can drive wildlife evolution in many ways. For example, pathogens can cause
severe population bottlenecks, and they have played key roles in speciation
events and the evolution of sociality. Pathogens can also drive the evolution
of colouration through sexual selection. This phenomenon has been widely
studied in carotenoid-based colouration systems but less is known about the roles
of the other pigment types present in vertebrates: pteridines and melanins.
These pigments differ in how they are acquired and produced; carotenoids are
acquired from the diet and pteridines and melanins are endogenously produced
and tyrosine, respectively.
The link between pathogens and carotenoid-based colouration is well understood,
with carotenoid intake determined by foraging ability, which in turn is
influenced by pathogen load. In contrast, much less is known about the relationship
between pteridine- and melanin-based colouration and pathogens. Conflicting
results have been reported with regards to associations between non-carotenoid
colouration and pathogens, and the suggestion of a link between pteridine- and
melanin-based pigments and the immune system is controversial. We propose to
examine whether pathogen load is associated with secondary sexual colouration
in the tawny dragon (Ctenophorus decresii).
The tawny dragon is a small (<30g) agamid that inhabits rocky outcrops and
ranges within South Australia and uses pteridine- and melanin-based colour
patches in male-male confrontation and mate acquisition displays. We will
quantify colouration variation independently of the human visual system using
photograph-derived data. Pathogens will be identified, and pathogen load will
be determined, using morphological and molecular methods. Little is known about
the pathogens infecting tawny dragons. However, preliminary results show
individual variation in the abundance of ticks, mites and haemogregarine blood parasites.
This research will aid in understanding the role that pathogens play in the
evolution of secondary sexual colouration in an agamid pteridine- and
melanin-based colour system.