Weak phylogenetic effects on ecological niches of Sylvia warblers

To understand the evolution of ecological niches it is important to know whether niche evolution is constrained by phylogeny. We approached this question for Sylvia warblers by testing if closely related species are more similar in 20 ecologically relevant morphological traits than distantly related species. Phylogenetic relatedness was quantified using a molecular phylogeny based on the mitochondrial cytochrome b gene. By Principal Component Analysis (PCA) two major niche axes were extracted. We tested the individual ecomorphological traits and the positions of the species on the PCA axes for phylogenetic effects using Mantel tests. The results demonstrated small but significant phylogenetic effects only for the length of the middle toe, a trait probably correlated with locomotion. In general, however, phylogenetic effects were very weak. This suggests that ecological niches in passerine birds have the potential to evolve rapidly and are not subject to major phylogenetic constraints.

Genetic differentiation and phylogeography of gulls in the Larus cachinnans-fuscus group (Aves: Charadriiformes)

We studied mitochondrial genetic differentiation among nine taxa of large gulls of the Larus cachinnans-fuscus group, which form part of the circumpolar Herring Gull complex. Our primary interest was to see if there were unrecognized gene flow barriers, to what extent mitochondrial genetic population structure conformed to current taxonomic boundaries, and what it might reveal about possible differences in population history. Sequences (430 nucleotides) of the hypervariable control region I (HVR-I) were obtained from 580 individuals and proved highly informative within this recently diverged group of birds. Contrary to current classification, a basal split was revealed between an Atlantic-Mediterranean clade (atlantis, michahellis, armenicus) and a NW Palearctic-Central Asian clade (cachinnans, barabensis, mongolicus, fuscus-group). There was almost no mitochondrial gene flow between these two groups, although they are in geographical contact in two areas (eastern North Atlantic, Black Sea). Within each of the two major groups, there was strong phylogeographic structure with gene flow barriers between some neighbouring taxa (e.g. cachinanns vs. barabensis), but also a case of poor genetic differentiation between phenotypically distinct forms (barabensis vs. heuglini). At the subspecies level, current taxonomy corresponded well to molecular genetic structure: over 80% of the molecular genetic variance was partitioned among six (groups of) taxa. This is in sharp contrast to previous studies using allozymes and amplified fragment length polymorphism (AFLP) markers, which seemed to indicate extensive nuclear gene flow. Within-taxon haplotype phylogenies and mismatch distributions revealed contrasting demographic histories: cachinnans (Ponto-Caspian region) and atlantis (NE Atlantic) represent ancient lineages with large long-term population sizes, inland forms stem from very recent colonization events (barabensis, mongolicus) or passed through a population bottleneck (armenicus).

Molecular phylogeny of Palearctic-African Acrocephalus and Hippolais Warblers (Aves: Sylviidae)

Phylogenetic relationships of the reed warbler group (genera Acrocephalus, Hippolais, Chloropeta; Aves: Passeriformes) and their potential relatives were studied using nucleotide sequences (1 kb) of the mitochondrial cytochrome b gene. This species-rich but morphologically poorly differentiated group of insectivorous passerines is distributed in Eurasia, Africa, and Australasia. Intergeneric relationships were poorly resolved, but monophyly of the reed warbler group (including Chloropeta) versus other Sylviidae was strongly supported. A basal polytomy within the reed warbler group consists of seven branches and may indicate a rapid early radiation. In the genus Acrocephalus three major clades were identified, which corresponded to phenotypic groups characterized by body size and plumage patterns. However, current delimitation of some subgenera (Acrocephalus, Lusciniola, Bebrornis) is at variance with our phylogeny estimate, and appropriate revisions are proposed. The genus Hippolais, which may or may not be monophyletic, consisted of two well-supported clades of four species each. Some Acrocephalus taxa whose species status had been doubted (griseldis, tangorum, orientalis, australis) proved to be highly distinct genetically. Genetic distances between members of two pairs of allopatric Hippolais taxa (caligata/rama; opaca/elaeica) were as large or larger than between other closely related warbler species. Overall, cytochrome b sequences resolved phylogenetically young relationships quite well, whereas more ancient nodes remained poorly resolved.

