Genetic studies of various Prosopis species (Leguminosae,Section Algarobia) co‐occurring in oases of the Atacama Desert (northern Chile)

In the Atacama Desert from northern Chile (19–24°S), Prosopis (Leguminosae) individuals are restricted to oases that are unevenly distributed and isolated from each other by large stretches of barren landscape constituting an interesting study model as the degree of connectivity between natural populations depends on their dispersal capacity and the barriers imposed by the landscape. Our goal was to assess the genetic diversity and the degree of differentiation among groups of Prosopis individuals of different species from Section Algarobia and putative hybrids (hereafter populations) co‐occurring in these isolated oases from the Atacama Desert and determine whether genetic patterns are associated with dispersal barriers. Thirteen populations were sampled from oases located on three hydrographic basins (Pampa del Tamarugal, Rio Loa, and Salar de Atacama; northern, central, and southern basins, respectively). Individuals genotyped by eight SSRs show high levels of genetic diversity (H _O = 0.61, A _r = 3.5) and low but significant genetic differentiation among populations (F _ST = 0.128, F _ST‐ENA = 0.129, D _JOST = 0.238). The AMOVA indicates that most of the variation occurs within individuals (79%) and from the variance among individuals (21%); almost, the same variation can be found between basins and between populations within basins. Differentiation and structure results were not associated with the basins, retrieving up to four genetic clusters and certain admixture in the central populations. Pairwise differentiation comparisons among populations showed inconsistencies considering their distribution throughout the basins. Genetic and geographic distances were significantly correlated at global and within the basins considered (p < .02), but low correlation indices were obtained (r < .37). These results are discussed in relation to the fragmented landscape, considering both natural and non‐natural (humans) dispersal agents that may be moving Prosopis in the Atacama Desert.     

Landscape genetics of a specialized grasshopper inhabiting highly fragmented habitats: a role for spatial scale

Aim The study of geographical discontinuities in the distribution of genetic variability in natural populations is a central topic in both evolutionary and conservation research. In this study, we aimed to analyse (1) the factors associated with genetic diversity at the landscape spatial scale in the highly specialized grasshopper Mioscirtus wagneri and (2) to identify the relative contribution of alternative factors to the observed patterns of genetic structure in this species. Location La Mancha region, Central Spain. Methods We sampled 28 populations of the grasshopper M. wagneri and genotyped 648 individuals at seven microsatellite loci. We employed a causal modelling approach to identify the most influential variables associated with genetic differentiation within a multiple hypothesis‐testing framework. Results We found that genetic diversity differs among populations located in different river basins and decreases with population isolation. Causal modelling analyses showed variability in the relative influence of the studied landscape features across different spatial scales. When a highly isolated population is considered, the analyses suggested that geographical distance is the only factor explaining the genetic differentiation between populations. When that population is excluded, the causal modelling analysis revealed that elevation and river basins are also relevant factors contributing to explaining genetic differentiation between the studied populations. Main conclusions These results indicate that the spatial scale considered and the inclusion of outlier populations may have important consequences on the inferred contribution of alternative landscape factors on the patterns of genetic differentiation even when all populations are expected to similarly respond to landscape structure. Thus, a multiscale perspective should also be incorporated into the landscape genetics framework to avoid biased conclusions derived from the spatial scale analysed and/or the geographical distribution of the studied populations.     

Low genetic diversity of a high mountain burnet moth species in the Pyrenees

The burnet moth Zygaena anthyllidis, endemic to the high elevations of the Pyrenees, is vulnerable to land-use. In order to identify conservation priorities based on an assessment of genetic diversity within populations and gene flow among populations, we examined Z. anthyllidis’ genetic variability and differentiation based on allozyme electrophoresis from seven populations scattered across its entire range. In comparison to other mountain Lepidoptera, the populations studied exhibit a low level of genetic diversity. Remarkable between-population differentiation (F _ST = 0.053), the presence of private alleles, and the lack of significant isolation-by-distance pattern characterises the genetic make-up of the species. We interpreted the pattern of genetic differentiation as a consequence of low dispersal power in combination with insufficient landscape connectivity. Ongoing land-use change might reinforce genetic differentiation due to habitat fragmentation and additionally affect negatively allozyme variability at shifting range margins, i.e. the capacity to adapt to changing environments. We therefore suggest creating a network of suitable habitats at the landscape scale to facilitate genetic exchange and to conserve the species’ overall genetic variability.     

