A recent study conducted by Mareike Koppik and her colleagues from Uppsala University, Sweden, has shed light on a fascinating trade-off faced by male beetles. Published in the open-access journal PLOS Biology, the research suggests that these beetles must choose between competing with other males for mating opportunities and repairing damage to their sperm DNA.
To understand this trade-off, the researchers worked with laboratory colonies of seed beetles (Callosobruchus maculatus) that had undergone 50 generations of experimental evolution. They compared male beetles from two lineages: one that was manipulated to be monogamous, minimizing sexual selection (“N males”), and another that experienced intense sexual selection but minimal natural selection (“S males”).
The results showed that S males, who faced greater competition for mates, fathered more offspring than N males in sperm competition experiments. However, when exposed to DNA-damaging radiation, S males produced lower-quality offspring compared to N males and control males. The researchers also conducted RNA sequencing and identified 18 genes that exhibited changes in activity in the reproductive tracts of males in response to radiation. Some of these genes are known to be involved in cellular maintenance and DNA repair. Interestingly, a male’s gene expression profile after radiation exposure was correlated with the survival and fertility of his offspring.
Based on these findings, the authors concluded that males from lineages exposed to intense sexual selection prioritize competition with other males over repairing DNA damage. This suggests that sexual selection can drive the evolution of greater flexibility in male reproductive traits.
Overall, this study provides valuable insights into the delicate balance male beetles must strike between reproductive competition and DNA repair, highlighting the evolutionary implications of sexual selection.
Co-author David Berger emphasizes that intense competition among rival males persists even after mating has occurred in these beetles, as is the case in many other species with internal fertilization. He further explains that their study reveals a crucial insight: males who invest excessive effort in this post-mating competition, triumphing in the race to fertilize female eggs, appear to prioritize quantity over quality when it comes to their sperm. Regrettably, this strategy comes at a cost, as it impacts the well-being of their future offspring.
Source: Public Library of Science