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HYPOTHESIS: The Red Queen Hypothesis argues coevolving parasites maintain sex; therefore, more sexuals are expected at areas with greater coevolution with parasites.
PARASITE LIFE CYCLE Highly virulent parasite Microphallus sp. infects two hosts: a duck and a freshwater snail called P.antipodarum.
COST OF SEX Sexual reproduction is common, despite its cost of males.
1 km
Lake average
sexualasexual
2013 2014
Julie Xu ([email protected]), Amanda K. Gibson, Curt Lively
METHODS:1. Collect adult snails from 12 different sites on lake.2. Assay prevalence of infection in field.3. Determine proportion of sexuals at each site usingflow cytometry.
SPATIAL VARIATION IN SEX
CONCLUSION:Susceptibility is a stronger predictor of sex than prevelance of infection in field. The strong, positive relationship between sex and susceptibility, acting as a proxy for coevolution, supports the Red Queen Hypothesis.
Frequency of sexual females varies significantly in space and time.
Weak relationship between field disease and sex at a site
Spatial variation in susceptibility in 2013 and 2014
Sexual Asexual
Strong positive relationship between susceptibility and sex in 2013 and 2014
slower growth
eggs
larval cystsuninfected
infected, sterilized
01
Does fine-scale spatial variation in coevolution explain variation in sex?
DOES FIELD PREVALENCE OF INFECTION PREDICT VARIATION IN SEX? 02 DOES HOST SUSCEPTIBILITY
PREDICT VARIATION IN SEX?
- Spatial variation in field disease prevalence- How Microphallus infection varies between years depends upon site.
METHODS:1. Expose juvenile snails to parasites collected from the lake.2. Assay for susceptibility by determining infection rate in lab.3. Determine proportion of sexuals at each site using flow cytometry.
Unpublished data suggests: Susceptibility reflects degree parasites are adapted to infect host = strength of coevolution.Many studies use disease prevalence in field as a measure of strength
of coevolution. RESULTS: RESULTS:
WORKS CITED Graphics and pictures by Amanda K. Gibson, Gabe Harp Jaenike, J. (1978). An hypothesis to account for the maintenance of sex within populations. Evolutionary Theory 3: 191–194.
BACKGROUND
Lively, C.M. (1989). Adaptation by a parasitic trematode to local populations of its snail host. Evolution 43: 1663-1671.
Maynard Smith, J. (1978). The Evolution of Sex. Cambridge, UK: Cambridge University Press.
Vergara, D.,Lively, C.,King, K., Jokela, J. (2013). The Geographic Mosaic of Sex and Infection in Lake Populations of a New Zealand Snail at Multiple Spatial Scales. The American Naturalist 182: 484-493.