Animal Diversity Web

Geographic Range

Achatinella mustelina is an arboreal pulmonate gastropod that is endemic to the island of O’ahu in the Hawaiian archipelago. This endangered terrestrial snail has a fairly large distribution from the southern edge of the island to the northern boundary of the Wai’anae Mountains. ("Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella", 1992; Holland and Hadfield, 2002; Kobayashi and Hadfield, 1996)

• Biogeographic Regions
• oceanic islands
  • native

• Other Geographic Terms
• island endemic

Habitat

Achatinella mustelina inhabits elevated forests that are dry, wet, or mesic. Generally, A. mustelina attaches itself to leaves at the tops of native trees and shrubs such as Metrosideros polymorpha, Dubautia plantanginea, Myrsine lessertiana, Pisonia sandwicensis, Antidesma platyphyllum and Nestegis sandwicensis. Individuals may live on a single tree for their entire lifetime. ("Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella", 1992; Hadfield, et al., 1993; Holland and Hadfield, 2002; Killian, 2007)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• forest
• mountains

• Range elevation

  600 to 1158 m

  1968.50 to 3799.21 ft

Physical Description

Achatinella mustelina from different locations vary in size, shape, and color, but no specific patterns in these differences have been described. In general, adults range 19 – 24 mm in length, with an average length of 21.4 mm. The shells have a shiny finish and are usually brown with light bands that circle the suture convex, or they are white with transverse black or brown lines. Shells of A. mustelina can be either dextral or sinistral and consist of five to seven convex whirls. The shell is relatively high-spiraled and oblong to ovate with an aperture that is also oblong and ovate. The columella of A. mustelina is short, stout, and slightly twisted, and it has a well-developed spiral lamella, or ridge. A callus on the columella closes the umbilicus. The lip of the organism does not have any ridges, ribs, or folds. ("Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella", 1992; Aubry, et al., 2005; Baily, 1943; Hadfield, et al., 1993; Killian, 2007; Schilthuizen and Davison, 2005; Welch, 1938)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Range length

  18.5 to 23.1 mm

  0.73 to 0.91 in

• Average length

  21.4 mm

  0.84 in

Development

Achatinella mustelina develops from an intrauterine embryo, and its growth in utero is thought to be logarithmic. Young are born live and are approximately 4.5 mm in length. The snail grows at a relatively slow rate of 2 mm per year, and over the course of four to five years, it will only grow to be five times its birth length. Growth in A. mustelina is determinate and individuals reach their maximum size before becoming reproductively mature. A unique characteristic of development in A. mustelina is that individuals of different sizes grow at the same rate. (Hadfield and Mountain, 1980; Hadfield, et al., 1993)

Reproduction

Achatinella mustelina is hermaphroditic, and may self-fertilize. (Hadfield and Mountain, 1980; Holland and Hadfield, 2007; Kobayashi and Hadfield, 1996)

• Mating System
• polygynandrous (promiscuous)

Achatinella mustelina has a lengthy gestation period and gives birth to large, live young that mature late and have a low fecundity. Although reproductive maturity occurs after the maximum size is reached, reproductive maturity may be dependent on age, not size. Reported age at maturity varies, ranging from 3 to 6.9 years. Similarly, reports of fecundity vary, but rates as low as 0.4 offspring/adult/year have been observed, as well as rates as high as 7 offspring/adult/year.

Little information about reproductive behavior in Achatinella mustelina is known, but this species is hermaphroditic and thought to breed year-round. Some species of the genus Partulina, sister to Achatinellidae, are thought to self-fertilize, so A. mustelina may self-fertilize as well. Partulina redfieldii can reproduce even in long-term absence of mates. The mechanism of this form of reproduction is not clear, however. Possibilities include parthenogenesis and long-term sperm storage, in addition to self-fertilization.

Genetic evidence suggests interchiral mating takes place for A. mustelina. Other terrestrial gastropods with high-spired shells like A. mustelina align themselves parallel and mount the other snail’s shell when mating. One snail inserts its penis in to the other and releases spermatophores. Embryos are intrauterine, and no more than two large embryos are contained in the uterus; usually there is only one. The large size of newborn A. mustelina, approximately 4.5 mm in length, limits the size of the maternal snail. (Hadfield and Mountain, 1980; Hadfield, 1986; Hadfield, et al., 1993; Holland and Hadfield, 2007; Killian, 2007; Kobayashi and Hadfield, 1996; Schilthuizen and Davison, 2005)

• Key Reproductive Features
• year-round breeding
• simultaneous hermaphrodite
• sexual
• fertilization
  • internal
• ovoviviparous
• sperm-storing

• Breeding season

  Achatinella mustelina breeds year-round.

