Stable and unstable environments influence the genetic diversity of the nematode Teladorsagia circumcincta, a parasite of small ruminants.

Acclimation of animal parasitic nematodes in the laboratory is the result of environmental disturbance; moderate numbers of infective larvae are introduced into and develop in a few naive hosts (versus many hosts with a resistance status to parasite infection under natural conditions), and stable conditions such as convenient moisture and temperature (versus the unstable climatic environment in the field) are offered to the free-living stages. The acclimation of sheep and goat lines of the nematode Teladorsagia circumcincta in lambs was arranged in the following putative order of increasing disturbance: sheep line and high success of experimental infection, sheep line and poor success of infection, goat line and high success of infection, sheep line with very poor success of infection, goat line and poor success of infection, and sheep isofemale line with founder and inbreeding effects. The genetic variability was assessed using the enzymes glucose-phosphate isomerase, lactate dehydrogenase, malate dehydrogenase, mannose-phosphate isomerase, and phosphoglucomutase, in starch-gel electrophoresis. The ranking on increasing Fst values (increasing genetic differentiation) observed between initially introduced and twice-passaged generations ranged from 0.003 (sheep line in sheep with high infective success) to 0.19 (sheep isofemale line) and matched to a certain extent with disturbance. The introduction of a goat line in sheep was a major disturbance, whereas in sheep lines the major factor of variation was due to the founder effect, i.e., the effective number of nematodes introduced to seed the acclimated lines. The deficiency in heterozygotes, which remains largely unexplained, was not modified during acclimation. In most cases the introduction of worms from nature resulted in lower overall genetic variability in the subsequent laboratory-reared populations.