Landscape Genetics of Leaf-Toed Geckos in the Tropical Dry Forest of Northern Mexico

Habitat fragmentation due to both natural and anthropogenic forces continues to threaten the evolution and maintenance of biological diversity. This is of particular concern in tropical regions that are experiencing elevated rates of habitat loss. Although less well-studied than tropical rain forests, tropical dry forests (TDF) contain an enormous diversity of species and continue to be threatened by anthropogenic activities including grazing and agriculture. However, little is known about the processes that shape genetic connectivity in species inhabiting TDF ecosystems. We adopt a landscape genetic approach to understanding functional connectivity for leaf-toed geckos (Phyllodactylus tuberculosus) at multiple sites near the northernmost limit of this ecosystem at Alamos, Sonora, Mexico. Traditional analyses of population genetics are combined with multivariate GIS-based landscape analyses to test hypotheses on the potential drivers of spatial genetic variation. Moderate levels of within-population diversity and substantial levels of population differentiation are revealed by F _ST and D _est. Analyses using structure suggest the occurrence of from 2 to 9 genetic clusters depending on the model used. Landscape genetic analysis suggests that forest cover, stream connectivity, undisturbed habitat, slope, and minimum temperature of the coldest period explain more genetic variation than do simple Euclidean distances. Additional landscape genetic studies throughout TDF habitat are required to understand species-specific responses to landscape and climate change and to identify common drivers. We urge researchers interested in using multivariate distance methods to test for, and report, significant correlations among predictor matrices that can impact results, particularly when adopting least-cost path approaches. Further investigation into the use of information theoretic approaches for model selection is also warranted.     

A geometric morphometric and microsatellite analyses of <Emphasis Type="Italic">Scaptotrigona mexicana</Emphasis> and <Emphasis Type="Italic">S. pectoralis</Emphasis> (Apidae: Meliponini) sheds light on the biodiversity of Mesoamerican stingless bees

Geometric morphometrics and molecular methods are effective tools to study the variability of stingless bee populations and species that merit protection given their worldwide decline. Based on previous evidence of cryptic lineages within the Scaptotrigona genus, we tested the existence of multiple evolutionary lineages within the species S. mexicana and we investigated the status of S. pectoralis. By analyzing their population structure, we found differences between the Pacific and Atlantic populations of each of these species, although geometric morphometrics of the wing only confirmed these results in S. mexicana. There was a tendency towards enhanced genetic differentiation over larger distances in the Atlantic populations of both species but not in the Pacific populations. These results revealed a pattern of differentiation among evolutionary units and a specific distribution of genetic diversity within these Scaptotrigona species in Mesoamerica, suggesting the need for future taxonomic revisions, as well as activities aimed at management and conservation.     

Comparative population genetics of a parasitic nematode and its host community: the trichostrongylid Neoheligmonella granjoni and Mastomys rodents in southeastern Senegal

Contrasting host and parasite population genetic structures can provide information about the population ecology of each species and the potential for local adaptation. Here, we examined the population genetic structure of the nematode Neoheligmonella granjoni at a regional scale in southeastern Senegal, using 11 microsatellite markers. Using the results previously obtained for the two main rodent species of the host community, Mastomys natalensis and Mastomys erythroleucus, we tested the hypothesis that the parasite population structure was mediated by dispersal levels of the most vagile host. The results showed similar genetic diversity levels between host and parasite populations, and consistently lower levels of genetic differentiation in N. granjoni, with the exception of one outlying locus with a high F_ST. The aberrant pattern at this locus was primarily due to two alleles occurring at markedly different frequencies in one locality, suggesting selection at this locus, or a closely linked one. Genetic differentiation levels and isolation by distance analyses suggested that gene flow was high and random in N. granjoni at the spatial scale examined. The correlation between pair-wise genetic differentiation levels in the parasite and its main host was consistent with the hypothesis tested. Models of local adaptation as a function of the dispersal rates of hosts and parasites suggest that opportunities for local adaptation would be low in this biological system.     

