RESUMO
The Mexican highlands are areas of high biological complexity where taxa of Nearctic and Neotropical origin and different population histories are found. To gain a more detailed view of the evolution of the biota in these regions, it is necessary to evaluate the effects of historical tectonic and climate events on species. Here, we analyzed the phylogeographic structure, historical demographic processes, and the contemporary period, Last Glacial Maximum (LGM) and Last Interglacial (LIG) ecological niche models of Quercus castanea, to infer the historical population dynamics of this oak distributed in the Mexican highlands. A total of 36 populations of Q. castanea were genotyped with seven chloroplast microsatellite loci in four recognized biogeographic provinces of Mexico: the Sierra Madre Occidental (western mountain range), the Central Plateau, the Trans-Mexican Volcanic Belt (TMVB, mountain range crossing central Mexico from west to east) and the Sierra Madre del Sur (SMS, southern mountain range). We obtained standard statistics of genetic diversity and structure and tested for signals of historical demographic expansions. A total of 90 haplotypes were identified, and 29 of these haplotypes were restricted to single populations. The within-population genetic diversity was high (mean h S = 0.72), and among-population genetic differentiation showed a strong phylogeographic structure (N ST = 0.630 > G ST = 0.266; p < .001). Signals of demographic expansion were identified in the TMVB and the SMS. The ecological niche models suggested a considerable percentage of stable distribution area for the species during the LGM and connectivity between the TMVB and the SMS. High genetic diversity, strong phylogeographic structure, and ecological niche models suggest in situ permanence of Q. castanea populations with large effective population sizes. The complex geological and climatic histories of the TMVB help to explain the origin and maintenance of a large proportion of the genetic diversity in this oak species.
RESUMO
Although the Mexican Highlands has the highest diversity of small-bodied rattlesnakes in the world, studies on the species found throughout this region have been relatively scarce. This has led to challenges with examining venom phenotypic characteristics, as well as species misidentifications and misclassifications. In the current study we investigated venom variation among four subspecies of Crotalus lepidus (C. l. klaluberi, C. l. lepidus, C. l. maculosus, C. l. morulus) and four subspecies of C. willardi (C. w. amabilis, C. w. obscurus, C. w. silus, and C. w. willardi) that inhabit regions of southwestern United States and central México. SDS-PAGE patterns show the presence of many of the major compounds found in other rattlesnake venoms, although minor variations in protein banding patterns and intensity are recognizable. Most notably, PI-metalloproteinase (SVMP) bands appear to be very faint to absent in northern C. l. lepidus and C. l. klauberi subspecies, but are fairly prominent in all other C. lepidus and C. willardi subspecies. Enzyme activity assays revealed that C. lepidus subspecies exhibit higher SVMP and thrombin-like activities when compared to C. willardi subspecies. Significant differences between subspecies were also observed for kallikrein-like serine protease, L-amino acid oxidase, and phosphodiesterase activities, although these differences appear to be random and fail to follow a geographical or phylogenetic trend. The same relationship was also observed for fibrinogenolytic and coagulation assays. Toxicity assays conducted on lab mice (Mus musculus), house geckos (Hemidactylus frenatus), and house crickets (Acheta domestica) revealed varying toxicities between subspecies, with C. l klauberi being the most toxic towards mice (LD50 = 1.36 µg/g) and house geckos (LD50 = 0.17 µg/g), and C. w. silus being most toxic to house crickets (LD50 = 1.94 µg/g). These results provide additional evidence that geographical isolation, natural selection, and adaptive evolution in response to diets may be driving forces contributing to population-level variation in venom composition.
