Joanito Liberti:
Molecular and phenotypic adaptation in social insect reproductive fl uids

Date: 15-03-2017    Supervisor: Jacobus J. Boomsma

The fluids produced by animal reproductive tracts are composed of a great variety of molecules whose effects expand well beyond the mere assistance of sperm in their voyage to fertilize eggs. In this PhD thesis I present four studies to analyse such effects in evolutionarily derived lineages of ants and bees where queens always mate with multiple males, either on a single day or, very rarely, on a few consecutive days, but never again after they have started to lay eggs.

The ability of sperm to move in a fluid environment is of key importance directly after insemination, when the ejaculates of multiple males compete for access to the sperm storage organ of a queen. I show that queen reproductive tract secretions of Acromyrmex echinatior leaf-cutting ants activate and enhance sperm motility but without discriminating between the spermatozoa of different males. In a parallel study, I show that upon mixing of ejaculates of different males in vitro, sperm become activated and swim faster when encountering seminal fluid secretions of rival males. This implies that ant sperm has evolved a self–non-self-recognition mechanism to modulate motility to improve the likelihood of storage in situations of sperm competition.

The seminal fluid of ants and bees with multiply mated queens are known to have evolved proteins that are able to kill the sperm of rival males, but the identity of the proteins involved has remained poorly understood. I sequenced the seminal fluid proteomes of four fungus-growing ant species that span the evolutionary transition from single to multiple queen-mating in the fungus-growing ant phylogeny. I then reconstructed the evolutionary histories of these proteins and identified a number of their functions related to energy production, control of oxidative stress, and proteolysis that may be important in the regulation of sperm competition.

Queens of honeybees undergo a series of physiological and behavioural changes after mating but it is not known whether any of these changes are under control of males (drones) whose reproductive interests would be reduced when their queen mate embarks on a second mating flight the next day. I experimentally show that visual perception is rapidly reduced when virgin queens receive male seminal fluid by artificial insemination. This effect is consistent with males having seminal fluid compounds that discourage queens to pursue an additional mating flight even if they would not have stored enough sperm to maximize their reproductive success.