CISAB Speaker| Marlene Zuk

C E N T E R F O R T H E I N T E G R A T I V E S T U D Y O F A N I M A L B E H A V I O R

S P E A K E R S E R I E S

Marlene Zuk

Professor
Department of Biology
University of California - Riverside

Immunity, Sexual Selection and Life History

Guest Lecture for Spring 2001 Graduate Seminar:
Interdisciplinary Seminar in Animal Behavior | International Hamilton Symposium

ABSTRACT:
For the latter half of his life, Bill Hamilton was virtually obsessed with parasites. He suggested that the continual barrage of insults by pathogens large and small could keep sexual reproduction advantageous in long-lived multicellular organisms, and later became convinced that parasites held the answer not only to the question of sex itself, but to the extraordinary elaborations that accompanied it. Several studies have shown that indeed, parasites affect those traits which females use to make mate choice decisions, and that females prefer males resistant to disease. In a larger sense, this focus on parasites fits into a more general view of the importance of disease in evolution. Disease resistance should be closely linked to fitness in many organisms, which makes understanding how animals resist infection, and under what circumstances they remain susceptible, crucial. Because infection is resisted via the immune system, studying immune response as a life history character can be very valuable. For example, in red jungle fowl, immune response is linked to ornamentation, but males of different quality pay different costs to maintain both traits. When placed in small flocks, high quality males with large combs become dominant and even increased their comb size, as well as having more robust immune responses. The disparity between males that achieved dominance and those that became subordinate was only exacerbated by being placed in a presumably more stressful social environment. Invertebrates such as Drosophila may more clearly exhibit a direct phenotypic trade-off between male sexual activity and the immune response, which supports the view that immune system function and levels of disease susceptibility are traits shaped by trade-offs with other costly fitness components. Parasites can thus act in a range of situations to influence sexual traits.

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