The functional significance of aperture form in gastropods

Aperture form of marine prosobranch gastropods has evolved under the influence of a number of different selective forces, including: generation of shell form; protection from predation; accommodation of the foot during clamping behavior: and accommodation of water currents in and out of the mantle cavity. Aperture form correlates positively with foot shape in most gastropods and foot shape, in turn, correlates moderately well with substrate preference. Almost all gastropods that have non-round apertures elongate the aperture parallel to the foot so that water currenth tend to flow anteriorly to posteriorly. Fresh-water pulmonates have responded to somewhat different stresses. They exhibit clamping behavior and thus show correspondence between foot shape and aperture shape. They show less apertural strengthening as crab (or crayfish) predation is less of a factor and presumably because calcium carbonate is less available. They also lack anterior-posterior apertural elongation due to the absence of water currents through their mantle cavity. Due to the absence of mantle cavity water currents and clamping behavior, terrestrial gastropods do not show the apertural modifications associated with these two factors. In addition. few adaptations of apertural form are present to resist predation. Instead, many of the apertural modifications of terrestrial pulmonates seem to be concer-ned with the problems of water loss during estivation.     

Adaptive design of locomotion and foot form in prosobranch gastropods

A comparison of the locomotor types, speed, tenacity, and foot form of nearly 300 species in 52 families of marine prosobranchs has revealed that foot size and shape and even subtle variations of locomotion affect the speed and strength of adhesion to the substratum.Gastropods inhabiting soft substrata move primarily by pedal cilia or by discontinuous locomotion in which shell and foot move alternately. Both types of movement are accompanied by low tenacity. A specialized type of discontinuous locomotion, namely, leaping, surpasses all other methods of movement in speed. Species with ciliary locomotion have a very large foot while those with discontinuous movement have an exceedingly small foot relative to shell size.The majority of prosobranchs inhabit hard substrata, move by continuous pedal muscular gliding, and have moderately high tenacity during movement. Arhythmic pedal locomotion yields lower maximum speeds and tenacities than do rhythmic pedal waves. Foot size and shape relative to shell length in species with arhythmic locomotion vary from very short and broad to long and narrow. Studies of transects at several temperate and tropical marine littoral stations showed that these species are confined to low littoral or sublittoral habitats that are sheltered from heavy wave action. High speed and tenacity are simultaneously attained only by species with rhythmic pedal waves.Speed and tenacity do not represent competing selective pressures on the size and shape of the foot. Speed increases among species as the foot approaches or exceeds shell length and is highest if the foot is also broad; the greatest tenacities are attained by species with a long, broad foot whose dimensions do not exceed that of the shell. The optimal shape for both high tenacity and speed is a broad foot somewhat shorter than the shell; neither speed nor tenacity are much compromised by this form. In general, only species with rhythmic pedal waves whose foot size and shape approximate the optimal form for high tenacity and speed are found in habitats exposed to much wave action. Long rhythmic waves, moving a large proportion of foot area at once, are in theory energetically more economical than small, very rapid waves resulting in the same overall speed, but experiments showed that tenacity is significantly reduced in gastropods which increase speed by enlarging the waves. The optimal wave pattern of a species should be a balance between the demand for speed with the least expenditure of energy, favored by a pattern of many large waves at once, and the demand for tenacity, favored by a pattern of few and small waves.Retrograde ditaxic waves of elongation are the most common pattern encountered among prosobranchs, and are associated with a large range of foot sizes and shapes. Such waves are at least one third as long as the foot, while direct waves and other waves of compression are frequently much smaller. The range of foot forms of species with waves of compression is restricted, tending to be optimal for high tenacity or to be long and narrow. Waves of compression appear to be a specialization with the potential for maintaining high tenacity even at high speeds since the waves can be very small, and for giving superior speed since they can travel very rapidly.     

