Abstract
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.
Highlights
As reported previously (Cotton et al, 2010; Wilkinson et al, 1998), eyespan was reduced in SR males and this effect persisted after controlling for body size (Figure 1)
The difference in eyespan between males carrying the XSR and XST chromosomes was not condition-dependent; there was no evidence for amplified reduction in the sexual ornament of SR males under high environmental stress
The environmental stress used in this study follows previous work on stalk-eyed flies using larval food reductions (Cotton et al, 2004b), which has a similar effect to other stresses, such as thermal shock and desiccation (Bjorksten et al, 2001)
Summary
A standard (ST) stock was obtained from Ulu Gombak in Malaysia (3°190N 101°450E) in 2005 by Andrew Pomiankowski and Sam Cotton. Four eggs from Cross A were mixed with eight eggs from Cross B, generating all genotypes (XSTXST, XSRXST, XSRXSR females and XSTY, XSRY males) in a 1:2:1:1:1 ratio on average This design was used previously for measuring egg-to-adult survival (Finnegan et al, 2019). In Cross B, absolute female eyespan did not differ between heterozygotes and XST homozygotes under high (mean ± SE, XSTXST = 4.0866 ± 0.0415, XSRXST = 4.1947 ± 0.0489, F1,266 = 2.9528, p = .0883) or low stress (mean ± SE, XSTXST = 5.6153 ± 0.0415, XSRXST = 5.5876 ± 0.0398, F1,208 = 1.1933, p = .2759), nor was there a food treatment by genotype interaction (F1,475 = 2.8579, p = .0916). The results from the second experiment are in broad agreement with those from the first experiment
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