According to a recent study led by Uppsala University in Sweden, male beetles face a trade-off between competing with other males for mating opportunities and investing in repairing damage to their sperm DNA.
Since mutations in sperm and egg DNA often reduce the fitness and survival of offspring, many species of animals use a diversity of repair and maintenance mechanisms to increase the health of their reproductive cells. Previous studies have shown that sperm DNA has more mutations than egg DNA, a finding suggesting that some species of animals may face a trade-off between sexual competition and investing energy in repairing damaged sperm DNA.
To test this hypothesis, the experts used laboratory colonies of seed beetles (Callosobruchus maculatus) that underwent 50 generations of experimental evolution, and compared male beetles from lineages which were genetically manipulated to be monogamous at the expense of sexual selection (“N males”) with males from lineages that experienced intense sexual selection but very little natural selection (“S males”).
The analysis revealed that, while S males fathered more offspring than N males in sexual competition experiments, after exposure to DNA-damaging radiation, they produced lower quality offspring than both N males and beetles from a control group.
By using RNA sequencing, the scientists have identified 18 different genes which changed their activity in males’ reproductive tracts during radiation exposure, with some of them playing critical roles in DNA repair and cellular maintenance. Moreover, males’ gene expression profiles after radiation seemed to be significantly associated with their offspring’s survival and fertility rates.
These findings suggest that S males invest more resources in sexual competition with other males, at the expense of repairing DNA damage.
“In these beetles, as in many other species with internal fertilization, intense male competition for mating success continues among the sperm of rival males inside the female after the mating itself is done. Our study shows that males that invest too much into this competition, while winning the race for fertilization of female eggs, seem to care less about maintaining the quality of their sperm, with the cost of this strategy being paid by their future offspring,” concluded co-author David Berger, an expert in Evolutionary Biology at Uppsala.
The study is published in the journal PLoS Biology.
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