Aim
Alpine spring ecosystems have long been considered as highly isolated, island‐like habitats. This presumption, however, is insufficiently supported empirically and conclusions about spring ...isolation have been based on indirect evidence. Therefore, we investigated the population genomic structure of Partnunia steinmanni Walter, 1906, a strictly spring‐dwelling water mite (Hydrachnidia) species, to shed light on the degree of interconnection among freshwater spring habitats.
Location
Protected areas across the Alps, Central Europe.
Methods
Partnunia steinmanni populations were sampled by hand‐net from 12 springs. Population genomic structure was inferred with 2263 polymorphic restriction site‐associated DNA (RADseq) loci of 256 individuals. We assessed genomic admixture, the phylogenetic relationship, isolation by distance, contemporary migration, effective population sizes, and genetic diversity among individuals from different springs.
Results
We observed strong genetic differentiation between individuals from different springs. Water mites from each spring qualified as well‐delimited distinct populations with only little intra‐spring migration, even when these were located in close geographic proximity. Furthermore, we found subtle shared genetic structure among springs within the same area, and a southwestern genotype associated with the Rhône catchment that extended into eastern populations. Effective population size estimates and standing genetic variation within springs were generally low.
Main conclusions
Our findings indicate strong insularity of freshwater springs and headwater areas, likely caused by intra‐alpine Pleistocene isolation and limited dispersal abilities of strictly spring‐bound species like P. steinmanni. Our results support the concept of spring habitat isolation and highlight the importance of alpine protected areas to conserve springs as substantial components of freshwater biodiversity.
Ever-faster rates of urbanization have led to the substantial loss of agricultural land and natural areas. Furthermore, vegetated land is often fragmented and dominated by nonnative plant species ...within urban areas, which is likely to impact plant-pollinator interactions. However, the study of plant-pollinator interactions is labor intensive and remains challenging. Here, we compared plant species visited by honeybees in urban versus non-urban sites, using metabarcoding to identify pollen in honey samples. We identified a total of 262 plant genera, 15 of which were represented predominantly. Samples varied greatly in terms of plant composition, the number of nonnative genera and the number of crop plant genera. Even though land cover differed between urban and non-urban sites, plant diversity in the honey did not. We discuss our results in the light of challenges associated with the spatial scale of bee activity, preference behavior in flower visitation, and statistical power.
The three-spined stickleback is a widespread Holarctic species complex that radiated from the sea into freshwaters after the retreat of the Pleistocene ice sheets. In Switzerland, sticklebacks were ...absent with the exception of the far northwest, but different introduced populations have expanded to occupy a wide range of habitats since the late 19th century. A well-studied adaptive phenotypic trait in sticklebacks is the number of lateral plates. With few exceptions, freshwater and marine populations in Europe are fixed for either the low plated phenotype or the fully plated phenotype, respectively. Switzerland, in contrast, harbours in close proximity the full range of phenotypic variation known from across the continent. We addressed the phylogeographic origins of Swiss sticklebacks using mitochondrial partial cytochrome b and control region sequences. We found only five different haplotypes but these originated from three distinct European regions, fixed for different plate phenotypes. These lineages occur largely in isolation at opposite ends of Switzerland, but co-occur in a large central part. Across the country, we found a strong correlation between a microsatellite linked to the high plate ectodysplasin allele and the mitochondrial haplotype from a region where the fully plated phenotype is fixed. Phylogenomic and population genomic analysis of 481 polymorphic amplified fragment length polymorphism loci indicate genetic admixture in the central part of the country. The same part of the country also carries elevated within-population phenotypic variation. We conclude that during the recent invasive range expansion of sticklebacks in Switzerland, adaptive and neutral between-population genetic variation was converted into within-population variation, raising the possibility that hybridization between colonizing lineages contributed to the ecological success of sticklebacks in Switzerland.
Ecological speciation and adaptive radiation are key processes shaping northern temperate freshwater fish diversity. Both often involve parapatric differentiation between stream and lake populations ...and less often, sympatric intralacustrine diversification into habitat‐ and resource‐associated ecotypes. However, few taxa have been studied, calling for studies of others to investigate the generality of these processes. Here, we test for diversification within catchments in freshwater sculpins in a network of peri‐Alpine lakes and streams. Using 8047 and 13 182 restriction site‐associated (RADseq) SNPs, respectively, we identify three deeply divergent phylogeographic lineages associated with different major European drainages. Within the Aare catchment, we observe populations from geographically distant lakes to be genetically more similar to each other than to populations from nearby streams. This pattern is consistent with two distinct colonization waves, rather than by parapatric ecological speciation after a single colonization wave. We further find two distinct depth distribution modes in three lakes of the Aare catchment, one in very shallow and one in very deep water, and significant genomewide differentiation between these in one lake. Sculpins in the Aare catchment appear to represent an early‐stage adaptive radiation involving the evolution of a lacustrine lineage distinct from parapatric stream sculpins and the repeated onset of depth‐related intralacustrine differentiation.
