Postglacial colonization shows evidence for sympatric population splitting of Eurasian perch (Perca fluviatilis L) in Lake Constance

Previous microsatellite analysis showed that two subpopulations of perch (Perca fluviatilis L) exist in Lake Constance. This raises questions of whether (i). Lake Constance was colonized by two populations that diverged in allopatry, or (ii). the two subpopulations diverged in sympatry. Sequence analysis of a 365 bp mtDNA fragment (5'-end of the D-loop) of perch from Lake Constance and adjacent waters revealed 10 haplotypes. We suggest colonization via the Danube river, based on the frequency and dispersion of haplotypes, and knowledge of the lake's palaeohydrological development. Pairwise FST-values using mitochondrial DNA sequences showed no significant population subdivision. Our study provides strong evidence that subpopulations of perch in Lake Constance have diverged in sympatry.     

Consequences of unequal population size, asymmetric gene flow and sex-biased dispersal on population structure in brook charr (Salvelinus fontinalis)

Unravelling relationships between dispersal and population structure requires considering the impacts of assumption violations of indirect gene flow models in a given system. We combined temporal, individual and coalescent-based analyses of microsatellite DNA variation to explore the general hypothesis that unequal effective population size (Ne), asymmetric gene flow (m) and nonrandom (sex-biased) individual dispersal had an important effect on spatiotemporal population structuring in lake-dwelling brook charr (Salvelinus fontinalis). This integrative examination shed light on the dichotomous structuring observed between an outlet and three tributary-spawning populations and their potential for adaptive divergence. It revealed further that finer tributary population structuring incongruent with drainage structure has been shaped by asymmetric m from one population with a large Ne towards two populations of smaller Ne. Gene flow among the tributaries was also mediated mainly by male-biased dispersal. However, longer distance dispersal from tributaries to the outflow was female-biased. Spatially dependent sex-biased dispersal may have contributed therefore to gene flow at different levels of population structuring. Our results demonstrate how dispersal and population structure may interrelate to produce spatial variation in intraspecific diversity, and are therefore relevant for conservation programmes seeking to define conservation units or predict recolonization rates of extirpated populations.     

Genetic subdivision, glacial refugia and postglacial recolonization in the golden-striped salamander, Chioglossa lusitanica (Amphibia: urodela)

The golden-striped salamander (Chioglossa lusitanica) is an ecologically specialized species, endemic to north-western Iberia. Patterns of genetic variation were assessed at seven polymorphic enzyme loci and one mitochondrial DNA (mtDNA) marker (cytochrome b) in 17 populations across its range. Estimates of enzyme genetic diversity revealed a high degree of genetic subdivision (FST = 0.68), mainly attributable to the existence of two groups of populations. The groups were located, respectively, north and south of the Mondego River, indicating that this river coincided with a major historical barrier to gene flow. A significant decrease in genetic variability from the Mondego northwards was associated with the Douro and Minho rivers. mtDNA sequence variation revealed a congruent pattern of two haplotype groups (d = 2.2%), with a geographical distribution resembling that of allozymes. The pattern and depth of genetic variation is consistent with the following hypotheses: (i) subdivision of an ancestral range of the species prior to the middle Pleistocene; (ii) secondary contact between populations representing historical refugia; (iii) relatively recent range expansion giving rise to the northern part of the species range; and (iv) loss of genetic variation through founder effects during range expansion across major rivers.     

Towards the understanding of the origin of the Polish remote population of Polyommatus (Agrodiaetus) ripartii (Lepidoptera: Lycaenidae) based on karyology and molecular phylogeny

Many species of the subgenus Agrodiaetus have dotlike distribution ranges, and the delimitation of the majority of species is only possible on the basis of chromosomal and/or molecular data. In our research, we used a combination of chromosomal and molecular mitochondrial and nuclear markers to analyse the taxonomic identity and to study the phylogeographic history of an enigmatic Agrodiaetus population from South Poland. We discovered this population to be chromosomally and genetically indistinguishable from the widely distributed West Palaearctic species Polyommatus ripartii (Freyer, 1830). Moreover, this population was found to be genetically homogenous and to share the single identified COI+COII haplotype with populations from remote localities in Spain, Bulgaria and Ukraine. Coalescence‐based dating with COI+COII marker estimated that the Polish population originated most likely 10 600–14 300 years ago. This estimation corresponds well to the age (11 700–12 000 years) of palaeontological remnant of Onobrychis arenaria, a food plant of P. ripartii, found in Poland. Generally, the data obtained support the hypotheses that (1) the common ancestor of the Central European populations originated in a refugium in the North Balkan, (2) after the last glacial maximum, this ancestor became broadly distributed in Europe and (3) the Nida population in Poland represents a relict of this ancient distribution.     

