Carole S. Hickman

Moorean tree snail survival revisited: a multi-island genealogical perspective.

BackgroundThe mass extirpation of the island of Mooreas endemic partulid tree snail fauna, following the deliberate introduction of the alien predator Euglandina rosea, represents one of the highest profile conservation crises of the past thirty years. All of the islands partulids were thought to be extirpated by 1987, with five species persisting in zoos, but intensive field surveys have recently detected a number of surviving wild populations. We report here a mitochondrial (mt) phylogenetic estimate of Moorean partulid wild and captive lineage survival calibrated with a reference museum collection that pre-dates the predators introduction and that also includes a parallel dataset from the neighboring island of Tahiti.ResultsAlthough severe winnowing of Mooreas mt lineage diversity has occurred, seven of eight (six Partula; two Samoana) partulid tip clades remain extant. The extinct mt clade occurred predominantly in the P. suturalis species complex and it represented a major component of Mooreas endemic partulid treespace. Extant Moorean mt clades exhibited a complex spectrum of persistence on Moorea, in captivity, and (in the form of five phylogenetically distinct sister lineages) on Tahiti. Most notably, three Partula taxa, bearing two multi-island mt lineages, have survived decades of E. rosea predation on Moorea (P. taeniata) and in the valleys of Tahiti (P. hyalina and P. clara). Their differential persistence was correlated with intrinsic attributes, such as taxonomy and mt lineages, rather than with their respective within-island distribution patterns.ConclusionConservation efforts directed toward Moorean and Tahitian partulids have typically operated within a single island frame of reference, but our discovery of robust genealogical ties among survivors on both islands implies that a multi-island perspective is required. Understanding what genetic and/or ecological factors have enabled Partula taeniata, P. hyalina and P. clara to differentially survive long-term direct exposure to the predator may provide important clues toward developing a viable long term conservation plan for Society Island partulid tree snails.

Experimental Release of Endemic Partula Species, Extinct in the Wild, into a Protected Area of Natural Habitat on Moorea

Extinction of tree snails of the genus Partula on Moorea, following introduction of the predatory snail Euglandina rosea, has challenged conservation biology during years of successive captive breeding of small rescued populations. An experimental release of three Partula species into a predator-proof patch of native forest on Moorea was designed to test effectiveness of physical and chemical methods of predator exclusion and to evaluate behavior of animals bred for up to six generations in highly artificial environments. At the close of the experimental release, there had been multiple incursions of E. rosea, and too few Partula spp. remained to assess effects of captive breeding on ecological responses. However, results demonstrated the effectiveness of the exclosure under ideal maintenance and monitoring. Captive breeding methods were validated by reproduction and growth to sexual maturity in the wild as well as retention of genetic variability in the form of persistent color polymorphism in one species.

Crosseolidae, a New Family of Skeneiform Microgastropods and Progress Toward Definition of Monophyletic Skeneidae

Abstract. n Preliminary review of 130 available genus-group names for the notoriously polyphyletic group of skeneiform microgastropods has revealed a concentration of biodiversity in Australasia, primarily on the shelf and on or in clastic substrates. Forty-four of the names are based on type species from Australia or New Zealand, and some of the most speciose genera are abundantly represented and well preserved in the Cenozoic fossil record. Many skeneiform species were not illustrated at the time of description, and remain unillustrated except by inadequate line drawings. Features observed in scanning electron micrographs are used to define a set of new shell characters and to name and diagnose a new vetigastropod family Crosseolidae. Diagnostic features are the shallow anterior canal at the base of the columellar lip, a prominent umbilical keel, and a pseudumbilicus between the umbilical keel and the sharply defined inner lip. The shell of the type species of Crosseola, C. concinna (Angas, 1868), is illustrated with SEM for the first time, along with variation in shells of Crosseola striata (Watson, 1883). Three additional genera are assigned to the family: Conjectura Finlay, 1927, Conradia A. Adams, 1860, and Crossea A. Adams, 1865. Dolicrossea Iredale, 1924 is excluded on external anatomical evidence that the type species is a rissooidean caenogastropod. Intraspecific variation in crosseolids is partly a consequence of terminal growth features: adult variciform thickening of the outer lip, descending suture, and modifications of the columella and umbilical region. A restrictive definition of Skeneidae is provided along with examples of Australasian genera that can be allocated confidently to other families. Three predominantly Australasian groups of Cenozoic skeneiform taxa are identified for intensified study and potential allocation to new families. The constituency of vetigastropod family-groups and inferences of their relationships are too poorly resolved at this time to warrant the use of superfamily names.

