Water balance and resistance to desiccation in rock-dwelling snails

Abstract

We have examined the resistance to desiccation among rock-dwelling land snails of various phylogenetic groups: Cristataria genezarethana (Clausiliidae), Rupestrella rhodia (Chondrinidae) and Levantina caesareana (Helicidae), all from the same location in Israel. L. caesareana was the most resistant and R. rhodia the least resistant to desiccation and C. genezarethana was of intermediate resistance. Differences in the rates of water loss during desiccation were determined mainly by rate of water loss during the first 2 days of desiccation. The high rates of water loss in rock-dwelling species exceed those of other snails in the Mediterranean habitat of Israel. However, snails collected in the field at the end of aestivation were in only a mild state of dehydration, suggesting that the rocky habitat protects its occupants against desiccation. We also suggest that among the rock-dwelling species, the protective role of the rock is more important in the more evolutionarily primitive genera (the chondrinid Rupestrella and the clausiliid Cristataria) and that physiological capacities are more effective in the more highly evolved helicid Levantina.

Desiccation and Rehydration in Land Snails—a Test for Distinct Set Points in Theba Pisana

“…This is the result of their lower mass (fluid) loss during desiccation. The present findings also show that the osmotic changes in the extra-pallial compartment were larger than expected from total mass (fluid) loss and thus suggest that water is preferentially moved to the soft body tissue, as has been previously suggested by Arad et al (1992Arad et al ( , 1995. In general, the osmolality of this fluid is lower than that of the hemolymph in pulmonate snails (Potts, 1975;Smith, 1981).…”

Disruptive selection by predation offsets stabilizing selection on shell morphology in the land snail Iberus g. gualtieranus

“…More globose snails have difficulties in to use fissures, the most protective refuges against dehydration, as shelter, and it is possible that these specimens had a higher risk of dying from desiccation. On the other hand, more flattened snails have a lower body volume, and thus less capacity to store reserves and to survive the periods of aestivation (Arad et al 1995), which can last six months in the study area (unpublished data). Kingsolver et al (2001) found a median value of 0.10 for gradients of non-linear selection, although these values seem to overestimate the true strength of selection (Hersch and Phillips 2004).…”

Short- and long-term resistance to desiccation in a minute litter-dwelling land snail Lauria cylindracea (Pulmonata: Pupillidae)

“…4.5% per day) was the highest found so far in our series of studies (Arad, Goldenberg & Heller, 1989, 1992, 1995Arad, 1990Arad, , 1993aArad, Goldenberg, Avivi et al, 1993). Apparently, this snail's rate of water loss (approx.…”

“…Morphometric characteristics of four groups of Lauria cylindracea: original group brought from the ®eld and of snails aestivating in the laboratory for 2, 3, and 4 months (June, May, and April, respectively) under condition of full hydration, desiccation, and after aestivation. Our studies of the small-size juvenile and adult Cristataria genezarethana (Clausiliidae) and adult Rupestrella rhodia (Chondrinidae) indicated that snail size alone cannot explain the differences in resistance to desiccation between these two species (Arad, Goldenberg & Heller, 1995). m i, initial fully-hydrated mass; m t, ®nal mass (after desiccation or aestivation); msh, shell mass; mwb, wet soft body mass; mdb, dry soft body mass; shf, shell free.…”