Translator Disclaimer
1 January 2011 Intense Natural Selection on Morphology of Cliff Swallows (Petrochelidon Pyrrhonota) a Decade Later: Did the Population Move between Adaptive Peaks?
Author Affiliations +
Abstract

Unusual climatic events often lead to intense natural selection on organisms. Whether episodic selection events result in permanent microevolutionary changes or are reversed by opposing selection pressures at a later time is rarely known, because most studies do not last long enough to witness rare events and document their aftermath. In 1996, unusually cold and wet weather in southwestern Nebraska led to the deaths of thousands of Cliff Swallows (Petrochelidon pyrrhonota) over a 6-day period. Survivors were skeletally larger, with shorter wings and tails, and had less asymmetry in wing length than those that died. We determined trajectories of morphological traits in the decade following this event by measuring yearling birds each year from 1997 to 2006. Wing and middle tail-feather lengths continued to decrease, bill length and width continued to increase, tarsus length was unchanged, and levels of asymmetry in wing length increased. Cumulative directional change in wing, tail, and bill length was greater in the decade after selection than during the selection event itself. Morphological variation could not be explained by phenotypic plasticity resulting from better environmental conditions during growth, because weather variables (that influence food supply and ectoparasitism) were not significantly different before and after selection. There was no evidence that opposing selection restored skeletal size or wing or tail length to that before the selection event. The reasons for continued change in morphology in this population are unclear but may represent a population shift to a different fitness peak in the adaptive landscape as a consequence of the intense selection in 1996.

© 2011 by The American Ornithologists' Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website, http://www.ucpressjournals.com/reprintInfo.asp.
Mary Bomberger Brown and Charles R. Brown "Intense Natural Selection on Morphology of Cliff Swallows (Petrochelidon Pyrrhonota) a Decade Later: Did the Population Move between Adaptive Peaks?," The Auk 128(1), (1 January 2011). https://doi.org/10.1525/auk.2011.10219
Received: 21 September 2010; Accepted: 1 October 2010; Published: 1 January 2011
JOURNAL ARTICLE
9 PAGES


SHARE
ARTICLE IMPACT
RIGHTS & PERMISSIONS
Get copyright permission
Back to Top