Research of Susanne den Boer
I am interested in the mating biology of insects and study post-copulatory sexual selection. Post-copulatory sexual selection acts on traits in males and females that are important during and after mating and that can influence an individual's reproductive success. How can a male make sure that his sperm cells are used for the fertilization of a female's eggs? How can females affect this process? Factors that can be important for the reproductive success of a male are, for example, the quality of his ejaculates and the number of sperm in his ejaculates. This is especially important if females mate with more than one male and the ejaculates of these males have to compete with each other (sperm competition). For a female it could be beneficial if she could influence which male ends up being the father of her offspring, and she might be able to exert choice between ejaculates after mating (cryptic female choice).
I use social insects as model species to study post-copulatory sexual selection, and in particular the leafcutter ant species Acromyrmex echinatior and Atta colombica, and the honeybee Apis mellifera. In all three species the females (queens) mate with multiple males, so that sperm competition and cryptic female choice is expected to occur. These species are furthermore ideal model species, as they can easily be kept in the lab and artificial insemination techniques are available that allow the separation of pre- and post-copulatory sexual selection. In addition, the genome of Apis mellifera is available and that of Atta and Acromyrmex will become available in the coming years, facilitating proteomic analyses of the reproductive fluids of males and queens.
Previous reseach projects
During my PhD and first Post-doc I mainly looked at factors affecting sperm viability in social insects. Social insect queens mate only once at the start of their lives, with one or multiple males depending on the species. During and after mating, ejaculates are transferred to a special storage organ in the queen (spermatheca), and queens will use this sperm supply to internally fertilize eggs and build colonies that can consist of millions of workers. Queens never remate after colony foundation, which means that sperm cells will have to survive in the queen as long as she will live, which can be several decades in some ant species. This imposes a selection pressure on males to produce high quality ejaculates that survive the many years of storage and on queens to provide the optimal environment for sperm to survive in. We found that the seminal fluid that accompanies sperm in an ejaculate is necessary for the survival of a male's sperm in ants and bees and that secretions in the spermatheca of queens are equally effective in keeping sperm alive
As a next step we examined how sperm survival is affected when queens mate with multiple males and the ejaculates of these males overlap. We found that in polyandrous species, the seminal fluid of one male has a negative effect on the sperm survival of other males, while this effect is absent in monandrous species where ejaculates never interact. This provides the first evidence for sperm competition in social insects. In addition, queens seem to be able to control these sperm competition effects. We then examined how, after it is stored, queens use the sperm cells for the fertilization of their eggs. As queens can never remate later in life, their reproductive success is determined by the number of sperm they store and the number of sperm they use to fertilize each egg. We found that Atta queens only use a minimal number of sperm per egg, but that this number increases with queen age, probably due to senescence of the sperm cells or the queen herself
Future reseach projects
For the coming two years I will work as an Outgoing Marie Curie Fellow at the University of Western Australia I will mainly use the honeybee to characterize female contributions towards sperm and to experimentally test for their effects on male ejaculates. My previous research has shown that proteins in the reproductive fluids of males and queens are likely responsible for the effects described above. I will therefore incorporate proteomic analyses in my research; I hope to identify the proteome of the reproductive tract of queens using peptide mass spectrometry, providing an insight into the molecular environment in which sperm is transferred. In a next step I will test for the effects that these female secretions have on ejaculate physiology and function and I hope to be able to identify the networks of proteins responsible for these effects.
Contact informationDo you want to know more about my research or would you like to do a Masters / Honours project with me? Feel free to contact me: E-mail susanne.denboer(at)uwa.edu.au Mobile phone +61 4 1606 8940 Office phone +61 8 6488 4471