Replication of the mitochondrial genome depends on the single DNA polymerase (pol gamma). Mutations in the POLG gene, encoding the catalytic subunit of the human polymerase gamma, have been linked to a wide variety of mitochondrial disorders that show remarkable heterogeneity, with more than 200 sequence variants, often very rare, found in patients. The pathogenicity and dominance status of many such mutations remain, however, unclear. Remarkable structural and functional conservation of human POLG and its S. cerevisiae ortholog (Mip1p) led to the development of many successful yeast models, enabling to study the phenotype of putative pathogenic mutations. In a group of patients with suspicion of mitochondrial pathology, we identified five novel POLG sequence variants, four of which (p.Arg869Ter, p.Gln968Glu, p.Thr1053Argfs*6, and p.Val1106Ala), together with one previously known but uncharacterised variant (p.Arg309Cys), were amenable to modelling in yeast. Familial analysis indicated causal relationship of these variants with disease, consistent with autosomal recessive inheritance. To investigate the effect of these sequence changes on mtDNA replication, we obtained the corresponding yeast mip1 alleles (Arg265Cys, Arg672Ter, Arg770Glu, Thr809Ter, and Val863Ala, respectively) and tested their effect on mitochondrial genome stability and replication fidelity. For three of them (Arg265Cys, Arg672Ter, and Thr809Ter), we observed a strong, partially dominant phenotype of a complete loss of functional mtDNA, whereas the remaining two led to partial mtDNA depletion and significant increase in point mutation frequencies. These results show good correlation with the severity of symptoms observed in patients and allow to establish these variants as pathogenic mutations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00439-015-1578-x) contains supplementary material, which is available to authorized users.

Hypotheses postulating parasite‐mediated mate choice intrinsically assume that parasitic infections deteriorate the quality of male ornamentation. Although this assumption has often been studied in the context of carotenoid‐based colouration, only few studies investigated this with reference to structural feather colouration, which in many species plays a vital role in sexual selection. Here, using a three‐years dataset from a wild blue tit Cyanistes caeruleus population, we examined the relationship between the haemosporidian infection status and the structural as well as the carotenoid‐based colouration of adult birds. Furthermore, we investigated potential differences in the impact on feather colouration between two examined parasite genera: Plasmodium and Haemoproteus. For analysis of the feathers spectral reflectance we used both the tristimulus model and the avian tetrahedral colour space model, incorporating visual phenotype of the blue tit. Contrary to expectations we found that infected birds showed higher brightness, in both the structural and the carotenoid‐based colours. We also found no differences in the feather colouration between birds infected with Plasmodium and Haemoproteus. Observed pattern might be best explained by the parasite‐mediated selection hypothesis, as only individuals of superior quality should be able to survive the acute stage of infection and therefore they could produce more elaborate ornamental colouration.

Abstract. The wasp spider Argiope bruennichi (Scopoli, 1772) is of Mediterranean-Pontian origin, but for decades it has been expanding northwards, including into the territory of Poland. Based on well-documented expansion records, we can distinguish ''old'' (south-eastern and south-western) and ''new'' populations (north-eastern), respectively, from the 1930s to the 2000s. In Poland, some populations of A. bruennichi were expected to be more genetically isolated from others, due to distance effects or differential times of arrival. We evaluated whether the oldest populations were in a state of HardyWeinberg equilibrium (HWE), and whether recently founded populations were in an expansion phase. Specimens of A. bruennichi (n ¼ 184) were collected at six localities in Poland and single sampling sites in Italy and Japan. Nine microsatellite loci were amplified although only five were useful in the final analyses. Based on the genotypes obtained, we estimated basic measures of genetic diversity and tested for deviation from HWE. The results showed a low level of polymorphism amongst the investigated markers, and accordingly, we found a low genetic diversity in populations. Only populations from Italy and Japan, and one population from Poland, were in HWE. The level of genetic differentiation among sampling sites from Poland was also very low. The high dispersal ability of the wasp spider appears to have facilitated high gene flow among populations. The peripheral and recently settled populations were characterized by the highest heterozygosity and the lowest inbreeding coefficient (F IS ) . The remaining Polish populations are therefore still in the expansion phase, as indicated by deviations from HWE.

