The effect of chirality phenotype and genotype on the fecundity and viability of Partula suturalis and Lymnaea stagnalis:  implications for the evolution of sinistral snails Journal Article


Author(s): Davison, Angus; Barton, Nicholas H; Clarke, Bryan
Article Title: The effect of chirality phenotype and genotype on the fecundity and viability of Partula suturalis and Lymnaea stagnalis:  implications for the evolution of sinistral snails
Affiliation IST Austria
Abstract: Why are sinistral snails so rare? Two main hypotheses are that selection acts against the establishment of new coiling morphs, because dextral and sinistral snails have trouble mating, or else a developmental constraint prevents the establishment of sinistrals. We therefore used an isolate of the snail Lymnaea stagnalis, in which sinistrals are rare, and populations of Partula suturalis, in which sinistrals are common, as well as a mathematical model, to understand the circumstances by which new morphs evolve. The main finding is that the sinistral genotype is associated with reduced egg viability in L. stagnalis, but in P. suturalis individuals of sinistral and dextral genotype appear equally fecund, implying a lack of a constraint. As positive frequency-dependent selection against the rare chiral morph in P. suturalis also operates over a narrow range (< 3%), the results suggest a model for chiral evolution in snails in which weak positive frequency-dependent selection may be overcome by a negative frequency-dependent selection, such as reproductive character displacement. In snails, there is not always a developmental constraint. As the direction of cleavage, and thus the directional asymmetry of the entire body, does not generally vary in other Spiralia (annelids, echiurans, vestimentiferans, sipunculids and nemerteans), it remains an open question as to whether this is because of a constraint and/or because most taxa do not have a conspicuous external asymmetry (like a shell) upon which selection can act.
Keywords: Chirality; asymmetry; canalization; left–right asymmetry; Spiralia
Journal Title: Journal of Evolutionary Biology
Volume: 22
Issue 8
ISSN: 1420-9101
Publisher: Wiley-Blackwell  
Date Published: 2009-08-01
Start Page: 1624
End Page: 1635
URL:
DOI: 10.1111/j.1420-9101.2009.01770.x
Notes: We owe a great debt to Jim Murray for his many contributions to the study of Partula, in the field, in the laboratory, in the interpretation of data, and in generating new ideas about evolution. With pleasure and respect we dedicate this paper to him. Jim Murray played a leading role in making the collections used here. We are very grateful also to Ann Clarke and Elizabeth Murray for help with collecting, to Lorna Stewart for snail dissections, to Joris Koene for the gift of snails, to Natasha Constant for entering the data, and Takahiro Asami, Edmund Gittenberger and Gerhard Falkner for establishing the sinistral stock of L. stagnalis. Comments from an anonymous referee, A. Richard Palmer and the editorial board improved the manuscript. Work in the field was supported by the Royal Society, The Carnegie Trust, the Percy Sladen Trust and the National Science Foundation. The Science Research Council (B/SR/4144), the National Science Foundation (GB-4188), the Royal Society and the University of Nottingham supported work in the laboratory.
Open access: yes (repository)