An investigation of parasitism and the Immunocompetence Handicap Hypothesis in Red-winged Blackbirds (Agelaius phoeniceus)

Peadar Brehony -

That is the title of my Undergraduate Bachelor of Science Honours thesis, from back in 2011, while I was at University College Cork BEES.

A lot of work usually goes into an undergraduate honours thesis, and yet they are rarely read by more than yourself, your supervisor (that was the brilliant Dr. Tom Kelly for me), and sometimes by an external examiner (my thesis was reviewed by Prof. Robert (Bob) Furness).

Of course, students who have the time, energy, resources, and confidence can look to publish their thesis.

In my case, I used data that I collected with other colleagues (like my friend Dr. Tara Stewart) while I was studying at the University of California, Santa Barbara. The research was all part of a bigger project, led by Dr. Loren Merill and Prof. Steve Rothstein. The data I helped to collect, and which I used in my thesis, were subsequently published in two papers:

  • Merrill, L. et al. (2015) Epaulet size and current condition in red-winged blackbirds: examining a semi-static signal, testosterone, immune function, and parasites. Physiological and Biochemical Zoology, 88:11-21
  • Stewart, T.E.,* & L. Merrill. (2015) Host sex and parasitism in red-winged blackbird (Agelaius phoeniceus): examining potential causes of infection biases in a sexually dimorphic species. Canadian Journal of Zoology, 93:21-29

I, on the other hand, never got around to publishing my findings. I look back now wishing I had the kind of data analysis tools and skills I have developed since, to have another go at it. But oh well...

So instead, I'm posting the thesis abstract below, together with a link to download the full thing for anyone who might be interested... I'll be amazed if I get even one download!

Abstract

In order to investigate the highly debated immunocompetence handicap hypothesis (ICHH), this study examined secondary sexual signals, parasites and immune function in Red-winged Blackbirds (Agelaius phoeniceus). Secondary sexual signals investigated included body condition, physiological condition and epaulets. Parasites investigated included ectoparasites, endoparasites and blood parasites, and immune function tests included blood bacteria killing capacity, haemolysis and haemagglutination. Overall this study found that there were some significant intersexual differences in parasite infections, especially in endoparasites which occurred more often in males. In addition, there were no significant effects of parasites or immune function on signals related to either body condition or physiological condition. However, significant effects which show some support for the ICHH were found in the relationship between immune function, parasites and male epaulet areas. A similar relationship was also interestingly found in females, related to female epaulet scores. Overall, results seem to suggest that infection by ectoparasites has a significant effect on the expression of various secondary sexual signals. Further research, under controlled laboratory conditions are required for more significant conclusions relating to the ICHH.

The full thesis can be downloaded here.

Here are some of the figures from the thesis: