Structure and formation of the adventitious tube of the Japanese watering-pot shell Stirpulina ramosa (Bivalvia, Anomalodesmata, Clavagellidae) and a comparison with that of the Penicillidae

Abstract. Stirpulina ramosa is the only extant endobenthic representative of the Clavagellidae and is restricted to the waters of Japan. A single intact adventitious tube of this species has been obtained and its structure is described. The right valve is 16 mm long and located within the adventitious tube. It has an opisthodetic ligament located on resilifers. There are anterior and posterior adductor muscle scars, a thick pallial line, and pallial and pedal gape (right valve only) sinuses. The left shell valve is but 9 mm long and is united into the fabric of the adventitious tube via the intermediary of a shelly saddle. Internally, only the anterior adductor muscle scar and a small element of the pallial line scar are identifiable on the left valve. The posterior adductor and the rest of the pallial line scar (including a pallial sinus) are, remarkably, located on the adventitious tube beyond the shell valve margin. The adventitious tube of S. ramosa is formed in a manner wholly dissimilar from that of Brechites vaginiferus (Penicillidae). In B. vaginiferus, the tube is secreted as a single entity from the general outer mantle surface, including the siphons, covering the body. As a consequence, both shell valves are incorporated into the structure of the tube and the watering pot is bilaterally symmetrical. In S. ramosa, the tube and watering pot are secreted from the mantle margin and surface surrounding and extending from the left shell valve, so that only the left valve is incorporated into its structure. A dorsally derived mantle element is progressively extended over to the right side of the body, meeting a ventrally derived counterpart that passes beneath it, forming a pleat in the calcareous structure of the right side of the tube that they secrete. This pleat extends into the complex of watering‐pot tubules and forms the pedal gape. The watering pot is thus Ω shaped. The ventrally derived mantle element forms a sinusoidal crest on the right‐hand base of the watering pot, creating a pedal gape sinus scar on the right valve. The Clavagellidae radiated widely in the Mesozoic, leaving behind a rich fossil record for Stirpulina. Only S. ramosa, however, has survived until the present. In contrast, the Cenozoic Penicillidae has a poor fossil record, but there is a rich variety of extant endobenthic watering‐pot shells. It has been argued hitherto that the two families represent a remarkable example of convergent evolution. In view of the success of the Penicillidae and thus the endobenthic, tube‐dwelling lifestyle, however, it is hard to understand why Stirpulina has largely died out—even S. ramosa being known by but one or two specimens. A study of the anatomy of S. ramosa might one day answer this question.     

Biology and functional morphology of a new species of endolithic Bryopa (Bivalvia: Anomalodesmata: Clavagelloidea) from Japan and a comparison with fossil species of Stirpulina and other Clavagellidae

Abstract. A new species of Clavagellidae, Bryopa aligamenta, from Okinawa, Japan, is described. The species is endolithic in living corals, with the left valve cemented to the crypt wall, as in all clavagellids. The free right valve exhibits an unusual growth pattern, with commarginal lines seemingly arising from the posterior valve margin and extending towards the anterior. This results from: (i) progressive anterior erosion of the umbones, probably as a consequence of the boring process; (ii) the apparent migration posteriorly, as the umbones are eroded, of the dorso‐ventral growth axis of the shell; and (iii) enhanced posterior inter‐commarginal growth. Unlike other clavagellid genera and species, however, there is no discernible primary ligament, at least in the adult. It is possible, however, that if a juvenile ligament were present (as in B. lata), it too would be lost as a consequence of antero‐dorsal erosion during boring. To retain valve alignment in the absence of a primary ligament, and possibly upon reaching an adult size, the mantle lays down alternating layers of calcium carbonate and proteinaceous periostracum onto the interior surface of the shell to thicken it, most noticeably marginally and, especially, posteriorly. The two valves are united dorsally, therefore, by thin layers of periostracum that probably exert a minimal opening force. B. aligamenta is, however, further characterised by large adductor, pallial, and siphonal retractor muscles so that the entire animal is encased tightly within an internally strengthened shell within a crypt. Movement must be minimal, blood being pumped into pallial haemocoels to push open the valves and extend the siphons. Despite a suggestion to the contrary, Bryopa is retained in the Clavagellidae, its unusual growth processes resulting from an endolithic life style within living corals. The fossil clavagellid Stirpulina bacillus, from the Pliocene/Pleistocene of Palermo, Sicily, Italy, was, unlike Bryopa aligamenta and other clavagellids, endobenthic, with a long adventitious tube and anterior watering pot superficially similar to species of Penicillidae, another family of the Clavagelloidea. Furthermore, as in all clavagellids only the left valve is fused into the fabric of the tube, the right being free within it. In all penicillids, both valves are fused into the fabric of their tubes. The watering pots of the fossil S. coronata, S. vicentina, and S. bacillus, moreover, are formed in a different manner to that of penicillids, by progressive encasement of the right valve inside the tube. In penicillids, the tube is secreted in a single event from the general mantle surface and the incorporation of both valves into its fabric. The constituent genera of the Clavagellidae thus constitute an example of parallel evolution with members of the Penicillidae.     

Developmental instability of vascular plants in contrasting microclimates at ‘Evolution Canyon’

Rocellaria dubia bores into subtidal rocks of karsted limestone in the Adriatic Sea and elsewhere. It also bores into the shells of various bivalve species. The mechanism of boring has hitherto been debated, but examination of occupied shells suggest that this is achieved by mechanical (the shell) abrasion and chemical etching using secretions produced from glands in the anterior mantle. Fast‐growing bivalves such as Ostrea edulis and Pinna nobilis carry heavy R. dubia burdens, and encapsulate the borer in secreted calluses. Slow‐growing bivalves such as the burrowing Venus verrucosa and Glycymeris violacescens carry low R. dubia burdens, are less able to encapsulate the borers, and probably incur enhanced mortalities as a result. Individuals of R. dubia removed from their limestone boreholes re‐secreted adventitious tubes around their siphons, probably from glands in the posterior mantle. The lifestyle of R. dubia is now better understood, and its ability to bore bivalve shells in particular suggests how the more advanced tropical gastrochaenids Cucurbitula and Eufistulana have evolved from initial (as juveniles) bivalve shell borers into occupants of adventitious crypts and tubes, respectively. It is further argued that the Gastrochaenidae show convergent similarities with the similar crypt‐ and tube‐building representatives of the Clavagelloidea. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 786–804.     

Biology and functional morphology of Kendrickiana gen. nov. veitchi (Bivalvia: Anomalodesmata: Clavagelloidea) from southern Australia

Abstract. The largest extant species of the adventitious tube-building Clavagelloidea has hitherto been placed in the genus Foegia (itself formerly a subgenus of Brechites ), the type species of which is the Western Australian F. novaezelandiae (B ruguiére 1792). Following examinations of and comparison with F. novaezelandiae and the southern Australian F. veitchi , the latter is herein placed in its own new genus Kendrickiana .
Individuals of both F. novaezelandiae and K. veitchi are essentially amyarian in terms of adductor and pedal retractor muscles, but in the latter species the connection to the adventitious tube is located dorsally by an unique horseshoe-shaped array of muscular papillae, which are inserted into holes in the tube. K. veitchi is different from other clavagelloids too in that the siphons are capable of only limited retraction into the tube. Their extension in K. veitchi is almost exclusively by hydraulic means because the complex internal siphonal muscles seen in other species of the Clavagelloidea, and which act antagonistically with extensive blood-filled haemocoels, are vestigial. Kendrickiana can also be separated from Foegia in other anatomical respects. For example, members of the former have paired anterior suspensory muscles, and vestigial posterior pedal retractor muscles with pericardial proprioreceptors associated with them (as in Humphreyia and Dianadema ), whereas the latter does not. Similarly, in Foegia there is a muscularized pedal disc, not found in Kendrickiana . Members of F. novaezelandiae are inhabitants of intertidal hypoxic muds, whereas those of K. veitchi apparently live exclusively in subtidal sea grass beds.     

A cadaver unearthed: the anatomy of the Japanese living fossil Stirpulina ramosa (Bivalvia: Anomalodesmata: Clavagellidae) – the unique specimen in the collections of Emperor Shōwa

