Population Genetics of the Red Claw Crayfish Recently Introduced to the Island of Puerto Rico

Crayfish introductions have been widely recognized as a threat to native diversity and ecosystem function.  Introduction events involve a few founding individuals which could limit genetic diversity and establishment potential. Diversity within introduced populations will decrease due to bottlenecks and drift, or increase as a result of multiple introduction events. I present here a case study which documents the current population dynamics and genetic variation of Cherax quadricarinatus (Red Claw) recently introduced to the island of Puerto Rico. Red Claw were sampled from six reservoirs (Loiza, Cidra, Carite, Güajataca, El Guineo, Dos Bocas) throughout the island, as well as an aquaculture facility (Caribe Fisheries) located in the Southwest. Relative abundance was estimated using a Catch-Per-Unit-Effort approach (the number of individuals per trapnight ~24hrs) with Cidra having the highest (2.20). A length-mass relationship developed a power equation where Biomass (M) is predicted by taking Standard Carapace Length (SCL) to the power b= 3.4451 and multiplying by a = 0.0057 (M = (0.0057) SCL (3.4451)). ANOVA suggested differences in overall SCL (F(4,134)= 16.96, P< 0.0001) and Biomass (F(4,145)=15.59, P<0.0001) among sample sites with Loiza being significantly different in both cases. Seven microsatellite loci were used to assess genetic variation between populations. Allelic diversity was observed to be highest in Caribe and lowest in Cidra. AMOVA supported significant variation within total individuals (50%; p<0.001). Pairwise Fst was lowest between Cidra and Guajataca (Fst = 0.007), and the number of migrants per generation (Nm) was highest between these two populations (Nm = 36.167). Permutated Mantel tests indicated that isolation-by-distance has had little influence on genetic variation (r= 0.038, p = 0.384). STRUCTURE results supported a K = 2 as being the most probable number of populations. This study supports previous surveys indicating that Red Claw is established in Puerto Rico. My work is the first to present island wide distribution and relative abundance estimates for areas not previously surveyed. Genetic analysis supports strong structuring between populations as the result of small founder events. Biomass estimates will allow for a standardized measure to assess the role of Red Claw in ecosystem processes.  Overall, results will contribute to the concern of Red Claw introduction outside of its native range.

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