Abstract
Homochromy (i.e. that individuals have a similar color as their environment) is frequent in grasshoppers, and probably functions to reduce detection by potential predators. Nymphs of several soil-perching grasshopper species are known to show color changes during development that increase homochromy, with color being determined with each molt. While this is well documented for young individuals, the only color change in response to the environment that has been recorded for adult grasshoppers of these species is an overall darkening of the individual when exposed to dark surfaces. Whether grasshoppers can also adaptively change color hue is relevant for our understanding of the evolution of locally adapted crypsis. We therefore exposed two groups of adult grasshoppers to a bluish-gray substrate or a reddish-brown substrate, and recorded their color over time. Quantitative digital image analysis showed that adult soil-perching grasshoppers remained capable of adapting to changes in the color of their surroundings through a plastic response. Compared to nymphs, the changes are not as strong and much slower. We suggest that color change in adults occurs through the ongoing deposition of melanins, with eumelanin making individuals more bluish-gray and pheomelanin making individuals more reddish-brown. The fact that color change is possible but slow supports that other mechanisms, such as habitat choice or selective predation, may also play a role in adapting local populations to substrate color. In addition, the ability of these grasshoppers to produce different melanins in response to the environment supports a previous suggestion that they might be useful in the future development of animal models to study melanin-related diseases like melanoma and Parkinson´s disease.
Highlights
Crypsis is a well known anti-predation mechanism observed in a wide variety of species
Adaptive phenotypic plasticity is often key to optimizing crypsis in animals whose habitat is heterogeneous through space or time (Umbers et al 2014, Valverde and Schielzeth 2015, Kang et al 2016)
Regarding the color change of grasshoppers after freezing and cleaning, we found strong statistical supports that substrate color influenced adult grasshopper color, the patterns were somewhat different to those for live grasshoppers (Fig. 3)
Summary
Crypsis is a well known anti-predation mechanism observed in a wide variety of species. For grasshoppers four types of color change have been recorded: greenbrown morph switching, color pattern changes, hue shifting and blackening (Rowell 1972). While color pattern has often been found to be determined mostly by genes and maternal effects (Karlsson et al 2009, Forsman 2011, Karpestam et al 2012b), hue variation is thought to be driven to a great extent by an adaptive plasticity response to environmental cues, as the new overall color tends to match that of the subject’s surroundings (Ergene 1955, Yerushalmi and Pener 2001, Valverde and Schielzeth 2015). The environmental cues that are used for adaptive plasticity to enhance crypsis are often unknown, but effects of temperature, humidity and/or visual input have been recorded (Rowell 1972, Umbers et al 2014, Valverde and Schielzeth 2015)
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