Certain environmental conditions facilitate the control of primary producers by herbivores. Environmental change can, therefore, mediate the strength of consumption relative to production such that ...the abundance of primary producers is altered, potentially driving phase-shifts from one habitat type to another (e.g. the displacement kelp forests by mats of turfs along temperate coasts). Here, we assessed the extent to which herbivores may counter the increased cover of kelpcompetitors (i.e. turfs) anticipated to be caused by enriched nutrients and CO sub(2). Specifically, we experimentally enriched nutrients and CO sub(2) and quantified the change in cover of algal turfs in the presence and absence of gastropod grazers. In the absence of grazers, turf algae responded positively to the combination of enriched nutrients and CO sub(2) such that they occupied >95% of available space. In contrast, where grazers were present, sparse covers of algal turfs were maintained even under CO sub(2) and nutrient enrichment (i.e. turfs occupied <5% of available space). This result indicates that consumption by grazers increased where enrichment of nutrients and CO sub(2) facilitated greater algal cover such that cover continued to be largely restricted. By recognising the environmental conditions which will maintain or disrupt the balance between the processes of production and consumption, we may improve forecasts regarding the probability of habitat stasis or shifts.
Evidence of intense naticid drilling predation occurs on turritelline prey from a turritelline-dominated assemblage (TDA) which lies below the K-T boundary sections in Rajahmundry, India. Previously, ...it was believed that drilling frequency (DF) on turritelline taxa was low during the Cretaceous. Data from the study area indicates that the Cenozoic level of predation on turritelline taxa already occurred by the Late Cretaceous in the study area. The paleobiogeography of naticid predation is extended from the western world to India, which was located in the southern hemisphere during the Cretaceous. In addition to the high drilling frequency, the Indian fossil record shows that many aspects of naticid behavior; for example, size and site stereotypy, which are characteristic features of Cenozoic predators, were also established by the Late Cretaceous. These data support previous views that the Mesozoic Marine Revolution had minimal influence on morphological change in Late Cretaceous turritelline gastropods and that turritelline gastropods may have developed behavioral and/or physiological antipredatory adaptations. TDAs in general may indicate tremendous fecundity that may act as a buffer against high juvenile mortality due to predation.
Strombids are frequent fossils in Neogene nearshore deposits but are rarely used for biostratigraphy due to their poorly defined stratigraphic ranges. Herein, we document the biostratigraphic value ...of the group based on a succession of short-lived distinct species in Neogene deposits in the circum-Mediterranean area. These have been intermingled so far into two "super-species", viz. Persististrombus bonelli and P. coronatus, seemingly ranging from the Oligocene to the Pliocene. Based on morphometric measurements on 219 specimens we refine the taxonomic concept for this group and document at least 5 distinct species of high biostratigraphic and biogeographic significance. European Persististrombus species display a tendency to produce strongly sculptured populations with marked spines or to form populations with elongate shells and reduced sculpture. The development of sculptured morphs is an iterative process as exceptionally sculptured taxa occur in stratigraphically and geographically discrete phases and areas. Yet, within these species the morphology is very variable. Although some of these taxa are distinct species, there is no continuous evolutionary lineage leading to the Pliocene P. coronatus with which some of these taxa were confused in the literature so far. Successfully reproducing populations of extant species of Persististrombus in the Panamic Province and the African-Eastern Atlantic Province are limited in their distribution by the 20 degree C isotherm. This value may thus be a realistic estimate for the cool-season sea surface temperatures for Persististrombus-bearing formations. Persististrombus pannonicus sp. nov. is established for a late Badenian species.
The karyotypes of Sinotaia quadrata using air-drying method collected from Hyogal-ri, Pungyang-myeon, Yecheon-gun, Gyeongbuk, Korea were investigated. The diploid number of chromosomes is 2n=16. The ...eight chromosome pairs were identified and classified into three groups. The diploid cell has 1 pair of metacentric, 5 pairs of submetacentric and 2 pairs of subtelocentric chromosomes. Observed chromosomes ranged from 3.10 to 4.90 μm and the total length was 34.12 μm. The karyotype of S. quadrata is described for the first time.
'Cryptic' species are an emerging biological problem that is broadly discussed in the present study. Recently, a cryptic species definition was suggested for those species which manifest low ...morphological, but considerable genetic, disparity. As a case study we present unique material from a charismatic group of nudibranch molluscs of the genus Trinchesia from European waters to reveal three new species and demonstrate that they show a dual nature: on one hand, they can be considered a 'cryptic' species complex due to their overall similarity, but on the other hand, stable morphological differences as well as molecular differences are demonstrated for every species in that complex. Thus, this species complex can equally be named 'cryptic', 'pseudocryptic' or 'non-cryptic'. We also present evidence for an extremely rapid speciation rate in this species complex and link the species problem with epigenetics. Available metazoan-wide data, which are broadly discussed in the present study, show the unsuitability of a 'cryptic' species concept because the degree of crypticity represents a continuum when a finer multilevel morphological and molecular scale is applied to uncover more narrowly defined species making the 'cryptic' addition to 'species' redundant. Morphological and molecular methods should be applied in concordance to form a fine-scale multilevel taxonomic framework, and not necessarily implying only an a posteriori transformation of exclusively molecular-based 'cryptic' species into morphologically-defined 'pseudocryptic' ones. Implications of the present study have importance for many fields, including conservation biology and fine-scale biodiversity assessments.
