Investimento maternal diferenciado e uma nova abordagem de fotometria em filhotes de boto-vermelho (Inia geoffrensis) em uma área de várzea na Amazônia central.

Abstract

Polygynous species usually have strong competition between males. This fact favours the development of certain characteristics that will give them advantages in order to have access to females, since bigger males may have higher reproductive success. The evolution of sexual dimorphism may show differences between sexes during growth period and also in relation to growth rates, which can be affected by maternal behaviour through parental care period. According to sex-biased investment theory, across that period it may be a sex-biased investment toward males, not just in growth rates but also may be reflected in duration of parental care and offspring size at the end of it. Odontocetes spent most of their time below the water surface making difficult to gather population and reproductive parameters. This challenge has enhance the development of non-invasive research tools, as photogrammetry, which in addition to a long term research with marked animals may allow access to the estimation of those parameters. Besides, it may allow retrieving size data from calves when the parental care period is long. The first chapter describes a new photogrammetry approach in order to estimate the body length of a target dolphin in situations where part of the body of another animal of known (or estimated) length - the reference animal - is in close proximity. The distance from blowhole to tip of dorsal fin was used as proportion to estimate the total length of the calf in the image. The accuracy of the technique was tested using 33 images of mother and calf pairs of Amazon River dolphin (Inia geoffrensis), given a mean error of 3.8%. In the second chapter, the sex-biased maternal investment theory and its influence in the ontogeny process of sexual dimorphism was tested. A total of 211 (172 capture and 39 photogrammetry) observations from 74 individuals (43 females and 31 males) of known length, age and sex were used. Age and length at the end of maternal period was analysed using Generalized Linear mixed models (GLMM) with binomial distribution. In order to test for slope differences between sexes across dependent period and independence period Mixed Linear Models (LME) were used. No differences were found in age at the end of maternal care between sexes (3.07 years, p > 0.5); however, differences at length were found (172.21 cm males and 165.58 females, p < 0.05). These length differences are the result of the growth rate differences observed within a maternal care period (p <0.05), on the other hand, no differences within juvenile period were found between sexes. Males still growing after females reach their asymptote, having a longer juvenile period than females. Therefore, the results indicates that during the same period of maternal care for male and females, males will became independents with a bigger size as a consequence of the different growth rates found within dependent period. Also, as growth rates in juvenile period were the same for both sexes, we can assume that sex-biased investment is applied in botos. Thus, differences in growth rates by additional maternal investment and different periods of growing are the processes from which Amazon River dolphin reached sexual dimorphism.