Life cycle variation and the genetic structure of nematode populations

Abstract

Few data are available on population genetic structure in nematode species, and little of the available data allows direct comparison of the genetic structures of species having di erent life cycles. Here we use mtDNA sequence data to describe the genetic structure of a heterorhabditid nematode, and compare results to published data on other nematode species. Heterorhabditis marelatus is a parasite of soil-dwelling insects. Its life cycle and local ecology should result in small e ective population sizes and restricted gene¯ow. As predicted, H. marelatus shows much lower mtDNA diversity within populations and over the species as a whole, and has a much more strongly subdivided population structure, than parasites of mobile vertebrate hosts. From data such as these we can begin to generalize about the e ects of life cycle variation on genetic structure in di erent nematode species.Keywords: e ective size, gene¯ow, Heterorhabditis, mitochondrial DNA, ND4. IntroductionWe still know little about the population genetic structure of most parasite species, the exceptions being mostly species of medical or agricultural importance (e.g. Lymbery et al., 1990; Tibayrenc et al., 1991;Day et al., 1992; Anderson et al., 1995; Blouin et al., 1995; Dybdahl & Lively, 1996; Babiker & Walliker, 1997; Blair et al., 1997). This oversight is surprising because data on genetic structure are necessary for understanding important evolutionary processes such as adaptation to host defences, host-race formation, speciation, and the evolution of resistance to drugs or vaccines. Nematodes in particular are a grossly understudied taxon. Even though nematodes are one of the most speciesrich, ecologically diverse and economically important taxa, we have information on genetic structure for only a handful of nematode species, and almost all of these are human or agricultural parasites (recently reviewed in Anderson et al., 1998). Virtually nothing is known of the genetic structure of any free-living nematode species (including Caenorhabditis elegans). Thus, more comparative studies on genetic structure in nematode species are clearly needed. Indeed, Hughes et al. (1997) speci®cally called for more data on nematodes in their recent review of patterns of population di erentiation in di erent taxa. Parasitic nematodes display a wide variety of life cycles and life histories. For example, they parasitize almost all groups of plants and animals, and occur in virtually every marine, terrestrial and freshwater habitat. Their breeding system can be obligately or facultatively amphimictic (two distinct sexes), parthenogenetic or hermaphroditic. They range from highly host-speci®c to undiscriminating, and vary in the presence or absence of free-living stages and intermediate hosts. How this diversity of life cycles in¯uences genetic structure in di erent nematode species is unknown. We currently have too few comparative data from which to make any but the simplest predictions.What is needed are comparative studies of the genetic structure of nematode s...

Spiculopteragia mathevossianiRuchliadev, 1948 is the minor morph ofSpiculopteragia spiculoptera(Gushanskaya, 1931): molecular evidence

“…We used mtND4 which exhibits less conservation sites than COX-1 [7] and is often suggested for prospecting closely related species [5,29]. The average nucleotide diversity for S. spiculoptera morph spiculoptera and S. spiculoptera morph mathevossiani together is consistent with values computed for various Haemonchidae species such as Ostertagia ostertagi, Haemonchus contortus, Haemonchus placei and Teladorsagia circumcincta from domestic hosts and Mazamastrongylus odocoilei from white-tailed deer (Odocoileus virginianus) [3,6]. We suggest that the average nucleotide diversity difference between the two morphs may be due to the low sampling of mathevossiani in light of its low occurrence [11].…”

The molecular epidemiology of parasite infections: Tools and applications

“…In populations of Teleodorsagia from sheep, for example, 98% of genetic variation occurs within infrapopulations [68], a result consistent with other studies of trichostrongyloid nematodes [69,70]. Even in parasites which have a life cycle predisposed to selfreinfection, such as Strongyloides ratii, less than 5% of genetic variation is distributed among infrapopulations in definitive hosts [71].…”

Population genetic structure of the parasitic nematode Camallanus cotti inferred from DNA sequences of ITS1 rDNA and the mitochondrial COI gene

“…For the nematode parasites of vertebrates, effective sizes and rates of gene flow are largely affected by host mobility and parasite life history traits (Blouin et al, 1995(Blouin et al, , 1999. So far, most researches related to nematode parasite focus on nematodes associated tightly with human activities, such as parasites of humans, domestic animals, and they show high genetic diversity within populations, but low differentiation among locations, indicating high levels gene flow among populations (Blouin et al, 1992(Blouin et al, , 1995(Blouin et al, , 1999Hawdon et al, 2001). For example, the trichostrongylid parasites of sheep and cattle have little genetic structure, consistent with high gene flow among populations, where extensive host movement results in large Ne (Blouin et al, 1995).…”

“…breeding) of the populations (Ne) and the rates of gene flow among them (Blouin et al, 1995;Hawdon et al, 2001). For the nematode parasites of vertebrates, effective sizes and rates of gene flow are largely affected by host mobility and parasite life history traits (Blouin et al, 1995(Blouin et al, , 1999. So far, most researches related to nematode parasite focus on nematodes associated tightly with human activities, such as parasites of humans, domestic animals, and they show high genetic diversity within populations, but low differentiation among locations, indicating high levels gene flow among populations (Blouin et al, 1992(Blouin et al, , 1995(Blouin et al, , 1999Hawdon et al, 2001).…”