Alexandra Staikou

Bateman Gradients in Hermaphrodites: An Extended Approach to Quantify Sexual Selection

Sexual selection is often quantified using Bateman gradients, which represent sex‐specific regression slopes of reproductive success on mating success and thus describe the expected fitness returns from mating more often. Although the analytical framework for Bateman gradients aimed at covering all sexual systems, empirical studies are biased toward separate‐sex organisms, probably because important characteristics of other systems remain incompletely treated. Our synthesis complements the existing Bateman gradient approach with three essential reproductive features of simultaneous hermaphrodites. First, mating in one sex may affect fitness via the opposite sex, for example, through energetic trade‐offs. We integrate cross‐sex selection effects and show how they help characterizing sexually mutualistic versus antagonistic selection. Second, male and female mating successes may be correlated, complicating the interpretation of Bateman gradients. We show how to quantify the impact of this correlation on sexual selection and propose a principal component analysis on male and female mating success to facilitate interpretation. Third, self‐fertilization is accounted for by adding selfed progeny as a separate category of reproductive success to analyses of Bateman gradients. Finally, using a worked example from the snail Biomphalaria glabrata, we illustrate how the extended analytical framework can enhance our understanding of sexual selection in hermaphroditic animals and plants.

Response of Mytilus galloprovincialis (L.) to increasing seawater temperature and to marteliosis: metabolic and physiological parameters.

In the context of climate change the present work aimed to illustrate whether the energetic and metabolic pattern of mussels Mytilus galloprovincialis will be affected by increase in the temperature of seawater. Moreover we examined whether an outbreak of Marteilia sp. infestation as a result of increase in sea water temperature will impair the energetic balance of mussels. M. galloprovincialis was acclimated at 18 degrees C, 24 degrees C, 26 degrees C and 28 degrees C for 30 days and the energetic pattern of its tissues was estimated by determining the factor Scope for Growth (SFG), while the metabolic pattern of mussels was estimated by determining the activities of pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK). The decrease in PK activity and the decrease in the ratio PK/PEPCK indicated an activation of anaerobic component of metabolism during acclimation of mussels at temperature 24 degrees C. At temperatures higher than 24 degrees C the values of SFG turned negative probably associated with a significant reduction in clearance rate. Compared to the non infected mussels, the SFG values of infected mussels were significantly lower (P<0.05). These differences were attributed to the higher filtration rate and the lower absorption efficiency detected in the infected mussels. Also the degree of SFG reduction is dependent on the intensity levels of infection by Marteilia sp.

The outcome of sperm competition is affected by behavioural and anatomical reproductive traits in a simultaneously hermaphroditic land snail.

Sperm competition is important in species with reproductive strategies that involve multiple mating and prolonged sperm storage such as the simultaneously hermaphroditic land snail Cornu aspersum. Double mating trials in this species have revealed that mating order and courtship behaviour affect paternity success. We investigated the effect of behavioural and anatomical reproductive traits on paternity success from triple mating trials. Triple mating resulted in triple fertilization in 58% of the cases whereas zero paternity was observed in 16% of sperm donors. Third sperm donors achieved higher paternity followed by first and second sperm donors. Snails with a longer epiphallus, the spermatophore forming organ, sired more offspring regardless of their mating order. Genetic compatibility between sperm donor and recipient did not influence paternity success. The results of the present study identified mating order and epiphallus length, as traits affecting the outcome of sperm competition in this species.

Geographical variation in shell morphology and isoenzymes of Helix aspersa Müller, 1774 (Gastropoda, Pulmonata), the edible land snail, from Greece and Cyprus

Geographic variation of shell morphology and isoenzymes of the edible snail Helix aspersa Müller was studied in 24 different regions of Greece and Cyprus. Principal components analysis and cluster analysis showed a geographical trend in seven variable characters examined jointly. Morphological variation between populations was of a sufficient magnitude to create discriminant functions that were able to classify 100 per cent of the cases correctly in only three populations whereas the classifications of the rest varied from 20 per cent to 60 per cent.For the assessment of the genetic polymorphism 13 enzymic systems with 15 loci and 47 alleles were investigated. Three were monomorphic in all populations. The percentage of polymorphic loci (P) ranged from 33.3 per cent to 66.7 per cent and the mean expected heterozygosity from 0.152 to 0.254. Significant deviations from Hardy-Weinberg equilibrium were found in most loci in most populations. Polymorphism varied greatly from one population to another, but there was not correlation between morphological and genetic variation.Spatial autocorrelation in continental populations tended to decrease significantly with increasing distance for several loci. The results found by correspondence analysis and the dendrogram produced by the UPGMA algorithm using Neis identity (I) showed that the degree of genetic identity was high among the populations studied, apart from the group of N. W. Greek populations. The pattern of genetic diversity seem to be influenced by different forces in continental and island populations.

Glycolytic adjustments in tissues of frog Rana ridibunda and land snail Helix lucorum during seasonal hibernation

The present work aimed to contribute to the understanding of the adaptation of the glycolytic pathway in tissues of frog Rana ridibunda and land snail species Helix lucorum during seasonal hibernation. Moreover responses of glycolytic enzymes from cold acclimated R. ridibunda and H. lucorum were studied as well. The drop in Po(2) in the blood of hibernated frogs and land snails indicated lower oxygen consumption and a decrease in their metabolic rate. The activities of glycolytic enzymes indicated that hibernation had a differential effect on the glycolyis in the two species studied and also in the tissues of the same species. The activity of l-LDH decreased significantly in the skeletal muscle and heart of hibernated R. ridibunda indicating a low glycolytic potential. Similar biochemical responses were observed in the same tissues during cold acclimation. The continuous increase in the activities of glycolytic enzymes studied, except for HK, might indicate a compensation for the impacts of low temperature on the enzymatic activities. In contrast to R. ridibunda, the activities of the enzymes increased and remained at higher levels than those of the prehibernation controls indicating maintenance of glycolytic potential in the tissues of hibernating land snails.

