Ontogenetic change in the venom composition of one Mexican black-tailed rattlesnake (Crotalus molossus nigrescens) from Durango, Mexico.

To corroborate the ontogenetic shift in the venom composition of the Mexican Black-tailed Rattlesnake (Crotalus molossus nigrescens) previously reported through the census approach, we evaluated the shift in the protein profile, lethality, and proteolytic and phospholipase activities of four venom samples obtained in 2015, 2018, 2019, and 2021 from one C. m. nigrescens individual (CMN06) collected in Durango, Mexico. We demonstrated that the venom of C. m. nigrescens changed from a myotoxin-rich venom to a phospholipase A2 and snake venom metalloproteinase-rich venom. Additionally, the proteolytic and phospholipase activities increased with age, but the lethality decreased approximately three times.

Does size matter? An analysis of the niche width and vulnerability to climate change of fourteen species of the genus Crotalus from North America.

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.

Evidence of niche shift and invasion potential of Lithobates catesbeianus in the habitat of Mexican endemic frogs.

Invasive alien species are one of most severe threats to biodiversity and natural resources. These biological invasions have been studied from the niche conservatism and niche shifts perspective. Niche differentiation may result from changes in fundamental niche or realized niche or both; in biological invasions, niche differences between native and non-native ranges can appear through niche expansion, niche unfilling and niche stability. The American bullfrog Lithobates catesbeianus is an invasive species that can have negative impacts on native amphibian populations. This research examines the climate niche shifts of this frog, its potential range of expansion in Mexico and the risk of invasion by bullfrog in the habitats of 82 frog species endemic to Mexico, that based on their climatic niche similarity were divided in four ecological groups. The results indicate that species in two ecological groups were the most vulnerable to invasion by bullfrog. However, the climate niche shifts of L. catesbeianus may allow it to adapt to new environmental conditions, so species from the two remaining groups cannot be dismissed as not vulnerable. This information is valuable for decision making in prioritizing areas for conservation of Mexican endemic frogs.