Centre for Evolutionary Biology

Publications

I use several social insects to study some extreme examples of reproductive adaptation and sexual conflict. Mating systems of social insects have a number of unique characteristics: First, because males are haploid, ejaculates consist of clonal sperm, which eliminates intra-ejaculate sperm competition and may have promoted unsual cooperation between sperm cells through kin selection. Second, partners commit for life on a single mating flight and stored sperm may survive and remain viable for decades (the life span of some ant queens), requiring unusual adaptations to ensure lasting sperm quality. Third, where males or ejaculates in normal promiscuous animals compete for fertilizations, this may be different in social insects. In those species where queens mate with multiple males, unrelated sperm survive together in the sperm storage organ for many years. This may have limited the expression of hostile chemical interactions between ejaculates, but may also have produced unique adaptations to enhance fertilization fitness relative to sperm of other males. Finally, extended sperm storage must have produced very special adaptations in queens to maintain sperm viability and to use sperm as economically as possible.

I study social insect reproduction using several interconnected approaches:

	I use Proteomics and Metabolomics to analyse sperm and gland secretions, both within the sperm storage organ (spermatheca) and in the male accessory glands (the glands that produce mating plugs in various species). A first analysis showed that the size of the honeybee sperm proteome is relatively small. We detected several proteins within the seminal fluid that are normally produced in response to viral and bacterial infections as well as several chemosensory proteins, that function as pheromone carriers and are known to elicit behavioral responses in honeybees. Experimental studies currently test the biological relevance of these proteins in vivo. I hope that proteomics will also allow me to identify proteins that are instrumental for prolonged sperm storage.
	I try to unravel the sophisticated interactions between the ejaculate(s) and the receiving female, to provide a mechanistic explanation for our recent quantification of the cost of sperm storage in ant and bumblebee queens. I am investigating interactions between stored ejaculate(s) and the female immune system. I am quantifying the capacity of sperm and spermathecal fluid to defend microbial infections, and investigate the potential consequences of ejaculate driven immunity for female physiology.
	Is there sexual selection via sperm competition and/or cryptic female choice in social insects? Sperm competition, which is the competition between ejaculates from two or more different males over a set of eggs, is widespread in insects and vertebrates. Cryptic female choice is a female mediated process affecting male reproductive success after successful copulation and insemination. Female discrimination between ejaculates is cryptic in the sense that it is a hidden process, taking place inside her body after her more obvious decision to copulate. In social insects, we currently do not know whether sperm competition or cryptic female choice really occurs. Part of my work is therefore testing for the possible presence of sperm competition or cryptic female choice in honeybees and leaf cutting ants.

External affiliations

ARC Centre of Excellence in Plant Energy Biology

Centre of Excellence for Social Evolution

Smithsonian Tropical Research Institute (STRI)

Main collaborators

Koos Boomsma, Harvey Millar, Holger Eubel, Sophie Armitage, Susanne den Boer

Honeybee queen

Funding

Discovery grant (2008-2010): What defines sperm success? The influence of sperm on storage and paternity success in the honeybee Apis mellifera (Australian Research Council).

Large infrastructure grant (2008): MALDI imaging and protein analysis facility for Western Australia (Australian Research Council).

Large infrastructure grant (2008): A cryopreparation facility for Western Australia (Australian Research Council).

Queen Elisabeth II fellowship (2007-2011) “Sex, sperm and society”, offered by the Australian Research Council.

External collaborator of the “Centre of Excellence for Social Evolution” at the University of Copenhagen (2005-2010), funded by the Danish National Research Foundation.

Stipend for advanced scientists (2005-2006) “Sexual selection in social insects”, offered by the Swiss National Science Foundation.

Marie Curie Outgoing Individual Fellowship “Social Insect Sperm”, offered by the European Community (declined).

Marie Curie Individual Fellowship (2001-2002) offered by the Swiss National Science Foundation (IHP replacement).

Boris Baer