Testing the depth-differentiation hypothesis in a deepwater octocoral

The depth-differentiation hypothesis proposes that the bathyal region is a source of genetic diversity and an area where there is a high rate of species formation. Genetic differentiation should thus occur over relatively small vertical distances, particularly along the upper continental slope (200–1000 m) where oceanography varies greatly over small differences in depth. To test whether genetic differentiation within deepwater octocorals is greater over vertical rather than geographical distances, Callogorgia delta was targeted. This species commonly occurs throughout the northern Gulf of Mexico at depths ranging from 400 to 900 m. We found significant genetic differentiation (F_ST = 0.042) across seven sites spanning 400 km of distance and 400 m of depth. A pattern of isolation by depth emerged, but geographical distance between sites may further limit gene flow. Water mass boundaries may serve to isolate populations across depth; however, adaptive divergence with depth is also a possible scenario. Microsatellite markers also revealed significant genetic differentiation (F_ST = 0.434) between C. delta and a closely related species, Callogorgia americana, demonstrating the utility of microsatellites in species delimitation of octocorals. Results provided support for the depth-differentiation hypothesis, strengthening the notion that factors covarying with depth serve as isolation mechanisms in deep-sea populations.     

Molecular and morphological delimitation of Australian <Emphasis Type="Italic">Triops</Emphasis> species (Crustacea: Branchiopoda: Notostraca)—large diversity and little morphological differentiation

Australia has a very rich and diverse large branchiopod fauna with approximately 140 described or provisionally delimited species, but only one species of Triops, Triops australiensis (Spencer and Hall 1895), is currently recognized. Previous studies identified extensive genetic diversity within T. australiensis that suggested the presence of cryptic species. Herein, we employed an integrative approach to taxonomy to delimit putative species, integrating COI and EF1α sequence data and morphological data. Putative species were initially delimited based on COI by two computational approaches (GMYC and ABGD). The results were interpreted in the light of several species concepts, with particular emphasis on reproductive isolation. Twenty to 27 genetic lineages were delimited. Of these, up to 26 represent species following an evolutionary or phylogenetic species concept. Eighteen are biological species, though reproductive isolation could not be unambiguously established for allopatric species or species without known males. The level of co-occurrences was exceptionally high for Triops, with up to three syntopic and six sympatric species. Species delimitation was impeded by extensive overlap between intraspecific variability and interspecific variation in the genetic as well as morphological datasets. Without prior delimitation of putative species via COI, morphological delimitation would have been impossible. A potential explanation for the morphological variability is the retention of ancestral polymorphisms over long periods of time and across multiple speciation events without subsequent differentiation.     

Paragonimus westermani: Identification and characterization of the fasciclin I domain-containing protein

Paragonimus westermani is a trematode parasite that causes inflammatory lung disease as well as systemic infections in carnivorous mammals. The interaction of the parasite with host cells and paired worms is initiated by adhesion and plays an important role in parasite proliferation and differentiation. In this study, we isolated a cDNA encoding a P. westermani fasciclin I domain-containing protein (Pwfas-I). The fasiclin-I domain is suggested to be involved in cell adhesion, migration, and differentiation. Immunohistochemical analysis of P. westermani adult worms with polyclonal anti-Pwfas-I serum revealed immunoreactivity in the egg shells and the cells lining the sub-tegumental layer of adult worm throughout the contact regions of the cyst wall and paired worms. Using cell adhesion and spreading assays, we showed that Pwfas-I supports cell adhesion and spreading. Furthermore, we determined that the ανβ5 integrin was a functional receptor for the Pwfas-I. Taken together, these results suggest that Pwfas-I may be functional for the modulation of cell adhesion via binding with ανβ5 integrin in the extracellular matrix of Paragonimus.     

A complex history of introgression and vicariance in a threatened montane skink (<Emphasis Type="Italic">Pseudemoia cryodroma</Emphasis>) across an Australian sky island system

Species endemic to sky island systems are isolated to mountain peaks and high elevation plateaux both geographically and ecologically, making them particularly vulnerable to the effects of climate change. Pressures associated with climate change have already been linked to local extinctions of montane species, emphasizing the importance of understanding the genetic diversity and population connectivity within sky islands systems for the conservation management of remaining populations. Our study focuses on the endangered alpine skink Pseudemoia cryodroma, which is endemic to the Victorian Alps in south-eastern Australia, and has a disjunct distribution in montane habitats above 1100 m a.s.l. Using mitochondrial DNA (mtDNA) and microsatellite loci, we investigated species delimitation, genetic connectivity and population genetic structure across the geographic range of this species. We found discordance between genetic markers, indicating historical mtDNA introgression at one of the study sites between P. cryodroma and the closely related, syntopic P. entrecasteauxii. Molecular diversity was positively associated with site elevation and extent of suitable habitat, with inbreeding detected in three of the five populations. These results demonstrate the complex interaction between geography and habitat in shaping the population structure and genetic diversity of P. cryodroma, and highlight the importance of minimising future habitat loss and fragmentation for the long-term persistence of this species.     

Recent low levels of differentiation in the native <Emphasis Type="Italic">Bombus ephippiatus</Emphasis> (Hymenoptera: Apidae) along two Neotropical mountain-ranges in Guatemala

Recent anthropogenic fragmentation has led to population differentiation threatening viability of many species, including species specialized on mountainous ecosystems. Bombus ephippiatus, a widespread species mostly found in mountains in the Neotropics, seems to use the highlands as island, and deforested lowland areas may represent barriers to their dispersal, leading to isolation and potentially loss of genetic diversity. Yet, lack of knowledge of its population structure does not allow adequate management and conservation. To fill this knowledge gap, we assessed the population structure and inferred dispersion of B. ephippiatus in two mountain-ranges in Guatemala (Volcanic Chain and Sierra de las Minas). This region is characterized by high topographic variation and considerable deforestation strain. We analyzed the effects of elevation and land-use on genetic differentiation of B. ephippiatus populations and inferred its demography in the region. Our results suggest that B. ephippiatus is able to disperse long distances across most landscape types, reflected by its high genetic diversity, high effective population size, considerable gene flow, low population differentiation, as well as the lack of isolation by distance. Hence, B. ephippiatus may be a resilient species for the provision of pollination services. However, we detected a subtle divergence of B. ephippiatus into two clusters, of which Sierra de las Minas has been identified as a regional hotspot of genetic and species endemism. Yet, differentiation is very recent and hence likely caused by lowland deforestation. The combined effects of current forest cover and elevation partially explain the observed subtle patterns of differentiation suggesting that the maintenance of suitable habitat is crucial to ensure population connectivity of this keystone pollinator.     

Genetic differentiation and delimitation of Pugionium dolabratum and Pugionium cornutum (Brassicaceae)

Species delimitation has been a major research focus in evolutionary biology. However, the genetic delimitation of recently diverged species varies depending on the markers examined. In this study, we aimed to examine genetic differentiation and delimitations between only two species of Pugionium Gaertn (Brassicaceae)—Pugionium cornutum (L.) Gaertn and Pugionium dolabratum Maxim—that occur in the desert habitats of central Asia and have parapatric distributions. We genotyped 169 individuals from 25 populations, using two chloroplast (cp) DNA fragments (trnV-trnM and trnS-trnfM), seven simple repeated sequence (SSR) loci and the nuclear ribosomal internal transcribed spacer (ITS). Four cp haplotypes were identified, three of which commonly occur in the two species, suggesting incomplete species-specific lineage sorting. Between-species cpDNA differentiation (F _CT) was low, even lower than among populations of the same species. However, we found higher than average SSR F _CT values, and both Bayesian clustering of SSR variables and maximum-likelihood genetic analyses divided all sampled individuals into two groups, agreeing well with morphological separation, although gene flow between species was obvious according to the SSR loci data. However, two types of ITS sequences were highly consistent with the morphological delimitation of the two species in all sampled individuals. These results together suggest that these two species shared numerous ancestral cpDNA polymorphisms and point to the importance of nuclear DNA (ITS or genetic accumulation at multiple loci) in delimiting recently diverged species.     

