The great tit (Parus major) – a misclassified ring species

The great tit (Parus major) has been considered to be the most typical example of an avian ring species. The terminal taxa of the ring (major and minor sectors) are supposed to be reproductively isolated in a zone of secondary contact in the middle Amur valley, Siberia. Our study combines molecular markers (cytochrome‐b), bioacoustic analyses and morphological characters to judge the ring species status of the great tit complex. Despite a notable percentage of intermediately coloured birds in the mixed population of middle Amur, a lack of mitochondrial introgression between the major and minor sectors and a small number of true hybrids among voucher specimens from this area suggest at least a partial reproductive barrier between both sectors. In contrast, variation of morphological and especially acoustic characters along the ring‐shaped area and the phylogenetic structure of the P. major group do not match the ring species concept. Bioacoustic and molecular data (cytochrome‐b sequences) reveal two large and closely related subspecies blocks, the sectors major and bokharensis in the Western Palaearctic and central Asia, and the sectors minor and cinereus in the Eastern Palaearctic and South‐east Asia, respectively. The two western sectors diverged only recently (0.5 Mya) and they were separated from the eastern group by Pleistocene events about 1.5 Mya. Songs from allopatric regions of the two subspecies blocks differ distinctly in frequency parameters and element composition. In the area of secondary contact, males of all phenotypes share the same frequency range of song, close to the range of the typical minor song. Hybrids and major males sing mixed repertoires of typical major and minor strophe types as well as mixed strophes. In contrast, phenotypic minor males display only pure minor strophes. Differences in mate choice and mating success based on repertoire size are believed to uphold the reproductive barrier between major and minor birds in the area of sympatry. Taxonomic consequences suggest three separate species in the Parus major complex: Parus major s.s. (including the very closely related bokharensis sector), Parus minor and Parus cinereus. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 153–174.     

Effects of elevated carbon dioxide and ozone on aphid oviposition preference and birch bud exudate phenolics

The effect of atmospheric change on birch aphid ( Euceraphis betulae Koch) oviposition preference was examined and plant characteristics that are possibly responsible for the observed effects were investigated. It was hypothesized that the increasing concentrations of CO₂ and O₃ affect singly or in combination the oviposition of birch aphids via changes in host plant characteristics. Two genotypes of field-growing silver birch ( Betula pendula Roth) trees (clones 4 and 80), which were exposed to doubled ambient concentration of CO₂ and O₃, singly and in combination, in a 3-year open-top chamber experiment, were used in an aphid oviposition preference test. It was found that elevated CO₂, irrespective of ozone concentration, increased the number of aphid eggs laid on clone 4, but not in clone 80. Several flavonoid aglycones were identified from the exudate coating of birch buds. Although elevated CO₂ and O₃ affected these phenolic compounds in clone 4, the effects did not correlate with the observed changes in aphid oviposition. It is suggested that neither bud length, which was not affected by the treatments, nor surface exudate phenolics mediate birch aphid oviposition preference.     

Do elevated atmospheric CO2 and O3 affect food quality and performance of folivorous insects on silver birch?

The individual and combined effects of elevated CO₂ and O₃ on the foliar chemistry of silver birch (Betula pendula Roth) and on the performance of five potential birch‐defoliating insect herbivore species (two geometrid moths, one lymantrid moth and two weevils) were examined. Elevated CO₂ decreased the water concentration in both short‐ and long‐shoot leaves, but the effect of CO₂ on the concentration of nitrogen and individual phenolic compounds was mediated by O₃ treatment, tree genotype and leaf type. Elevated O₃ increased the total carbon concentration only in short‐shoot leaves. Bioassays showed that elevated CO₂ increased the food consumption rate of juvenile Epirrita autumnata and Rheumaptera hastata larvae fed with short‐ and long‐shoot leaves in spring and mid‐summer, respectively, but had no effect on the growth of larvae. The contribution of leaf quality variables to the observed CO₂ effects indicate that insect compensatory consumption may be related to leaf age. Elevated CO₂ increased the food preference of only two tested species: Phyllobius argentatus (CO₂ alone) and R. hastata (CO₂ combined with O₃). The observed stimulus was dependent on tree genotype and the measured leaf quality variables explained only a portion of the stimulus. Elevated O₃ decreased the growth of flush‐feeding young E. autumnata larvae, irrespective of CO₂ concentration, apparently via reductions in general food quality. Therefore, the increasing tropospheric O₃ concentration could pose a health risk for juvenile early‐season birch folivores in future. In conclusion, the effects of elevated O₃ were found to be detrimental to the performance of early‐season insect herbivores in birch whereas elevated CO₂ had only minor effects on insect performance despite changes in food quality related foliar chemistry.