Effects of water temperature and substrate type on spore production and release in eastern Tubifex tubifex worms infected with Myxobolus cerebralis

Eastern Tubifex tubifex worms were exposed to Myxobolus cerebralis spores at 9, 13, 17, and 20 C in 1-L jars that contained sand, mud, or leaf litter as substrata. Beginning 60 days after exposure, water from each jar was filtered daily and examined for the presence of waterborne triactinomyxon spores (TAMs). On discovering a single TAM from an experimental jar, 48 T. tubifex worms from that jar were placed individually into 24-well plates. Spores released from individual infected T. tubifex worms were quantified to determine the first day of TAM release from infected worms, the infection rate, the total number of TAMs released per worm, and the duration of release. No TAMs were found in any of the jars incubated at 20 C or in uninfected, control worms at any temperature. The total number of TAMs released by infected worms in mud and sand was highest at 13 C compared with other temperatures. Infection rates among individual worms increased with temperature between 9 and 17 C. Higher temperatures (up to 17 C) induced earlier TAM releases among infected worms, and substratum did not influence this production parameter. The average duration of TAM release decreased as the temperature increased from 9 to 17 C, and there was a significant effect of substratum in the groups maintained at 13 and 17 C. In all temperature treatments between 9 and 17 C, the duration of release was least in the worms maintained in leaf litter, as was the total number of TAMs released during the experimental period and the median number of TAMs per production day.     

Secondary settlement of cockles Cerastoderma edule as a function of current velocity and substratum: a flume study with benthic juveniles

Some newly-settled bivalve molluscs can experience a second dispersal stage in the water column and colonize areas distant from initial settlement zone ('secondary settlement'). To document mechanisms involved in such a process, experiments were conducted in a recirculating 13-m flume, using juvenile cockles Cerastoderma edule (shell length between 0.8 and 5.7 mm). After 4 h and under current surface velocities of 10, 20 and 24 cm s^?1, all juveniles left the plexiglass substratum (site of initial introduction) and 42.4, 58.6 and 76.2% of juveniles, respectively, were retrieved from a downstream sand area (which only represented 7.7% of the total flume surface). Naked-eye observations showed that smaller individuals were borne within the water column, whereas larger individuals tended to roll or slip on the substratum. Byssus threads produced by the juveniles were often seen, sometimes covered in sand grains. These observations were confirmed by finding larger juveniles in the upstream part of the sand area. When sand was replaced by mud, a reduced proportion of cockles was retrieved in the experimental substratum (18.4, 20.0 and 16.4%, respectively). Observations showed that juveniles rarely succeeded in anchoring themselves in mud. When initially introduced on a favourable substratum (medium sand), more than 87% of juveniles were retrieved from that sand array at all flow velocities. This study shows that secondary settlement occurs for juvenile cockles up to 5.7 mm in shell length and depends not only on flow velocity but on substratum type.     

Meandering worms: mechanics of undulatory burrowing in muds

Recent work has shown that muddy sediments are elastic solids through which animals extend burrows by fracture, whereas non-cohesive granular sands fluidize around some burrowers. These different mechanical responses are reflected in the morphologies and behaviours of their respective inhabitants. However, Armandia brevis, a mud-burrowing opheliid polychaete, lacks an expansible anterior consistent with fracturing mud, and instead uses undulatory movements similar to those of sandfish lizards that fluidize desert sands. Here, we show that A. brevis neither fractures nor fluidizes sediments, but instead uses a third mechanism, plastically rearranging sediment grains to create a burrow. The curvature of the undulating body fits meander geometry used to describe rivers, and changes in curvature driven by muscle contraction are similar for swimming and burrowing worms, indicating that the same gait is used in both sediments and water. Large calculated friction forces for undulatory burrowers suggest that sediment mechanics affect undulatory and peristaltic burrowers differently; undulatory burrowing may be more effective for small worms that live in sediments not compacted or cohesive enough to extend burrows by fracture.     

