Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Value of ovarian scars to determine individual reproductive history parameters in small cetaceans

Prior to the project, it was common knowledge and use in cetacean biology to consider that ovarian scars were permanent features and therefore could provide an insight into female individual reproductive history. Basic demographic characteristics, such as inter-birth intervals or number of past pregnancies, were estimated from ovarian counts. As part of BIOCET WP5, it was planned to use these structures in order to assess the number of past pregnancies because this parameter is central to modelling pollutant transfer to calves through both gestation and lactation, which is a route a pollutant elimination unique to females.

The examination of ovaries from common dolphins showed that once maturity is reached ovarian scar counts do not increase with age, unlike what would be expected from the literature. Instead, ovarian scar counts remain at 0 until puberty and then vary over quite an extended range irrespective of age, the overall trend being flat.

There can be many ovulations per year, as shown by animals in their first post-pubertal year showing scar counts in the upper part of the species range. This additionally confirms that scars represent past ovulations and not only those ovulations followed by a gestation, as it was sometimes suggested in the literature. In contrast to this lack of relationship with age there is a strong relationship with instantaneous reproductive status.

Indeed pregnant females show on average about 50% less ovarian scars than non-pregnant ones. These observations suggest that, unlike previously thought, ovarian scars heal out completely in the common dolphin. Therefore the scar count at any particular time of the life is the combination of past ovulations and healing rate. The rate of healing can be approached by the observations made on pregnant females which suggest that the half-life time of ovarian scars in shorter than the duration of pregnancy (11 months in the common dolphin).

Data on harbour porpoise were less clear, mostly because of a smaller sample size of mature individuals. However, they were apparently in general agreement with the lines suggested by data of common dolphins.

These findings had profound effect on the way in which pollutants, age and reproductive data could linked together in the BIOCET project. Externally these results are also of importance because they are a strong invitation for cetacean biologists to fully revise the significance of ovarian scars and their value as a tool to investigate individual reproductive history and derive meaningful demographic parameters. It can be noted that in most mammals ovarian scars do regress fully and do not accumulate simply with age.

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Reported by

Centre de Recherche sur les Mammifères Marins andCentre de Recherche sur les Ecosystèmes Littoraux Anthropisés, UMR6217
Université de la Rochelle
17071 La Rochelle
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