Populations and chromosomal races of a species often show variation in life-history characteristics due to phylogeny and environmental factors. We analysed variation in snout–vent length (SVL) and reproductive variables, such as minimum SVL at sexual maturity, litter size and embryo volume in females of the Sceloporus grammicus lizard complex, which includes seven chromosomal races as well as hybrid zones among different combinations of races (F5, F5 + 6, potential but unverified F5 + 6, F6, FM1, FM2, FM2 × F5 hybrid zone, FM3, LS and unverified SGG). The SGG, F5 and LS females were larger than F6 and FM3 females. Females with non-vitellogenic follicles and vitellogenic follicles were smaller than females with embryos. The SVL of females containing embryos varied among chromosomal races, the largest being the same as indicated above, but the smallest was the FM2 × F5 hybrid zone. Litter size was similar among chromosomal races (5.8 embryos), while embryo volumes varied among them. Two patterns of reproductive activity were found: seasonal and continuous reproduction. Our results showed the influence of environmental factors of each locality, which supports the ecological hypothesis. The use of chromosomal races did not reveal a significant phylogenetic effect, because allozyme and molecular data show only small pairwise genetic distances among the S. grammicus populations on the Mexican Plateau.
The niche comprises the set of abiotic and biotic environmental conditions in which a species can live. Consequently, those species that present broader niches are expected to be more tolerant to changes in climatic variations than those species that present reduced niches. In this study, we estimate the amplitude of the climatic niche of fourteen species of rattlesnakes of the genus Crotalus to evaluate whether those species that present broader niches are less susceptible to the loss of climatically suitable zones due to the projected climate change for the time period 2021–2040. Our results suggest that for the species under study, the breadth of the niche is not a factor that determines their vulnerability to climatic variations. However, 71.4% of the species will experience increasingly inadequate habitat conditions, mainly due to the increase in temperature and the contribution that this variable has in the creation of climatically suitable zones for most of these species.
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