Mating system evolution in skinks

Lizards are a morphologically diverse group with some 3,000 species in 21 families, yet understanding how sexual selection contributes to the diversity of traits and behaviours remains enigmatic. Male reproductive success has only been accurately measured in a few species and these studies demonstrated considerable disparity between the observed behavioural mating system and realised genetic mating system, consistent with findings in other taxa. I used genetic techniques to accurately measure male reproductive success in the field and in experimental enclosures in two species of lizards with different mating systems.

I investigated the influence of male and female territorial behavioral tactics on mating patterns and offspring size in a natural population of E .heatwolei. In this species individuals adopt floater or territorial tactics. I quantified male and female territorial tactics in the field during the breeding season and determined paternity with microsatellite loci. Territorial females were not more likely to have a single paternity clutch and territorial males were not more likely to father a single paternity clutch. However, larger females were more likely to have a clutch with multiple fathers, even when we controlled for clutch size. Floater females produced heavier offspring then their territorial counterparts and offspring fathered by floaters were heavier then half sibs fathered by territorial males. The results of the study demonstrate that different territorial tactics in both sexes can influence offspring weight. Therefore parental behavioral tactics may provide genetic benefits to offspring.

Marked pair of  E. heatwolei

In another study I investigated the relationship between male traits and body size in P. entrecasteauxii and tested how these influence male reproductive success in a semi-natural enclosure experiment. Populations were sampled from Namadgi over two years and measurements of body size and male colouration were recorded. The frequency of orange colouration (badge) in males was predominantly bimodal, with some males developing a strong orange badge and some that did not. There was little difference between the male snout vent length or condition of males with and without a colour badge. Large males with a colour badge had a greater number of ectoparasites in the skin evaginations under the forelimns (mite pockets). Mating trials were established to test for the influence of male badge and body size on reproductive success. Behavioural observations revealed that the species social system could be categorised as a dominance hierarchy. Males with an orange badge were dominant over males without irrespective of body size, suggesting that male colour badges may act as status signalling badges in this species. Male reproductive success estimated using polymorphic microsatellite loci was greatest in large males with orange badges. This provides was one of the first study to demonstrate that male badge colour strongly influences reproductive success when accurately measured with genetic markers.

P. entrecasteauxii in semi-natural enclosures







Related publications

Stapley J, Hayes C., Scott IAW and Keogh JS. (2003). Population genetic differentiation and multiple paternity determined by novel microsatellite markers from the Mountain Log Skink (Pseudemoia entrecasteauxii). Molecular Ecology Notes 3: 291-293.

Stapley J and Keogh JS. (2005) Behavioral syndromes influence mating systems: floater pairs of a lizard have heavier offspring. Behavioral Ecology 16:514-520.

Stapley J and Keogh JS. (2006) Experimental and molecular evidence that body size and ventral color interact to influence male reproductive success in a lizard. Ethology, Ecology and Evolution 18:275-288.