Conservation biology of parasites

The capture, captive breeding, and reintroduction of California condors into the wild was the most expensive species conservation project in United States history. The bird was saved from extinction while its louse Colpocephalum californici became extinct.

A large proportion of living species on Earth live a parasitic way of life.[1] Parasites have traditionally been seen as targets of eradication efforts, and they have often been overlooked in conservation efforts. In the case of parasites living in the wild – and thus harmless to humans and domesticated animals – this view is changing.

Endangered parasite species

A note published in 1990 pointed out that the captive breeding and reintroduction program to save the black-footed ferret would cause the loss of its specific parasites and demanded "equal rights for parasites!".[2] Then a paper in 1992 has warned that not only the loss of certain host species from the wild, but even host population bottlenecks or the fragmentation of host populations would predictably lead to the extinction of several host specific parasite species.[3] It also noted that parasites are not only components of biodiversity by definition, but they also exert selective pressures upon their host populations that increase host genetic diversity. Firstly, this view met with open scepticism.[4] Soon after, it became clear that the co-extinction of hosts and their specific parasites is likely to increase the current estimates of extinction rates significantly.[5] A decade later, a study focusing on some highly host-specific groups (such as fig wasps, parasites, butterflies, and myrmecophil butterflies) estimated the number of co-endangered species (i.e. endangered by the endangered status of the host) at about 6300.[6] Other authors argued that host specific parasite faunae have an unexpected advantage for conservation scientists. Their genealogies and population genetic patterns may help to illuminate their hosts' evolutionary and demographic history.[7] Recently, scientists suggested that rich parasite faunae are inevitably needed for healthy ecosystem functioning [8] and also that parasites and mutualists are the most endangered species on Earth.[9] Even vets have started to argue about the conservational values of parasite species.[10]

A recent study on parasites of coral reef fish suggested that extinction of a coral reef fish species would eventually result in the coextinction of at least ten species of parasites. Although this number might seem high, the study included only large parasites such as parasitic worms and crustaceans, but not microparasites such as Myxosporea and Microsporidia.[11]

Example: extinct avian lice

The list below follows that of Mey (2005)[12]

Additionally, Columbicola extinctus is a parasite of the extinct passenger pigeon (Ectopistes migratorius). However, recent taxonomic studies show that it is conspecific with the lice living on band-tailed pigeon (Columba fasciata), thus it is not extinct.[14]

Larvae of the guinea worm: probably the next species to exterminate.

Extermination by purpose

Naturally, medical (and veterinary) science and practice aim to exterminate parasites and pathogens living in humans (and in domesticated animals). In case of the few highly host-specific pathogens, this equals the extinction of the pathogen species. Throughout human history, however, only a single one species, i.e. smallpox virus, was eradicated from the Globe. The last cases of smallpox occurred 1978. However, secured stocks still exist in the United States and Russia for defensive purposes such as developing new vaccines, antiviral drugs, and diagnostic tests.[15] [16][17] It is not known whether or not these superpowers have shared their stocks with some of their allies during the Cold War.[18]

A second candidate for purposeful extermination is the Dracunculus medinensis (guinea worm). Once widespread across some 20 nations of Africa and Asia, the parasite nowadays is much withdrawn occurring only in four countries in Sub-Saharan Africa with only a few hundred known cases of infection in 2011.[19] Prevalent civil wars in the region, such as the War in Darfur have ensured the survival of this species up to the present.

