The Bolund Lab

 Our main focus is the evolution of sexual dimorphism in life histories. Striking differences between females and males are wide-spread across taxa and occur in all mating systems, but we still know little about the evolutionary processes that lead to such sexual dimorphism. We use three study systems to approach this from different angels, using observational studies on historical human populations and experimental evolution studies on the nematode worm C. remanei and the seed beetle C. maculatus. We are part of the well-equipped Nematode Lab at the Animal Ecology Unit, led by two collaborating PIs (Dr. Bolund and Dr. Lind) and collaborating with Dr. Maklakov in the UK. We also collaborate locally with two groups that work on the seed beetles (Dr. Berger and Dr. Immonen). We are all interested in experimental evolutionary biology and working in areas such as life history evolution, sexual selection and sexual conflict, transgenerational inheritance and ageing.

​

 

The theory

 

The genetics of sexual conflict, what is G and B?

Males and females often have different phenotypic optima for important life history traits, but because they share much of their genome this can lead to a conflict over trait expression.  Sexual conflict can be present in all mating systems except under obligate random monogamy with no re-mating, because then the interests of the sexes completely coincide. As the possibilities for re-mating and/or simultaneous multiple mating increases, so does the potential for conflict because the optimal life history strategies will diverge between the sexes. Different selection pressures in the two sexes leads to a decoupling of the genetic basis of the trait and the evolution of sexual dimorphism which resolves the conflict. However, a focus on single traits ignores the fact that traits are seldom independent and evolutionary trajectories are affected by covariances between different traits.

 

We apply a multivariate perspective that accounts for the sex-specific structure of additive genetic variances and covariances between traits (the G matrix) by partitioning G into inheritance within females (GF), within males (GM) and between the sexes (B and its transpose BT). The evolution of sexual dimorphism is facilitated when GF and GM become different from each other. Further, the B matrix can reorient the response to selection away from the direction of selection differently in the two sexes. The stability of G and B over evolutionary time remains an open question. A better understanding of GF, GM and B and their stability over time will impact how we view long-term constraints on the independent evolution of the sexes and how different populations are expected to evolve under sex-specific selection.

 

​

​The study systems

 

Sexually dimorphic life histories in nematodes

​

​

​

​

​

​

​

​

​

​

​

​

​

 

C. elegans is a model species in experimental evolution studies, including studies of ageing and the evolution of the two sexes, but since it is primarily hermaphroditic it is less suitable to study sexual conflict. Hence, C. remanei has appeared as a promising system for the study of sexual conflict because it reproduces strictly by outcrossing (gonochoristic reproduction). Experimental evolution allows us to evolve genetically heterogeneous populations under conditions that favour or disfavour sexual conflict. This can allow the dissociation of genetic relationships between different life history traits within and between the two sexes. We combine this with quantitative genetic breeding designs which allows us to study the stability over evolutionary time of additive genetic variances and covariances, both within individuals as well as between the sexes, and the interaction between genes and their environments.

​

​

Sexually dimorphic life histories in seed beetles

​

​

​

​

​

​

​

​

​

​

​

​

​

We are using  populations of the seed beetle, C maculatus, that have gone through experimental evolution for over 30 generations under different imposed mating systems (ancestral polygyny, enforced monogamy, and male-limited selection) to study how the G and B matrices of key life history traits have responded to the novel selection pressures in these treatments. This work is in collaboration with Dr. David Berger.

​

 

Sexually dimorphic life histories in humans

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

 

 

 

 

 

 

 

It remains largely unknown whether heritabilities and genetic correlations with fitness are different between the two sexes in humans. In a pre-industrial Finnish population, I found that phenotypic selection gradients on key life history traits differed in the two sexes, but genetic correlations between the sexes constrained the evolution of further sexual dimorphism to resolve the conflict. Pre-industrial Finland represents a highly monogamous population with no divorce, while a more polygynous mating system leads to more intense sexual selection and greater scope for conflict between the sexes. Humans are unusual in that the mating system is highly flexible between populations ranging from strictly monogamous, to polygynous, polyandrous and polygynandrous, and there is large inter-population variation in the ratio of male to female variance in reproductive success. Thus humans offer the opportunity to compare levels of sexual conflict across different mating systems within the same species. 

 

Currently, I am studying a human population with higher levels of re-marriage than the Finnish population and periods with allowed polygyny (using the Utah Population Database) to explore the effects of the mating system on sexual conflict over reproduction and lifespan. This work is in collaboration with Dr. Virpi Lummaa in Sheffield, Prof. Ken R. Smith at the University of Utah and Dr. Alexei Maklakov at the University of East Anglia. The central focus of human behavioural ecology has recently begun to shift from asking how the behaviour of modern humans reflects the history of our species, to looking at natural selection and finally to measuring current selection in contemporary populations. By studying humans from an evolutionary perspective, we hope to contribute to the growing understanding of humans as a species among other species by exploring the possibilities and limitations of an evolutionary approach to human behaviour, life-history evolution and the interplay between the sexes.

​

 

 

 

 

 

 

 

 

 

 

​