Maria Faye Parmer
A Comparison of Immunological Parameters in Two Recently Diverged Songbird (Junco hyemalis) Populations following a Unique Colonization Event.
BSES Senior Research Project 2008

Abstract

In the early 1980’s, an isolated population of dark-eyed juncos (Junco hyemalis thurberi), previously confined to a montane environment, became established in the coastal environment of the campus of the University of California San Diego (UCSD). Since then, the coastal juncos have diverged from the native-range juncos in various life-history traits and behaviors, including many traits associated with the hormone testosterone (T), and preliminary data suggests that males from the mountain population have higher levels of T. Expression of T has been casually implicated in the regulation of immune function, with less T corresponding to investment away from the mating effort and toward immunity and overall survival. As such, it is hypothesized that there will be differences in innate immunity between male juncos from the two populations. To test this, blood samples were taken from male juncos from each population during incubation and nestling stages, and leukocyte analyses, including total leukocyte count, heterophil to lymphocyte ratio, and identification of any parasites, were completed from hematological slides. After controlling for various factors known to affect avian lymphocyte counts, the colonist juncos were found to have higher total white blood cell counts, while no difference was found between the two populations in the heterophil:lymphocyte ratio or presence of parasites. Ongoing research of additional parameters of immune function in both sexes will further clarify how the physiology of the colonist birds has responded to the novel environment. In the broader sense, this study will serve to help characterize how individuals and populations respond to novel environments and selection pressures. Such understanding is increasingly important in an age of rapid anthropogenic climate change and habitat alteration.