Mechanical properties of mallard humeral bone in dependence on the form

The mechanical behaviour of bony material taken from humeral bone of the mallard duck was analysed. Wing-clipping led to a change in the values and distribution of the dynamic shear modulus and damping. The distribution of the values of the modulus shows a specific pattern in which the highest values are found ventrally. This pattern changes when there is a disturbance of the functional forces acting upon the humerus -- in this study induced by wing-clipping. The hypothesis is put forward that in birds the bone with its specific shape will resist any change in this shape. For a specific shape required for other functions than simply resisting load, it is functionally advantageous to respond to a change in required forces by adapting the pattern of moduli. An adaptation according Wolff's law will only occur in extreme cases, but an alteration of the bone shape will be avoided.     

Cardioactive neuropeptides in gastropods

At least five neuropeptides that are active on an isolated snail heart can be recovered from extracts of gastropod nervous tissue. These peptides have been divided into three classes. The class of the lowest molecular weight, termed the small cardioactive peptides (SCPs), is made up of two peptides. SCPs have been found in all gastropods studied and appear to be involved in the control of the gut. They have been localized by microdissection and bioassay to several identified central neurons that send their axons out to innervate the gut. These neurons act centrally to enhance the motor output of the ganglia responsible for the control of feeding, and peripherally to modulate gut activity. In one pair of these neurons, the classical transmitter acetylcholine coexists with an SCP. The next larger peptide class (medium cardioactive peptide), found only in Aplysia, shares both its mode of cardiac activity and tissue distribution with the SCPs. As yet, there is no evidence that either of these peptide classes acts as a physiological modulator of cardiac activity. The class of the highest molecular weight (large cardioactive peptide [LCPs]) is made up of two peptides and is found only in Helix. The LCPs are circulating neurohormones involved in the regulation of heart, gut, and neuromuscular activity. Their primary release site is a neurohemal region in the auricle. The significance of these findings is discussed in light of recent advances in the study of mammalian neuropeptides.     

Mechanical signalling,calcium and plant form

Calcium is a dynamic signalling molecule which acts to transduce numerous signals in plant tissues. The basis of calcium signalling is outlined and the necessity for measuring and imaging of calcium indicated. Using plants genetically transformed with a cDNA for the calcium-sensitive luminescent protein, aequorin, we have shown touch and wind signals to immediately increase cytosol calcium. Touch and wind signal plant cells mechanically, through tension and compression of appropiate cells. Many plant tissues and cells are very sensitive to mechanical stimulation and the obvious examples of climbing plants, insectivorous species as well as other less well-known examples are described. Touch sensing in these plants may be a simple evolutionary modification of sensitive mechanosensing system present in every plant. The possibility that gravitropism may be a specific adaptation of touch sensing is discussed. There is a growing appreciation that plant form may have a mechanical basis. A simple mechanical mechanism specifying spherical, cylindrical and flat-bladed structures is suggested. The limited morphological variety of plant tissues may also reflect mechanical specification. The article concludes with a discussion of the mechanisms of mechanical sensing, identifying integrin-like molecules as one important component, and considers the specific role of calcium.     

Mechanical constraints canalizing the evolutionary transformation of tetrapod limbs

A reconstruction of the anagenetic transformations from fins to tetrapod limbs is represented considering the self-evident mechanical constraints which must have limited the construction and thus the function and the transformation.     

Sialic acids in gastropods.

The occurrence of N-acetylneuraminic acid and N-glycolylneuraminic acid residues in preparations of the slug Arion lusitanicus (Gastropoda) was determined by sodium dodecyl sulphate electrophoresis of the proteins followed by lectin blots stained with the sialic acid specific lectin from Maackia amurensis, by the sensitivity of this binding to sialidase from Clostridium perfringens, by specific fluorescent labelling of sialic acids with 1,2-diamino-4,5-methylenedioxybenzene, by the determination of the sensitivity to sialate-pyruvate-lyase, by co-migration with standards on high performance anion exchange chromatography with pulsed amperometric detection and by identification of the typical masses in the fragmentation patterns of the trimethylsilyl derivatives after gas chromatography. It is the first time sialic acids are identified in gastropods.     

Finding the way in phenotypic space: the origin and maintenance of constraints on organismal form

BACKGROUND: One of the all-time questions in evolutionary biology regards the evolution of organismal shapes, and in particular why certain forms appear repeatedly in the history of life, others only seldom and still others not at all. Recent research in this field has deployed the conceptual framework of constraints and natural selection as measured by quantitative genetic methods. SCOPE: In this paper I argue that quantitative genetics can by necessity only provide us with useful statistical summaries that may lead researchers to formulate testable causal hypotheses, but that any inferential attempt beyond this is unreasonable. Instead, I suggest that thinking in terms of coordinates in phenotypic spaces, and approaching the problem using a variety of empirical methods (seeking a consilience of evidence), is more likely to lead to solid inferences regarding the causal basis of the historical patterns that make up most of the data available on phenotypic evolution.     

Mechanical and spatial determinants of Paranthropus facial form

It is well documented in the anthropological literature that the distinctive morphology of the “robust” hominid facial skeleton reflects its dietary specialization. Rak (1983) has provided the most comprehensive evaluation of Paranthropus facial morphology and this important study concluded that bone strain generated during mastication was responsible for the scaling of measures of facial height and breadth. The present study evaluated Rak's analysis by examining the relationship between bizygomatic breadth and facial height in an ontogenetic series of Pan and Gorilla crania. Results of this analysis indicate that facial height and breadth dimensions were not mechanically scaled in the “robust” australopithecines. Structural analysis of African ape facial maturation was also used to examine alternative spatial methods of malar elongation in Paranthropus. It is concluded that the increased height of the malar region in these specimens is not related to either vertical expansion of the posterior facial skeleton or to expansion of the temporal fossa. Malar elongation is, however, consistent with a derived pattern of facial growth in crania possessing a thickened hard palate. © 1994 Wiley-Liss, Inc.     

The effect of wind on shore gastropods

A preliminary investigation into the effect of wind on shore gastropods has been undertaken. Moderate winds displace some Monodonta lineata (da Costa) from boulders on the shore and some individuals detach within six hours in weaker winds in the laboratory (5–10 km/h, 10°C, 94% humidity). Sheltered aspects of the rock are used to minimize the effects of the wind on shores, and maintenance movements on the shore are extensive.  

Summary:

In calm conditions and in light winds Monodonta lineata is more widely dispersed about the rocks than in moderate winds when the animals are either sheltering in cracks or displaced.
Providing the rock surface is damp then animals continue to move about during emersion in light winds. On a small boulder beach animals moved as much as 4 m upshore during one tidal cycle. Only slight reorientation movements were recorded during moderate winds.
Animals withstand a windspeed of 4 km/h for six hours in a wind tunnel in a humidity of 94% at 10°C, but are displaced within an hour by 10 km/h winds in similar conditions.     

Non-indigenous land and freshwater gastropods in Israel

Few comprehensive works have investigated non-indigenous snails and slugs as a group. We compiled a database of non-indigenous gastropods in Israel to explore how they arrived and spread, characteristics of their introduction, and their biological traits. Fifty-two species of introduced gastropods are known from Israel (of which nine species subsequently went extinct): 19 species of freshwater snails and 33 species of terrestrial gastropods. The majority of these species are found only in human-dominated habitats. Most of those found in natural habitats are aquatic species. Most snails are introduced unintentionally from various parts of the Holoarctic region, reaching Israel as stowaways with horticultural imports and the aquarium trade, but some are brought intentionally to be used as pets or for food. Because the study of this group in Israel is very limited, information regarding their distribution in the country and their effects on other species is incomplete. Though only nine species of non-indigenous snails have been found to date in natural habitats, some of these are very abundant. More information and research is required to enable effective management schemes.     

