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First published online September 19, 2006
Journal of Experimental Biology 209, 3786-3794 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02447

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Tests of absolute photorefractoriness in four species of cardueline finch that differ in reproductive schedule

Scott A. MacDougall-Shackleton^1,*, Madhusudan Katti² and Thomas P. Hahn³

¹ Departments of Psychology and Biology, University of Western Ontario, London ON, N6A 5C2, Canada
² Department of Biology, California State University, Fresno, USA
³ Section of Neurobiology, Physiology and Behavior, Animal Communication Laboratory, University of California, Davis, USA

^* Author for correspondence (e-mail: smacdou2{at}uwo.ca)

Accepted 18 July 2006

Species with different reproductive schedules may differ in how they respond to the annual change in photoperiod (the adaptive specialization hypothesis). Seasonally breeding species are predicted to use photorefractoriness to terminate reproduction prior to inclement conditions in autumn and winter, whereas opportunistically breeding species may not exhibit photorefractoriness. We tested for absolute photorefractoriness in four species of cardueline finch that differ in their reproductive schedules: opportunistically breeding red crossbills, flexibly breeding pine siskins, and seasonally breeding Cassin's finches and gray-crowned rosy-finches. Field observations indicated that all four species regress their gonads and begin prebasic feather molt in late summer or autumn. However, exposure to a long day photoperiod in autumn (24 h:0 h L:D) resulted in elevation of gonadotropins and testicular recrudescence in all species except Cassin's finches. Thus, by this criterion, some of the seasonally breeding species tested here did not exhibit absolute photorefractoriness. These results indicate that phylogenetic history needs to be taken into account when considering the adaptive nature of photoperiod response systems.

Key words: photoperiod, reproduction, Loxia curvirostra, Carduelis pinus, Carpodacus cassinii, Leucosticte tephrocotis

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