title: Y-linked Mendelian inheritance of giant and dwarf male morphs in shell-brooding cichlids.
abstract: Behavioural variation among conspecifics is typically contingent on individual state or environmental conditions. Sex-specific genetic polymorphisms are enigmatic because they lack conditionality, and genes causing adaptive trait variation in one sex may reduce Darwinian fitness in the other. One way to avoid such genetic antagonism is to control sex-specific traits by inheritance via sex chromosomes. Here, controlled laboratory crossings suggest that in snail-brooding cichlid fish a single locus, two-allele polymorphism located on a sex-linked chromosome of heterogametic males generates an extreme reproductive dimorphism. Both natural and sexual selection are responsible for exceptionally large body size of bourgeois males, creating a niche for a miniature male phenotype to evolve. This extreme intrasexual dimorphism results from selection on opposite size thresholds caused by a single ecological factor, empty snail shells used as breeding substrate. Paternity analyses reveal that in the field parasitic dwarf males sire the majority of offspring in direct sperm competition with large nest owners exceeding their size more than 40 times. Apparently, use of empty snail shells as breeding substrate and single locus sex-linked inheritance of growth are the major ecological and genetic mechanisms responsible for the extreme intrasexual diversity observed in Lamprologus callipterus.
authors.affiliation: Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, Hinterkappelen 3032, Switzerland.
authors.forename: Sabine
authors.initials: S
authors.lastname: Wirtz Ocana
authors.affiliation: Institute of Science and Technology Austria, am Campus 1, Klosterneuburg 3400, Austria.
authors.forename: Patrick
authors.initials: P
authors.lastname: Meidl
authors.affiliation: Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, Hinterkappelen 3032, Switzerland.
authors.forename: Danielle
authors.initials: D
authors.lastname: Bonfils
authors.affiliation: Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, Hinterkappelen 3032, Switzerland michael.taborsky@iee.unibe.ch.
authors.forename: Michael
authors.identifier: http://orcid.org/0000-0002-1357-4316
authors.initials: M
authors.lastname: Taborsky
mesh_terms: D060105:Animal Shells; D000818:Animals; D049628:Body Size / Q000235:genetics*; D023681:Cichlids / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology; D005260:Female; D005306:Fertilization / Q000235:genetics; D050173:Genes, Y-Linked; D008297:Male; D010641:Phenotype; D011110:Polymorphism, Genetic; D012098:Reproduction / Q000235:genetics*; D012726:Sexual Behavior, Animal; D013094:Spermatozoa / Q000502:physiology
keywords: Mendelian polymorphism; alleles of large effect; alternative tactics; cichlid fish; genetic architecture; sex-linked inheritance