HOW DOES FEMALE-SPECIFIC SELECTION AFFECT MALE FERTILITY?

October 2021 - Present
Supervisors: Dr Nicola Hemmings, Dr Alison Wright and Dr Barbara Tschirren.

The sexes are defined by divergent reproductive strategies, and selection often acts in a sex-specific manner. However, because males and females share an autosomal genome, selection acting on one sex is likely to have fitness consequences on the opposite sex. The aim of my PhD is to examine how female-specific selection influences male fertility traits, including sperm function and testis structure, to better understand the co-evolution of male and female reproductive traits. I will investigate this question in two ideally suited avian study systems. Firstly, I will use lines of Japanese quail (Coturnix japonica) that have been artificially selected for divergent female investment in reproduction (large and small egg size). A positive genetic correlation between female reproductive investment and male reproductive success has previously been demonstrated in this study system, but the underlying mechanisms driving this correlation are not yet known. Secondly, I will use a range of domestic chicken (Gallus gallus domesticus) breeds. Domestic chickens have been selected for female fecundity for over 100 generations, leading to specialised egg-laying breeds. However, other chicken breeds have been selected for growth traits, or cockfighting/show traits which are expected to be under relaxed selection for female fecundity. Together, these genetically differentiated chicken breeds can be leveraged as a long-term artificial selection experiment. In both systems, female reproductive investment will be measured as egg and oviduct size relative to body size; and sperm function (morphology, density, velocity, motility and viability) as well as testis structure (mass, asymmetry and proportion of spermatogenic tissue) will be measured in males. Differences in ejaculate and testis traits will be identified across lines/breeds where female reproductive investment is increased or relaxed. This work will have direct applications to commercial animal breeding, as well as broader implications for our understanding of the causes of variation in male reproductive success.

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This work is funded by the NERC ACCE Doctoral Training Partnership.