Shape variability of Mactra isabelleana from two different habitats off Buenos Aires province Coast

JAVIER H. SIGNORELLI; GUIDO PASTORINO

Antwerp, Belgica

Congreso; World Congress of Malacologia. Antwerp Belgium. July 15-20.; 2007

Unitas Malacologica

The frequent species Mactra isabelleana (d?Orbigny, 1846) can be found in several locations alongthe coast of the province of Buenos Aires, including the Rio de la Plata estuary. The differentenvironmental processes present at these locations can produce morphological variation in thespecimens. In order to prove this hypothesis we analyze, using geometric - morphometric methods,the shell shape variation of Mactra isabelleana. In addition, we also compare this species with thecogeneric M. marplatensis to verify the generic variability. All specimens were collected by atrawling net in two locations that represent the estuary and the open sea. They were San Clemente(36º20?50?? S, 56º 43? 40?? W) and Mar del Plata (38º01?45??S, 57º30?05??W) respectively. Sixteenad hoc landmarks were digitalized from shell pictures. Principal Component and Canonical Variationanalysis were carried out with IMP software, in order to investigate the shape variability betweenspecimens and samples from different habitats. Samples from Mar del Plata were the most variableand those from San Clemente were the most homogeneous, perhaps because all of them belonged inthe same population. Principal Component analysis allowed us to unquestionably separate the twospecies. However, Canonical variation analysis was necessary to reveal the shape variation in M.isabelleana. According to Bartlett?s test, we found significative differences between specimens fromSan Clemente and Mar del Plata. This analysis also allowed us to verify the distance between the twospecies. Finally, to prove the cause of this variability, tests will be carried out of the differentenvironmental factors like salinity, sediments and tide and wave dynamic, among others.