Extreme weather change and the dynamics of oviposition behavior in the pipevine swallowtail, Battus philenor
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Prospects of global increases in extreme weather change provide incentive to examine how such change influences animal behavior, for example, behavior associated with resource use. In this study, we examined how oviposition behavior in a southern Arizona population of pipevine swallowtails (Battus philenor L.) responded to changes in their Aristolochia host resource and vegetative background caused by the North American monsoon system. Summer monsoon rains resulted in a flush of non-host vegetation and a more than doubling in rate of landings by host-searching females on non-host vegetation. Rates of discovery of the host species A. watsoni Woot. Standl. decreased by 50% after monsoon rains. Rains did not alter host density appreciably, but resulted in significant increases in host plant size and new growth, two indicators of host suitability for B. philenor larvae. After the rains, mean clutch size on individual host plants increased by a factor of 2.5; the mean proportion of host plants encountered on which a female laid eggs also increased significantly. Females were discriminating about the host plants on which they laid eggs after alightment; plants accepted for oviposition were larger, bore more new growth, and bore fewer larvae than rejected plants. Contrary to predictions from foraging theory, degree of discrimination did not change seasonally. Finally, the rate at which eggs were laid increased seasonally, suggesting that oviposition rates were limited more before monsoon rains by the relatively low quality of hosts than they were after the rains by the relatively low rate at which hosts were found. This latter result suggests that, while butterflies possess behavioral flexibility to respond to extreme weather change, such flexibility may have limits. In particular, expected increases in the severity and frequency of droughts may result in reduced oviposition rates, reductions that could have adverse demographic consequences.
KeywordsClimate change Host selection Egg load Clutch size Butterfly
Thanks to Joshua Garcia, Laura Mojonnier, and Ginny Newsom for field assistance, and to the Papaj lab group for discussions. We acknowledge helpful comments by J. Rosenheim and two anonymous reviewers. Funding was provided by the National Science Foundation (award no. IBN0112067). C. Heinz was funded by the Center for Insect Science through an NIH award (no. 1K12Gm00708). We are grateful to Mark Heitlinger and the SRER Executive Committee for permission to work on the Santa Rita Experimental Range, and to Bill Emmerich for rain gauge data.
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