Intricate evolutionary histories in montane species: a phylogenetic window into craniodental discrimination in the Peromyscus mexicanus species group (Mammalia: Rodentia: Cricetidae)

Mountain‐associated species, which exhibit allopatric distributions associated with elevation, endemisms and complex evolutionary histories, pose challenging evolutionary scenarios in which to discern the diversification of species. The Peromyscus mexicanus mice group, distributed along mountains in southern Mexico and Central America, is morphometrically variable, a key rationale for the ongoing controversy regarding its species delimitation. Based on the recognized 15 mitochondrial lineages for the group, we analysed external and craniodental morphometric variables to test whether lineages can be differentiated morphometrically and allow for the delimitation of species. We also aimed to test the prediction that the phylogenetic structure of the morphometric data is concordant with that of the molecular information. Based on 19 craniodental measurements from 521 specimens, multivariate and discriminant analyses showed that lineages are morphometrically discernible, representing distinct phenotypes, and that overall size and mandible measurements are significant features that discriminate lineages, supporting hypotheses about differences in feeding habits between species. Also, a pattern of increasing size with elevation was observed, further supported by specific morphological differences exhibited between highland and lowland lineages inhabiting the same mountain. Our results demonstrate that P. mexicanus is both genetically and morphometrically variable, where most highland montane species are differentiated from lowland species; also, a significant correlation between mitochondrial and morphometric information is indicative of phenetic concordance, altogether in agreement with a recent taxonomic proposal for the group. We suggest that the group's intricate diversification responds to ecological diversification and adaptation to a variety of mountain habitats and Pleistocene biogeographic climatic dynamics.     

Mitochondrial diversification of the Peromyscus mexicanus species group in Nuclear Central America: biogeographic and taxonomic implications

The mountain mice of the Peromyscus mexicanus group currently encompass six known species; however, the limits between species remain uncertain, with two considered monotypic and the other four having multiple associated subspecific names. Based on the most comprehensive sampling of the group throughout its distribution in Nuclear Central America, we used data of the mitochondrial cytochrome b gene to assess its genetic diversity, phylogeny, and main biogeographic and diversification patterns. Our mitochondrial phylogeny only partially reflects the current taxonomy of the group, in agreement with some of the taxonomically recognized species. Specifically, our phylogenetic results show that the group is highly structured, including four main clades with genetic distances ranging from 11 to 8.6%. A remarkable level of differentiation is found at a more local level, defined as 15 different lineages with high nucleotide and haplotype diversity (π = 0.068, h = 0.99), and with divergence and genetic distance values (p‐uncorrected = 9.9–2.4%; K2P = 10.8–3.0%) similar to values observed between species within Peromyscus. Accordingly, we propose that the reference name P. mexicanus is polyphyletic and should be restricted to the mountains of central Mexico west of the Isthmus of Tehuantepec. We suggest to limit the other five recognized specific names to equal number of lineages, as monophyletic, and to revalidate three junior synonyms: Peromyscus salvadorensis, P. nicaraguae and P. tropicalis. The Isthmus of Tehuantepec, the Motagua‐Polochic‐Jocotán fault system, the Maya Highlands and the Honduras Depression are examples of geographic features that are likely associated with the differentiation of main lineages. Some other lineages may represent candidate species, hence the need to review the taxonomic status of the entire P. mexicanus group.     

