COI gene and ecological data suggest size-dependent high dispersal and low intra-specific diversity in free-living terrestrial protists (Euglyphida: Assulina)

Abstract

Aim Propagule size and ecological requirements are believed to be major factors influencing the passive dispersal of free-living terrestrial protists. We compared the colonization potential of three closely related testate amoeba species (Assulina muscorum, A. seminulum, A. scandinavica, ranging from 40 to 100 lm in length).Location Europe.Methods We collected individual Assulina species cells from Sphagnum peatlands across Europe. We sequenced a 550-bp fragment of the mitochondrial cytochrome c oxidase subunit I gene (COI) to estimate the within-species variability, as a proxy for gene flow. We reviewed existing ecological and palaeoecological data to assess the ecological tolerance of Assulina species and how rapidly they colonized developing peatlands.Results We obtained COI sequences for 30 individuals of A. seminulum from eleven sites, for 39 of A. muscorum from six sites, and for six of A. scandinavica from two sites. We observed three haplotypes for A. seminulum and two for A. muscorum, often co-existing in the same sites. The sequences of A. scandinavica from the two sites were identical. Assulina muscorum and A. seminulum haplotypes varied by only 1-2 nucleotides, resulting in >99.5% similarity. Genetic diversity within A. seminulum was higher than that within A. muscorum. Ecological and palaeoecological records showed that A. muscorum was much more frequent and abundant than A. seminulum, and had a somewhat broader ecological tolerance for pH, moisture and water-table depth. Assulina muscorum always appeared early during the developmental history of peatlands, either before or simultaneously with A. seminulum.Main conclusions The lack of genetic structure observed with a variable marker such as COI suggests high gene flow between the sites and thus rapid transport (at an evolutionary scale) over large distances, in agreement with the palaeoecological records. Thus, geographical distance alone does not seem to prevent the dispersal of testate amoebae, at least within Europe. Nevertheless, genetic diversity was significantly lower within A. muscorum than within A. seminulum, suggesting that its smaller size and abundance and/or broader ecological tolerance influence its effective dispersal capacity. These results are in agreement with the often earlier colonization of peatlands by A. muscorum and its broader ecological tolerance.

Stochastic distribution of small soil eukaryotes resulting from high dispersal and drift in a local environment

“…EcM and pathogenic fungi exhibited relatively higher spatial turnover than expected by the null model, whereas saprotrophic fungi and Rhizaria had significantly lower spatial turnover than expected (Figure 3). These results are consistent with random dispersal that has been reported for soil protozoa and mesofauna (Petersen and Luxton, 1982;Esteban et al, 2006;Lara et al, 2011). This can be attributed to their high dispersal rate, which overwhelms both environmental selection and ecological drift.…”

Water–energy balance, past ecological perturbations and evolutionary constraints shape the latitudinal diversity gradient of soil testate amoebae in south‐western South America

“…It is worth mentioning that this does not rule out the possible existence of endemic species of testate amoebae in areas with harsh abiotic conditions. Small generalist species are thought to be among the earliest colonizers of new habitats (Lara et al, 2011;Fournier et al, 2016) and of previously glaciated areas (Wilkinson, 1990;Carlson et al, 2010;Fern andez et al, 2012), which also suggests that the recolonization of northern and southern areas is a recent and still ongoing process. 3).…”

Checklist, diversity and distribution of testate amoebae in Chile

“…pH, temperature and moisture ranges) and thus, the number of inter-specific interactions that occur on islands (Hutchinson 1957). Besides the above prediction, the airborne dispersal hypothesis (Wilkinson 2001;Lara et al 2011;Wilkinson et al 2012) predicts that the small species (those having a size of below a certain threshold, such as 100 or 20 m) are more likely to be passively dispersed over long distances than large species. Although the mechanism proposed by this hypothe-sis could be a surrogate of other physiological traits of protists (e.g.…”