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Gene flow in riparian ecosystems is influenced by landscape features such as orography, climate, and salinity. The downstream increase in genetic diversity (DIGD) hypothesis states that the unidirectionality of the watercourse causes an accumulation of genetic diversity toward downstream populations, while upstream populations are more structured and less diverse, especially in water-dispersed organisms.We used chloroplast and nuclear microsatellites to characterize genetic diversity, structure, and gene flow patterns among populations of Salix humboldtiana across an elevation and salinity gradient on three rivers (Actopan, Antigua, and Blanco) in Mexico. We used optimization of resistance surface methods to determine whether genetic distances between populations are correlated with landscape features.Positive FOur results depict that the DIGD and gene flow patterns in S. humboldtiana result from the complex interaction among physiography, climate, river salinity, and life-history traits of the species.

Aim To infer the geological and climatic factors that have shaped the genetic diversity and structure of a willow species (Salix humboldtiana) in three basins of Central Mexico. Location Central Mexico. Methods We collected samples from 11 populations across two hydrological basins (Balsas and Lerma) and one population from another basin (Ameca) within the Mexican Central Plateau (MCP). Individuals were analyzed using sequences of two chloroplast DNA (cpDNA) regions and eight nuclear simple sequence repeats (nSSR). Population genetic diversity and structure were determined from these data. To evaluate whether genetic structure was associated with ecological niche differentiation, we determined whether there is niche equivalence, overlap, or divergence between the Balsas and Lerma basins. Also, we evaluated the relative contributions of geographic distribution and climatic variation on population genetic structuring through redundancy analysis (RDA) and partial RDA. Results Both cpDNA and nSSRs data indicated the presence of three highly differentiated genetic groups, mostly geographically congruent with the three main hydrological basins. According to nSSRs, the three genetic groups can be further subdivided into eight subgroups corresponding to different rivers within the main basins. The niche equivalency test showed that the niches of the species in the Balsas and Lerma basins are significantly nonequivalent. The RDA indicated a significant association of genetic variation among populations with climate variables (particularly those related to the precipitation regime), while controlling for geographic distribution. Main conclusions The genetic structure of S. humboldtiana is strongly associated with the historical and current geological configuration of the basins and the rivers within basins. The observed hierarchical genetic differentiation can be due to gene flow limitation resulting from physical barriers to the dispersal of S. humboldtiana, but also to some degree of isolation by environment, as suggested by the significant association between genetic variation among populations and precipitation regime.

Land use changes are threatening the maintenance of biodiversity. Genetic diversity is one of the main indicators of biological diversity and is highly important as it shapes the capability of populations to respond to environmental changes. We studied eleven populations of Pseudoeurycea robertsi, a micro-endemic and critically endangered species from the Nevado de Toluca Volcano, a mountain that is part of the Trans-Mexican Volcanic Belt, Mexico. We sequenced the mitochondrial cytochrome b gene from 71 individuals and genotyped 9 microsatellites from 150 individuals. Our results based on the cytochrome b showed two divergent lineages, with moderate levels of genetic diversity and a recently historical demographic expansion. Microsatellite-based results indicated low levels of heterozygosity for all populations and few alleles per locus, as compared with other mole salamander species. We identified two genetically differentiated subpopulations with a significant level of genetic structure. These results provide fundamental data for the development of management plans and conservation efforts for this critically endangered species.

Roberts’ False Brook Salamander (Pseudoeurycea robertsi) is a critically endangered plethodontid salamander, endemic to the Nevado de Toluca Volcano (NTV), Mexico. Little is known about the biology and ecology of this species, including its microhabitats. Thus, this study aimed to collect basic information about P. robertsi. We sampled fourteen forested sites in the NTV; to corroborate the correct identification of the species we used genetic data, we assessed the variation in head morphometric measurements and dorsal colouration patterns amongst localities and the microhabitat features associated with P. robertsi presence. Of the four potential salamander species, P. robertsi was the most abundant (89.80%) and widely distributed (approximately within 130 km2) salamander in the NTV. We did not find significant variations in morphometry; however, we found significant differences in dorsal patterns between populations (in the number and size of segments of the dorsal stripe). The average total length for 185 adults was 89.15 mm (38.7–117.9 mm); we found seven patterns of dorsal stripe. We found 98% of P. robertsi individuals under the bark of fallen logs in Abies religiosa and A. religiosa-Pinus sp. forests, with a higher number of detected salamanders in naturally-fallen logs than in cut logs (34% vs. 10%). Thus, keeping well-preserved A. religiosa forests and retaining fallen logs is essential to P. robertsi conservation.

