“Geographic variation of Burmeister’s porpoise, Phocoena spinipinnis (Burmeister, 1865) (Cetacea: Phocoenidae), on the Atlantic and Pacific coasts of South America” (Thesis content in English)
A total of 142 skulls from Burmeister’s porpoises, Phocoena spinipinnis from museums and scientific collections from Argentina, Brazil, Chile, Peru and Uruguay were analyzed to explore the geographical variation in relation to size and shape on skulls of P. spinipinnis. In addition, an oceanographic characterization of the area of distribution of Burmeister’s porpoise by historical data of temperature, salinity and oxygen the 0 and 50m of depth on the Pacific and Atlantic coast was carried out. The age of the animals was obtained by reading the Growth Layer Group in dentine. The oldest male and female were 10 years of age. Measurements in dentine showed sexual dimorphism in the first GLG and geographic differences between porpoises from Peru and Atlantic. Three types of anomalies were recorded in teeth, and the marker lines seem to be associated to “El Niño”. Twenty-eight characters were used to explore sexual dimorphism and growth. Physical maturity of the skull was established when 95% of condylobasal length was attained (≥266mm in the males and ≥277mm in the females). Differences in size and shape of skull were analyzed by traditional and geometric morphometrics. The results revealed sexual dimorphism, being the females larger than male, and the differences in size and shape are concentrated mainly in the rostral region and neurocranium. Geographic variation between porpoises from Atlantic, Chile, and Peru was observed. P. spinipinnis from Peru are smaller compared to porpoises from Chile and Atlantic. Porpoises from Chile have an intermediate shape, and porpoises from Atlantic are larger (mainly related to orbital region, skull height and rostral region). The distance of Mahalanobis showed more separation between porpoises from Peru and Atlantic, and less distance between specimens from Chile and Atlantic. Geometric morphometrics was more useful for show differences between specimens from Chile and Atlantic, especially in the ventral and lateral views. The correlation between environmental and morphometric variables by canonical analysis and two-block partial least squares suggests that the differences observed in the size and shape of skulls would have an important spatial influence, associated to the seasonal variability of the oceanographic conditions present in the two oceans, and directly related to the three oceanographic areas proposed in this study: (1) from Paita, Peru (05°01’S, 81°W) to south of Arauco Gulf, Chile (~39°S); (2) from south of Arauco Gulf to south of La Plata River, Argentina (~38°S); and (3) from La Plata River to Santa Catarina, Brazil (28°48’S; 49°12’W). In addition, it is proposed that P. spinipinnis presents a continuous distribution from Paita, Peru to La Plata River basin, Argentina, being able to reach Uruguayan and Brazilian waters under certain oceanographic conditions (intrusion of colder and less saline waters toward the north associated with the Subtropical Convergence).