Summary
In this study we examined trematode and nematode lung helminths commonly found in two species of host ranid frogs for competitive interactions. We examined 147 adult (breeding and non-breeding) and juvenile northern leopard frogs, and 84 breeding male wood frogs in Bishops Mills, Ontario for Haematoloechus spp. (Trematoda) and Rhabdias sp. (Nematoda) infections. A strong negative association between phyla of helminth was observed in breeding and juvenile northern leopard frogs, and also in breeding wood frogs, but not in non-breeding adult northern leopard frogs. Few hosts carried both types of worm concurrently. Thirteen northern leopard frogs carried dual infections, while 77 carried only one phylum of helminth. Twenty-seven wood frogs carried dual infections, while 54 carried only one phylum of helminth. We also observed spatial segregation of the two phyla in host lungs. Our study informs future research on the dynamics of interactions among lung helminths in these two host species.
Methodology
Road-killed northern leopard frogs (n ¼ 147) were collected from Bishops Mills, Ontario (44°20'60.0" N 75°40'0.0" W). High vehicle-related mortality occurs particularly during seasonal migration periods when cohorts of frogs move en masse over a few short days. We collected 54 male and 20 adult female northern leopard frogs in the spring (2–26 April 2007) as they migrated from their hibernation sites to breeding ponds, and another 73 frogs (45 juveniles, 12 adult females, 16 adult males) in late summer/early fall (11–26 August 2007) when they were moving between feeding grounds and hibernation sites. Northern leopard frogs were identified to age (juveniles/yearlings and adults) and sex (breeding male individuals were identified by the presence of a swollen, darkened thumb, a secondary trait that is not present in non-breeding adult males; sex in juveniles was determined only by the examination of gonads). Only frogs in which both lungs were intact were used for our analyses.
Wood frogs do not make these migrations across roads, and thus we captured live adult male frogs from breeding ponds from the same local wetland area in Bishops Mills as the northern leopard frogs. A small number (n = 18) of wood frog males were collected in the first week of April 2008 and another larger sample group (n = 66) on 23 April 2008.
Rhabdias (nematodes) and Haematoloechus (flukes) found in the lungs were removed and enumerated. The genus Haematoloechus is a species complex comprising morphologically indistinguishable species (Bolek & Janovy, 2007) that require genetic testing for identification. However, some of these flukes display strong host specificity among intermediate odonate hosts; researchers may be able to establish which species infect final host frogs by determining the species composition of odonates in an area. At present, the odonate species composition in our sample area has not been documented. Thus for this study we use the taxon name Haematoloechus spp. As well, recent evidence suggests that the lungworm nematode, Rhabdias bakeri (thought to infect wood frogs), is a genetically distinct species from R. ranae, typically found in northern leopard frogs (Tkach et al., 2006). However, experimental infections have shown that both species of Rhabdias (R. bakeri and R. ranae) will successfully infect and reproduce in either host frog species (Dare et al., 2008); exclusive use of one or the other host frog by either worm species in nature is unknown. A revision of the life cycles and host use of these Rhabdias species is required. However, for the purposes of this study we refer to Rhabdias lungworms as Rhabdias sp.
We report prevalence, abundance and intensity as response parameters for parasitological counts (according to Bush et al., 1997). We observed no differences between the dead frogs in this study or live frogs we have examined in other studies, in the locations of the worms in the lungs.