• Range number of offspring

  <1 per year to 7 per year

• Range age at sexual or reproductive maturity (female)

  3 to 6.9 years

Although the literature does not include specific information about parental investment in Achatinella mustelina, in general, terrestrial gastropods do not provide parental care after birth. The most common form of parental investment for terrestrial gastropods comes in the form of calcium carbonate and other nutrients given to the developing egg. (Baur, 1994)

• Parental Investment
• pre-fertilization
  • provisioning

Lifespan/Longevity

Achatinella mustelina has a relatively long lifespan compared to other terrestrial gastropods. Longevity is estimated to be 10 years, but individuals may live up to 15 or 20 years. (Hadfield, et al., 1993; Killian, 2007)

• Typical lifespan
  Status: wild

  20 (high) years

• Average lifespan
  Status: wild

  10 years

Behavior

The Oahu tree snail is a terrestrial snail that is primarily found in native Hawaiian trees, such as Osmanthus sandwicensis, Gouldia sp., Metrosideros polymorpha, and large bushes. Generally, this snail attaches to leaves at the tops of native trees and shrubs, and is nocturnal. Individuals of A. mustelina enter a stage of inactivity during the numerous dry periods of its environment, curtailing feeding and growth. Individuals are not highly motile, resulting in many small, relatively isolated populations of A. mustelina. (Hadfield, et al., 1993; Holland and Hadfield, 2007; Killian, 2007)

• Key Behaviors
• arboreal
• nocturnal
• motile
• sedentary

Home Range

The home range of A. mustelina is often limited to a single tree and the nearby surrounding shrubbery. Individuals rarely move between trees.

Communication and Perception

Achatinella mustelina, like most terrestrial gastropods, communicates through both touch and chemical signaling, using the lower set of head tentacles. Individuals transmit pheromone signals both through direct contact and through the mucous trail left during locomotion. This includes warning of predator presence.

Achatinella mustelina has simple eyes for visual perception, albeit limited to larger objects. However, vision is not a primarily means of searching or foraging, given the snail’s nocturnal habits. (Chelazzi, 1990; Pakarinen, 1991)

• Communication Channels
• tactile
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• visual
• tactile
• chemical

Food Habits

Achatinella mustelina feeds primarily at night. This species is a mycophage, grazing upon epiphytic fungi growing on the bark or leaves of native plant species, such as Osmanthus sandwicensis, Gouldia sp. or Metrosideros polymorpha. Few imported species of plant are suitable for the fungi eaten by this snail species. In captivity, A. mustelina has been grown on cornstarch or sooty mold, with a supplement of cuttlebone providing the calcium necessary for shell growth. (Killian, 2007; Kobayashi and Hadfield, 1996)

• Primary Diet
• mycophage

• Other Foods
• fungus

Predation

The primary predator of Achatinella mustelina is the introduced carnivorous snail, Euglandina rosea, and A. mustelina has no defense mechanisms for this species. Several rat species eat A. mustelina, particularly the larger individual snails. Other foreign species that prey upon A. mustelina include the terrestrial flatworms Geoplana septemlineata and Platydemis manokwari. The Hawaiian Thrush (Phaerornis obscura) eats A. mustelina, although it isn't the bird's primary food source. (Hadfield, et al., 1993; Hart, 1978; Killian, 2007)

• Known Predators

  • Rats, Murinae
  • Rosy wolfsnail, Euglandina rosea
  • terrestrial flatworm, Geoplana septemlineata
  • New Guinea flatworm, Platydemis manokwari
  • Hawaiin thrush, Phaerornis obscura

Ecosystem Roles

Achatinella mustelina consumes fungi from plant bark and leaves. Historically, A. mustelina had no natural predators that relied upon it as a food source. With the introduction of the predatory snail Euglandina rosea, A. mustelina, along with other sympatric members of the genus Achetinella have become prey for this species. (Hadfield and Mountain, 1980)

Economic Importance for Humans: Positive

Due to their vibrant coloration, Achatinella mustelina shells were collected by human inhabitants of the island of Oahu to craft traditional leis and other ornaments. Shells from the genus Achatinella are still collected and sold as ornaments today as part of Hawaii’s tourist trade. (Hart, 1978)

Economic Importance for Humans: Negative

There are no known negative effects of Achatinella mustelina on humans.