The only extant, preserved and complete specimen of Stirpulina ramosa has been discovered in the collections of the late Emperor Shōwa (Hirohito) and is described herein. Hitherto, only shells and the adventitious tubes of this species have been described. This study of the anatomy complements previous ones and adds further information as to how the adventitious tube is formed: that is, by the laying down of an organic, periostracum‐like, template that is then biomineralized internally to form the tube and is externally plastered with the clasts that constitute the enclosing burrow wall. Such secretions are produced by pallial lobes that unite on the right side to create the characteristic sutured pleat in this region of the tube. The periostracum enclosing the so‐interred animal is then secreted against the internal template of the tube. The shell of S. ramosa and, as a consequence, the musculature, is greatly disfigured as a result of the incorporation of the left valve into the fabric of the adventitious tube. This valve can, however, continue to grow within the tube, especially posteriorly. The right valve remains free inside the tube but grows only a little more anteriorly. The anterior mantle, with a minute pedal gape, is greatly thickened and secretes the watering pot component of the tube. In many anatomical respects, for example simultaneous hermaphroditism, S. ramosa still reflects the basic anomalodesmatan plan and such modifications as there are from the clavagellid form relate principally to the structure, formation and thus functioning of the adventitious tube. This study of S. ramosa has allowed the full spectrum of clavagellid adaptive radiation to be analysed and an evolutionary picture created which suggests that species of Clavagella/Dacosta and Stirpulina are Mesozoic (Late Cretaceous) remnants. Conversely, species of Bryopa and Dianadema are more modern, Late Oligocene and Palaeocene (Cenozoic), respectively, and possibly evolved in association with the emergence of the Indo‐West Pacific centre of coral diversity, with a postulated average age of just 30 Myr. © 2013 The Linnean Society of London     

Large-Scale Trade in Legally Protected Marine Mollusc Shells from Java and Bali,Indonesia

Background

Tropical marine molluscs are traded globally. Larger species with slow life histories are under threat from over-exploitation. We report on the trade in protected marine mollusc shells in and from Java and Bali, Indonesia. Since 1987 twelve species of marine molluscs are protected under Indonesian law to shield them from overexploitation. Despite this protection they are traded openly in large volumes.

Methodology/Principal Findings

We collected data on species composition, origins, volumes and prices at two large open markets (2013), collected data from wholesale traders (2013), and compiled seizure data by the Indonesian authorities (2008–2013). All twelve protected species were observed in trade. Smaller species were traded for <USD1.00 whereas prices of larger species were USD15.00–40.00 with clear price-size relationships. Some shells were collected locally in Java and Bali, but the trade involves networks stretching hundreds of kilometres throughout Indonesia. Wholesale traders offer protected marine mollusc shells for the export market by the container or by the metric ton. Data from 20 confiscated shipments show an on-going trade in these molluscs. Over 42,000 shells were seized over a 5-year period, with a retail value of USD700,000 within Indonesia; horned helmet (Cassis cornuta) (>32,000 shells valued at USD500,000), chambered nautilus (Nautilus pompilius) (>3,000 shells, USD60,000) and giant clams (Tridacna spp.) (>2,000 shells, USD45,000) were traded in largest volumes. Two-thirds of this trade was destined for international markets, including in the USA and Asia-Pacific region.

Conclusions/Significance

We demonstrated that the trade in protected marine mollusc shells in Indonesia is not controlled nor monitored, that it involves large volumes, and that networks of shell collectors, traders, middlemen and exporters span the globe. This impedes protection of these species on the ground and calls into question the effectiveness of protected species management in Indonesia; solutions are unlikely to be found only in Indonesia and must involve the cooperation of importing countries.     

Occurrence of adventitious sprouting in short-lived monocarpic herbs: a field study of 22 weedy species

Background and Aims

Adventitious sprouting from the hypocotyle and roots in monocarpic herbs has been confirmed in previous experimental studies as a means to avoid bud limitation after severe injury in annual and biennial plants. Data regarding the role of adventitious sprouting in natural populations, however, were lacking. The aim of the present study was to assess whether adventitious sprouting occurs in natural populations and how it is affected by plant size, plant injury, plant cover and environmental characteristics.

Methods

Data were sampled from 14 037 individual plants from 389 populations belonging to 22 annual and biennial species. Growth parameters were measured in individual plants, species composition and plant cover in communities were evaluated, and environmental characteristics were estimated using Ellenberg indicator values.

Key Results

It was confirmed that adventitious sprouting occurs in natural populations of all but five species examined. Adventitious sprouting was positively affected by plant size and plant injury. Environmental factors including availability of soil nitrogen were not shown to affect adventitious sprouting. Annual and biennial plants did not differ in sprouting, but upright annuals had a lower number of and longer adventitious shoots than prostrate annuals.

Conclusions

Adventitious bud formation is used to overcome meristem limitation when stem parts are lost due to injury, and thus resprouting in short-lived monocarps should not be overlooked.     

Character displacement, frequency-dependent selection, and divergence of shell colour in land snails Mandarina (Pulmonata)

Endemic land snails of the genus Mandarina of the oceanic Bonin Islands offer an exceptional example of habitat and character divergence among closely related species. In this study, microhabitat differences between sympatric ground-dwelling species were studied by distinguishing habitats on the basis of vegetation and types of litter. In all sites where two ground species coexisted, segregation occurred with each species showing preference for the microhabitat in which they were found. When they were in sympatry, one species was predominant in relatively wet and sheltered sites and the other in relatively dry and exposed sites. Although most species can live in both types of habitat, occupation by one species is inhibited by occupation by another. This suggests that competitive interaction between sympatric species caused segregation. Except for populations that have undergone interspecific hybridization, no examples were found of sympatric populations of two ground species sharing a similar shell colour. Species that were predominant in relatively wet and sheltered sites possessed shells with dark coloration and their colour patterns were mostly of one type. Species that were predominant in relatively dry and exposed sites possessed shells with bright coloration and their color patterns were polymorphic. Most populations from areas in which single species were distributed had shells with medium coloration. Microhabitat differentiation between sympatric species possibly caused diversification of shell colour, because bright shells are advantageous in sites where snails are largely exposed, and dark shells are advantageous in sites in where they are mostly sheltered from sunlight. In addition, frequency-dependent selection by predators hunting by sight may have operated to maintain colour polymorphism in the populations which are restricted to exposed habitats by competition with other sympatric species. This reveals the importance of interaction among closely related species as a cause of diversification in ecological and morphological traits.     

Use of molluscs,fish, and other marine taxa by tourism in Zanzibar,Tanzania

The collection of shells is a popular tourist activity in coastal areas of tropical countries. Tourists also buy shells, particularly large gastropods, which may be important species in marine ecosystems. While some, though outdated, information exists on the magnitude of the international trade with ornamental shells, virtually nothing is known about the extent of the regional tourist-related curio trade. A survey in Zanzibar, Tanzania, showed that 39% of the tourists had collected shells and 7% had bought shells, contributing US$ 136,000 to the local economy. The weight of shells exported from Zanzibar by tourists may have been in the order of 13t. Regarding other marine species, tourists consume only 1% of the fish catches, but they have substantially increased the consumption of crustaceans and the trade in shark teeth and jaws.     

Ethylene Controls Adventitious Root Initiation Sites in <Emphasis Type="Italic">Arabidopsis</Emphasis> Hypocotyls Independently of Strigolactones

Adventitious root formation is essential for cutting propagation of diverse species; however, until recently little was known about its regulation. Strigolactones and ethylene have both been shown to inhibit adventitious roots and it has been suggested that ethylene interacts with strigolactones in root hair elongation. We have investigated the interaction between strigolactones and ethylene in regulating adventitious root formation in intact seedlings of Arabidopsis thaliana. We used strigolactone mutants together with 1-aminocyclopropane-1-carboxylic acid (ACC) (ethylene precursor) treatments and ethylene mutants together with GR24 (strigolactone agonist) treatments. Importantly, we conducted a detailed mapping of adventitious root initiation along the hypocotyl and measured ethylene production in strigolactone mutants. ACC treatments resulted in a slight increase in adventitious root formation at low doses and a decrease at higher doses, in both wild-type and strigolactone mutants. Furthermore, the distribution of adventitious roots dramatically changed to the top third of the hypocotyl in a dose-dependent manner with ACC treatments in both wild-type and strigolactone mutants. The ethylene mutants all responded to treatments with GR24. Wild type and max4 (strigolactone-deficient mutant) produced the same amount of ethylene, while emanation from max2 (strigolactone-insensitive mutant) was lower. We conclude that strigolactones and ethylene act largely independently in regulating adventitious root formation with ethylene controlling the distribution of root initiation sites. This role for ethylene may have implications for flood response because both ethylene and adventitious root development are crucial for flood tolerance.     

Developmental anatomy of seedlings of Indodalzellia gracilis (Podostemaceae)

In Tristichoideae, aquatic angiosperms in the family Podostemaceae, Terniopsis, Tristicha, Indotristicha and Cussetia have creeping roots with flanking (sub)cylindrical shoots, while Dalzellia is rootless and has crustose shoots. Indodalzellia gracilis, sister to a clade of Dalzellia zeylanica and Indotristicha ramosissima, has subcrustose shoots on the side of creeping roots, suggesting that I. gracilis may be a key species to reveal how saltational evolution of the body plan occurred in these three species. We investigated developmental morphology of I. gracilis seedlings grown in culture, using scanning electron microscopy and semi‐thin serial sections. As in D. zeylanica, the plumular apical meristem in the seedling gives rise to two shoot apical meristems, which develop into horizontal subcrustose shoots with dorsal and marginal leaves. Neither radicle nor adventitious root is produced from the hypocotyl, but an adventitious root arises endogenously from the juvenile shoot and from some shoots of adult plants. These results, together with the phylogenetic relationships, suggest that the Indodalzellia seedling evolved by loss of the adventitious root derived from the hypocotyl, appearance of shoots in the axil of cotyledons, and appearance of adventitious roots from adventitious shoots. The difference in place of origin of the root between Indodalzellia and I. ramosissima suggests differing evolutionary origin of the root in Tristichoideae.     

SHELL MICROSTRUCTURE OF GASTROPODS FROM LAKE TANGANYIKA,AFRICA: ADAPTATION,CONVERGENT EVOLUTION,AND ESCALATION

Gastropod shells from Lake Tanganyika, with their heavy calcification, coarse noded ribbing, spines, apertural lip thickening and repair scars, resemble marine shells more closely than they resemble other lacustrine shells. This convergence between Tanganyikan and marine gastropod shells, however, is not just superficial. Scanning electron microscope (SEM) studies reveal that the Tanganyikan shells are primarily layers of crossed-lamellar crystal architecture (that is, needle-like aragonite crystals arranged into laths that are packed into sheets such that the aragonite needles of adjacent laths are never parallel). The number of crossed-lamellar layers can vary from one to four between different Tanganyikan gastropod species. In species with two or more crossed-lamellar layers, the orientation of the lamellae is offset by approximately 90° between the different layers. The number of crossed-lamellar layers in the shell wall is positively correlated with shell strength and with predation resistance. Three and four crossed-lamellar layers in the shell wall evolved several times independently within the endemic thiarid gastropod radiation in Lake Tanganyika. Repeated origins of three and four crossed-lamellar layers suggest that they may be specific adaptations by Tanganyikan gastropods to strengthen their shells as a defense against shell-crushing predators.     

Focus Issue on Roots: Branching Out in Roots: Uncovering Form,Function, and Regulation

Root branching is critical for plants to secure anchorage and ensure the supply of water, minerals, and nutrients. To date, research on root branching has focused on lateral root development in young seedlings. However, many other programs of postembryonic root organogenesis exist in angiosperms. In cereal crops, the majority of the mature root system is composed of several classes of adventitious roots that include crown roots and brace roots. In this Update, we initially describe the diversity of postembryonic root forms. Next, we review recent advances in our understanding of the genes, signals, and mechanisms regulating lateral root and adventitious root branching in the plant models Arabidopsis (Arabidopsis thaliana), maize (Zea mays), and rice (Oryza sativa). While many common signals, regulatory components, and mechanisms have been identified that control the initiation, morphogenesis, and emergence of new lateral and adventitious root organs, much more remains to be done. We conclude by discussing the challenges and opportunities facing root branching research.Branching through lateral and adventitious root formation represents an important element of the adaptability of the root system to its environment. Both are regulated by nutrient and hormonal signals (Bellini et al., 2014; Giehl and von Wirén, 2014), which act locally to induce or inhibit root branching. The net effect of these adaptive responses is to increase the surface area of the plant root system in the most important region of the soil matrix for resource capture (e.g. surface layers for phosphorus uptake and deeper layers for nitrate uptake) or to secure anchorage. Different species use different combinations of lateral or adventitious roots to achieve this, with lateral roots dominating the root system of eudicots while adventitious (crown and brace) roots dominate the root system of monocots, including in cereal crops.Our understanding of the mechanisms controlling lateral and adventitious root development has accelerated in recent years, primarily through research on model plants. The simple anatomy and the wealth of genetic resources in Arabidopsis (Arabidopsis thaliana) have greatly aided embryonic and postembryonic root developmental studies (De Smet et al., 2007; Péret et al., 2009a; Fig. 1, A and E). Nevertheless, impressive recent progress has been made studying root branching in other crop species, notably cereals such as maize (Zea mays) and rice (Oryza sativa).Open in a separate windowFigure 1.A to D, Schematics showing diversity in root system architecture at both seedling (left) and mature (right) stages in eudicots (A and C) and monocots (B and D). A, Arabidopsis root system. B, Maize root system. C, Tomato root system (for clarity, stem-derived adventitious roots are only shown in the labeled region). D, Wheat root system. E and F, Cross sections of emerging lateral root primordia in Arabidopsis (E) and rice (F). E and F are adapted from Péret et al. (2009b).In this Update, we initially describe the diversity of postembryonic root forms in eudicots and monocots (Fig. 1). Next, we highlight recent advances in our understanding of the genes, signals, and mechanisms regulating lateral root and adventitious root branching in Arabidopsis, rice, and maize. Due to space limits, we cannot provide an exhaustive review of this subject area, focusing instead on recent research advances. However, we direct readers to several recent in-depth reviews on lateral root (Lavenus et al., 2013; Orman-Ligeza et al., 2013) and adventitious root development (Bellini et al., 2014).     