A preliminary revision of sordidus-like species of Ilyocryptus Sars, 1862 (Anomopoda, Branchiopoda) in North America, with description of I. bernerae n. sp.

Presently the inter-generic structure of the Ilyocryptus Sars, 1862 is not clear, and we regard as `sordidus-like' all the species with (1) incomplete moulting, (2) valves without lateral horns or other remarkable structures, (3) non-distal position of anus on postabdomen, (4) long lateral setae on the postabdomen, which reaches the anus; (5) single or doubled teeth on preanal margin of postabdomen. Available material on sordidus-like forms of Ilyocryptus Sars, 1862 (Anomopoda, Branchiopoda) from North America was investigated. We also analyzed a limited amount of material similar to I. sordidus s. str., but not enough to be presented now. Three other conventional species were found and redescribed: the exclusively North American I. gouldeni Williams, 1978, as well as I. cuneatus?tifter, 1988 and I. spinosus?tifter, 1988, both described earlier from Europe. An original analysis of the differences between all species was performed. A new sordidus-like species, I. bernerae n. sp., from a single locality in South Carolina, U.S.A., is described. The main diagnostic features of this new species within sordidus-like members of the Ilyocryptusare: thin and sharp dorsal keel; exclusively single preanal teeth, greatly increasing in size in basal direction; lateral setae on postabdomen, not decreasing in size basad; absence of denticles on base of postabdomen; complete absence of any denticles on distal and middle portion of ventral margin of postabdominal claws; distalmost spine on claw base longer than basalmost; bases of antennules compressed against each other (although not touching); slightly different armature of two sides of lateral swimming setae; presence of small hooks on tips of lateral swimming setae; distal segments of setae on trunk of limb I setulated only in basal portion; sensillum on gnathobase II curved.     

Effects of environment on electric field detection by small spotted catshark Scyliorhinus canicula (L.)

This study evaluated the influence of environment (substratum type and depth) on the electroreception capabilities of small spotted catsharks Scyliorhinus canicula in response to prey-simulating electric fields. In experiments where electric fields (applied current 15 μA) were presented beneath different substrata (sand, pebbles, rocks and control) it was found that search effort was not different between substrata or S. canicula sexes, however, both rates of turning and biting towards active electrodes were decreased over pebbles and rocks compared with sand and the control (no substratum). There was no significant effect of sex on turn and bite rates over any substrata. Electric fields were then presented beneath different depths of sand to examine the depth-limits of fish electroreception. Turn and bite rates were significantly lower at depths below 10 mm, with no bites towards electrodes made when they were >30 mm depth. Search effort was not found to be different between different burial depth treatments or between sexes. These results indicate substratum type and depth influences the ability of S. canicula to detect prey-simulating electric fields. This variation in electroreceptive performance may influence space use of sharks.     

Physiological Plasticity to Water Flow Habitat in the Damselfish,Acanthochromis polyacanthus: Linking Phenotype to Performance

The relationships among animal form, function and performance are complex, and vary across environments. Therefore, it can be difficult to identify morphological and/or physiological traits responsible for enhancing performance in a given habitat. In fishes, differences in swimming performance across water flow gradients are related to morphological variation among and within species. However, physiological traits related to performance have been less well studied. We experimentally reared juvenile damselfish, Acanthochromis polyacanthus, under different water flow regimes to test 1) whether aspects of swimming physiology and morphology show plastic responses to water flow, 2) whether trait divergence correlates with swimming performance and 3) whether flow environment relates to performance differences observed in wild fish. We found that maximum metabolic rate, aerobic scope and blood haematocrit were higher in wave-reared fish compared to fish reared in low water flow. However, pectoral fin shape, which tends to correlate with sustained swimming performance, did not differ between rearing treatments or collection sites. Maximum metabolic rate was the best overall predictor of individual swimming performance; fin shape and fish total length were 3.3 and 3.7 times less likely than maximum metabolic rate to explain differences in critical swimming speed. Performance differences induced in fish reared in different flow environments were less pronounced than in wild fish but similar in direction. Our results suggest that exposure to water motion induces plastic physiological changes which enhance swimming performance in A. polyacanthus. Thus, functional relationships between fish morphology and performance across flow habitats should also consider differences in physiology.     

