Trematodes in the desert: The parasitization of Trematodes in the desert: The parasitization of Scaphiopus couchiiScaphiopus couchii by by Pseudodiplorchis Pseudodiplorchis

americanusamericanus

Jeffery CoteJeffery Cote

A Toad and its parasiteA Toad and its parasite

The Spadefoot toad (The Spadefoot toad (Scaphiopus couchiiScaphiopus couchii) is ) is found in the deserts of southwest North America.found in the deserts of southwest North America.

The parasite is the monogenean, The parasite is the monogenean, Pseudodiplorchis americanusPseudodiplorchis americanus (no common (no common name)name)

One host system in this case.One host system in this case.

Spadefoot toadSpadefoot toad

Surviving in the desertSurviving in the desert

How does an amphibian survive the How does an amphibian survive the desert? desert?

How does a parasite, whose How does a parasite, whose ancestors evolved in an aquatic ancestors evolved in an aquatic environment, survive and infect its environment, survive and infect its host in the desert?host in the desert?

Toad coping mechanismsToad coping mechanisms

Toad enters hibernation for 10 monthsToad enters hibernation for 10 months Toads breed in temporary pools created Toads breed in temporary pools created

by intense summer storms.by intense summer storms. Usually a single breeding period, occurring Usually a single breeding period, occurring

on one day after storm from 9pm to 4am.on one day after storm from 9pm to 4am.

Problems faced by the trematodeProblems faced by the trematode

The trematode’s larval stage requires water to infect the The trematode’s larval stage requires water to infect the toad.toad.

Limited to a 7 hour time frame, with no second chances Limited to a 7 hour time frame, with no second chances (usually).(usually).

The larval stage enters the nostrils, though toad is not The larval stage enters the nostrils, though toad is not entirely submerged.entirely submerged.

Mature adults found in toad bladder, must survive the Mature adults found in toad bladder, must survive the stomach to get there.stomach to get there.

Parasite lifecycleParasite lifecycle Mature adult dwells in bladder, produces eggs, eggs Mature adult dwells in bladder, produces eggs, eggs

leave the bladder and enter the water.leave the bladder and enter the water. The oncomiracidia hatch instantly upon entering the The oncomiracidia hatch instantly upon entering the

water and swim a toad’s nostrils.water and swim a toad’s nostrils. The worms stay in the nostrils for 24 hrs. Lose cilia cells The worms stay in the nostrils for 24 hrs. Lose cilia cells

within 1-2 hours of invasion.within 1-2 hours of invasion. Worms move to mouth and nearby cavities and begin to Worms move to mouth and nearby cavities and begin to

feed on blood, this stage lasts 1 week.feed on blood, this stage lasts 1 week. Worms next migrate to the lungs and remain there for 1-Worms next migrate to the lungs and remain there for 1-

2 weeks.2 weeks. The juvenile worms go back up to the buccal cavity, then The juvenile worms go back up to the buccal cavity, then

migrate to the bladder.migrate to the bladder. Adult worms in bladder, simultaneously produce eggs Adult worms in bladder, simultaneously produce eggs

and grow.and grow.

Modified uterusModified uterus The oncomiracidia developed to the infective stage in the The oncomiracidia developed to the infective stage in the

adult.adult. Adult worms have a modified uterus.Adult worms have a modified uterus. Trematode uses cytoplasmic connections to the lining of Trematode uses cytoplasmic connections to the lining of

the egg capsule, to mimic a placenta. Supplies nutrients the egg capsule, to mimic a placenta. Supplies nutrients on tap to the larvae’s tegument.on tap to the larvae’s tegument.

Egg capsule is made of elastin.Egg capsule is made of elastin. Larvae size increases as it progresses through the Larvae size increases as it progresses through the

uterus.uterus. Storage of eggs lasts 2 months, dead eggs recycled.Storage of eggs lasts 2 months, dead eggs recycled.

Benefits of modified uterusBenefits of modified uterus

Resource efficientResource efficient Can store 100 eggs on average.Can store 100 eggs on average. Constant alert for infection Constant alert for infection

transmission possibility.transmission possibility.

Parasite timingParasite timing Parasite must be able to time egg release with host entry Parasite must be able to time egg release with host entry

into water.into water. Parasite relies on host sexual cues, host sexual Parasite relies on host sexual cues, host sexual

excitement.excitement. Studies conducted on related parasite used Studies conducted on related parasite used

immunostaining of neurons associated with ootype immunostaining of neurons associated with ootype musculature.musculature.

Immunostains were strongly present during periods of Immunostains were strongly present during periods of rapid egg production in parasite, triggered by toad rapid egg production in parasite, triggered by toad spawning.spawning.

Immunostains were absent after toads finished Immunostains were absent after toads finished spawning.spawning.

Super LarvaeSuper Larvae

Largest larvae of the MonogeneaLargest larvae of the Monogenea Oncomiracidia can swim for periods longer than Oncomiracidia can swim for periods longer than

4 hrs.4 hrs. Oncomiracidia swim via cilia, which can resist Oncomiracidia swim via cilia, which can resist

drying out for 1 hour, maintaining maximum drying out for 1 hour, maintaining maximum swimming capability.swimming capability.

Average lifespan is 15 hours. Average lifespan is 15 hours.

Mean abundanceMean abundance

Mean abundance cont.Mean abundance cont.

Back to back storms create heightened infection Back to back storms create heightened infection levels.levels.

1988 study, mean abundance of 44 worms per 1988 study, mean abundance of 44 worms per toad after 2 consecutive storms.toad after 2 consecutive storms.

After 3After 3rdrd storm, mean abundance of 81 worms storm, mean abundance of 81 worms per toad, 100% infection level.per toad, 100% infection level.

Probability of successful infection by individual Probability of successful infection by individual larvae: 0.3larvae: 0.3

Larvae migrationLarvae migration

No known adaptations for passage in and out of lungs.No known adaptations for passage in and out of lungs. Protection needed for crossing stomach.Protection needed for crossing stomach. Worms artificially transplanted from lungs to digestive Worms artificially transplanted from lungs to digestive

tract, all died within 2 min. Tegument stripped away..tract, all died within 2 min. Tegument stripped away.. Cue for migration to bladder is also cue to produce Cue for migration to bladder is also cue to produce

protection.protection. Juvenile worms develop two types of vesicles, unaltered Juvenile worms develop two types of vesicles, unaltered

until migration. Vesicles discharged as worm moves until migration. Vesicles discharged as worm moves through gut.through gut.

TemperatureTemperature

Parasite reproduction fastest at 25 degrees Parasite reproduction fastest at 25 degrees Celsius and inhibited at 16 degrees or lower.Celsius and inhibited at 16 degrees or lower.

Temperatures only favourable for 4.5-5 months Temperatures only favourable for 4.5-5 months out of the year.out of the year.

Older worms continue to grow and produce Older worms continue to grow and produce eggs, no maturation period.eggs, no maturation period.

Trend continues with worm age.Trend continues with worm age.

Environmental restraint summaryEnvironmental restraint summary

Questions?Questions?