Shell variation in sympatric freshwater Lymnaea peregra and L. ovata (Gastropoda: Lymnaeidae)

Abstract

Snails of the genus Lymnaea are morphologically variable and their taxonomy is unclear. In particular, the forms peregra and ovata, distinguished by shell shape, are often considered variants of the same species, L. peregra. We studied a rare situation in a Swiss mountain lake where both forms are sympatric. First, we found that the forms shows complete separation for a number of allozymes. Second, we examined the response of the two snail forms to infection by the trematode Diplostomum phoxini. For the ovata form, there was a transitory, 10% increase in the growth of infected snails compared to uninfected controls. The peregra form showed no gigantism and had higher parasite‐induced mortality. Third, we assessed differences between the forms in reproduction under different environmental conditions. Density negatively influenced egg production to the same degree in both forms. However, decreasing water levels, characteristic of part of the lake studied, led to a 30% decrease in egg production for the ovata form, but only a 10% decrease for the peregra form. These differences are discussed in relation to the microdistributions of the snails in the lake and we conclude that the two forms are almost certainly separate species.

Molecular phylogenetic relationships in the aquatic snail genus Lymnaea , the intermediate host of the causative agent of fascioliasis: insights from broader taxon sampling

“…Hubendick (1951) considered the latter as a synonym of R. peregra, a view that also appears to have been adopted by Jackiewicz (1993) in her morphologicalsystematic study of European lymnaeids. In contrast, shell morphology and allozyme data indicated that R. peregra and R. ovata are distinct (Glo¨er et al 1987;Ward et al 1997), which is concordant with the 16S data since sequence divergence between these two species is relatively large (8.9%). The tree topologies further show that R. ovata is more closely allied to R. auricularia (bs=76-98%; di=2) than it is to R. peregra.…”

Evidence for age-dependent mating strategies in the simultaneous hermaphrodite snail,Lymnaea stagnalis(L.)

“…Body growth is indeterminate in Lymnaea although it slows down substantial after about 9-11 months of age in ad libitum fed, captive populations (Janse et al, 1989). In consequence, young sexually mature animals are usually smaller than their more senior conspecifics although body size can differ greatly even within age cohorts (Lam and Calow, 1989a;Lam and Calow, 1989b;Ward et al, 1997) (and own unpublished observations). Although evidence exist that egg-laying slows down and may come to a halt in aged animals (Janse et al, 1989), very few if any studies have systematically investigated male and female copulation incidence across the species' life cycle.…”

“…In general, larger animals are older, however, the correlation between size and age is far from perfect. In fact, same-aged snails, including Lymnaea often differ greatly in size and same sized animals might be of different age [present study (Lam and Calow, 1989a;Lam and Calow, 1989b;Ward et al, 1997)]. Thus, size is an unreliable estimate of age and age could be a confounding effect when dealing with size-dependent mating strategies, i.e.…”

“…For example, in many hermaphrodites, female fecundity, but not male fecundity, correlates significantly with body size (DeWitt,Age-dependent mating in Lymnaea Other studies provide evidence for the existence of size-assortative mating strategies in various simultaneous hermaphrodites (SwitzerDunlap et al, 1984;Baur, 1992;DeWitt, 1996;Yusa, 1996;Angeloni et al, 2002;Ohbayashi-Hodoki et al, 2004;Chaine and Angeloni, 2005). However, although most invertebrates are indeterminate growers, same-aged snails often differ greatly in size (Forbes and Crampton, 1942;Lam and Calow, 1989a;Lam and Calow, 1989b;Ward et al, 1997). It is therefore conceivable that whereas it is known that hermaphrodites change their reproductive strategies as they grow (Cadet et al, 2004), interpretation of these data could be confounded by the fact that for many of them age is a covariant of size.…”

Does habitat-specific variation in trematode infection risks influence habitat distribution of two closely related freshwater snails?

“…The snails are commonly considered as variants of the same species because they do not dier in internal anatomy (Hubendick 1951), and because dierences in shell morphology have been found to correspond with enzyme variation only in some, but not in all populations (Lam and Calow 1988;Evans 1989). However, consistent variation between the morphs has been found in shell morphology, population genetic structure, parasite susceptibility (Ward et al 1997), and habitat choice (Wullschleger and Ward 1998). In a laboratory experiment, L. peregra preferred mud over hard substrate, but showed no preference for low or high water level, while L. ovata did not show a preference for a speci®c substrate type, but signi®cantly preferred deeper water (Wullschleger and Ward 1998).…”