Gorillas’ Small Genitalia May Hold Clues to Human Infertility
While silverback gorillas are renowned for their imposing physique, their genitalia are remarkably modest. Scientists have now uncovered a potential genetic link between these apes’ diminutive reproductive organs and infertility issues in human males.
Adult male gorillas possess the smallest penises among all apes, averaging just 1.1 inches (3 centimeters) in length. This diminutive size is accompanied by other reproductive disadvantages, such as low sperm count and poor sperm motility. These characteristics, which are also associated with male infertility in humans, have perplexed researchers given their prevalence among all male gorillas.
The explanation, according to Kevin Bowman, lead author of a recent study and a postdoctoral researcher at the University at Buffalo, lies in gorillas’独特的mating system. Gorillas live in polygynous groups, where a dominant male has near-exclusive access to females. The silverback’s formidable physique ensures its dominance, eliminating the need for sperm competition. Consequently, its sperm does not require exceptional motility or quantity to achieve reproductive success.
This lack of competition is hypothesized to have driven the evolution of gorillas’ small genitalia. To investigate this theory, Bowman and his colleagues searched for genetic variations associated with spermatogenesis (sperm production) in gorillas. They reasoned that if they could identify suspect genes in gorillas, they could subsequently examine their counterparts in the human genome.
Approximately 15% of couples in the United States face difficulties conceiving, with male infertility accounting for over half of those cases. Despite this prevalence, the genetic basis of male infertility remains poorly understood.
Bowman and his team analyzed a database of over 13,000 genes across 261 mammal species. Their focus was on identifying genes in the gorilla lineage that had undergone relaxed purifying selection. This evolutionary process allows harmful mutations to accumulate in a species when there is no significant pressure to eliminate them. In the case of gorillas, this relaxed selection may have contributed to their low-quality sperm.
The researchers identified 578 genes in the gorilla lineage that exhibited this type of selection. Many of these genes were found to play a role in sperm production. To gain a deeper understanding of their function, the team utilized fruit flies, a commonly employed genetic model organism. They systematically silenced each of these genes in male flies to assess their impact on reproductive capacity.
Through this approach, they discovered 41 novel genes previously unknown to be involved in male fertility. The researchers then extended their investigation to humans, examining a genetic database of 2,100 infertile men and comparing their genetic profiles to fertile men. They identified 109 genes from the gorilla study where infertile men carried more loss-of-function mutations, which disrupt a gene’s ability to produce its encoded protein.
While these findings suggest a potential genetic link between these genes and human male infertility, further research is necessary to elucidate their precise roles and interactions within the complex interplay of factors that influence human fertility. Nevertheless, the study opens up new avenues for exploring the genetic underpinnings of infertility and potentially developing novel therapeutic approaches.
The study was published in the journal *Molecular Biology and Evolution* on May 9, 2023.
