Platydemus manokwari
| Platydemus manokwari | |
|---|---|
| |
| Platydemus manokwari, head is on the right. | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Order: | |
| Suborder: | |
| Family: | |
| Subfamily: | |
| Genus: | |
| Binomial name | |
| Platydemus manokwari De Beauchamp, 1962
| |
Platydemus manokwari, also known as the New Guinea flatworm, is a species of large predatory land flatworm. It is an invasive species.
Native to New Guinea, it has been accidentally introduced to the soil of many countries. It was also deliberately introduced into two Pacific islands in an attempt to control an invasion of the Giant East African Snail. It eats a variety of invertebrates including land snails, and has had a significant negative impact on the rare endemic land snail fauna of some Pacific islands. It has become established in a wide variety of habitats.
General ecology
Description
This flatworm is relatively large, about 40 to 65 mm in length and about 4–7 mm wide. Its body is however quite flat, being less than 2 mm in thickness. Both ends of the animal are pointed, but the head end is more pointed than the tail end.[1] Near the tip of the head end are two eyes.[2] The color of this animal is dark brown on the upper surface, with a lighter central line. The underside is pale grey.[1]
Natural habitat
Platydemus manokwari, also known as the New Guinea flatworm, is a flatworm species native to the island of New Guinea in the Pacific Ocean. This species of large flatworm preys on land mollusks and has been categorized as one of the 100 worst invasive species. It was discovered in 1962 by De Beauchamp in Queensland, Australia.
The original habitat of Platydemus manokwari is within tropical areas, but it has been found in almost all temperate regions of the world including in agricultural, coastland, and disturbed areas, as well as, natural forests, planted forests, riparian zones, scrub/shrublands, urban areas, and wetlands.[3] However, Platydemus manokwari does not live in urban coastal areas, perhaps due to environmental factors, such as lack of vegetation.[3]
Prey
Platydemus manokwari mainly preys on small land snails, but it has been known to feed on various soil invertebrates, such as earthworms, slugs, and arthropods.[4] Platydemus manokwari is the main predator of land mollusks, and preys upon the snails during most of their life cycle including young hatchlings.[5] Furthermore, Platydemus manokwari does not recognize early-stage snail eggs as a possible food source, but it does feed on young hatchlings and late-stage eggs of land snails.[5] Platydemus manokwari uses a chemical-based tracking method to follow snail mucus trails and track down its prey, sometimes even into trees.[6] In areas where the land snail population has been exhausted, it has been known to eat other flatworms.[4] The diet of Platydemus manokwari is also affected seasonally. According to studies done by Sugiura, more than 90% of the land snails were preyed upon by Platydemus manokwari in the period from July to November, and only 40% of the land snails were eaten during the other months. It was thus found that there was a positive correlation between snail mortality and temperature. This seasonal difference can be explained by different foraging behaviors, different microclimactic conditions, and different densities.[7]
Predators
There are no known predators of Platydemus manokwari. However, Platydemus manokwari is a paratenic host for the nematode Angiostrongylus cantonensis, also known as the rat lungworm. This nematode parasitizes Platydemus manokwari as well as the Giant African land snail, and both of these organisms are transmission vectors of the parasite. A. cantonensis parasitizes humans as well and causes angiostrongyliasis. Platydemus manokwari acts as a transmission vector of the parasite to humans and affects the epidemiology of angiostrongyliasis.[8] In an outbreak of angiostrongyliasis in the Okinawa Prefecture, populations of Angiostrongylasis cantonensis intermediates were examined in order to find the most frequently infected intermediates. Platydemus manokwari was found to be one of the prevailing infected hosts, with an infection rate of 14.1%. It is likely that Platydemus manokwari is a vector because it deposits A. cantonensis larvae on the underside of cabbage leaves, where it commonly lives.
Invasive species characteristics
Islands invaded
Platydemus manokwari has been introduced to several tropical and subtropical islands such as Micronesia, the Marquesas, the Society Islands, Samoa, Melanesia, and the Hawaiian Islands. These islands often harbor endemic radiations of rare and endangered snail species, which are a primary source of nutrition for Platydemus manokwari.[5] Platydemus manokwari has also been introduced to several Japanese Islands.
