The capacity for viable egg production by the monogenean Protopolystoma xenopodis in single and multiple infections

Abstract

The distribution of Protopolystoma xenopodis in Xenopus laevis populations greatly restricts the opportunities for cross-fertilization in the parasite population: 60% of hosts carry single adult worms. Regular collections recording total egg output from naturally-infested Xenopus revealed that eggs produced by isolated worms are as viable as those from multiple burdens: 96% of 2111 eggs from single parasites hatched, compared with 93% of 16,454 eggs produced by burdens of 2–12. P. xenopodis has no visible means of sperm storage, yet during periods of up to 60 days egg production by single worms no decline in viability was recorded. Under natural conditions, there may be more frequent opportunities for cross-insemination: (1) continuous worm recruitment to (and loss from) the urinary bladder may generate a throughput of potential co-copulants, and (2) whilst the majority of infected toads harbour isolated parasites, two-thirds of the worm population still exists in multiple burdens