Matteo Mondani’s research while affiliated with University College London and other places

Meiotic drive systems are associated with low frequency chromosomal inversions. These are expected to accumulate deleterious mutations due to reduced recombination and low effective population size. We test this prediction using the "sex-ratio" (SR) meiotic drive system of the Malaysian stalk-eyed fly Teleopsis dalmanni. SR is associated with a large inversion (or inversions) on the X chromosome. In particular, we study eyespan in males carrying the SR chromosome, as this trait is a highly exaggerated, sexually dimorphic trait, known to have heightened condition-dependent expression. Larvae were raised in low and high larval food stress environments. SR males showed reduced eyespan under the low and high stress treatments but there was no evidence of a condition-dependent decrease in eyespan under high stress. Similar but more complex patterns were observed for female eyespan, with evidence of additivity under low stress and heterosis under high stress. These results do not support the hypothesis that reduced sexual ornament size in meiotic drive males is due to a condition-dependent response to the putative increase in mutation load. Instead, reduced eyespan likely reflects compensatory resource allocation to different traits in response to drive-mediated destruction of sperm.

Male mate preferences have been demonstrated across a range of species, including the Malaysian stalk-eyed fly, Teleopsis dalmanni. This species is subject to sex-ratio (SR), an X-linked male meiotic driver, which causes the dysfunction of Y-sperm and the production of all-female broods. While there has been work considering female avoidance of meiotic drive males, the mating decisions of drive-bearing males have not been considered previously. Drive males may be less able to bear the cost of choice as SR is associated with a low-frequency inversion that causes reduced organismal fitness. Drive males may also experience weaker selection for preference maintenance if they are avoided by females. Using binary choice trials, across two experiments, we confirmed male preference for large (fecund) females but found no evidence that the strength of male preference differs between drive and standard males. We showed that large eyespan males displayed strong preference for large females, whereas small eyespan males showed no preference. Taken together, these results suggest that, even though meiotic drive is associated with lower genetic quality, it does not directly interfere with male mate preference among available females. However, as drive males tend to have smaller eyespan (albeit only ~5% on average), this will to a minor extent weaken their strength of preference.

Male mate preferences have been demonstrated across a range of species, including the Malaysian stalk-eyed fly, Teleopsis dalmanni . This species is subject to SR, an X-linked male meiotic driver, that causes the dysfunction of Y-sperm and the production all female broods. SR is associated with a low frequency inversion spanning most of the X chromosome that causes reduced organismal fitness. While there has been work considering female avoidance of meiotic drive males, the mating decisions of drive-bearing males have not been considered previously. As drive males are of lower genetic quality they may be less able to bear the cost of choice or may experience weaker selection for its maintenance if they are avoided by females. We investigated preference of drive males using binary choice trials. We confirmed that males prefer to mate with large females (indicative of greater fecundity) but found no evidence that the strength of male mate preference differs between drive and standard males. This suggests that the cost of choice does not restrict male reference among drive males. In a further experiment, we found that large eyespan males showed strong preference whereas small eyespan males showed no preference. This is likely to weaken mate preference in drive males, as on average they have reduced eyespan compared to standard males. In this respect, drive males are subject to and exert weak sexual selection. Lay summary We studied male mate preference in stalk-eyed flies. This species suffers from meiotic drive, a selfish genetic element that causes a reduction in sperm production and organismal fitness. We predicted that males with meiotic drive would show weak mate preference. Males preferred to mate with large females, but there was no difference in the strength of preference between drive and non-drive males. Males with larger eyespan showed stronger mate preference. Meiotic drive males usually have reduced eyespan so on average they exert weaker sexual selection on females, but this is mediated by eyespan, not genotype per se .