Sex role evolution:
testing the impacts of ecology, demography and genes
Sex roles are some of the most diverse social behaviours since courtship, pair-bonding and parenting exhibit an immense variation between and within species. My research group has made a major contribution to sex role research although significant issues remained to be resolved. We are focusing on shorebirds – avian taxa that exhibit an unusually diverse sex role behaviour including conventional sex roles (i.e., males compete for females and the females look after the young) and sex role reversal (i.e., females compete for males and the males look after the young). Recently we showed that a significant – but somehow neglected – aspect of sex role evolution is adult sex ratio (ASR, the proportion of males in the adult population), a demographic property of populations – since the more abundant sex in the population has more mating options than the rarer sex. We also showed that sexual selection instead of being an engine of speciation as commonly thought, it slows down diversification.
In this ÉLVONAL SHOREBIRD SCIENCE project, we propose to synthesize research and fill major knowledge gaps. This is a cross-disciplinary project that uses behavioural ecology, population demography, comparative genomics and theoretical modelling to investigate the causes and implications of sex role variation. By building upon decades of skills, experience and knowledge in various shorebirds, we propose to carry out experimental, demographic and genomic projects to separate the roles of ecological and demographic processes on sex roles. This is an ambitious project that has the potential to go beyond state-of-the-art in sex role research, and it will propose future directions for this research field.
The ÉLVONAL SHOREBIRD SCIENCE project has 5 specific objectives:
to investigate the association between components of sex roles,
test the roles of ecology driving sex role variation,
investigate the demographic causes of ASR and sex role variation,
use genomic tools to explore the causes of differential mortalities, and
develop a new theoretical model to analyse the feedbacks between sex roles, environment and demography.
To address these objectives, we are:
collecting behavioural, environmental and demographic data from shorebirds that breed in Cape Verde, Madagascar and other worldwide locations
carrying out a mate-removal experiment in ecologically diverse habitats of 5 plover population in China,
using demographic data to test whether courtships, pair-bonding and parenting track fluctuations in ASR over time,
using a genome-based method to detect parasites and diseases in male and female plovers at various age cohorts, and
build an evolutionary game-theoretic model to investigate feedbacks between sex roles, environment and demography.
Taken together, the proposed projects will be the most comprehensive cross-disciplinary investigation of sex roles in any taxa.
Understanding the causes and implications of sex roles is important for five major reasons.
First, sexual selection is a major selective force in evolution, and fundamental ideas about sexual selection (and their alternatives) are constantly evaluated – see for instance the ASAB Winter Meeting (December 2017) that has sexual selection its sole focus. Thus sex role research is a central component in evolutionary biology of sexes.
Second, sex role behaviours are directly relevant for reproduction and thus the impact on population (and individual) fitness. Thus by choosing a mate, divorcing a partner or looking after the young can have major fitness implications that have knock-on effects on population growth and population dynamics. Sexual behaviours also have impacts on diseases especially sexually transmitted diseases such as HIV/AIDS with implications for mortality.
Third, the understanding appropriate breeding behaviour is essential for captive breeding and biodiversity conservation programs. By quantifying sex role variations and assessing their reproductive function in wild populations, the project will generate practical information for zoos and wildlife parks, and also, for biodiversity conservation.
Fourth, the genomic data generated by the project will boost data availability for genetical non-model organisms. In addition, the genomic data will contribute to research on ageing and senescence.
Finally, gender studies and gender identity (i.e., the internal perception of one‘s gender, and how they label themselves) is a major issue in contemporary human populations, and the proposed study using evolutionary biological principles will serve as a benchmark for follow-up sociological studies.
Sex roles, (i.e., behavioural roles of males and females in reproduction) excites both scientists and the public, since understanding the evolutionary roots of this behaviour is challenging. For example, why do males court females and compete with other males whereas usually, the females look after the young, although in a small number of species these “conventional” sex roles are completely reserved?
My research group is investigating sex roles for several decades and we made major contributions to this field. For example, recently we showed that the best explanation for the existence of conventional and reversed sex roles in shorebirds (plovers, sandpipers and allies) is adult sex ratio – since members of the rarer sex in the population have more mating opportunities and thus are more selective that the members of the more common sex.
Here we propose to continue this successful research by focusing on specific research topics that have not been resolved. Building upon our previous research, we continue using shorebirds as model organisms, and by a series of field-based experiments, observations, demographic and genomic analyses, reveal why (and how) certain sex roles have evolved and maintained in the population.
Beyond evolutionary biology, this work is important for biodiversity conservation of endangered species since sex role behaviours make major impacts on reproductive success and thus on future population strategies.
– Tamás Székely, November 2018