Nonlinear Effects of Female Mate Choice in Wild Threespine Sticklebacks

Abstract

Abstract. Sexual selection by mate choice represents a very important selective pressure in many animal species and might have evolutionary impacts beyond exaggeration of secondary sexual traits. Describing the shape and strength of the relationships linking mating success and nonsexual traits in natural conditions represents a challenging step in our understanding of adaptive evolution. We studied the effect of behavioral (nest site choice), immunological (trematode level of infection), genetic diversity (measured by mean d 2 ) and morphological (standard length and pectoral fin size) traits on male mating success in a natural population of threespine sticklebacks Gasterosteaus aculeatus. Male mating success was measured by microsatellite genotyping of embryos used to infer female genotypes. First, we analyzed all territorial males (full analysis) but also considered independently only males with a nonzero mating success (reduced analysis) because some of the males with no eggs could have been part of a later breeding cycle. Multiple linear regressions identified a significant negative effect of parasite load in the full analysis, whereas no linear effect was found in the reduced analysis. The quadratic analyses revealed that nest location and parasite load were significantly related to mating success by positive (concave selection) and negative (convex selection) quadratic coefficients respectively, resulting in a saddle-shaped fitness surface. Moreover, there were significant interactions between nest location, mean d 2 and parasite load in the reduced analysis. The subsequent canonical rotation of the matrix of quadratic and cross-product terms identified two major axes of the response surface: a vector representing mostly nest site choice and a vector representing parasite load. These results imply that there exists more than one way for a male threespine stickleback to maximize its mating success and that such nonlinear relationships between male mating success induced by female mate choice and male characteristics might have been overlooked in many studies.

Putative causes and consequences of MHC variation within and between locally adapted stickleback demes

“…2008). Moreover, previous work within the SW deme of the St. Lawrence system revealed an effect of parasite load on reproductive success (Blais et al. 2004).…”

“…2005). While this approach may be beneficial in terms of separating the role of MHC from other traits, it cannot be forgotten that actual mate choice is multimodal (Blais et al. 2004) and that absence of complete information can potentially bias outcomes (Nilsson & Nilsson 2000; McLennan 2003).…”

Estimating Nonlinear Selection Gradients Using Quadratic Regression Coefficients: Double or Nothing?

“…Canonical analysis of the matrix of nonlinear selection gradients allows an interpretation of stabilizing and disruptive selection to be made on trait combinations that describe the greatest amount of nonlinear variation on fitness surfaces (Phillips and Arnold 1989; Simms 1990; Simms and Rausher 1993; Blows and Brooks 2003). Although canonical analysis has been advocated for > 15 years (Phillips and Arnold 1989; Simms 1990), its potential utility in empirical studies and meta‐analyses has only recently become more widely appreciated (Björklund and Senar 2001; Blows and Brooks 2003; Blais et al 2004; Brooks et al 2005; Bentsen et al 2006; Holleley et al 2006; Blows 2007a,b; Garant et al 2007; Hunt et al 2007; Kruuk and Garant 2007).…”

Reproductive success in a natural population of male three‐spined stickleback Gasterosteus aculeatus: effects of nuptial colour, parasites and body size

“…This study showed that male colour and reproductive success are unaffected by parasites for males in Lynne Lake, which is consistent with some populations of G. aculeatus but not others (FitzGerald et al ., ; Bakker & Mundwiler, ; Kraak et al ., ; Blais et al ., ; Macnab et al ., , ). For Lynne Lake, one possible explanation for this relationship is that males are generally in good condition and can tolerate infection more effectively.…”