Molecular comparisons of freshwater and marine isolates of the same morphospecies of heterotrophic flagellates

Abstract

Heterotrophic flagellates are key components of all ecosystems. Understanding the patterns of biodiversity of these organisms is thus particularly important. Here we analyzed the intraspecific diversity of 10 morphospecies of heterotrophic flagellates comprising representatives of the Apusozoa (2 morphospecies) and Kinetoplastea (8 morphospecies), all belonging to the most common flagellates with worldwide distribution. Most morphospecies showed a mixing of lineages isolated from diverse habitats, indicating that some lineages of these morphospecies had been able to colonize different habitats several times. Furthermore, our results revealed remarkable levels of genetic divergence within most of the morphospecies studied, underlining the difficulty of correctly determining species by means of morphology alone. Many cryptic or pseudocryptic species seem to occur. Our results revealed clear divergence between marine and freshwater lineages of the morphospecies Ancyromonas sigmoides, showing that freshwater lineages have not been able to colonize marine environments and marine lineages have not been able to colonize freshwater environments for a long time.

FIG. 1.

Maximum likelihood tree of the phylum Apusozoa obtained by using all aligned positions. The tree was rooted using Choanozoa as the outgroup. The numbers at the nodes are bootstrap support percentages calculated from 100 replicates for maximum likelihood (left) and minimum evolution (right) analyses. Values less than 70% are omitted or are indicated by a hyphen. The model for nucleotide substitution chosen was TrN + Γ + I. GenBank accession numbers are indicated. Strains sequenced in this study are indicated by boldface type. Scale bar = 0.1 substitution per site. Freshwater and marine clades of A. sigmoides are labeled. Mean p-distances for the species studied (Ancyromonas and Apusomonas) and for the major clades within A. sigmoides are shown. Sample locations for the morphospecies strains studied are indicated as follows: diamonds, marine; stars, freshwater; plus sign, soil; and asterisk, groundwater.

FIG. 2.

Consensus tree (50% majority rule) of the class Kinetoplastea obtained by using all aligned positions. The tree was rooted using Prokinetoplastida as the outgroup. The model for nucleotide substitution chosen was GTR + Γ. Scale bar = 0.1 substitution per site. Some clades are labeled according to their sample locations. Mean p-distances for all of the mono- and paraphyletic species studied and for the major clade of N. designis are shown. Sample locations for the morphospecies strains studied are indicated as follows: large diamonds, marine; stars, freshwater; plus signs, soil; cloverleaves, marine sediment; and clusters of four small diamonds, freshwater sediment. For further details see the legend to Fig. 1.