Page 10 - Land Snails of New Mexico

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receivedmuch attentionlargelybecauseitisusedforhuman foodandisgrowncommerciallyinland-snailfarms,especially in France (Cabaret, et al., 1988).
detectingpotentialmates.McAndrew (1975)conductedT-maze experimentsforspecimensofAshmunella rhyssafromNew Mexico and Sonorella metcalf from the Franklin Mountains in Texas. Itappeared that individuals of both species were capable o f d i s c e r n i n g a n d f o l l o w i n g s l i m e t r a i l s l a i d d o w n b y m e m b e r s oftheirspecies.Some studieshaveindicatedthatsnailsand slugs can discern airborne odors, as well as cues from slime trails--anabilitypossiblyusefulinlocatinghomesites(Chelazzi, et al., 1988).
The relationship ofsnailsand the organisms that supply their f o o d is, o f c o u r s e , a n i n t e g r a l a s p e c t o f t h e i r e c o l o g i c a l n i c h e . NewMexicolandsnailsareherbivorous,althoughcarnivorous speciesexistinotherpartsoftheUnitedStatesandinMéxico. Land snails have been recorded as eating many kinds of
angiosperm plants, fungi, and lichens. In experiments, they have eaten apple, cabbage, carrot, clover, dandelion, lettuce, potato, and pelletsmade ofwheatflour, cornmeal, or peas. They exhibit preferencesforsome foods over others. Commercial foods have been produced for use in Helix aspersa farms. Snails eat plant materialsthatareliving,decaying,ordead.Toaidindigesting this diet, snails produce cellulase, an enzyme that digests cellulose, and chitinase, which digests the complex carbohydrate chitin, found in higher fungi and in lichens. The earliest land snailsmayhavebeenthefirstlandanimalstoproducethese enzymes, asssumingthattheywere eatingplantsoftheirtime, the late Paleozoic. M o s t present-day herbivores (e.g., termites and cows), which have large proportions of cellulose in their
The cues discussed above may be used to form aggregations. This phenomenon, called huddling (Waite, 1988), has been observed in some kinds of snails and slugs. Hibernating aggregations of Ashmunella rhyssa have been noted during winterintheSacramentoMountains.Clustersoftheintroduced
diet,depend on cellulasefrom theirgut microorganisms to digest cellulose. Large numbers of bacteria may be found in the digestivetractsoflandsnails,buttheseseem toenterandpass o u t a l o n g w i t h i n g e s t e d f o o d o r soil. H o w e v e r , s u c h b a c t e r i a m a y produce additional cellulase and chitinase during their time in the snail gut (Charrier, 1990). T h e relative importance of snail produced versus bacteria-produced enzymes is far from clear. Neither isitentirelyclearjustwhere snail-produceddigestive e n z y m e s a r e s y n t h e s i z e d , a l t h o u g h it h a s b e e n a s s u m e d t h a t t h e y arise within cells of the digestive glands of the animals. S o m e snails are k n o w n to interact with the abiotic part of their niche by eating soil, which seems to serve as a source of calcium and m a g n e s i u m u s e d i n s h e l l c o n s t r u c t i o n ( G o m o t e t al., 1 9 8 9 ) . T h e importance of these elements in the diet has been shown
mucus laid down by their own species, Pakarinen (1992) showed that,in Finland, several kinds of slugs and snails avoided aqueoussolutionsofcrushedsnailsoftheirown species.Itmight be adaptive toavoid areas in which conspecifics had been killed.
experimentally.
FoodhabitsofNew Mexicanlandsnailshavenotbeen
Variouskindsofbirdsandmammalsareknowntopreyon land snails. In Europe, songbirds, such as thrushes, have been reported as predators. Individual birds m a y use a favorite stone as an anvil in snail-bashing, crushing the shell to extract the soft parts. Pilsbry (1940:933) reported that crops of wild turkeys taken in the northern Sierra Blanca Mountains, Lincoln Co., contained Ashmunella rhyssa. Also in this area, well-crushed Ashmunella shells have been seen in the scat of an unidentified kind of mammal. Some shells, which we have observed,
studied, but several European species have been recorded as eating nettle (Urtica) leaves. Collectors, to their discomfort, have learned that nettle patches are good places to search for somekindsofNewMexicosnails.
appeared to have been chewed, probably by rodents. Heller and Godot (1984) reported that, in Israel, gerbils preyed on land snails. Beetles also m a y prey on snails. Shells of urocoptid snails found in southern N e w Mexico sometimes contained small
Land snails interact with various kinds of animals, especially, of course, with members of their own species (conspecifics). The land snails of N e w Mexico have both female and male
round holes drilled by a carabid beetle. Land-snailparasiteshavereceivedlittleattention,probably
reproductive organs (hermaphroditic) within a single animal. Most commonly, two individuals come together and one transfers a sperm packet to the other. However, reciprocal exchange of sperm packets has been reported (Duncan,
because few seem to be involved in parasite life cycles that include humans or domestic animals, as is the case in some freshwater pulmonate snails. Redetzke and Canaris (1977) analyzed the life cycle of the parasitic trematode flatworm, Brachylaime microti in Montana, which used Oreohelix strigosaasanintermediatehostandtworodentsasdefinitive hosts. Canaris (1960:524) listed five species of land snails in WashingtonandOregonthatwerefoundtoharbor"cysticercoids
1975:355). Also reported for a few kinds of snails has been self fertilization, as in certain succineid snails and in Rumina
decollata,anintroducedspeciesinNew Mexico(Selanderetal., 1974). Eventually, continued self-fertilizationmay produce a
clone-likepopulation.InNewMexicomountainswhere ofthetapewormLigasoricisNeilamd1953."InaEuropean
considerable numbers of land snails of the genus Ashmunella occur, pairs m a y be observed in copula during the rainy s u m m e r months.
study, Cabaret, et al. (1988) reported infection of a Helix aspersa population by three kinds of nematode parasites. If so m a n y species of parasites infect land snails in general, there m a y be many kinds of these parasites yet to be discovered and identified.
Studieshaveshownthatlandsnailscandetectandfollowthe slimetrailsofmembersoftheirspecies;thismay beusefulin
slugLimacusflavuswereobservedalongtheGilaRiverValley,
aggregating behavior in this species has been reported in Europe
as well (Chelazzi, et al., 1988). Incontrasttotheattractionthatsomesnailsseemtohavefor
Some landsnailsmay useslimetrailsorairbornecuesin homing or other orientation. Cook (1979) and Bailey (1989) have documented them as having homesites in rock crevices or more general areas, from which they venture a few feet for food andthenreturn.Othersnailsseemtowanderatrandomwithin
anarea,whichmayormaynotbeconstruedasahomerange (Baur and Baur, 1993). -