Inbreeding in the exploited limpet Patella aspera across the Macaronesia archipelagos (NE Atlantic): Implications for conservation

The genetic erosion of populations exposed to human exploitation plays a detrimental role on a species ability to adapt to changing environmental conditions. The Macaronesia (NE Atlantic) endemic limpet Patella aspera (Röding 1798) has been subject to overexploitation throughout its geographic distribution. We analysed 841 limpet specimens from eleven islands across the archipelagos of Azores, Madeira and Canaries. Results from 11 nuclear microsatellite markers showed significant population structure between populations from Azores and populations from Madeira and Canaries, and absence of current or historic gene flow between these. M-ratios showed that both population clusters have experienced demographic changes over time. Heterozygote deficits were common across populations, which can be better accounted for by inbreeding than by null alleles or Wahlund effect. Such levels of inbreeding are likely a consequence of a significant reduction of reproductive units due to decades of intensive exploitation. As a sequential protandrous hermaphrodite, the size-selective harvesting of larger individuals likely fosters unbalanced sex-ratios and a consequent reproductive shortage. A recent compensatory hypothesis suggests that males are compensating the removal of larger females by undergoing sex change earlier and presumably at smaller sizes, as an adaptive response of the species under high size-biased fishing pressure. Despite such response, a dramatic reduction of Ne emerging from a large variation in the reproductive success due to overfishing and artificial genetic drift, can simply explain the inbreeding scenario observed in this Macaronesia endemic key species. This study provides valuable insights for management and conservation of P. aspera throughout Macaronesia.