Land snail faunas of the Napier and Oscar Ranges, Western Australia; diversity, distribution and speciation

The snail faunas of the Napier and Oscar Ranges, Western Australia have two major components: large camaenid species which are restricted endemics, with tiny geographical distributions and a pattern of geographical replacement within the Ranges, and smaller species of wider distribution, most of which are found throughout the Ranges. Sampling of 55 similar sites, protected from fire, over the length of the Ranges reveals this pattern clearly, with γ diversities being far higher for camaenids than for others, in which there is no pattern of geographical replacement. This difference is not found in temperate and subtropical snail faunas from elsewhere, nor does the camaenid pattern occur in surveys of diversity in other organisms. These results are discussed in terms of dispersal and allopatric speciation related to demonstrable environmental fluctuation. An additional finding is that within one major taxonomic group (Gastropoda), a community may be partly structured by competition and exclusion and partly by accidents of colonization and accumulation: some, but not all niches may be full.     

Myxomycetes from the Kimberley Region, Western Australia

An account of the Myxomycetes of the Kimberley Region of north Western Australia is presented. It is based on collections obtained mainly from the Napier and Oscar Ranges during the Kimberley Research Project, 1988. The thirty-two collections represent eighteen species, four of which are new records for Australia and twelve new to Western Australia. All but one are new to the Kimberley region, from where only four species were previously known.     

Soil Manganese Enrichment from Industrial Inputs: A Gastropod Perspective

Manganese is one of the most abundant metal in natural environments and serves as an essential microelement for all living systems. However, the enrichment of soil with manganese resulting from industrial inputs may threaten terrestrial ecosystems. Several studies have demonstrated harmful effects of manganese exposure by cutaneous contact and/or by soil ingestion to a wide range of soil invertebrates. The link between soil manganese and land snails has never been made although these invertebrates routinely come in contact with the upper soil horizons through cutaneous contact, egg-laying, and feeding activities in soil. Therefore, we have investigated the direct transfer of manganese from soils to snails and assessed its toxicity at background concentrations in the soil. Juvenile Cantareus aspersus snails were caged under semi-field conditions and exposed first, for a period of 30 days, to a series of soil manganese concentrations, and then, for a second period of 30 days, to soils with higher manganese concentrations. Manganese levels were measured in the snail hepatopancreas, foot, and shell. The snail survival and shell growth were used to assess the lethal and sublethal effects of manganese exposure. The transfer of manganese from soil to snails occurred independently of food ingestion, but had no consistent effect on either the snail survival or shell growth. The hepatopancreas was the best biomarker of manganese exposure, whereas the shell did not serve as a long-term sink for this metal. The kinetics of manganese retention in the hepatopancreas of snails previously exposed to manganese-spiked soils was significantly influenced by a new exposure event. The results of this study reveal the importance of land snails for manganese cycling in terrestrial biotopes and suggest that the direct transfer from soils to snails should be considered when precisely assessing the impact of anthropogenic Mn releases on soil ecosystems.     

To eat or not to eat—relationship of lichen herbivory by snails with secondary compounds and field frequency of lichens

Aims The biochemical defense of lichens against herbivores and its relationship to lichen frequency are poorly understood. Therefore, we tested whether chemical compounds in lichens act as feeding defense or rather as stimulus for snail herbivory among lichens and whether experimental feeding by snails is related to lichen frequency in the field.Methods In a no-choice feeding experiment, we fed 24 lichen species to snails of two taxa from the Clausilidae and Enidae families and compared untreated lichens and lichens with compounds removed by acetone rinsing. Then, we related experimental lichen consumption with the frequency of lichen species among 158 forest plots in the field (Schw?bische Alb, Germany), where we had also sampled snail and lichen species.Important findings In five lichen species, snails preferred treated samples over untreated controls, indicating chemical feeding defense, and vice versa in two species, indicating chemical feeding stimulus. Interestingly, compared with less frequent lichen species, snails consumed more of untreated and less of treated samples of more frequent lichen species. Removing one outlier species resulted in the loss of a significant positive relationship when untreated samples were analyzed separately. However, the interaction between treatment and lichen frequency remained significant when excluding single species or including snail genus instead of taxa, indicating that our results were robust and that lumping the species to two taxa was justified. Our results imply lichen-feeding snails to prefer frequent lichens and avoid less frequent ones because of secondary compound recognition. This supports the idea that consumers adapt to the most abundant food source.     

