Examining the causes and consequences of variation in offspring growth and survival in an altricial bird

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  • March 19, 2019
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  • Aldredge, Robert
    • Affiliation: College of Arts and Sciences, Department of Biology
Abstract
  • Understanding why parents often produce supernumerary offspring and increase the variation in offspring growth and survival is a fundamental question in evolutionary ecology. This behavior occurs primarily in species that live in unpredictable environments and is thought to be an adaptive strategy used by parents to maximize the number of offspring that survive to breed. In this dissertation, I explore both how and why female birds increase the variation in growth and survival of supernumerary offspring. To do this, I collected observational and experimental data over four years in a free-living population of house sparrows. In Chapter 2, I developed a novel technique to uncover variation in growth (e.g. mass change) not detected by conventional analyses. I show that variation in growth occurs when some offspring increase mass slowly, likely owing to a lack of food resources. Some of these offspring recover and increase mass rapidly to approach a similar pre-fledging mass as offspring that do not delay development, whereas others continue to increase mass slowly and are light at fledging. This plasticity in growth likely increases the number of high quality offspring that fledge. In Chapter 3, I tested whether female birds begin embryonic development (incubation) before all eggs are laid either 1) as an adaptive strategy to maximize the number of embryos that survive to hatch or 2) as an adaptive strategy to maximize the number or quality of hatched young that fledge. I show that early incubation occurs too late to maximize survival of all embryos but early enough to reduce growth and survival of late-hatched young. Thus, early incubation likely is a tradeoff between increasing embryo survival and maintaining growth and survival of late-hatched young. Overall, my dissertation shows that house sparrows exhibit considerable plasticity in offspring growth, and that early incubation likely maximizes the number of embryos that survive the incubation and nestling periods to fledge as high quality young. Thus, the variation in offspring growth caused by early incubation may occur as consequence of unique adaptations (prolonged oviposition and parental incubation) for offspring production and development in house sparrows and other birds.
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  • In Copyright
Advisor
  • Sockman, Keith
  • Lohmann, Kenneth
  • Hurlbert, Allen
  • Burmeister, Sabrina
  • Kier, William
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2015
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  • Chapel Hill, NC
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  • There are no restrictions to this item.
Date uploaded
  • January 21, 2016

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