Glacial refugia and modern genetic diversity of 22 western North American tree species

North American tree species, subspecies and genetic varieties have primarily evolved in a landscape of extensive continental ice and restricted temperate climate environments. Here, we reconstruct the refugial history of western North American trees since the last glacial maximum using species distribution models, validated against 3571 palaeoecological records. We investigate how modern subspecies structure and genetic diversity corresponds to modelled glacial refugia, based on a meta-analysis of allelic richness and expected heterozygosity for 473 populations of 22 tree species. We find that species with strong genetic differentiation into subspecies had widespread and large glacial refugia, whereas species with restricted refugia show no differentiation among populations and little genetic diversity, despite being common over a wide range of environments today. In addition, a strong relationship between allelic richness and the size of modelled glacial refugia (r² = 0.55) suggest that population bottlenecks during glacial periods had a pronounced effect on the presence of rare alleles.     

Population genomic analysis suggests strong influence of river network on spatial distribution of genetic variation in invasive saltcedar across the southwestern United States

Understanding the complex influences of landscape and anthropogenic elements that shape the population genetic structure of invasive species provides insight into patterns of colonization and spread. The application of landscape genomics techniques to these questions may offer detailed, previously undocumented insights into factors influencing species invasions. We investigated the spatial pattern of genetic variation and the influences of landscape factors on population similarity in an invasive riparian shrub, saltcedar (Tamarix L.) by analysing 1,997 genomewide SNP markers for 259 individuals from 25 populations collected throughout the southwestern United States. Our results revealed a broad‐scale spatial genetic differentiation of saltcedar populations between the Colorado and Rio Grande river basins and identified potential barriers to population similarity along both river systems. River pathways most strongly contributed to population similarity. In contrast, low temperature and dams likely served as barriers to population similarity. We hypothesize that large‐scale geographic patterns in genetic diversity resulted from a combination of early introductions from distinct populations, the subsequent influence of natural selection, dispersal barriers and founder effects during range expansion.     

The African timber tree <Emphasis Type="Italic">Entandrophragma congoense</Emphasis> (Pierre ex De Wild.) A.Chev. is morphologically and genetically distinct from <Emphasis Type="Italic">Entandrophragma angolense</Emphasis> (Welw.) C.DC

Interpreting morphological variability in terms of species delimitation can be challenging. However, correcting species delineation can have strong implications for the sustainable management of exploited species. Up to now, species delimitation between two putative timber species from African forests, Entandrophragma congoense and E. angolense, remained unclear. To investigate their differences, we applied an integrated approach which combines morphological traits and genetic markers. We defined 13 morphological characters from 81 herbarium specimens and developed 15 new polymorphic microsatellite markers to genotype 305 samples (herbarium samples and specimens collected in the field across the species distribution ranges). Principal component analysis (PCA) of morphological data and the Bayesian clustering analyses of genetic data were used to assess differentiation between putative species. These analyses support two well-differentiated groups (F_ST?=?0.30) occurring locally in sympatry. Moreover, these two groups present distinct morphological characters at the level of the trunk, leaflets, and seeds. Our genetic markers identified few individuals (4%) that seem to be hybrids, though there is no evidence of genetic introgression from geographic patterns of genetic variation. Hence, our results provide clear support to recognize E. congoense as a species distinct from E. angolense, with a much lower genetic diversity than the latter, and that should be managed accordingly. This work highlights the power of microsatellite markers in resolving species boundaries.     

Landscape-level comparison of genetic diversity and differentiation in a small mammal inhabiting different fragmented landscapes of the Brazilian Atlantic Forest

