Head morphometry of Orestias (Cyprinodontiformes). Response to extreme Southern Altiplano systems?

Abstract

The distribution ofOrestias(Cypriniforms) species in the southern western Altiplano (17oS-22oS) is allopatric; the seven species described inhabit different freshwater systems with extreme climatic characteristics and different ecological conditions, factors that would have enhanced interspecific differentiation. To analyze their head differences we compared jaw morphology of eight species ofOrestias, seven southern ones and one from Puno Peru, using linear and geometric morphometrics. We found differences among the species with both methods. Nevertheless, none of the external measurements by themselves allows classification of any of the species or populations. The geometric analysis showed differences related to feeding structures such as a protractile jaw, separating the western species in two groups: a northern group withO.chungarensis, O.parinacotensis, O.piacotensis, O.laucaensis,O.puniandO. cf.agassii anda southern group,O.gloriaeandO.ascotanensis. The results from this methodology reaffirmed the importance of the extreme environmental conditions of the Altiplano systems to explain the process of adaptation described for the specious genusOrestias.