Poster presentation 12th International Mammalogical Congress

Cryptic male choice: Experimental evidence of sperm sex ratio and seminal fluid adjustment in relation to coital rate (#738)

Amy M Edwards 1 , Elissa Z Cameron 2
  1. La Trobe University, Bundoora, Victoria, Australia
  2. School of Biological Sciences, University of Canterbury, Christchurch, New Zealand

The differential allocation hypothesis suggests that a mother should adjust the sex of her offspring in relation to her mate’s attractiveness, thereby increasing future reproductive fitness when her sons inherit the attractive traits. More attractive males have been shown to sire more sons, but it is possible that the sex ratio skew could be a result of paternal rather than maternal manipulation, which would be a more parsimonious explanation. Sex allocation research in mammals has focused almost exclusively on mothers under the assumption that the male contribution is genetically determined during meiosis and therefore not under adaptive control. However, we have recently challenged this assumption and shown variation under conditions where you would not expect it. Here we manipulated coital rate (an indicator of attractiveness) in laboratory mice and showed that males that mate more often have higher levels of glucose in their semen despite lower blood glucose levels. Since peri-conceptual glucose levels in utero increase male conceptus survival, this could result in male-biased sex ratios. The males that mated most also had more remaining X-chromosome-bearing-spermatozoa, suggesting depletion of Y-chromosome-bearing-spermatozoa during mating. We hypothesise that males may alter both seminal fluids and X:Y ratios in an ejaculate to influence subsequent sex ratios. Our results further support a paternal role in sex allocation.