Riccardo Ton

Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

Thomas E. Martin

Commitee Members

Raymond B. Huey, John L. Maron, Bret W. Tobalske, H. Arthur Woods


University of Montana


Rates of embryonic and post-natal growth vary extensively among species and geographic space. This variation is well represented in songbird offspring from different latitudes and can strongly influence organismal quality and fitness. However, environmental and evolutionary causes and consequences of variation in embryonic and post-natal growth remain unclear. Here we experimentally show in the field that, within the constraints imposed by physiological trade-offs, warmer incubation temperatures shortened embryonic period length among nine species of songbirds from two latitudes. Yet, the magnitude of the response varied and species-specific reaction norms of embryonic reduction in response to our treatment positively correlated with the natural temperature experienced during incubation. Furthermore, we found little evidence for potential metabolic costs imposed on offspring by faster development, but we detected benefits for size at hatching instead. These results question the generality of theories considering avian development to be strictly dictated by intrinsic trade-offs and suggest that shorter embryonic periods caused by warmer temperature may not be as detrimental as traditionally thought. Costs of shorter development due to warmer embryonic temperature may appear later in life as stunted post-natal growth via influences on offspring metabolism and parental feeding and brooding effort. Our treatment increased metabolic rate without producing appreciable changes in parental care yielding slower post-natal growth rates in two species, faster growth in one and no effects for the majority of the species studied. These results suggest that shorter embryonic periods are not generally associated to costs paid during the post-natal stages but also question the role of metabolism for growth. We tested for the association between metabolism and growth using a comparative approach. We discovered that metabolic rate and body mass of nestlings predicted variation in post-natal growth rates among 59 species of songbirds at three latitudes. These results beg the question of what are the possible evolutionary bases of metabolic variation. We found that nest depredation may be a selective force favoring increased metabolic rate to achieve faster growth independently from the constraints of adult mortality. This study advances our understanding of ecological and physiological causes and consequences underlying variation in embryonic time and post-natal growth.



© Copyright 2016 Riccardo Ton