COS 14-2
Comparative reproductive biology in contrasting wet and dry environments in a group of Neotropical livebearers (Cyprinodontiformes: Poeciliidae)
The predicted drastic changes in global precipitation levels and distribution will lead to drought like conditions in previously abundantly wet areas. Poecilia spp. are livebearers and are ubiquitously distributed across the Americas, making the genus a good model to study adaptations across wet and dry environments. In an attempt to understand the processes governing adaptations to dry environments, this study was conducted to elucidate which traits are evident in the dry populations that allows these fish(es) to persist in ephemeral dry environments. A hierarchical sampling scheme was employed where six species of Poecilia were collected across Central and South America. Each species was collected from one site, containing two stations, and two substations to each station. The sites in Central America were considered the wet environments, while the sites in South America were the dry. Each species was regarded as a replicate for adaptation. Specimens were dissected and various reproductive parameters recorded and dry masses acquired. The effect of environment on reproductive parameters was analyzed using a multivariate analysis of covariance (MANCOVA), with female dry mass and species as covariates. For Poecilia vandepolli — a dry environment species — seasonal comparisons were made using an analysis of covariance (ANCOVA) and a MANCOVA.
Results/Conclusions
Results of a rank-transformed MANCOVA (median ± median absolute deviation) showed that fishes in the wet environment produced significantly more massive eggs (2.7±1.0 vs. 1.1±0.23 mg), but significantly fewer eggs (14±7.5 vs. 18±5.0 eggs). Furthermore, reproductive allotment was significantly lower in the wet environment (7.6±2.6% vs. 14±3.2%), but no difference in condition factor was detected (wet: 0.0068±0.00094 vs. dry: 0.0064±0.00055). For P. vandepolli an ANCOVA (mean ± SE) revealed both more massive ovulated eggs (1.8±0.31 vs. 1.5±0.33 mg) and neonates (parturition ready embryos; 1.2±0.30 vs. 0.89±0.30 mg) during the wet season. Additionally for P. vandepolli, fecundity was significantly lower in the wet season (13±1.2 vs. 21±1.5 eggs), but no difference in reproductive allotment was detected (wet season: 11±1.0% vs. dry season: 13±0.8%). Species in the dry environment invested more heavily in reproduction, and consequently produced disproportionately more but smaller eggs, suggesting that a greater abundance of offspring are required to persist in drier environments. Furthermore, P. vandepolli sacrificed fecundity for ova/neonate size during the wet season. By producing more and larger offspring during the wet season, neonates are potentially better equipped to handle a greater predatory pressure during the wet season in ephemeral dry environments.