‘Good-genes’ and ‘compatible-genes’ effects in an Alpine whitefish and the information content of breeding tubercles over the course of the spawning season

Abstract

Some models of sexual selection predict that individuals vary in their genetic quality and reveal some of this variation in their secondary sexual characteristics. Alpine whitefish (Coregonus sp.) develop breeding tubercles shortly before their spawning season. These tubercles are epidermal structures that are distributed regularly along the body sides of both males and females. There is still much unexplained variation in the size of breeding tubercles within both sexes and with much overlap between the sexes. It has been suggested that breeding tubercles function to maintain body contact between the mating partners during spawning, act as weapons for defence of spawning territories, or are sexual signals that reveal aspects of genetic quality. We took two samples of whitefish from their spawning place, one at the beginning and one around the peak of spawning season. We found that females have on average smaller breeding tubercles than males, and that tubercle size partly reveals the stage of gonad maturation. Two independent full-factorial breeding experiments revealed that embryo mortality was significantly influenced by male and female effects. This finding demonstrates that the males differed in their genetic quality (because offspring get nothing but genes from their fathers). Tubercle size was negatively linked to some aspects of embryo mortality in the first breeding experiment but not significantly so in the second. This lack of consistency adds to inconsistent results that were reported before and suggests that (i) some aspects of genetic quality are not revealed in breeding tubercles while others are, or (ii) individuals vary in their signaling strategies and the information content of breeding tubercles is not always reliable. Moreover, the fact that female whitefish have breeding tubercles of significant size while males seem to have few reasons to be choosy suggests that the tubercles might also serve some functions that are not linked to sexual signaling.

Predicting the mating system from phenotypic correlations between life-history and sperm quality traits in the Alpine whitefish Coregonus zugensis

“…In the case of whitefish, the secondary sexual traits are breeding tubercles, i.e., little horny structures (Wiley and Collette 1970). In a previous studies we found that the size of breeding tubercles can sometimes be a significant predictor of offspring survival in whitefish (Wedekind et al 2001(Wedekind et al , 2007a. In roach (Rutilus rutilus), another iteroparous group spawner with external fertilization, the size of breeding tubercles is positively linked to male dominance (Kortet et al 2004a) and male size (Wedekind 1992), but not Table 2 for statistics significantly to sperm velocity (Kortet et al 2004c) nor offspring viability (Kortet et al 2004b).…”

“…They also started the breeding season with larger GSI, i.e., they were able to invest more than younger males into their relative gonad weight (Hellriegel and Blanckenhorn 2002), and their condition factor K was not significantly lower than that of younger males at any time during the spawning season. Recently, Wedekind et al 2007a tested the viability of embryos sired by young and old males of C. zugensis and found no significant negative effect of sire age on offspring viability.…”

“…In roach (Rutilus rutilus), another iteroparous group spawner with external fertilization, the size of breeding tubercles is positively linked to male dominance (Kortet et al 2004a) and male size (Wedekind 1992), but not Table 2 for statistics significantly to sperm velocity (Kortet et al 2004c) nor offspring viability (Kortet et al 2004b). Although the function of breeding tubercles is still not fully clear yet (see also Müller and Ward 1995;Wedekind et al 2007a), the fact that, in the present study, older males had significantly larger tubercles than younger males suggests again that the reduced sperm velocity of older males is not due to a reduced male health and vigor. Our study cannot fully distinguish age from size effects, because age and size is usually linked in fish like the whitefish.…”

“…Artificial fertilization may, therefore, change the genetics of wild populations as compared to natural reproduction, and it would be important to know the long-term evolutionary consequences of this change (Wedekind et al 2001(Wedekind et al , 2007bWedekind 2002;Wedekind and Müller 2004;Rudolfsen et al 2005;Pitcher and Neff 2006). However, not much is known about the natural mating system of Alpine whitefish except that they are external fertilizers with no parental care, that they typically aggregate for spawning once a year for a few weeks, and that they have so-called breeding tubercles, i. e., secondary sexual traits that are developed shortly before breeding season and that fall off immediately afterwards (Wiley and Collette 1970;Wedekind et al 2007a).…”

Genetic and potential non-genetic benefits increase offspring fitness of polyandrous females in non-resource based mating system

“…As the genetic variability is extremely low in many natural Arctic charr populations [67] inbreeding avoidance can be an important mechanism explaining the evolution of polyandry in the Arctic charr. As it has been demonstrated that good genes and compatible genes may both be involved in female choice at the same time [68-70], these two mechanisms are not mutually exclusive mechanisms of sexual selection.…”