Enhancing structural complexity: An experiment conducted in the Black Forest National Park, Germany.

We report on a structural complexity enhancement (SCE) experiment that was designed to test ecological restoration measures in the Black Forest National Park, Germany. The main goal was to understand as to whether the creation of standing and downed deadwood within previously managed, single-layered Norway spruce (Picea abies L.) forests accelerates the development of forest structure, richness, and diversity of a range of taxonomic groups. Here we introduce the experimental design and describe the development of stand structure including abundance and richness of tree-related microhabitats (TreMs) within 5 years after initiation of the experiment in October 2016. To enhance structural complexity in treatment plots, 10 trees per plot were toppled using a skidder winch, and another 10 trees were ring barked at a height of around 60 cm above ground level with a chainsaw. To monitor stand structure, we collected data on common forest attributes such as diameter at breast height (DBH), tree height, and TreMs of all trees in the six experimental and six control plots measuring 0.25 ha in size before the treatments were carried out in 2016 and again in 2020/21. We analyzed the abundance and richness of TreMs using generalized linear mixed models with DBH and treatment vs. control as predictors. The SCE treatment resulted in a significant increase in deadwood volumes (4.2 vs. 439.5 m3) as well as in TreM abundance and richness (increase of 0.74 TreMs per tree). This indicates that the SCE treatment was effective to increase biodiversity-relevant structures such as deadwood and TreMs, in previously managed Norway spruce-dominated stands. The ongoing monitoring of a range of taxonomic groups (birds, bats, small mammals, coleoptera, fungi, mosses, and vascular plants) in this experiment will demonstrate to what extent the enhancement in structural complexity will lead to an enrichment in species richness and diversity.

Genome-wide evidence supports mitochondrial relationships and pervasive parallel phenotypic evolution in open-habitat chats.

In wheatears and related species ('open-habitat chats'), molecular phylogenetics has led to a comprehensively revised understanding of species relationships and species diversity. Phylogenetic analyses have suggested that, in many cases, phenotypic similarities do not reflect species' relationships, revealing traditionally defined genera as non-monophyletic. This led to the suggestion of pervasive parallel evolution of open-habitat chats' plumage coloration and ecological phenotypes. However, to date, the molecular evidence for the phylogenetic relationships among open-habitat chats is mainly limited to mitochondrial DNA. Here, we assessed whether the mitochondrial relationships are supported by genome-wide data. To this end, we reconstructed the species tree among 14 open-habitat chat taxa using multi-species coalescent analyses based on ~1'300 SNPs. Our results confirm previous ones based chiefly on mitochondrial DNA; notably the paraphyly of the Oenanthe lugens complex and the clustering of individual species formerly placed in the genera Cercomela and Myrmecocichla within Oenanthe. Since several variable morphological and ecological characteristics occur in multiple places across the open-habitat chat phylogeny, our study consolidates the evidence for pervasive parallel evolution in the plumage coloration and ecology of open-habitat chats.

Parallel plumage colour evolution and introgressive hybridization in wheatears.

Genetic and phenotypic mosaics, in which various phenotypes and different genomic regions show discordant patterns of species or population divergence, offer unique opportunities to study the role of ancestral and introgressed genetic variation in phenotypic evolution. Here, we investigated the evolution of discordant phenotypic and genetic divergence in a monophyletic clade of four songbird taxa-pied wheatear (O. pleschanka), Cyprus wheatear (Oenanthe cypriaca), and western and eastern subspecies of black-eared wheatear (O. h. hispanica and O. h. melanoleuca). Phenotypically, black back and neck sides distinguish pied and Cyprus wheatears from the white-backed/necked black-eared wheatears. Meanwhile, mitochondrial variation only distinguishes western black-eared wheatear. In the absence of nuclear genetic data, and given frequent hybridization among eastern black-eared and pied wheatear, it remains unclear whether introgression is responsible for discordance between mitochondrial divergence patterns and phenotypic similarities, or whether plumage coloration evolved in parallel. Multispecies coalescent analyses of about 20,000 SNPs obtained from RAD data mapped to a draft genome assembly resolve the species tree, provide evidence for the parallel evolution of colour phenotypes and establish western and eastern black-eared wheatears as independent taxa that should be recognized as full species. The presence of the entire admixture spectrum in the Iranian hybrid zone and the detection of footprints of introgression from pied into eastern black-eared wheatear beyond the hybrid zone despite strong geographic structure of ancestry proportions furthermore suggest a potential role for introgression in parallel plumage colour evolution. Our results support the importance of standing heterospecific and/or ancestral variation in phenotypic evolution.

