Boa constrictor occidentalis, the only subspecies of the genus Boa present in Argentina, is endangered because of the strong hunting pressure due to the skin and pet-shop trade and the destruction and fragmentation of its habitat. We estimated levels of protein polymorphism and determined the degree of genetic differentiation between two populations of B. c. occidentalis in Córdoba province, Argentina. We obtained blood samples from 93 specimens in two sampling sites 200 km apart. A total of 17 proteins affording information on 25 presumptive loci were studied by gel electrophoresis techniques. Only four loci were polymorphic: 6-Pgdh-1, Cat-1, Ldh and Hp. The mean heterozygosity per locus was low (0.06 and 0.07). Life history and ecological traits of this snake may explain the low levels of polymorphism found. No evidence of inbreeding was detected. The average genetic differentiation between the two sampled areas was not significant ( = 0.004). These results would indicate a relatively recent fragmentation of an original gene pool.
We provide data on intrapopulation variation of life history traits of Boa constrictor occidentalis in the District of Pocho, Córdoba, Argentina. A total of 153 individuals were captured. The distribution of individuals among four size classes differed significantly among the five years of study. The proportion of mature individuals did not differ between sexes but it showed variation among years. Females were longer and heavier than males. The mean litter size of the species was 24 and there was a linear relationship between litter size and maternal snout-vent length. Most boas were captured during the dry season. There were no significant sex differences in the time of capture and air temperature in either the wet or the dry seasons. However, we found significant differences in the time of capture and air temperature between the seasons. The long-term monitoring of wild populations should be a priority for the development of conservation and management plans for this boid.
Understanding factors that shape ranges of species is central in evolutionary biology. Species distribution models have become important tools to test biogeographical, ecological and evolutionary hypotheses. Moreover, from an ecological and evolutionary perspective, these models help to elucidate the spatial strategies of species at a regional scale. We modelled species distributions of two phylogenetically, geographically and ecologically close Tupinambis species (Teiidae) that occupy the southernmost area of the genus distribution in South America. We hypothesized that similarities between these species might have induced spatial strategies at the species level, such as niche differentiation and divergence of distribution patterns at a regional scale. Using logistic regression and MaxEnt we obtained species distribution models that revealed interspecific differences in habitat requirements, such as environmental temperature, precipitation and altitude. Moreover, the models obtained suggest that although the ecological niches of Tupinambis merianae and T. rufescens are different, these species might co-occur in a large contact zone. We propose that niche plasticity could be the mechanism enabling their co-occurrence. Therefore, the approach used here allowed us to understand the spatial strategies of two Tupinambis lizards at a regional scale.
The viviparous snake species Epicrates cenchria alvarezi and Boa constrictor occidentalis inhabit the Gran Chaco region of South America. Ecological factors determining their distribution are poorly known. GIS-based modelling of a species' environmental requirements using occurrence records provides essential information of the species' distribution. We modelled the geographical distribution of E. c. alvarezi and B. c. occidentalis in the Gran Chaco and analyzed the degree to which their distribution is associated with different environmental variables (precipitation, normalized difference vegetation index (NDVI), land surface temperature and altitude) using Logistic Regression Analysis. We found that E. c. alvarezi and B. c. occidentalis would be more frequent in areas with high levels of NDVI (positive relationship with NDVI1), with low levels of precipitation (negative relationship with PRE1) and with lower altitude (negative relationship with ALT). However, the analysis also revealed specific differences in the environmental requirements of the snakes, showing that B. c. occidentalis is more frequent than E. c. alvarezi at sites with higher levels of NDVI. Additionally, E. c. alvarezi is more frequent at sites with lower temperatures in the dry season. The maps obtained show that both are highly likely to be present in the Dry subregion of the Gran Chaco. The results of the present study can be an important contribution to a better understanding of the ecological requirements of the species and of the impact of global environmental change on its distribution.