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Terrestrial mollusks (land snails and slugs) are an important component of the terrestrial ecosystem, yet for most species their distribution is not well known. This study was a comprehensive inventory of terrestrial mollusks in Knox County, Tennessee; an area within the Valley and Ridge physiographic region rich in calcareous soils and bluffs. Knox County supports a total of 151 species, including 70 newly reported to the county and 15 newly reported to Tennessee. Sixteen species non-native to North America were found, mostly in urban/ residential habitats. Limestone/sandstone bluffs were found to have the highest diversity of terrestrial mollusks.
Fecundity in outcrossing species can be influenced by both maternal and paternal parents. To tease out these influences, we observed egg production in two populations of the hermaphroditic freshwater snail, Planorbella trivolvis (Say 1817). We carried out both intra- and inter-population matings between individuals from an inbred albino laboratory strain and individuals one generation removed from a natural population, and measured egg production for two 3-week periods - immediately after mating and 11 weeks later. In the female role, individuals from the albino laboratory population produced significantly more egg masses than the wild derived snails, regardless of whether they were mated to a partner of wild or laboratory origin, indicating that egg mass production is controlled by the maternal parent. Conversely, regardless of their own origin (laboratory or wild), snails mated to individuals from the wild derived population laid more eggs in each egg mass than those fertilized by sperm from the lab population. These results indicate that the number of egg masses a snail lays is determined at least in part by a maternal contribution, and that the number of eggs deposited in each mass may be influenced by the origin of the sperm donor. In addition, we confirmed a short-term trade-off between growth and reproduction as differences in egg production among mating types were mirrored by differences in body size. Further investigation into the nature of these differences will lead to better understanding of the reproductive biology of these hermaphrodite mollusks.
Where a stream enters a large lake, the mouth represents a transitional environment that is neither truly lotic nor lentic in nature and therefore is likely to affect the fauna present. Theory on habitat area and stream size predicts that species richness will increase farther downstream as watershed size increases, but as stream gradient and thus flow rate declines, stream mouths present a different and understudied habitat. Freshwater mussels in the family Unionidae are in decline, and therefore understanding how they respond across diverse habitats is also critical. We sampled mussel assemblages from 2010 to 2012 in the lower reaches of twelve small tributaries and two large embayments of the western and central basins of Lake Erie, where watershed size ranged from 10 to 4000 km2. These watersheds were assessed for land use by remote sensing and for basic water chemistry and the composition of their benthos by standard protocols. Evidence of native unionid mussels occurred in all watersheds, with 14 species found alive, which make up 75% of mussel species still present throughout Lake Erie. A species-area relationship occurred, although the effect was weaker than that present for flowing streams in the region. Additionally, the habitat and corresponding assemblages were characterized as depositional in nature, which logically follow high agricultural land use and corresponding high levels of turbidity and the proportion of silt and clay. Therefore, the lake environment influenced mussel assemblages, yet these conditions appear to limit dreissenid mussels in river mouths.
