Redefining dispersal boundaries of Siganus fuscescens in the Coral Triangle using genetic methods

Background/Question/Methods

Siganus fuscesens (Rabbitfish) is an overexploited reef fish in the Coral Triangle that provides food and income for local populations. S. fuscesens spawn year-round, and are often caught when they are filled with roe before spawning. Adults have a limited home range of approximately one quarter-hectare. However, most dispersal occurs during a 25-day pelagic larval phase when fish larvae disperse on ocean currents. We used genetic methods to examine larval dispersal dynamics of S. fuscesens across the Coral Triangle. We compared samples of S. fuscesens from 6 locations in Indonesia and comparable data from the Philippines to test three hypotheses: 1) Larvae disperse passively by sea currents; 2) populations are isolated by distance; and 3) each population is locally adapted to specific environmental conditions. We extracted DNA from fin-clip tissue using Chelex extraction and amplified the mitochondrial control region. We visualized the PCR products on 1% agarose gel and sent them to be sequenced at UC Berkeley. We analyzed the sequenced data using computational based programs (MEGA5, Arlequin, and dnasp).

Results/Conclusions

For the Indonesian samples, we found haplotype diversity to be low (0 – 0.56). One haplotype was shared among all populations, two haplotypes were shared between two populations (Komodo and Selayar; Lembeh and Seribu) and there were twenty unique haplotypes. There was no genetic differentiation among Indonesian populations (Fst=0), indicating that all samples could be considered one population. However, some populations had unique (private) haplotype, suggesting that populations may not be panmictic, and that genetic homogeneity results from a recent gene expansion in Indonesian populations. Haplotype diversity was higher in the Philippines, and there was population structure suggesting more limited dispersal in this region. Larvae dispersal may be subject to the strength of the currents. Additional studies may examine migration during critical life stages to determine when S. fuscesens populations are most sensitive to fishing pressure. This will allow them to spawn and reproduce before being harvested for market, in order to make them a more sustainable catch.