Mollusc-microbe mutualisms extend the potential for life in hypersaline systems.

Metazoans in extreme environments have evolved mutualisms with microbes that extend the physical and chemical capabilities of both partners. Some of the best examples are bivalve molluscs in evaporite and hypersaline settings. Mollusc tissue is developmentally and evolutionarily amenable to housing vast numbers of symbiotic microbes. Documented benefits to the host are nutritional. Multiple postulated benefits to the microbes are related to optimizing metabolic performance at interfaces, where heterogeneity and steep gradients that cannot be negotiated by microbes can be spanned by larger metazoan hosts. A small cockle, Fragum erugatum, and its photosymbiotic microbes provide a remarkable example of a mutualistic partnership in the hypersaline reaches of Shark Bay, Western Australia. Lucinid bivalves and their endosymbiotic chemolithotrophic bacteria provide examples in which hosts span oxic/anoxic interfaces on behalf of their symbionts at sites of seafloor venting. Multiple lines of evidence underscore the antiquity of mutualisms and suggest that they may have played a significant role in lifes first experiments above the prokaryotic grade of complexity. The study of metazoan-microbe mutualisms and their signatures in extreme environments in the geologic record will provide a significant augmentation to microbial models in paleobiology and astrobiology. There are strong potential links between mutualisms and the early history of life on Earth, the persistence of life in extreme environments at times of global crisis and mass extinction, and the possibilities for life elsewhere in the universe.

Interacting Constraints and the Problem of Similarity in Gastropod Structure and Function

Abstract. n Gastropods have served as research subjects for investigating questions that transcend both the taxon and the field of malacology. A major set of questions arises from repeated patterns in the microstructure, sculptural features, and coiling geometry of gastropod shells. The problem of similarity is one of distinguishing among alternative explanations of repetition and close resemblances. What explains the repetition of structural features? Are features similar as a consequence of shared ancestry (homology) or as a consequence of evolutionary convergence on good functional solutions (analogy)? There is increasing evidence for a third alternative that lies outside the evolutionary sphere, invoking the laws of physics and chemistry, building materials, and the assembly rules that apply strongly to the inorganic calcium carbonate of the gastropod shell. Three concepts are introduced to help organize the analysis of recurring similarities in the shells of marine gastropods. They are (1) remote biomineralization, (2) heterotectonic construction and ontogenetic reorganizations of shell secretion, and (3) structural funicity of the shell. Remote biomineralization produces organized structures without influence of the mantle, extrapallial space, and periostracum. Reticulate meshworks of aragonite on the exterior surfaces of larval shells are an example. Heterotectonic construction recognizes repeated instances of change in coiling geometry of the larval shell (protoconch) and the adult shell (teleoconch). Heterostrophy is an example of heterotectonic construction that is specific to the clade Heterobranchia; but there are many constructional changes that recur in other groups that are not closely-related. Examples include the set of changes that thicken larval shells (imbricate thickening) during the metamorphic reorganization of shell secretion and transition to secretion of new calcium carbonate microstructures. Funicity is a property of shell that results in recurring features that record ontogenetic history and ecological events. Funeous details include growth increments as records of periodic environmental rhythms, isotopic records of climate, and records of interaction with other organisms, including non-lethal damage inflicted by predators and modifications of shells by symbionts. Shells also record details of their post-mortem history, including a rich funeous record in deep time on and in shells in the fossil record.