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We present evidence of mitochondrial and nuclear introgression from the Atlantic herring Clupea harengus into the Pacific herring C. pallasii in northern European seas, where the two species have come into secondary contact following the post-glacial trans-Arctic invasion of Pacific herring to the Atlantic realm. Although the breeding areas of the two species are thought to be separate, 7 % of the resident Pacific herring in samples from the White Sea were found to possess Atlantic herring mitochondria. The percentage was even higher (21 %) in the local Balsfjord stock of the Norwegian Sea, whereas it was nil in Pechora Sea samples. Similar or somewhat lower levels of genomic admixture were estimated from four diagnostic or nearly diagnostic nuclear allozyme loci. The absences of inter-locus and cytonuclear disequilibria, together with the patterns of mtDNA haplotype diversity, suggest recurrent backcrossing and hybridization over a long period in the post-glacial time frame. From a reassessment of published allozyme data, a hypothesis is presented that the patterns of intra-species geographical variation previously recorded in North European herrings may largely reflect varying levels of introgression. The study presents new information on the processes that affect the genetic structure of one of the most abundant fishes of the northern seas. It also adds to the knowledge on the occurrence of inter-species gene flow in marine fishes and on the consequences of trans-Arctic biotic invasions in general.

Background The relationships between North Atlantic and North Pacific faunas through times have been controlled by the variation of hydrographic circumstances in the intervening Arctic Ocean and Bering Strait. We address the history of trans-Arctic connections in a clade of amphi-boreal pelagic fishes using genealogical information from mitochondrial DNA sequence data. The Pacific and Atlantic herrings ( Clupea pallasii and C. harengus ) have basically vicarious distributions in the two oceans since pre-Pleistocene times. However, remote populations of C. pallasii are also present in the border waters of the North-East Atlantic in Europe. These populations show considerable regional and life history differentiation and have been recognized in subspecies classification. The chronology of the inter-oceanic invasions and genetic basis of the phenotypic structuring however remain unclear. Results The Atlantic and Pacific herrings both feature high mtDNA diversities (large long-term population sizes) in their native basins, but an ocean-wide homogeneity of C. harengus is contrasted by deep east-west Pacific subdivision within Pacific C. pallasii . The outpost populations of C. pallasii in NE Europe are identified as members of the western Pacific C. pallasii clade, with some retained inter-oceanic haplotype sharing . They have lost diversity in colonization bottlenecks, but have also thereafter accumulated abundant new variation. The data delineate three phylogeographic groups within the European C. pallasii : herring from the inner White Sea; herring from the Mezen and Chesha Bays; and a strongly bottlenecked peripheral population in Balsfjord of the Norwegian Sea. Conclusions The NE European outposts of C. pallasii are judged to be early post-glacial colonists from the NW Pacific. A strong regional substructure has evolved since that time, in contrast to the apparent broad-scale uniformity maintained by herrings in their native basins. The structure only partly matches the previous biological concepts based on seasonal breeding stocks or geographical subspecies designations. The trans-Arctic herring phylogeography is notably similar to those of the amphi-boreal mollusk taxa Macoma and Mytilus, suggesting similar histories of inter-oceanic connections. We also considered the time dependency of molecular rates, critical for interpreting timing of relatively recent biogeographical events, by comparing the estimates from coding and non-coding mitochondrial regions of presumably different mutation dynamics.

