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Séminaire présenté par S. Greiner

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Endocrinological aspects of reproduction in polygynous bats of the Neotropics

Par : Dr. Sabine GREINER (Freie Universität Berlin & Leibniz Institute for Zoo and Wildlife Research, Berlin) invité par G. Eichhorn
Date : Jeudi 13 octobre 2011 à 13h30
Lieu : Bibliothèque du DEPE

Résumé :

Bats have evolved a diverse set of reproductive strategies, varying more than in most other mammalian orders. While in bats of the temperate zones the reproductive cycle is interrupted by hibernation and reproduction strongly seasonal, tropical ecosystems warrant the evolution of a broad spectrum of reproductive patterns and mating systems.

The timing of reproduction as well as trade-offs between reproduction and other competing traits have been studied in two polygynous bats species of the Neotropics, Saccopteryx bilineata and Carollia perspicillata. Both species exhibit a harem polygynous social organization and live in year-round stable groups. By measuring oestrogen and progesterone metabolites from faeces, female oestrus dates were detected and related to environmental factors that may trigger reproductive timing. Plasma levels of testosterone (T) were analysed during mating- and non-mating season in males to see if T increases during mating season as know from bats of the temperate zones. As T is supposed to have negative effects on the organism, e.g. immunosuppression, the relation between T levels and the immune system has been studied by measuring immune responses to an experimental challenge.

Results showed that reproduction is, despite living in an almost a-seasonal tropical environment, highly seasonal. Females exhibit only one oestrus per year around the first half of December that is probably influenced by long-term cues like photoperiod and short-term cues like sudden changes in rainfall and temperature. Despite a highly seasonal reproduction, males do not exhibit a pronounced T peak during mating season and seem to avoid high levels of T. The immune challenge experiment revealed that the presumption of an immunosuppressive effect of T was not supported, but suggests that an activation of the immune system reduces plasma T.

Therefore data revealed a trade-off between reproductive investment and investment to immune functions and further showed that reproduction is timed depending on environmental factors and internal trade-offs.