Is delayed selfing adjusted to chemical cues of density in the freshwater snail Physa acuta?

Authors

  • Pierre-Yves Henry,

  • Ludovic Vimond,

  • Thomas Lenormand,

  • Philippe Jarne


P.-Y. Henry, L. Vimond, T. Lenormand and P. Jarne, Centre d'Ecologie Fonctionnelle et Evolutive, C.N.R.S., 1919 route de Mende, FR-34293 Montpellier cedex 5, France. Present address for PYH: Département Ecologie et Gestion de la Biodiversité, UMR 5173, Muséum National d'Histoire Naturelle, 55 rue Buffon, F-75005 Paris, France (philippe.jarne@cefe.cnrs.fr).

Abstract

Delayed selfing allows self-fertile organisms to reproduce even in the absence of mate, and is thought to have evolved as a reproductive assurance strategy. In animal species with strong inbreeding depression, the time during which selfing should be postponed in the absence of mates (referred to as the waiting time) is predicted to have evolved as a function of inbreeding depression, resource reallocation and survival. Under the same theoretical perspective, variation in population density should trigger the evolution of a plastic adjustment of the waiting time. A condition is that individuals should be able to perceive environmental cues (e.g. chemicals) of the density of potential mates. These predictions were tested here using the hermaphroditic freshwater snail Physa acuta, based on two experiments in which rearing water was conditioned such as to manipulate the probability of mate encounter through chemical signals emitted by snails. First, a choice trial experiment showed that the exploration behaviour of individuals is sensible to chemical signals. The second experiment aimed at documenting fitness components (age at first reproduction, growth before and after reproduction, and fecundity over a three-week period) under five treatments (20 individuals per treatment) with different water-conditioning and access to mate. As predicted theoretically, this experiment detected the occurrence of a waiting time (11 days) and resource reallocation to growth when comparing individuals from pure water (no chemicals) and outcrossing individuals. However, the waiting time and resource reallocation to future fecundity did not increase with increasing chemical cues of conspecifics density. There is therefore no evidence that delayed selfing is plastic and adjusted according to mate encounter probability.

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