Conservation Status

Achatinella mustelina is the currently the most abundant species of the O’ahu tree snails and has been studied considerably for conservation efforts. The slow growth, long pre-reproductive life, and low fertility of A. mustelina, in conjunction with its relatively sedentary lifestyle and small geographic range, make A. mustelina populations very vulnerable to disturbances, either from predation, human collection, or habitat destruction. Lowland habitat destruction by human inhabitants for the purposes of farming and logging have reduced the geographic range of A. mustelina to only high elevation mountainous forests.

However, the introduction of the invasive predatory snail Euglandina rosea from North America led to the rapid and widespread decline and destruction of A. mustelina populations. Euglandina rosea predates opportunistically on a number of species of terrestrial snails. Only a few hundred individuals of A. mustelina are estimated to remain in the wild. (Hadfield, 1986; Hadfield, et al., 1993)

• IUCN Red List

  Critically Endangered

• US Federal List

  Endangered

• CITES

  Appendix I

• State of Michigan List

  No special status

Contributors

Peter Bicescu (author), The College of New Jersey, Colleen Stalter (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Renee Mulcrone (editor), Special Projects.

References

Makua Military Reservation. Final Implementation Plan for Makua Military Reservation, Island of Oahu. Schofield Barracks, HI: United States Army Garrison, Hawaii Directorate of Public Works Environmental Division. 2003. Accessed January 03, 2013 at http://manoa.hawaii.edu/hpicesu/DPW/2003_MIP/Sec_1/2003_MIP_edited.pdf.

U.S. Fish and Wildlife Service. Recovery Plan for the O’ahu Tree Snails of the Genus Achatinella. Portland, OR: U.S. Fish and Wildlife Service. 1992. Accessed January 06, 2013 at http://ecos.fws.gov/docs/recovery_plan/920630.pdf.

Aubry, S., F. Magnin, V. Bonnet, R. Preece. 2005. Multi-scale altitudinal patterns in species richness of land snail communities in south-eastern France. Journal of Biogeography, 32: 985-998.

Baily, J. 1943. Zoogeography of tree snails. Ecology, 90: 75-85.

Baur, B. 1994. Parental care in terrestrial gastropods. Cellular and Molecular Life Sciences, 50: 5-14.

Chelazzi, G. 1990. Eco-ethological aspects of homing behavior in mollusks. Ethology Ecology & Evolution, 2(1): 11-26.

Hadfield, M. 1986. Extinction in Hawaiian achatinelline snails. Malacologia, 27: 67-81.

Hadfield, M., S. Miller, A. Carwile. 1993. The decimation of endemic Hawai'ian tree snails by alien predators. Integrative and Comparative Biology, 33(6): 610-622. Accessed January 06, 2013 at http://icb.oxfordjournals.org/content/33/6/610.short.

Hadfield, M., B. Mountain. 1980. A field study of a vanishing species, Achatinella mustelina (Gastropoda, Pulmonata), in the Waianae Mountains of Oahu. Pacific Science, 34(4): 345-358. Accessed January 06, 2013 at http://scholarspace.manoa.hawaii.edu/handle/10125/1633.

Hart, A. 1978. The onslaught against Hawaii’s tree snails. Natural History, 87(10): 46.

Holland, B., M. Hadfield. 2002. Islands within an island: phylogeography and conservation genetics of the endangered Hawaiian tree snail Achatinella mustelina. Molecular Ecology, 11: 365-375.

Holland, B., M. Hadfield. 2007. Molecular systematics of the endangered O’ahu tree snail Achatinella mustelina: synonymization of subspecies and estimation of gene flow between chiral morphs. Pacific Science, 61(1): 53-66.

Killian, H. 2007. Status of the species – Achatinella mustelina tree snails (Oahu Tree Snails). Mauka FEIS, 2(H-1): 295-450.

Kobayashi, S., M. Hadfield. 1996. An experimental study of growth and reproduction in the Hawaiian tree snails Achatinella mustelina and Partulina redfieldii (Achatinellinae). Pacific Science, 50: 338-354.

Pakarinen, E. 1991. Feeding avoidance of terrestrial gastropods to conspecific and nonspecific material. Journal of Molluscan Studies, 58(2): 109-120.

Schilthuizen, M., A. Davison. 2005. The convoluted evolution of snail chirality. Naturwissenschaften, 92: 504-515.

Welch, D. 1938. Distribution and variation of Achatinella mustelina Mighels in the Waianae Mountains, Oahu. B.P. Bishop Museum Bulletin, 152: 1-164.