When two males battle for the affections of a female, the rivalry actually serves to improve the quality of sperm cells — at least in animals.
However, while the presence of sexual rivalry improves sperm quality, it is also shown to have a negative effect on the DNA.
Competition Boosts Zebrafish Sperm, But Damages DNA
In a study published in the Journal of Evolutionary Biology, researchers from the University of Alicante and the University of Upsala reveal that spermatozoa exposed to competition become dramatically faster and more competitive.
The team analyzed the effects of competition among male zebrafish by keeping competition high in one group with two males and one female, while another group saw less competition with one male and two males.
Findings reveal that the group exposed to high competition develop enhanced spermatozoa.
Unfortunately, one of the other effects noted by the team is distinct damage to the DNA.
In a press release in Phys Org, lead author Paula Sáez explains that one possible reason for this is because males with highly competitive environments experience higher stress levels, which goes on to trigger greater production of reactive oxygen species. In turn, this causes the damage seen in the DNA chains, which affects fertilization success as well as offspring survival.
"Overall, males facing the presence of rival males may produce faster swimming and more competitive sperm but this may come at a cost for the next generation," the researchers wrote on the paper.
Role Of Sperm Variation In Shape, Size
According to study co-author Alejandro Romero, a researcher at the UA Department of Biotechnology, different species have spermatozoa of different shapes and sizes. It's still unclear if these factors affect cell design and sperm rivalry.
By applying geometric morphometry, which is a technique combining biology and geometry, the research team found that the presence of a rival male is linked to the production of spermatozoa with a phenotype of smaller heads and longer intermediate pieces and flagella.
Analyzing animal biology is a step toward understanding the mechanisms of human biology and development. Zebrafish is a particularly ideal animal to study due to the marine animal's high level of fertility, genetic similarity to humans, and their external fertilization process that create transparent embryos.
By focusing on analyzing the effects of competition on zebrafish males, the study researchers are able to provide scientists with new information on the potential effects of sexual competence on sperm quality.