The population dynamics of macroparasite infection routes: a study of the patterns and processes of oxyurid aggregation

Daniel Grear, Penn State

February 11, 2010 @ 12:20 pm to 01:10 pm

10 Tyson

Aggregation of macroparasites among hosts is commonly observed in natural host-parasite systems, so that a few hosts harbor heavy infections while most hosts have few or no parasites._ The variation in parasite abundance per host is consistently greater than the mean and follows Taylor s power law._ Taylor s power law describes a remarkably consistent relationship among the mean and variance in the number of individuals per host/habita-patch/population among parasite and host taxa, as well as among free-living species, suggesting that similar constraints drive the degree of aggregation._ Nematode parasites in the family Oxyuridae infect a wide range of mammalian hosts and have an unique reproductive life-history strategy that involves horizontal transmission between hosts (the route by which all nematode parasites transmit) and the ability to cause self-infection of a host. Whereas, conventional nematode parasites are subject to the population processes of death (natural senescence and host mediated) and infection (immigration), pinworms are able to introduce some level of birth (host-self-infection) to their population dynamics._ The unique aspects of pinworm life-history provide an interesting case to study the trade-offs between direct-reproduction within hosts (birth rates), transmission (immigration & emigration), and death (parasite death rate and host death rate) on generating the widely observed patterns of aggregation of parasite populations._ I empirically examined the differences among Oxyuridae (genus: Syphacia) parasite aggregation in two rodent hosts with similar ecology, the yellow-necked mouse (Apodemus flavicollis) from Trento, Italy and the white-footed mouse (Peromyscus leucopus) from Pennsylvania, USA._ I also examined the distribution of a non-pinworm nematode parasite, Heligmosomoides polygyrus, in A. flavicollis._ I hypothesized that the self-infecting characteristic of oxyurids leads to a greater variance-mean relationship than nematode parasites with a direct life-cycle that do not have the ability to self-infect a host. Finally, to further investigate the effects of pinworm life-history characteristics on generating the observed variance-mean relationship, I present a stochastic simulation model that compares simulated variance-mean relationships under a range of host-self-infection, parasite death, and transmission scenarios. _

Contact

Kristen Granger
klg297@psu.edu