Blue Tit Cyanistes caeruleus
Phylogenetic studies of the Blue Tit complex have demonstrated that European Blue Tits are more closely related to Azure Tit Cyanistes cyaneus than to Blue Tits from North Africa and the Canary Islands (Salzburger et al. 2002, Kvist et al. 2005, Päckert et al. 2007, 2013a, Illera et al. 2011, Gohli et al. 2015, Stervander et al. 2015). The discovery of these two major clades of blue tits has led to the recognition of Canary Islands Tit/African Blue Tit C. teneriffae as a separate species (e.g. Clements 2007, Dickinson & Christidis 2014). However, this clade itself consists of multiple evolutionary lineages, as shown by congruent variation in morphology, vocalizations, mitochondrial and nuclear DNA sequences, genome-wide DNA markers, and sperm morphology.
Five reciprocally monophyletic groups, identified by phylogenetic analysis of mitochondrial and nuclear DNA sequences, occur in the Canary Islands and North Africa (Kvist et al. 2005, Päckert et al. 2007, 2013a, Dietzen et al. 2008, Gohli et al. 2015). These are (i) palmensis (La Palma), (ii) ombriosus (El Hierro), (iii) teneriffae/hedwigii (Tenerife, Gran Canaria and Gomera), (iv) ultramarinus/degener (Lanzarote, Fuerteventura, Morocco to Tunisia), and (v) cyrenaicae (Libya). Of these, cyrenaicae and palmensis are phylogenetically the most distinctive; they may be sister taxa (Päckert et al. 2013a) or successive outgroups to the other three clades (Gohli et al. 2015, Stervander et al. 2015).
The Canary Islands taxa palmensis, ombriosus, teneriffae/hedwigii and degener differ from each other and from ultramarinus in plumage (Cramp & Perrins 1993, Harrap & Quinn 1996, Dietzen et al. 2008). Even the two most closely related clades, ombriosus and teneriffae/hedwigii, differ diagnosably in two plumage characters: coloration of the upperparts (greenish in ombriosus; slaty-blue in teneriffae/hedwigii) and the presence of a narrow wing-bar (present in ombriosus; absent in teneriffae/hedwigii).
Pair-wise comparisons among the songs of these four groups are significant in 3–5 characters each, except teneriffae and ombriosus (Schottler 1995, see also Moreno 2000, Dietzen et al. 2008). In addition, palmensis shows strongly reduced response to the songs of caeruleus and the other Canarian taxa but not to its own songs, indicating song discrimination (Schottler 1995). Conversely, caeruleus, ombriosus, teneriffae/hedwigii and degener/ultramarinus discriminate among songs of their own phylogroup and those of palmensis (Schottler 1995).
Cytochrome b sequence divergence among the Canarian and North African clades ranges from 2.2% to 4.8% (Dietzen et al. 2008; see Päckert et al. 2013a), which exceeds the level of sequence divergence between European Blue and Azure Tits (1.6–1.9%, Salzburger et al. 2002).
A study of microsatellite patterns showed that (i) caeruleus, (ii) palmensis, (iii) ombriosus/teneriffae/hedwigii, and (iv) degener/ultramarinus form separate clusters (Hansson et al. 2014), a pattern very similar to that revealed by mitochondrial and nuclear DNA sequences; cyrenaicae was not studied.
The taxa caeruleus and palmensis showed significantly longer sperm lengths than ombriosus, teneriffae/hedwigii and degener/ultramarinus (Gohli et al. 2015). Divergence in this trait may indicate reproductive incompatibilities (Gohli et al. 2015).
Based on the entire body of evidence (plumage, songs, differential response to playback, reciprocal monophyly, levels of sequence divergence, microsatellite data, sperm morphology), the Azure Tit/Blue Tit complex is best treated as a complex of seven species.
• European Blue Tit Cyanistes caeruleus (polytypic, with multiple subspecies)
• Azure Tit Cyanistes cyanus (polytypic, with multiple subspecies)
• Cyrenaica Blue Tit Cyanistes cyrenaicae (monotypic)
• La Palma Blue Tit Cyanistes palmensis (monotypic)
• Hierro Blue Tit Cyanistes ombriosus (monotypic)
• Teneriffe Blue Tit Cyanistes teneriffae (polytypic, including hedwigii and teneriffae)
• North African Blue Tit Cyanistes ultramarinus (polytypic, with subspecies ultramarinus and degener)
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