GASTROPOD CHEMORECEPTION

(I). Gastropods use chemoreception for a wide variety of behaviours including feeding, homing, escape from predators and a variety of social and reproductive behaviours. Chemoreception is used to locate distant food sources, and to discriminate between potential foods. Responses to chemical food stimuli result from a combination of innate and experiential factors. Gastropods use chemical cues in mucus trails to home. They also home by direct olfactory orientation. Reproductive behaviour in a variety of gastropods appears to involve chemical cues. Evidence exists for pheromones controlling aggregation and mating. Numerous gastropods use chemical cues to avoid or escape from predators. (2). Amino acids appear as likely candidates for attractants and phagostimulants for gastropod feeding. Macromolecules are probably also involved. Amino acids have also been shown to stimulate reproductive behaviours in certain gastropods, thus suggesting a pheromonal function. However, the significance of this finding to the behaviour of the organisms in the field has yet to be evaluated. Saponins have been implicated as the active substances found in sea stars that elicit escape responses of marine gastropods. Choline esters may play a homologous role in gastropod—prey and gastropod-predator interactions. (3). Gastropods can apparently use a number of different methods to orient to olfactory cues. These include anemotaxis or rheotaxis, klinotaxis and tropotaxis. (4). The major chemosensory organs of gastropods have been identified. They include the anterior and posterior tentacles and lips of terrestrial pulmonates; the cephalic tentacles, the lips and buccal cavity lining, and possibly the osphradium of aquatic pulmonates; the cephalic and mantle tentacles, the anterior margin of the foot, the siphon tip, and the osphradium of prosobranchs; and the rhinophores, tentacles, oral veil and osphradium of opisthobranchs. (5). Many of the organs named above have been examined by both light and electron microscopy. The most common anatomical organization includes bipolar primary sensory cells with cell bodies located subepithelially, and a distal dendrite extending to the free surface. Often a peripheral ganglion is located deep to the sensory epithelium. It is unclear whether axons of the sensory cells project directly to the central ganglion or by way of interneurones located in the peripheral ganglia. (6). The dendritic specializations of the sensory cells vary considerably. Most bear cilia or a combination of cilia and microvilli. The functional significance of the variation in the types of sensory endings is unknown, although the chemosensory epithelia also respond to other sensory modalities, and it is often difficult to ascribe any one cell type to any one modality. Species-specific variations may also complicate the picture. (7). Prospects for and importance of future studies on gastropod chemoreception are discussed.     

生态位态势理论与扩充假说

生态位态势理论,即从个体到生物圈,无论是自然还是社会中的生物单元都具有生态和势两个方面的属性,态是指生物的状态,是过去生长发育,学习,社会经济发展以及与环境相互和积累的结果;势是指生物单元对环境的现实影响力或支配力,始能量和物质变换的速率,生产力,生物增长率,经济增长率,占据新生境的能力,生物单元态的变化一般呈“Ｓ”型曲线,而势的变化则呈“钟”型曲线,特定生态系统中某生物单元的生态位即是该生物单元     

ON THE TITRATION OF BACTERIOPHAGE AND THE PARTICULATE HYPOTHESIS

1. The theory of the serial dilution method of titration of bacterio-phage has been worked out on the basis of the simple particulate hypothesis. 2. It has been shown that, if the dilution constant is .1, only about 60 per cent of parallel runs on the same solution should give the same end-point, the average being taken over a great number of titrations of each of a great variety of solutions. 3. The discrepancy between this figure, 60 per cent, and Dr. Bronfenbrenner''s estimate, 85 per cent, is considerable. 4. Inasmuch as the particulate hypothesis is well founded, no explanation of the discrepancy is suggested.     

REPRODUCTIVE SYSTEM AND SPERMATOGENESIS IN THE OPISTHOBRANCH GASTROPOD RETUSA OBTUSA (MONTAGU)

The cephalaspidean opisthobranch Retusa obtusa has an ovotestissimultaneously producing eggs and spermatozoa. Reproductiveorgans are characterized by the hermaphrodite duct and seminalreceptacle together joining the pallial glandular duct whichis differentiated anteriorly to form the ‘albumen’gland, membrane or capsule gland, and mucus gland. The ductof a copulatory bursa joins the common central chamber of thiscomplex. Eggs presumably pass through extended tracts in the3 glands to emerge at a hermaphrodite aperture in the rightside of the mantle cavity. Spermatozoa also emerge at this apertureto a ciliated seminal groove along the right side of the headwhich, in turn, joins copulatory organs folded within the headand opening close behind the right cephalic tentacle: a muscularpenial sac receives 4 elements of prostate gland. Spermatophoreswere never seen. Oocytes, surrounded by several thin folliclecells, reach 150–330 µ, m diameter in larger wintersnails, mostly in the periphery of theovotestis. Spermatocytesand spermatids develop as clusters in association with accessory(Sertoli) cells. The acrosome appears in the centre of a denseanterior plaque, develops as a domed acrosome vesicle on a shortpeduncle and eventually becomes a terminal spike on the nucleustip. The Golgi complex is seen sometimes near the early acrosomebut more often behind the nucleus. Mitochondria aggregate firstahead of the nucleus but then form a mitochondrial derivative,with a glycogen helix, spiralled around the axoneme throughoutthe mid-piece of the tail. This region is marked off from theend-piece of the tail by the annulus. The nucleus becomes long,spiralled with a strong keel, and surrounds the centriolar derivativeat the base of the axoneme.     