Explaining the evolutionary origin and maintenance of color polymorphisms is a major challenge in evolutionary biology. Such polymorphisms are commonly thought to reflect the existence of alternative behavioral or life‐history strategies under negative frequency‐dependent selection. The European common wall lizard Podarcis muralis exhibits a striking ventral color polymorphism that has been intensely studied and is often assumed to reflect alternative reproductive strategies, similar to the iconic “rock–paper–scissors” system described in the North American lizard Uta stansburiana. However, available studies so far have ignored central aspects in the behavioral ecology of this species that are crucial to assess the existence of alternative reproductive strategies. Here, we try to fill this gap by studying the social behavior, space use, and reproductive performance of lizards showing different color morphs, both in a free‐ranging population from the eastern Pyrenees and in ten experimental mesocosm enclosures. In the natural population, we found no differences between morphs in site fidelity, space use, or male–female spatial overlap. Likewise, color morph was irrelevant to sociosexual behavior, space use, and reproductive success within experimental enclosures. Our results contradict the commonly held hypothesis that P. muralis morphs reflect alternative behavioral strategies, and suggest that we should instead turn our attention to alternative functional explanations. Ventral color morphs in wall lizards have often been assumed to reflect alternative reproductive strategies. In this study, we study the social behavior, space use, and reproductive success of Podarcis muralis color morphs both in a free‐ranging population from the eastern Pyrenees and in ten experimental mesocosm enclosures. Overall, our results suggest that color morphs do not reflect alternative strategies concerning sociosexual behavior or space use.

The Japanese skeleton shrimp Caprella mutica, originally from the north-west Pacific, artificially introduced to many parts of the world, is recorded in Sweden for the first time. The new record is from Eastern Skagerrak, slightly north of the border between the North Sea and the Baltic Sea. A detailed morphological description of the specimens from Swedish waters with notes on habitat is presented. In comparison with the specimens from the native range, the large males of C. mutica from Sweden, and material earlier reported from elsewhere in Europe, are characterized by rather long pereonites 1 and 2, which are longer than the combined length of pereonites 3 and 4; and long segments of antenna 1 peduncle; among them segment 3 is longer than flagellum.

Hybrid zones provide insights into the evolution of reproductive isolation. Sexual selection can contribute to the evolution of reproductive barriers, but it remains poorly understood how sexual traits impact gene flow in secondary contact. Here, we show that a recently evolved suite of sexual traits that function in male-male competition mediates gene flow between two lineages of wall lizards (Podarcis muralis). Gene flow was relatively low and asymmetric in the presence of exaggerated male morphology and coloration compared to when the lineages share the ancestral phenotype. Putative barrier loci were enriched in genomic regions that were highly differentiated between the two lineages and showed low concordance between the transects. The exception was a consistently low genetic exchange around ATXN1, a gene that modulates social behavior. We suggest that this gene may contribute to the male mate preferences that are known to cause lineage-assortative mating in this species. Although female choice modulates the degree of reproductive isolation in a variety of taxa, wall lizards demonstrate that both male-male competition and male mate choice can contribute to the extent of gene flow between lineages.

Abstract The Mediterranean Basin has experienced extensive change in geology and climate over the past six million years. Yet, the relative importance of key geological events for the distribution and genetic structure of the Mediterranean fauna remains poorly understood. Here, we use population genomic and phylogenomic analyses to establish the evolutionary history and genetic structure of common wall lizards (Podarcis muralis). This species is particularly informative because, in contrast to other Mediterranean lizards, it is widespread across the Iberian, Italian, and Balkan Peninsulas, and in extra-Mediterranean regions. We found strong support for six major lineages within P. muralis, which were largely discordant with the phylogenetic relationship of mitochondrial DNA. The most recent common ancestor of extant P. muralis was likely distributed in the Italian Peninsula, and experienced an “Out-of-Italy” expansion following the Messinian salinity crisis (∼5 Mya), resulting in the differentiation into the extant lineages on the Iberian, Italian, and Balkan Peninsulas. Introgression analysis revealed that both inter- and intraspecific gene flows have been pervasive throughout the evolutionary history of P. muralis. For example, the Southern Italy lineage has a hybrid origin, formed through admixture between the Central Italy lineage and an ancient lineage that was the sister to all other P. muralis. More recent genetic differentiation is associated with the onset of the Quaternary glaciations, which influenced population dynamics and genetic diversity of contemporary lineages. These results demonstrate the pervasive role of Mediterranean geology and climate for the evolutionary history and population genetic structure of extant species.

