Condition, Genotype-by-Environment Interaction, and Correlational Selection in Lizard Life-History Morphs

Abstract

We compared reproductive allocation and variation in condition and survivorship of two heritable female throat color morphs (orange and yellow) in a free-living population of side-blotched lizards (Uta stansburiana). Using path analysis and structural equation modeling, we investigated how variation in the social environment affected clutch size and egg mass and two condition traits (postlaying mass, immunological condition) and how these traits in turn affected female field survival. In the presence of many neighbors, both morphs increased their clutch sizes, although these effects were only significant in yellow females. In addition, yellow females increased their egg mass in the presence of many orange neighbors. Orange females surrounded by many orange neighbors showed sign of stress in the form of immunosuppression, whereas this effect was less pronounced in yellow females. The morphs also differed in the impact of variation in clutch size and egg mass on both condition traits. Finally, female morphotype and immune responsiveness affected fitness interactively, and hence these two traits showed signs of fitness epistasis: Selection gradients on this trait were opposite in sign in the two morphs. The correlational selection gradient (gamma throat x antibody response) between female throat color and antibody responsiveness was -0.365. Our data thus reveal important interactive effects such as genotype-by-environment interaction toward the social environment and morph-specific trade-offs as well as the occurrence of correlational selection. We discuss the use of naturally occurring and conspicuous genetic polymorphisms in field studies of selection and life-history allocation.

Density-dependent competition and selection on immune function in genetic lizard morphs

“…The correlational selection gradient (␥; ref. 26) between female throat color and antibody responsiveness was Ϫ0.365 (28).…”

“…Even if this is the case, correlational selection (26,28) between these traits will, in the long run, lead to the buildup of adaptive linkage disequilibrium that will result in a genetic correlation between female throat color and antibody responsiveness (Fig. 3).…”

“…Our results indicate that a genetic correlation between a signaling trait (throat coloration) and a condition trait (immunological condition) need not be restricted to the male sex and hence could be a more general phenomenon in natural populations. The genetic correlation arises because correlational selection (14,26,28) couples genetic variation in both throat color and immune function through these two trait's interactive effects on fitness (cf. ''pure epistasis models''; ref.…”

Offspring size and timing of hatching determine survival and reproductive output in a lizard

“…Hatchlings from earlier clutches tend to have higher survival to hibernation and adulthood in U. stansburiana, but lower survival to hibernation in A. muricatus (although early hatched offspring have higher per-week survival; . Furthermore, in U. stansburiana, lay date and egg mass have been shown to be subject to correlational selection that varies across environmental conditions (Svensson and Sinervo 2000;Svensson et al 2001;Calsbeek and Sinervo 2007). In contrast, egg size does not affect juvenile survival in A. muricatus .…”

Seasonal changes in parasite load and a cellular immune response in a colour polymorphic lizard

“…Female polymorphism is much less documented (Svensson et al 2009), but in the few cases studied, female morphs tend to differ in reproductive traits such as clutch size and egg mass, and the success of either morph depends strongly on the social environment (Svensson et al 2001;Vercken et al 2007). Here too, differences in immune function between morphs may arise from direct energetic trade-offs, or via the adverse effects of hormones (e.g.…”