Molecular phylogeny and population genetic structure of the shallow-water spiny lobster Panulirus homarus in the South West Indian Ocean region : implications for management.

Abstract

The scalloped spiny lobster, Panulirus homarus has a subspecies trio that are widely distributed in shallow-water habitats in the South West Indian Ocean. Subspecies are defined by differences in colour and abdominal sculptural pattern. A red variety with the megasculptural carapace pattern, P. h. rubellus is distributed along the south east coast of Africa and Madagascar, where they are endemic. Along the African coast P. h. rubellus stocks traverse political boundaries, Mozambique and South Africa. This project aimed to facilitate regional fisheries management of shared stocks by employing genetic tools to determine whether stocks (or populations) are indeed shared between countries. Lobster samples were collected from seven localities throughout the east African coast. The mitochondrial cyctochrome c oxidase subunit 1 region was sequenced to assess the genetic diversity 1) between different subspecies, P. h. homarus and P. h. rubellus and 2) between populations of P. h. rubellus across its African distribution range. Using DNA barcoding methods, genetic diversity was also found between morphologically distinct subspecies, Panulirus homarus homarus and P. h. rubellus which differed genetically by ca. 2-3% in sequence divergence. Both subspecies were monophyletic relative to the out-group taxa and formed well supported sister clades (BI: 1.00, ML: 93%, P: 100%, NJ: 100%). The distribution of P. h. rubellus along the African coast occurs adjacent to different current regimes and therefore varied larval transport modes (i.e. Agulhas Current and inshore countercurrents along the Eastern Cape). This may have driven the formation of subpopulations (ΦPT = 0.104, p = 0.010) which differ by ca. 1.7% in sequence difference. The pattern of gene flow of populations of P. h. rubellus lends support to the Agulhas Current being a major mode of larval transport as well as corroborates previous abundance and distribution records. Time since population expansion estimates for the P. h. homarus and P. h. rubellus subspecies as well as for the P. h. rubellus subpopulations dated back to the mid-Holocene Epoch in accordance with a warmer, more stable marine environment. Genetically distinct subspecies of P. homarus as well as differentiated subpopulations of P. h. rubellus calls for a re-visit of the current collective management of P. homarus as well as P. h. rubellus as a single genetic stock along the south east African coast.