Colour polymorphism is associated with lower extinction risk in birds

Abstract

Colour polymorphisms have played a major role in enhancing current understanding of how selection and demography can impact phenotypes. Because different morphs often display alternative strategies and exploit alternative ecological niches, colour polymorphism can be expected to promote adaptability to environmental changes. However, whether and how it could influence populations' and species' response to global changes remains debated. To address this question, we built an up-to-date and complete database on avian colour polymorphism based on the examination of available data from all 10,394 extant bird species. We distinguished between true polymorphism (where different genetically determined morphs co-occur in sympatry within the same population) and geographic variation (parapatric or allopatric colour variation), because these two patterns of variation are expected to have different consequences on populations' persistence. Using the IUCN red list, we then showed that polymorphic bird species are at lesser risk of extinction than nonpolymorphic ones, after controlling for a range of factors such as geographic range size, habitat breadth, life history, and phylogeny. This appears consistent with the idea that high genetic diversity and/or the existence of alternative strategies in polymorphic species promotes the ability to adaptively respond to changing environmental conditions. In contrast, polymorphic species were not less vulnerable than nonpolymorphic ones to specific drivers of extinction such as habitat alteration, direct exploitation, climate change, and invasive species. Thus, our results suggest that colour polymorphism acts as a buffer against environmental changes, although further studies are now needed to understand the underlying mechanisms. Developing accurate quantitative indices of sensitivity to specific threats is likely a key step towards a better understanding of species response to environmental changes.

Variable colour patterns indicate multidimensional, intraspecific trait variation and ecological generalization in moths

“…Broad niches, in turn, may promote establishment success, stabilize population dynamics, allow for faster range expansions, and reduce extinction risk (Bolnick et al , Forsman et al , Hughes et al , Wennersten and Forsman , Forsman , ). Consistent with these predictions, empirical evidence from experiments and comparative analyses largely suggest that variation in colour patterns, and in other traits, among individuals improves the ecological and evolutionary success of populations and species [(Lomnicki , Galeotti et al , Forsman and Åberg , Hughes et al , Krüger and Radford , Forsman and Hagman , Pizzatto and Dubey , Delhey et al , Forsman , Forsman and Wennersten , Betzholtz et al , Ducatez et al , Des Roches et al , Takahashi and Noriyuki ), but see Bolton et al () for a conflicting opinion].…”

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

“…[7]). Moreover, melanin-based coloration is associated with many critical biological functions, including metabolism, reproduction, stress response and immunity [8], which can have consequences for the ability of differently coloured morphs to respond to natural and human-driven environmental changes [9][10][11]. However, the relationship between melanin-based coloration and host -parasite interactions has been understudied for a long time, thereby hindering our ability to predict the response of wild populations to changing environments and disease risk.…”

“…B 285: 20180285 thermoregulation, better ability to detoxify pollutants and/or higher competitive abilities (reviewed in [9]). As a result, colour polymorphic species might be able to respond to a wider range of environmental conditions, and colour polymorphism within a species might act as a buffer against extinction [10]. In this context, the effects of parasites on differently coloured individuals should be considered in depth.…”

Colour polymorphism influences species' range and extinction risk

“…Although previous comparative studies have demonstrated that colour polymorphism facilitates large-scale ecological phenomena such as expansion of geographical distribution and mitigation of the extinction risk of a species [13,14], some exceptions have been highlighted [16,17]. The generality of the ecological effects of colour polymorphism with regard to ecological success remains uncertain.…”