From isolates to a synthetic laboratory population: maintenance of variability in the nematode Haemonchus contortus.

Haemonchus contortus isolates were collected from goats of five locations with different climatic characteristics in Guadeloupe archipelago. They were investigated for morphology, morphometrics and allozyme diversity after passage in immunosuppressed lambs using long acting corticoids. The basic aim of the work was to construct a synthetic strain in laboratory conditions which was representative of the isolates. The isolates were only slightly different although climatic conditions were very different. The resemblance of isolates might be due to the practice of goat exchanges between farms or to their insular origin. However the isolate from a smaller island (Les Saintes) was different (mostly on morphometrics) from all the others originating from Guadeloupe main Island. The first assemblage in laboratory resulting from the installation from a mixture of the five isolates was not very representative, whereas the next generation (synthetic strain) resembled all the isolates as shown from allozyme study. Female fecundity and length in established synthetic strain were lower than that recorded in isolates, indicating a decrease in fitness, possibly due to the stability of experimental environment. The representativity of the synthetic strain was good but the strain could still evaluate on further passages and should be evaluated on a large number of generations maintained in laboratory.