COMPARATIVE LIFE-CYCLE, BIOMASS AND SECONDARY PRODUCTION OF THREE SYMPATRIC FRESHWATER GASTROPOD SPECIES

The life cycles, biomass and secondary production of three sympatricfreshwater basommatophoran snails, Lymnaea palustris (MÜller),Physa fontinalis Linnaeus and Anisus rotundatus (Poiret) werestudied during two years in a freshwater ditch. L. palustrisexhibited an iteroparous life-cycle whereas the two other speciespresented a semelparous life-cycle, adults died just after oviposition.L. palustris secondary production (dry weight) value was higher(P = 11 298.4 mg 0.1 m^–1 yr^–1) than those of P.fontinalis (P = 846.3 mg 0.1 m^–2 yr^–1) and A. rotundatus(P = 1192 mg 0.1 m^–2 yr^–1). (Received 16 March 1992; accepted 30 June 1992)     

INTRASPECIFIC VARIATION IN ANT SEX RATIOS AND THE TRIVERS-HARE HYPOTHESIS

We consider worker-controlled sex investments in eusocial Hymenoptera (ants in particular) and assume that relatedness asymmetry is variable among colonies and that workers are able to assess the relatedness asymmetry in their own colony. We predict that such “assessing” workers should maximize their inclusive fitness by specializing in the production of the sex to which they are relatively most related, i.e., colonies whose workers have a relatedness asymmetry below the population average should specialize in males, whereas colonies whose workers have a higher than average relatedness asymmetry should specialize in making females. Our argument yields the expectation that colony sex ratios will be bimodally distributed in ant populations where relatedness asymmetry is variable owing to multiple mating, worker reproduction, and/or polygyny. No such bimodality is expected, however, in ant species where relatedness asymmetry is known to be constant, or in cases where relatedness asymmetry is supposed to be irrelevant due to allospecific brood rearing under queen control, as in the slave-making ants. Comparative data on colony sex ratios in ants are reviewed to test the predictions. The data partly support our contentions, but are as yet insufficient to be considered as decisive evidence.     

ULTRASTRUCTURAL AND ECOLOGICAL ASPECTS OF THE DEVELOPMENT OF CHLOROPLAST RETENTION IN THE SACOGLOSSAN GASTROPOD ELYSIA TIMIDA

Elysia timida is a common and endemic inhabitant of shallowand very well lit waters in the Mediterranean. This sacoglossanslug retains functional symbiotic chloroplasts derived fromits algal food, Acetabularia acetabulum, although the chloroplastsare not transmitted in the spawn. After hatching and until day12, Elysia timida juveniles do not retain these chloroplastsin the digestive gland. However, newly hatched juveniles retainchloroplasts from Cladophora dalmatica. Development varies seasonallybetween direct (December to April) and lecithotrophic (October,November and May), and this variation may be an adaptation toseasonal calcification of the algal food Acetabularia acetabulum. (Received 12 February 1991; accepted 15 July 1992)     

INTEGRATING DEVELOPMENTAL EVOLUTIONARY PATTERNS AND MECHANISMS: A CASE STUDY USING THE GASTROPOD RADULA

Determining the connection between ontogeny and phylogeny continues to be a major theme in biology. However, few studies have combined dissection of pattern and process that lead to transformation of complex morphological structures. Here we examine the patterns and processes of shape change in a model system—the gastropod radula. This system is a simple one having only two processes: initial secretion and postsecretional movement of teeth. However, it produces a tremendous amount of shape variability and fusion patterns. To determine both pattern and mechanism of shape change in an evolutionary context, we use three complementary approaches and datasets. First, we use a phylogenetic hypothesis to determine the polarity of developmental events. Second, we perform a morphometric analysis of shape change using relative warp analysis that allows us to locate and compare the direction and magnitude of ontogenetic and phylogenetic shape divergence. These comparisons are the basis for testing hyptheses of heterochrony and heterotopy, and we show how our results do not conform to expectations of pure heterochrony. The rejection of heterochrony as a hypothesis is based on empirically demonstrating (1) initial shape differs in each taxon; (2) a single dimension of shape variability does not simultaneously describe ontogenetic and evolutionary shape changes; and (3) a significantly different shape and size covariance between taxa. This rejection is probably based on spatial changes in initial conditions and not spatial changes caused by the process itself. Finally, we construct a mechanistic model that explains how shape change happens based on the sequence of events during ontogeny. By using the parameters in the model as characters in the phylogenetic dataset, we show that different parts of the system have arisen at different times and become co-opted into the process. By integrating our analyses together we show that spatial process parameters can be responsible for our nonspatial patterns and that different ontogenetic processes can create similar end morphologies.