Date of Award

Spring 4-23-2020

Semester of Degree

May

Document Type

Open Access Dissertation

Degree Name

Ph.D. in Environmental and Forest Biology

Department

Environmental and Forest Biology

Major Professor

Dylan Parry

Steering Committee Member

Melissa Fierke

Steering Committee Member

Kristine Grayson

Abstract

Climatic gradients result in life-history tradeoffs across diverse taxa. Studying range-expanding invasive species can offer insight to environmental conditions that drive adaptive responses. Insects, which have rapid generations and high fecundity, can adapt rapidly to novel or changing environmental conditions, making them ideal model organisms for studying evolution in situ. European gypsy moth was introduced to North America in 1869 near Boston, Massachusetts, USA, and has since expanded its range to occupy 12 ̊ of latitude and diverse thermal regimes. I investigated environmental drivers of adaptation across the latitudinal-climatic range of gypsy moth in North America.

I linked variation in wing length, a proxy for body size, of pheromone-trapped males to metrics of habitat quality including forest composition, phenology, and population density. I found support for previously reported seasonal phenology-linked decline in wing length in both endemic and outbreaking gypsy moth populations. Furthermore, I found significant differences in wing length between males from forests of different quality by using discrete forest quality estimates, but not using continuous metrics of forest quality. Mean wing length of males from outbreak populations was smaller on than those from endemic populations.

Male flight capacity is an important aspect of fitness, and has important implications for mate- finding and establishment success during range expansion. Using fixed-arm flight mills, I found that body size is the most important predictor for total flight distance and maximum speed, and forewing aspect and relative thorax mass also had a significant effect on flight capacity.

Using a reciprocal transplant study, I found evidence for adaptive shifts in hatch timing occurring in populations from across the latitudinal range of gypsy moth, which may serve to reduce asynchrony with budburst of preferred host tree species at latitudinal range margins. I demonstrated that fitness costs of hatching ahead of or behind red oak budburst may provide sufficient selective pressures to drive the change observed in natural populations.

The results herein may inform current gypsy moth management priorities, and identify knowledge gaps where future research can improve our understanding of the barriers to range expansion in gypsy moth and perhaps other invasive species.

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