Fig. 4

Results from laboratory cross-inoculation experiment. The graph gives the mean infection frequencies for snails exposed to parasites’ eggs collected at Lake Alexandrina. The vertical bars give one standard error of the means. The asterisk indicates a statistically significant difference. Note that the parasites collected from Lake Alexandrina were significantly more infective to snails collected from the shallow-water margins of the same lake than to snails collected from the deep water. Also note that the Lake Alexandrina parasites were no more infective to shallow-water snails collected from Lake Kanieri than to deep-water snails from Lake Kanieri. These results suggest that the shallow-water margin of Lake Alexandrina is a coevolutionary hot spot, while the deep habitat is a coevolutionary cold spot