Reproductive biology of two species of semiterrestrial crabs of the genus Armases (Brachyura, Sesarmidae) living in sympatry in a southern Caribbean coastal stream

Abstract

Abstract The reproductive biology of two sesarmid species, Armases americanum and A. roberti, was investigated for 12 months between 2012-2013 in the San Miguel stream, a coastal stream in the southern Caribbean. Sampling encompassed wet and dry season months. The two species are in general allopatrically distributed on islands and the mainland in the Caribbean Sea but were found living in sympatry in the sampled locality. For these two species living in sympatry, here we addressed the question whether there will be differences in their reproductive traits that would allow us to understand their coexistence. Reproductive parameters included sex ratio, maturity size, frequency of mature individuals, fecundity, embryo size, and reproductive output. We collected 1417 individuals (1188 A. americanum, 229 A. roberti). Populations were male-biased, but ratios were only significantly different from parity for A. americanum. Both species reached sexual maturity at similar sizes, but A. americanum females matured at smaller sizes than males (♀ 12.68 ± 0.50 mm, ♂ 13.26 ± 0.90 mm), producing numerous small embryos (23 003 ± 13 451 embryos; 0.0208 ± 0.0048 mm3), while A. roberti females matured at larger sizes than males (♀ 14.38 ± 1.74 mm, ♂ 13.19 ± 0.73 mm), and producing fewer and larger embryos (17 948 ± 11 738 embryos; 0.0363 ± 0.0104 mm3). Fecundity did not correlate with female size. Reproductive output was slightly higher for A. roberti when compared to A. americanum (9.1 vs. 7.5%). Fecundity, embryo size, and reproductive output ranged within reported values for other American sesarmids. Our results revealed that both species presented distinct reproductive strategies, underscoring the significance of species-specific differences in comprehending their coexistence. Future studies involving allopatric populations of both species will help to determine whether differences in their reproductive strategies are less pronounced when compared to the sympatric populations examined here.