EFFECT OF CROWDING ON GROWTH AND MORTALITY IN THE EDIBLE SNAIL HELIX LUCORUM (GASTROPODA: PULMONATA) IN GREECE

ABSTRACT The effect of crowding on growth and mortality in Helix lucorum L. hatched in the laboratory was tested experimentally. The higher the number of grouped individuals, the smaller was the growth and the higher the mortality. The optimum density for this snail under the conditions studied seemed to be 50 individuals/m2 floor area. Densities observed in nature ranged 3–80 individuals/m2.

High level of sperm competition may increase transfer of accessory gland products carried by the love dart of land snails

Abstract Postcopulatory adaptations that increase reproductive success compared to rivals, like the transfer of accessory gland products that promote paternity, are common when sperm competition occurs among males. In land snails, the dart shooting behavior and its adaptive significance, in promoting individual fitness through enhanced paternity of the successful dart shooter, have been considered such an adaptation. The fitness result gained is mediated by the transfer of mucus components on the love dart capable of altering the physiology of the receivers reproductive tract. In this context, dart shooting and mucus transfer could be considered as processes targeted by sexual selection. While the effect of dart mucus is beneficial for the dart user, so far it has remained unknown whether its transport is greater when snails experience a higher level of sperm competition. Here, we report results of a study on inter‐ and intraspecific variations of dart and mucus gland morphometry, considered to be traits reflecting the ability of snails to adjust the production and transfer of mucus under varying sperm competition scenarios. We investigated four populations with different densities from four dart‐bearing species, Arianta arbustorum, Cepaea nemoralis, Cornu aspersum, and Helix lucorum. The results indicate that different adaptations of these traits occur among the studied species that all seem to achieve the same goal of transferring more mucus when sperm competition is higher. For example, the presence of longer and more branched mucous glands or an increase in dart surface most likely reflect increased mucus production and enhanced ability of mucus transport, respectively. Interestingly, the species for which the use of the dart is reported to be facultative, A. arbustorum, did not show any variation among the examined traits. To conclude, sexual selection in the form of sperm competition intensity seems to be an important selective force for these simultaneously hermaphroditic dart‐bearing snails, driving differences in sexual traits.

Effects of Prolonged Acclimation to Cold on the Extra‐ and Intracellular Acid‐Base Status in the Land Snail Helix lucorum (L.)

The aim of this study was to examine the effect of prolonged acclimation to cold on the acid‐base status of extra‐ and intracellular fluids in the land snail Helix lucorum. For this purpose, acid‐base parameters in the hemolymph and tissues were determined. In addition, the buffer values of hemolymph and tissues were determined in order to examine whether they change in the snails during acclimation to cold. According to the results presented, there is an inverse pH‐temperature relationship in the hemolymph within the first day of acclimation, which is consistent with alphastat regulation. The Pco2 decreased, and pH in the hemolymph (pHe) increased by 0.32 U within the first day of acclimation to cold, which corresponds to a change of 0.013 U °C−1. After the first day of acclimation, Pco2 increased in the hemolymph, resulting in a significant drop in pHe by 90 d of acclimation to cold. Acclimation of snails to low temperatures did not change the buffer value of the hemolymph. Also, intracellular pH (pHi) and intracellular buffer values remained stable during acclimation to cold for prolonged periods. The latter results in conjunction with those obtained by the in vitro determination of the passive component of intracellular fluids indicate an active regulation of pHi in H. lucorum during acclimation to cold.

Laboratory studies on the thermal tolerance and response of enzymes of intermediate metabolism in different land snail species

Land snails species occur in a range of habitats from humid to semi-arid and arid ones and seasonal variations in their physiology and biochemical composition have been linked to annual cycles of photoperiod, temperature, humidity and water availability. In an effort to understand the thermal tolerance and the impact of temperature elevation on tissue metabolism of land snails we determined the mortality, heamolymph PO2 and the activities of enzymes of intermediary metabolism in three land snail species (Helix lucorum, Helix pomatia and Cornu aspersum) differing in their geographical distribution and inhabiting areas with different climatic characteristics. No mortality was observed in both population of Cornu aspersum, while Helix pomatia exhibited higher mortality than Helix lucorum. PO2 dropped within the first 10days of exposure to elevated temperature in all species, although in Cornu aspersum this decrease was significantly lower. No significant reduction in the enzymatic activities of all glycolytic enzymes studied, as well as of citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HOAD) was observed in the more thermal tolerant species C. aspersum from both populations studied. Significant reductions of enzymatic activity of the glycolytic enzymes phosphofructokinase (PFK), pyruvate kinase (PK) and d-Lactate dehydrogenase (d-LDH) was observed in Helix lucorum and Helix pomatia. The observed inter-specific differences seem to be in accordance with the life cycle characteristics of each species and may be attributed to climatic differences among habitats within their distribution range.