Burrowing mechanisms and sculptures in Recent gastropods

Savazzi, Enrico 1989 01 15: Burrowing mechanisms and sculptures in Recent gastropods. Lethaia , Vol. 22, pp. 31–48. Oslo. ISSN 0024–1164.
Burrowing was observed in 32 gastropod species, belonging to 8 families, from Italy and the Philippines. Most species burrow by repeating a three-phase sequence: (1) digging with the foot, (2) dragging the shell forward and downward, and (3) rocking the shell around its longitudinal axis. Minor specific differences in the burrowing dynamics are common, and totally different mechanisms also occur. Burrowing sculptures consisting of terraces or asymmetrical tubercles are observed in the majority of the studied species. Characteristics of the burrowing process explain some cases of apparent divergence of burrowing sculptures from the paradigm. Burrowing sculptures in the Gastropoda should be expected to occur mostly among medium-slender, rather than markedly high-spired, shell morphologies. □ Mollusca, Gastropoda, Cerithiidae, Nassariidae, Mitridae, Costellariidae, Conidae, Terebridae, Turridae, Hydro-biidae, shell, sculpture, burrowing, functional morphology, ecology, behaviour, Holocene, Indo-Pacific. Philippines, Mediterranean, Italy .     

Eulimid gastropods parasitic on echinoderms in the New Zealand region

Abstract

Eulimindae (Prosobranchia) of the New Zealand region that parasitise echinoderms are recorded and discussed. Fuscapex ophioacanthicola n.gen. & sp. is parasitic on Ophioacantha sp., Ophieulima fuscoapicata n.sp. is a parasite of Ophioactis profundi Lütken & Mortensen, Punctifera ophiomoefrae n.gen. & sp. lives partly buried among the radial shields of Ophiomoeris projecta Matsumato, and Stilapex sp. is recorded, but not described, from Ophiothrix oliveri Benham (all hosts ophiuroids). Stilifer sp. lives in galls in an undescribed oreasterid (Asteroidea). Annulobalcis marshalli n.sp. is described from Crotalometra rustica (A. H. Clark) (Crinoidea). Eulima infrapatula Murdoch & Suter is transferred to Sabinella Monterosato and recorded from Ogmocidaris benhami Mortensen; Fusceulima goodingi n.sp. is described from Centrostephanus rodgersi (A. Agassiz) (both hosts echinoids). Two earlier records of sea urchin parasites from New Zealand are discussed, and the species are referred to Pelseneeria.     

性畸变对腹足类生殖和种群的影响

具有内分泌干扰效应的三丁基锡能引起腹足类产生性畸变现象。在性畸变过程中 ,雌性个体会由于生殖孔口被前列腺取代或被输精管阻塞、贮精囊或卵囊腺开裂、卵囊腺内部被阻塞以及卵巢转化为精巢等多种原因而丧失生殖能力 ,甚至死亡。并由此引起雌、雄性比和幼、成年个体比的降低 ,导致种群衰退。有浮游幼体的种类可以通过外来种群的成功迁入使种群得以维持 ,而无浮游幼体的种类 ,由于幼体迁移能力差而最终导致种群的区域性灭绝。性畸变这种典型的功能效应对其他内分泌干扰物质的生态效应研究有启示作用。     

Coexistence patterns of benthic gastropods on the Uruguayan shelf

Community assembly rules theory attempt to understand the processes that determine the composition of local communities from a regional species pool. Nestedness and negative co‐occurrence are two of the most commonly reported meta‐community patterns, but almost exclusively from terrestrial and freshwater ecosystems. Here we analyzed the structure of species coexistence in six datasets containing presence/absence data for 120 marine benthic gastropod species in 249 sampling units on the Uruguayan continental shelf and Río de la Plata estuary. The ecological features of this system, such as the idiosyncratic nature of the biogeographic and oceanographic realms, are clearly different from those observed in other systems previously targeted by studies on coexistence structure. Community patterns were evaluated using null models and four structure indices. The existence of patterns in community assembly, and in particular segregated co‐occurrence, was verified only when analyzing the number of checkerboard units (CH index). This indicates more mutually exclusive species pairs than expected by chance. Nestedness, on the other hand, was not detected in any dataset. Storage and rescue effects related to overall high immigration and low local extinction rates are plausible mechanisms to account for the general pattern of random species coexistence, while the segregated co‐occurrence pattern depicted by the CH index may be related to differential habitat requirements within species pairs. Our study highlights the importance of analyzing metacommunity structures in alternative biological, environmental, and historical contexts in order to advance on the construction of a general ecological theory, relating patterns with the processes dominating in particular ecosystems.