Due to climate change, Arctic ice sheets are retreating. This leads to the formation of numerous new periglacial ponds and lakes, which are being colonized by planktonic organisms such as the water flea Daphnia. This system provides unique opportunities to test genotype colonization dynamics and the genetic assemblage of populations. Here, we studied clonal richness of the Daphnia pulex species complex in novel periglacial habitats created by glacial retreat in the Jakobshavn Isbrae area of western Greenland. Along a 10 km transect, we surveyed 73 periglacial habitats out of which 61 were colonized by Daphnia pulex. Hence, for our analysis, we used 21 ponds and 40 lakes in two clusters of habitats differing in age (estimated <50 years vs. >150 years). We tested the expectation that genetic diversity would be low in recently formed (i.e. young), small habitats, but would increase with increasing age and size. We identified a total of 42 genetically distinct clones belonging to two obligately asexual species of the D. pulex species complex: D. middendorffiana and the much more abundant D. pulicaria. While regional clonal richness was high, most clones were rare: 16 clones were restricted to a single habitat and the five most widespread clones accounted for 68% of all individuals sampled. On average, 3·2 clones (range: 1-12) coexisted in a given pond or lake. There was no relationship between clonal richness and habitat size when we controlled for habitat age. Whereas clonal richness was statistically higher in the cluster of older habitats when compared with the cluster of younger ponds and lakes, most young habitats were colonized by multiple genotypes. Our data suggest that newly formed (periglacial) ponds and lakes are colonized within decades by multiple genotypes via multiple colonization events, even in the smallest of our study systems (4 m(2) ).

One of the most prominent manifestations of the ongoing climate warming is the retreat of glaciers and ice sheets around the world. Retreating glaciers result in the formation of new ponds and lakes, which are available for colonization. The gradual appearance of these new habitat patches allows us to determine to what extent the composition of asexual Daphnia (water flea) populations is affected by environmental drivers vs. dispersal limitation. Here, we used a landscape genetics approach to assess the processes structuring the clonal composition of species in the D. pulex species complex that have colonized periglacial habitats created by ice-sheet retreat in western Greenland. We analysed 61 populations from a young (<50 years) and an old cluster (>150 years) of lakes and ponds. We identified 42 asexual clones that varied widely in spatial distribution. Beta-diversity was higher among older than among younger systems. Lineage sorting by the environment explained 14% of the variation in clonal composition whereas the pure effect of geographical distance was very small and statistically insignificant (Radj2 = 0.010, P = 0.085). Dispersal limitation did not seem important, even among young habitat patches. The observation of several tens of clones colonizing the area combined with environmentally driven clonal composition of populations illustrates that population assembly of asexual species in the Arctic is structured by environmental gradients reflecting differences in the ecology of clones.

Founder effects introduce stochasticity in the genetic structure of species at the regional scale. To the extent that founder effects are important, they will result in a reduced signature of space, time, and environmental variation in landscape genetic data. We studied the metapopulation genetic structure of recently founded populations of the microcrustacean Daphnia sinensis in 10 Ethiopian water reservoirs. We used three different approaches to estimate the number of effective founders and applied them to two independent genetic marker sets in an effort to investigate the role of founder effects and to estimate effective size of the founding population. Estimates of founding sizes rarely exceeded eight individuals but were most often limited to less than four individuals. No associations of genetic identities, gene frequencies, measures of genetic diversity, or differentiation with environmental and spatial variables were found. Age and size of the reservoirs were not correlated with genetic diversity measures or number of founders in these reservoirs. These findings indicate that neither strong selection, nor dispersal limitation are responsible for the observed pattern of genetic variation. Our results suggest a regional population structure that is strongly impacted by founder events, reflecting colonization by just a few founders per waterbody, and not noticeably influenced by subsequent dispersal and gene flow. Our results show that rapid colonization of empty habitats and fast population growth by a handful of founders can result in strong founder effects, even in relatively large habitats that are likely regularly reached by new immigrants.

