Brooding in a temperate zone land snail: seasonal and regional patterns

Abstract

The goal of this study is to assess if the reproductive strategy of a brooding land snail shifts along a climatic gradient. We focused on the following traits: timing and length of the reproductive season, brood size, ontogenetic dynamics of embryos, and reproductive mode (viviparity versus egg-laying). We dissected the central European door snail Alinda biplicata, collected monthly from eight populations covering the oceaniccontinental climatic gradient within the species’ distribution range. Forty percent of the 1706 dissected individuals were brooding. The species displayed a spring-summer reproductive activity pattern: intrauterine brooding was recorded between March and September; first embryos of a developmental stage that equals that of live-born neonates appeared in late April. Brooding started approximately when the mean daily temperature of a month exceeds ca. 5°C, thus the ontogenetic development of embryos is advancing earlier in populations under the influence of mild oceanic climate, and later in the eastern, more continental part of the range, or in submontane localities. A range-wide synchrony in reproduction occurred in May, when average temperatures and precipitation display a high rangewide similarity. The mean number of intrauterine eggs decreased between spring and summer in all populations (April: 10.9 ± 2.9; September: 6.4 ± 2.4), suggesting a gradual release of neonates which are not immediately replaced in uteri by new eggs. Snails from areas with long frosty winters do not invest much in a second reproductive period in late summer. Embryos of advanced embryonic stage were found in the reproductive tract of individuals from each population, thus we refute the hypothesis that A. biplicata switches its reproductive strategy towards oviparity under the influence of oceanic climate.