title: Environmental heterogeneity generates opposite gene-by-environment interactions for two fitness-related traits within a population.
abstract: Theory predicts that environmental heterogeneity offers a potential solution to the maintenance of genetic variation within populations, but empirical evidence remains sparse. The live-bearing fish Xiphophorus variatus exhibits polymorphism at a single locus, with different alleles resulting in up to five distinct melanistic "tailspot" patterns within populations. We investigated the effects of heterogeneity in two ubiquitous environmental variables (temperature and food availability) on two fitness-related traits (upper thermal limits and body condition) in two different tailspot types (wild-type and upper cut crescent). We found gene-by-environment (G × E) interactions between tailspot type and food level affecting upper thermal limits (UTL), as well as between tailspot type and thermal environment affecting body condition. Exploring mechanistic bases underlying these G × E patterns, we found no differences between tailspot types in hsp70 gene expression despite significant overall increases in expression under both thermal and food stress. Similarly, there was no difference in routine metabolic rates between the tailspot types. The reversal of relative performance of the two tailspot types under different environmental conditions revealed a mechanism by which environmental heterogeneity can balance polymorphism within populations through selection on different fitness-related traits.
authors.affiliation: Centro de Investigaciones Cientificas de las Huastecas "Aguazarca", 392 Colonia Aguazarca, Calnali, Hidalgo, 43230, Mexico; Division of Biology, Kansas State University, Manhattan, Kansas, 66506. zach@cichaz.org.
authors.forename: Zachary W
authors.initials: ZW
authors.lastname: Culumber
authors.forename: Molly
authors.initials: M
authors.lastname: Schumer
authors.forename: Scott
authors.initials: S
authors.lastname: Monks
authors.forename: Michael
authors.initials: M
authors.lastname: Tobler
mesh_terms: D000483:Alleles; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D003532:Cyprinodontiformes / Q000235:genetics / Q000502:physiology*; D004777:Environment; D059647:Gene-Environment Interaction; D056084:Genetic Fitness; D014644:Genetic Variation; D008297:Male; D011110:Polymorphism, Genetic; D013696:Temperature
keywords: Balancing selection; CTmax; body condition; poeciliidae; polymorphism; upper thermal limit