CONFLICTS · The post-copulatory interplay between females and ejaculates in social insects

The post-copulatory interplay between females and ejaculates in social insects.

The hymenopteran eusocial insects (ants, bees, wasps) not only have impressive colony lives, but also spectacular adaptations for the years-long storage of live sperm. Where human medicine requires cryotechnology to ensure prolonged sperm storage, the queens of honeybees and ants produce glandular secretions to maintain sperm at ambient temperatures inside a specialized storage organ (spermatheca) until it is used for the fertilization of eggs often months or years after the mating event. The sperm storage process is the result of interactions between males (competing for the fertilization of a queen’s eggs – sperm competition) and between male and queen (potentially influencing which sperm inseminates the eggs – cryptic female choice), and interests between these parties might not always be aligned. After it was shown that male ejaculates can kill sperm of other males, research has suggested that female secretions can influence the outcome of this process and thereby possibly influence paternity of offspring. This project investigated the dynamics behind ejaculate – female interactions on a molecular level, using honeybees and leafcutter ants as model species. To do so, sexual selection theory explaining the evolution of such adaptations was combined with biochemical technologies for the first time in social insects. The first aim of this project was to analyze the secretions produced by the female reproductive tract. An artificial insemination technique was successfully adapted for leafcutter ants, to allow the collection of female secretions, and work was undertaken to identify proteins contained within these secretions. Close to 500 proteins were identified and roughly two thirds of these were only found in female secretions when comparing to male reproductive fluids. This group of proteins thus likely contains proteins important for the long term sperm survival in the female. Secondly, the effect of female secretions on sperm function and ejaculate-ejaculate interaction was studied. In honeybees, fluids from both the lateral oviduct and spermatheca were shown to have a positive effect on sperm survival. In leafcutter ants, fluid from the spermatheca could furthermore be shown to stop sperm death caused by competing ejaculates. It was shown that the queen’s proteins are responsible for this effect. These results suggest that the female (the secretions produced by her reproductive tract) will influence sperm fate after sperm has been transferred to her after mating, at which the males’ impact dwindles. The last aim was to examine the molecular mechanism responsible for these effects. An analysis comparing the proteome of seminal fluid before and after exposure to female secretions has just revealed that a number of proteins in seminal fluid is down regulated after contact with spermathecal fluid. These proteins have been identified as proteases and protease inhibitors, and they thus likely represent the key players involved in sperm competition on a molecular level. In addition, some female proteins were found to be up regulated after contact with the male ejaculate, suggesting their role in sperm maintenance when in storage, and in cryptic female choice. In summary, this study has provided a first list of candidate proteins that can influence sperm survival. This has shed light on factors affecting male and female fertility in these economically important species and thus brings us a step closer to unraveling how long-term sperm storage is accomplished. In addition, this project has provided first evidence for a molecular mechanism behind sperm competition in social insects and the molecular mechanism behind cryptic female choice in any animal. Both cryptic female choice and sperm competition are central concepts in sexual selection theory and evolutionary biology. These results will therefore advance the field of sexual selection theory, and show that social insects are ideal model systems to study these evolutionary questions.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз