Body size, age and growth pattern of Physalaemus fernandezae (Anura: Leiuperidae) of Argentina

We studied body size, age structure, age at maturity, longevity, and growth pattern of Physalaemus fernandezae from a population living at the Reserva Natural Punta Lara, Buenos Aires, Argentina by skeletochronological methods. Furthermore, we evaluated the sexual size dimorphism of this species in relation to age at maturity and growth rate. We also discussed the chronological formation of the Lines of Arrested Growth (LAGs) in relation to the reproductive activity of P. fernandezae. Body size was sexually dimorphic; females were significantly, on average, larger and heavier regardless of age, than males. Out of 91 samples that were processed, 65 (36 male, 22 female, 7 juveniles) sections showed well-defined LAGs in the periosteal bone. The minimum number of LAGs counted was 2 for males and 3 for females. We did not find sexual differences in longevity. Thus, the difference in potential reproductive lifespan between sexes was of 1 year. Although the mean age was higher in females, it did not differ significantly between sexes. There was a strong positive and significant correlation between snout-vent length and body mass. The growth coefficients (K), estimated by the von Bertalanffy growth equation, were higher in males than in females for both size and body mass. The results indicate that females, with lower growth rate than males, took longer time to reach the minimum maturation size, and thus, were older and larger at first reproduction. We assumed that the number of LAGs observed in P. fernandezae is equivalent to only one period of decreasing growth found each year immediately prior to the winter reproductive season. We suggest that this decrease in growth rate may occur between May and June, due to the decrease of temperatures, but also in combination with the scarcity of precipitation.