title: Colour polymorphism torn apart by opposing positive frequency-dependent selection, yet maintained in space.
abstract: Polymorphic warning signals in aposematic species are enigmatic because predator learning and discrimination should select for the most common coloration, resulting in positive frequency-dependent survival selection. Here, we investigated whether differential mating success could create sufficiently strong negative frequency-dependent selection for rare morphs to explain polymorphic (white and yellow) warning coloration in male wood tiger moths (Parasemia plantaginis). We conducted an experiment in semi-natural conditions where we estimated mating success for both white and yellow male moths under three different morph frequencies. Contrary to expectations, mating success was positively frequency-dependent: white morph males had high relative fitness when common, likewise yellow morph males had high relative fitness when instead they were common. We hence built a model parameterized with our data to examine whether polymorphism can be maintained despite two sources of positive frequency dependence. The model includes known spatial variation in the survival advantage enjoyed by the yellow morph and assumes that relative mating success follows our experimentally derived values. It predicts that polymorphism is possible under migration for up to approximately 20% exchange of individuals between subpopulations in each generation. Our results suggest that differential mating success combined with spatial variation in predator communities may operate as a selection mosaic that prevents complete fixation of either morph.
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biological and Environmental Sciences, University of Jyväskylä, yväskylä, Finland.
authors.forename: Swanne P
authors.initials: SP
authors.lastname: Gordon
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Kokko
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biological and Environmental Sciences, University of Jyväskylä, yväskylä, Finland.
authors.forename: Bibiana
authors.initials: B
authors.lastname: Rojas
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biological and Environmental Sciences, University of Jyväskylä, yväskylä, Finland.|Department of Zoology, University of Cambridge, Cambridge, UK.
authors.forename: Ossi
authors.initials: O
authors.lastname: Nokelainen
authors.affiliation: Centre of Excellence in Biological Interactions, Department of Biological and Environmental Sciences, University of Jyväskylä, yväskylä, Finland.
authors.forename: Johanna
authors.initials: J
authors.lastname: Mappes
mesh_terms: D000818:Animals; D003116:Color; D005260:Female; D005387:Finland; D056084:Genetic Fitness; D008297:Male; D009036:Moths / Q000235:genetics / Q000502:physiology*; D010858:Pigmentation; D011110:Polymorphism, Genetic; D012726:Sexual Behavior, Animal
keywords: aposematism; coloration; mating success; modelling; predation; sexual selection; spatial mosaic