Climate change may affect bird populations both directly by changing theweather conditions, and indirectly through changes in the food chain.While both theoretical and empirical studies have shown climate change having drastic impacts on polar areas, its consequences on Arctic bird species are still poorly known. Here we investigated how weather and changes in predator–prey interactions affected the annual growth rates of sub-Arctic birds bymonitoring the breeding numbers of three duck and sevenwader species in the alpine tundra of Finnish Lapland during 2005–2015 (except for 2006). We hypothesized that growth rates ofwaterbirdswould be positively associated with warm and dry weather due to improved reproductive success. Furthermore, we tested the hypothesis that waterbirds have a higher reproductive success during the cyclic rodent peaks, when predators mainly prey on rodents, than during the decline and low phases of the cycle, when predation pressure towards waterbirds increases. Results showed that population growth rates of breeding ducks were negatively associated with the sumof rainfall in the previous year. In waders, growth rates were positively associated with the phase of the rodent cycle in the same year. Our results emphasize the importance of monitoring Arctic bird populations on their breeding areas to explorewhat the consequences of climate changemight be for breeding waterbirds by linking the effects of both weather and rodent abundance.

Climate change may affect bird populations both directly by changing the weather conditions, and indirectly through changes in the food chain. While both theoretical and empirical studies have shown climate change having drastic impacts on polar areas, its consequences on Arctic bird species are still poorly known. Here we investigated how weather and changes in predator-prey interactions affected the annual growth rates of sub-Arctic birds by monitoring the breeding numbers of three duck and seven wader species in the alpine tundra of Finnish Lapland during 2005-2015 (except for 2006). We hypothesized that growth rates of waterbirds would be positively associated with warm and dry weather due to improved reproductive success. Furthermore, we tested the hypothesis that waterbirds have a higher reproductive success during the cyclic rodent peaks, when predators mainly prey on rodents, than during the decline and low phases of the cycle, when predation pressure towards waterbirds increases. Results showed that population growth rates of breeding ducks were negatively associated with the sum of rainfall in the previous year. In waders, growth rates were positively associated with the phase of the rodent cycle in the same year. Our results emphasize the importance of monitoring Arctic bird populations on their breeding areas to explore what the consequences of climate change might be for breeding waterbirds by linking the effects of both weather and rodent abundance. Ilmaston on ennustettu muuttuvan voimakkaimmin arktisilla alueilla, mutta muutosten vaikutuk set arktisiin lintukantoihin tunnetaan huonosti. Ilmastonmuutos voi vaikuttaa lintukantoihin suoraan muuttamalla saaolosuhteita tai epasuorasti ravintoverkon kautta. Tutkimme pitkaaikaisaineiston avulla miten vuosittaiset saaolosuhteet ja pikkunisakassyklin vaihe vaikuttavat kolmen arktisen sorsalinnun ja seitseman kahlaajalajin pesimamaariin. Aineisto kerattiin Suomen Kasivarren tunturipaljakalta lahelta Kilpisjarvea vuosina 2005-2015 (poislukien 2006). Oletuksemme oli, etta pikkunisakashuipun aikaan pedot kayttavat ravintonaan pikkunisakkaita, paljakalla etenkin tunturisopulia, jolloin sorsien ja kahlaajien pesimamenestys on suurempikuin pikkunisakassyklin pohjavuosina. Lisaksi oletimme pesintojen onnistuvan paremmin lampimina ja kuivina kesina verrattuna kylmiin ja sateisiin. Tutkimuslajien kannankehityksissa ei ollut merkitsevia pitkaaikaissuuntauksia. Poikasia hoitavien kahlaajien lukumaarat olivat suurimmillaan pikkunisakashuipun aikaan, jolloin saalistuspaine on alhainen. Pesivien sorsien lukumaarat kasvoivat edellisen kesan oltua kuiva, mutta olivat runsaimmillaan pikkunisakashuippua seuraavana vuonna. Sadanta ja myyrasyklin vaihe korreloivat keskenaan, jonka takia niita ei voitu tarkastella mallissa samanaikaisesti. Tutkimustuloksemme painottavat, etta lintukantojen muutokset ovat alttiita pikkunisakaskannan vaihtelulle, mutta sadannallakin on merkitysta. Ilmastonmuutoksella voi olla kohtalokkaita seurauksia arktisille lajeille, mikali se lisaa pesimaaikaista sadantaa ja heikentaa pikkunisakassyklien voimakkuutta.

