The nematode genus Strongyloides consists of parasites that live as. parthenogenetic females in the small intestines of their hosts. In addition. to producing parasitic offspring, they can also form a facultative free-. living generation with males and females (for review see Viney and Lok,. 2007).. Generally all Strongyloides found in farm ruminants were considered to. belong to the species S. papillosus, first described as a parasite of. sheep. We have analyzed the 18S rDNA sequence of Strongyloides isolated. from sheep and cattle from Germany, Mali and the USA. Our data clearly. indicate that the predominant Strongyloides of cattle and the Strongyloides. of sheep form different, genetically isolated, sympatric populations and. belong therefore to different, relatively closely related, species.. While some species of Strongyloides, like S. ratti, and the human parasite. S. stercoralis, employ an XX/XO sex determining system, S. papillosus. contains no true X chromosome but males have a chromosome pair where one of. the homologous chromosomes is intact and the other one lacks a large. portion as the result of a sex specific chromatin diminution event (for. review see Streit, 2008). Contrary to earlier reports that were based on. cytological observations, males of S. ratti (Viney et al., 1993) and S.. papillosus (Eberhardt et al., 2007) do contribute genetic information to. the next generation. We have generated molecular genetic markers for S.. ratti and S. papillosus and we are analyzing their inheritance and linkage. both genetically and molecularly (FISH). We have shown that in both species. recombination within chromosomes occurs. All this indicates that these two. species undergo standard sexual reproduction and are therefore amenable to. classical genetic analysis. One of our goals is to complement the ongoing. S. ratti whole genome sequencing with a genetic linkage map for this. species. We are particularly interested in genetic differences between the. two species, which relate to the different sex determining systems.. Eberhardt, A.G., Mayer, W.E., Streit, A. (2007) Int. J. Parasitol. 37:989-. 1000. Streit, A. (2008) Parasitol. 38 in press. Viney, M.E., Lok, J.B.. (2007) In: Community, T.C.e.R. (Ed.), WormBook,
http://www.wormbook.org.. Viney, M.E., Matthews, B.E., Walliker, D. (1993) Proc. R. Soc. Lon. B. 254:213-219.