AIM: A fundamental problem in evolutionary biology has been understanding the role of environmental factors in the process of genetic diversification. Our main goal was to define the ecological niches of two Boa imperator lineages, in order to assess if environmental drivers could be associated with the divergence and genetic variation between them. We quantified the environmental niches at two evolutionary and geographical scales: regional‐historical (lineages) and local‐ecological (individuals within lineages). LOCATION: Neotropical region of Mexico and mainland Central America. METHODS: We performed ecological niche modelling (ENM) methods by defining the accessibility area per B. imperator lineage, based on their geographic ranges, to analyse ecological and geographical distributions. We applied statistics of niche overlap, interpredictability, equivalency and similarity. We tested the niche‐centrality hypothesis within lineages by evaluating the relationship between genetic metrics and the distance to ecological and geographical centroids. RESULTS: Temperature seasonality, precipitation and elevation were the most informative environmental variables (GARP and MaxEnt). Ecological interprediction and niche similarity and equivalency tests revealed a dynamic process of niche evolution, where the niches of the two lineages are not identical but still showed a signature of niche conservatism. Correlation analyses between genetic variability and structure showed negative correlations with distance to ecological and geographical centroids at the local level. MAIN CONCLUSIONS: Our results support the role of environmental variables as significant and highly accurate predictors of lineage distribution and divergence, in agreement with the boa's evolutionary history. The niches of the two lineages are not identical, sharing environmental niche space but not all ecological variables. A historically more recent signal of genetic structure within lineages was evident, where the quality of the ecological niche further influences genetic distribution patterns within populations. Our results illustrate how ENM may validate evolutionary patterns from a biogeographical and phylogeographical framework.

Aim To infer the geological and climatic factors that have shaped the genetic diversity and structure of a willow species (Salix humboldtiana) in three basins of Central Mexico. Location Central Mexico. Methods We collected samples from 11 populations across two hydrological basins (Balsas and Lerma) and one population from another basin (Ameca) within the Mexican Central Plateau (MCP). Individuals were analyzed using sequences of two chloroplast DNA (cpDNA) regions and eight nuclear simple sequence repeats (nSSR). Population genetic diversity and structure were determined from these data. To evaluate whether genetic structure was associated with ecological niche differentiation, we determined whether there is niche equivalence, overlap, or divergence between the Balsas and Lerma basins. Also, we evaluated the relative contributions of geographic distribution and climatic variation on population genetic structuring through redundancy analysis (RDA) and partial RDA. Results Both cpDNA and nSSRs data indicated the presence of three highly differentiated genetic groups, mostly geographically congruent with the three main hydrological basins. According to nSSRs, the three genetic groups can be further subdivided into eight subgroups corresponding to different rivers within the main basins. The niche equivalency test showed that the niches of the species in the Balsas and Lerma basins are significantly nonequivalent. The RDA indicated a significant association of genetic variation among populations with climate variables (particularly those related to the precipitation regime), while controlling for geographic distribution. Main conclusions The genetic structure of S. humboldtiana is strongly associated with the historical and current geological configuration of the basins and the rivers within basins. The observed hierarchical genetic differentiation can be due to gene flow limitation resulting from physical barriers to the dispersal of S. humboldtiana, but also to some degree of isolation by environment, as suggested by the significant association between genetic variation among populations and precipitation regime.

