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a. Ancestral area reconstruction based on the DIVA+J model from BioGeoBEARS. Pie charts at phylogeny nodes indicate the probability of the ancestral range occupied by that ancestor. Each color represents a reconstructed designated area, the black parts within the pies, indicated the areas with probabilities <5%. The arrows show the vicariance events and the rays the dispersal events. Rhombus (C. basiliscus), circle (C. m. molossus), triangle (C. ornatus), star (C. totonacus), cross (C. m. nigrescens), pentagon (C. m. oaxacus); b. Fifteen North American Terrestrial Ecoregions-Level III considered for the area’s reconstruction; c. Hypothetical scenario explaining the biogeographical structure of the black-tailed rattlesnakes’ group. Photos by Eric Centenero-Alcalá and Sociedad Herpetológica del Noreste de México A.C.
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The phylogenetic relationships among black-tailed rattlesnakes remain poorly understood and some authors indicated that the diversity of this group has been underestimated and additional analyses are required to clarify the biogeographic patterns throughout its distribution in Mexico. Therefore, the aim of this study was to elucidate the phylogenet...
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Mexico has the highest diversity of snake species in the world, following Australia when considering just venomous snakes. Specifically, in Sonora, the second largest state in the country, more than 15 highly venomous species occur, including the northern black-tailed rattlesnake (Crotalus molossus). This specie’s venom has not been as thoroughly researched in contrast with other Mexican vipers, nevertheless some studies report its biological activity and even pharmacological potential with antibacterial and cytotoxic activity. In this study we identified the main protein components from a pool of C. molossus venom through a gel-free proteomics approach, reporting ∼140 proteins belonging to the SVMP (38.76%), PLA2 (28.75%), CTL (11.93%), SVSP (6.03%) and LAAO (5.67%) toxin families. To study its biological activities, we evaluated its hemolytic, antibacterial, and cytotoxic activity in red blood cells, Gram positive and negative bacteria and a luminal A breast carcinoma cell line (T47D), respectively, in vitro. We report that concentrations < 100 μg/mL are potentially not hemolytic and reduced the bacteria viability of E. coli and S. aureus with an IC50 of 10.27 and 11.51 μg/mL, respectively. Finally, we determined the C. molossus venom as cytotoxic against the T47D breast carcinoma cell line, with an IC50 of 1.55 μg/mL. We suggest that the evaluated cytotoxicity was due to a high abundance of SVMPs and PLA2s, since it’s been reported that they affect the extracellular matrix and membrane permeation. This may provide a useful tool for pharmaceutical screening in the future.
Phylogenomics allows us to uncover the historical signal of evolutionary processes through time and estimate phylogenetic networks accounting for these signals. Insight from genome-wide data further allows us to pinpoint the contributions to phylogenetic signal from hybridization, introgression, and ancestral polymorphism across the genome. Here we focus on how these processes have contributed to phylogenetic discordance among rattlesnakes (genera Crotalus and Sistrurus), a group for which there are numerous conflicting phylogenetic hypotheses based on a diverse array of molecular datasets and analytical methods. We address the instability of the rattlesnake phylogeny using genomic data generated from transcriptomes sampled from nearly all known species. These genomic data, analyzed with coalescent and network-based approaches, reveal numerous instances of rapid speciation where individual gene trees conflict with the species tree. Moreover, the evolutionary history of rattlesnakes is dominated by incomplete speciation and frequent hybridization, both of which have likely influenced past interpretations of phylogeny. We present a new framework in which the evolutionary relationships of this group can only be understood in light of genome-wide data and network-based analytical methods. Our data suggest that network radiations, like seen within the rattlesnakes, can only be understood in a phylogenomic context, necessitating similar approaches in our attempts to understand evolutionary history in other rapidly radiating species.
Anthropogenic changes pose a significant threat to global biodiversity, especially in reptiles. Mexico, renowned for its diverse reptile population, is experiencing habitat disturbance and fragmentation, endangering rattlesnakes in particular due to their specific habitat requirements and limited mobility. The loss of structural connectivity further increases the risk of extinction for reptiles. Our study focuses on predicting the distribution and connectivity of nine Crotalus species in the Trans-Mexican Volcanic Belt (TMVB), using environmental modeling. We used climate models (CNRM-CM5 and MPI-ESM-LR) for the year 2050 and Representative Concentration Pathways (RCP 85) alongside changes in vegetation cover and land use. The Maxent modeling method in ENMeval helped assess distribution patterns and to identify key environmental variables influencing these species’ distributions and niche overlap. We also conducted an analysis of the structural connectivity of the different Crotalus species. Our findings indicate reductions in suitable habitats due to changes in agriculture, urbanization, and forest cover. The Maxent models showed high accuracy in predicting species distributions. The most influential variables varied among species and included forest types and climatic factors. We observed limited connectivity among small Crotalus species, although some species exhibited greater connectivity than others. Future models suggest potential distribution reductions for all species, with C. armstrongi facing the greatest reduction (78%) according to the cn85 global climate model. Protected areas do not encompass the majority of potential distribution for these small rattlesnake species. These findings highlight the urgency of conservation efforts and the need to mitigate the impacts of future environmental changes on reptile populations.
