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White-throated sparrow gives insight into chromosomal rearrangement and behaviour
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Studies on the white-throated sparrow have given a rare insight into how a chromosomal rearrangement resulting in genetic polymorphism directly impacts behaviour in a vertebrate. The study, led by researchers in Emory University, was published in early edition this week in the Proceedings of that National Academy of Sciences in the United States of America (PNAS). It has linked differences in parenting and aggression behaviour in two different white-throated sparrow phenotypes to the oestrogen receptor ER-alpha.

The PNAS study examined white-throated sparrows (Zonotrichia albicollis) with two different, long-recognised phenotypes caused by a rearrangement in a chromosome sequence known as chromosomal polymorphism ZAL2/2m. This polymorphism results in two readily distinguishable forms of the sparrow, the tan-striped morph and the white-striped morph, respectively. The attached picture clearly shows how they can be distinguished by their plumage (copyright/credit Brent Horton, http://esciencecommons.blogspot.ie/2014/...ocial.html). Sparrows with the rearranged ZAL2m polymorphism (white-striped) are recognised to be more aggressive and less parental than the tan-striped birds.

In the study, parenting behaviour was assessed in the wild by monitoring frequency with which the birds returned to the nest to feed their young while aggression monitoring was based on analysis of song rate in the presence of a perceived threat to the sparrow’s territory. Such patterns of behaviour are thought to be mediated by sensitivity to sex steroids in vertebrates. An examination of the polymorphic region revealed various candidate genes, among them ESR1, the gene for oestrogen receptor ER-alpha. Levels of expression of this receptor affect sensitivity to sex hormones including testosterone. The study demonstrated that in the region of the ESR1 gene that controls its expression, known as the promoter, there were fixed differences (polymorphisms) between the tan-striped and white-striped birds. These polymorphisms affected the transcription of ESR1 in vitro. When expression of the ESR1 protein product, ER-alpha, was examined in brain regions associated with aggression, white-striped birds (the more aggressive ZAL2m polymorphism type) had three times the level of ER-alpha than the tan-striped birds. By correlating behavioural data and lab data, the researchers were able to show that expression of ER-alpha in that region and others predicted variation in territorial aggression and parenting.

This is an unusual example of a study being able to demonstrate directly how a chromosomal rearrangement causes behavioural difference in a vertebrate. The authors are currently examining a suite of further neuroendocrine genes captured by the chromosome rearrangement to examine their impact on behaviour.

Sources
HORTON, B.M., HUDSON, W.H., ORTLUND, E.A., SHIRK, S., THOMAS, J.W., YOUNG, E.R., ZINZOW-KRAMER, W.M. and MANEY, D.L., 2014. Estrogen receptor α polymorphism in a species with alternative behavioral phenotypes. Proceedings of the National Academy of Sciences. 2014 Jan; Available from: http://dx.doi.org/10.1073/pnas.1317165111.

Press release: http://esciencecommons.blogspot.ie/2014/...ocial.html

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White-throated sparrow gives insight into chromosomal rearrangement and behaviour00