Here we report on the frequency, shape, and position of sublethal, predatory-induced breakage on shells of the common pterineid bivalve genus Ptychopteria from the Middle Devonian of New York. ...Twenty-six of the 115 well-preserved shells of Ptychopteria examined displayed evidence of at least one repair scar. The capacity to retract the vulnerable mantle deep within the shell and squeeze the valve margins together tightly to seal the shell enabled Ptychopteria to sustain marginal shell damage that was often severe. Repair scars resemble traces made by modern shell-breaking predators, especially decapod arthropods. Stereotyped positioning of the repair scars on the posterior portion of the valve also suggests active selection of an attack site by unknown shell-breaking predators. The relatively high repair frequency for Ptychopteria supports a growing body of evidence that suggests predation pressure intensified in the middle Paleozoic.
We have previously shown that lamellar body-like particles, the form in which pulmonary surfactant is secreted, spontaneously disintegrate when they contact an air-liquid interface, eventually ...creating an interfacial film. Here, we combined these studies with a new technique enabling the simultaneous and non-invasive measurement of surface tension (
γ). This method is a refinement of the pendant-drop principle. A sapphire cone with a 300-
μm aperture keeps the experimental fluid by virtue of surface coherence in a fixed and nearly planar position above the objective of an inverted microscope. The radius of curvature of the fluid meniscus is related to
γ and determines the pattern of light back-reflection upon epi-illumination. This method, which we name “inverted interface”, has several novel aspects, in particular its microscopic dimensions. When using lamellar body-like particles freshly released by alveolar type II cells, we found that their conversion at the interface resulted in
γ-reduction close to 30 mN/m. After a fast initial decay,
γ-decrease proceeded slowly and in proportion to single particle conversions. These conversions ceased with time whereas
γ decreased further, probably due to reorganization of the already deposited material. The present investigation indicates that surface film formation by adsorption of large surfactant aggregates is an important mechanism by which
γ is reduced in the lung.
Gradients in salt marsh ecosystems that result from reduced tidal inundation time in the high marsh offer an opportunity to assess the importance of predation as a selective agent (indexed by the ...time‐averaged record of unsuccessful predation, which integrates potentially confounding short‐term – inter‐seasonal and inter‐annual – fluctuations in predation pressure). Spatial patterns in selection pressure are expected to decrease landward from the seaward edge of the marsh. Interaction between shell‐breaking predators and their snail prey, Littoraria irrorata, however, generated a pattern in the frequency of sublethal injury (shell repair), standardized for snail size, that did not follow this simple, single‐variable prediction of decreasing repair frequencies with distance from the seaward edge of the marsh, based on inundation time alone. Patterns of repair frequency increased landward from the seaward edge of the marsh, only declining as predicted after a zone of dense stands of salt marsh grass. The interaction of tidal inundation time and primary habitat structure (e.g. physical vegetative barriers to dispersion of predators into the marsh) is hypothesized to shape selection gradients in salt marshes, as inferred from the record of unsuccessful predation.
Edge drilling is a form of predation in which a predatory snail excavates a hole at a point along the margin of the closed valves of a bivalved animal. We tested the hypothesis that edge-drilling ...attacks by the predatory snail Chicoreus dilectus on its clam prey Chione elevata shorten the duration of the predation process relative to the alternative behaviour of drilling through the prey's shell wall away from its edges. The time required to complete an edge-drilling attack was on average about three times less than when prey were attacked through the shell wall. This improvement in predation speed was a function of the thickness of the prey's shell at the point of attack. We suggest that owing to the shorter length of time required to kill prey, the edge-drilling behaviour may be selectively advantageous in environments where enemies are abundant, especially competitors that might attempt to steal prey. Behaviours that speed up the predation process may create opportunities for more effective exploitation of available prey resources in highly competitive environments.
A major challenge facing conservation biology today is predicting how often species will be able to adapt to environmental change. We need to know which, and under what environmental conditions, ...ecologically important traits are likely to evolve and keep species in the evolutionary game. Conservation biologists currently lack enough data across a broad range of traits and taxa to address this problem, which impedes the development of scenarios of possible adaptive management responses. Here I outline how trait‐based data and methods that palaeobiologists use to address the long‐term dynamics of evolving lineages can be applied to address this challenge. We need an impassioned community‐wide effort to view evolutionary stasis with an ecological lens.
•We used live, dead, midden and fossil mollusks to establish an ecological baseline.•Ecological change did not increase with pollution toward New York City as expected.•Commercial shellfishing had a ...more significant impact than reduced water quality.•Reducing pollution alone may not be an adequate option to restore eutrophied estuaries.•Paleoecology studies reveal that ecological baseline information is relevant to restoration.
Benthic communities in Long Island Sound (LIS) have experienced over 150years of commercial shellfishing and excess nutrient loading (eutrophication) which causes hypoxia. We established an ecological baseline using a combination of live, dead, archaeological, and fossil material to investigate the impacts of these stressors on the molluscan community. We expected that ecological change would increase with eutrophication-hypoxia west towards New York City. Instead we found that taxonomic similarity, rank-order abundance, and drilling frequency are more strongly controlled by commercial fishing pressure than by decreasing dissolved oxygen. Commercial fisherman collecting quahog clams (Mercenaria mercenaria), physically disrupt surface-dwelling organisms and also kill large numbers of predatory gastropods, including the channeled whelk, Busycotypus canaliculatus, and the drilling moonsnails Neverita duplicata and Euspira heros, to protect hard clam stocks. As a result, areas dredged by commercial fishermen yield fewer shells with drill-holes and fewer surface-dwelling organisms than unfished sites. In spite of recent reductions in lobster fishing, crushing predation by crabs and lobsters on clams has been suppressed below baseline levels throughout LIS, even in the well oxygenated east. The absence of a clear relationship between eutrophication-hypoxia and ecological change questions the effectiveness of nitrogen reduction alone as a restoration strategy. LIS fossils revealed a relatively ancient loss of those mollusks associated with seagrass and oyster habitats (e.g., oysters, Crassostrea virginica; jingle shells, Anomia simplex; scallops, Argopecten irradiens; and the gastropod Bittiolum alternatum) that predates the accumulation of dead shells and underscores the need for older material to reveal the shifting baseline. The interactive nature of multiple stressors means that past overfishing may have dampened the response of communities in LIS to eutrophication or inhibited their capactiy to recover. The unexpected role of hypoxic areas protected from commercial fishing as refuges highlights the utility of no-take marine preserves in eutrophied estuaries worldwide.
Conservation decision-making is a forward-looking process that involves choices among alternative images of how the future will unfold. Scenarios, easily understood as stories about plausible ...futures, are emerging as a powerful approach used by the conservation community to define a range of socio-ecological futures when standard, predictive modelling approaches to decision-making are inappropriate, providing a framework for making robust decisions under uncertainties. Conservation palaeobiologists can help the conservation community imagine the future. The utility of the past centres on orienting us to the present—grounding the future in the realm of what is plausible—by providing context against which to think about future scenarios, which may help stakeholders and decision-makers to develop a new mental map of a conservation problem, inspiring our intentions and moving us purposefully toward a desirable tomorrow.
This article is part of a discussion meeting issue 'The past is a foreign country: how much can the fossil record actually inform conservation?'
Pulmonary surfactant is secreted by alveolar type II cells as lipid-rich, densely packed lamellar body-like particles (LBPs). The particulate nature of released LBPs might be the result of structural ...and/or thermodynamic forces. Thus mechanisms must exist that promote their transformation into functional units. To further define these mechanisms, we developed methods to follow LBPs from their release by cultured cells to insertion in an air-liquid interface. When released, LBPs underwent structural transformation, but did not disperse, and typically preserved a spherical appearance for days. Nevertheless, they were able to modify surface tension and exhibited high surface activity when measured with a capillary surfactometer. When LBPs inserted in an air-liquid interface were analyzed by fluorescence imaging microscopy, they showed remarkable structural transformations. These events were instantaneous but came to a halt when the interface was already occupied by previously transformed material or when surface tension was already low. These results suggest that the driving force for LBP transformation is determined by cohesive and tensile forces acting on these particles. They further suggest that transformation of LBPs is a self-regulated interfacial process that most likely does not require structural intermediates or enzymatic activation.
Species belonging to the family Naticidae (commonly called moon snails) are important infaunal gastropod predators found in soft-bottom marine communities worldwide that traditionally have been ...thought to prey on other mollusks, giving them the expected trophic position of a predator (trophic position = 3). Realized trophic position estimates of the naticid Neverita duplicata from Long Island Sound, however, range between 2.3 and 2.5, indicating omnivory or an anomalously low nitrogen (N) fractionation factor. To evaluate the likelihood of omnivory, this study presents whole body stable isotopic analysis of nitrogen and carbon from the soft tissues of laboratory-reared and field-collected N. duplicata. Experimental organisms were maintained on a diet of the bivalve prey Mercenaria mercenaria for one year. The median N fractionation factor derived from the experimental moon snails was 3.58 ‰ thus precluding the presence of an atypical fractionation factor (substantially lower than 3.4 ‰). Numerous molluscan taxa were collected from Long Island Sound in order to evaluate the trophic ecology of N. duplicata in the context of a natural food web. Evidence from the carbon (C) signatures of field-collected N. duplicata indicate a reliance on littoral food sources that is inconsistent with a diet of filter-feeding M. mercenaria, even when calculated using the species-specific C fractionation factor derived from the laboratory experiments. Field-collected N. duplicata also show considerable isotopic overlap (N and C) with grazing Littorina littorea. For these reasons, we hypothesize that N. duplicata feeds on some combination of benthic primary producers (most likely macroalgae and/or epiphytic diatoms), carrion, and bivalve/gastropod tissue and discuss the ecological implications of potential naticid omnivory.
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