We get excited about lots of things! What occupies most of our time, however, is trying to understand the enormous diversity of adaptations that help males succeed at siring offspring, especially those that influence fertilization success. While much of our research has focused on passerine birds, we are interested in working in a variety of taxa in order to try and understand broad scale evolutionary patterns and processes. This page describes the three main research themes we are currently working on. For information on past projects, please visit the publications page.
Sperm-microbe interactions and the evolution of ejaculates
Organisms are constantly exposed to pathogens, and the ability of individuals to combat microbial attack is an important component of fitness. Sperm cells are not immune to microbial exposure; sperm encounter bacteria in the testes and ejaculate, during mating, and in the female reproductive tract. Bacteria can cause reductions in sperm quality and compromise male fertility. Moreover, ejaculate-borne bacteria can be transferred during mating (i.e. sexually transmitted infections; STIs), with potentially negative consequences for females. Our research investigates the consequences of ejaculate-borne bacteria for male sperm quality and reproductive success and examines the role of bacteria in the evolution of ejaculates.
In birds, the existence of STIs is suggested to have significant implications for the evolution of reproductive biology, mating behaviour, and male ornamentation. Moreover, birds appear to be especially predisposed to ejaculate-borne pathogens because the avian cloaca functions in both gamete transfer and excretion; consequently gut bacteria may become incorporated into ejaculates and bacterial loads are thought to be relatively. We use passerine birds to investigate the impact of bacteria on sperm function and male paternity success, the function and evolution of antimicrobial substances in ejaculates and the relationship between ejaculate immune function and general immunocompetence, and the role of ejaculate-borne bacteria in the evolution of male secondary sexual traits.
Funding for this work is provided by:
The Research Council of Norway (project# 230434) and the British Ornithological Union.
Post-copulatory sexual selection and the evolution of sperm
Evolutionary biology endeavors to understand trait diversification. Sperm cells are the most diverse cell type known, exhibiting remarkable levels of morphological variation among species, among populations of the same species, among males within a population, as well as both among and within ejaculates from a single individual. A recurrent theme in our previous and current research is to understand why sperm cells are so morphologically diverse. More generally, our research asks (1) What are the evolutionary consequences of sperm competition for male reproductive biology and sperm phenotype? and (2) What is the adaptive and functional significance of sperm phenotypic variation?
The basic function of sperm is universal – to find and fertilize ova. Given this, the observed variation in sperm form and function across the animal kingdom is intriguing. We investigate how post-copulatory sexual selection influences the evolution of sperm morphology and performance, how sperm form relates to sperm function within and across species, and how male investment into ejaculate traits might influence investment into traits that influence pre-copulatory mating success. More recently, we have begun exploring the molecular basis of sperm form and function in passerine birds using proteomics.
Sex, sperm, and speciation
What stops newly formed species from interbreeding? Answering this question is fundamental to our understanding of speciation and lies at the heart of evolutionary biology. The origin of species is only slightly less mysterious now than it was when Darwin referred to the species problem (i.e. how do new species form?) as the ‘mystery of mysteries’. Most notably, the study of speciation has largely ignored barriers acting between copulation and formation of the zygote (i.e. post-mating, pre-zygotic barriers; PMPZ), likely due to the complex and cryptic nature of sexual reproduction. Research in the lab integrates organismal and molecular approaches to determine the role of post-copulatory traits and ejaculate-female interactions in PMPZ barriers.
Birds have long been at the centre of research on sexual selection and speciation. With collaborators in Australia (Simon Griffith) and Norway (Glenn-Peter Sætre), we are investigating barriers to reproduction in two passerine systems: (1) the Long-tailed finch, and (2) the Passer sparrow system, including the house, Spanish, and Italian sparrow. We are investigating the phenotypic and molecular basis of PMPZ barriers, testing for reproductive character displacement in sperm traits at the morphological (i.e. size) and molecular (i.e. proteome) levels, and exploring the consequences of hybridization for male and female gamete (i.e. sperm and ovum) form and function.
Funding for this work is provided by:
The Nansenfondet (Fridtjof Nansen Foundation) and the Australian Research Council.