Patterns of Parasite Infection Dynamics during a Biological Invasion

Abstract

Biological invasions may impact native ecosystems by affecting host-parasite dynamics. Introduced species can harbor parasites transported from their native range and these parasites can spillover to infect native taxa, often with deleterious effects. When parasite-spillover is suspected, it is vital to identify the origin of the parasite accurately, especially if the native taxa are adversely affected. I examined an introduced population of Burmese pythons (Python bivittatus) in the Florida Everglades and investigated their potential for altering host-parasite relationships within their invasive range. Native snakes and pythons were collected during road surveys and through opportunistic encounters. All native snakes were salvaged as road-kill to reduce my impact on native populations. Snakes were dissected and lung parasites (i.e. pentastomes) were collected. Pentastomes were identified to species using molecular analyses and three pentastome species (Porocephalus crotali, Kiricephalus coarctatus and Raillietiella orientalis) were recovered. Two genera (Porocephalus and Kiricephalus) are known to infect North American snakes, while R. orientalis is native to southeast Asia where it is known to infect Burmese pythons. Raillietiella orientalis was collected from pythons and snakes in southern Florida, indicating this parasite has spilled over from pythons to infect native snakes. I examined the impact of R. orientalis infection on native snakes through quantifying and comparing parasite infection dynamics within pythons and native snakes. Raillietiella orientalis exhibited increased fitness in snake hosts native to the parasite’s introduced range compared with pythons. Native snakes displayed increased prevalence and infection intensity of R. orientalis. Additionally, female R. orientalis obtained larger sizes in native Florida snakes and adult female parasites consisted of a larger proportion of the total number of R. orientalis within a host. The current distribution of R. orientalis in Florida extends northward from Miami-Dade and Monroe counties to southern Lake county. The distribution of R. orientalis extends beyond the known range of pythons indicating this parasite can spread among native snakes independent of pythons. Raillietiella orientalis has infected 13 species of native Florida snakes encompassing two families. I investigated the ability of R. orientalis to infect a diversity of hosts by examining potential variation of morphological structures associated with feeding that may allow this parasite to successfully infect a wide array of host species. Oral morphology of R. orientalis varied significantly depending upon the host species infected, which may allow for R. orientalis to adapt to the specific internal conditions of its host. To investigate whether anthropogenic influences, such as landscape disturbance, impact infection dynamics of R. orientalis among native snake and pythons, I compared parasite prevalence and intensity in snakes and examined variation of these metrics among disturbed and undisturbed landscapes. Parasite prevalence was significantly higher in undisturbed landscapes for native snakes compared with disturbed habitats, however, prevalence of R. orientalis of pythons did not differ across landscapes. Infection intensity of R. orientalis did not differ among native snakes and pythons in response to landscape, which indicates that once infected, the ability of the host’s immune system to ameliorate infection is similar in undisturbed and disturbed environments. This study provides the first documentation of a non-native endoparasite that has spilled over from an invasive snake to infect native taxa. As parasites can regulate host populations, and non-native parasites are significantly more virulent in naïve hosts within their invaded range compared to their non-indigenous host, it is likely that native snakes face deleterious impacts at both the level of the individual and population.