Fish have an ecologically significant role in the life-history of unionid freshwater mussels, as the larvae of most species are obligate ectoparasites (glochidia) on fish hosts. Although this ecological interaction is vital to freshwater mussel conservation, there is a paucity of data on fish-host specificity for many species. A species-specific DNA barcoding dataset utilizing the mitochondrial NADH dehydrogenase subunit 1 (ND1) gene was used to identify 154 glochidia attached to wild fish collected from March through August of 2013 in the Sabine and Neches rivers in Texas, U.S.A. These data include the first report of potential hosts for two state-threatened species, Fusconaia askewi (Marsh, 1896) and Pleurobema riddellii (I. Lea, 1862), as well as potential hosts for Amblema plicata (Say, 1817), Obliquaria reflexa (Rafinesque, 1820), Plectomerus dombeyanus (Valenciennes, 1827), Potamilus purpuratus (Lamarck, 1819), Quadrula mortoni (I. Lea, 1831), Q. verrucosa (Rafinesque, 1820), and Truncilla truncata (Rafinesque, 1820). Cyprinella lutrensis appears to be the primary host for F. askewi, as 50% (54/108) of its glochidia were found on this minnow species alone. Pleurobema riddellii may be a cyprinid specialist, infesting only C. lutrensis and Pimephales vigilax. Alternatively, F. askewi may be a host generalist, as glochidia were found encysted on 17 fish species suggesting that host fish availability may not be an important factor contributing to observed population declines. The findings here will be instrumental in the future conservation of these species, through the translocation to correct habitat and developing successful propagation programs
Population density commonly affects snail biology and is an important ecological factor to consider in any pest control program because population growth rates can be affected. Lissachatina fulica (Bowdich, 1822) is a pest of plants throughout the worldwide tropics; however, its biology is not completely known. We studied the effects of three rearing densities: low (5 snails per 25 × 38 × 17 cm (L × W × H) cage), medium (15 snails), or high (35 snails), on L. fulica growth, reproduction, and survival. High rearing density reduced growth, affected the initiation of egg laying, and reduced the number of eggs laid per snail and per clutch. Mortality did not increase with high rearing density, nor was any cannibalism observed, even when snails were deprived of food. Juvenile snail survival was more affected by lack of food than was adult survival, and availability of calcium did not compensate for lack of food. High-density rearing effects were not likely caused by limited food, calcium, or oxygen.
Cave-obligate (troglobiotic) land snails are among the most understudied taxa inhabiting cave systems because of their small size and cryptic nature. Other than locality records and general descriptions of species' morphology, information regarding most cave snail taxa is minimal. Given the importance of land snails as indicator species and as important drivers of ecosystem processes, this lack of knowledge on cave-obligate taxa impedes conservation management of subterranean snails and subterranean ecosystems in general. As a first step, we compiled and georeferenced all available distributional records for troglobiotic snail species within two major karst regions in the United States: The Interior Low Plateau (ILP) and Appalachians. We identified 16 new localities among these species from caves in Alabama, Tennessee, and Georgia from 2012 to 2016, yielding 8 new occurrences of two species in the ILP and 8 new occurrences of three species in the Appalachians. In total, we report 143 occurrences for five species in 124 caves, representing the most comprehensive dataset on the distribution of caveobligate snails in the eastern United States to date. We also provide the first IUCN Red List conservation assessments for all five troglobiotic taxa and reexamine NatureServe conservation ranks. Our assessments indicate that three of the five species are considered at an elevated risk of extinction. Given these ranks and the threats identified to each species, we offer recommendations concerning the conservation and management of these cave snails and outline future areas of research for these taxa.
There are few studies on pelagic mollusks from the California Current, despite their ecological importance and vulnerability to climate change (e.g., ocean acidification and hypoxia). We analyzed abundances of holoplanktonic mollusks during three years (2006–2008) along a transect-line parallel to the Baja California coast. The main differences in physical factors were increasing temperature and salinity from north to south, and lower dissolved oxygen concentration south of Punta Eugenia (28°N). The lowest oxygen concentrations occurred in summer, with hypoxic conditions (< 0.5 ml · L-1) in the upper 100 m depth at some locations. Planktonic mollusk abundance did not differ along the latitudinal gradient, excepting Desmopterus pacificus Essenberg, 1919 and individuals from the genus Pterotrachea Forskal, 1775. In contrast, the temporal variability was high, mainly in a seasonal scale but also among years. The influence of El Niño 2006–2007 and La Niña 2007–2008 were evident by a sharp increase of Corolla spectabilis Dall, 1871 in April 2007 during the El Niño-La Niña transition. During 2008, pelagic mollusks remained with moderate abundance in winter-spring despite the high chlorophyll concentrations recorded (up to 3.26 mg · m-3). Subsequently, during the relaxation of a first pulse of La Niña in July 2008, there was a rebound in the abundance of the heteropod Atlanta Lesueur, 1817. and individuals in the Order Gymnosomata. The oxygen gradient inversely influenced mollusk abundance in most of the genera (Clio Linnaeus, 1767, Limacina Bosc, 1817, Atlanta, and Firoloida Lesueur, 1817) and the order Gymnosomata, but for Cavolinia Abildgaard, 1791, Creseis Rang, 1828, Desmopterus, and Pterotrachea, the salinity gradient was more influential. Therefore, holoplanktonic mollusks genera were useful indicators of climatic variability.
