Sex differences in local adaptation: what can we learn from reciprocal transplant experiments?

Abstract

Local adaptation is of fundamental interest to evolutionary biologists. Traditionally, local adaptation has been studied using reciprocal transplant experiments to quantify fitness differences between residents and immigrants in pairwise transplants between study populations. Previous studies have detected local adaptation in some cases, but others have shown lack of adaptation or even maladaptation. Recently, the importance of different fitness components, such as survival and fecundity, to local adaptation have been emphasized. Here, we address another neglected aspect in studies of local adaptation: sex differences. Given the ubiquity of sexual dimorphism in life histories and phenotypic traits, this neglect is surprising, but may be partly explained by differences in research traditions and terminology in the fields of local adaptation and sexual selection. Studies that investigate differences in mating success between resident and immigrants across populations tend to be framed in terms of reproductive and behavioural isolation, rather than local adaptation. We briefly review the published literature that bridges these areas and suggest that reciprocal transplant experiments could benefit from quantifying both male and female fitness components. Such a more integrative research approach could clarify the role of sex differences in the evolution of local adaptations.This article is part of the theme issue 'Linking local adaptation with the evolution of sex differences'.

Keywords: female demographic dominance; gene flow; intersexual genetic correlation; local adaptation; reciprocal transplant experiments; sexual dimorphism.

Figure 1.

Relationship between the location of sex-specific local fitness optima in two different environments (‘Environment 1’ on first row and ‘Environment 2’ on second row) and expected outcomes from reciprocal transplant experiments. Male fitness functions are shown in solid lines, blue and filled symbols, whereas female fitness functions are shown in dashed lines, red and open symbols. Left column (a–d): The location of the male fitness optimum is similar in environments 1 and 2, whereas the female optima differ between the two environments (a,b). Consequently, a reciprocal transplant experiment reveals no evidence for local adaptation or a fitness trade-off for males (c), but evidence for local adaption and a strong fitness trade-off between environments in females (d). Right column (e–h): The locations of male and female fitness optima are similar in environment 1, where selection is concordant between the two sexes (e). By contrast, in environment 2, the location of male and female optima differ, leading to sexually antagonistic selection in that environment (f). As both male and female optima differ between environments 1 and 2 (e,f), reciprocal transplant experiments reveal local adaptation and fitness trade-offs between environments in both males and females (g,h).

Figure 2.

Local adaptation in relation to sexual selection as revealed by reciprocal transplant experiments and assessment of male fitness components in damselflies (Odonata: Zygoptera). Reciprocal transplant experiments in two species of damselflies: Enallagma cyathigerum (a) and Calopteryx splendens (e). In E. cyathigerum, replicated reciprocal transplant experiments (two population pairs) were carried out, whereby coastal and inland males were released in native and foreign environments (b,c). A significant phenotype × environment interaction revealed local adaptation that was asymmetric in nature, with local adaptation being present in the two inland populations where residents had higher recapture probability (a measure of local survival), but not in the coastal populations, where immigrants and residents had similar survival (c). This suggests that the coastal populations form a demographic sink [56]. Closer inspection of three fitness components revealed that isolation between the environments is mainly caused by reduced survival of immigrants rather than by sexual isolation or fecundity (d). In C. splendens (e), reciprocal transplant experiments (male presentations to local females) between two populations (Klingavälsån and Höje Å) show significant evidence for a phenotype × population interaction (f), where females show strong preference for local over immigrant males [57].