Colonization history and clonal richness of asexual Daphnia in periglacial habitats of contrasting age in West Greenland

Abstract

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) ).

Environment not dispersal limitation drives clonal composition of Arctic Daphnia in a recently deglaciated area

“…In contrast, we observed a quite high local and regional clonal diversity (Haileselasie et al . ), which is comparable or higher to that found in previous studies from Arctic sites in Canada (Hobaek et al . ), Iceland and the Godhavn (Disko Island) region in Greenland (Weider et al .…”

“…Genomic DNA extraction and PCR amplifications followed the methods stated in Haileselasie et al . (). Amplified PCR products were separated on an ABI 3130 capillary sequencer (Applied Biosystems ® ), and allele sizes (fragment lengths) were scored against an internal size standard (Liz500) using the software genemapper (GeneMapper ® v4.0; Applied Biosystems ® , Foster City, CA, USA).…”

“…During an expedition in 2012 to the Jakobshavn Isbræ near Ilulissat, water fleas ( Daphnia ) were sampled from 61 populations (see Haileselasie et al . for details). We surveyed the clonal structure of Daphnia pulex s.l.…”

“…; Haileselasie et al . ). Although this species complex contains both sexual (cyclically parthenogenetic) and asexual (obligately parthenogenetic) lineages (the latter often polyploid), polar regions typically harbour only asexual lineages (reviewed in Decaestecker et al .…”

“…The analysis of clonal composition of populations of asexual Daphnia species that inhabit recently colonized periglacial ponds and lakes offers an excellent model system to investigate to what extent such patterns of environmental sorting are already evident in metapopulations that developed in recently created habitats, or whether these metapopulations are mainly structured by dispersal limitation or dominance of GPGs (Haileselasie et al . ).…”