Sexual selection, genetic differentiation and reproductive isolation in birds
Description of Project:
Detailed population genetic studies and DNA-barcoding have identified two species in the avian sub-family Saxicolinae with highly divergent patterns of genetic and morphological differentiation and varying degree of reproductive isolation (the bluethroat Luscinia svecica, the common redstart Phoenicurus phoenicurus). This project will investigate patterns of genetic and morphological differentiation in this bird group in detail, using a combination of field experiments, molecular methods and measurements of study skins in museum collections. The project consists of two main parts: (1) investigating phylogeographic patterns of the redstarts, and (2) performing experiments on the possible role of a sexually selected character in subspecies discrimination in one of these species, the bluethroat.
Part one: Phylogeography of the redstart
Redstarts and bluethroats show highly divergent patterns of genetic and morphological differentiation, and have a varying degree of reproductive isolation. Bluethroats show high morphological divergence and low genetic divergence, while redstarts show little or no morphological divergence combined with high genetic divergence.
Previous studies of the bluethroat, based on the mitochondrial control region, cytochrome b gene, DNA-barcoding of the mitochondrial COI gene and sequencing of three nuclear Z-linked introns, have shown little genetic support for the subspecies (Questiau et al. 1998, Zink et al. 2003, Johnsen, unpublished data). However, some support has been found based on microsatellite allele frequency variation (Johnsen et al. 2006). Redstarts show a contrasting pattern compared to the bluethroats. They show a deep split within their ranges, but they have no known morphological differentiation or reproductive isolation. The redstarts have well-defined haplotype groups that are interbreeding in Europe today (Johnsen et al. 2010).
Main focus: A phylogeographic history of the redstarts will be reconstructed in order to identify their areas of origin, and their dispersal patterns. DNA will be extracted from skin collections and freshly collected blood samples in order to do these analyses. We will try to explain the different patterns mentioned above. Are the patterns seen in the bluethroats due to more recent genetic divergence than those seen in the redstarts? Previous studies have suggested that sexual selection has acted differently in the bluethroat and redstart (Johnsen et al. 2001, Kleven et al. 2007). The bluethroat show signs of stronger sexual selection which might explain a faster rate of differentiation than the redstart.
A second goal of this project will be to investigate possible isolation mechanisms (such as assortative mating and differences in sperm morphometrics) between the two haplotypes of the redstart. Here, three different subpopulations will be used; from Norway, Czech Republic (in collaboration with Jiri Porkert) and Turkey (in collaboration with Tamer Albayrak and Bekir Kabasakal).
Part two: Is throat spot colorations a sexually selected subspecies discrimination cue in bluethroat?
The Bluethroat consists of about ten morphologically distinct subspecies distributed in Europe, Asia and Alaska (Cramp 1988). The subspecies are distinguished by body size, and most strikingly by the ornamental plumage pattern and coloration of males (Johnsen et al. 2006). The central spot of the male throat patch shows a qualitative color variation (chestnut, white or absent), among subspecies. A study by Johnsen et al (2006) based on microsatellite variation shows a high degree of consistency between genetic differentiation and throat spot coloration suggesting that this character serves as a subspecies discrimination cue in areas of secondary contact. The male ornament is used by males for courtship display, and is a potential target for sexual selection.
Main focus: Do female bluethroats discriminate against males from a different subspecies based on throat spot coloration? This question will be answered by manipulating males in the Norwegian svecica population. The manipulated males will look like central European males of the cyanecula subspecies. If spot coloration functions as a subspecies recognition cue, then the manipulated males will have a lower mating success, and in the case where they do get a mate, they will get a lower paternity than control males. A female might choose to become socially paired with a male from the “wrong” subspecies in order to exploit his resources or because of constraints on mate searching. The female might attempt to adjust for this choice by being fertilized by a male of the right subspecies.
Johnsen A, Andersson S, Fernandez JG, Kempenaers B, Pavel V, Questiau S, Raess M, Rindal E, Lifjeld JT (2006) Molecular and phenotypic divergence in the bluethroat (Luscinia svecica) subspecies complex. Mol. Ecol. 15:4033-4047
Johnsen A, Lifjeld JT, Andersson S, Örnborg J, Amundsen T (2001) Male characteristics and fertilization success in bluethroats. Behaviour 138:1371-1390
Johnsen A, Rindal E, Ericson P, Zuccon D, Kerr K, Stoeckle M, Lifjeld J (2010) DNA barcoding of Scandinavian birds reveals divergent lineages in trans-Atlantic species. J. Ornithol. in press
Kleven O, Øigarden T, Foyn BE, Moksnes A, Røskaft E, Rudolfsen G, Stokke BG, Lifjeld JT (2007) Low frequency of extrapair paternity in the common redstart ( Phoenicurus phoenicurus ). J. Ornithol. 148:373-378
Questiau S, Eybert MC, Gaginskaya AR, Gielly L, Taberlet P (1998) Recent divergence between two morphologically differentiated subspecies of bluethroat (Aves: Muscicapidae: Luscinia svecica) inferred from mitochondrial DNA sequence variation. Mol. Ecol. 7:239-245
Zink RM, Drovetski SV, Questiau S, Fadeev IV, Nesterov EV, Westberg MC, Rohwer S (2003) Recent evolutionary history of the bluethroat (Luscinia svecica) across Eurasia. Mol. Ecol. 12:3069-3075