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| Author(s): |
Marie Odile Monier Chelini
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Psicologia (IP/SBD) |
| Defense date: | 2010-02-26 |
| Examining board members: |
Luciano Freitas Felicio;
Vera Silvia Raad Bussab;
Marcelo Alcindo de Barros Vaz Guimarães;
Rupert Palme;
Maria Bernadete Cordeiro de Souza
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| Advisor: | Emma Otta; Luciano Freitas Felicio |
| Abstract | |
The flexibility of sociality found in many species suggests that many of the behavioral and physiological mechanisms responsible for highly developed social interactions are present as latent traits, even in species usually considered as solitary. Social hierarchy and reproductive skew are typical features of social species. Syrian hamsters (Mesocricetus auratus) are an ideal model for the investigation of social stress and its physiological, neuroendocrine, and behavioral effects. The present research focused on the effects of group-housing prior to mating and on the first days of gestation of the female hamster. We investigated if social stress produces some degree of reproductive skew in this solitary species, and if female reproductive success varies as a function of social rank. Two experiments were carried out. The first one involved 34 females group-raised from weaning until the beginning of the trial and the second one 76 singly raised females. In each case one third of the animals were singly housed. Pairs of unrelative females were formed with the remaining animals. Pair behavior was observed through 10 days for assessment of the social rank of each female. All females were mated during this period. On day 4 post-partum, pups were counted, sexed, and weighed and litters were culled to six, three males and three females. Litters and dams were observed daily through 40-min sessions and 13 behavioral categories recorded. In order to assess the physiological relationship between social stress and fertility, we monitored reproductive hormones and glucocorticoids of solitary and pair-housed females during pregnancy by utilizing recently established non-invasive methods for measuring the respective hormone metabolites in the feces. The suitability of an enzyme immunoassay and of a commercial radioimmunoassay for respective quantification of fecal glucocorticoid metabolites of hamsters of both sexes and fecal testosterone metabolites in the male but not in the female was proven for the first time. The patterns of fecal progesterone, estrogen, and glucocorticoid metabolites were similar to blood profiles reported in the literature for pregnant hamsters. Our results showed that when female hamsters are singly housed from weaning, social stress did not affect their fertility. However, when females are group-raised, both isolation and subordination stress induced a significant reproductive skew, which is a characteristic feature of cooperative breeders. It seems that group-keeping of adult hamsters evokes social physiological and behavioral mechanisms present as latent traits in this solitary species. As in other rodents, sociability seems flexible in the Syrian hamster and our findings support the idea that social interactions may be a function of ecological conditions. (AU) | |
| FAPESP's process: | 05/59377-0 - Effects of social stress on the maternal behavior of the Syrian hamster |
| Grantee: | Marie Odile Monier Chelini |
| Support Opportunities: | Scholarships in Brazil - Doctorate |