The metabolic costs of meiotic drive
Selfish genetic elements, such as meiotic drive genes, disrupt Mendels law of equal segregation by biasing their own transmission, often at a detriment to the rest of the genome. The Malaysian stalk-eyed fly (Teleopsis dalmanni) sex-ratio (SR) meiotic drive system is located within a series of large inversions on the X chromosome subject to low recombination and is associated with deleterious effects on fitness. Here we examine the metabolic effects of meiotic drive across male and female stalk-eyed flies. High-resolution O2k respirometry coupled with whole-organism respirometry were used to obtain mitochondrial function and metabolic rates. Complimentary assays on food consumption established downstream effects of metabolism on nutrient acquisition. The experiments demonstrate that individuals with SR meiotic drive elements have impaired mitochondrial function and reduced capacity for ATP synthesis, as shown by a lower respiratory control ratio and weaker contribution of Complex I to respiration. Drive individuals also exhibited an increased basal metabolic rate and consumed a greater amount of food than wild-type individuals. These findings show that the drive genotype imposes metabolic costs in both male and female hosts. The disruption in mitochondrial function likely leads to compensation via an increase in both basal metabolic rate and nutrient acquisition. A potential cause lies in the accumulation of deleterious mutations in the inversions on the X chromosome that house the meiotic drive, which are subject to weak natural selection. In females, the drive chromosome has a dominant effect, with a single copy causing substantial metabolic compromise. There was little evidence of male-specific metabolic costs, nor evidence of an accumulation of sexually antagonistic effects of drive chromosomes on female metabolism. These results suggest that direct metabolic costs from meiotic drive on spermatogenesis and from sexually antagonistic selection are relatively weak. This research provides new insight into the interplay between meiotic drive and metabolism, drawing attention to the broader physiological repercussions selfish genetic elements may have on their hosts.