World Congress of Malacology Antwerp ... - Unitas Malacologica

Polyandrous mothers maximize hatchling size in the opisthobranch Chelidonura sandrana
Sprenger, Dennis; Anthes, Nils ; Michiels, Nico
University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany,
Email: dennis.sprenger@uni-tuebingen.de; nils.anthes@uni-tuebingen.de; nico.michiels@unituebingen.de
Offspring size can have pervasive effects throughout the life history of many marine invertebrates. In
external fertilizers, variation in egg size is largely determined by environmental conditions, since a
mother has no direct control over fertilization. In internally fertilizing species maternal resource
allocation might additionally vary in response to the number and quality of male mating partners.
Although positive effects of mating multiply with several different males (polyandry) have been
confirmed for a variety of taxa, such investigations are entirely lacking for internally fertilizing
marine invertebrates. With many being simultaneous hermaphrodites, there is some evidence that the
male function gains an almost linear fitness increase with the number of different partners
inseminated, while the effects of multiple mating on the female function remain unresolved. We
tested the effects of ejaculate amount (repeated matings with the same ‘male’) and ejaculate diversity
(repeated matings with different ‘males’) on maternal provisioning in the hermaphroditic sea slug
Chelidonura sandrana. We found that polyandric focal 'females' produced significantly larger egg
capsules and larger veligers, while repeatedly mated focals suffered from reduced mid-term
fecundity. Our findings are consistent with two alternative hypotheses on the effects of polyandry,
where females either benefit from the genetic diversity of their offspring (‘genetic diversity’/ ‘bethedging’)
or are manipulated by their male partners.
In a subsequent study we determined the relationship between mating rate and female provisioning.
We found that i) focal ‘female’ fecundity decreased with elevated mating rate, but that ii) maternal
investment in egg capsule volume was maximized at an intermediate mating rate that corresponds to
the natural mating rate observed in the field. Our results show that mating strategies are an important
addition to understanding variation in offspring size in internally fertilizing marine invertebrates.
Moreover, they suggest that polyandry indeed increases female fitness in simultaneous
hermaphrodites.
The neoplastic disease in Macoma balthica (L.) – an impact on condition of the Baltic clam
population from the Gulf of Gdańsk (Baltic Sea)
Stachnik, Magdalena; Wołowicz, Maciej
Laboratory of Estuarine Ecology, Department of Marine Ecosystems Functioning, Institute of
Oceanography, University of Gdańsk, Al. Piłsudskiego 46, 81- 378 Gdynia, Poland,
Email: magdas@ocean.univ.gda.pl; ocemw@univ.gda.pl
Neoplasia is a kind of cancer found in over 20 bivalve species around the world. Although etiology of
this disease still remains uncovered, many authors suggest a cause-and–effect relationship with
environmental conditions. Characteristic patterns of disease are aneuploidy, the presence of
microchromosomes or unpaired chromosomes, hypertrophy of nucleus and high frequency of mitotic
divisions. In the late stages of neoplasia animals exhibit weakness, emaciation and show degenerative
changes in atypical cells and organs that increases mortality rate. The presence of neoplasia is a
significant environmental and aquacultural problem due to the fact that the occurrence of the disease
is linked organisms metabolic activity and condition. Neoplastic changes in the population of
Macoma balthica (L.) from the Gulf of Gdańsk (Baltic Sea) have been observed since 1996 with an
average prevalence of 27.8%. This high prevalence of tumor makes the Baltic clam especially
interesting as a test organism for studying the disease etiology mechanisms and the environmental
importance of the cancer. The aim of study was to determine neoplasia occurrence in years 2005-
2006 and evaluation of tumor influence on the Baltic clam population from the Gulf of Gdańsk.
During whole sampling period the prevalence of the tumor ranged from 0-60 % and was dependent
on the investigated station as well as the season. The spatial differentiation of neoplasia prevalence
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