Genetic and morphological differentiation of the Lusitanian toadfish (Halobatrachus didactylus) between estuarine and coastal areas in Portugal

The Lusitanian toadfish, Hnlobatrachus didactvlus (Bloch and Schneider. 1801), is distributed from the Ghana coast to the Iberian Peninsula, being particularly abundant on the south coast of Portugal. The differentiation of this species alone the Portuguese coast was assessed through the analysis of 10 samples, considering morphological characters (20 morphometric and 16 meristic) and genetic markers (10 allozymes, 11 loci). Southern samples included estuaries and their adjacent coastal areas, given that this species inhabits both environments. whereas western samples only comprised estuaries. Morphometric and meristic data discriminant analysis evidenced some differentiation between estuarine and coastal populations. This was not entirely corroborated by the genetic analysis, which showed an overall pattern of low F-ST (0.042) and Nei's genetic distance, even between geographically distant areas. However, higher values of these parameters were found between estuaries of the south coast and their adjacent coastal areas, suggesting that estuarine systems play a major role in such differentiation. Results are discussed regarding toadfish life-history pattern and Portuguese coast geomorphology, giving an insight into the biological and environmental factors influencing population sub-structuring.