Patterns of setal numbers conserved during early development of swimming legs of Copepoda (Crustacea)

During swimming leg development, the number of setae present on the exopod and endopod of the bilobed bud, the transformed swimming leg with 1-segmented rami and the swimming leg with 2-segmented rami of copepods is analysed. For swimming leg 1, the most frequent number of setae on the presumptive rami of the bilobed bud is found at a higher percentage among copepod species than the most frequent number of setae for either the transformed swimming leg with 1-segmented rami or the swimming leg with 2-segmented rami. However, for swimming legs 2–4 the most frequent number of setae for the the transformed swimming leg with 1-segmented rami is found at a higher percentage of species than that on either the bilobed bud or the swimming leg with 2-segmented rami. Thus, in the cases of swimming legs 2–4, species with different numbers of setae on the presumptive exopod and endopod of the bud bilobed bud develop the same number of setae on the rami of the transformed swimming leg with 1-segmented rami. Increasing the number of species analysed is expected to make more robust the hypothesis that the number of setae on the transformed swimming leg with 1-segmented rami is conserved relative to the number of setae on the bilobed bud.     

Nereis succinea nuptial behavior: Does size matter?

Summary

Although Darwin noted that size may affect sexual selection, the effect of size on reproduction is controversial. Mature Nereis succinea, a polychaete that mates in pheromone-mediated twilight nuptial swarms, varies greatly in size, ranging more than 10-fold in body weight from 30 mg to >300 mg. Swim speed of swarming male worms increases with worm size, with the fastest males swimming more than twice the speed of the slowest. The female-produced spawning pheromone, nereithione, stimulates both swimming speed and spawning in males at concentrations of 10^?6 M and above, and lower concentrations cause significant activation of swimming. Individual worms can be stimulated to release sperm up to 40 or more times in a single experimental session. Larger worms release cumulatively more sperm than smaller ones, resulting in significant loss of body mass from repetitive spawning activated by nereithione. Size may enhance mating success of male N. succinea due to encountering more females as a result of faster swimming speed and due to the higher sperm density and number of spawning responses of large animals.     

Experimental studies on the foraging behavior of the sand fiddler crab Uca pugilator (Bosc, 1802)

The purpose of this study was to test the hypothesis that foraging sand fiddler crabs. Uca pugilator (Bosc), move through the habitat in response to low substratum food levels even though these movements may take the crabs considerable distances from the safety of the burrow area. Chl a and ATP concentrations were used as measures of food density in foraged and unforaged substratum. Field and laboratory feeding experiments showed that crab foraging intensity in a habitat patch was directly correlated with food density in the patch either in the presence or absence of alternative food patches. Other experiments showed that sand fiddlers can respond to differences in food level on a scale of millimeters and do this by probing the substratum with minor chelae. Food levels in aggregations of non-ingested particles harvested by sand fiddlers, feeding pellets, correspond to low foraging intensities predicted from foraging experiments and crabs exhibit low foraging intensities on substratum patches derived from feeding pellets. Substratum food levels in two distinct areas corresponded to high predicted foraging intensities and there was no consistent trend in the level of food in the burrow vs. the nonburrow microhabitats. These results suggest that the movements of foraging sand fiddlers are to some extent controlled by the reduction in substratum food levels due to feeding during a single foraging episode. Sand fiddlers can extract over 70% of the food from harvested substratum over a broad range of substratum food densities but harvest only 42% of the available substratum.     