Methods and purpose of introduction
Although native to New Guinea, Platydemus manokwari has been found in many tropical and temperate regions of the world. There are several methods by which Platydemus manokwari has been introduced to these areas. Some methods are accidental. One such is the sale of tropical plants and potting soil that contains Platydemus manokwari.[7] Another method of accidental introduction occurs through the movement of machinery and equipment. Platydemus manokwari are often found in the leftover soil on the construction equipment and when the soil is transferred, Platydemus manokwari is also transported.[9] Platydemus manokwari can also be transferred to new areas through the accidental transfer of seed material used to restore vegetation.[9]
Platydemus manokwari has also sometimes been introduced intentionally, as a biological control agent. In various areas such as Guam and the Okinawa islands, Platydemus manokwari was introduced to control the population of the invasive Giant African land snail, which had damaged crops and threatened the agricultural industry. It has been said that "much of the 'evidence' that these predators can control Achatina fulica populations is based on a poor understanding of ecological principles. That the predators will prey on [Giant African land snail] is not evidence that they can control its populations...".[9] The flatworm controlled the population of the Giant African land snail but it also began preying on populations of endemic land snail, which led to an unprecedented increase in the Platydemus manokwari populations and a marked decrease in the endemic land snail populations.[6]
Ecological effects of invasion
Platydemus manokwari has had several effects on the ecology of the communities that it has been introduced to. In the Pacific Islands that Platydemus manokwari has invaded, several native land snails, specifically the Partula, Mandarina, juvenile M. aureola, juvenile A. fulica, B. similaris, Allopeas kyotoense, Meghimatium bilineatum, and A. fulica have either gone extinct or their numbers have drastically reduced.[10] Platydemus manokwari is such an efficient and invasive species that it has caused the decline and extinction of gastropods in several islands and is known as one of the ‘100 world’s worst invaders’.[11]
The success of Platydemus manokwari as an invasive species can be attributed to several factors. One explanation is that Platydemus manokwari has very few, if any, known predators and thus has few biotic limiting factors. Also, Platydemus manokwari exhibits high tolerance for several environments. However, Platydemus manokwari cannot survive in colder environments.[7] Platydemus manokwari has also shown versatility in prey tracking and attack methods of snail species. Experiments conducted by Yamaura and Sugiura indicated that Platydemus manokwari can climb trees and track down nonmarine mollusks using olfactory cues.[6]
Experiments have shown that out of five other flatworm species, Platydemus manokwari was by far the most efficient.[9] In an experiment done by Isamu Okochi and colleagues, 5 different flatworm species (including Platydemus manokwari) were kept in various storage units containing endemic snail species. Out of these five species, Platydemus manokwari was the only species that had started to prey on the snail species within a day of introduction. Two of the other predatory flatworm species did prey on the snails, but their rates of predation were not consistent.[9] This indicates that Platydemus manokwari outcompetes other predatory flatworm species and consumes more endemic land species than other species. Furthermore, these data indicate that Platydemus manokwari can begin consuming endemic land snails right after introduction. In other words, Platydemus manokwari can adjust to a new environment fairly quickly and can even destroy fragile ecosystems quickly.
Control methods
Currently, there are no known methods for controlling the population of Platydemus manokwari. This makes the eradication of the invasive species especially difficult. However, in several other cases, modified versions of parasites and viruses have been used as a biological control agent for invasive species. For example, the Myxoma virus has been used in Australia to control the spread of rabbits, which became an invasive species after their introduction to the area in the late 1800s. Similarly, the nematode parasite Phasmarhabditis hermaphrodita has been proposed as a biological control for the grey garden slug, Deroceras reticulatum. The major controversy in using this parasite to control the population of the grey garden slug is that the parasite may also kill earthworm species, a non-intentional consequence of using the parasite as a biological control.[12] According to studies conducted, there is no significant evidence that Phasmarhabditis hermaphrodita caused mortality in earthworm or flatworm species, but it did affect many terrestrial gastropods.[12]
Using this principle, a modified version of the nematode parasite Angiostrongylasis cantonensis can be used to control the flatworm population. However, since this parasite is also a parasite to humans and mollusks, the introduction of Angiostrongylasis cantonensis may have harmful effects on non-target organisms
Several scientists have theorized that one of the few limiting factors that prevents the expansion of Platydemus manokwari is low tolerance to colder temperatures. Platydemus manokwari thrive best in habitats that range of 18 C to 28 C, which is commonly found in many tropical and subtropical islands. In an experiment done by Shinji Sugiura, Platydemus manokwari were placed in several containers that had a certain amount of land snails in each and allowed to interact with them for a period of fourteen days in temperatures varying from 10 C to 26 C.[13] Of those in the containers kept at 10 C, only 23.3% survived all fourteen days and none of them fed on the snails. As temperatures increased, an increase in predation and survival of Platydemus manokwari was observed.[13] This shows that Platydemus manokwari is significantly limited in distribution at lower temperatures, but can often flourish at higher temperatures.
Future of the invaded communities
The major uncertainty regarding communities invaded by Platydemus manokwari involves the survival of endemic snail populations. According to current data, predation by Platydemus manokwari is the biggest cause of the extinction of several native and introduced gastropods (a class of mollusks that include snails and slugs).[10] These data suggest that the population of endemic land snails that have not already gone extinct is sharply decreasing in the areas the Platydemus manokwari has been introduced. Furthermore, there is little hope for endemic land snail populations in areas inhabited by Platydemus manokwari to recover to their original population size before Platydemus manokwari was introduced.[10] This is because the species is such an efficient and active predator that species that its controls prey populations and prevents them from recovering.[9] Although beneficial for farmers and agriculture of the area, this decrease of snail population is problematic because it can drastically alter the food webs and interactions between endemic organisms in the island, which can then affect the delicate ecosystem of the islands. Thus, it is uncertain how ecosystems will change with persisting predation by Platydemus manokwari.
References
- ^ a b Platydemus manokwari. zipcodezoo.com, accessed 27 October 2009.
- ^ [1]. cms.jcu.edu.au, accessed 29 October 2009.
- ^ a b Sugiura S, Okochi I, Tamada H (2006) “High predation pressure by an introduced flatworm on land snails on the oceanic Ogasawara Islands.” Biotropica 38:700–703
- ^ a b Ogren, R. (June 1995). “Predation Behavior of Land Planarians.” Hydrobiologia 305:105-111
- ^ a b c Iwai, N., S. Sugiura, et al. (2010). "Predation impacts of the invasive flatworm Platydemus manokwari on eggs and hatchlings of land snails." Journal of Molluscan Studies 76(3): 275-278
- ^ a b c Yamaura Y. (2008) "Potential impacts of the invasive flatworm Platydemus manokwari on arboreal snails". Biological Invasions 11(3): 737-742
- ^ a b c Sugiura, S. (2009). "Seasonal fluctuation of invasive flatworm predation pressure on land snails: Implications for the range expansion and impacts of invasive species." Biological Conservation 142(12): 3013-3019
- ^ Ryuji, A. et al (July 2004). “Changing Epidemiology of Angiostrongyliasis Cantonensis in Okinawa Prefecture, Japan”. Japanese Journal of Infectious Diseases 54; 184-186
- ^ a b c d e f Okochi, Isamu, Sato Hiroki, and Ohbayashi Takashi. "The cause of mollusk decline on the Ogasawara Islands." Biodiversity & Conservation 13.8 (2004): 1465-1475. Environment Complete. EBSCO. Web. 4 Mar. 2011
- ^ a b c Hopper DR, Smith BD (1992) “Status of tree snails (Gastropoda: Partulidae) on Guam, with a resurvey of sites studied by H. E. Crampton in 1920.” Pac Sci 46:77–85
- ^ Lowe S, Browne M, Boudjelas S, De Poorter M (2000) “100 of the world’s worst invasive alien species: a selection from the global invasive species database.” The Invasive Species Specialist Group (ISSG) a specialist group of the Species Survival Commission (SSC) of the World Conservation Union (IUCN), Auckland, 12 pp. http://www.issg.org/database/species/search.asp?st=100ss>
- ^ a b Rae, R. et al (September 2005). “Susceptibility of indigenous UK earthworms and an invasive pest flatworm to the slug parasitic nematode Phasmarhabditis hermaphrodita.” Biocontrol Science and Technology 15(6): 623-626
- ^ a b Sugiura S. (21 August 2009) "Prey preference and gregarious attacks by the invasive flatworm Platydemus manokwari". Biological Invasions
Further reading
- Kaneda M., Kitagawa K. & Ichinohe F. (1990) "Laboratory rearing method and biology of Platydemus manokwari De Beauchamp (Tricladida: Terricola: Rhynchodemidae)". Applied Entomology and Zoology 25(4): 524–528. PDF
- Muniappan R. (1990) "Use of the planarian, Platydemus manokwari, and other natural enemies to control the giant African snail". In: Bay-Petersen J. (ed.) The use of natural enemies to control agricultural pests. Food and Fertilizer Technology Center for the Asian and Pacific Region, Taipei, pp 179–183.
- Sherley G. (ed.) (June 2000) Invasive species in the Pacific: A technical review and draft regional strategy. South Pacific Regional Environment Programme, Apia, Samoa. 190 pp., PDF ISBN 982-04-0214-X.
- Sugiura S., Okochi I. & Tamada H. (2006) "High predation pressure by an introduced flatworm on land snails on the oceanic Ogasawara Islands". Biotropica 38(5): 700–703. doi:10.1111/j.1744-7429.2006.00196.x.
External links