Microgeographic evolution of snail shell shape and predator behavior

Genetic divergence in geographically isolated populations is a prerequisite for allopatric speciation, one of the most common modes of speciation. In ecologically equivalent populations existing within a small, environmentally homogeneous area, an important role for environmentally neutral divergence is often found or inferred. We studied a species complex of conspicuously shaped Opisthostoma land snails on scattered limestone outcrops within a small area of lowland rainforest in Borneo. We used shell morphometrics, mitochondrial and nuclear DNA sequences, and marks of predation to study the factors involved in allopatric divergence. We found that a striking geographic divergence exists in shell morphology, which is partly associated with neutral genetic divergence. We also found geographic differentiation in the behavior of the snails' invertebrate predator and evidence of an evolutionary interaction between aspects of shell shape and predator behavior. Our study shows that adaptation to biotic aspects of the environment may play a more important role in allopatric speciation than previously suspected, even on a geographically very small scale.     

Trade-offs between force and fit: extreme morphologies associated with feeding behavior in carabid beetles

We explored how functional trade-offs in resource handling strategies are associated with the divergent morphology of predators. The malacophagous carabid Damaster blaptoides shows two extreme morphologies in the forebody; there is an elongate small-headed type and a stout large-headed type. A feeding experiment showed that the small-headed type obtained a high feeding performance on snails with a thick shell and a large aperture by penetrating the shell with its head. In contrast, the large-headed type showed a high feeding performance on snails that had a thin shell and a small aperture, and they ate these prey by crushing the shell. The large-headed, strong-jawed beetles are efficient at shell crushing but are ineffective at shell entry; the large mandibles and musculature that allow for shell crushing make the beetle's head too wide to penetrate shell apertures. On the other hand, small-headed, weak-jawed beetles crush poorly but can reach into shells for direct predation on snail bodies. These findings are hypothesized to be functional trade-offs between force and fit due to morphological constraints. This trade-off would be a primary mechanism affecting both resource handling ability in animals and phenotypic diversity in predators and prey.     

Food partitioning between coexisting Atlantic salmon and brook trout in the Sainte‐Marguerite River ecosystem, Quebec

Food resource partitioning between similar‐sized, sympatric Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis was examined as a possible mechanism enabling their coexistence in a stream (Allaire) of the Sainte‐Marguerite River ecosystem, Quebec, Canada. Fish stomach contents and invertebrate drift were collected concurrently during three diel cycles in August to September 1996. The food and feeding habits of an allopatric brook trout population in a nearby stream (Epinette) were studied for comparison. The diel feeding rhythms of the two coexisting fish species were similar. The composition of their diet, however, showed significant differences. Atlantic salmon predominantly (60–90%) fed on aquatic insects, mainly Ephemeroptera (35–60% of the diet). The brook trout mostly (50–80%) fed upon the allochthonous terrestrial insects (mainly adults of Coleoptera, Hymenoptera and Diptera) which comprised 5–40% of the stream drift. The allopatric brook trout fed opportunistically on the more abundant aquatic insects and terrestrial insects rarely formed 25% of its diet. The allopatric trout fed nearly twice as much as the sympatric brook trout during a day. The results suggest that the differences in feeding by brook trout in the two streams (with and without Atlantic salmon) are the result of inter‐specific interaction with Atlantic salmon and are not related to the differences in food availability between the two streams. Food resource partitioning between Atlantic salmon and brook trout may be viewed as an adaptive response resulting in a greater exploitation of available resources and coexistence.     

