Search

Despite being simultaneously male and female, hermaphrodites may still need to assume the male or female sexual role in a mating encounter, with the option to swap roles afterwards. For the great pond snail, Lymnaea stagnalis, deciding which sexual role to perform has important consequences, since sperm transfer and male reproductive success can be decreased. We hypothesised that detecting cues that indicate a possible mating encounter could help them to adapt their mating behaviour. Therefore, we experimentally assessed whether signalling the presence of a conspecific with an odour can affect the sexual role of Lymnaea stagnalis. The results showed that learning resulted in either an increased ability to mate as a male or in faster mating compared to the control group. These findings reveal that learning shapes the mating dynamics of Lymnaea stagnalis, thus showing that cognitive processes not only affect mating in separate-sexed species but also in hermaphrodites. [ABSTRACT FROM AUTHOR]

Studies of aquatic environments exposed to 17α-ethinylestradiol (EE2) have demonstrated detrimental effects on fish communities. However, much less is known about effects on macro-invertebrates and especially how long-term exposure may affect critical life stages and ultimately population dynamics. We studied the effects of EE2 on relevant endpoints for population growth in two common freshwater gastropods, Radix balthica and Bithynia tentaculata, that differ in reproductive, foraging and anti-predator strategies and endocrine systems. We quantified critical life-history parameters (mortality, somatic growth rate, days to and size at first reproduction, egg production and hatching success) in a concentration-response, life cycle experiment. The two species responded to EE2 exposure in different ways, B. tentaculata showing a significantly lower somatic growth rate and R. balthica a higher somatic growth rate. However, the magnitudes of the effects were small and EE2 exposure did not have any significant effect on estimated population growth rates for the two snail species. The significant effects of EE2 on individual endpoints, but not on population growth rate for both species, emphasise the importance of evaluating higher level effects from long-term exposure studies. [ABSTRACT FROM AUTHOR]

The VD and RPD neurons of Lymnaea stagnalis innervate other central neurons, certain skin areas, the pneumostome area, and the auricle of the heart. Recently, a set of four (λ, ω, α, β) neuropeptides produced by these giant neurons and by certain other central neurons has been characterized. Although alternative splicing of the preprohormone of these neurons yields at least 10 different α neuropeptides, an affinity-purified antiserum directed against a domain common to all α neuropeptides has previously been shown to be highly selective in staining VD, RPD and other neurons that produce the preprohormone. Since the gene encoding the neuropeptides is structurally similar to that expressed in R15 of the marine opisthobranch Aplysia californica, we have used the affinity purified antiserum as a marker for VD/RPD-related systems in other molluscs. Immunopositive neurons and fibers are observed in the central nervous systems of all species studied ( Achatina fulica, Anodonta sp., Aplysia brasiliana, A. californica, Bulinus truncatus, Cepea sp., Eobania vermiculata, Helix aspersa, H. pomatia, Limax maximus, Mytilus edulis, Nassarius reticulatus, Viviparus viviparus). Several medium-sized and small neurons and 1-4 giant neurons are found in the pulmonates and opisthobranchs. The giant neurons in pulmonates have locations in the subesophageal ganglion, axonal branching patterns, and terminal arborizations in the auricle of the heart; all these characteristics are similar to those of VD and RPD. Double-labelling (Lucifer yellow injection, immunocytochemistry) confirms that the two giant neurons in Helix pomatia are Br and Br. The immunoreactive cells in A. fulica appear to include the VIN and PON neurons. The antiserum also stains cells that appear to be the R15 neurons in two Aplysia species. The small and medium-sized neurons are distributed widely over the central ganglia of opisthobranchs and pulmonates. In prosobranchs and bivalves, small neurons are found in the cerebral and abdominal ganglia. No evidence has been found for innervation of the heart in these latter groups but in M. edulis, immunoreactive terminals can be observed in the gill. The results suggest the evolutionary conservation of immunoreactive peptides and the neurons that produce them, and thus support and extend previous hypotheses regarding the homology of certain giant neurons across molluscan species. [ABSTRACT FROM AUTHOR]

The ultrastructure of the cells involved in the formation of the periostracum in Helisoma duryi duryi is described. Two distinct types of periostracal cells can be recognized: light and dark. The Golgi complexes of the light cell are involved in the biogenesis of periostracal units which are extruded at the base of the periostracal groove. Here they algin into a single row so as to form the membrane-like lamellar covering of the periostracum. While the secretions of the dark periostracal cells contribute to the initial components of the dark layer of the periostracum, the mantle edge gland cells are responsible for its thickening. The adult periostracum is about 2-3 μm thick and it consists of a single drak layer covered by a membrane-like lamellar structure. [ABSTRACT FROM AUTHOR]