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Niche choice and niche conformance in colour polymorphic grasshoppers

Holger Schielzeth

Grasshoppers are highly variable in behaviour and body colouration. Escape behaviour represents a behavioural niche that is expressed when individuals are face predation hazard – thus one of the main challenges in their lives. Body colouration is directly related an individual’s niche because different colours are cryptic on different backgrounds and because body colour affects thermoregulation and thus a grasshopper’s time window for its daily activities. In the first phase of the NC³, we have quantified inter-individual variation in predictability of escape behaviour in grasshoppers. The project has shed new light on the role, development and limits of behavioural flexibility within individuals. The project was conceived as studying the diversity of individual strategies to the common challenge of an approaching predator. Diversity of individual strategies represent behavioural niches in the sense of alternative coping styles. We have addressed behavioural variation in a colour polymorphic species of grasshoppers that was exposed to variable environments during ontogeny. As an auxiliary result of the breeding design (that we had implemented to estimate the heritability of predictability) we found that the genetic inheritance mechanisms of colour morphs was remarkably simple, apparently involving only three loci. In the second phase of the NC³, we will address niche choice and niche conformance in colour polymorphic grasshoppers specifically. From the first phase of the NC³ we know that in some species colour morphs are determined genetically and from other projects we know that other species are colour-changers. We also know that colour morph ratios vary among naturals population and that body colour affects thermoregulation. We hypothesise that colour polymorphisms are maintained by trade-offs between thermoregulation and crypsis and that selection is broadly similar between colour-changing species (niche conformers) and non-changing species (niche choosers). We will comparatively study microhabitat choice in niche conformers and niche choosers, address the thermoregulatory consequences and temporal niche choice related to different heating capacities. Furthermore, we will address the role of mate choice in maintaining colour phenotype variation. While the broad morph categories are discrete, we will also address the consequences of more fine-grained variation in colour, in particular the role of differences in melanisation that varies between individuals and likely affect both thermoregulation and microhabitat choice. While the first phase of the NC³ has shed light on individualised behavioural strategies, the second phase will specifically address the consequences of individual body colour for individualised niche choice and conformance. This will provide valuable evidence for why populations are so individually variable in colouration and niche-relations.