Sexual dimorphism is the phenotypic differences between sexes of the same species. In snakes, this dimorphism may result in diet divergence. Since snakes have to consume their prey whole, head size establishes the limits of prey size. One snake that shows sexual dimorphism is the Boa constrictor, with females being larger than males. The species is native to Central and South America, but has been reported since 1992 as an invasive species in Puerto Rico, with the largest population on the west side of the island. The objective of this study was to determine if sexual dimorphism is present within populations of Boa constrictor in Puerto Rico, since it has been reported that species in island populations become smaller when compared to mainland populations. In addition we wanted to know if there is a difference in gap size between adults and juveniles proving a possible ontogenetic change in diet. To prove our hypothesis we measured 266 adults and 105 juvenile individuals of B. constrictor captured between May 2011 to September 2014. The head width, head height, head length, snout to vent length (SVL) and total length (SVL + tail length) were recorded for each individual during necropsies.
Results/Conclusions
The Total Length of female Boa constrictor (n=157) averaged (1881.041±.20.064mm) and males (n=109) average size was (1808.528±23.933mm) which demonstrate sexual dimorphism. The average head measurements for females (n=157) were: head length (59.271±0.585mm); head width (43.045±0.515mm) and head height (16.510±0.243mm). For males (n=109) head length (55.568±0.554mm); head width (39.017±0.495mm) and head height (15.455±0.301mm).Males head measurements were smaller than females. Our results suggest this invasive species is still maintaining certain allometrical characteristics outside of their native range. The relationship of the head measurements when compared to the total length best explained the ontogenetic shift on the diet between the juveniles and adults, especially between sexes. The adult female (n=157) average was (116.342±1.496mm) while the juvenile female (n=45) average was (92.779±2.498mm). The adult male (n=109) average was (119.500± 1.668mm) while the juvenile male average was (93.291±2.307mm). These results demonstrate head height significantly varies from juveniles to adults in both sexes, proving a change in the diet of the invasive snake. In conclusion, our study indicates the Boa constrictor is still maintaining their sexual dimorphism in Puerto Rico. In addition, this invasive specie has modified their gap size from juveniles to adults in order to adapt to the prey size of the island.