Do parasites really have a charm deficiency?

While drafting yesterday’s post (which was my 150th for Increasing Disorder!), I included some discussion about parasites being intentionally lost as part of conservation efforts for their hosts. While it didn’t make the final cut, it is worth talking about as further evidence that parasites are not on a level playing field for conservation. Do parasites really have a charm deficiency? Or is there something else going on? There is a perceptible degree of arrogance with regard to conservation of species – that some species are more equal than others. It won’t matter if some little worms are lost, as long as the cute fluffies are saved, right? Wrong.

One way in which parasites can be lost is through translocation of their hosts. Translocation is a method used to counter loss of species. It is expected to be used more frequently in coming years as habitat loss, environmental perturbation and climate change affect populations of endangered species (Sainsbury & Vaughan-Higgins 2012). Translocation can be as simple as rounding up a number of individuals from one site and releasing them in another, but usually there are various holding periods where the individuals are kept in captivity to breed and increase the overall population size before being released. Translocated individuals could therefore potentially either lose parasites (or other pathogens, commensals or mutualists) or introduce parasites (or other pathogens, commensals or mutualists) into the new area. The former is of particular importance for plants, which often rely on certain invertebrates for pollination, or have invertebrates that rely on them for habitat (see Moir et al. 2012 for discussion on this).

A famous case of parasites being lost via captive breeding is that of the louse Colpocephalum californici. It was intentionally removed (as part of a comprehensive de-parasite treatment) from its host, the critically endangered Californian condor (Gymnogyps californianus), when the last 22 known condors from the wild were brought into captivity (Mihalca et al. 2011, Colwell et al. 2012). However, while many lice are highly species-specific, it appears that there has been little study on the released condors, or any co-occurring related birds to examine whether the condor’s ectoparasites have managed to survive on other hosts (Colwell et al. 2012). Although there is evidence that endoparasites (such as nematodes or cestodes) do stand a greater chance of survival in a translocation event than ectoparasites (Moir et al. 2012); if all hosts held in captivity are treated with anthelmintic drugs to remove parasites, then they will most likely be lost anyway. This is bad if there are either no other wild hosts (e.g., the Californian condors), or if the parasite is not distributed evenly across the whole geographic range of the host.

While the loss of parasites during captive breeding and translocation is bad for biodiversity, allowing parasites to travel with their hosts into the translocated area can cause problems too, by introducing new pathogens into wild populations. Parasites occurring in hosts being translocated may not occur in the population being supplemented. Or, translocated hosts may become a new host for an existing parasite/pathogen, increasing its presence in the environment. Such changes to host and parasite/pathogen balances can potentially cause outbreaks of disease, or could intensify the infection rate disease in the translocated naïve population (Sainsbury & Vaughan-Higgins 2012). It is critical that an adequate understanding of the parasites, pathogens, commensals and mutualists is required for any translocation or captive breeding to succeed. Interestingly, however, captive breeding programs are often subject to human intervention and interaction on a number of direct and indirect levels. In a recent study, it was found that captive breeding of brush-tailed rock wallabies (Petrogale penicillata) appeared to have conferred a degree of antibiotic resistance in their gut bacteria, via inclusion of mobile genetic elements (integrons) of bacteria (Power et al. 2013). Such integrons were absent in bacteria from wild populations, indicating that the gut flora of the wallabies acquired them during their time in captivity (Power et al. 2013).

There are obviously many elements to consider when making large steps towards conservation in form of species translocation. Parasites (and commensals and mutualists) are an essential – and immense – component of healthy ecosystems, and there is still much to learn about their role in regulating ecosystem function (Dobson et al. 2008). They should not be ignored when decisions on conservation are being made for their larger, more charismatic (and charming?) hosts.

placard

References

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

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

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

Moir, ML et al. (2012) Considering extinction of dependent species during translocation, ex situ conservation and assisted migration of threatened hosts. Cons. Biol. 26, 199-207.

Power, ML et al. (2013) Into the wild: dissemination of antibiotic resistance determinants via a species recovery program. Plos One 8, e63017.

Sainsbury, AW & Vaughan-Higgins, RJ (2012) Analyzing disease risks associated with translocations. Cons. Biol. 26, 442-452.

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.

Monday Awesome: Quoll spotted in Victoria

Oh, man that was a bad pun in the title. For those not familiar, quolls have spots.

Dasyurus maculatus (image from Wikipedia)

The reason why a quoll-sighting in Victoria is exciting is because they are critically endangered in that region. Dasyurus maculatus, the spotted-tail or tiger quoll, is a largish marsupial found in Tasmania, parts of western Victoria and also has a coastal distribution from eastern Victoria into parts of coastal Queensland. However, none had been seen in the western part of Victoria for nearly 10 years, and there was concern that they’d become locally extinct. Today, via the ABC News website, we have word that a quoll was sighted and a scat taken that confirmed it came from a quoll. Yay! Hopefully that means that their numbers are increasing as a result of conservation efforts in the area.