Evaluation of female aphally in imposex-affected populations of Nucella lapillus at the southernmost distributional limit of the species in Europe

Male and female aphally in Nucella lapillus has been reported in some populations from the northeastern Atlantic coast, namely in localized areas in southeastern England, northwestern France and northwestern Spain. This occurrence has been associated with Dumpton syndrome (DS), a genetic anomaly that causes under-development of the male genital tract and confers resistance to the masculinizing effects of tributyltin (TBT), i.e. to the development of imposex (superimposition of male sexual characters on neogastropod females). In an effort to elucidate the potential occurrence of DS among Portuguese populations of N. lapillus, data obtained from imposex levels monitoring campaigns performed from 2000 to 2006, during which female aphally was frequently observed, were compiled and analysed. Several characteristics associated with a demasculinizing syndrome were observed in two sampling sites near the port of Lisbon: high frequency of female aphally, undersized penises in males and lower incidence of TBT-induced imposex together with the simultaneous presence of females with contrasting vas deferens sequence values (0 and 4) at the same site. Despite the similarities with DS, the relatively lower levels of TBT pollution recorded in Portugal in comparison with other European coastal areas, and the fact that male aphally was only occasionally found, are reasons to suggest that other nongenetic causes are potentially involved in the development of female aphally in this geographical area. Nevertheless, a lower sensitivity to TBT of Portuguese N. lapillus populations that present a high frequency of aphally is apparent and this hypothetical resistance is discussed.