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Sex-biased mortality associated with inbreeding in Drosophila melanogaster.

Robinson SP, Simmons LW, Kennington WJ - BMC Evol. Biol. (2014)

Bottom Line: We found increased female mortality and male biased sex ratios associated with inbreeding in our high, but not low, X-inbreeding pedigree.While our results are more consistent with being driven by inbreeding on the X-chromosome than on the autosomes, the marked difference between treatments does not fit closely the expectations of either model.Our results are only partly consistent with the hypothesis that inbreeding on the X-chromosome can cause greater fitness reductions in the homogametic sex.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Evolutionary Biology, School of Animal Biology (M092), The University of Western Australia, Crawley, WA 6009, Australia. stephen.robinson@graduate.uwa.edu.au.

ABSTRACT

Background: One proposed consequence of inbreeding is a skewed sex ratio arising from sex specific mortality in the homogametic sex caused by inbreeding on the sex chromosome. However, recent work suggests that random distortions in sex ratio due to autosomal inbreeding may be of greater importance. In this study, we investigate the effect of biologically realistic levels of inbreeding on sex ratio and sex specific mortality in Drosophila melanogaster. We use two pedigree crossing designs to either maximise or minimise inbreeding on the X-chromosome whilst producing identical autosomal inbreeding.

Results: We found increased female mortality and male biased sex ratios associated with inbreeding in our high, but not low, X-inbreeding pedigree. While our results are more consistent with being driven by inbreeding on the X-chromosome than on the autosomes, the marked difference between treatments does not fit closely the expectations of either model.

Conclusions: Our results are only partly consistent with the hypothesis that inbreeding on the X-chromosome can cause greater fitness reductions in the homogametic sex. Whilst the results of our study are not conclusive, they suggest that directional distortions in sex ratio due to inbreeding can occur, and highlight the need for further investigation on this topic.

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Pedigree crossing design. All individuals without origins within the pedigrees were sourced from the mass population. Females marked with a * indicate the focal female group in each pedigree, with which males were crossed to produce the desired levels of inbreeding. The blue, green and brown colourings trace the inheritance of X-chromosomes that may be shared between the focal females and their mates. Same pair indicates that this same pair of individuals was shared in common between the two pedigrees.
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Figure 5: Pedigree crossing design. All individuals without origins within the pedigrees were sourced from the mass population. Females marked with a * indicate the focal female group in each pedigree, with which males were crossed to produce the desired levels of inbreeding. The blue, green and brown colourings trace the inheritance of X-chromosomes that may be shared between the focal females and their mates. Same pair indicates that this same pair of individuals was shared in common between the two pedigrees.

Mentions: From this stock population we used two different pedigrees, each of which generated inbreeding levels equal to crosses between: full siblings (ƒ = 1/4), double 1st cousins (ƒ = 1/8), 1st cousins (ƒ = 1/16), 2nd cousins (ƒ = 1/64) and unrelated individuals (ƒ ≈ 0). Although each pedigree generated identical levels of inbreeding on the autosomes, by altering the sex of the individuals chosen to continue each step in the pedigree, one pedigree was set up to maximise inbreeding on the X-chromosome while the other was set up to minimise inbreeding on the X-chromosome (Figure 5). These will be referred to as the high X-inbreeding and the low X-inbreeding pedigrees respectively. Inbreeding on the X-chromosome was calculated following Crow and Kimura [27] and is listed for each cross within each pedigree in Figure 5. It should be noted that while the low X-inbreeding pedigree aimed to minimise inbreeding on the X-chromosome, this was not always possible and in the case of double first cousin and full sibling crosses, inbreeding on the X-chromosome could not be avoided (see Figure 5). For each level of autosomal inbreeding within each pedigree we also calculated the relative differences in sex ratio expected due to the differences in X-chromosome inbreeding (Figure 1).


Sex-biased mortality associated with inbreeding in Drosophila melanogaster.

Robinson SP, Simmons LW, Kennington WJ - BMC Evol. Biol. (2014)

Pedigree crossing design. All individuals without origins within the pedigrees were sourced from the mass population. Females marked with a * indicate the focal female group in each pedigree, with which males were crossed to produce the desired levels of inbreeding. The blue, green and brown colourings trace the inheritance of X-chromosomes that may be shared between the focal females and their mates. Same pair indicates that this same pair of individuals was shared in common between the two pedigrees.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4234498&req=5

Figure 5: Pedigree crossing design. All individuals without origins within the pedigrees were sourced from the mass population. Females marked with a * indicate the focal female group in each pedigree, with which males were crossed to produce the desired levels of inbreeding. The blue, green and brown colourings trace the inheritance of X-chromosomes that may be shared between the focal females and their mates. Same pair indicates that this same pair of individuals was shared in common between the two pedigrees.
Mentions: From this stock population we used two different pedigrees, each of which generated inbreeding levels equal to crosses between: full siblings (ƒ = 1/4), double 1st cousins (ƒ = 1/8), 1st cousins (ƒ = 1/16), 2nd cousins (ƒ = 1/64) and unrelated individuals (ƒ ≈ 0). Although each pedigree generated identical levels of inbreeding on the autosomes, by altering the sex of the individuals chosen to continue each step in the pedigree, one pedigree was set up to maximise inbreeding on the X-chromosome while the other was set up to minimise inbreeding on the X-chromosome (Figure 5). These will be referred to as the high X-inbreeding and the low X-inbreeding pedigrees respectively. Inbreeding on the X-chromosome was calculated following Crow and Kimura [27] and is listed for each cross within each pedigree in Figure 5. It should be noted that while the low X-inbreeding pedigree aimed to minimise inbreeding on the X-chromosome, this was not always possible and in the case of double first cousin and full sibling crosses, inbreeding on the X-chromosome could not be avoided (see Figure 5). For each level of autosomal inbreeding within each pedigree we also calculated the relative differences in sex ratio expected due to the differences in X-chromosome inbreeding (Figure 1).

Bottom Line: We found increased female mortality and male biased sex ratios associated with inbreeding in our high, but not low, X-inbreeding pedigree.While our results are more consistent with being driven by inbreeding on the X-chromosome than on the autosomes, the marked difference between treatments does not fit closely the expectations of either model.Our results are only partly consistent with the hypothesis that inbreeding on the X-chromosome can cause greater fitness reductions in the homogametic sex.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Evolutionary Biology, School of Animal Biology (M092), The University of Western Australia, Crawley, WA 6009, Australia. stephen.robinson@graduate.uwa.edu.au.

ABSTRACT

Background: One proposed consequence of inbreeding is a skewed sex ratio arising from sex specific mortality in the homogametic sex caused by inbreeding on the sex chromosome. However, recent work suggests that random distortions in sex ratio due to autosomal inbreeding may be of greater importance. In this study, we investigate the effect of biologically realistic levels of inbreeding on sex ratio and sex specific mortality in Drosophila melanogaster. We use two pedigree crossing designs to either maximise or minimise inbreeding on the X-chromosome whilst producing identical autosomal inbreeding.

Results: We found increased female mortality and male biased sex ratios associated with inbreeding in our high, but not low, X-inbreeding pedigree. While our results are more consistent with being driven by inbreeding on the X-chromosome than on the autosomes, the marked difference between treatments does not fit closely the expectations of either model.

Conclusions: Our results are only partly consistent with the hypothesis that inbreeding on the X-chromosome can cause greater fitness reductions in the homogametic sex. Whilst the results of our study are not conclusive, they suggest that directional distortions in sex ratio due to inbreeding can occur, and highlight the need for further investigation on this topic.

Show MeSH
Related in: MedlinePlus