Genetic Diversity in Introduced Bass Populations in Puerto Rico Reservoirs

Abstract

Founding population size and genetic diversity are critical factors influencing the long-term viability of introduced fish populations but are often understudied in the context of newly impounded or reclaimed waterbodies. We investigated whether bass populations introduced to Puerto Rico and isolated for the past 50 years showed reduced genetic diversity compared to populations in the native range of largemouth bass (Micropterus nigricans), Florida bass (M. salmoides), and their hybrids (M. nigricans × M. salmoides). We also assessed possible reproductive contributions from recent stocking in Puerto Rico reservoirs. Genetic diversity metrics were estimated for 12 reservoir populations and a contemporary hatchery broodstock at the Maricao Hatchery using microsatellite loci and compared to populations from Florida and Texas, where these taxa are native. Bass populations in Puerto Rico exhibited significantly lower observed heterozygosity, expected heterozygosity, and allelic richness than mainland populations. The hatchery broodstock showed the lowest diversity, possibly due to effects of limited numbers and size-selectivity of broodstock collected from reservoirs with the greatest proportion of Florida bass ancestry. Recent hatchery ancestry was low in many reservoirs, which suggested that recent stockings have had limited success in shaping the genetic makeup of these populations. Reduced genetic diversity in Puerto Rico’s bass populations is likely due to limited and possibly non-random founding events, along with genetic drift and artificial selection. The results suggest that genetics may help explain the unusual population patterns in these systems and highlight the need to use genetically diverse founders and consider genetic supplementation in isolated reservoirs and small impoundments. Where bass are native, use of locally adapted stocks remains the preferred management approach.