Spatiotemporal environmental heterogeneity and the maintenance of the tailspot polymorphism in the variable platyfish (Xiphophorus variatus)

Abstract

Genetic variation is critical for adaptive evolution. Despite its importance, there is still limited evidence in support of some prominent theoretical models explaining the maintenance of genetic polymorphism within populations. We examined 84 populations of Xiphophorus variatus, a livebearing fish with a genetic polymorphism associated with physiological performance, to test: (1) whether niche differentiation explains broad-scale maintenance of polymorphism, (2) whether polymorphism is maintained among populations by local adaptation and migration, or (3) whether heterogeneity in explicit environmental variables could be linked to levels of polymorphism within populations. We found no evidence of climatic niche differentiation that could generate or maintain broad geographic variation in polymorphism. Subsequently, hierarchical partitioning of genetic richness and partial mantel tests revealed that 76% of the observed genetic richness was partitioned within populations with no effect of geographic distance on polymorphism. These results strongly suggest a lack of migration-selection balance in the maintenance of polymorphism, and model selection confirmed a significant relationship between environmental heterogeneity and genetic richness within populations. Few studies have demonstrated such effects at this scale, and additional studies in other taxa should examine the generality of gene-by-environment interactions across populations to better understand the dynamics and scale of balancing selection.

GxG epistasis in growth and condition and the maintenance of genetic polymorphism inGambusia holbrooki

“…; Culumber et al. ; Gulisija and Kim ; Culumber and Tobler ), there is little understanding of how variation in the social environment—and particularly the genetic composition of the social environment—can influence the maintenance of variation (Saltz and Nuzhdin ). Phenotypic differences caused by genetic variation in the social environment are generally termed "indirect genetic effects" (IGEs: Moore et al.…”

“…Although a number of theoretical and empirical studies have suggested that spatially or temporally fluctuating selection can maintain adaptive genetic variation (Levene 1953;Gillespie and Turelli 1989;Huang et al 2014;Culumber et al 2015;Gulisija and Kim 2015;Culumber and Tobler 2016), there is little understanding of how variation in the social environment-and particularly the genetic composition of the social environment-can influence the maintenance of variation (Saltz and Nuzhdin 2014). Phenotypic differences caused by genetic variation in the social environment are generally termed "indirect genetic effects" (IGEs: Moore et al 1997;Wolf et al 1998).…”

Natural quantitative genetic variance in plant growth differs in response to ecologically relevant temperature heterogeneity

“…Wigg (Vavrek, McGraw, & Yang, 1996), while annually varying moisture conditions in a desert may conserve flower color polymorphism in the annual Linanthus parryae (A.Gray) Greene (Schemske & Bierzychudek, 2001). In the fish Xiphophorus variatus, the level of temperature variability within days and years has been found to be positively associated with withinpopulation diversity in tail spot richness (Culumber & Tobler, 2016), with the fitness rank of different spot types depending for instance on the thermal environment (Culumber, Schumer, Monks, & Tobler, 2015).…”

Genotype-environment interaction and the maintenance of genetic variation: an empirical study ofLobelia inflata(Campanulaceae)

“…Population genetic theory indicates that environmental heterogeneity can maintain additive quantitative genetic variation [21][22][23], a result supported by some of the few empirical studies on the topic [24][25][26][27][28], but not by others (e.g. [29]).…”