THE DISTRIBUTION AND PREVALENCE OF HELMINTHS, COCCIDIA AND BLOOD PARASITES IN 2 COMPETING SPECIES OF GECKO - IMPLICATIONS FOR APPARENT COMPETITION

Across the Pacific the invading gecko species Hemidactylus frenatus ha s competitively displaced the resident gecko species Lepidodactylus lu gubris in urban/surburban habitats. Do parasites enhance, inhibit, or have no effect on this invasion? Parasites can confer an advantage to an invading species when the invader (1) introduces a new parasite to a resident species that has a greater detrimental effect on the reside nt than the invader, (2) is less susceptible to endemic parasites than the resident, and/or (3) increases the susceptibility of the resident to parasites. Conversely, parasites may protect a resident against in vasion when endemic parasites have a greater impact on the invader tha n the resident. We screened more than one thousand H. frenatus and L. lugubris in areas of sympatry and allopatry from 28 islands and 5 site s on mainland Asia for a broad array of blood parasites, coccidia and helminths in order to evaluate the potential for parasites to affect t heir interaction. We found that I) There were no parasites which appea r to protect L. lugubris against invasion by H. frenatus. 2) H. frenat us does not introduce the same parasite to L. lugubris is in every loc ation where the two come in to contact, but probably has introduced di fferent parasites in different locations. L. lugubris also seems to ha ve introduced at least one parasite to H. frenatus. 3) The prevalence of parasite species shared by the two hosts is generally higher in H. frenatus; however, prevalence is determined by many factors and cannot be directly translated as susceptibility. We discuss the implications of this difference in prevalence for the Red Queen hypothesis. 4) The prevalence of the cestode Cylindrotaenia sp. is significantly higher in L. lugubris that are sympatric with H. frenatus than those which ar e allopatric.