Clusters of gastropod egg capsules, inferred to be of neritoids and attached to the inner shell wall of the ultimate whorl of a large volutid gastropod, are here recorded from the upper Nekum Member ...(Maastricht Formation; late Maastrichtian) of the ENCI-Heidelberg Cement Group quarry, St Pietersberg (Maastricht, southeast Netherlands). Because the aragonitic shell of the volutid has dissolved, the outlines of the egg capsules are now revealed on the steinkern of indurated biocalcarenite, having been subsequently overgrown by cheilostome bryozoan colonies and preserved as mould bioimmurations. This represents the first example of gastropod eggs preserved through bioimmuration, as well as the first record of gastropod eggs from the Cretaceous.
Land snails are highly tolerant to cadmium exposure and are able to accumulate soil cadmium independently of food ingestion. However, little information exists on the kinetics of cadmium retention in ...terrestrial gastropods exposed to an increase in the soil cadmium content, over time. There is also little knowledge about how exposure to cadmium-polluted soils influences shell growth and architecture. In this context, we examined cadmium accumulation in the hepatopancreas and shell of juvenile Cantareus aspersus exposed to elevating high levels of cadmium in soil. Also, the toxicity of cadmium to snails was assessed using a range of conchological endpoints, including shell height, width, volume, allometry and integrity. Test snails, aged three months, were reared under semi-field conditions, fed an uncontaminated diet and exposed first, for a period of 30 days, to a series of soil cadmium concentrations, and then, for a second period of 30 days, to soils with higher cadmium content. Cadmium showed a dose-dependent accumulation in both the hepatopancreas and shell. The kinetics of cadmium retention in the hepatopancreas of snails previously exposed to cadmium-spiked soils was significantly influenced by a new exposure event. The shell was not a relevant bioaccumulator for soil cadmium. Under the present experimental conditions, only high cadmium exposure significantly affected either the shell growth or snail survival. There was no consistent effect on shell allometry, but the shell integrity, especially in rapidly growing parts, appeared to be affected by high cadmium exposure. Our results attest to the value of hepatopancreas for describing cadmium retention in land snails and to the difficulty of using conchological parameters in field surveys for estimating the environmental hazard of soil cadmium.
A scanty but varied ensemble of finds challenges the idea that Neandertal material culture was essentially static and did not include symbolic items. In this study we report on a fragmentary ...Miocene-Pliocene fossil marine shell, Aspamarginata, discovered in a Discoid Mousterian layer of the Fumane Cave, northern Italy, dated to at least 47.6-45.0 Cal ky BP. The shell was collected by Neandertals at a fossil exposure probably located more than 100 kms from the site. Microscopic analysis of the shell surface identifies clusters of striations on the inner lip. A dark red substance, trapped inside micropits produced by bioeroders, is interpreted as pigment that was homogeneously smeared on the outer shell surface. Dispersive X-ray and Raman analysis identify the pigment as pure hematite. Of the four hypotheses we considered to explain the presence of this object at the site, two (tool, pigment container) are discarded because in contradiction with observations. Although the other two ("manuport", personal ornament) are both possible, we favor the hypothesis that the object was modified and suspended by a 'thread' for visual display as a pendant. Together with contextual and chronometric data, our results support the hypothesis that deliberate transport and coloring of an exotic object, and perhaps its use as pendant, was a component of Neandertal symbolic culture, well before the earliest appearance of the anatomically modern humans in Europe.
In vertebrates, the steroidogenesis enzyme 5α-reductase converts testosterone to the more potent androgen 5α-dihydrotestosterone. Homologues of 5α-reductase genes have been identified in molluscs. ...However, recent findings suggest that vertebrate-type steroid androgens are not utilised in molluscan reproductive development. Genomic searches have revealed that molluscs do not possess many of the steroidogenic enzymes required to make testosterone, nor a nuclear androgen receptor. Consequently, the role of 5α-reductase in molluscs presents a mystery. Here, developmental exposures of Biomphalaria glabrata to selective pharmaceutical 5α-reductase inhibitors elicited a strong, highly reproducible phenotypic response characterised by the development of elongated "banana-shaped" shell morphology. In comparison to untreated snails, the shells are open-coiled and the whorls are unattached. Dutasteride (5α-reductase inhibitor) is approximately 10-times more potent at provoking the banana-shaped shell phenotype than finasteride, paralleling the pharmaceuticals' efficacy in humans. Other enzyme inhibitors with different modes of action were tested to investigate the specificity of the phenotype. However, only the pharmaceutical 5α-reductase inhibitors provoked the response. Dutasteride elicited the same phenotype in a second gastropod, Physella acuta. In the absence of evidence for de novo androgen steroidogenesis in molluscs, these findings suggest that novel substrates for 5α-reductase exist in gastropods, lending support to the contention that molluscan endocrinology differs from the well-characterised vertebrate endocrine system.
Strain Hiromi 1, a sulfur-oxidizing gammaproteobacterium was isolated from a hydrothermal vent chimney in the Okinawa Trough and represents a novel genus that may include a phylogenetic group found ...as endosymbionts of deep-sea gastropods. The SSU rRNA gene sequence similarity between strain Hiromi 1 and the gastropod endosymbionts was approximately 97%. The strain was shown to grow both chemolithoautotrophically and chemolithoheterotrophically with an energy metabolism of sulfur oxidation and O2 or nitrate reduction. Under chemolithoheterotrophic growth conditions, the strain utilized organic acids and proteinaceous compounds as the carbon and/or nitrogen sources but not the energy source. Various sugars did not support growth as a sole carbon source. The observation of chemolithoheterotrophy in this strain is in line with metagenomic analyses of endosymbionts suggesting the occurrence of chemolithoheterotrophy in gammaproteobacterial symbionts. Chemolithoheterotrophy and the presence of homologous genes for virulence- and quorum sensing-related functions suggest that the sulfur-oxidizing chomolithotrophic microbes seek animal bodies and microbial biofilm formation to obtain supplemental organic carbons in hydrothermal ecosystems.
PDF
