Nancy T. BurleyProfessor, Ecology & Evolutionary Biology |
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| URL | ecoevo.bio.uci.edu/Faculty/Burley/Burley.html | |
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Research Abstract |
My research focuses on the mate choice component of sexual selection. The importance of mate choice in the evolution of bright coloration, sexual dimorphism, and intraspecific signaling has been debated since Charles Darwin (1871) suggested that many secondary sexual traits evolved through the latent "aesthetic" mate preferences of females. Since that time, alternative hypotheses have been advanced (g.g., runaway selection - Fisher 1930; "good genes" models - Zahavi 1977; Hamilton & Zuk 1982; Kodric-Brown & Brown 1984), while I (e.g., Burley 1985; Burley & Symanski 1998) and others (e.g., Basolo 1990; Ryan et al. 1990) have amplified on Darwin's idea. The evolutionary significance of mate preferences remains a central question in social evolution. I work primarily on the zebra finch (Taeniopygia guttata) and related Australian grassfinches. This group of birds is socially monogamous, shows substantial biparental care of altricial young, and most species are gregarious and non-territorial. The zebra finch is one of the more sexually dichromatic estrildines: males have several plumage markings that females typically lack entirely; they have additional markings that are more striking than those of females; and males tend to have redder beaks than females, but there is considerable overlap between the sexes in expression of this trait (Burley & Coopersmith 1987). Coworkers and I have studied mate preferences for beak color, a trait that shows great natural variation. Both wild and captive-reared female zebra finches prefer males with bright red beaks, whereas males prefer females with yellow-orange beaks (Burley & Coopersmith 1987; 1999). In captive colonies, individuals of both sexes having preferred phenotypes gain high reproductive success (Price & Burley 1994). Heritability of beak color is maintained in part by the opposing sexual selection on the sexes (Price & Burley 1993). Zebra finch beak color appears to be an example of a trait whose expression is constrained by lack of a good mechanism of sex-limited expression. Thus, beak color expression has not reached an evolutionary equilibrium. We have also identified mate preferences for traits/trait values that do not exist. Both sexes of zebra finches have preferences for certain novel leg band colors, and aversions to other colors (Burley et al. 1982; Burley 1985; Burley 1986). Two other species of grassfinches have also been shown to respond to novel band color traits. In captive breeding colonies, birds with attractive band colors have high social parentage and low parental investment (Burley 1988). Attractive, red-banded male zebra finches also achieve high rates of "unforced" extra-pair copulation and extra-pair fertilization (Burley et al. 1996). These results imply that novel attractive traits have high potential to evolve through via latent aesthetic mate preferences. Presently, research in my lab focuses on the preferences of female grassfinches for males wearing artificial white crests (Burley & Symanski; 1998; see Figure). Although there are no crested species among extant estrildine finches (nearly 300 species world-wide), crests have evolved in many avian orders and in many passerine families. In the two species whose preferences have been studied, females reared with wild-type parents prefer males wearing white crests, but are not attracted to males wearing other colors of crests. Normally reared male zebra finches prefer uncrested females; they find white-crested females unattractive. Recently we have begun exploring the possibility that strength of preference for white crests is influenced by parental phenotype. Results to date indicate that males respond to maternal phenotype. Males reared with white-crested mothers adopt the preferences for white crests; but if they are instead reared with grey-crested mothers, they prefer grey crests. Males, simply put, prefer to mate with a female that closely resembles their mother! Females do not show this "sexual imprinting" response. Females prefer white-crested males regardless of whether their own father was uncrested, white-crested, or grey-crested. Current and planned research investigates the significance of these hypotheses generated from the theories of sexual selection and optimal outcrossing. The goal is to understand the role of early learning on the development of mate preferences, and why sex differences in tendency to display sexual imprinting occur. We are also beginning to explore the heritability of mate preferences of female zebra finches for both beak color and white crests. The strength of these preferences shows considerable variability and tend to "run in families". If significant heritability of preferences is detected, long-range plans include mapping of quantitative trait loci (QTLs) for preference traits collaboration with Dr. Tony Long of this department. |
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| Publications |
Burley, N.T. & C.B. Coppersmith. 1999. Redundant signals or multiple messages?: Beak color, song rates, and the design of zebra finch "mate choice" experiments. Animal Behavior. |
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| Burley N.T. & R. Symanski. 1998. "A taste for the beautiful": latent aesthetic mate preferences for white crests in two species of Australian grassfinches. The American Naturalist 152:792-802. | ||
| Parker, P.G. & N.T. Burley, eds. 1997. Avian Reproductive Tactics: Female and Male Perspectives. Ornithological Monographs #49, American Ornithologists' Union, Washington, D.C. | ||
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Burley, N.T., P.G. Parker, & K. Lundy. 1996. Sexual selection and extra-pair fertilization in a socially monogamous passerine, the zebra finch (Taeniopygia guttata). Behavioral Ecology 7:218-226. |
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| Price, D.K. & N.T. Burley. 1994. Constraints on the evolution of attractive traits: selection in male and female zebra finches. The American Naturalist 144:908-934. | ||
| Burley, N. 1988. The differential allocation hypothesis: an experimental test. The American Naturalist 132:611-628. | ||
| Link to this profile | http://www.faculty.uci.edu/profile.cfm?faculty_id=2138 | |
| Last updated | 02/22/2002 | |