Nürnberger, Beate; Barton, Nick HISTA ; Maccallum, Catriona; Gilchrist, Jason; Appleby, Michael
Observations on the means, variances, and covariances of quantitative traits across hybrid zones can give information similar to that from Mendelian markers. In addition, they can identify particular traits through which the cline is maintained. We describe a survey of six traits across the hybrid zone between Bombina bombina and Bombina variegata (Amphibia: Discoglossidae) near Pescenica in Croatia. We obtained laboratory measuments of the belly pattern, skin thickness, mating call, skeletal form, egg size, and the developmental time of tadpoles. Although offspring from hybrid populations showed no evidence of reduced viability, a third of the F1 families failed completely, irrespective of the direction of the cross. All traits differed significantly between the taxa. Clines in belly pattern, skin thickness, mating call, and skeletal form were closely concordant with clines in four diagnostic enzyme loci. However, the cline in developmental time was displaced towards bombina, and the cline in egg size was displaced towards variegata. This discordance could be because the traits are not inherited additively or because they are subject to different selection pressures. We favor the latter explanation in the case of developmental time. We show that moderate selection acting directly on a trait suffices to shift its position; rather stronger selection is needed to change its width appreciably. Within hybrid populations, there are significant associations among quantitative traits, and between traits and enzymes. Phenotypic variances also increase in hybrid populations. These observations can be explained by linkage disequilibria among the underlying loci. However, the average magnitude of the covariance between traits is about half that expected from the linkage disequilibria between enzyme loci. The discrepancy is not readily explained by nonadditive gene action. This puzzle is now unresolved and calls for further investigation.
The project would not have been possible without F. Perovic's extensive knowledge of the natural history of the Pegdenica area, and his assistance in the field. Particular thanks are due to the Perovie family for their generous hospitality. The Croatian Museum of Natural History and the Croatian Ministry of the Environment were helpful in granting all the necessary permits. J. Szymura assisted with allozyme tech-niques and in sharing unpublished data from his original survey of the area. M. Davidson and K. Grant prepared the histological specimens, and G. Patterson volunteered time and expertise in X-raying our toads. All members of L. Partridge's lab generously provided us with toad food on a daily basis, in the form of uncountably many spare Drosophila. G. Malarky and M. Oh stoically coped with much tedious toad care. We thank W. G. Hill, L. Kruuk, D. Rand, J. Szymura, and an anonymous reviewer for helpful comments on the manuscript. This research was supported by a grant from the Natural Environment Research Council (GR3/8002) to N.B.
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Nürnberger B, Barton NH, Maccallum C, Gilchrist J, Appleby M. Natural selection on quantitative traits in the Bombina hybrid zone. Evolution. 1995;49(6):1224-1238. doi:10.1111/j.1558-5646.1995.tb04449.x
Nürnberger, B., Barton, N. H., Maccallum, C., Gilchrist, J., & Appleby, M. (1995). Natural selection on quantitative traits in the Bombina hybrid zone. Evolution. Wiley-Blackwell. https://doi.org/10.1111/j.1558-5646.1995.tb04449.x
Nürnberger, Beate, Nicholas H Barton, Catriona Maccallum, Jason Gilchrist, and Michael Appleby. “Natural Selection on Quantitative Traits in the Bombina Hybrid Zone.” Evolution. Wiley-Blackwell, 1995. https://doi.org/10.1111/j.1558-5646.1995.tb04449.x.
B. Nürnberger, N. H. Barton, C. Maccallum, J. Gilchrist, and M. Appleby, “Natural selection on quantitative traits in the Bombina hybrid zone,” Evolution, vol. 49, no. 6. Wiley-Blackwell, pp. 1224–1238, 1995.
Nürnberger B, Barton NH, Maccallum C, Gilchrist J, Appleby M. 1995. Natural selection on quantitative traits in the Bombina hybrid zone. Evolution. 49(6), 1224–1238.
Nürnberger, Beate, et al. “Natural Selection on Quantitative Traits in the Bombina Hybrid Zone.” Evolution, vol. 49, no. 6, Wiley-Blackwell, 1995, pp. 1224–38, doi:10.1111/j.1558-5646.1995.tb04449.x.
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