Ever heard of a non-human example of a “Transsexual”? The Australian giant male cuttlefish, Sepia apama, entices many with its superb mimicry skills to disguise as a female cuttlefish in order to increase its chance in mating with the female cuttlefish.
But why? The ratio of male to female cuttlefishes is four to one, females reject almost 70% of mating attempts, this creates fierce competition among the males. Thus, smaller size males have very slim chances to mate with females when compared to the bigger and more dominant-like male (Hanlon et al., 2005).
How? The Alternate mating strategy- “Visual deception is achieved when small males suddenly hide their sexually dimorphic fourth arms, acquire the mottled skin patterning typical of females, and shape their arms to mimic the posture of egg-laying females, who are not receptive to mating” (Hanlon et al., 2005). As many large males will be busy combating other large males and would not take these “transvestite” cuttlefish as a threat, these smaller males then take the chance to move near the female and attempt to make with it.
Success rate? Studies have shown that these female mimickers were able to escape the larger males through deception and position near the female in 30 out of 62 attempts, some large males also tried to mate with the mimickers (Hanlon et al., 2005). When mating with females, some mimickers show male displays of banners and moving stripes while some remained as the disguised female. Returning large males, which were involved in conflicts, tried to aggressively separate the mating pair (mimicker and female) or ignore the pair when they spot them. Females therefore may be subsequently fertilized by both the large males and the mimickers (Norman et al., 1999).
Second source which supports the above:
Norman, M.D., Finn, J., & Tregenza. T. (1999). Female Impersonation as an Alternative Reproductive Strategy in Giant Cuttlefish. Biological Sciences, 266 (1426): 1347-1349.
Hanlon, R.T., Naud, M., Shaw, P.W., & Havenhand, J.N. (2005). Transient sexual mimicry leads to fertilization. Nature, 433: 212.
“Cuttlefish wimps ‘dress as girls,'” by unknown. BBC News, 19 Jan 2005. URL: http://news.bbc.co.uk/2/hi/science/nature/4188495.stm (accessed on 6 April 2010).
“Mating trick,” by Sciencentral. Sciencentral YouTube Channel, 11 Feb 2009. URL: http://www.youtube.com/watch?v=OEqsgwyvtqc (accessed on 6 April 2010).