Annotated type catalogue of Bothriembryon (Mollusca, Gastropoda, Orthalicoidea) in Australian museums, with a compilation of types in other museums

Type material of 41 Australian Bothriembryon taxa present in Australian museums is critically listed, indicating systematic issues that need to be resolved in further studies. Information on additional type material of 22 taxa in non-Australian museums is compiled. The seven fossil taxa known so far are included in this catalogue. Based on the current systematic position, 38 species are treated in this paper. Bothriembryon jacksoni Iredale, 1939, Bothriembryon notatus Iredale, 1939, Bothriembryon praecelsus Iredale, 1939 and Bothriembryon serpentinus Iredale, 1939 are elevated to species level. Bothriembryon gratwicki (Cox, 1899) is listed as status to be determined.     

Invasiveness Does Not Predict Impact: Response of Native Land Snail Communities to Plant Invasions in Riparian Habitats

Studies of plant invasions rarely address impacts on molluscs. By comparing pairs of invaded and corresponding uninvaded plots in 96 sites in floodplain forests, we examined effects of four invasive alien plants (Impatiens glandulifera, Fallopia japonica, F. sachalinensis, and F.×bohemica) in the Czech Republic on communities of land snails. The richness and abundance of living land snail species were recorded separately for all species, rare species listed on the national Red List, and small species with shell size below 5 mm. The significant impacts ranged from 16–48% reduction in snail species numbers, and 29–90% reduction in abundance. Small species were especially prone to reduction in species richness by all four invasive plant taxa. Rare snails were also negatively impacted by all plant invaders, both in terms of species richness or abundance. Overall, the impacts on snails were invader-specific, differing among plant taxa. The strong effect of I. glandulifera could be related to the post-invasion decrease in abundance of tall nitrophilous native plant species that are a nutrient-rich food source for snails in riparian habitats. Fallopia sachalinensis had the strongest negative impact of the three knotweeds, which reflects differences in their canopy structure, microhabitat humidity and litter decomposition. The ranking of Fallopia taxa according to the strength of impacts on snail communities differs from ranking by their invasiveness, known from previous studies. This indicates that invasiveness does not simply translate to impacts of invasion and needs to be borne in mind by conservation and management authorities.     

Changes in biofilms induced by flow regulation could explain extinctions of aquatic snails in the lower River Murray,Australia

Notopala sublineata, Notopala hanleyi(Viviparidae) andThiara balonnensis (Thiaridae) are prosobranchgastropodsthat were once abundant in the lower River Murray. These andothersnail taxa have declined markedly over the last 50 years,coinciding with increased flow regulation by dams and weirs.Inthis paper we speculate that the decline may be linked tochangesin the nature of food resources. Before regulation, most ofthebiofilm biomass in the lower Murray probably was microbial, asfluctuating water levels and high turbidity would havemaintainedthese communities in a state of early succession. Bystabilisingseasonal water levels, we suggest that regulation has promotedthegrowth of filamentous algae, perhaps at the expense ofbacteria.Evidence from gut and faecal pellet analysis, and fromanalysis ofcarbon stable-isotopes, suggests that the gastropod taxa aredetritivores, feeding mainly on amorphous organic detritus.Algaehave a relatively high C:N ratio (low nutritional value) andmay bean inadequate food to maintain female growth and reproduction,especially in viviparous snails.     

Intraspecific trait cospecialization of constitutive and inducible morphological defences in a marine snail from habitats with different predation risk

1.?Studies examining the integration of constitutive and inducible aspects of multivariate defensive phenotypes are rare. 2.?I asked whether marine snails (Nucella lamellosa) from habitats with and without abundant predatory crabs differed in constitutive and inducible aspects of defensive shell morphology. 3.?I examined multivariate shell shape development of snails from each habitat in the presence and absence of waterborne cues from feeding crabs (Cancer productus). I also examined the influence of constitutive and inducible shell morphology on resistance to crushing. 4.?Regardless of the presence of crabs, snails from high-risk (HR) habitats developed rotund, short-spired shells, while snails from low-risk habitats developed elongate shells, tall-spired shells, indicating among-habitat divergence in constitutive shell shape. Moreover, allometry analyses indicated that constitutive developmental patterns underlying this variation also differed between habitats. However, snails from HR habitats showed greater plasticity for apertural lip thickness and apertural area in the presence of crab cues, indicating among-habitat variation in defence inducibility. 5.?Both shell shape and apertural lip thickness contributed to shell strength suggesting that constitutive shell shape development and inducible lip thickening have evolved jointly to form an effective defence in habitats where predation risk is high.     

