Sex bias in biopsy samples collected from free-ranging dolphins |
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Authors: | Sophie Quérouil Luís Freitas Ana Dinis Filipe Alves Irma Cascão Rui Prieto Mónica A Silva Sara Magalhães José A Matos Ricardo S Santos |
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Institution: | 1.Departamento de Oceanografia e Pescas da Universidade dos A?ores,Instituto do Mar (IMAR),Horta,Portugal;2.Departamento de Biotecnologia,INETI,Lisbon,Portugal;3.Museu da Baleia,Rua da Pedra d’Eira,Cani?al,Portugal;4.Biology Department,Woods Hole Oceanographic Institution,Woods Hole,USA;5.UR175 - CAVIAR,IRD,Montpellier,France |
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Abstract: | Biological samples of free-ranging dolphins are increasingly used to gain information on population structure and ecology.
In small cetaceans, the gender of individuals usually cannot be determined at sea, and population sex ratio has to be inferred
indirectly. We used molecular sexing to determine the gender of 340 biopsy samples of bottlenose dolphins, Tursiops truncatus, spotted dolphins, Stenella frontalis, and common dolphins, Delphinus delphis, collected around the Azores and Madeira. Sex ratio was globally skewed in favor of males, and differed between species and
archipelagos. Skew was probably influenced by the selectivity of biopsy collectors and seasonal or year-round predominance
of males in natural populations. Skew was also influenced by sampling duration and intensity. In the Azores, when several
samples were successively collected within the same group, the proportion of female samples decreased as a function of sample
order. This trend indicated a tendency for females to increasingly avoid the boat while samples were being collected. It showed
that males and females reacted differently to the perturbation caused by the biopsy sampling process (i.e., sample collection
and driving style). |
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