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The costs associated with the production and maintenance of colour patches is thought to maintain their honesty. Although considerable research on sexual selection has focused on structurally coloured plumage ornaments, the proximate mechanisms of their potential condition dependence, and thus their honesty, is rarely addressed, particularly in an experimental context. Blue tit (Cyanistes caeruleus) nestlings have ultraviolet (UV)–blue structurally coloured tail feathers, providing a unique opportunity for investigation of the causes of variation in their colour. Here, we examined the influence of early growing conditions on the reflectance and structural properties of UV–blue-coloured tail feathers of blue tit nestlings. We applied a two-stage brood size manipulation to determine which stage of development more strongly impacts the quality of tail feather colouration and microstructure. We used small-angle X-ray scattering (SAXS) and electron microscopy to characterise the nanoscale and microscale structure of tail feather barbs. Nestlings from the broods enlarged at a later stage of growth showed a sex-specific rectrix development delay, with males being more sensitive to this manipulation. Contrary to predictions, treatment affected neither the quality of the barbs’ nanostructures nor the brightness and UV chroma of feathers. However, at the microscale, barbs’ keratin characteristics were impaired in late-enlarged broods. Our results suggest that nanostructure quality, which determines the UV–blue colour in tail feathers, is not sensitive to early rearing conditions. Furthermore, availability of resources during feather growth seems to impact the quality of feather microstructure more than body condition, which is likely to be determined at an earlier stage of nestling growth.

Carotenoid‐based coloration occurs predominantly in adult birds, yet in some species from the family Paridae, this trait is also present at the nestling stage. One of the factors proposed to affect the expression of this trait in immature birds is hatching date. Here, using the avian tetrahedral colour space model, we examined the influence of hatching date on the breast carotenoid‐based plumage coloration of the Blue Tit Cyanistes caeruleus nestlings. Because Blue Tits are sexually dichromatic, we also investigated the potential interaction between hatching date and sex that could arise from differences in condition dependence of this trait between males and females. We found a positive relationship between UV chroma of breast feathers and hatching date. The amount of UV reflectance is thought to be negatively related to carotenoid content in feathers. The observed increase of UV chroma through the breeding season might therefore be caused by a seasonal decline in the availability and quality of Lepidoptera larvae – the main source of carotenoids in food of the Tits. We also observed a sex difference in the relationship between brightness of breast feathers (achromatic, structural component) and hatching date, which in males was negative and in females not significant. Our study provides further evidence that the timing of breeding is related to the expression of nestling carotenoid‐based coloration, a potentially meaningful element of offspring–parent communication, and suggests a sex‐specific effect of hatching date on its structural component.

Genetic variation is one of the key concepts in evolutionary biology and an important prerequisite of evolutionary change. However, we know very little about processes that modulate its levels in wild populations. In particular, we still are to understand why genetic variances often depend on environmental conditions. One of possible environment-sensitive modulators of observed levels of genetic variance are maternal effects. In this study we attempt to experimentally test the hypothesis that maternally transmitted agents (e.g. hormones) may influence the expression of genetic variance in quantitative traits in the offspring. We manipulated the levels of steroid hormones (testosterone and corticosterone) in eggs laid by blue tits in a wild population. Our experimental setup allowed for full crossing of genetic and rearing effects with the experimental manipulation. We observed that birds treated with corticosterone exhibited a significant decrease in broad-sense genetic variance of tarsus length, and an increase in this component in body mass on the 2nd day post-hatching. Our study indicates, that maternally transmitted substances such as hormones may have measurable impact on the levels of genetic variance and hence, on the evolutionary potential of quantitative traits.

Achromatic patches are a common element of plumage patterns in many bird species and there is growing body of evidence that in many avian taxa they can play a signalling role in mate choice. Although the blue tit Cyanistes caeruleus is a well-established model species in the studies on colouration, its white wing patch has never been examined in the context of sex-specific trait expression. In this exploratory study, we examined sexual size dimorphism and dichromatism of greater covert’s dots creating white wing patch and analysed its correlations with current body condition and crown colouration - a trait with established role in sexual selection. Further, we qualitatively analysed microstructural barb morphology underlying covert’s colouration. We found significant sexual dimorphism in the dot size independent of covert size, and sexual dichromatism in both white dot and blue outer covert’s vane spectral characteristics. Internal structure of covert barbs within the white dot was similar to the one found in barbs from the blue part, i.e. with a medullary area consisting of dead keratinocytes containing channel-type ß-keratin spongy nanostructure and centrally located air cavities. However, it lacked melanosomes which was the main observed difference. Importantly, UV chroma of covert’s blue vane was positively correlated with crown UV chroma and current condition (the latter only in males), which should be a premise for further research on the signal function of the wing stripe.