In recent years, it has become apparent that introduced or novel pathogens
or parasites may have a significant negative impact on endangered species.
Here we examine experimentally the effect of an exotic fluke from guppies o
n the endangered Gila topminnow. Populations from different sources showed
variable responses (although statistically non-significant) to the fluke an
d, in particular, the most homozygous population had high fluke infections
and high subsequent mortality. Homozygotes for a MHC (major histocompatibil
ity complex) gene had lower (although statistically non-significant) surviv
al when infected with flukes than did heterozygotes. An inbred line from on
e of the populations had statistically significant lower survival and highe
r fluke infection than did a simultaneous outbred control. Overall, Gila to
pminnows appear quite susceptible to infection by the non-native fluke comp
ared to other related species. In addition, it was shown that Gila topminno
ws can be infected by casual contact with infected guppies. This is another
example of the potential detrimental effects of a parasite on an endangere
d species, a threat that may constitute a particular problem for species wi
th low genetic variation, either in general, for important MHC genes, or fo
r populations with a past history of inbreeding.