The evolution of parasitism in Nematoda

Abstract

SUMMARYNematodes are abundant and diverse, and include many parasitic species. Molecular phylogenetic analyses have shown that parasitism of plants and animals has arisen at least 15 times independently. Extant nematode species also display lifestyles that are proposed to be on the evolutionary trajectory to parasitism. Recent advances have permitted the determination of the genomes and transcriptomes of many nematode species. These new data can be used to further resolve the phylogeny of Nematoda, and identify possible genetic patterns associated with parasitism. Plant-parasitic nematode genomes show evidence of horizontal gene transfer from other members of the rhizosphere, and these genes play important roles in the parasite-host interface. Similar horizontal transfer is not evident in animal parasitic groups. Many nematodes have bacterial symbionts that can be essential for survival. Horizontal transfer from symbionts to the nematode is also common, but its biological importance is unclear. Over 100 nematode species are currently targeted for sequencing, and these data will yield important insights into the biology and evolutionary history of parasitism. It is important that these new technologies are also applied to free-living taxa, so that the pre-parasitic ground state can be inferred, and the novelties associated with parasitism isolated.

The Geological Record of Parasitic Nematode Evolution

“…According to recent molecular studies (e.g. Blaxter and Koutsovoulos, 2015), plant parasitism has evolved at least three times, animal parasitism has arisen at least ten times across a wide range of invertebrates and five times in vertebrates hosts within the three nematodes subclasses. However, many additional origins of parasitism could be proposed based on firm morphological data.…”

Targeting internal processes of plant-parasitic nematodes in the pursuit of novel agents for their control

“…Genomic and transcriptomic data connect researchers of varied disciplines and interests (Dillman et al, 2012;Kumar et al, 2012), and provide the opportunity to ex plore the biological nature of parasitism (Dieterich & Sommer, 2009;Dillman et al, 2012;Blaxter & Koutsovoulos, 2014). In light of the long histories of research on plant-parasitic nematodes and on C. elegans, extensive information exchange between the respective research communities has been rather recent, but notably produc tive.…”

The genomic basis of nematode parasitism

“…Since then the genomes of other nematodes have also been sequenced, particularly those of parasitic species. There are currently about 25 nematode genome sequences published, with about 100 projects ongoing [14]. This work has already revealed substantial diversity in the size and content of nematode genomes.…”

“…In contrast, comparisons between taxa with different lifestyles within the same clade can reasonably be used to infer the genomic bases of those differences in lifestyle. Given the extensive genomic diversity among the nematodes, it is arguable that we currently have too few nematode genomes to make strong inferences about common genomic themes underlying parasitism across different nematode clades [14,25]. Instead, more phylogenetically local, focused comparisons are probably more appropriate.…”