. villosa. The species probably originated in South America during the late Pliocene/middle Pleistocene and subsequently dispersed to Central America and the Transitional Nearctic-Neotropical zone during the late Pleistocene, with an increase in its population size ca. 30 thousand years ago. The limited phylogeographic structure observed in N. villosa supports its late Pleistocene range expansion and gene flow among distant geographic areas in central and southern Mexico and Central America.

Comparative landscape genetics of pond-breeding amphibians in Mediterranean temporal wetlands: The positive role of structural heterogeneity in promoting gene flow.

Comparative landscape genetics studies can provide key information to implement cost-effective conservation measures favouring a broad set of taxa. These studies are scarce, particularly in Mediterranean areas, which include diverse but threatened biological communities. Here, we focus on Mediterranean wetlands in central Iberia and perform a multi-level, comparative study of two endemic pond-breeding amphibians, a salamander (Pleurodeles waltl) and a toad (Pelobates cultripes). We genotyped 411 salamanders from 20 populations and 306 toads from 16 populations at 18 and 16 microsatellite loci, respectively, and identified major factors associated with population connectivity through the analysis of three sets of variables potentially affecting gene flow at increasingly finer levels of spatial resolution. Topographic, land use/cover, and remotely sensed vegetation/moisture indices were used to derive optimized resistance surfaces for the two species. We found contrasting patterns of genetic structure, with stronger, finer scale genetic differentiation in Pleurodeles waltl, and notable differences in the role of fine-scale patterns of heterogeneity in vegetation cover and water content in shaping patterns of regional genetic structure in the two species. Overall, our results suggest a positive role of structural heterogeneity in population connectivity in pond-breeding amphibians, with habitat patches of Mediterranean scrubland and open oak woodlands ("dehesas") facilitating gene flow. Our study highlights the usefulness of remotely sensed continuous variables of land cover, vegetation and water content (e.g., NDVI, NDMI) in conservation-oriented studies aimed at identifying major drivers of population connectivity.

Integrative inference of population history in the Ibero-Maghrebian endemic Pleurodeles waltl (Salamandridae).

Inference of population histories from the molecular signatures of past demographic processes is challenging, but recent methodological advances in species distribution models and their integration in time-calibrated phylogeographic studies allow detailed reconstruction of complex biogeographic scenarios. We apply an integrative approach to infer the evolutionary history of the Iberian ribbed newt (Pleurodeles waltl), an Ibero-Maghrebian endemic with populations north and south of the Strait of Gibraltar. We analyzed an extensive multilocus dataset (mitochondrial and nuclear DNA sequences and ten polymorphic microsatellite loci) and found a deep east-west phylogeographic break in Iberian populations dating back to the Plio-Pleistocene. This break is inferred to result from vicariance associated with the formation of the Guadalquivir river basin. In contrast with previous studies, North African populations showed exclusive mtDNA haplotypes, and formed a monophyletic clade within the Eastern Iberian lineage in the mtDNA genealogy. On the other hand, microsatellites failed to recover Moroccan populations as a differentiated genetic cluster. This is interpreted to result from post-divergence gene flow based on the results of IMA2 and Migrate analyses. Thus, Moroccan populations would have originated after overseas dispersal from the Iberian Peninsula in the Pleistocene, with subsequent gene flow in more recent times, implying at least two trans-marine dispersal events. We modeled the distribution of the species and of each lineage, and projected these models back in time to infer climatically favourable areas during the mid-Holocene, the last glacial maximum (LGM) and the last interglacial (LIG), to reconstruct more recent population dynamics. We found minor differences in climatic favourability across lineages, suggesting intraspecific niche conservatism. Genetic diversity was significantly correlated with the intersection of environmental favourability in the LIG and LGM, indicating that populations of P. waltl are genetically more diverse in regions that have remained environmentally favourable through the last glacial cycle, particularly southern Iberia and northern Morocco. This study provides novel insights into the relative roles of geology and climate on the biogeography of a biodiversity hotspot.

Concordant morphological and molecular clines in a contact zone of the Common and Spined toad (Bufo bufo and B. spinosus) in the northwest of France.

BACKGROUND: Hybrid zones are regions where individuals of two species meet and produce hybrid progeny, and are often regarded as natural laboratories to understand the process of species formation. Two microevolutionary processes can take place in hybrid zones, with opposing effects on population differentiation. Hybridization tends to produce genetic homogenization, reducing species differences, whereas the presence of mechanisms of reproductive isolation result in barriers to gene flow, maintaining or increasing differences between taxa. RESULTS: Here we study a contact zone between two hybridizing toad species, Bufo bufo and B. spinosus, through a combination of molecular (12 polymorphic microsatellites, four nuclear and two mitochondrial SNP markers) and morphological data in a transect in the northwest of France. The results show largely concordant clines across markers, defining a narrow hybrid zone of ca. 30 km wide. Most hybrids in the centre of the contact zone are classified as F2 or backcrossed individuals, with no individuals assigned to the F1 hybrid class. CONCLUSIONS: We discuss the implications of these results for our understanding of the evolutionary history of these species. We anticipate that the toad contact zone here described will become an important asset in the study of hybrid zone dynamics and evolutionary biology because of its easy access and the abundance of the species involved.

Salt lakes of La Mancha (Central Spain): A hot spot for tiger beetle (Carabidae, Cicindelinae) species diversity.

The tiger beetle assemblage of the wetlands of La Mancha (central Spain) comprises nine species: Calomera littoralis littoralis, Cephalota maura maura, Cephalota circumdata imperialis, Cephalota dulcinea, Cicindela campestris campestris, Cicindela maroccana, Cylindera paludosa, Lophyra flexuosa flexuosa, and Myriochila melancholica melancholica. This assemblage represents the largest concentration of tiger beetles in a single 1º latitude / longitude square in Europe. General patterns of spatial and temporal segregation among species are discussed based on observations of 1462 specimens registered during an observation period of one year, from April to August. The different species of Cicindelini appear to be distributed over space and time, with little overlapping among them. Three sets of species replace each other phenologically as the season goes on. Most of the species occupy drying or dried salt lakes and salt marshes, with sparse vegetation cover. Spatial segregation is marked in terms of substrate and vegetation use. Calomera littoralis and Myriochila melancholica have been observed mainly on wet soils; Cephalota circumdata on dry open saline flats; Cephalota dulcinea and Cylindera paludosa in granulated substrates with typical halophytic vegetation; Cephalota maura is often present in man-modified areas. Cephalota circumdata and Cephalota dulcinea are included as species of special interest in the list of protected species in Castilla-La Mancha. Conservation problems for the Cicindelini assemblage arise from agricultural activities and inadequate use of sport vehicles. Attempts at restoring the original habitat, supressing old semi-industrial structures, may affect the spatial heterogeneity of the lakes, and have an effect on Cicindelinae diversity.

The complete mitogenome of the trilobite beetle, Platerodrilus sp. (Elateroidea: Lycidae).

The nucleotide sequence of the complete mitogenome of the trilobite beetle, Platerodrilus sp. was determined. This is the first complete mitogenome reported for the family Lycidae (Elateroidea: Coleoptera). The newly determined sequence is 16,394 bp long and shows a relatively high AT content (76.2%). The gene arrangement of the trilobite beetle mt genome is the same found in other related beetle mitogenomes. The reconstructed tree recovered Elateroidea as a strongly supported monophyletic group but could not resolve phylogenetic relationships among studied elateroid families, including Lycidae.