Trojan Genes or Transparent Genomes? Sexual Selection and Potential Impacts of Genetically Modified Animals in Natural Ecosystems

Introgression of genetically engineered modifications (GMs) into natural populations represents a new realm for mutation theory. GMs, like mutations, have direct and pleiotropic impacts that can disrupt evolved adaptive suites. If GM males are more competitive or attractive mates, the “Trojan Gene Hypothesis” predicts potentially drastic impacts. We examined sexual selection in transgenic growth hormone (Tg) mice that are strong Trojan candidates given their exceptional size and extensive pleiotropic deficits. We hypothesized that the sophisticated olfactory abilities of females would recognize dysregulation of Tg males (the Transparent Genome Hypothesis). Females expressed interest in Tg males and their volatile scent, but when allowed nasal contact with urine (critical to mate choice) they preferred normal males. Tg male urine had reduced major urinary proteins (important in social signaling) and contained albumin and transferrin indicative of pathology. Novel Tg males failed to elicit pregnancy block in recently inseminated females (the “Bruce Effect”) whereas normal males were highly effective. Normal males expressed high aggression but Tg males were placid, non-aggressive and were largely ignored by normal males. Female mice also strongly preferred normal males over p53^± knockout males in response to volatiles, contact with urine and male presence. This study suggests that conspecific discrimination of fitness may be more powerful than generally appreciated. This has great implications for introductions of GM animals and sexual selection generally.