When the mere presence of reproductive females activates sperm production

Reproduction is a fundamental process in the animal kingdom, however, for it to occur, coordination is necessary between social behavior, that is, in the search for a partner, courtship and mating, and physiological behavior, such as the mobilization of energy or change of diet, added to the production of gametes.

The symbiosis between social signals and gametogenesis in females has been widely studied to date. However, its existence in males remained largely unknown.

In a new study, the presence of reproductive females of the fruit fly (Drosophila melanogaster) has been found to trigger sperm production in nearby males of that species. In such males, cells in their reproductive organs are activated to increase sperm production after sensing the presence of females through pheromones that they emit.

The study was led by the Andalusian Centre for Developmental Biology (CABD), a joint centre of the Spanish National Research Council (CSIC), the Pablo de Olavide University (UPO) and the Andalusian Regional Government (JA).

The study has analysed for the first time how the social context affects the correct functioning of the testicle. This research shows in the species Drosophila melanogaster, known as the fruit fly, how sperm production only increases when potential reproductive partners are detected, which represents a step forward in the study of possible similar mechanisms that could affect reproductive health in humans.

In this project, led by Salvador Herrera, a Ramón y Cajal researcher at the CABD, the male of the fly Drosophila melanogaster was used as a model. To obtain concrete results, a protocol was tested where individual males were selected and kept in a virgin state and isolated from any female to subsequently study the effects of living with three females that had not previously mated.

The work shows that the presence of the female, a possible reproductive partner, is detected by the male due to sexual pheromones that they secrete, which induce an activation of the stem cells of the testicle that leads to increased sperm production. In addition, it has been possible to describe the interorgan signaling that triggers the testicular response: the brain produces and releases more octopamine (a molecule derived from the metabolism of amino acids), the homologue of adrenaline in insects, and the muscles generate a stress signal, the TNF-alpha factor.

Although the fly is an organism distant from humans, by describing for the first time how social context affects fertility in males, new possibilities are opened to study whether similar mechanisms affect human reproductive health and can improve it. This could be a great step forward in better understanding the causes and factors involved in the progressive and accelerated decline in male fertility observed throughout the world, since, according to studies, sperm counts have decreased by more than 50% in the last 50 years.

Artist’s impression of a sperm cell. (Illustration: Amazings / NCYT)

“This study is the first to describe how the social context affects testicular function, causing sperm production to increase only when potential reproductive partners are detected. This mechanism allows for optimizing the energy expenditure required to produce sperm. It is also an example of how the social context or situations of isolation affect our physiology,” notes Javier Martín-Díaz, a researcher at the CABD and co-author of the study.

The study is titled “A stem cell activation state coupling spermatogenesis with social interactions in Drosophila males.” It has been published in the academic journal Cell Reports. (Source: CSIC)