Growth rate in Bothrops insularis: comparison between wild and captive animals

The golden lancehead, Bothrops insularis, is endemic of Ilha da Queimada Grande, São Paulo, Brazil. Its diet relies mainly on two migratory bird species that travel to the island in March and July. Given that B. insularis is a critically endangered species, the maintenance of ex situ populations is recommended, so that Laboratório de Ecologia e Evolução (Instituto Butantan), houses a population with almost 70 animals. Once these individuals may feed more frequently than those in the island, the aim of the present study was to test the hypothesis that captive animals show higher growth rate. Additionally, since the species show sexual dimorphism, and females are larger than males, we aimed on testing whether the former show higher growth rate. Therefore, we used morphometric data from 34 captive-born, and 28 wild animals (mark-recapture events). In accordance to our assumption, both in wild and captive populations, growth rate was higher in females (x♀WILD=0.18mm/day, x ̅♂WILD=0.098mm/day, FWILD =6.447, p<0.05; x ̅♀CAPTIVE=0.49mm/day, x ̅♂CAPTIVE=0.38mm/day, FCAPTIVE =10.705, p<0.05). Also corroborating our initial hypothesis, captive B. insularis showed higher growth rate, both males (F♂=39.68, p<0.05) and females (F♀=47.456, p<0.05). Interestingly, not only do captive individuals have higher growth rate, but also attain greater body size, with a couple females and a male surpassing the total length reported for wild animals. These data evidence that both diet and sex may exert influence on the body size of the species. Additional influences of maintenance in captivity, and its interface with conditions in the wild need further investigation.