Date of Award

Spring 2023

Document Type

Open Access Dissertation


Biological Sciences

First Advisor

Carol L Boggs


Adaptation has been used as the framework to understand the power of natural selection in structuring biodiversity and driving biological interactions. However, recent examples have indicated that many organisms are maladapted to their local conditions. Maladaptation can result from various causes including rapid environmental change, novel environments, interplay of evolutionary forces (viz: gene flow-selection balance) and anthropogenic disturbance.

To dissect the genetic mechanisms underlying maladaptation, I used the interaction between Pieris macdunnoughii (Remington) (Lepidoptera: Pieridae) which lays eggs on an invasive mustard Thlaspi arvense (L.) (Brassicaceae), which is lethal to the larvae.

First, local adaptation to avoid laying eggs on or adapt to feed on T. arvense could be dampened by maladaptive gene flow. To evaluate this, I used a population genomics approach to identify population structure, quantify gene flow, and identify signatures of local adaptation. I found signatures of local adaptation in the face of rampant gene flow highlighting the potential of adaptation to occur in a fine-grained landscape.

Second, maladaptation in this system could arise due to underlying genetic differences in females preferring T. arvense to the native plant and differences in the larvae that fed on the toxic plant. Using a transcriptomic approach, I elucidated that the females preferring T. arvense and the native host plant had similar gene expression profiles. However, gene expression differences between the larvae reflected host-plant specific changes suggesting signs of impaired feeding on T. arvense. Thus, I was able to identify that selection would likely act on larval ability to feed on T. arvense rather than females' ability to differentiate the hostplants.

Finally, the rate of adaptation and hostplant range could be related to the underlying rate of evolution and size of gene families related to detoxification enzymes along with those underlying gustatory and olfactory genes. I used a comparative phylogenomic approach to quantify gene family evolution of genes involved in plant compound detoxification and sensory genes between specialist and generalist brassicaceous feeders to address the causes of hostplant range and specialization. I found that gustatory and olfactory genes had a higher rate of gene evolution compared to other genes and genes related to detoxification evolved faster in generalist feeders compared to specialist feeders thus indicating that generalist feeders are more likely to incorporate new host plants in their diet compared to specialist feeders.


© 2023, Nitin Ravikanthachari

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