Molecular systematics of the endemic Leptaxini (Gastropoda: Pulmonata) on the Azores islands

The Azorean representatives of the Leptaxini (Pulmonata) are single island endemics, where a high-spired shell distinguishes the monotypic genus Helixena from two slightly different low-spired forms within Leptaxis (azorica and caldeirarum type). We studied the evolutionary history of putative taxa and the three shell-types using 12 allozyme loci and sequences of nuclear (ITS-1 and ITS-2) and mitochondrial DNA (COI and 16S rRNA). While little variation was found in both ITS genes, allozyme and mtDNA divergence was among the highest reported for pulmonate land snails. Generally, phylogeographic patterns are indicative of allopatric differentiation via the successive colonization of (younger) islands, while a major role for adaptive evolution is not supported. The azorica shell-type is monophyletic and has no common history with other sympatric shell-types on the same islands. The (ambiguous) position of Helixena sanctaemariae makes Leptaxis paraphyletic on the Azores and possibly also the caldeirarum shell-type. Helixena can therefore not be distinguished as a separate genus on the Azores. Following a lineage-based concept, representatives on all (ancient) islands should be considered distinct species.     

Prospects for Studies of Morphological Variability of Land Pulmonate Snails

The main goal of modern investigations into the morphological variability of land pulmonate snails was defined as designing the patterns of taxa structure on the basis of historical analysis of their taxonomic studies. Transition from the investigation of individual characters to an analysis of the organism as a whole assumes the application of the system approach. Systemic properties of the organism can be revealed through the key characters reflecting the process of evolutionary transformation of the correlation chains. In the case of land pulmonate snails, the relationship between the operative and conservative subsystems of the organism can serve as such a key character. The operative subsystem-cephalopodium-fulfills the function of active contacts with the environment; the conservative subsystem-the shell and its content-exercises protective functions. The subsystems are in conflict, and its resolution establishes the main patterns of the organization of pulmonate snails.     

Two new Campanulaceae from New Guinea

Two new species of Campanulaceae from New Guinea are described, Lobelia victoriensis and Wahlenbergia papuana. Keys to and enumerations of the species of both genera of New Guinea taxa are provided.     

Patterns of growth and energy allocation in northern California populations of Littorina (Gastropoda: Prosobranchia)

Seasonal patterns in shell growth rates, tissue weights, and female reproductive efforts were monitored for three species of western North American rocky shore gastropods, Littorina keenae Rosewater (supralittoral), L. scutulata Gould (high intertidal), and L. plena Gould (high intertidal). Growth rates conformed to the Von Bertalanffy growth model. Relative to male snails, female L. keenae appeared to sacrifice shell growth to expend more energy on the production of large quantities of gametes during the spring; growth rates of females and large males were highest during autumn when microalgal food supplies were seasonally abundant. In contrast, spring tended to be the best season for shell growth of L. scutulata and L. plena; however, reproductive output was poor and sporadic for these two species, and growth rates in the field during all seasons were low compared to growth rates of snails held under laboratory conditions with abundant food. High population densities of snails at shore levels occupied by L. scutulata and L. plena may greatly reduce food levels upon which individual snails rely for growth and reproduction.     

Evaluating the efficacy of land snail survey techniques in Hawaii: implications for conservation throughout the Pacific

Terrestrial micromolluscs (snails with an adult maximum shell dimension <5 mm) constitute a considerable proportion of the land snail fauna of the Pacific. However, micromolluscs are often underestimated in biological surveys because of size bias. It has been argued that visual searches are preferable on Pacific islands because: (1) size biases are limited based on the understanding that most native Pacific island land snails are very small, and (2) amount of labor is less than other methods such as soil surveys and adequate for inventory purposes (though not for abundance assessments). To test whether visual surveys and soil surveys were accurately recording all taxa, land snail inventories were completed in three forest reserves (5 sampling sites in each) on the island of Oahu, Hawaii. Visual surveys involved 30-min visual search in a 10 m² site; soil surveys involved sieving leaf litter and topsoil from four 0.3 m² quadrats and extracting snails with the aid of a microscope. The data indicate a size and microhabitat bias associated with both techniques. Visual surveys consistently collected large arboreal and litter-dwelling species but missed a significant portion of micromolluscs, while soil surveys collected micromolluscs but missed larger snails. Because of such biases, employing both methods is critical for collecting all taxa at a survey location. As such, we recommend that future land snail surveys on Pacific Islands incorporate both survey techniques. Obtaining a complete inventory is critical if we are to understand species distributions and patterns of diversity and make well-informed conservation recommendations.     