Habitat loss and fragmentation can have detrimental effects on all levels of biodiversity, including genetic variation. Most studies that investigate genetic effects of habitat loss and fragmentation focus on analysing genetic data from a single landscape. However, our understanding of habitat loss effects on landscape-wide patterns of biodiversity would benefit from studies that are based on quantitative comparisons among multiple study landscapes. Here, we use such a landscape-level study design to compare genetic variation in the forest-specialist marsupial Marmosops incanus from four 10,000-hectare Atlantic forest landscapes which differ in the amount of their remaining native forest cover (86, 49, 31, 11 %). Additionally, we used a model selection framework to evaluate the influence of patch characteristics on genetic variation within each landscape. We genotyped 529 individuals with 12 microsatellites to statistically compare estimates of genetic diversity and genetic differentiation in populations inhabiting different forest patches within the landscapes. Our study indicates that before the extinction of the specialist species (here in the 11 % landscape) genetic diversity is significantly reduced in the 31 % landscape, while genetic differentiation is significantly higher in the 49 and 31 % landscapes compared to the 86 % landscape. Results further provide evidence for non-proportional responses of genetic diversity and differentiation to increasing habitat loss, and suggest that local patch isolation impacts gene flow and genetic connectivity only in the 31 % landscape. These results have high relevance for analysing landscape genetic relationships and emphasize the importance of landscape-level study designs for understanding habitat loss effects on all levels of biodiversity.     

Life in the desert: The impact of geographic and environmental gradients on genetic diversity and population structure of Ivesia webberi

For range‐restricted species with disjunct populations, it is critical to characterize population genetic structure, gene flow, and factors that influence functional connectivity among populations in order to design effective conservation programs. In this study, we genotyped 314 individuals from 16 extant populations of Ivesia webberi, a United States federally threatened Great Basin Desert using six microsatellite loci. We assessed the effects of Euclidean distance, landscape features, and ecological dissimilarity on the pairwise genetic distance of the sampled populations, while also testing for a potential relationship between I. webberi genetic diversity and diversity in the vegetative communities. The results show low levels of genetic diversity overall (H _e = 0.200–0.441; H _o = 0.192–0.605) and high genetic differentiation among populations. Genetic diversity was structured along a geographic gradient, congruent with patterns of isolation by distance. Populations near the species’ range core have relatively high genetic diversity, supporting in part a central‐marginal pattern, while also showing some evidence for a metapopulation dynamic. Peripheral populations have lower genetic diversity, significantly higher genetic distances, and higher relatedness. Genotype cluster admixture results suggest a complex dispersal pattern among populations with dispersal direction and distance varying on the landscape. Pairwise genetic distance strongly correlates with elevation, actual evapotranspiration, and summer seasonal precipitation, indicating a role for isolation by environment, which the observed phenological mismatches among the populations also support. The significant correlation between pairwise genetic distance and floristic dissimilarity in the germinated soil seed bank suggests that annual regeneration in the plant communities contribute to the maintenance of genetic diversity in I. webberi.     

Genetic admixture increases phenotypic diversity in the nectar yeast Metschnikowia reukaufii

Understanding the relationship between population genetic structure and phenotypic diversity is a fundamental question in evolutionary biology. Yeasts display wide genetic diversity and exhibit remarkably diverse heterotrophic metabolisms that allow a variety of niche occupations. However, little is known about how intra-species genetic population structure is related to trait diversity in yeasts. In this study, we investigated the link between intra-species genetic population structure and trait diversity in the floral nectar-inhabiting yeast Metschnikowia reukaufii (Ascomycota). A total of 73 strains obtained from 11 plant species were genotyped by whole genome sequencing, followed by single nucleotide polymorphism (SNP) calling, and phenotyped using a robot-assisted high-throughput screening platform. Analysis of the population structure estimated the number of ancestral populations to be K = 5, each one including strains from different locations and host plants, and 26% of strains showed significant genetic admixture (<80% ancestry from a single population). These mosaic strains were scattered throughout a maximum-likelihood phylogenetic tree built from SNP data, and differed widely in their ancestry. While yeast strains varied in nutrient assimilation and tolerance to inhibitors, trait differentiation among genetic lineages was in most cases negligible. Notably, outlier phenotypes largely corresponded to the mosaic strains, and removal of these from the data had a dramatic effect on the intra-species phylogenetic signal of studied phenotypes and patterns of trait evolution. Overall, these results suggest that genetic mosaicism broadens the phenotypic landscape explored by M. reukaufii and may allow adaptation to highly variable nectar environments.