Shape variability of Mactra isabelleana (Heterodonta: Bivalvia) from two different habitats off Buenos Aires province Coast.

SIGNORELLI, J.; PASTORINO, G.

Anveres, Bélgica

Congreso; 16th International Congress of UNITAS MALACOLOGICA y World Congress of Malacology, .; 2007

Unitas Malacologica

The frequent species Mactra isabelleana (d’Orbigny, 1846) can be found in several locations along the coast of the province of Buenos Aires, including the Rio de la Plata estuary. The different environmental processes present at these locations can produce morphological variation in the specimens. 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 the cogeneric M. marplatensis to verify the generic variability. All specimens were collected by a trawling 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. Sixteen ad hoc landmarks were digitalized from shell pictures. Principal Component and Canonical Variation analysis were carried out with IMP software, in order to investigate the shape variability between specimens and samples from different habitats. Samples from Mar del Plata were the most variable and those from San Clemente were the most homogeneous, perhaps because all of them belonged in the same population. Principal Component analysis allowed us to unquestionably separate the two species. 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 from San Clemente and Mar del Plata. This analysis also allowed us to verify the distance between the two species. Finally, to prove the cause of this variability, tests will be carried out of the different environmental factors like salinity, sediments and tide and wave dynamic, among others.