High genetic differentiation with no evidence of hybridisation between four limpet species (<i>Patella</i> spp.) revealed by allozyme loci

Abstract

SUMMARY: The occurrence of hybridisation between limpet species of the genus Patella has always been a contentious issue. Although a previous allozyme study reported high differentiation and no hybridisation between Patella vulgata Linnaeus, 1758, Patella depressa Pennant, 1777 and Patella ulyssiponensis Gmelin, 1791 along English shores, the recent finding of an mtDNA haplotype of P. depressa in a P. vulgata individual raised new doubts on this issue. To further study the possibility of hybridisation between limpet species and their level of genetic differentiation, ten allozyme loci were screened using starch gel electrophoresis for P. ulyssiponensis, P. depressa, P. vulgata and Patella rustica Linnaeus, 1758, from the Atlantic coast of the Iberian Peninsula. Our results show high differentiation between species, which could be clearly separated into different clusters with a Bayesian clustering algorithm. No significant signs of hybridisation were detected between any of the four species. Thus, the hypothesis of hybridisation between P. vulgata and P. depressa across their sympatric distribution is not supported. Two sympatric clusters were recovered within P. vulgata that could be related to HardyWeinberg disequilibrium found in locus MPI. Finally, due to the high level of intraspecific variability, the studied loci are interesting tools for the analysis of population structure and stock identification.Keywords: Patellidae, Patella spp., starch gel electrophoresis, allozymes, hybridisation, genetic polymorphism. RESUMEN: ELEVADA DIFERENCIACIÓN GENÉTICA Y AUSENCIA DE HIBRIDACIÓN ENTRE CUATRO ESPECIES DE LAPAS (PATELLA SPP.) REVELADA POR LOCI ALOENZIMÁTICOS. -La hibridación entre distintas especies de lapas del género Patella siempre ha sido un tema polémico. Aunque un estudio anterior de aloenzimas presenta una elevada diferenciación y ausencia de hibridación entre Patella vulgata Linnaeus, 1758, Patella depressa Pennant, 1777 y Patella ulyssiponensis Gmelin, 1791 en la costa inglesa, el reciente descubrimiento de un individuo de P. vulgata con un haplotipo mitocondrial de P. depressa ha planteado nuevas dudas respecto a este tema. Para estudiar más detalladamente la posibilidad de hibridación entre especies de lapas y su diferenciación genética se han analizado 10 loci aloenzimáticos por electroforesis en gel de almidón, en muestras de P. ulyssiponensis, P. depressa, P. vulgata y Patella rustica Linnaeus, 1758, de la costa atlántica de la península Ibérica. Los resultados así obtenidos evidencian la gran diferenciación existente entre especies, las cuales se separan claramente en distintos grupos con un algoritmo de agrupamiento Bayesiano. La ausencia de evidencias significativas de hibridación entre cualquiera de las cuatro especies estudiadas no permite respaldar la hipótesis de hibridación entre P. depressa y P. vulgata en su área de simpatría. La identificación de dos grupos simpátricos en P. vulgata puede estar relacionada con el desequilibrio de Hardi-Weinberg en el locus MPI. La elevada variabilidad i...

A three-way contact zone between forms of Patella rustica (Mollusca: Patellidae) in the central Mediterranean Sea

“…Nine allozyme loci, corresponding to eight enzymatic systems, were analysed by starch gel electrophoresis: malate dehydrogenase (MDH, EC 1.1.1.37), malic enzyme (ME, EC 1.1.1.40), isocitrate dehydrogenase (IDH, EC 1.1.1.42), glutamate‐oxaloacetate transaminase (GOT, EC 2.6.1.1), phosphoglucomutase (PGM, EC 2.7.5.1, two detectable loci hereafter referred to as PGM1 and PGM2), peptidase D (PEP D, EC 3.4.13.9), glucosephosphate isomerase (GPI, EC 5.3.1.9) and 6‐phosphogluconate dehydrogenase (PGD, EC 1.1.1.44). Electrophoretic and staining procedures were carried out according to Sá‐Pinto, Alexandrino & Branco (2007).…”

Barriers to Gene Flow in the Marine Environment: Insights from Two Common Intertidal Limpet Species of the Atlantic and Mediterranean

“…The morphological taxonomy of limpets [32] is consistent with genetically distinct units [33], [28]. Samples of P. rustica and P. ulyssiponensis , identified according to this taxonomy were collected from 19 localities (Table 1, Figure 1), between 2002 and 2006.…”

“…Individuals were transported in dry ice and preserved at −80°C. Data from samples used in previous studies were also included [34], [28], [35], [31].…”

“…For P. ulyssiponensis PGD was not scored and only one locus was detectable for PGM. Electrophoretic conditions, buffer systems and staining procedures are described elsewhere [28].…”

“…These two species have high census density and pelagic larvae which may spend up to 31.5 days in the water column [25], [26], [27] and thus might be expected to show little differentiation across their distribution range. The limited data available for the continental range of P. ulyssiponensis suggests no differentiation across Iberian Atlantic shores [28] and a pattern of isolation-by-distance (IBD) at the scale of NEA and MS [29]. For P. rustica , previous studies revealed high genetic homogeneity along the Iberian coast [28], [30] but strong genetic substructure within the MS, with two distinct forms meeting in South Italy where they form a hybrid zone [31].…”