Neutral and adaptive variation among populations within a species is a major component of biological diversity and may be pronounced among insular populations due to geographical isolation and island ...specific evolutionary forces at work. Detecting and preserving potential evolutionary significant units below the species rank has become a crucial task for conservation biology. Combining genetic, phenotypic and ecological data, we investigated evolutionary patterns among the enigmatic threespine stickleback populations from western Mediterranean islands, all of which are threatened by habitat deterioration and climate change. We find indications that these populations derive from different genetic lineages, being genetically highly distinct from the stickleback of mainland Europe and the northern Atlantic as well as from each other. Mediterranean island stickleback populations are also phenotypically distinct from mainland populations but interestingly stickleback from Iceland have converged on a similar phenotype. This distinctive island stickleback phenotype seems to be driven by distinct selective regimes on islands versus continents. Overall, our results reveal the status of western Mediterranean island stickleback as evolutionarily distinct units, important for conservation of biodiversity.
Rapid phenotypic diversification during biological invasions can either arise by adaptation to alternative environments or by adaptive phenotypic plasticity. Where experimental evidence for adaptive ...plasticity is common, support for evolutionary diversification is rare. Here, we performed a controlled laboratory experiment using full-sib crosses between ecologically divergent threespine stickleback populations to test for a genetic basis of adaptation. Our populations are from two very different habitats, lake and stream, of a recently invaded range in Switzerland and differ in ecologically relevant morphological traits. We found that in a lake-like food treatment lake fish grow faster than stream fish, resembling the difference among wild type individuals. In contrast, in a stream-like food treatment individuals from both populations grow similarly. Our experimental data suggest that genetically determined diversification has occurred within less than 140 years after the arrival of stickleback in our studied region.
Wolbachia is an endosymbiont common to most invertebrates, which can have significant evolutionary implications for its host species by acting as a barrier to gene flow. Despite the importance of ...Wolbachia, still little is known about its prevalence and diversification pattern among closely related host species. Wolbachia strains may phylogenetically coevolve with their hosts, unless horizontal host-switches are particularly common. We address these issues in the genus Erebia, one of the most diverse Palearctic butterfly genera. We sequenced the Wolbachia genome from a strain infecting Erebia cassioides and showed that it belongs to the Wolbachia supergroup B, capable of infecting arthropods from different taxonomic orders. The prevalence of Wolbachia across 13 closely related Erebia host species based on extensive population-level genetic data revealed that multiple Wolbachia strains jointly infect all investigated taxa, but with varying prevalence. Finally, the phylogenetic relationships of Wolbachia strains are in some cases significantly associated to that of their hosts, especially among the most closely related Erebia species, demonstrating mixed evidence for phylogenetic coevolution. Closely related host species can be infected by closely related Wolbachia strains, evidencing some phylogenetic coevolution, but the actual pattern of infection more often reflects historical or contemporary geographic proximity among host species. Multiple processes, including survival in distinct glacial refugia, recent host shifts in sympatry, and a loss of Wolbachia during postglacial range expansion seem to have jointly shaped the complex interactions between Wolbachia evolution and the diversification of its host among our studied Erebia species.
We present a genome assembly from an individual female
Erebia aethiops
(the scotch argus; Arthropoda; Insecta; Lepidoptera; Nymphalidae). The genome sequence is 473 megabases in span. The complete ...assembly is scaffolded into 20 chromosomal pseudomolecules, with the W and Z sex chromosomes assembled. The complete mitochondrial genome was also assembled and is 15.2 kilobases in length.
Spatial heterogeneity in diversity and intensity of parasitism is a typical feature of most host-parasite interactions, but understanding of the evolutionary implications of such variation is ...limited. One possible outcome of infection heterogeneities is parasite-mediated divergent selection between host populations, ecotypes or species which may facilitate the process of ecological speciation. However, very few studies have described infections in population-pairs along the speciation continuum from low to moderate or high degree of genetic differentiation that would address the possibility of parasite-mediated divergent selection in the early stages of the speciation process. Here we provide an example of divergent parasitism in freshwater fish ecotypes by examining macroparasite infections in threespine stickleback (Gasterosteus aculeatus) of four Swiss lake systems each harbouring parapatric lake-stream ecotype pairs. We demonstrate significant differences in infections within and between the pairs that are driven particularly by the parasite taxa transmitted to fish from benthic invertebrates. The magnitude of the differences tended to correlate positively with the extent of neutral genetic differentiation between the parapatric lake and stream populations of stickleback, whereas no such correlation was found among allopatric populations from similar or contrasting habitats. This suggests that genetic differentiation is unrelated to the magnitude of parasite infection contrasts when gene flow is constrained by geographical barriers while in the absence of physical barriers, genetic differentiation and the magnitude of differences in infections tend to be positively correlated.
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