Sex-biased dispersal and high levels of gene flow among local populations in the argentine boa constrictor, Boa constrictor occidentalis

The knowledge of dispersal is essential to understand the ecology of any species, since population dynamics, spatial distribution and genetic structure are closely tied to patterns of movement. In this paper we estimate dispersal patterns in natural populations of the endangered snake Boa constrictor occidentalis (Serpentes, Boidae), using allozymes as genetic markers. Blood samples were obtained from a total of 120 adult individuals of nine localities from two areas, Sobremonte and Pocho, in Argentina. Only four out of a total of 24 loci were polymorphic: 6-Pgdh-1, Cat-1, Ldh and Hp. The values of expected and observed mean heterozygosities, the percentage of polymorphic loci and mean number of alleles per locus for each population confirm the low levels of genetic variability in this snake. F-ST and N(e)m mean values were 0.0089 and 46.1 for Sobremonte and 0.0379 and 7.46 for Pocho, indicating important levels of gene flow. A comparison of F-ST between genders in both areas suggests a male-biased dispersal, which could be explained by the characteristics of the mating system: males carry out an active mate search of receptive females, and philopatry could be selected in females due to the benefits of the familiarity with the natal area in the use of local resources.