Maternal Effects on Brood Reduction in Common Grackles
Maddox, Joseph Dylan
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Permalink
https://hdl.handle.net/2142/87021
Description
Title
Maternal Effects on Brood Reduction in Common Grackles
Author(s)
Maddox, Joseph Dylan
Issue Date
2009
Doctoral Committee Chair(s)
Weatherhead, Patrick J.
Department of Study
Ecology, Evolution and Conservation Biology
Discipline
Ecology, Evolution and Conservation Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Evolution and Development
Language
eng
Abstract
The main goal of my dissertation research was to investigate how maternal effects influence offspring productivity in common grackles ( Quiscalus quiscula). Maternal effects are largely considered adaptive, but my research provides little supporting evidence because few of the maternal effects I assessed were relevant. In general, asynchronous hatching had by far the largest effect on offspring performance even when additional maternal effects were present. However, I found that egg size can have positive effects on nestling growth and survival especially early in the nesting period, but those effects are largely overwhelmed by asynchronous hatching. Adaptive evidence is lacking in the two other maternal effects---sex and yolk hormones---in which I focused. I found that brothers and sisters are equally susceptible to starvation even when environmental conditions are extremely poor. This suggests that mothers cannot increase the number of fledglings they produce by preferentially allocating sex. I did not find the predicted patterns of yolk testosterone and estradiol relative to clutch size and laying order that would suggest yolk hormones act as a compensatory mechanism to offset the deleterious effects of asynchronous hatching. Finally, I found a disconnect between the maternal effects that were beneficial to mothers versus their offspring. Within nests offspring that hatched earlier than their siblings were heavier and more likely to fledge, whereas among nests mothers that initiated their clutches early in the breeding season fledged more young than females breeding later in the population. Thus, the one maternal effect that repeatedly had the largest impact on offspring performance had absolutely no effect on the productivity of mothers in the short term. There are two ways to interpret this result. First, asynchronous hatching may be a nonadaptive hormonal constraint that for some reason varies extensively among females. Second, asynchronous hatching may enable mothers to increase their productivity in the long term by adjusting brood size to food availability in the short term. Consequently, future research regarding the adaptive allocation of maternal effects in common grackles should focus on identifying the strategies of mothers in the short term that may increase their fitness in the long term.
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