Phylogeography of North Atlantic intertidal tardigrades: refugia,cryptic speciation and the history of the Mid‐Atlantic Islands

Aim To analyse the phylogeographical history of intertidal tardigrades in the North Atlantic in order to improve our understanding of geographical differentiation in microscopic organisms, and to understand the potential importance of the Mid‐Atlantic Islands as stepping stones between the American and European coasts of the Atlantic Ocean. Location Twenty‐four localities from the Mid‐Atlantic Islands (Greenland, Iceland and the Faroe Islands) and both sides of the North Atlantic Ocean. Methods A mitochondrial marker (cytochrome c oxidase subunit I) was sequenced from individual tardigrades belonging to the genus Echiniscoides. The existence of cryptic species was detected using generalized mixed Yule coalescence analysis; lineage ages were estimated with relaxed clock methods; and the degree of geographical differentiation was analysed with samova analyses, haplotype networks and Mantel tests. Results Echiniscoides hoepneri, previously known only from Greenland, was recovered throughout the Mid‐Atlantic Islands. The Faroe Islands population was isolated from Greenland and Iceland, but overall genetic variation was low. The morphospecies Echiniscoides sigismundi had high genetic variation and consisted of at least two cryptic species. A northern and a southern species were both recovered on both sides of the Atlantic, but only the northern species was found on the Mid‐Atlantic Islands. The northern species showed signs of long‐term isolation between the Western and Eastern Atlantic, despite the potential of the Mid‐Atlantic islands to act as stepping‐stones. There was no sign of long‐term isolation in the southern species. The Mid‐Atlantic individuals of the northern species were of Eastern Atlantic origin, but Greenland and Iceland showed signs of long‐term isolation. The genetic pattern found in the southern species is not clearly geographical, and can probably be best explained by secondary contact between former isolated populations. Main conclusions North Atlantic intertidal tardigrades from the genus Echiniscoides showed strong geographical differentiation, and the Mid‐Atlantic Islands seemed unimportant as stepping stones across the Atlantic. The geographical variation of the northern species of E. sigismundi suggests post‐glacial recolonization from several refugia.     

Animal Colonization of Restored Peatlands: Inoculation of Plant Material as a Source of Insects

Ecological restoration of mined peatlands in North America involves active reintroduction of bog plant species. Animals are not actively reintroduced, thus the re‐establishment of peatland fauna must occur either by inoculation along with introduced plant material or by dispersal. We examined the extent to which insects are reintroduced to restored sites with plant material by rearing insects from shredded vegetation collected in three donor sites. We assessed differences in abundance, diversity, and composition of taxonomic and trophic groups among seasons and sites. Abundance and species richness did not differ by season, but species assemblages did. The three sites were significantly different in abundance, but not in species richness and assemblages. Few insects emerged from the vegetation, suggesting that shredded plant material may not be the primary source of insect colonists. Insects likely recolonize by active or passive dispersal from the surrounding area. The species pool was similar among donor sites; consequently a mined site could be inoculated with vegetation from another peatland in the same region and this would not affect the insect assemblages at the initial stage of establishment. Diapause may be a major factor for emergence success among seasons of collection. Knowledge of how restoration techniques influence establishment of insect communities will help predict longer‐term outcomes of restoration on biotic communities in peatlands.     

Documenting the biogeographic history of Microtus cabrerae through its fossil record

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Do pathogens reduce genetic diversity of their hosts? Variable effects of sylvatic plague in black‐tailed prairie dogs

Introduced diseases can cause dramatic declines in—and even the loss of—natural populations. Extirpations may be followed by low recolonization rates, leading to inbreeding and a loss of genetic variation, with consequences on population viability. Conversely, extirpations may create vacant habitat patches that individuals from multiple source populations can colonize, potentially leading to an influx of variation. We tested these alternative hypotheses by sampling 15 colonies in a prairie dog metapopulation during 7 years that encompassed an outbreak of sylvatic plague, providing the opportunity to monitor genetic diversity before, during and after the outbreak. Analysis of nine microsatellite loci revealed that within the metapopulation, there was no change in diversity. However, within extirpated colonies, patterns varied: In half of the colonies, allelic richness after recovery was less than the preplague conditions, and in the other half, richness was greater than the preplague conditions. Finally, analysis of variation within individuals revealed that prairie dogs present in recolonized colonies had higher heterozygosity than those present before plague. We confirmed plague survivorship in six founders; these individuals had significantly higher heterozygosity than expected by chance. Collectively, our results suggest that high immigration rates can maintain genetic variation at a regional scale despite simultaneous extirpations in spatially proximate populations. Thus, virulent diseases may increase genetic diversity of host populations by creating vacant habitats that allow an influx of genetic diversity. Furthermore, even highly virulent diseases may not eliminate individuals randomly; rather, they may selectively remove the most inbred individuals.     

A greener Greenland? Climatic potential and long-term constraints on future expansions of trees and shrubs

Warming-induced expansion of trees and shrubs into tundra vegetation will strongly impact Arctic ecosystems. Today, a small subset of the boreal woody flora found during certain Plio-Pleistocene warm periods inhabits Greenland. Whether the twenty-first century warming will induce a re-colonization of a rich woody flora depends on the roles of climate and migration limitations in shaping species ranges. Using potential treeline and climatic niche modelling, we project shifts in areas climatically suitable for tree growth and 56 Greenlandic, North American and European tree and shrub species from the Last Glacial Maximum through the present and into the future. In combination with observed tree plantings, our modelling highlights that a majority of the non-native species find climatically suitable conditions in certain parts of Greenland today, even in areas harbouring no native trees. Analyses of analogous climates indicate that these conditions are widespread outside Greenland, thus increasing the likelihood of woody invasions. Nonetheless, we find a substantial migration lag for Greenland''s current and future woody flora. In conclusion, the projected climatic scope for future expansions is strongly limited by dispersal, soil development and other disequilibrium dynamics, with plantings and unintentional seed dispersal by humans having potentially large impacts on spread rates.