Exploring the causes of small effective population sizes in cyst nematodes using artificial Globodera pallida...

The effective size of a population is the size of an ideal population which would undergo genetic drift at the same rate as the real population. The balance between selection and genetic drift depends on the effective population size ( N_e), rather than the real numbers of individuals in the population ( N). The objectives of the present study were to estimate N_e in the potato cyst nematode Globodera pallida and to explore the causes of a low N_e/ N ratio in cyst nematodes using artificial populations. Using a temporal analysis of 24 independent populations, the median N_e was 58 individuals (min N_e = 25 and max N_e = 228). N_e is commonly lower than N but in the case of cyst nematodes, the N_e/ N ratio was extremely low. Using artificial populations showed that this low ratio did not result from migration, selection and overlapping generations, but could be explain by the fact that G. pallida populations deviate in structure from the assumptions of the ideal population by having unequal sex ratios, high levels of inbreeding and a high variance in family sizes. The consequences of a low N_e, resulting in a strong intensity of genetic drift, could be important for their control because G. pallida populations will have a low capacity to adapt to changing environments.