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Uncoupling clutch size, prolactin, and luteinizing hormone using experimental egg removal
Calen P Ryan1, Alistair Dawson2, Peter J Sharp3
1Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada.
General and Comparative Endocrinology
|February 18, 2015
Summary
This study investigated the role of prolactin (PRL) in avian clutch size determination. Results indicate PRL does not directly control clutch size but may coordinate incubation with clutch completion in female birds.
Area of Science:
- Avian reproductive physiology
- Endocrinology
- Animal behavior
Background:
- Clutch size is a critical factor in avian fitness and life history.
- A long-standing physiological model suggests prolactin (PRL) suppresses luteinizing hormone (LH) to determine clutch size, but experimental evidence is limited and equivocal.
- Recent studies, including pharmacological manipulation of PRL in zebra finches, have not supported this hormonal role in clutch size determination.
Purpose of the Study:
- To experimentally test the proposed physiological model of clutch size determination (CSD) involving prolactin (PRL) and luteinizing hormone (LH).
- To investigate the relationship between PRL, LH, and clutch size by manipulating clutch size through egg removal and experimentally extended laying in zebra finches.
- To explore alternative roles for PRL in avian reproduction, specifically in coordinating incubation with clutch completion.
Main Methods:
- Experimental manipulation of clutch size via egg removal in zebra finches.
- Measurement of prolactin (PRL) and luteinizing hormone (LH) levels during different reproductive stages.
- Analysis of hormonal co-variation with clutch size changes and clutch completion.
Main Results:
- Increasing clutch size through egg removal did not alter PRL or LH levels, contradicting key predictions of the PRL-based CSD model.
- No significant differences in PRL were observed between experimental and control groups, nor did PRL levels predict clutch size.
- A positive correlation was found between late-laying PRL levels and the timing of clutch completion, suggesting a role in coordinating incubation.
Conclusions:
- The study provides evidence against a direct role for PRL and LH in determining clutch size in zebra finches.
- Findings suggest PRL may function in coordinating the onset of incubation with the completion of laying to optimize hatching synchrony.
- This hormonal coordination is potentially amplified in females that lay larger clutches, influencing reproductive success.
