Present address: Allan Wilson Centre for Molecular Ecology and Evolution, School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand.
Genetic drift outweighs balancing selection in shaping post-bottleneck major histocompatibility complex variation in New Zealand robins (Petroicidae)
Article first published online: 15 NOV 2004
Volume 13, Issue 12, pages 3709–3721, December 2004
How to Cite
MILLER, H. C. and LAMBERT, D. M. (2004), Genetic drift outweighs balancing selection in shaping post-bottleneck major histocompatibility complex variation in New Zealand robins (Petroicidae). Molecular Ecology, 13: 3709–3721. doi: 10.1111/j.1365-294X.2004.02368.x
- Issue published online: 15 NOV 2004
- Article first published online: 15 NOV 2004
- Received 11 June 2004; revision received 9 September 2004; accepted 9 September 2004
- balancing selection;
- black robin;
- class II B MHC;
- gene conversion;
- genetic variation
The Chatham Island black robin, Petroica traversi, is a highly inbred, endangered passerine with extremely low levels of variation at hypervariable neutral DNA markers. In this study we investigated variation in major histocompatibility complex (MHC) class II genes in both the black robin and its nonendangered relative, the South Island robin Petroica australis australis. Previous studies have shown that Petroica have at least four expressed class II B MHC genes. In this study, the sequences of introns flanking exon 2 of these loci were characterized to design primers for peptide-binding region (PBR) sequence analysis. Intron sequences were comprised of varying numbers of repeated units, with highly conserved regions immediately flanking exon 2. Polymerase chain reaction primers designed to this region amplified three or four sequences per black robin individual, and eight to 14 sequences per South Island robin individual. MHC genes are fitness-related genes thought to be under balancing selection, so they may be more likely to retain variation in bottlenecked populations. To test this, we compared MHC variation in the black robin with artificially bottlenecked populations of South Island robin, and with their respective source populations, using restriction fragment length polymorphism analyses and DNA sequencing of the PBR. Our results indicate that the black robin is monomorphic at class II B MHC loci, while both source and bottlenecked populations of South Island robin have retained moderate levels of variation. Comparison of MHC variation with minisatellite DNA variation indicates that genetic drift outweighs balancing selection in determining MHC diversity in the bottlenecked populations. However, balancing selection appears to influence MHC diversity over evolutionary timescales, and the effects of gene conversion are evident.