Research

Sex allocation:

Sex allocation theory predicts that parents should overproduce the sex with the highest fitness prospects given the environment and their own characteristics. This theory has been widely investigated in birds and mammals, but with mixed results.

Using black-legged kittiwake (Rissa tridactyla) as a study model, I investigated the fitness benefits of sex-ratio bias and whether parents could indeed manipulate offspring sex-ratio to maximise their fitness.

The main findings were that sons are more energetically more costly to rear than daughters and that control parents overproduced daughters as compared to experimentally fed parents. However, yet unpublished data suggest that this is not true on a larger dataset, where we found that, surprisingly, pair-bond duration is a strong predictor of offspring sex.

See publications 3 and 8 for more details.

Ongoing projects: oxidative stress and offspring sex-ratio; age, pair-bond duration and offspring sex-ratio

Function and evolution of colour in lizards

Colour signals have been extensively studied in birds, especially carotenoid-based signals. Those colours are thought to be honest indicators of individual quality, but this is far from clear in reptiles. Contrary to birds, no studies managed to influence colour via carotenoid supplementation and, other pigments such as pteridines can produce similar colours.

I investigated the mechanisms underlying colouration as well as its evolutionary role in 2 Australian dragon speices: the frillneck lizard (Chlamydosaurus kingii) and the water dragon (Intellagama lesueurii).

The main findings were that the colour red was due to carotenoids in the frill of frillneck lizards but was produced by pteridines on water dragons' ventral parts. Only the latter seem to be used for male-male competition and likely result from sexual selection. Also, in the frillneck lizard, we found that frill colour varies geographically mostly due to carotenoid content variation, likely due to food.

See publications 11 for more details.

Ongoing projects: colouration in water dragons, function of frill colour

Evolution of sex-determining mechanisms

Sex-determining mechanisms is a evolutionary labile trait across vertebrates, with many transitions between genotypic and environmental sex determination. However, we are still missing a general explanation for these transitions. Schwanz et al. (2016) recently published a theoretical model suggesting that sex differences in age at maturity could explain the evolution of sex-determining mechanisms.

In collaboration with Lisa Schwanz, I am currently analysing data across reptiles using phylogenetic comparative methods to test predictions of the theoretical model.

Photo: Martin Whiting

Sibling competition:

Parents usually produce more offspring than they can actually rear, leading to a strong within-nest competition for food. In most species, it takes the form of scramble competition via begging, but in other species chicks can be aggressive against their siblings and sometimes kill them (siblicide). The older chick is usually benefiting from its larger size to dominate its sibling.

I investigated the role of hatching asynchrony magnitude and yolk hormones on sibling competition in the black-legged kittiwake, a facultatively siblicidal seabird.

The main findings were that intermediate (and natural) hatching asynchrony magnitude led to the lowest costs for parents and younger chicks, although older chicks paid a cost of being dominant (higher baseline corticosterone). Yolk hormones might be another mean that mothers can use to influence sibling competition: our results suggest that younger chicks would benefit from high levels of yolk hormones, especially when environmental conditions are intermediate.

See publications 5, 6 and 12 for more details.

Ongoing projects: do parents directly interfere in sibling aggression ?

Collaborators:

  • Fabrice Helfenstein (Institute of Biology, Neuchâtel, Switzerland): oxidative stress
  • Martin Whiting (Macquarie University, Sydney, Australia): water dragon colouration
  • Lisa Schwanz (University of New South Wales, Sydney, Australia): sex determining mechanisms
  • Sarah Leclaire (University of Toulouse, France): odour, genetic distance
  • Olivier Chastel (Centre d'Etudes Biologiques, Chizé, France): hormones analyses
  • Scott A. Hatch (Institute for Seabird Research and Conservation, Anchorage, AK, USA) : host responsible of Middleton Island