Shape differentiation and characterization in the two morphotypes of the Antarctic limpet Nacella concinna using elliptic Fourier analysis of shells

MARÍA CARLA DE ARANZAMENDI; JUAN JOSÉ MARTÍNEZ; RICARDO SAHADE

Buenos Aires

Congreso; XXXI SCAR and Open Science Conference; 2010

Scientific Committee on Antarctic Research

The limpet Nacella concinna presents two ecotypes: the littoral (migrant) and the sublittoral one (non-migrant). They differ in morphological and behavioral characteristics and recently discovered, in physiological traits and genetic population structure. In the present work, Elliptic Fourier analysis (EFA) of shells was used to study the shape of the two morphotypes in six localities along the Antarctic Peninsula. At each locality, limpets were collected at two different depths: Littoral and Sublittoral 15 or 20 m depth. Four localities were sampled in summer when the two ecomorphs are spatially separated; two localities were sampled in autumn when the littoral morphotype could have already started its migration to the sublitoral zone. The use of EFA confirmed the morphometric differences. The littoral morphotype has higher and globose shells with the apex displaced to the anterior part; the sublittoral individuals are more flatten and pointed, and have the apex very well defined. The discriminant analysis revealed that 55% of the sublittoral individuals sampled in autumn were assigned to the littoral confirming the presence of the migratory behavior and the existence of two distinct morphotypes. The same pattern was detected in a previous work of our group using genetic markers. EFA resulted more precise than the conventional metrical approach for identification of the morphotypes and allowed a quantitative approach to analyze the differences in the shape independently of size. It takes into account the whole profile of the shell that may include axes of variation not considered by traditional morphometrics.