Size and sex matter: infection dynamics of an invading parasite (the pentastome Raillietiella frenatus) in an invading host (the cane toad Rhinella marina)

Abstract

Correlations between host phenotype and vulnerability to parasites can clarify the processes that enhance rates of parasitism, and the effects of parasites on their hosts. We studied an invasive parasite (the pentastome Raillietiella frenatus, subclass Pentastomida, order Cephalobaenida) infecting a new host (the invasive cane toad Rhinella marina), in tropical Australia. We dissected toads over a 27-month period to investigate seasonal changes in pentastome population dynamics and establish which aspects of host phenotype are related to infection. Pentastome prevalence and intensity varied seasonally; male toads were 4 times more likely to be infected than were females; and prevalence was highest in hosts of intermediate body size. The strong sex effect may reflect habitat or dietary divergence between the sexes, resulting in males encountering parasites more often. The relationship between pentastome prevalence and host size likely reflects a role for acquired immunity in preventing re-infection. Infection did not influence host body condition (fatbody size), suggesting that R. frenatus does not impose high energy costs in cane toads. Infected toads had heavier spleens (likely an immune response to infection) and larger testes (perhaps since reproductively active hosts have altered microhabitat use and/or immunocompetence) than did uninfected conspecifics. Although experimental studies are required to identify the causal bases of such patterns, our data confirm that infection status within a population can be strongly linked to host phenotypic traits.

Immune Response Varies with Rate of Dispersal in Invasive Cane Toads (Rhinella marina)

“…At least one of the 100 toads brought to Australia from Hawaii in 1935 harbored a nematode lungworm native to South America [49] and this parasite is now common in Australian toad populations [50], though it lags behind the frontline of the toad invasion, where host density is too low for transmission [35]. Aside from harboring and outrunning a lungworm with which they have a long association, toads in Australia are also exposed to and can become infected with a suite of native pathogens [51]–[53], including pentastomids [37], myxosporea [54], and native nematode lungworms (GPB unpublished data).…”

“…Invasive species may provide especially robust opportunities for investigating interactions between strenuous activity, immune function, and encounters with truly novel pathogens or release from prevalent ones [21], [33], [34], [37]. Introduced species can be viewed as experimental manipulations, albeit misguided ones.…”

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

“…On 5 September 2012, we collected 19 adult cane toads from Marlow Lagoon Recreational Reserve (12 ° 29 ′ S, 130 ° 58 ′ E) where Ra. frenata infects toads (Kelehear et al 2012), and brought them back to the Univ. of Sydney Tropical Ecology Research Facility at nearby Middle Point (12 ° 37 ′ S, 131 ° 18 ′ E).…”

The costs of parasite infection: Effects of removing lungworms on performance, growth and survival of free‐ranging cane toads

“…Cane toads ( Rhinella marina Linnaeus 1758) in Australia are a notorious example of an introduced species that imperils native ecosystems (Shine, ). As such, their parasites and pathogens have been intensively studied (Barton, ; Hartigan et al., ; Kelehear, Brown, & Shine, ; Speare, ). Although cane toads lost many native‐range parasites during their translocation from South America to Australia (Selechnik, Rollins, Brown, Kelehear, & Shine, ), they retained the native‐range lungworm Rhabdias pseudosphaerocephala Kuzmin et al.…”

“…Cane toads (Rhinella marina Linnaeus 1758) in Australia are a notorious example of an introduced species that imperils native ecosystems (Shine, 2010). As such, their parasites and pathogens have been intensively studied (Barton, 1997;Hartigan et al, 2011;Kelehear, Brown, & Shine, 2012b;Speare, 1990).…”