SEAFWA 2018

AUTHORS: Michael D. Tringali, Elizabeth M. Wallace – Florida Fish & Wildlife Commission

ABSTRACT: The demographic history of a population is a central element for conservation genetic assessment. Severe reductions in abundance, whether in the present or past, can increase inbreeding levels within a population and lead to the loss of genetic variation and fixation of deleterious alleles, which in turn can reduce intrinsic fitness and long-term adaptive potential. Characterizing the demographic status of a population through censusing and other direct approaches can be difficult and time consuming. Moreover, direct approaches do not provide information regarding previous demographic contractions and expansions. A potentially useful alternative derives from molecular analyses, which under certain assumptive circumstances can allow inference on past demography from observed contemporaneous distributions of genetic polymorphism. Rather than census-based information, this method relies on a proportional metric – the genetic effective population size – which may be viewed as the ‘stochastically-adjusted’ number of individuals contributing genes to the next generation. Here, we implement a coalescent method to comparatively test for genetic signals of past demographic changes in heavily fished populations of Atlantic Tarpon (Megalops atlanticus) and bonefish (Abula vulpes), based on microsatellite allelic data. Both taxa have lengthy pelagic larval durations facilitated by a leptocephalus life stage. Whereas the mean PLD for bonefish is approximately twice that of Atlantic tarpon, adult Atlantic tarpon are capable of extensive movement. Thus, the potential influences of genetic connectivity and dispersal on demography are investigated. The analyses represent a diagnostic check on the genetic ‘health’ of these taxa and provide context for interpreting extensive range-wide genetic surveys.