Intraspecific variation in avian growth and development: Patterns and mechanisms

Winnicki-Smith, Sarah K.

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https://hdl.handle.net/2142/125686 Copy

Description

Title

Intraspecific variation in avian growth and development: Patterns and mechanisms

Author(s)

Winnicki-Smith, Sarah K.

Issue Date

2024-07-02

Director of Research (if dissertation) or Advisor (if thesis)

• Benson, Thomas J
• Hauber, Mark E

Doctoral Committee Chair(s)

• Benson, Thomas J
• Hauber, Mark E

Committee Member(s)

• Bell, Alison M
• Ward, Michael P
• Paitz, Ryan T

Department of Study

School of Integrative Biology

Discipline

Ecol, Evol, Conservation Biol

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• bird
• growth
• development
• hormones
• embryo

Abstract

Parents can shape offspring phenotypes by passing resources and developmental cues to growing embryos and hatched or born progeny, giving rise to intraspecific growth variation that may have short- and long-term consequences for offspring survival and future reproductive success (Schwagmeyer and Mock 2008). Growing birds rely on the resources that parents invest in eggs; variation in egg contents has been shown to influence avian growth trajectories, yet there remain many unanswered questions about the roles that egg content variation plays in the production of offspring growth variation (Groothuis et al. 2019). In this dissertation, I explored the effect of egg contents on intraspecific growth variation in domestic and wild birds. I assessed the way a suite of understudied maternally derived steroids interacts with early life environments in domesticated Japanese Quail (Coturnix japonica) by exposing fertile quail eggs to 24 hours of light or 12 hours of light (followed by 12 hours of darkness) throughout incubation and assessing hormone concentration changes across incubation and embryonic growth to ~2 days pre-hatch (Chapter 2). Steroid hormone concentrations declined with development and this decline was more pronounced in the eggs exposed to 12 hours of light on/off, but embryonic size on Day 15 was not affected by light treatment. In Chapter 3, I determined whether and how the timing of exposure to elevated yolk steroids testosterone and androstenedione affected quail embryonic size by injecting a biologically relevant dose of an androgen hormone cocktail or an oil control into eggs at Day 0 and Day 6 of incubation in a factorial design. Hormone injection did not elevate yolk androgens 24 hours after treatment, yet there was an effect of hormone injection treatment on the size of embryonic body parts that differed between sexes on Day 6, and by Day 15 the double androgen exposure (Day 0 and Day 6 injections) treatment impacted the size of some body parts (Chapter 3). In Chapter 4, I quantified the correlates of laying order on egg morphology and contents in wild American Robins (Turdus migratorius) and related laying order to embryonic growth. Laying order or interactions between laying order and time of year (early or late breeding season) predicted variation in egg size, yolk mass, yolk steroid and carotenoid concentrations, and eggshell color, but laying order did not predict embryo size ~4 days prior to hatch (Chapter 4). I then explored the effect of experimentally elevating the concentration of one steroid (DHEA) which varied with laying order in wild robin eggs (Chapter 4) on robin embryonic development (Chapter 5) by injecting a biologically relevant dose of DHEA or an oil control into freshly laid robin eggs of known laying order and measuring embryonic size at Days 6 and 9 of incubation. DHEA injection treatment interacted with egg size and laying order to influence growth to Day 6 of incubation, and DHEA injected eggs had lighter embryos with shorter headbills on Day 9 than oil injected eggs (Chapter 5). Once evidence indicated that robin eggs consistently vary with laying order, I performed a fostering experiment to test whether laying order influenced robin incubation duration, size at hatch, hatching asynchrony, and post-hatch growth (Chapter 6), constructing nests with fostered eggs of a single laying order or mixed laying orders and following resulting nestlings until fledge. Laying order did not impact incubation duration, size at hatch, or hatching asynchrony, but did predict post-hatch nestling growth, with first-laid eggs producing nestlings that reached peak mass gain and headbill growth slower than eggs of other laying orders (Chapter 6). Finally, I tested the effect of known drivers of growth variation in a wild bird species that experiences extreme variation in early life environments, the parasitic Brown-headed Cowbird (Molothrus ater), testing a novel hypothesis about the way cowbird growth is tuned to the full nesting period across diverse host species (Chapter 7). Cowbird nestling growth varied with host species, brood size, and cowbird nestling sex. Using previously published data on cowbird Day 8 mass, we determined size at Day 8 was predicted by the asynchrony between the hosts’ nesting (incubation and brooding) period and the average cowbird nesting period, with shorter host nesting periods producing larger cowbird nestlings.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125686

Copyright and License Information

Copyright 2024 S.K. Winnicki

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