The shapes of neutral gene genealogies in two species: probabilities of monophyly,paraphyly, and polyphyly in a coalescent model

Abstract.— The genealogies of samples of orthologous regions from multiple species can be classified by their shapes. Using a neutral coalescent model of two species, I give exact probabilities of each of four possible genealogical shapes: reciprocal monophyly, two types of paraphyly, and polyphyly. After the divergence that forms two species, each of which has population size N , polyphyly is the most likely genealogical shape for the lineages of the two species. At ∼ 1.300 N generations after divergence, paraphyly becomes most likely, and reciprocal monophyly becomes most likely at ∼1.665 N generations. For a given species, the time at which 99% of its loci acquire monophyletic genealogies is ∼5.298 N generations, assuming all loci in its sister species are monophyletic. The probability that all lineages of two species are reciprocally monophyletic given that a sample from the two species has a reciprocally monophyletic genealogy increases rapidly with sample size, as does the probability that the most recent common ancestor (MRCA) for a sample is also the MRCA for all lineages from the two species. The results have potential applications for the testing of evolutionary hypotheses.     

Speciation within blidingia minima (chlorophyta) in japan: evidence from morphology, ontogeny, and analyses of nuclear rdna its sequence

The genus Blidingia is a common, sometimes abundant, component of northern hemisphere temperate and subarctic shores. Species determination relies on characteristic differences in morphology and early ontogenic development. Within the species Blidingia minima (Naegeli ex Kuetzing) Kylin in Japan, however, there appear to be three distinct types, the F-, D-, and M-types, which are differentiated in early ontogeny. The M-type can be further categorized into three subtypes. Results of intensive field and culture studies supported the view that morphological characteristics do not reliably separate the F-, D-, and M-types and that all three may potentially cross breed. The F-type has characteristics in early ontogeny of the species B. chadefaudii (  J. Feldmann) Bliding in European waters and this, combined with the morphological and cross breeding studies, suggest that B. chadefaudii should be merged with B. minima. In this study, molecular analyses of nuclear rDNA from samples of the F- and D-types indicated that both have a distinctive and characteristic identity. Sequence data also examined from two of the M-type subtypes indicated that each of these also has a characteristic molecular identity clearly distinguished from that of the F- and D-types. Analyses indicated that there is a close relationship between the D-type and one of the M-type subtypes, and that these are more closely related to the F-type than to the other M-type examined. Comparison with studies of this gene region in other ulvophytic algae indicated a wide range of variation within B. minima. Such variation may be useful in assessing distribution patterns in Japanese waters of the developmental types within this species.     

Bioerosion of shells by terrestrial gastropods

Empty shells of terrestrial gastropods remain intact and become fossilized only under particular conditions. The usually thin shells are readily dissolved by rainwater, a process starting often during life. Results indicate that with this chemical weathering they may lose some 1% in weight per month. But this is not the only process by which shell biominerals disappear. During field experiments, living terrestrial gastropods have been observed to actively remove calcareous material from empty shells apparently to use for building their own shell. Empty shells lost ∼30% of their weight in 2 months, indicating this process to be much more important than simple dissolution, and explaining the rapid disappearance of empty shells in the field. Previously, mainly anecdotal mention has been made of this shell scraping. Bones of birds were not scraped by terrestrial gastropods; they lost ∼1% in weight per month at the start due to chemical weathering alone, but weight loss decreased with time and was only 6.5% after 16 months.     

