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)
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)
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)
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)
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)
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)
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)
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)
The home range of A. mustelina is often limited to a single tree and the nearby surrounding shrubbery. Individuals rarely move between trees.
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)
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)
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)
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)
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)
There are no known negative effects of Achatinella mustelina on humans.
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)
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.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
fertilization takes place within the female's body
animals that live only on an island or set of islands.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
an animal that mainly eats fungus
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
breeding takes place throughout the year
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