title: Investigating the genetic architecture of conditional strategies using the environmental threshold model.
abstract: The threshold expression of dichotomous phenotypes that are environmentally cued or induced comprise the vast majority of phenotypic dimorphisms in colour, morphology, behaviour and life history. Modelled as conditional strategies under the framework of evolutionary game theory, the quantitative genetic basis of these traits is a challenge to estimate. The challenge exists firstly because the phenotypic expression of the trait is dichotomous and secondly because the apparent environmental cue is separate from the biological signal pathway that induces the switch between phenotypes. It is the cryptic variation underlying the translation of cue to phenotype that we address here. With a 'half-sib common environment' and a 'family-level split environment' experiment, we examine the environmental and genetic influences that underlie male dimorphism in the earwig Forficula auricularia. From the conceptual framework of the latent environmental threshold (LET) model, we use pedigree information to dissect the genetic architecture of the threshold expression of forceps length. We investigate for the first time the strength of the correlation between observable and cryptic 'proximate' cues. Furthermore, in support of the environmental threshold model, we found no evidence for a genetic correlation between cue and the threshold between phenotypes. Our results show strong correlations between observable and proximate cues and less genetic variation for thresholds than previous studies have suggested. We discuss the importance of generating better estimates of the genetic variation for thresholds when investigating the genetic architecture and heritability of threshold traits. By investigating genetic architecture by means of the LET model, our study supports several key evolutionary ideas related to conditional strategies and improves our understanding of environmentally cued decisions.
authors.affiliation: Centre for Evolutionary Biology, School of Animal Biology (M092), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia bruno.buzatto@gmail.com.
authors.forename: Bruno A
authors.identifier: 0000-0002-2711-0336
authors.initials: BA
authors.lastname: Buzatto
authors.affiliation: CNRS, Université Paul Sabatier, ENFA; UMR5174 EDB (Laboratoire Évolution and Diversité Biologique), 118 route de Narbonne, Toulouse 31062, France.
authors.forename: Mathieu
authors.identifier: 0000-0001-7053-3767
authors.initials: M
authors.lastname: Buoro
authors.affiliation: Department of Biology, DePauw University, Greencastle, IN 46135, USA.
authors.forename: Wade N
authors.initials: WN
authors.lastname: Hazel
authors.affiliation: Centre for Evolutionary Biology, School of Animal Biology (M092), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Tomkins
mesh_terms: D000818:Animals; D005260:Female; D059647:Gene-Environment Interaction; D014644:Genetic Variation; D007313:Insecta / Q000033:anatomy & histology / Q000235:genetics*; D008297:Male; D008957:Models, Genetic; D012727:Sex Characteristics; D006113:United Kingdom
keywords: alternative reproductive tactics; intrasexual dimorphism; male dimorphism; phenotypic plasticity; polyphenism; quantitative genetics