How Can We Understand the Genomic Basis of Nematode Parasitism?

Abstract

Nematodes are very common animals and they have repeatedly evolved parasitic lifestyles during their evolutionary history. Recently, the genomes of many nematodes, especially parasitic species, have been determined, potentially giving an insight into the genetic and genomic basis of nematodes' parasitism. But, to achieve this, phylogenetically appropriate comparisons of genomes of free-living and parasitic species are needed. Achieving this has often been hampered by the relative lack of information about key free-living species. While such comparative approaches will eventually succeed, I suggest that a synthetic biology approach - moving free-living nematodes towards a parasitic lifestyle - will be our ultimate test of truly understanding the genetic and genomic basis of nematode parasitism.

Figure 1

Phylogenetic Comparisons to Understand Nematode Parasitism. (A) A hypothetical phylogeny of two nematodes clades, A and B, where the ancestral species had a free-living lifestyle. Within each clade parasitism evolves giving parasite species A in clade A and parasite species B in clade B. Comparisons of parasite species A with free-living species within its own clade is informative to understand the evolution of parasitism within that clade. Comparisons across clades can confound the clade-specific evolutionary history with the species’ lifestyle. (B) A phylogeny of 226 nematode species based on an alignment of 18S rRNA from release 128 of the SILVA rRNA database , where animal parasites are in red, plant parasites are in green, and free-living species are in black, showing the principal nematode clades (I–V) after , showing Pristionchus pacificus, C. elegans and Strongyloides spp., which are mentioned in the text. Scale is expected substitutions per nucleotide site.

Figure 2

The Phylogeny of Strongyloides and Its Relatives and the Evolution of Parasitism. A phylogeny of four species of Strongyloides, Parastrongyloides trichosuri, and Rhabditophanes sp. Rhabditophanes is a free-living species. Parastrongyloides can have multiple free-living adult generations, but can also be parasitic, making it a facultative parasite. Strongyloides is an obligate parasitic species because, even though it has a free-living adult generation (as does Parastrongyloides), Strongyloides’ life cycle requires a parasitic adult generation every generation. Where parasitism and obligate parasitism are inferred to have arisen is shown. The boxes show the number of astacin metallopedtidase (top) and SCP/TAPS protein (bottom) coding genes that have been acquired (+, in red) and lost (–, in blue) across the phylogeny. The tree branch lengths do not show the relative distance among the taxa. Data from .