Invasive species represent a major threat for biodiversity. The numbers of independent introductions, introduced propagules, and introduction episodes are critical aspects for invasion success. Here, we traced the source(s) of introduction and determined the historical route of invasion in order to understand the main stages of the invasion process. However, we often must rely on indirect information when studying invasive species (i.e., not knowing where the invasive population originated), hence requiring robust analytical methods to solve those questions. The invasive population of the snake Boa constrictor in the Mexican Caribbean (Cozumel Island) has been studied ecologically and genetically, but, despite several lines of evidence suggesting its invasive nature, a full account of its invasive history is lacking. Here, we aimed to reconstruct the boa's invasion history by deciphering the original source(s) of the Cozumel population, routes of invasion, likely number of propagules, and estimation of historical genetic and demographic parameters, based on a comprehensive set of analytical tools including tree topology-based methods and Approximate Bayesian Computational algorithms. The phylogenetic relationship of the Cozumel boa within the Boa constrictor complex was unknown; hence, to identify the source populations, we first needed to clarify its genealogical relationships. We used mitochondrial and nuclear sequences and nuclear microsatellites, together with the widest geographic sampling along the species' entire continental distribution. With our genetic approach, we demonstrate that the Cozumel population was derived from an admixture of individuals from different geographic localities. Moreover, our demography results allowed us to successfully confirm both anecdotal and previous genetic information, concordant with a scenario in which a likely small number of propagules were released on the island about 50 years ago. Notably, national law hinders the possibility of performing any control protocols for the boa, hence our results highlight a rather unique conservation paradox, where the Cozumel boa has a novel endangered protected species status as B. imperator, but it is also an invasive exotic predator threatening the critically endangered endemic and native biota of Cozumel. Therefore, any conservation decisions should consider that boas in Cozumel are invasive, opening the possibility to legally allow implementing control or eradication programs.

Aim To evaluate the genetic diversity and phylogeographical structure of Boa constrictor imperator, in order to identify the key historical events responsible for its current distribution and diversity. Location The Neotropical region of Mexico and mainland Central America. Methods We used data from the mitochondrial cytochrome b gene, nuclear ornithine decarboxylase intron and microsatellites to perform spatial genetic analyses, and coalescence methods to infer phylogeographical structure, divergence times and historical demography. Results Cytochrome b results revealed two main reciprocally monophyletic lineages, one along the Mexican Pacific coast and another along the Gulf of Mexico, Yucatan Peninsula and Central America, diverging c. 5.2 Ma. Both lineages are subdivided into haplogroups and show steady historical growth and a more recent population expansion. High genetic diversity was observed for both cytochrome b (h = 0.944) and microsatellites (HNei = 0.810–0.900). Main conclusions We demonstrate deep phylogeographical structure with two reciprocally monophyletic lineages and five genetic clusters in Mexico and Central America. Our results suggest that several geographical barriers (including the Trans-Mexican Volcanic Belt and the Motagua–Polochic–Jocotan faults) and ecological features generated this structure. We report genetic diversity values for the boa at a regional scale and suggest that the two lineages may be considered distinct species.

Only one study has described the population genetic structure of Boa constrictor imperator and only in a single naturally colonized island. B.c. imperator, a snake with a naturally wide distribution across the Neotropics, was introduced to Cozumel Island, Mexico, in 1971. At present, it is one of the most abundant, widely distributed, terrestrial vertebrate on the island. We analysed the genetic diversity and structure, based on seven microsatellite loci, of 76 individuals of B.c. imperator from Cozumel. We also included 96 samples from different localities across mainland Mexico, to review the potential origin of the founder individuals. We identified two genetically differentiated populations on Cozumel that showed moderate levels of genetic diversity (Ho = 0.590–0.620), with a low but significant level of genetic structure (FST = 0.032). Individuals were highly unrelated (71 %) and the majority of genetic variation was distributed within individuals (84 %). We detected a signal of reduction in population size and evidence of genetic bottleneck. The genetically closest mainland populations, indicating potential source of island founders, are localities from the Gulf of Mexico and Yucatan peninsula. Results are in agreement with a recently introduced population, founded by a few individuals originating from several sources, which has been successful. B.c. imperator is jeopardizing a highly vulnerable insular ecosystem, hence its eradication from Cozumel is urgently needed. Our information is also valuable for other introduced-boa cases or as a basis for its conservation elsewhere given its classification as a threatened species.