Jacques Daguzan

INBREEDING AND FITNESS IN THE FRESHWATER SNAIL LYMNAEA PEREGRA: AN EVALUATION OVER TWO GENERATIONS OF SELF-FERTILIZATION

Inbreeding depression was estimated from an outbreeding population of the freshwater snail Lymnaea peregra, on the basis of two successive generations of enforced selling and outcrossing, and 70 maternal lineages. Outcrossing was analyzed under two treatments, groups of two and five individuals. The fitness parameters measured included fecundity, growth, and survival. In the first generation, we contrasted three treatments (selfers vs. paired outcrossers and group outcrossers). Very similar results were obtained between the two outcrossing treatments. A strong self‐fertilization depression (which includes parental fecundity and progeny fitness) was detected in the selling treatment (about 90%). In the second generation, there was again marked evidence for self‐fertilization depression, with the highest contributions coming from parental fecundity and progeny hatching rate. Our results suggest that the decreased parental fecundity is a consequence of the mating system in the previous generation, although the role of partial self‐incompatibility and the copulation behavior could not be ruled out. Hatching rate and early survival data are suggestive of purging of lethal mutations. Significant variation in fitness among selfing lineages was found for most fitness traits. Our experimental design also allowed to test for interactions among fitness loci. Only one trait of the nine studied behaved as expected under synergistic interactions. However we cannot rule out some purging during the experiment, which could have biased results towards linearity. Inbreeding depression was also inferred from the change of inbreeding level across generations in the same population. We obtained a value similar to the experimental estimate.

Cold-hardiness and freezing in the land snail Helix aspersa m̈uller (gastropoda; pulmonata)

Abstract 1. 1. Decreasing daylength from 16 to 12 hr depresses significantly mean supercooling points (SCP) and water content of Helix aspersa Muller. 2. 2. There is a significant correlation between SCP and water content but for the same water content, SCPs of the snails submitted to a 12L-12D photoperiod were lower. 3. 3. Helix aspersa is freezing susceptible but tissue damage is much more significant in long day snails than in short day ones.

A note on sex ratio, length and diet of a population of cuttlefish Sepia officinalis L. (Mollusca: Cephalopoda) sampled by three fishing methods

Abstract The population of the cuttlefish Sepia officinalis L. reproducing in Morbihan Bay (South Brittany, France) was fished by three different methods (a trammel net, a benthic trawl and traps), and from the resulting samples, some biological parameters were studied: sex ratio, length frequency and diet. The net was the only gear which gave a well-balanced sex ratio; fishing with traps appears to be less selective for length. The diet determined from the stomach contents is similar for the three gears. These three fishing gears were equally suitable for a study on feeding of the cuttlefish, but they have to be used with care for stock assessments.

The effect of antibiotic treatment on the supercooling ability of the land snail Helix aspersa (Gastropoda: Pulmonata)

The land snail Helix aspersa is a partially freezing tolerant species whose supercooling ability is limited to ca. -3 to -5 degrees C. One hundred adult snails were subjected to the following two experimental conditions: (i) a starved group, provided with water; (ii) an antibiotic-treated group that was provided with a solution containing a mixture of two antibiotics. The antibiotic group exhibited a T(c) significantly lower than the starved group (-3.94 +/- 1.32 degrees C, n = 40 and -3.07 +/- 0.99, n = 30, t test, p < 0.005). This study showed that bacteria of the gut are likely to elevate animal supercooling points. It is also the first report in which a possible ice-nucleating activity of the gut microflora in a land snail has been suggested by the action of antibiotics on the T(c).

Oral water consumption in Helix aspersa Müller (Gastropod mollusc: Stylommatophora) according to age, reproductive activity and food supply

Abstract 1. 1. The brown garden snail Helix aspersa Muller, young or adult, takes in and absorbs water orally through its digestive system. 2. 2. During the first month, Helix aspersa is able to absorb 70% of its total weight, in water, daily. This consumption suddenly drops at the end of the fourth week and progressively stabilizes around 150 μ1/g living animal daily when the snail reaches adult age. 3. 3. During its growth, Helix aspersa achieves better control of its water balance. 4. 4. Helix aspersa needs to drink and the water taken is always excessive and followed by excretion of the surplus through the faeces. 5. 5. Inactive snails minimize their water loss. 6. 6. Helix aspersa water balance appears to be very sensitive to physiological changes.

Study of the nitrogen content and amino-acids composition of the tissues of some trochidae of the Brittany coast (prosobranch gastropod molluscs)

Abstract 1. 1. The total nitrogen of the tissues is high (between 8.00 and 8.89% of the animals dry weight), and seems to be related to the quality of the food eaten. 2. 2. The uric nitrogen content present in the animal is high (between 0.24 and 0.44% of the animals dry weight); however the ammonical nitrogen content is low. 3. 3. The amino-acids composition of tissues shows a certain homogeneity within the Trochidae family. 4. 4. Whatever the species considered, the quantitatively most important amino-acids are: glutamic acid, aspartic acid and glycine.

Température et plasticité du chromatisme de la coquille chez le mollusque pulmoné Helix aspersa

Phenotypic plasticity of shell pigmentation in the land snail Helix aspersa was investigated with the help of image processing followed by pixel counting for each colour present on the shell. Thus, the use of three different growth temperatures under artificial conditions showed, for the two subspecies considered, a continuous colour gradient from red to dark of the shell banding. Darker pigmentation characterized low temperatures while red bands were related to the higher temperature (25 °C). No interpretable difference appeared between the two forms.