June 17, 2024

Assessment of Nonmetric Skull Characters of the Franciscana (Pontoporia blainvillei) in Determining Population Differences


Micaela Trimble and Ricardo Praderi


Abstract: The franciscana (Pontoporia blainvillei) is a small endemic dolphin of the Atlantic coast of Brazil, Uruguay, and Argentina that presents conservation problems because of its incidental mortality in nets of artisanal fisheries throughout its entire distribution. An important step in managing small cetaceans is to define the populations involved because each identified population requires evaluation and treatment as a separate unit. Since 1991, morphological and genetic differences among franciscanas of different regions have been detected. Nonmetric characters (i.e., coded by discrete states and also known as qualitative traits) have been employed for the analysis of population differentiation of more than 50 mammal species because it has been assumed that they are exposed to minimum selection pressure. The aim of this study was to identify potentially useful nonmetric skull characters of the franciscana for comparison among individuals from different locations in order to investigate geographic variation in these traits and to determine their frequencies in individuals of the Uruguayan coast. Twenty-six characters were examined for 115 skulls belonging to the cetacean collection of the National Museum of Natural History and Anthropology (Montevideo, Uruguay). The potential existence of character dependence on body length, sex, and time period was examined. A total of 12 characters were excluded from subsequent analyses: seven were not sufficiently variable, four were dependent on body length, and one showed sexual dimorphism. Only 14 characters were remaining, and their frequencies were calculated. None of them was dependent on time period. Due to the low number of potentially useful nonmetric skull characters found in this study, the utility of this technique as an additional tool for franciscana population assessment is uncertain. The authors give some general methodological recommendations for use of nonmetric characters in population differentiation studies.

Key Words: Nonmetric characters, discrete characters, skull, geographic variation, populations, franciscana, Pontoporia blainvillei

Document Type: Research article

DOI: 10.1578/AM.34.3.2008.338

Page Numbers: 338-348

Info SKU: Vol__34__Iss__3__Trimble_et__al_ Category: