World Congress of Malacology Antwerp ... - Unitas Malacologica

lacking. Accordingly, one of the objectives of the Franco-British Interreg European programme,
which studies endocrine disruptors and their effects on the aquatic fauna, was to improve the
understanding of estrogenic contamination of bivalve molluscs.
Two sentinel species, Mytilus edulis and Dreissena polymorpha, were studied in order to monitor
bioavailable xenoestrogens in marine, estuarine and freshwater ecosystems. To provide a better
understanding of mussel reproductive biology, the gametogenic cycle was first surveyed by
histological sections of the gonad and then correlated with oestrogen levels. The population followed
the known gametogenic cycle and clearly showed a vitellogenic period in early spring which
corresponded to a marked increase of the gonadosomatic index. However, the association of
oestrogen levels with the gametogenic condition remained ambiguous. Using an in-vitro assay for
estrogenic activity, it was shown that mussels sampled from sites with high concentrations of
(xeno)estrogens were heavily contaminated with (esterified) steroidal estrogens compared with
samples from reference sites. Experimental exposure confirmed that waterborne estrogens were
rapidly taken up and esterified by both species into lipophilic metabolites. Vitellogenin geneexpression
was investigated as a possible biomarker for oestrogen contamination in M. edulis.
Laboratory studies revealed that vitellogenin gene expression was not induced by oestrogen
exposure. These studies suggest that either expression of the vitellogenin gene is not oestrogendependent
or that the sequestration of steroids via esterification may inhibit the induction of the gene.
Thus, the implication of estrogens in mussel reproductive physiology remains to be unravelled before
they may be used as indicators of endocrine disruption.
The fate of received sperm in the genital tract of Lymnaea stagnalis
Koene, Joris M. 1 , Montagne-Wajer, Kora 1 ; ter Maat, Andries 2
1. Department of Animal Ecology, Faculty of Earth and Life Sciences, Vrije Universiteit, De
Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands,
Email: joris.koene@falw.vu.nl; kora.montagne.wajer@falw.vu.nl
2. Max-Planck-Institut für Ornithologie, Postfach 1564, 82319 Seewiesen, Germany,
Email: termaat@mail.orn.mpg.de
In animal species that mate promiscuously, store sperm and fertilise internally, the sperm from two or
more donors usually compete for access to eggs. For simultaneous hermaphrodites it remains unclear
how general sperm competition and the resulting sexual conflicts are. For the great pond snail
Lymnaea stagnalis it has previously been shown that stored sperm can be used for over three months.
In this species, and Basommatophora in general, this storage allegedly occurs in the “carrefour”
region (i.e. fertilisation pouch, junction where hermaphroditic duct divides in a male and female
tract). This assumption seems entirely based on extrapolations from Stylommatophora, which have a
well-defined allosperm storage organ attached to their fertilisation pouch. We have therefore
investigated the fate of donated sperm by looking at sperm digestion, sperm storage and sperm
utilisation. We find that within three hours after copulation most sperm has been transported into the
bursa copulatrix, where it is digested in the subsequent hours. By fluorescently labelling sperm in
histological sections made at different times after copulation, we find that allosperm is not stored in
the carrefour, but probably in the hermaphroditic duct or the seminal vesicles, where ripe autosperm
are also stored. Finally, using microsatellites, we show that sperm of different partners do compete
within one recipient, and that in double matings this leads to a roughly equal share of paternity. The
implications of these findings for understanding the mechanisms underlying sperm competition and
mixed mating (the production of both selfed and outcrossed offspring within one egg mass) will be
discussed.
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