Anthropogenic impacts on marine environments can be far-reaching and variable, and in an effort to mitigate these impacts, marine protected areas (MPAs) have been established globally. Indirect effects of MPAs on marine food webs and consumer behavior can be revealed through the diet of generalist predators, like octopuses, since their diet is a reflection of both preference and prey availability. Octopuses (Octopus bimaculatus Verrill, 1883) and invertebrate prey species were collected around Santa Catalina Island, CA in the summer of 2012, 2013, and 2014, and muscle tissues were analyzed for δ13C and δ15N. The δ13C and δ15N signature of octopuses caught within the MPA area and the non-MPA area were compared within diet space. Estimated contribution of prey species to octopus diet was calculated using a Bayesian mixing model. Octopuses caught in MPA areas had significantly different isotopic signatures than octopuses caught outside MPA areas in 2012 and 2013, but not 2014. Prey contributions to diet were highly variable between areas and years. Bivalves were a consistent contributor to MPA octopus diet, and the large snail Megastrea undosa (W. Wood, 1828) made up a relatively large proportion of the diet of octopuses from all areas and years. Additionally, there were more moray eels, a nocturnal predator outside MPA areas but more diurnal predators inside MPA areas. These results suggest octopus foraging behavior could be influenced by variation in predation risk reveal an indirect impact of diurnal predator recovery in the MPA. To fully understand the impact of anthropogenic change on marine environments, we must assess changes in the entire community and the interactions that drive community function.
In this study, trophic ecology of Octopus hubbsorum (Berry, 1953) was examined in relation to the species life cycle and dry and rainy seasons. A total of 184 individuals were obtained from the commercial artisanal catches at different localities along the coast of Oaxaca, Mexican tropical Pacific, from January 2011 to December 2012. Analysis of digestive tract contents revealed that O. hubbsorum preyed upon 43 different prey species belonging to five zoological groups (Crustacean, Mollusca, Teleostei, Echinodermata and Polychaeta), cannibalism was only occasional. The most important prey was the porcelain crabs genus Petrolisthes, contributing 52.1% and 37.8% to the total Index of Relative Importance, in females and males, respectively. Dietary comparison between different maturity stages revealed significant changes in the diet with maturation. The proportion of empty stomachs observed between the dry (18.75 %) and rainy (12.5 %) seasons did not differ significantly (χ2 = 0.55, P > 0.05). Our results suggest that females likely migrate to shallow areas to feed in preparation for mating, they may do this to increase energy intake prior to egg caring and incubation, a period when they do not feed. The high productivity waters along the coast of Oaxaca seem to be important to the survival of this species because they offer key food resources at a critical reproductive stage.
Cephalopods are infested by a wide variety of internal and external parasites, and although they have the ability to remove them, this ability may be limited when a high parasitic load occurs. Additionally, when the parasite is harmful, it may cause adverse effects on the health of the host and even death if not timely eliminated. Several treatments have been applied to eliminate the parasites in cephalopods but few have proved to be effective. This study examines an effective treatment for the elimination of the leech Stibarobdela moorei present in the epidermis of the adult of Octopus bimaculatus (Verril, 1883) captured in the Mexican Pacific Ocean, which, if used properly, does not have any side effects on humans or organisms in cultivation. The treatment consists of immersions in seawater with clove oil at a concentration of 0.45 ml l-1 for two minutes; the advantage is that it can be applied as often as necessary until the leeches are eliminated completely from the octopods. It is recommended that the treatment be applied with a minimum interval of 3 days between each application with the purpose of reducing the stress of the octopuses, caused by the manipulation.