The Mediterranean Basin has experienced extensive change in geology and climate over the past six million years. Yet, the relative importance of key geological events for the distribution and genetic structure of the Mediterranean fauna remains poorly understood. Here, we use population genomic and phylogenomic analyses to establish the evolutionary history and genetic structure of common wall lizards (Podarcis muralis). This species is particularly informative because, in contrast to other Mediterranean lizards, it is widespread across the Iberian, Italian, and Balkan peninsulas, and in extra-Mediterranean regions. We found strong support for six major lineages within P. muralis, which were largely discordant with the phylogenetic relationship of mitochondrial DNA. The most recent common ancestor of extant P. muralis was likely distributed in the Italian Peninsula, and experienced an Out-of-Italy expansion following the Messinian salinity crisis (~5 Mya), resulting in the differentiation into the extant lineages on the Iberian, Italian and Balkan peninsulas. Introgression analysis revealed that both inter- and intraspecific gene flow have been pervasive throughout the evolutionary history of P. muralis. For example, the Southern Italy lineage has a hybrid origin, formed through admixture between the Central Italy lineage and an ancient lineage that was the sister to all other P. muralis. More recent genetic differentiation is associated with the onset of the Quaternary glaciations, which influenced population dynamics and genetic diversity of contemporary lineages. These results demonstrate the pervasive role of Mediterranean geology and climate for the evolutionary history and population genetic structure of extant species. Competing Interest Statement The authors have declared no competing interest.

BackgroundIn women, metabolic health deteriorates after menopause, and the role of physical activity (PA) in mitigating the change is not completely understood. This study investigates the changes in indicators of metabolic health around menopause and evaluates whether PA modulates these changes.MethodsLongitudinal data of 298 women aged 48–55 years at baseline participating in the ERMA and EsmiRs studies was used. Mean follow-up time was 3.8 (SD 0.1) years. Studied indicators of metabolic health were total and android fat mass, waist circumference, waist-to-hip ratio (WHR), systolic (SBP) and diastolic (DBP) blood pressure, blood glucose, triglycerides, serum total cholesterol, and high- (HDL-C) and low-density (LDL-C) lipoprotein cholesterol. PA was assessed by accelerometers and questionnaires. The participants were categorized into three menopausal groups: PRE-PRE (pre- or perimenopausal at both timepoints, n = 56), PRE-POST (pre- or perimenopausal at baseline, postmenopausal at follow-up, n = 149), and POST-POST (postmenopausal at both timepoints, n = 93). Analyses were carried out using linear and Poisson mixed-effect models.ResultsAt baseline, PA associated directly with HDL-C and inversely with LDL-C and all body adiposity variables. An increase was observed in total (B = 1.72, 95% CI [0.16, 3.28]) and android fat mass (0.26, [0.06, 0.46]), SBP (9.37, [3.34, 15.39]), and in all blood-based biomarkers in the PRE-POST group during the follow-up. The increase tended to be smaller in the PRE-PRE and POST-POST groups compared to the PRE-POST group, except for SBP. The change in PA associated inversely with the change in SBP (−2.40, [−4.34, −0.46]) and directly with the change in WHR (0.72, [0.05, 1.38]).ConclusionsIn middle-aged women, menopause may accelerate the changes in multiple indicators of metabolic health. PA associates with healthier blood lipid profile and body composition in middle-aged women but does not seem to modulate the changes in most of the studied metabolic health indicators during the menopausal transition.