Notes and references

  1. Windsor DA (1998). "Most of the species on Earth are parasites". International Journal for Parasitology. 28 (12): 1939–1941. doi:10.1016/S0020-7519(98)00153-2. PMID 9925276.
  2. Windsor DA (1990). "Heavenly hosts". Nature. 348 (6297): 104. doi:10.1038/348104c0.
  3. Rózsa L (1992). "Endangered parasite species" (PDF). International Journal for Parasitology. 22 (3): 265–266. doi:10.1016/S0020-7519(05)80002-5. PMID 1639560.
  4. Bush AO, Kennedy CR (1994). "Host fragmentation and helminth parasites: Hedging your bets against extinction". International Journal for Parasitology. 24 (8): 1333–1343. doi:10.1016/0020-7519(94)90199-6. PMID 7729985.
  5. Stork NE, Lyal CH (1993). "Extinction or 'co-extinction' rates?". Nature. 366 (6453): 307–8. doi:10.1038/366307a0.
  6. Koh LP, Dunn RR, Sodhi NS, Colwell RK, Proctor HC, Smith VS (2004). "Species Coextinctions and the Biodiversity Crisis" (PDF). Science. 305 (5690): 1632–1634. doi:10.1126/science.1101101. PMID 15361627.
  7. Whiteman NK, Parker PG (2005). "Using parasites to infer host population history: a new rationale for parasite conservation" (PDF). Animal Conservation. 8 (2): 175–181. doi:10.1017/S1367943005001915.
  8. Hudson PJ, Dobson AP, Lafferty KD (2006). "Is a healthy ecosystem one that is rich in parasites?". Trends in Ecology & Evolution. 21 (7): 381–385. CiteSeerX accessible. doi:10.1016/j.tree.2006.04.007.
  9. Dunn RR, Harris NC, Colwell RK, Koh LP, Sodhi NS (2009). "The sixth mass coextinction: are most endangered species parasites and mutualists?" (PDF). Proceedings of the Royal Society B. 276 (1670): 3037–3045. doi:10.1098/rspb.2009.0413. PMC 2817118Freely accessible. PMID 19474041.
  10. Pizzi R (2009). "Veterinarians and Taxonomic Chauvinism: The Dilemma of Parasite Conservation". Journal of Exotic Pet Medicine. 18 (4): 279–282. doi:10.1053/j.jepm.2009.09.005.
  11. Justine, J.-L., Beveridge, I., Boxshall, G. A., Bray, R. A., Miller, T. L., Moravec, F., Trilles, J.-P. & Whittington, I. D. 2012: An annotated list of fish parasites (Isopoda, Copepoda, Monogenea, Digenea, Cestoda, Nematoda) collected from Snappers and Bream (Lutjanidae, Nemipteridae, Caesionidae) in New Caledonia confirms high parasite biodiversity on coral reef fish. Aquatic Biosystems, 8, 22. doi:10.1186/2046-9063-8-22
  12. Mey E (2005). "Psittacobrosus bechsteini: a new extinct chewing louse (Insecta, Phthiraptera, Amblycera) off the Cuban Macaw Ara tricolor (Psittaciiformes), with an annotated review of fossil and recently extinct animal lice" (PDF). Anzeiger des Vereins Thüringer Ornithologen. 5: 201–217.
  13. Mey E (1992). "Eine neue ausgestorbene Vogel-Ischnozere von Neuseeland, Huiacola extinctus (Insecta, Phthiraptera)" (PDF). Zoologischer Anzeiger. 224: 49–73.
  14. Clayton, Dale H.; Roger D. Price (1999). "Taxonomy of New World Columbicola (Phthiraptera: Philopteridae) from the Columbiformes (Aves), with Descriptions of Five New Species" (PDF). Annals of the Entomological Society of America. Entomological Society of America. 92 (5): 675–85.
  15. Connor, Steve (2002-01-03). "How terrorism prevented smallpox being wiped off the face of the planet for ever". The Independent. Retrieved 2009-12-13.
  16. Hammond, Edward (2007). "Should the US and Russia destroy their stocks of smallpox virus?". BMJ. 334 (7597): 774. doi:10.1136/bmj.39155.695255.94. PMC 1851992Freely accessible. PMID 17431261.
  17. Agwunobi, John O. (2007). "Should the US and Russia destroy their stocks of smallpox virus?". BMJ. 334 (7597): 775. doi:10.1136/bmj.39156.490799.BE. PMC 1851995Freely accessible. PMID 17431262.
  18. Rózsa L, Nixdorff K 2006. Biological weapons in non-Soviet Warsaw Pact countries. In: Wheelis M et al. (eds.) Deadly cultures: biological weapons since 1945. Cambridge, US: Harvard University Press.
  19. "The Carter Center Guinea Worm Disease Eradication".
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