Parasites alter host phenotype and may create a new ecological niche for snail hosts

By modifying the behaviour and morphology of hosts, parasites may strongly impact host individuals, populations and communities. We examined the effects of a common trematode parasite on its snail host, Batillaria cumingi (Batillariidae). This widespread snail is usually the most abundant invertebrate in salt marshes and mudflats of the northeastern coast of Asia. More than half (52.6%, n=1360) of the snails in our study were infected. We found that snails living in the lower intertidal zone were markedly larger and exhibited different shell morphology than those in the upper intertidal zone. The large morphotypes in the lower tidal zone were all infected by the trematode, Cercaria batillariae (Heterophyidae). We used a transplant experiment, a mark-and-recapture experiment and stable carbon isotope ratios to reveal that snails infected by the trematode move to the lower intertidal zone, resume growth after maturation and consume different resources. By simultaneously changing the morphology and behaviour of individual hosts, this parasite alters the demographics and potentially modifies resource use of the snail population. Since trematodes are common and often abundant in marine and freshwater habitats throughout the world, their effects potentially alter food webs in many systems.     

Phylogeny recapitulates geography, or why New Zealand has so many species of skinks

The evolutionary history of 25 New Zealand scincid lizards in the endemic genera Oligosoma and Cyclodina was examined using 12S rRNA sequence data. Phylogenetic resolution was poor, despite there being up to 9% sequence divergence between taxa. Lack of resolution was not attributable to biases in the data, such as site saturation or differences in sites free to vary, so we infer that New Zealand skinks underwent two relatively rapid phases of divergence. The rate of substitution for the skink sequences appears to be similar to some bird and mammal groups for which times of divergence have been estimated. Using fhese calibrations diversification of Oligosoma skinks probably began at least 23 million years ago (Mya). The pattern of relationships and the timing of this diversification are interpreted as resulting from rapid allopatric speciation during the Oligocene (25–35 Mya) when New Zealand was fragmented into many low lying islands. A second major phase of speciation involving the Cyclodina seems to have occurred during the Miocene (15–24 Mya), probably as a consequence of increasing land area and habitat diversity. This pattern of skink evolution contrasts with the Oligocene 'environmental crisis' hypodiesis of Cooper & Cooper (Proc. R. Soc. Land. B. 261, 293–302), but can be attributed to differences in the ecology of different taxa. This can be tested by examination of other groups, such as land snails and geckos. The large number of lizard species in New Zealand can be considered a legacy both of past geography as well as the absence of small mammals which would have been both competitors and predators.     

Associations between shell morphology and land crab predation in the land snail Cerion

1. The land crab Gecarcinus lateralis is a significant predator of the abundant Bahamian land snails of the genus Cerion . The crabs typically 'scissor' the cylindrical shells in half or break the lip and peel back the shell to reach the animal which withdraws two or three whorls into the shell. Scars on shells of live adults at 73 sites in the Bahamas and Florida Keys show that about 8% (range: 0–44%) of the snails have survived attacks of this type.
2. An artificial crab claw was used to investigate the compressive force required to break Cerion shells of different morphotypes. Defining shell strength as the ability to withstand compressive forces, 10 morphotypes were found that exhibited mean relative strengths of between 30 and 300 newtons. Feeding trials with one adult crab showed that snails whose shells could withstand compressive forces of > 95 N were safe from this individual predator.
3. Multiple linear regression analyses showed that both shell size (length and width) and shell wall thickness were the ultimate determinants of shell strength. Ribs strengthen the shell by contributing to wall thickness and also by increasing overall shell width. The thickened adult shell lip and collabral ribs provide effective protection from attack by peeling.