Convergent evolution of morphological and ecological traits in the open-habitat chat complex (Aves, Muscicapidae: Saxicolinae).

Open-habitat chats (genera Myrmecocichla, Cercomela, Oenanthe and relative) are a morphologically and ecologically cohesive group of genera with unclear phylogenetic relationships. They are distributed mostly in open, arid and/or rocky habitats of Africa and Eurasia. Here, we present the most comprehensive molecular phylogenetic analysis of this group to date, with a complete taxon sampling at the species level. The analysis, based on a multilocus dataset including three mitochondrial and three nuclear loci, allows us to elucidate the phylogenetic relationships and test the traditional generic limits. All genera are non-monophyletic, suggesting extensive convergence on similar plumage patterns in unrelated species. While the colour pattern appear to be a poor predictor of the phylogenetic relationships, some of the ecological and behavioural traits agree relatively well with the major clades. Following our results, we also propose a revised generic classification for the whole group.

Morphological shifts of the external flight apparatus across the range of a passerine (Northern Wheatear) with diverging migratory behaviour.

We studied morphological differentiation in the flight apparatus of the four currently recognised sub-species of Northern Wheatears, Oenanthe oenanthe. Considering all measured birds without assigning them a priori to any sub-species we found a clinal morphological shift. Relative wing length, wing pointedness, and the degree of tail forking were positively correlated with migratory distance, whereas tail length (relative to wing length) was negatively correlated. The large-sized, long-distance migrant "Greenland" Wheatear, O. o. leucorhoa, is characterized by relatively longer, broader and more pointed wings and more forked tails, similar to the smaller-sized nominate Northern Wheatear, O. o. oenanthe, from North Europe, Siberia and Russia. In contrast, the short distance migrant "Seebohm's" Wheatear, O. o. seebohmi, from northwest Africa, possesses much rounder wings, and the tail is relatively longer and less forked. Sub-species with intermediate migratory habits (different populations of nominate Northern Wheatear, O. o. oenanthe, and "Mediterranean" Northern Wheatear, O. o. libanotica) show, as expected, intermediate features according to their intermediate migratory behaviour. Our results are congruent with other inter- and intraspecific studies finding similar adaptations for energy-effective flight in relation to migration distance (morphological migratory syndrome).

Phylogeny of the mourning wheatear Oenanthe lugens complex.

The phylogenetic relationship of many species and subspecies within the genus Oenanthe (wheatears) is still debated. Only recently molecular approaches have been used to clarify their basal taxonomy. One of the main unsolved groups is summarized under the name mourning wheatear O. lugens, which comprises depending on the underlying species concept 3-8 different taxa. These include the wheatears of the subspecies group lugens (halophila, lugens, persica), the subspecies group lugubris (lugubris, schalowi, vauriei), and the subspecies group lugentoides (lugentoides, boscaweni). In order to shed light on this unsolved issue we studied the taxonomy of the mourning wheatear complex by means of molecular markers and comparative morphometry. We found reasonable evidence to follow a narrow species concept treating all the three subspecies groups of the mourning wheatear in future as three independent taxonomic entities (super-species O. lugens, O. lugentoides, O. lugubris). Further within the subspecies group O. lugens we suggest treating halophila and lugens as members of the polytypic species O. lugens, while the Persian mourning wheatear O. persica merits the status of an independent monotypic species, endemic to the Iranian Plateau. Genetic and morphometric characters support a long separation of this form (a half to one Million years). For the black form "basalti" from Syria and Jordan our molecular data indicates a close relationship to lugens and this form is therefore probably best treated as a colour morph of lugens, adapted to the local habitat conditions. However, future behavioural studies have to show if there exist prezygotic barriers between both forms.

The species status of the Corsican finch Carduelis corsicana assessed by three genetic markers with different rates of evolution.

Citril finches Carduelis c. citrinella and Corsican finches Carduelis c. corsicana represent two closely related forms, endemic to European mountains and some Mediterranean Islands. Their taxonomic status has recently been disputed based on the results from mitochondrial genes. We show that the use of different genetic markers may lead to different results in these two putative species. Using the mitochondrial ATP8+6 we found a clear difference between C. c. citrinella and C. c. corsicana (3.2%) suggesting a divergence time of 1.2MYR. In contrast, no clear difference was found using two nuclear genes. The mismatch between the different markers suggests that the separation of C. c. citrinella and C. c. corsicana is likely to be a rather recent event, involving bottlenecks, which have enhanced the divergence in the mtDNA. Our results call for caution when using mtDNA alone for assessing times of divergence and rates of evolution. We did not find any support for the view that C. c. corsicana is more related to Carduelis carduelis than C. c. citrinella as proposed by previous studies.