Genetic conflict and the evolution of sexual dimorphism

In many animal species, the sexes differ strikingly in body size and shape, apparently as a result of sexual selection on males. We ask how and why such sexual dimorphism evolves, through lab and field research on flies and other insects.

In the giant long-legged fly Telostylinus angusticollis, males use their greatly elongated legs, heads and antennae to as weapons. T. lineolatus, which is native to tropical north-Queensland, is much less sexually dimorphic. We are interested in the genetic and phenotypic basis of variation in body size and shape in these species. Further information on our research can be found here.

T. angusticollis flies mating at sunset in the Fred Hollows Reserve, Sydney (Photo: R. Bonduriansky).

We are investigating the genetic basis of within-sex variation and sexual dimorphism in body size and shape. Since the sex-determination system of these flies is unknown, we are also investigating their karyotype (chromosome complement) to determine whether they exhibit an XX/XY, ZZ/ZW or some other form of sex determination.

Diploid mitotic chromosomes of T. angusticollis.

In the carrion fly Prochyliza xanthostoma, we found that males with longer heads are more attractive to females, and transfer more sperm, but fare poorly in combat with rival males. We also found that traits under sexual selection in males tend to be more strongly heritable through the father, a possible genomic adaptation to intralocus sexual conflict. Further information can be found here.

A mating pair of Prochyliza xanthostoma, (Photo: R. Bonduriansky).

P. xanthostoma males fighting (Photo: R. Bonduriansky).

The role of environment: condition dependence and parental effects

Although genes are extremely important, it is becoming increasingly clear that environmental effects can have a powerful influence on many traits. Phenotypic variation in response to an environmental gradient, known as ‘phenotypic plasticity’, can be a crucial aspect of adaptation. A special form of phenotypic plasticity called ‘condition dependence’ – the response of a phenotypic trait to variation in individual condition – is thought to play an important role in the evolution and expression of sexually selected traits. Moreover, recent findings suggest that many environmental effects can be transferred across generations.

Experiments on the neriid fly Telostylinus angusticollis have shown that body size and shape are extremely sensitive to environment and, especially, larval diet. Such ‘condition dependence’ is thought to play a key role in the evolution of sexually selected traits. Moreover, we have recently discovered that males transfer their condition to their offspring. We would like to understand the proximate basis and evolutionary implications of this effect. Further information on our research can be found here.

Brothers reared on contrasting larval diets: the male on the right is larger, has relatively larger secondary sexual traits, and would produce larger offspring (Photo: R. Bonduriansky).

As part of our investigation of the transfer of maternal and paternal condition to offspring, we are investigating the reproductive physiology of T. angusticollis and T. lineolatus.

Reproductive physiology of T. angusticolllis: a, male testes (T) and accessory glands (AG), b, female bursa copulatrix (BC), three spermathecae (S) and oviduct (O), c, sclerotized oviscape of female (Ov).