Body size, longevity, and growth rate in Lake Pannon melanopsid gastropods and their predecessors

Abstract

We investigate potential microevolutionary mechanisms of phenotypic change in a lineage of brackish-water gastropods from Lake Pannon. The lineage exhibits a threefold increase in body size and a pronounced increase in shell shouldering over a roughly 2.5-Myr interval. We use the stable oxygen isotope profiles of 13 shells to address the question of whether large size is due to more rapid growth or to greater longevity.Results indicate that larger individuals have significantly greater longevity. Growth rates in large snails are comparable to those of their smaller-bodied ancestors.Potentially relevant selective advantages of large size include escape from predators, avoidance of resource competition, and increased fecundity. We argue that the first two advantages may have accrued to larger individuals but are not likely to have driven the trend because selection for them would favor more rapid growth rates. Fecundity selection, on the other hand, is readily envisioned in a stable, predictable environment in which the need for early reproduction is relaxed. The evolution of large body size in Lake Pannon molluscs may be comparable to evolution on many islands, where reduced pressure from competition and predation lead to characteristic changes in body size.

Predictors of shell size in long‐lived lake gastropods

“…The only detailed study on size variation in a fossil brackish‐water gastropod lineage is provided by Geary et al . (). They demonstrated successive size increase in a melanopsid species lineage from Lake Pannon, interpreted as greater individual longevity.…”

“…Particularly among the families Lymnaeidae and Melanopsidae, several species lineages are famous for their outstandingly large shells (e.g. Moos, ; Geary et al ., ; Neubauer et al ., ). Members of the Valencienniinae, comprising large, low patelliform lymnaeids, attain maximum shell lengths of 125 mm (Moos, ).…”

Unparalleled disjunction or unexpected relationships? Molecular phylogeny and biogeography of Melanopsidae (Caenogastropoda: Cerithioidea), with the description of a new family and a new genus from the ancient continent Zealandia

“…The observed variability of the shell and the rich fossil record probably triggered interest in the group and resulted in quite a large number of studies being published since the beginning of the second half of the 20th Century. These studies focused largely on the underlying evolutionary processes that may have contributed to the observed morphological plasticity of the shell and also influenced the understanding of the paleobiogeography and historical biogeography of the family on different geographical scales (Papp, ; Geary, , ; Glaubrecht, , ; Heller et al., , ; Bandel, ; Heller and Sivan, , ,; Geary et al., , ; Elkarmi and Ismail, ; Bandel et al., ; Neubauer et al., , ,, ). It is therefore surprising that recent members of the group have received relatively little attention in morphology‐based or molecular phylogenetic studies until now, especially because the family, as currently understood, also exhibits an unparalleled Western Palearctic–Zealandian disjunct distribution pattern (see, e.g., Brot, ; Banarescu, ; Glaubrecht, , , ; Neiber and Glaubrecht, ).…”

Palaeobiology, palaeoecology and stratigraphic significance of the Late Miocene cockle Lymnocardium soproniense from Lake Pannon

“…L. soproniense, the largest specimen, appears to have the longest lifespan (at least 10 years). Geary et al (2012) observed that the Pannonian snail Melanopsis also seemed to achieve increased body size through increased longevity. They proposed that the reproductive advantage of larger body size coupled with an increase in resource availability and/or a decrease in predation drove this evolutionary trend in Melanopsis.…”