Sexual Selection in Caring Parents: A Male and Female Perspective

Post-mating parental care is common across taxa, yet the degree to which each parent is involved in care varies widely. Original theory suggests that care should be female-biased due to females' greater initial investment in offspring through eggs and zygotes and males' ability to maximise their fitness by investing in seeking additional mates over providing care. Empirical support for this idea appears strong in mammals where female-only care is the most common care strategy, but in other taxonomic groups this is not the case. In birds, more than 90% of species exhibit biparental care, and in fish, male-only care is prevalent. Subsequent theory has shown that other factors could have a greater influence on parental strategy. Sex ratios influence the availability of sexual partners thereby affecting the costs and benefits of care versus mate searching. Additionally, multiple mating by females leads to decreases in male paternity assurance decreasing the benefits of care to males. A greater understanding of the trade-offs involved in parental care strategies and the role of sexual selection has far-reaching benefits for the study of sex differences in morphology, ecology and life history but, despite extensive theoretical and empirical work, the processes involved in creating the observed diversity of parental strategies remain unclear.
During this PhD project, I will use experimental and comparative methods to investigate two understudied areas of parental investment: a) sexual selection for paternal care in fish b) selection for quality signalling in breeding females.
a) Male care in fish:
Experimental work into the factors that drive paternal care in fish has increased in the last few decades yet conclusions about why this strategy is so common across species in this group are lacking. I will use meta-analysis across fish species to explore how sexual selection, particularly female-choice for care, may have helped to drive this unusual pattern.
b) Female care and quality signalling:
Females, like males, are likely to be selected to advertise their reproductive quality through signalling, yet females also invest more heavily in reproduction than males and so face a greater trade-off between these two investments. Using experimental work in the laboratory on the African cichlid species Lamprologus ocellatus, I will investigate this trade-off during intra-sexual competition for breeding resources.
In addition, I will undertake a comparative analysis in birds, collecting data on plumage coloration combined with life-history data to understand how females may use signals of continuing fecundity to attract helpers in cooperatively breeding species and how this may influence investment in care.