Speciation and hybridisation in skuas (Catharacta spp.) [Elektronische Ressource] / von Markus Ritz

Denise Toros-Marter

Informations

• Publié par: friedrich-schiller-universitat_jena
• Publié le: 01 janvier 2009
• Nombre de lectures: 145
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Mixed pair of South Polar Skua male (left) and Brown Skua female





Speciation and hybridisation in skuas (Catharacta spp.)




Dissertation

zur Erlangung des akademischen Grades doctor rerum naturalium
(Dr. rer. nat.)






vorgelegt dem Rat der Biologisch-Pharmazeutischen Fakultät
der Friedrich-Schiller- Universität Jena am 4.12.2008
und am 16.3.2009 verteidigt

von Diplom-Biologe Markus Ritz
geboren am 17.08.1976 in Dresden

Gutachter:
Prof. Stefan Halle, Jena
Prof. Gerald Heckel, Bern, Schweiz
Prof. Peter de Knijff, Leiden, Niederlande
Markus Ritz: Speciation and hybridisation in skuas
CONTENT
INTRODUCTION ............................................................................................................................ 1
Speciation and hybridisation .................................................................................................. 1
Phylogeography and glaciation .............................................................................................. 3
Skua diversity ......................................................................................................................... 4
Hybridisation between southern skua taxa ............................................................................. 7
AIMS OF THE STUDY .................................................................................................................... 8
MANUSCRIPT 1 .......................................................................................................................... 10
Ritz, M.S., Millar, C., Miller, G.D., Phillips, R.A., Ryan, P., Sternkopf, V., Liebers-
Helbig, D. & Peter, H-U. (2008) Phylogeography of the southern skua complex – rapid
colonization of the southern hemisphere during a glacial period and reticulate evolution.
Molecular Phylogenetics and Evolution 49(1): 292-303
MANUSCRIPT 2 .......................................................................................................................... 23
Votier S.C., Kennedy M., Bearhop S., Newell R.G., Griffiths K., Whitaker H., Ritz M.S.
& Furness R.W. (2007) Supplementary DNA evidence fails to confirm presence of
Brown Skuas Stercorarius antarctica in Europe: a retraction of Votier et al. (2004). Ibis
149(3): 619-621
MANUSCRIPT 3 .......................................................................................................................... 27
Ritz M.S., Hahn S., Janicke T. & Peter H.-U. (2006) Hybridisation between South polar
skua (Catharacta maccormicki) and Brown skua (C. antarctica lonnbergi) in the
Antarctic Peninsula region. Polar Biology 29(3): 153-159
MANUSCRIPT 4 .......................................................................................................................... 35
Ritz M.S. & Peter H.-U. (re-submitted to Molecular Ecology on 30.11.2008) Hybrid
identification using AFLP markers in a hybrid zone between two recently diverged
seabird species – strong admixture and biased gene flow
DISCUSSION ............................................................................................................................... 61
Methods ................................................................................................................................ 61
Phylogeographic study (manuscript 1) ............................................................................ 61
SNP between South Polar Skua and all other southern skuas (manuscript 2) ................ 62
Hybrid zone description (manuscript 3) ........................................................................... 63
AFLP hybrid assignment (manuscript 4) ......................................................................... 63
Phylogeography of southern hemisphere skuas ................................................................... 65
Mitochondrial mutation rate ............................................................................................ 65
Colonisation of the southern hemisphere 66
Diversification of the southern skua complex .................................................................. 66
Glaciation and skua diversification ................................................................................. 68
Speciation mode ............................................................................................................... 68
Educated guesses concerning the skua enigma ................................................................ 68
Hybridisation between South Polar Skua and Brown Skua ................................................. 69
Hybrid zone characterisation ........................................................................................... 69
Preliminary fitness aspects ............................................................................................... 70
Degree of admixture and direction of introgression ........................................................ 71
Mate choice in skuas ........................................................................................................ 72
Taxonomic status of southern skuas ................................................................................. 73
OPEN QUESTIONS, ONGOING PROJECTS ...................................................................................... 75
SUMMARY ................................................................................................................................. 77
ZUSAMMENFASSUNG ................................................................................................................. 79
REFERENCES ............................................................................................................................. 81

Markus Ritz: Speciation and hybridisation in skuas Introduction
INTRODUCTION

Speciation and hybridisation

Speciation, the process of species formation, is a central topic in evolutionary biology. Whilst
the foundations of evolution, variability and selection, were quickly accepted amongst
scientists after the publication of “On the origin of species” (Darwin 1859), it proved much
harder to find how species actually diverge and evolve into distinct groups. One reason is that
the emergence of a new species can usually not be observed during time scales comparable to
a researcher’s career. Studies on speciation will thus have to try to reconstruct the past or to
confine to a specific stage in speciation. This raises the question at which stage two taxa can
be called separate species. So, Darwin went too far in his conclusions in the “Origin” that by
studying evolution “… we shall at least be freed from the vain search for the undiscovered
and undiscoverable essence of the term species.” Whilst it is now widely accepted that taxa
are variable and it is worthwhile to study biodiversity irrespective of the level of variation (e.g.
genera, species, subspecies, ecotypes,…), there are still reasons to adopt a definition for
“species” (Coyne and Orr 2004). Most scientists agree that species are real entities in nature
and not human constructs to classify organisms. However, in compliance with the saying that
“ in a room with ten evolutionary biologists you will hear at least eleven different species
concepts” I will not discuss any of the numerous species concepts but only describe the
“comprehensive biologic species concept” (CBSC, Johnson et al. 1999) which was introduced
with special emphasis on birds. It is a broader version of the biological species concept
(Dobzhansky 1937, Mayr 1942) and accounts for the observed stability of species in spite of
hybridisation. According to the CBSC an avian species “…is a system of populations
representing an essentially monophyletic, genetically cohesive, and genealogically
concordant lineage of individuals that share a common fertilisation system through time and
space, represent an independent evolutionary trajectory, and demonstrate essential but not
necessarily complete reproductive isolation from other such systems.”

Three main routes to speciation have been described based on the geographic circumstances
during divergence. Sympatric speciation assumes that divergence takes place within a
population due to for example disruptive selection. Numerous models have been developed to
explore the conditions under which sympatric speciation may occur (e.g. Higashi et al. 1999,
1 Markus Ritz: Speciation and hybridisation in skuas Introduction
Via 2001, Kirkpatrick and Ravigne 2002, Gavrilets 2003). The very restrictive conditions
allowing for evolution of reproductive isolation in the presence of gene flow argue against
sympatric speciation being a common mode of speciation in animals. Some scientists even
deny the possibility of sympatric speciation but a few model groups are discussed as
candidates for divergence in the presence of gene flow (Coyne and Orr 2004, Bolnick and
Fitzpatrick 2007). Parapatric speciation describes the process, where upon a taxon evolves
into two taxa with adjacent ranges. This is a likely scenario if the species has a wide range
with ecological breaks. Taxa may then diverge along an ecotone or perhaps a migratory divide.
The resulting