Morphometric and genetic characterizations of blue swimming crab Portunus segnis, (Forskal, 1775) along the Iranian coasts of the Persian Gulf and Oman Sea

Abstract

Portunid crabs form the basis of important fisheries in many parts of the world, however, their population biology is poorly understood. The more than 90 species of the Portunidae are widely distributed in global oceans often with indistinct boundaries among species, especially in the Indian Ocean. To clarify the species occurrence and population genetic structure of Portunus pelagicus and Portunus segnis in Iranian waters, crab specimens were collected from four sites along the Iranian coast of the Persian Gulf and Oman Sea. For a subset of 40 sampled crabs, the Cytochrome C Oxidase subunit 1 (COI) was sequenced and compared among the four sites. This analysis identified P. segnis as the predominant species (39 out of 40 sequenced samples) with the infrequent occurrence of P. pelagicus (one out of 40 sampled). Genetic diversity analysis for P. segnis samples identified high to moderate haplotype (0.98) and nucleotide (0.04) diversities. Analysis of molecular variance (AMOVA) (ΦST=0.09629 P = 0.00673) revealed significant genetic differentiation between two sampling sites inside the Persian Gulf, at Chabahar and Qeshm which are 500 km apart. Comparisons of the variation in the carapace morphometrics of 104 male P. segnis among sites using canonical variate analysis showed significant differences among the four sampling sites (P < 0.0001). Overall, the results revealed a high degree of morphological and genetic heterogeneity in P. segnis over relatively small spatial scales in this region of the Indian Ocean. The morphological variability of this species is such that it masked the sympatric presence of the species, P. pelagicus. It is likely that other cryptic portunid congeners will be identified in other Indo-Pacific regions given the high level of genetic variability that has been previously described for P. pelagicus from this region.