Relative costs and benefits of alternative reproductive phenotypes at different temperatures – genotype-by-environment interactions in a sexually selected trait

Abstract

BackgroundThe maintenance of considerable genetic variation in sexually selected traits (SSTs) is puzzling given directional selection expected to act on these traits. A possible explanation is the existence of a genotype-by-environment (GxE) interaction for fitness, by which elaborate SSTs are favored in some environments but selected against in others. In the current study, we look for such interactions for fitness-related traits in the bulb mite, a male-dimorphic species with discontinuous expression of a heritable SST in the form of enlarged legs that are used as weapons.ResultsWe show that evolution at 18 °C resulted in populations with a higher prevalence of this SST compared to evolution at 24 °C. We further demonstrate that temperature modified male reproductive success in a way that was consistent with these changes. There was a genotype-by-environment interaction for reproductive success – at 18 °C the relative reproductive success of armored males competing with unarmored ones was higher than at the moderate temperature of 24 °C. However, male morph did not have interactive effects with temperature with respect to other life history traits (development time and longevity).ConclusionsA male genotype that is associated with the expression of a SST interacted with temperature in determining male reproductive success. This interaction caused an elaborate SST to evolve in different directions (more or less prevalent) depending on the thermal environment. The implication of this finding is that seasonal temperature fluctuations have the potential to maintain male polymorphism within populations. Furthermore, spatial heterogeneity in thermal conditions may cause differences among populations in SST selection. This could potentially cause selection against male immigrants from populations in different environments and thus strengthen barriers to gene flow.

The role of genetic diversity in the evolution and maintenance of environmentally-cued, male alternative reproductive tactics

“…Previous empirical evidence in bulb mites not only demonstrates that scrambler morphs live longer [78], but importantly, that scrambler-selected lines produce more females that lay larger and more eggs over a longer period of time [79], and are generally more fecund than fighter-selected lines [60]. These morph-specific patterns may help to elucidate why we observed the genetic architecture of scramblers and females to be more similar to each other in contrast to fighters, patterns corroborated in gene expression profiles [52].…”

Male-limited secondary sexual trait interacts with environment in determining female fitness

“…Furthermore, the lifespan of bulb mites has been shown to increase at decreased temperature (Plesnar‐Bielak et al. ), so that at 18°C the oviposition period is probably extended with respect to that at both 24°C and 28°C. Hence, while both 18°C and 28°C can be considered novel environments for our populations, the increased temperature might in fact be more stressful than the decreased temperature.…”

Sexual and ecological selection on a sexual conflict gene

“…30 individuals was genotyped for 6Pgdh . Allele frequencies at the corresponding generations were assessed at different time points for different temperatures, as temperature strongly affects development time, with mites reaching adulthood after 16–21 days at 18°C and 10–15 days at 24°C (Plesnar‐Bielak et al., 2018).…”

“…However, while a number of studies have shown genotype‐by‐environment interactions for fitness in sexually selected traits (e.g. Qvarnström, 1999; Welch, 2003; Plesnar‐Bielak, Skwierzyńska, Hlebowicz, & Radwan, 2018; see Ingleby, Hunt, & Hosken, 2010 for review), less effort has been devoted into investigating maintenance of polymorphism in genes involved in sexual selection and conflict (Rostant, Kay, Wedell, & Hosken, 2015).…”