Inbreeding in three-spined sticklebacks (Gasterosteus aculeatusL.): effects on testis and sperm traits

Abstract

Mating between relatives often results in inbreeding depression, and is assumed to have a strong effect on fitness traits such as fertility and gonad/gamete quality. However, data concerning this topic are contradictory and particularly scarce in fishes. Three‐spined sticklebacks (Gasterosteus aculeatus L.) show inbreeding depression in fertilization and hatching success, survival rates, body symmetry and behavioural traits. To date, any knowledge of the impact of inbreeding on males' gonads and gametes is lacking in this species. In the present study, testis and sperm traits were quantified in outbred and inbred males. Overall, these traits were not generally impaired by inbreeding, and this result was not changed by a second/third generation of brother–sister matings. However, testes brightness, a potential measure of oxidative stress, was negatively correlated with sperm number. Additionally, inbred males with higher body condition had significantly brighter testes, whereas their sperm number was significantly negatively correlated with sperm quality (as estimated by head volume). Such a trade‐off did not appear in outbred males. The comparatively small impact of inbreeding on testis and sperm traits might be explained by the low number of inbred individuals that reached the reproductive phase. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107, 510–520.

The evolutionary ecology of testicular function: size isn't everything

“…the incorporation of pigments into the tissues of the testis) might have this function (Zieri, Taboga & De Oliveira, 2007;Galvan, Møller & Erritzøe, 2011) (although this has also been suggested to be linked to thermoregulation of spermatogenesis in a lizard that shows a striking pattern of unilateral testicular melanisation; Guillette, Weigel & Flater, 1983). A case in point is the three-spined stickleback (Gasterosteus aculeatus), where sperm are made several months before the mating season and stored in the testis (Borg, 1982;Zbinden, 2001), where the testis is strongly melanised (Mehlis et al, 2012), and where brood care and territorial defence are very energy demanding (Smith & Wootton, 2005). If this scenario is correct, testicular melanisation might be correlated with the amount of pre-mating sexual investment.…”

Lakes and ponds as model systems to study parallel evolution

“…Surprisingly, studies made on replicate populations of sticklebacks (popular models of ecological genetics research) in this context have been conspicuously scarce until lately (but see: Mazzi et al, 2002;Melhis et al, 2012). For instance, the genetically depauperate pond populations of nine-spined sticklebacks (Shikano et al, 2010;Trokovic et al, 2012) would provide good models to study variation in segregation and drift loads in isolated replicate populations not subject to confounding effects of gene flow.…”

Male reproductive traits of full-sibs of different age classes in three-spined sticklebacks (Gasterosteus aculeatus)

“…(L* total ) testis brightness (see Mehlis et al 2012 for details).In all models family identity was included as random factor and never removed to control for possible ancestral influences. The model with the lowest AIC (Akaike's information criterion) value represents the best approximating model.…”

“…Young (N young = 60) and old males (N old = 96) differed significantly in absolute (“lme”, χ 2 = 54.517, P < 0.001) and relative testis mass (“lme”, χ 2 = 20.887, P < 0.001) as well as in total testis brightness (“lme”, χ 2 = 64.591, P < 0.001), which is a measure of testicular melanisation (see Mehlis et al 2012). While absolute and relative testis mass were both significantly higher in older males, the results show that testis melanisation was significantly lower in young males meaning that the testes of old males were less pigmented (Figure 2a-b; Table 2).…”

“…However, it has to be mentioned that differences in absolute testis mass were better explained by differences in body size (lower AIC) than by male age alone, with larger males having significantly heavier testes (“lme”, χ 2 = 76.359, P < 0.001).

Figure 2 Representative testes and sperm of three-spined stickleback males. Testis of a young ( a ) and an old ( b ) male and on the right side the corresponding L*value for testis brightness as a measure of testis melanisation (see Mehlis et al 2012). ( c ) Sperm head, mid-piece, and tail can be distinguished on the SEM image.

…”