| intra-uterine larval development of the polystomatid monogeneans, pseudodiplorchis americanus and neodiplorchis scaphiopodis. | larvae of the monogeneans pseudodiplorchis americanus and neodiplorchis scaphiopodis develop within egg capsules retained in the uterus of the parent parasite. this study reveals adaptations for the storage and nutrition of infective stages which have no known precedent amongst other platyhelminths. the vitelline system is greatly reduced and appears to contribute little to embryo nutrition. an electron-dense 'shell' which encloses the newly formed embryos is subsequently replaced by a thin flex ... | 1991 | 1745551 |
| asymmetric reproductive output by the monogenean pseudodiplorchis americanus. | pseudodiplorchis americanus accumulates its entire reproductive output in utero during hibernation of its host, scaphiopus couchii. infective larvae are released only during the toads' brief entry into water for breeding. in one host population studied prior to transmission, in s.e. arizona, adult worms contained 0-326 infective stages; 19% of 178 worms produced 51% of the total larvae. reproductive output was positively correlated with body length which was considered to reflect worm age; first ... | 1991 | 1852489 |
| ovoviviparity in platyhelminth life-cycles. | the encapsulated embryos of platyhelminths may be retained and complete their development in utero in a range of circumstances. however, hatching within the parent (the criterion of ovoviviparity) is relatively rare and larvae generally emerge only after deposition. viviparity is characterized by the nutritional dependency of the unencapsulated larva upon the parent, but in several cases larvae retained within a shell also receive parental nutrients during intra-uterine development. uptake of ex ... | 1983 | 6346232 |
| the relationship between pseudodiplorchis americanus (monogenea) density and host resources under controlled environmental conditions. | a previous study has shown that, under natural conditions, energy reserves of the desert toad, scaphiopus couchii, are negatively related to the density of infection by pseudodiplorchis americanus. however, this was based predominantly on collections of active animals from breeding congregations and inevitably selected toads which were in good condition. the parasite, a blood-feeding monogenean, occurs in burdens of up to 30 worms/host (mean intensity 6 worms/host) and represents a significant d ... | 1994 | 8159463 |
| survival of pseudodiplorchis americanus (monogenea) under controlled environmental conditions. | populations of pseudodiplorchis americanus infecting the desert toad, scaphiopus couchii, have previously been shown to be remarkably stable from year to year, despite wide variation in conditions promoting invasion. the present study aimed to document the survival of both first-year and pre-existing adults under controlled laboratory temperatures. first-year worm survival in experimentally infected toads was shown to be very high for the first 5 months after migration to the definitive site, an ... | 1994 | 8159464 |
| parasitic disease in amphibians: control by the regulation of worm burdens. | this review considers three case studies based on macroparasites of anurans: (a) natural infections in the permanently-aquatic xenopus laevis which represent the worm burdens acquired, and the implications for pathology, when hosts are exposed to continuous, year-round, transmission; (b) the desert toad, scaphiopus couchii, which experiences invasion very briefly each year and provides a simplified system involving only a single significant infection (pseudodiplorchis americanus); (c) the mesic ... | 1995 | 8632921 |
| histological analysis of the egg capsule of the ovoviviparous polystomatid monogenean, pseudodiplorchis americanus. | transmission of pseudodiplorchis americanus is restricted to the brief period when its host, a desert toad, enters water to spawn. the parasite accumulates its entire annual reproductive output within an elongated uterus during the 10-11-month period of host hibernation. embryos of p. americanus, at all stages of development, are retained within the uterus which eventually becomes packed with around 150 encapsulated infective larvae. recently formed eggs, which comprise a fertilized ovum and 2-3 ... | 1997 | 9363490 |
| life history specializations of monogenean flatworms: a review of experimental and microscopical studies. | this review illustrates the use of experimental approaches combined with microscopy to study the biology of monogenean parasites. studies of feeding, development, reproduction, and systematics have been based on gyrodactylids, flatworms infecting teleost fishes. in a contrasting system involving an amphibian host in a desert environment, analysis of adaptations to extreme conditions has focused on pseudodiplorchis americanus. the unusual reproductive strategies, particularly the interactions bet ... | 1998 | 9764919 |
| parasite adaptation to extreme conditions in a desert environment. | deserts represent universally recognized extreme environments for animal life. this paper documents the highly specialized adaptations of pseudodiplorchis americanus, a monogenean parasite of the desert toad, scaphiopus couchii. building on a long-term record of parasite population ecology (continuing since the early 1980s), field studies focus on the effects of severe drought in the sonoran desert, arizona, in the mid 1990s. this provides a test of the ability of the host-parasite system to tol ... | 1999 | 11254147 |
| host factors limiting monogenean infections: a case study. | comprehensive field data on polystomatid monogeneans record low prevalence and intensity of infection and suggest that worm burdens in this group are strongly regulated: thus, in the majority of polystoma species infecting anuran amphibians mean abundance is typically less than one parasite/host. there is circumstantial evidence that the dominant control is attributable to host factors which over-ride variations in transmission success. this review provides a brief summary of information on pseu ... | 2002 | 11835975 |
| pathological effects of pseudodiplorchis americanus (monogenea: polystomatidae) on the lung epithelium of its host, scaphiopus couchii. | infection of the desert toad, scaphiopus couchii, by the monogenean pseudodiplorchis americanus involves 2 principal sites: post-invasion juveniles reside in the respiratory tract for 1 month before migrating to the urinary bladder where they reach sexual maturity and may live up to 4 years. while previous work has demonstrated the long-term impact on host condition of the blood-feeding adults, this study assesses pathological effects of the short-term pulmonary infection. lung ultrastructure wa ... | 2002 | 12211607 |