The radular apparatus of Biomphalaria occidentalisParaense, 1981, Biomphalaria oligoza Paraense, 1971, Biomphalaria peregrina (d'Orbigny, 1835), Biomphalaria schrammi (Crosse, 1864) and Biomphalaria tenagophila (d'Orbigny, 1835) from the Metropolitan Region of São Paulo, Brazil were analyzed from Scanning Electron Microscope (SEM) micrographs. The data support the usage of characters of central, lateral and intermediate teeth in the species identification of Biomphalaria. The use of SEM provided additional quantitative and structural details to radula descriptions, which are extremely important for elucidating the taxonomy of Biomphalaria species.
The Chinese mystery snail, Bellamya chinensis (Gray, 1834) is a gastropod native to East Asia and is considered an invasive species in North America where its impacts on native species and ecosystems are not well understood. Scientific literature describing its biology and life history are sparse. Thermal tolerance limits, or the maximum and minimum temperature under which a species can survive, are key to identifying the potential geographical range of a species. The ability of managers to control invasive species is directly impacted by the thermal tolerance limits of a species. We attempted to identify the thermal tolerance limits of B. chinensis in a laboratory setting. Using a random sampling design, we exposed groups of wild-caught B. chinensis to either extreme high or low temperature treatments. We identified the upper temperature tolerance limit as between 40 and 45 °C. This result indicates some hot water management techniques may successfully prevent spread of B. chinensis among waterways. Despite exposing B. chinensis to freezing temperatures for extended periods of time we did not identify a lower temperature limit. Identifying the thermal tolerance limits of this and other invasive species informs predictions of range expansion and identification of potential prevention efforts.
A recent molecular study on pelagic nudibranchs showed that Glaucus marginatus (Reinhardt and Bergh, 1864) is a complex of three cryptic species, whereas the congener G. atlanticus (Forster, 1777) remain as one species. The objective of the present study was to determine the identity of pelagic nudibranchs collected in the Gulf of California using both molecular and traditional taxonomy. New DNA sequences (COI) and GenBank data were used to confirm the specimens' identity as G. atlanticus. Records from G. atlanticus were obtained from databases to determine the species geographic range. Present results increase that range northwards by approximately 150 km in the Gulf of California. Molecular data indicate that G. atlanticus from the Gulf has a wide infl uence from populations from the North and South Pacific and Indian Oceans. There is no current evidence of other cryptic species.
Rumina decollata (Linnaeus 1758) is native to the Mediterranean region of Europe and north Africa. The first report in Argentina was in 1988 in Buenos Aires. In 2007, it was found in La Pampa and Mendoza. Here, we report its presence in Córdoba, extending its distributional range northwards more than 600 km. This finding is significant given that Rumina decollata is a facilitative predator and can deleteriously impact mollusk assembles causing ecological imbalances.
In many species, the difference between pigmented and non-pigmented individuals is due to a single recessive Mendelian gene. We have demonstrated that this is also the case in the freshwater hermaphroditic snail, Planorbella trivolvis (Say, 1817), and established an albino population with comparable genetic background to a wild population so that pigmentation can be used as a visible genetic marker to better understand the reproductive biology of these mollusks. We carried out Mendelian crosses between albino (A) individuals from an inbred laboratory strain and pigmented (P) individuals one generation removed from a natural population and assessed pigmentation of progeny from eggs collected immediately after mating and 11 weeks later. Results of parental, F1, and F2 generations and backcrosses to pure-breeding albinos were consistent with a Mendelian single gene inheritance pattern. Because we never observed albino progeny from any albino snails mated to pigmented sperm donors, we also confirmed that selfing is rare in P. trivolvis. A simple non-invasive paternity marker in this unusual hermaphrodite snail that displays almost no self-fertilization will facilitate experiments to understand its reproductive biology and provide a more complete picture of hermaphrodite mating strategies.
Robert Robertson (1934–2018) was systematic malacologist, natural historian, and reproductive biologist, focusing on marine gastropods and based at the Academy of Natural Sciences in Philadelphia (ANSP) for most of his career. An account of his professional life is presented, based in part on a brief autobiography here included. Lists of his 142 publications (published and unpublished, formal and informal) and 13 taxa, as well as taxa named for him and publications written about him, are provided.