Ivory Towers: Exposed: the fickleness of lizards

HAVE YOU ever wondered how male lizards select their mates? Given the choice between a female lizard they know, and one to whom they have only just been introduced, which would they prefer?

Thanks to recent research at the University of Miami, we now know the answer and are proud to present it in the first of this new series of selections of the most interesting of recent academic findings.

The paper begins: 'Male mate choice was studied in the lizard Anolis sagrei to determine whether the degree of familiarity males have with females affects their choice of mating partners'.

The experiment involved leaving the male in a cage for 16 days with a female so they could get to know each other. At the beginning of day 17, the female was removed. Soon after, she was put back in the cage, together with another female previously unknown to the male.

For the next 12 hours, the experimenter counted how many times the male copulated with each female. A simple marking system was used to avoid confusion. For the prurient, they added a little information about what they were watching:

'A male anole (lizard) mates with a female by first performing a series of rapid, low amplitude movements of the head as he approaches a female. If the female is sexually receptive she will remain in place as the courting male approaches. The male then moves alongside the female, obtains a grip of her neck skin with his jaws, mounts her back, swings his tail under her tail, and achieves copulation by inserting one of his two hemipenes into her cloacaca.'

And, over a series of experiments with different lizards, he did that an average of four times in the 12 hour period, once with his old mate and three times with the new one.

As the mating frequency of both females on the day before the experiment had been monitored to ensure parity, the research reached an inescapable conclusion:

'These results suggest that male Anolis sagrei are able to discriminate between a familiar and unfamiliar female and that they mate preferentially with the unfamiliar female under laboratory conditions.'

The author goes on to suggest that such behaviour outside the laboratory may have an evolutionary benefit for any lizard hoping to increase the size of his harem, and thereby produce more offspring.

These results may be compared with an earlier experiment in which male butterflies were shown to prefer virgin females.

Reference: Richard R Tokarz, Animal Behavior (44) 1992 pp. 843-9.