The Effects of a Nematode Lungworm (Rhabdias hylae) on its Natural and Invasive Anuran Hosts

Abstract

Biological invasions can bring both the invader and native taxa into contact with novel parasites. As cane toads ( Rhinella marina ) have spread through Australia, they have encountered lungworms (Rhabdias hylae) that occur in native frogs. Field surveys suggest that these lungworms have not host-switched to toads. In our laboratory studies, R. hylae infected cane toads as readily as it infected native frogs, but failed to reach the lungs of the novel host (i.e., were killed by the toads' immune response). Plausibly, then, R. hylae might reduce the viability both of their native hosts (frogs, that can exhibit high parasite burdens) and cane toads (that must deal with infective larvae traveling through the host body). Our laboratory trials suggest, however, that the impacts of the parasite on infected anuran hosts (both frogs and toads) were minimal, with no significant decrements to host survival, activity, growth, or locomotor performance. Ironically, the lack of impact of the parasite on its native hosts appears to be an outcome of co-evolution (frogs tolerate the lungworm), whereas the lack of impact on the novel host is due to a lack of co-evolution (toads can recognize and eliminate the lungworm).

Host–parasite interactions during a biological invasion: The fate of lungworms (Rhabdias spp.) inside native and novel anuran hosts

“…R. hylae larvae were extracted from the faeces of Lit. nasuta collected from the vicinity of Middle Point, Northern Territory TERF (DNA analysis confirmed the species of nematode used in the experiment: Nelson et al., 2015 ). We fed metamorphs with termites ad libitum over 15 days (excluding a 24-hour fasting period before euthanasia).…”

“…Cane toads and native frogs (excluding Litoria splendida ) experience no decline in major indicators of viability (survival, feeding rates, growth rates, speed or endurance) when exposed to (or hosting) a non-co-evolved rhabdiasid lungworm ( Pizzatto and Shine, 2011a, 2011b; Nelson et al., 2015 ). However, cane toads do suffer deleterious effects from their native parasite, R. pseudosphaerocephala ( Kelehear et al., 2009, 2011 ), whereas native frogs apparently suffer no ill effects from their co-evolved lungworm, R. hylae ( Nelson et al., 2015 ) . Again, this asymmetry implies a divergence in host–parasite evolutionary history.…”

“…Although cane toads can be penetrated by larvae of the frog lungworm species ( Nelson et al., 2015 ), field surveys have not found any crossover in lungworm fauna between native frogs and cane toads ( Pizzatto et al., 2012 ). R. pseudosphaerocephala can reduce survival, food intake, speed and endurance in metamorphs of its natural host, the cane toad ( Kelehear et al., 2009 ).…”

“…Laboratory experiments indicate that Australian frogs are penetrated by the cane toad lungworm, but that these lungworms generally do not survive ( Pizzatto et al., 2010; Pizzatto and Shine, 2011a, 2011b ). In most Australian frog species studied to date, morbidity and mortality of the host are unaffected by exposure to either the toad lungworm ( Pizzatto et al., 2010; Pizzatto and Shine, 2011a, 2011b ) or the native frog lungworm ( Nelson et al., 2015 ). In laboratory trials, the toad lungworm was less competent at locating the target tissue (the lungs) in non-co-evolved hosts (native frogs) than in the co-evolved host (the cane toad), and was more effectively destroyed by the non-co-evolved host's immune system ( Pizzatto et al., 2010 ).…”

Parasitism and host dispersal plasticity in an aquatic model system

“…Individuals may leave their patch to prevent relatives to be infected, even if dispersal is not favoured by other conditions (Hamilton & May, 1977;Poethke et al, 2010;Iritani & Iwasa, 2014;Iritani, 2015;Deshpande et al, 2020). In other cases, parasites do not seem to affect dispersal behaviour of their hosts (Mayer et al, 2015;Nelson et al, 2015;Csata et al, 2017;Taggart et al, 2018). In Australian Sleepy Lizards (Tiliqua rugosa) infected by ticks, dispersal is unaffected, potentially because T. rugosa has adapted to some level of parasite load in its natural system (Taggart et al, 2018).…”