Speciation in Ficedula flycatchers

 

Collared flycatcher. Photo credit Johan Träff

For sexually reproducing organisms, the development of reproductive isolation is considered a prerequisite for speciation. Research on speciation therefore aims to investigate how population divergence leads to the build up of reproductive isolation. We use a combination of ecological, behavioural and genomic studies in a natural hybrid zone between collared (Ficedula albicollis) and pied flycatchers (F. hypoleuca) in Sweden to approach this question.  These two species probably started to diverge in allopatry in glacial refugia of the Mediterranean area during the Pleistocene, candidate regions being the Iberian and Apennine peninsulas, respectively. Subsequent contact during repeated cycles of interglacial periods seems to have lead to periods of gene flow. Hybridization occurs in contemporary areas of sympatry, including the Swedish islands of Gotland and Öland.

We have concluded that;

  1. ecological differences are caused by divergence in life history traits,
  2. females prefer mates of their own species based on differences in both plumage and song characteristics,
  3. male plumage characteristics have diverged but their song has converged in sympatry,
  4. there is genetic incompatibility in accordance with Haldane’s rule, and
  5. the Z- chromosome, telomeres and centromeres are hotspots for genomic divergence.

Collaboration between three UCEG labs (Qvarnström, Ellegren and Ahlberg) currently aims to pinpoint the genetic regulation of development forms that connect heritable molecular variation (e.g. of allele frequencies) with the phenotypic variation that is the primary target of selection. Until now, studies on ecology are generally weakly integrated with studies on developmental biology, but our research will fully integrate the causal links between gene expression, developmental patterns and ecological adaptation.

Selected publications

Nadachowska-Bryzska, K., Burri, R., Olason P.I., Kawakami, T., Smeds, L., and Ellegren. 2012. Demographic divergence history of pied flycatcher and collared flycatcher inferred from whole-genome re-sequencing data.  PLOS Genetics 9 (11): e1003942

Ålund, M. Immler, S, Rice, A.M. and Qvarnström, A. 2013. Low fertility of wild hybrid male flycatchers despite recent divergence. Biology Letters 9: 20130169.

Ellegren, H., Smeds, L., Burri, R., Olason, P.I., Backström, N., Kawakami, T., Kunstner, A., Makinene, H., Nadachowska-Brzyska, K, Qvarnström, A., Uebbing, S., Wolf, J.B.W. 2012. The genomic landscape of species divergence in Ficedula flycatchers. Nature  491: 756-760

Qvarnström, A. Rice, A and Ellegren, H. 2010. Speciation in Ficedula flycatchers. Philosophical Transactions of the Royal Society London. B, 365, 1841-1852.

Sæther, S.A, Sætre, G-P., Borge, T., Wiley, C., Svedin, N. Andersson, G., Veen, T., Haavie, J., Servedio, M., Bures, S., Kral, Hjernquist, M., Gustafsson, L, Träff, J.and Qvarnström.A.  2007.Sex chromosome-linked species recognition and evolution of reproductive isolation in flycatchers. Science318, 95-97. 

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