Parasites: the Cinderellas of wildlife conservation.

Think of an endangered animal. What’s the first one that pops into your head? Chances are it was something large, charismatic, and probably a mammal – and it’s fairly safe to say that you didn’t think of a louse or a cestode.

Spied in the news, (The Australian newspaper, screenshot below) an article laments that many of Australia’s endangered species are “charm-deficient”. One result of this perceived deficiency is that dollars going towards conservation programs seem to go to more charismatic and exotic species like pandas, tigers, elephants etc. The grey-headed flying fox is mentioned in the article as one such uncharming native species. It is Australia’s biggest bat, and it’s listed as vulnerable (ref: http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=186). Apparently, many people don’t like bats, so it stands to reason that they might not want to donate money to save a species they do not like.

The Oz 13 June

Excerpt screenshot of the article, The Australian 13 June 2013.

While this is distressing for the 94 species of mammals currently listed as vulnerable, endangered or critically endangered nationally in Australia, perhaps a thought can be spared for some even more charm-deficient animals: parasites. Not only are they almost always absent from lists of threatened species (there are a few notable exceptions), they generally suffer from an image problem. Most people like parasites far less than they like bats. So what’s a parasite to do, in order to get attention for conservation?

There is currently only one species of parasite listed on the IUCN Red List. The louse, Haematopinus oliveri, is listed as critically endangered but only because its host, the pygmy hog (Porcula salvania), is critically endangered (Dunn et al. 2009). In Australia, only one parasite species is listed as endangered, and it isn’t even at national level. The tapeworm Dasyurotaenia robusta has been listed as rare under the Tasmanian Threatened Species Protection Act, because it has only been found once, in one host, the Tasmanian devil (Sarcophilus harrisii). Many parasite species have been described from endangered host species. Two such examples are the louse Felicola isidoroi was described from the Iberian lynx (Lynx pardinus) (Perez & Palma 2001); and the protozoan Caryosprora durelli was described from the Round Island boa (Casarea dussumeiri) (Daszak et al. 2011).

Depiction of H. oliveri (via Wikipedia).

The concept of coextinction (parasites, mutualists and commensals becoming extinct alongside their hosts) has been around since the 1990s. Parasites are integral parts of ecosystems, and their richness in a given system will decline as the free-living species are lost (Lafferty 2012). A problem with estimating parasite biodiversity is aggregation, where parasites are not distributed in a uniform manner across a host population. This means that as hosts are sampled, parasites can be missed, reducing or skewing the overall snapshot of complete parasite biodiversity of the given host. We may never know how many parasites are endangered because we will probably never be able to find them all before they (and their hosts) go extinct (Dobson et al. 2008).

D.robusta

D. robusta – 1) Scolex with rostellum retracted (scale 1.0mm), 2) Rostellar hooks (scale 0.1mm). From Beveridge 1984.

To complicate matters, some parasites are generalists, and can infect a range of host species, whereas some are highly species-specific. The generalists may be able to survive a host extinction event by switching to a new host, but the species-specific parasites will most likely not survive if their host, or their intermediate host, dies out. However, one thing remains constant: parasites (and to an extent, other invertebrates) do not feature as highly on the conservation agenda as they should. For all the talk about ‘conserving biodiversity’, it seems remarkably narrow-minded to exclude an entire element of the biodiversity in question. We know parasites are at risk of coextinction. There is a growing body of research providing evidence for this (some nice reviews on the topic include Dunn et al. 2009, Mihalca et al. 2011, Colwell et al. 2012 and Lafferty 2012), but still parasites are treated like Cinderella. The phrase “equal rights for parasites” was coined by Windsor in 1990, and it is probably more relevant now than ever in light of our growing understanding of coextinction risk. Perhaps when compared to the intestinal helminths they harbour, the flying foxes aren’t so uncharming after all.

References

Beveridge, I (1984) Dasyurotaenia robusta Beddard, 1912, and D. dasyuri sp. nov., from carnivorous Australian marsupials. Trans. R. Soc. S.A. 108, 185-195.

Colwell, R et al. (2012) Coextinction and persistence of dependent species in a changing world. Ann. Rev. Eco. Evol. Syst. 43, 183-203.

Daszak, P et al. (2011) A new species of Caryospora Leger, 1094 (Apicomplexa: Eimeriidae) from the endangered Round Island boa Casarea dussumieri (Schlegel) (Serpentes: Bolyeridae) of Round Island, Mauritius: an endangered parasite? Sys. Parasitol. 78, 117-122.

Dobson A et al. (2008) Homage to Linnaeus: How many parasites? How many hosts? PNAS 105, 11482-11489.

Dunn, RR et al. (2009) The sixth mass coextinction: are most endangered species parasites and mutualists? Proc. R. Soc. B. 276, 3037-3045.

Lafferty, K (2012) Biodiversity loss decreases parasite diversity: theory and patterns. Phil. Trans. R. Soc. B 367, 2814-2827.

Mihalca, AD et al. (2011) Coendangered hard-ticks: threatened or threatening? Parasites & Vectors 4:71.

Perez, JM & Palma RL. (2001) A new species of Felicola (Phthiraptera: Trichodectidae) from the endangered Iberian lynx: another reason to ensure its survival. Biodiver. Cons. 10, 929-937.

Windsor DA (1990) Heavenly hosts. Nature 348, 104.