Invasive parasites in multiple invasive hosts: the arrival of a new host revives a stalled prior parasite invasion

Abstract

The success of a biological invasion can depend upon other invasions; and in some cases, an earlier invader may fail to spread until facilitated by a second invader. Our study documents a case whereby an invasive parasite has remained patchily distributed for decades due to the fragmented nature of available hosts; but the recent arrival of a broadly distributed alternative invasive host species provides an opportunity for the parasite to expand its range considerably. At least 20 years ago, endoparasitic pentastomids (Raillietiella frenata) were brought with their native host, the invasive Asian house gecko Hemidactylus frenatus, to the port city of Darwin in tropical Australia. These geckos rarely disperse away from human habitation, restricting the transmission of their parasites to urban environments – and thus, their pentastomids have remained patchily distributed and have only been recorded in scant localities, primarily surrounding Darwin. The recent range expansion of the invasive cane toad Rhinella marina into the Darwin area has provided an alternative host for this pentastomid. Our results show that the cane toad is a competent host for Ra. frenata– toads shed fully embryonated pentastomid eggs in their faeces – and that pentastomids are now common in cane toads near Darwin. Likely reflecting the tendency for the parasite's traditional definitive host (the Asian house gecko) and only known intermediate host (the cockroach) to reside around buildings, we found the prevalence of this parasite follows an urban distribution. Because cane toads are widely distributed through urban and rural habitat and can shed viable pentastomid eggs, the toad invasion is likely to facilitate the parasite's spread across the tropics, into areas (and additional susceptible hosts) that were previously inaccessible to it.

An introduced pentastomid parasite (Raillietiella frenata) infects native cane toads (Rhinella marina) in Panama

“…The prevalence of R. frenata declined with distance from the Port of Darwin, suggesting that the parasite was probably introduced to the port (Kelehear et al 2013). Importantly, this parasite originally infected only the introduced Asian House gecko (Hemidactylus frenatus) in Darwin and a few other isolated towns (Barton, 2007;Kelehear et al 2013).…”

“…The prevalence of R. frenata declined with distance from the Port of Darwin, suggesting that the parasite was probably introduced to the port (Kelehear et al 2013). Importantly, this parasite originally infected only the introduced Asian House gecko (Hemidactylus frenatus) in Darwin and a few other isolated towns (Barton, 2007;Kelehear et al 2013). The distribution of this gecko is strongly linked to the presence of buildings (Newbery and Jones, 2007;McKay et al 2009;Hoskin, 2011;Yang et al 2012); therefore, its parasites were initially restricted to urban areas (Kelehear et al 2013).…”

“…Recently, an introduced parasite (the pentastomid Raillietiella frenata = frenatus) was discovered infecting the lungs of invasive cane toads (Rhinella marina, previously Bufo marinus) in the tropical port city of Darwin, Australia (Kelehear et al 2011(Kelehear et al , 2013. The prevalence of R. frenata declined with distance from the Port of Darwin, suggesting that the parasite was probably introduced to the port (Kelehear et al 2013).…”

“…Importantly, this parasite originally infected only the introduced Asian House gecko (Hemidactylus frenatus) in Darwin and a few other isolated towns (Barton, 2007;Kelehear et al 2013). The distribution of this gecko is strongly linked to the presence of buildings (Newbery and Jones, 2007;McKay et al 2009;Hoskin, 2011;Yang et al 2012); therefore, its parasites were initially restricted to urban areas (Kelehear et al 2013). However, R. frenata switched hosts to infect cane toads after toads first colonized Darwin in 2005 (Kelehear et al 2013).…”

“…The distribution of this gecko is strongly linked to the presence of buildings (Newbery and Jones, 2007;McKay et al 2009;Hoskin, 2011;Yang et al 2012); therefore, its parasites were initially restricted to urban areas (Kelehear et al 2013). However, R. frenata switched hosts to infect cane toads after toads first colonized Darwin in 2005 (Kelehear et al 2013). Since cane toads are ubiquitous through the Australian tropics and occur in both rural and urban habitats (Lever, 2001), this host shift enabled the pentastomid to colonize Australia more widely than was originally possible in its urban gecko host (Kelehear et al 2013).…”