Biological Sciences, School of


Date of this Version

Spring 5-17-2014



A DOCTORAL DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Sciences (Ecology, Evolution, and Behavior), Under the Supervision of Professors Brigitte Tenhumberg & Jennifer A. Brisson. Lincoln, Nebraska: May, 2014

Copyright (c) 2014 Swapna R. Purandare


Organisms use environmental cues to gather information required to perform activities that are essential for their survival and reproduction, such as searching for food, avoiding danger, and finding mates. They respond to the acquired information by changing their behavior or physiology, which may result in increased fitness. Due to the fundamental importance of information in an organism’s life, it is important to understand its acquisition, processing, and the organism’s response to it. In the work presented here, we used the pea aphid (Acyrthosiphon pisum), an insect that produces multiple phenotypes, or morphs, that are genetically identical, but differ in morphology, ecology, and behavior, as a model system for investigations into sensory ecology and gene evolution.

First, we examined the influence of aphid honeydew, a prey-associated cue, on the interactions between pea aphids and their ladybird predators. We found that the honeydew influenced the foraging behavior of predator larvae, but the larvae were not able to distinguish between the honeydew of high and low nutritional quality prey. Next, we compared the wing polyphenic response of pea aphids to two factors that are potential indicators of poor habitat - predator cues and crowding. The wing polyphenic response occurs when wingless pea aphids produce winged offspring in response to environmental stress. We found that the intensity of the wing polyphenic response of pea aphids to crowding was much stronger than their response to predator cues, suggesting pea aphids acquire and process information from different cues to assess environment quality and differentially respond to it.

Thirdly, we compared chemosensory gene expression between different pea aphid morphs to investigate weather the chemosensory system changes with morph specialization. We found distinct chemosensory gene expression profiles of the pea aphid morphs that indicated intraspecific specialization of chemosensory systems. Finally, we compared the rates of evolution of morph-biased genes (genes highly expressed in one morph compared to the other morphs) with unbiased genes to explore the evolutionary consequences of phenotypic plasticity. Our results illustrated that morph-biased genes evolve faster than unbiased genes as a result of relaxed purifying selection.

Advisors: Brigitte Tenhumberg and Jennifer A. Brisson