1	White-throated Sparrow (Zonotrichia albicollis): Biology of Color Morphs Art McMorris DVOC April 1, 2004
2	Adult White-throated Sparrows occur in two different color morphs: White-striped and Tan-striped. Half of adult birds are of each color morph, regardless of sex. (Photos were shown at DVOC meeting.) Color differences are summarized as follows:
3	Morphological differences are associated with a chromosomal difference.
4	Behavioral differences
5	Mate choice Expected: 1:2:1 ratio of (TSxTS),(TSxWS),(WSxWS) Observed: over 95% of mated pairs are Tan-striped x White-striped Negative assortative mating (each bird prefers a mate of the opposite color morph) Offspring of TSxWS pairs are 1/2 TS and 1/2 WS
6	Biological consequences of negative assortative mating
7	Questions: How does chromosomal rearrangement result in morphological and behavioral differences? For reasons discussed at the meeting, structural rearrangements of chromosomes can result in complex and pervasive changes in the activity of many genes and gene products. The specific changes that occur in White-throated Sparrows are not known. Why do birds choose mates of the opposite morph? Although many hypotheses have been advanced, the answer to this question is not known with any certainty. However, the answer may lie in behavioral factors which make same-morph matings incompatible. White-striped birds are very aggressive and fight between themselves, possibly making WS x WS pairings unstable. Tan-striped birds exhibit reduced territorial behavior, and TS x TS pairs have difficulty keeping possession of a territory; this would weaken the pair bond. Occasionally, however, both of these pairings do occur, and they succeed in fledging young.
8	Unique among birds: Balanced chromosomal polymorphism Morphological polymorphism Behavioral polymorphism Negative assortative mating
9	References 1. Falls, J.B., and Kopachena, J.G., 1994. White-throated Sparrow (Zonotrichia albicollis). In The Birds of North America. No. 128 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithhologists’ Union. 2. Kopachena, J.G., and Falls, J.B., 1993a. Re-evaluation of morph-specific variations in parental behavior of the White-throated Sparrow. Wilson Bull. 105: 48-59. 3. Kopachena, J.G., and Falls, J.B., 1993b. Aggressive performance as a behavioral correlate of plumage polymorphism in the White-throated Sparrow (Zonotrichia albicollis). Behaviour 124: 249-266. 4. Lowther, J.K., 1961. Polymorphism in the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Can. J. Zool. 39: 281-292. 5. Thorneycroft, H.B., 1966. Chromosomal polymorphism in the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Science 154: 1571-1572. 6. Thorneycroft, H.B., 1975. A cytogenetic study of the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Evolution 29: 611-621.