Enigmatic phylogeny of skuas (Aves:Stercorariidae)

Multiple sources of evidence show that the skuas (Aves:Stercorariidae) are a monophyletic group, closely related to gulls (Laridae. On morphological and behavioural evidence the Stercorariidae are divided into two widely divergent genera, Catharacta and Stercorarius, consistent with observed levels of nuclear and mitochondrial gene divergence. Catharacta skuas are large-bodied and with one exception breed in the Southern Hemisphere. Stercorarius skuas otherwise known as jaegers) are smaller bodied and breed exclusively in the Northern Hemisphere. Evidence from both mitochondrial and nuclear genomes and from ectoparasitic lice (Insecta:Phthiraptera) shows that the Pomarine skua, S. pomarinus, which has been recognized as being somewhat intermediate in certain morphological and behavioural characteristics, is much more closely related to species in the genus Catharacta, especially to the Northern Hemisphere-breeding Great skua, C. skua, than it is to the other two Stercorarius skuas, the Arctic skua, S. parasiticus and the Longtailed skua, S. longicaudus. Three possible explanations that might account for this discordant aspect of skua phylogeny are explored. These involve (i) the segregation of ancestral polymorphism, (ii) convergent evolution of morphology and behaviour or (iii) inter-generic hybridization. The available evidence from both nuclear and mitochondrial genomes does not exclude any of these hypotheses. Thus, resolution of this enigma of skua phylogeny awaits further work.

Evolutionary history of New and Old World vultures inferred from nucleotide sequences of the mitochondrial cytochrome b gene

The phylogeny of 11 species of Old World vultures (Aves: Accipitriformes, Aegypiinae), three species of New World vultures (Cathartidae) and theri nearest relatives within and outside the order Accipitriformes was investigated based on 1026 nucleotides of the mitochondrial cytochrome b gene. The data support the contention that New World vultures are not birds of prey, but phylogenetic information was insufficient to identify whether they are closer to storks (Ciconiidae) or to Accipitriformes. Four species of Gyps are all closely related and probably speciated within the Pleistocene. Molecular data do not support the split of 'white-backed' vultures from Gyps in a separate genus Pseudogyps. The monotypic genera of large, heavy-billed vultures, Aegypius, Torgos, Trigonoceps and Sarcogyps, are of monophyletic origin. We propose to merge Torgos with Aegypius, but retain Trigonoceps and Sarcogyps as separate genera, Sarcogyps being clearly the most primitive of the four. All four, together with Gyps and Necrosyrtes, form a monophyletic subfamily or 'core group', to which the subfamily Aegypiinae should be restricted. This group shares a more recent common ancestor with several non-vulture genera of Accipitrids, among them Buteo, Aquila, Haliaeetus and Circaetus, than it does with the two aberrent vultures Gypaetus barbatus and Neophron percnopterus. The last two are much more primitive; they seem to be each other's sister species and are closer to Pernis than to other Accipitrids. We propose separating Gypaetus and Neophron in the subfamily Gypaetinae. If the cytochrome b gene tree accurately reflects vulture phylogeny, Old World vultures are polyphyletic with the Aegypius-Gyps clade having evolved convergently to the more ancient Gypaetus and Neophron vultures. Polyphyly of Old World vultures, although in conflict with the DNA-DNA hybridization phylogeny of Sibley & Ahlquist (1990), is well supported by molecular, karyotypic, morphological and other phenotypic evidence (behaviour, voice) indicating fundamental differences between the two evolutionary lines.

Experimental and analytical techniques used in bird orientation research

Our present understanding of orientation behaviour in birds is based on a broad array of observational, experimental and analytical (statistical) techniques, which are briefly reviewed here. As an extremely productive model the homing behaviour of pigeons has allowed especially diverse experimental manipulations documenting the involvement of magnetic, visual and olfactory cues in orientation. Work with migratory birds has profited greatly from the design of several kinds of orientation cages, now commonly used, and from hand-rearing test birds under controlled conditions. Free-flying birds, especially on long-distance migration, are still least amenable to study, but radio transmitter technology is providing important new opportunities in this respect. In general, the most valuable studies have been those involving the ontogenetic development of orientation, and those combining several methods of investigation. Some suggestions for further experiments are made.