Ecological processes maintaining landscape genetic variation and metacommunity structure in natural landscapes have traditionally been studied in isolation. Their integrated study may hold important information as to what extent the effect of major ecological processes are species- or landscape-specific, resulting in a more coherent picture on the spatial organization of biodiversity. Here, we explicitly compared the relative importance of spatial and environmental drivers of both cladoceran metacommunity structure as well as landscape genetic structure of its most widespread member, the water flea Daphnia magna, in soda pans of the Seewinkel region in Austria. The landscape of soda pans in this region is characterized by strong environmental gradients and unidirectional wind acting as a key dispersal agent among these temporary habitats. Our study shows both parallels and divergences in the relative importance of local environmental sorting and spatial connectivity in determining landscape genetic versus metacommunity structure. The metacommunity is structured primarily by the environment, while in the D. magna metapopulation, the spatial signal is predominant. The much weaker environmental signal in Daphnia can be explained by the fact that the microsatellite markers are presumably neutral and was confirmed by a per-allele analysis. An important parallel between metacommunity and landscape genetic structure is the strong signal of the prevailing wind direction in determining the spatial pattern. This suggests that for both community as well as population assembly in D. magna, wind plays an important role in determining connectivity among soda pans, thereby affecting dispersal and colonization rates influencing both local species and genetic composition.

Background: Habitat selectivity and ecology of freshwater fishes were studied in two selected streams and their junction point which consist a total of 39 microhabitats. The aims of this study were to describe the habitat preference and its availability to fish assemblage, as well as ecology, habitat use, and habitat characteristics. Methods: We collected fish with backpack electrofishing three times during August 2013, December 2013, and March 2014. Using a variation partitioning approach of R software, we studied the relationship of fish abundances with stream type, habitat type, and abundance of key macroinvertebrate taxa. Results: A total of 6554 fishes representing four species belonging to the family Cyprinidae were caught. A higher total fish abundance was recorded from Gereb Tsedo (4870; 74.3%) than from Elala stream (1684; 25.7%). Taking both streams together, the overall total relative fish abundance was significantly higher in pools (53%) than in runs (35%) and in riffles (12%) at P < 0.05. Species-wise comparisons showed that 71%, 15%, 13%, and 1% of the pool fish community were occupied by Garra blanfordii, Garra ignestii, Garra dembecha, and Garra aethiopica, respectively. Stream type, habitat type, and key macroinvertebrate taxa each explained a significant proportion of the variation in fish abundance. Based on the variation partitioning approach, fish abundance was higher in Gereb Tsedo stream (P < 0.01). Moreover, fish abundance increased with pool habitat type (P < 0.01) and with availability of key macroinvertebrate taxa (P < 0.01). Conclusion: Fish abundance differed between stream types, among habitats and among key macroinvertebrate taxa availability. Among the factors, habitat type was the most important driving factor behind variation among fish abundances, and pool supports the highest fish abundance.

Summary 1. Knowledge of the relationship between biodiversity and environmental factors provides insight into patterns of species richness and distribution in limnetic ecosystems. To this end, this study was conducted to test the effect of limnological characteristics of reservoirs on bird species richness and distribution along an age gradient of limnetic ecosystems in Tigray National Regional State. 2. To evaluate the relationship between limnological characteristics of reservoirs and patterns of bird species richness and distribution, six physicochemical variables, three morph-edaphic and biological variables were recorded for 35 reservoirs and analyzed by multivariate statistical techniques. Species richness data was subjected to a multiple regression analysis at limnological variables, biological variables and age of the reservoirs in order to investigate the most important explanatory factors influencing avian species richness and their distribution using Redundancy analysis (RDA). 3. 85 bird species from 54 genera, 25 families and 15 bird orders were recorded, with mean species richness 14.236.72 (mean  standard deviation) per reservoir. Five of these species are near threatened (NT) while other two species fall under critically endangered (CR) and vulnerable (VU) conservation status designations, respectively. Bird species richness was positively correlated with surface area of reservoirs. The RDA analysis identified two significant RDA axis and 34.4% of the variation in species richness is explained by environmental variation (R2adj = 0.34375; P < 0.001). Generally, water chemistry appears to play only a minor part in affecting bird species richness in reservoir in Tigray, Northern Ethiopia. However, chemical variables may be helpful to distinguish between used and unused sites for some species. 4. The result provides an important insight on the ecological relationship between waterbirds species richness and limnological characteristics of reservoirs. And plays a role towards strengthening our knowledge on aquatic bird ecology and natural history of African Eurasian Migratory waterbirds.

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