Marianne Davenport M.S. Thesis Defense

Published: April 13, 2020

The Department would like to congratulate Marianne on successfully defending her thesis.  Job well done!


Marianne Davenport

Masters Candidate in Dr. Ragland’s Lab
"Variability in Adult Reproductive Diapause of the Spruce Beetle, Dendroctonus rufipennis"
Organisms modify their life history strategies in highly variable environments, such as seasonally cycling temperature and precipitation. Many insects synchronize their life cycles with seasonally variable conditions by entering dormancy, or diapause, during unfavorable conditions while growing and reproducing during favorable conditions. Timing of diapause is particularly critical in determining voltinism, the number of generations per year. Because diapause induction is often environmentally sensitive, small changes in environmental conditions may change voltinism. Spruce beetle (Dendroctonus rufipennis), an eruptive forest pest, is often semivoltine (1generation/2yrs), but univoltinism (1gen/yr) has been observed in warm years, increasing population growth. There is a facultative, prepupal diapause that may flexibly produce univoltine or semivoltine life cycles, depending on temperature. Spruce beetles also enter an adult reproductive diapause that is typically assumed to be obligate. However, if aversion of adult diapause is possible, warming temperatures could produce more complex population dynamics. I tested whether beetles reared under atypically warm conditions could be flexibly induced to avert adult diapause. In summer of 2018, I cut infested spruce trees that were brought to lab and held at 22°C. Emerging beetles were collected and either scored for reproductive maturity or inserted into bolts with a mate to test for reproductive success.To determine how diapause terminates naturally in the field, I collected overwintering beetles during the winter of 2019 to score reproductive maturity. I found that indeed, a small but
statistically significant proportion of beetles can avert adult diapause and produce viable eggs without chilling, a trait that could potentially evolve and cause more rapid population growth. However, most beetles develop to reproductive maturity much more rapidly after relatively short exposures to cold temperatures in the field, providing an effective ‘brake’ enforcing mainly semi-voltinism under current field conditions. I discuss how warmer conditions may impact future population growth in light of these results.

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Meeting ID: 890 237 990