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Adaptive Changes in Antipredator Behavior of a Grasshopper During Development

Jack C. Schultz
Evolution
Vol. 35, No. 1 (Jan., 1981), pp. 175-179
DOI: 10.2307/2407951
Stable URL: http://www.jstor.org/stable/2407951
Page Count: 5
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Adaptive Changes in Antipredator Behavior of a Grasshopper During Development
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Abstract

Field observations and aviary studies of the antipredatory behavior of the desert grasshopper, Astroma riojanum M.-L., indicate the following: 1) nymphs (instars 2-4) are polymorphic for color and pattern but develop into adults which are relatively monomorphic; 2) nymphs and adult males posses an active jumping response to probing by predators (birds), but this response is lost in adult females; 3) handling time spent by birds increases more rapidly with grasshopper instar for the much larger females than it does for males; and 4) males are preferred over females as food by several bird species. These results suggest that the form of selection by birds on grasshoppers changes as the insects grow, and that this change is more profound for female grasshoppers. Evolutionary consequences include a marked change in antipredator behavior (from jumping to non-jumping) in females and a lesser one in males, and a reduction in color polymorphism within populations as individuals age.

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