Behavioural basis of intertidal zonation in Eurydice pulchra Leach

Eurydice pulchra Leach freshly collected at neap and spring tides exhibits an endogenous circatidal rhythm of swimming when kept without sand in constant conditions in laboratory aquaria. When provided with sand in the laboratory, tidally-phased swimming may occur spontaneously at some times of the lunar month, predominantly after the times of highest spring tides but not at neaps. In these cases, therefore, there appears to be clearly demonstrated for the first time in a marine animal a circasemilunar pattern of emergence from the substratum which is coupled to a circatidal rhythm of swimming; the isopods in the laboratory emerge from the sediment only when the swimming rhythm and emergence rhythm are at their maxima. In the field at neap tides some isopods emerge to swim at high tide, dependent upon their responses to water agitation, their feeding state and responses to light. At and just after spring tides in the field large numbers of the isopods swim at high tide, triggered by the endogenous circasemilunar rhythm of emergence which in the field is probably cued by the effects of increased water agitation. The main function of the endogenous circatidal rhythm of swimming appears to be to permit the isopods to return to their preferred zone in the sand before the fall of the tide. The coupled circasemilunar rhythm of emergence which induces greater swimming at spring tides reduces the risk of animals being stranded high on the shore during neap tides.     

Comparison of surface topography of three species of Diphyllobothrium (Cestoda,pseudophyllidea) by scanning electron microscopy

Plerocercoids of different sizes as well as adult worms of D. dendriticum, D. latum and D. ditremum were studied using scanning electron microscopy (S.E.M.). In the plerocercoids there were found distinct differences in appearance and length of microtriches between these three species, while the microtriches of adult worms were more similar. A regional difference in microtrix appearance was found in the larvae of D. ditremum and D. dendriticum. This was not apparent with S.E.M. in adult worms. The length of ‘body’ microtriches in D. dendriticum varied with the length of the larvae. The topography of the genital atrium of mature and gravid proglottids in adult worms of these three species is also described.     

The structure of anoline (Reptilia: Dactyloidae: Anolis) toe pads in relation to substratum conformity

Adhesive toe pads of geckos house modified components of vascular and/or connective tissues that promote conformity of the setal fields with the locomotor substratum. Similar modifications have been claimed for the digits of Anolis, but evidence for them is not compelling. Angiographic and histological investigations of Anolis failed to identify any evidence of either an intralamellar vascular reticular network or a central sinus. Instead, their vascularity more closely resembles that of lizards in general than that of pad‐bearing geckos. The loose connective tissue of the toe pads likely contributes to their general pliability and flexibility, promoting localized compliance with the substratum. Through the shedding cycle, the lamellae change shape as the replacing setae elongate. The outer epidermal generation lacunar cells on the inner lamellar faces simultaneously hypertrophy, providing for compatibility between overlapping lamellae, enabling reciprocity between them. This contributes to continuing compliance of the setal fields with the substratum. Overall, digital structure and attachment and release kinematics of the toe pads of Anolis are very similar to those of geckos exhibiting an incipient adhesive mechanism. Both lack major anatomical specializations for promoting conformity of the setae with the locomotor substratum beyond those of the seta‐bearing portions of the epidermis.     

A method for the culture of tropical seagrasses

Three tropical seagrass species were planted into 1.5 m² culture tanks and grown under the same conditions for 2 years. New shoot production and vegetation growth of both Syringodium filiforme Kütz. and Halodule wrightii Aschers. resulted in complete cover in monoculture tanks within the first year. The vegetative spread of Thalassia testudinum Banks ex König was slower than that of the other species. The culture of seagrasses in open mesocosm systems was most successful when continuous current circulation was maintained, water column nutrients were kept low, and extreme high temperatures (> 36°C) were avoided. Seagrass colonized and grew equally well in Indian River mud substratum and in quartz sand.     

The effects of sediment type on growth rate and shell allometry in the soft shelled clam Mya arenaria L

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets.Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.     