Blidingia minima var. stolonifera var. nov. (Ulvales, Chlorophyta) from British Columbia: systematics, life history and morphogenesis

Blidingia minima var. stolonifera var. nov. is described from Vancouver, British Columbia. In previous literature this variety may have been confused with B. chadefaudii and B. minima var. minima. The new variety is part of the B. minima species complex in which spores germinate by evacuating the original spore and forming a germ tube. B. minima var. stolonifera is characterized by the development of marginal filaments on the basal disc that have one to five colourless cells and terminate in a cell from which a new disc grows. Colourless cells are devoid of chloroplasts and nuclei, and contain only small remnants of cytoplasm. The runner system is considered a mechanism of vegetative growth and propagation that enables a disc to cover a large amount of substratum before producing erect, unbranched thalli. In field and in culture, B. minima var. stolonifera typically reproduces by means of quadriflagellate zoospores; however, three plants from Vancouver formed biflagellate spores. These germinated poorly and developed into highly irregular, branched thalli.     

Evaluation of the age of the red whelk Neptunea antiqua using statoliths, opercula and element ratios in the shell

Growth rings present in whole and sectioned statoliths were used to determine the age of red whelks Neptunea antiqua, from the North Sea. Validation of the periodicity of the rings was established in four whelks by comparing the number of statolith rings with the number of seasonal Mg:Ca ratio cycles present in shell calcium carbonate samples drilled sequentially from along the growth axis. There was exact correspondence between the number of growth rings and the number of element ratio cycles in two of the shells and a 1-year difference in the estimated age between the two methods in the other two shells, evidence which is strongly indicative of an annual periodicity of deposition to the statolith rings. The estimated age of the whelks using the statolith rings varied between 4 years (shell length 102 mm) and 17 years (shell length 148 mm). The age of the whelks ascertained from the statoliths was compared with age estimates from the number of adventitious layers in sectioned opercula. The number of adventitious layers in whelks from 51 to 148 mm shell length ranged between 1 and 12 years. No significant difference was observed between the number of strongly defined statolith rings and number of opercula adventitious layers.     

Phosphorylation and Palmitoylation of the Human D2L Dopamine Receptor in Sf9 Cells

Abstract: We have expressed and biochemically characterized the human D2_long (D2_L) dopamine receptor isoform using the baculovirus/Sf9 cell system. The expressed receptor bound ligands with a pharmacological profile similar to that reported for neuronal and cloned D2_L receptors expressed in mammalian cell lines. Dopamine binding to D2_L receptor was sensitive to guanine nucleotides, indicating receptor coupling to endogenous G proteins. A D2_L receptor-specific antibody identified two major protein species at ∼44 kDa and at ∼93 kDa in immunoblots, suggesting the presence of D2_L receptor monomers and dimers. Both species were purified by immunoprecipitation from digitonin-solubilized preparation of cells expressing D2_L receptor prelabeled with ³²P_i or [³H]-palmitate. These results constitute the first direct evidence for D2_L receptor phosphorylation and palmitoylation.     

Adventitious sprouting enables the invasive annual herb Euphorbia geniculata to regenerate after severe injury

Euphorbia geniculata, an annual weed of arable land native to America and invasive in subtropical and tropical regions, is able to regenerate from seeds and is also able to produce adventitious buds on the hypocotyl. Whether sprouting from adventitious buds represents a mechanism for surviving severe injury, and whether this ability is crucial for species invasion is, however, not known. The significance of such sprouting was investigated with a field survey and a pot experiment. Among 897 plants in 25 field populations surveyed in Indonesia, only a few exhibited marks of injury and sprouting from adventitious buds. When seeds were collected from 12 of the populations and used in a pot experiment, however, the seedlings were able to survive severe injury (removal of all tissue above the hypocotyl) by sprouting from adventitious buds on the hypocotyl and were able to set seed, although they produced less vegetative and generative (flowers and fruits) biomass than control plants. Growth but not fitness of plants in the pot experiment was population specific but neither growth characteristic correlated with disturbance level assessed in the field. Although the pot experiment indicates that E. geniculata can cope with severe injury by adventitious sprouting from the hypocotyl, the survey data are inconsistent with the hypothesis that such adventitious sprouting is important for the plant??s invasion in tropical regions.