DO ODOCOILEUS VIRGINIANUS MALES PRODUCE Y-CHROMOSOME-BIASED EJACULATES? IMPLICATIONS FOR ADAPTIVE SEX RATIO THEORIES

Abstract

The theory of adaptive sex ratio variation assumes that parents can increase their fitness by investing in the offspring sex that will gain the greatest lifetime reproductive success. Many adaptive sex ratio hypotheses imply or predict a female-mediated physiological mechanism that facilitates parental control. However, the ability of females to control offspring sex ratio could be significantly affected if males provided X- or Y-chromosome-biased ejaculates, as was recently discovered in domestic artiodactyls. To determine whether this occurs in white-tailed deer (Odocoileus virginianus), we examined semen sex ratio of captive deer using DNA fluorescence flow cytometry. We also used microsatellite markers to assign paternity of fawns sired in previous years to determine if temporal patterns existed in fawn sex relative to conception date. The ratio of X- and Y-sperm did not differ from an expected 1:1 among deer or between collection periods. Median conception dates of male and female fawns sired in previous years were similar, and there were no apparent temporal trends in offspring sex. We find no evidence that skewed ejaculates occur in white-tailed deer.