Melanin-based coloration and host-parasite interactions under global change

Abstract

The role of parasites in shaping melanin-based colour polymorphism, and the consequences of colour polymorphism for disease resistance, remain debated. Here we review recent evidence of the links between melanin-based coloration and the behavioural and immunological defences of vertebrates against their parasites. First we propose that (1) differences between colour morphs can result in variable exposure to parasites, either directly (certain colours might be more or less attractive to parasites) or indirectly (variations in behaviour and encounter probability). Once infected, we propose that (2) immune variation between differently coloured individuals might result in different abilities to cope with parasite infection. We then discuss (3) how these different abilities could translate into variable sexual and natural selection in environments varying in parasite pressure. Finally, we address (4) the potential role of parasites in the maintenance of melanin-based colour polymorphism, especially in the context of global change and multiple stressors in human-altered environments. Because global change will probably affect both coloration and the spread of parasitic diseases in the decades to come, future studies should take into account melanin-based coloration to better predict the evolutionary responses of animals to changing disease risk in human-altered environments.

Keywords: animal coloration; disease risk; host–parasite interactions; immunity; melanin pigments; sexual selection.

Figure 1.

Light (left) and dark (right) melanin-based colour variations in (a) feral pigeon Columba livia (credit: L. Jacquin), (b) grey squirrel Sciurus carolinensis (credit: L. Jacquin), (c) viviparous lizards Zootoca vivipara (credit: Martin M), (d) brown trout Salmo trutta (from Jacquin et al. [5]) and (e) pocket mice Chaetodipus intermedius (from Nachman et al. [6]). (Online version in colour.)

Figure 2.

Proposed links between melanin-based coloration and parasite load and their underlying mechanisms in vertebrates.

Figure 3.

Proposed links between colour polymorphism and parasitism under global change. (Online version in colour.)