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2003 The Society for the Study of Evolution. All rights reserved. Evolution, 57(4), 2003, pp. 872882
 

Summary: 872
2003 The Society for the Study of Evolution. All rights reserved.
Evolution, 57(4), 2003, pp. 872­882
PATTERNS OF NATURAL SELECTION ON SIZE AT METAMORPHOSIS IN
WATER FROGS
RES ALTWEGG1,2 AND HEINZ-ULRICH REYER1
1Institute of Zoology, University of Zu¨rich, Winterthurerstr. 190, CH-8057 Zu¨rich, Switzerland
Abstract. Strategies for optimal metamorphosis are key adaptations in organisms with complex life cycles, and the
components of the larval growth environment causing variation in this trait are well studied empirically and theoret-
ically. However, when relating these findings to a broader evolutionary or ecological context, usually the following
assumptions are made: (1) size at metamorphosis positively relates to future fitness, and (2) the larval growth envi-
ronment affects fitness mainly through its effect on timing of and size at metamorphosis. These assumptions remain
poorly tested, because data on postmetamorphic fitness components are still rare. We created variation in timing of
and size at metamorphosis by manipulating larval competition, nonlethal presence of predators, pond drying, and
onset of larval development, and measured the consequences for subsequent terrestrial survival and growth in 1564
individually marked water frogs (Rana lessonae and R. esculenta), raised in enclosures in their natural environment.
Individuals metamorphosing at a large size had an increased chance of survival during the following terrestrial stage
(mean linear selection gradient: 0.09), grew faster and were larger at maturity than individuals metamorphosing at
smaller sizes. Late metamorphosing individuals had a lower survival rate (mean linear selection gradient: 0.03) and
grew more slowly than early metamorphosing ones. We found these patterns to be consistent over the three years of

  

Source: Altwegg, Res - Avian Demography Unit, Department of Statistical Sciences, University of Cape Town

 

Collections: Environmental Sciences and Ecology