Effects of temperature on oviposition rate in Protopolystoma xenopodis (Monogenea: Polystomatidae).

Protopolystoma xenopodis is an oviparous monogenean occurring as an adult in the urinary bladder of the African clawed toad, Xenopus laevis. Egg production was monitored in two groups of infected hosts exposed to decreasing environmental temperatures. Despite possible upward trends in reproductive capacity with parasite age, oviposition rate was severely depressed at lower temperatures. In one experiment, egg production was monitored in a sample of seven hosts at 2 degrees C intervals between 20 and 8 degrees C. Overall mean egg production rate showed a consistent decline from 11.9 eggs/worm/day (e/w/d) at 20 degrees C (days 1-10) to 0.9 e/w/d at 8 degrees C (days 115-124). In a second experiment (n = 11 hosts) oviposition rate was recorded at the same intervals between 20 and 6 degrees C and then hosts were returned to 20 degrees C. Overall mean egg production rate decreased consistently from 4.1 e/w/d at 20 degrees C (days 1-10) to 0.2 e/w/d at 6 degrees C (days 124-131), at which temperature all infections continued to produce eggs. When parasites were then returned to 20 degrees C (141-150 days), mean oviposition rate at this temperature (12.7 e/w/d) was found to have increased by 310% from the start of the experiment (130 days earlier) and by 6350% from production at 6 degrees C (9 days earlier). P. xenopodis has been introduced to South Wales, U.K. and present results show that it could produce eggs here through almost all of the year. However, a massive annual reduction in the reproductive output of this parasite in the U.K., compared with that in natural sites, is predicted.