BackgroundColour-marking polymorphism is widely distributed among cryptic species. To account for the adaptive significance of such polymorphisms, several hypotheses have been proposed to date. Although these hypotheses argue over the degree of camouflage effects of marking morphs (and the interactions between morphs and their microhabitat backgrounds), as far as we know, most empirical evidence has been provided under unnatural conditions (i.e., using artificial prey).Methodology/Principal Findings Tetrix japonica, a pygmy grasshopper, is highly polymorphic in colour-markings and occurs in both sand and grass microhabitats. Even within a microhabitat, T. japonica is highly polymorphic. Using humans as dummy predators and printed photographs in which various morphs of grasshoppers were placed against different backgrounds, we addressed three questions to test the neutral, background heterogeneity, and differential crypsis hypotheses in four marking-type morphs: 1) do the morphs differ in the degree of crypsis in each microhabitat, 2) are different morphs most cryptic in specific backgrounds of the microhabitats, and 3) does the morph frequency reflect the degree of crypsis?Conclusions/SignificanceThe degree of camouflage differed among the four morphs; therefore, the neutral hypothesis was rejected. Furthermore, the order of camouflage advantage among morphs differed depending on the two types of backgrounds (sand and grass), although the grass background consistently provided greater camouflage effects. Thus, based on our results, we could not reject the background heterogeneity hypothesis. Under field conditions, the more cryptic morphs comprised a minority of the population. Overall, our results demonstrate that the different morphs were not equivalent in the degree of crypsis, but the degree of camouflage of the morphs was not consistent with the morph frequency. These findings suggest that trade-offs exist between the camouflage benefit of body colouration and other fitness components, providing a better understanding of the adaptive significance of colour-markings and presumably supporting the differential crypsis hypothesis.

The sexually size-dimorphic grasshopper Tetrix japonica exhibits variation in body-color markings on the pronotum even within a single local population. Such markings have been suggested to reduce the visual detectability of grasshoppers. However, some grasshoppers have no markings. In the present study, we examined the effect of the sex-related difference in body size and the spotted markings on the degree of camouflage. We hypothesized that: (i) large individuals (females) are potentially more readily detectable than small individuals; (ii) large individuals (females) with spotted markings would realize a moderate degree of the camouflage effect, whereas large individuals (females) without spotted markings would be quite poorly camouflaged; (iii) small individuals (males) would be sufficiently less detectable, with or without markings; and (iv) large individuals (females) would tend to have spotted markings in the wild. To test this hypothesis, we conducted a morph-frequency field survey and laboratory experiments on the body-size dependency of the spotted markings. The field survey confirmed that all females exhibited spotted markings and that the majority of males were non-spotted morphs. Next, to determine whether body size and the spotted markings affected crypsis, we conducted detection task experiments using humans as dummy predators by manipulating the body size, presence/absence of spotted markings, or both, of printed grasshoppers. The absence of spotted markings increased the detection risk in large and small grasshoppers, particularly in large-sized females. These results suggest that female-biased selective predation could have eliminated non-spotted female morphs because they were too conspicuous.

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Autotomy is the ability to spontaneously self-amputate a limb or other appendage, often as a reflexive action. This limb amputation typically occurs as a specialized defensive response to an attack from a predator and thereby enables the prey to escape from predation. Despite the benefits of escape, autotomized organisms lose the body part and its associated function. Here, we investigated the jumping behavior and performance of one-leg-autotomized and intact rice grasshoppers, Oxya yezoensis, to examine changes in jumping behavior after autotomy. The take-off elevation of autotomized grasshoppers was 7.8°lower than in intact grasshoppers, resulting in nearly a 45°angle of take-off, which maximized the jumping distance. Kinematic analyses of the jumping manner revealed that the angle of the femur during jumping differed between intact and autotomized grasshoppers, suggesting that the grasshoppers behaviorally change the take-off elevation after autotomy. According to analyses of jumping performance, the degree of decline in performance differed between horizontal distance and vertical height. Even though they jumped on only one hind leg, one-leg-autotomized grasshoppers realized 69% performance along a horizontal distance relative to intact grasshoppers. In contrast, autotomized grasshoppers realized only a 44% performance in vertical height compared to intact grasshoppers. The difference in take-off elevation between autotomized and intact grasshoppers is likely related to the observed difference in the magnitude of the decline in performance between horizontal distance and vertical height. These results suggest that rice grasshoppers may alter their take-off elevation after limb autotomy to minimize the reduction in jumping distance.