Phylogeography of amphi-boreal fish: tracing the history of the Pacific herring Clupea pallasii in North-East European seas

BackgroundThe 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.ResultsThe 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.ConclusionsThe 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

Increased heavy metal and nutrient contamination does not increase fluctuating asymmetry in the seagrass Halophila ovalis

Fluctuating asymmetry (random differences between symmetric structures, FA) is one of\ud the stress indices used recently to assess a subtle effect of environmental degradation on\ud organisms and is expected to increase under stress conditions. In this study, we developed\ud an original technique of measuring FA in seagrass, Halophila ovalis.We analysed five metric\ud and meristic characters on leaves of the seagrass from a polluted and several control\ud locations in a lagoon in Eastern Australia. The seagrass was sampled from three sites at\ud each location. The analyses revealed significant spatial heterogeneity of samples in fluctuating\ud asymmetry with the highest variability was observed among sites. There was no\ud increase in FA of H. ovalis from polluted location. Possible explanations suggest that whether\ud existing concentrations of heavy metals do not cause developmental stress in seagrass or\ud their effect is compensated or even surpassed by effect of uncontrolled factors

Higher Fluctuating Asymmetry: Indication of Stress on Anadara trapezia Associated with Contaminated Seagrass

Seagrasses are marine angiosperms that colonize near-shore environments. Concern\ud has arisen over increasing concentrations of heavy metals in these systems resulting\ud from industrial and urban development due to the ability of seagrass to accumulate\ud trace metals from the environment without showing any impact on their productivity.\ud This may pose a threat to a coastal community because the polluted seagrass will then\ud provide a source of contamination to seagrass consumers. The main aim of this study\ud was to determine whether there was any detectable effect of heavy metal pollution in\ud seagrass on associated fauna. Fluctuating asymmetry of shell structure of a bivalve,\ud Anadara trapezia, were employed as biomarkers for this environmental study. The\ud result from this study revealed that A. trapezia showed distinct morphological characters\ud and high shell asymmetry in the polluted location. Thus, A. trapezia associated\ud with seagrass may be responsive to heavy metal stress and possibly a good indicator of\ud heavy metal pollution in this system. The present study discusses the possibility of\ud using a more cost-effective biomarker to define areas of heavy metal pollution

Translational Fluctuating Asymmetry and Leaf Dimension in Seagrass, Zostera capricorni Aschers in a Gradient of Heavy Metals

Methodology for measuring translational fluctuating asymmetry (TFA) on leaves of\ud seagrass, Zostera capricorni Aschers has been developed and tested to detect a subtle\ud effect of environmental stress associated with heavy metal pollution on developmental\ud instability. Our analyses showed that concentration of heavy metals (Cd, Pb, Cu, Zn,\ud Se) in leaves and roots of the seagrass were significantly higher in the polluted location\ud than in relatively unpolluted locations. We found significant differences in TFA\ud between different locations, showing that the method is sensitive enough to detect spatial\ud differences even within a rather small water body, but these differences were not\ud associated with a higher concentration of heavy metals, i.e. plants from the polluted\ud location did not show higher TFA. Possibly, seagrass can store heavy metals in their\ud tissues and protect their development from the toxic effect, or the effect of heavy metals\ud in the natural environment is confounded by other environmental factors. At the same\ud time, we found that plants from the polluted location had narrower leaves than in relatively\ud unpolluted ones, which may be caused by heavy metals or associated factors

Heavy metal impact on growth and leaf asymmetry of seagrass, Halophila ovalis

Heavy metal impact on seagrass.A major threat to the seagrass ecosystem worldwide, due to the growth of human population along the coastal environment, is pollution or contamination resulting from industrial and urban development. Although seagrass appears to be rather resistant to heavy metal contaminants, these substances may possibly harm some components of the seagrass and such responses have not been examined to a significant extent. Lead (Pb) and copper (Cu) was tested on seagrass, Halophila ovalis, to see whether the metals are environmental sressor on the seagrass. Reduced growth rate of the seagrass was observed both in Pb and Cu treatments.Leaf size of the plant also reduced as the metal concentrations increased and when the plants were exposed to the heavy metal for longer duration. As increased leaf asymmetry was more apparent at the 2 mg/L Cu treatment and no significant increases in fluctuating asymmetry were found in Pb treatment or in low levels of Cu treatment. Further discussion were made in view of selecting non-costly bioindicators of heavy metal contamination

Relating Fluctuating Asymmetries and Mean Values and Discordances of Asymmetries in a Set of Morphological Traits

This study addresses the problem of concordance in fluctuating asymmetry (FA) across traits by analyzing the relationship between FAs and the mean values of character measurements in a set of morphological traits. Regression slopes vary in natural populations, thus, revealing discordance in FA across traits among these populations. Hence, commonly accepted techniques for measuring developmental instability with FA result in uncertainties. Here, I relate FA to mean as a two-dimensional complex to demonstrate the uniformly negative slopes of standardized FA vs. mean value regressions for sets of morphological traits from eighteen distinct natural marine and aquatic populations. Comprehensive analysis of the FA–mean complex cannot be recommended for wide use in assessing stress and fitness, but it offers promise to improve FA measuring methodologies and to better understand the nature of developmental instability

Introgressive hybridization between the Atlantic and Pacific herrings (Clupea harengus and C. pallasii) in the north of Europe.

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 invasion

Arlq_cytb_populations

Arlequin input files with population grouping for cytochrome-b data

Distance matrix for the MDS ordination

Pairwise interpopulation ΦST distance matrix of trans-Arctic lineage populations for MDS ordination

IM_CYTB_NWP_MEZCHE

IM input file for comparing NW Pacific lineage with Mezen-Chesha populations