A study published in the open-access journal PLOS Biology today, by Mareike Koppik and colleagues from Uppsala University in Sweden, suggests that male beetles encounter a dilemma where they must choose between competing with other males for opportunities to mate and repairing damage to their sperm DNA.

When it comes to mutations in sperm and egg DNA, they can hinder the survival and fitness of the offspring. Therefore, animals utilize multiple maintenance and repair mechanisms in their reproductive cells to counteract this.

Nonetheless, previous research has demonstrated that in several species, sperm DNA possesses more mutations than egg DNA, implying that there might be a conflict between competing for female access and expending energy on repairing damaged DNA.

In order to examine this theory, the researchers conducted an investigation utilizing laboratory colonies of seed beetles (Callosobruchus maculatus) that had undergone 50 generations of experimental evolution.

They analyzed male beetles from two different lineages – one that had been manipulated to be monogamous, thus reducing sexual selection (“N males”), and the other that had undergone extensive sexual selection but minimal natural selection (“S males”).

The study found that during sperm competition experiments, S males sired a greater number of offspring than N males. However, after being exposed to radiation that caused DNA damage, S males produced lower quality offspring in comparison to N males and control males.

The team utilized RNA sequencing to identify 18 genes that altered their activity in the reproductive tracts of males when exposed to radiation.

Some of these genes are believed to contribute to cellular maintenance and DNA repair. The gene expression profile of males after exposure to radiation was associated with their offspring’s survival and fertility.

The authors suggest that males from lineages that experienced significant sexual selection invest more in competing with other males, which hinders the DNA repair process. This implies that sexual selection can prompt the evolution of greater adaptability in male reproductive traits.

“In these beetles, as in many other species with internal fertilization, intense male competition for mating success,” adds co-author David Berger, “continues among the sperm of rival males inside the female after the mating itself is done.”

This new “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.”

Source: 10.1371/journal.pbio.3002049

Image Credit: Mareike Koppik (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)