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, 6 (2), 279-89

Interactive Effects of Inbreeding and Endocrine Disruption on Reproduction in a Model Laboratory Fish

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Interactive Effects of Inbreeding and Endocrine Disruption on Reproduction in a Model Laboratory Fish

Lisa K Bickley et al. Evol Appl.

Abstract

Inbreeding depression is expected to be more severe in stressful environments. However, the extent to which inbreeding affects the vulnerability of populations to environmental stressors, such as chemical exposure, remains unresolved. Here we report on the combined impacts of inbreeding and exposure to an endocrine disrupting chemical (the fungicide clotrimazole) on zebrafish (Danio rerio). We show that whilst inbreeding can negatively affect reproductive traits, not all traits are affected equally. Inbreeding depression frequently only became apparent when fish were additionally stressed by chemical exposure. Embryo viability was significantly reduced in inbred exposed fish and there was a tendency for inbred males to sire fewer offspring when in direct competition with outbred individuals. Levels of plasma 11-ketotestosterone, a key male sex hormone, showed substantial inbreeding depression that was unaffected by addition of the fungicide. In contrast, there was no effect of inbreeding or clotrimazole exposure on egg production. Overall, our data provide evidence that stress may amplify the effects of inbreeding on key reproductive traits, particularly those associated with male fitness. This may have important implications when considering the consequences of exposure to chemical pollutants on the fitness of wild populations.

Keywords: ecotoxicology; fitness; fungicide; reproduction; zebrafish.

Figures

Figure 1
Figure 1
Generation of inbred and outbred zebrafish lines through controlled pairwise crosses. F0–F3* shows annotation corresponding to Brown et al. .
Figure 2
Figure 2
Experiment I: all fish in each spawning group were either inbred (formula image) or outbred (formula image) and had either been previously maintained under control conditions or exposed to clotrimazole; Experiment II: spawning groups contained one female (either inbred or outbred) and two males (one inbred and one outbred), and all fish in each spawning group had either been previously maintained under control conditions or exposed to clotrimazole. *denotes treatment used for subsequent parentage analysis.
Figure 3
Figure 3
The effect of inbreeding and clotrimazole exposure on number of eggs spawned per female, over the 10-day study period of Experiment (I) and Experiment (II). Data presented are mean ± SE, n = 10. Each spawning group contained one female and two males. In Experiment I, all fish were either outbred or inbred and had either been previously maintained under control conditions or exposed to clotrimazole, as indicated. In Experiment II each spawning group contained one female (either inbred or outbred, as indicated) and two males (one inbred and one outbred), and all fish had either been previously maintained under control conditions or exposed to clotrimazole, again as indicated.
Figure 4
Figure 4
The effect of clotrimazole exposure on embryo viability at 2, 8 and 24 h post-fertilization (hpf), across the 10-day study period of Experiment (I) and Experiment (II). Data presented are mean ± SE, n = 10. * denotes significantly different to all other treatment groups (P = <0.001). In Experiment I, all fish were either outbred or inbred and had either been previously maintained under control conditions or exposed to clotrimazole, as indicated. In Experiment II each spawning group contained one female (either inbred or outbred, as indicated) and two males (one inbred and one outbred), and all fish had either been previously maintained under control conditions or exposed to clotrimazole, again as indicated.
Figure 5
Figure 5
Proportion of offspring sired by inbred males in competition with outbred males in control and exposed treatment groups (GLM with binomial error; F = 0.6221; df = 1, 18; P = 0.058). Data analysed for spawning groups containing outbred females only. The central line within the box is the median. The box represents the upper and lower quartiles, and the whiskers the 95% confidence intervals. Open circles are outliers beyond the 95% confidence intervals. n = 9.
Figure 6
Figure 6
Comparison of plasma 11-kt concentrations in male zebrafish from Experiment II between (A) control and exposed, outbred and inbred fish (n = 20), and (B) the most and least reproductively successful male zebrafish, split by treatment group and degree of inbreeding (n = 9). Reproductive success was determined by the number of offspring sired by each male within each spawning group. Different letters denote significant differences between treatment groups.

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