SOUTH AFRICA-AUSTRALIA: Young lizard 'transvestites'

Young male Augrabies Flat Lizards in northern South Africa mimic females by delaying the onset of bright colouring, scientists in South Africa and Australia have found. By pretending to be female these 'transvestites' not only avoid being attacked by aggressive older male rivals but are also able to court females that share a territorial male's area.

In an article in Proceedings of The Royal Society, titled "Flat Lizard Female Mimics Use Sexual Deception in Visual but not Chemical Signals", Martin J Whiting of the University of the Witwatersrand in Johannesburg, Jonathan K Webb of the University of Sydney and J Scott Keogh of the Australian National University point out that understanding what "constrains and maintains signal honesty is a central theme in animal communication".

While several studies have examined the mimicry of a single type of signal, they add, "we know of no study that has directly tested whether a single species is capable of producing multiple dishonest signals and how these signals may interact in the context of sexual selection". While female mimicry of visual signals and behaviour has been documented for lizard species, chemical mimicry is largely unknown.

The male Augrabies Flat Lizard, which features in Sir David Attenborough's series Life in Cold Blood, is brightly coloured, territorial and highly aggressive, while females are drab brown with dorsal stripes. Young males (she-males) look like females and hide and delay their colour development even once they are sexually mature because, once colour develops, they are often chased away or attacked by older males.

In a study in late 2003 at Augrabies Falls National park - which has a dense population of the lizards and thus frequent interactions between them - the scientists tested whether she-males conceal their identity from he-males using visual and scent signals. In lizards, visual signals are important at a distance and chemical signals during close encounters.

By delaying the onset of colour, the study found, young males were able to dupe older males into thinking they were females. By doing this, Whiting said, she-males made "the best of a bad situation".

"An immediate advantage is freedom of movement in the normally treacherous zones which make up the territories of highly aggressive males that already have extensive fighting experience. At the same time, these female mimics are able to court the myriad of females that share the territorial male's residence."

J Scott Keogh of the Australian National University added: "Young transvestite males appear to have a dual advantage: the avoidance of potentially dangerous bouts with dominant males and access to normally inaccessible nubile females."

The scientists also removed pheromones and skin lipids that identify gender and relabelled a group of females and she-males with either male or female scent, before presenting them to typical adult males.

Males use their tongues to sample chemical scent and responded by courting she-males labelled as females, but not she-males labelled as males. She-males are, therefore, able to deceive he-males using visual but not chemical signals.

"Males are fooled by looks, but not by scent," explained Jonathan Webb of the University of Sydney. "She-males are able to maintain this deception by staying one step ahead of a prying male and thereby avoiding a nosey tongue that might give the game away."

The length of time young males retain female-like coloration is variable and probably condition-dependent, wrote the scientists in the Royal Society article. "Although she-male flat lizards mimic females using visual and not chemical signals, by staying one step ahead of males and avoiding chemical contact, they are able to successfully maintain this deception.

"Consequently, she-males are able to approach, tongue-flick and court females in the presence of a resident male. Therefore, female mimicry in flat lizards is probably adaptive and favoured by sexual selection through its role as an alternative reproductive tactic."

karen.macgregor@uw-news.com