I investigated the maternal effects that take place in a joint-nesting bird: the
smooth-billed ani. Female anis were shown to respond to increasing group size by
increasing the number of eggs produced per capita, by tossing and burying more eggs per
capita, and by taking longer to reach the dedicated incubation phase. These results
support the hypothesis that females respond to increased egg laying competition by trying
to skew the contents of the final incubated clutch of eggs in their own favor.
I showed that in ani groups, yolk testosterone and estradiol deposited by females
in eggs increased from early- to late-laid eggs. Increases in yolk steroid levels over the
laying sequence may function to mitigate the disadvantage of being a later-hatched chick.
This maternal influence may not be a mere reflection of a female's hormonal status as
female plasma circulating levels of testosterone and estradiol did not vary in the same
direction as yolk hormone profiles.
I showed that yolk corticosterone levels, an indicator of maternal physiological
stress, increased with laying order in multi-female groups, but not in single-female
groups. Results suggest that laying females experience higher levels of stress in multifemale
groups. The above results suggest that communal life in anis generates
competition and egg production waste that likely reduces short-term per capita
reproductive benefits. Female anis can vary egg quality via deposition of hormones in eggs, and also lay eggs of different sizes. I showed that circulating plasma testosterone levels were higher in
nestlings with better begging abilities. Furthermore, nestlings hatched from eggs laid late
in the laying sequence had better begging abilities. These results suggest that testosterone
is an important controlling mechanism of begging behaviour, and that female testosterone
depositions in eggs rave long lasting effects on offspring development and behavior. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/23512 |
| Date | 07 1900 |
| Creators | Schmaltz, Gregory U. |
| Contributors | Quinn, James S., Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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