Effects of grazing and damselfish territoriality on internal bioerosion of dead corals : indirect effects

An experiment was performed on Britomart Reef, Great Barrier Reef (central region), to determine the relationship between fish grazing, damselfish territoriality, and internal bioerosion of dead coral substratum. The damselfish Hemiglyphidodon plagiometopon Bleeker (Pomacentridae) was used for the study because it actively excludes herbivorous fish, particularly scarids and acanthurids, from its territories, creating undergrazed patches in the environment. Its territories simulated conditions of naturally reduced grazing. Freshly killed pieces of the plating coral Pachyseris speciosa Dana were placed under four experimental conditions: (1) within cages, excluding grazing fish; (2) within damselfish territories; (3) beneath shade tops to control for light; and (4) outside damselfish territories, fully exposed to grazers. Internal bioeroders were identified by pattern of substratum excavation and characterization of borings, and were quantified by digitizing x-ray radiographs of the substratum. Three major categories of borers were identified: Cliothosa hancocki Topsent, “other sponges” (of the Cliona viridis Schmidt species complex), and “worms” (including polychaetes and sipunculids). Variations in grazing pressure were found to significantly alter the taxonomic composition of the bioeroder community. Bioerosion by C. hancocki, a boring sponge with large exposed papillae, was found to increase significantly when grazing was reduced within damselfish territories. By contrast, other boring sponges of the C. viridis complex decreased in abundance; they were not affected by higher sedimentation in cages. The response of bioerosion by “worms” was less clear but increased slightly within damselfish territories. This was due primarily to a shift in taxonomic composition and dominance from polychaetes to sipunculids (particularly Cleosiphon aspergillum Quatrefages). The effects of grazing on the internal bioeroder community were often altered or obscured in the caged treatments; this was most likely due to caging artifacts such as increased sedimentation and decreased light. In general, bioerosion rates of the substratum P. speciosa were low in comparison to rates established or estimated for corals with less dense skeletons. Total internal bioerosion rates did not vary significantly with changes in grazing pressure. This study implies that, overall, reduced grazing pressure will lead to production of fine sediments derived from internal bioeroders. Under high grazing pressures, the addition of external bioerosion effected directly by grazers would also produce coarse sediment, resulting in an increase in total bioerosion rates (internal and external) and an increased contribution of both coarse and fine sediments to the reef environment.     

Mechanism of secretion of the contents of the mandibular glands of Plodia interpunctella larvae

ABSTRACT. Larvae of Plodia interpunctella deposit droplets of mandibular gland secretion onto silk filaments connecting particles within the substrate they inhabit, and on to the substrate itself. Active participation of the mouthparts is necessary for both the formation and deposition of these droplets along the filaments and occurs as the silk is spun. Deposition of secretion directly on the substratum does not involve the mouthparts and appears to result from contact between the lower surface of the head and the substratum. Larvae from which the mandibular glands have been removed by excision neither produce droplets on silk nor deposit them on the substratum. Those which are incapable of spinning silk due to cauterization of the spinneret are still able to deposit secretion on the substratum, however. Deposition of secretion on silk webbing does not occur when the setae which regulate formation of droplets on filaments are removed by shaving. Droplets are not characteristic of a particular larval instar but are produced by larvae of all instars as a normal function which does not depend upon intraspecific encounters. Four other Lepidopteran pests, Ephestia elutella, Ephestia cautella, Anagasta kuehniella and Antigasta catolaunalis , were also found to produce droplets of mandibular gland secretion in a similar manner to larvae of P. interpunctella.     

Analytical study of the locomotor and respiratory movements of tubificid worms by means of video recording

Locomotory and respiratory movements of Tubifex tubifex (Müller, 1774) were observed in aquaria by filming living worms and analysing the videotapes. Worm galleries formed a network and the tubificids moved in all directions in their muddy substratum. Over half stayed in the mud for about 2 minutes; most stayed at the surface less than one hour. Many specimens were able to stay deep in the mud for more than five hours. The periodic return of tubificids to the surface, the duration of their stay there, the length of the body protuding from the mud and tail waving are a function of their respiratory needs.     

Localised intraspecific variation in the swimming phenotype of a coral reef fish across different wave exposures

Wave-driven water flow is a major force structuring marine communities. Species distributions are partly determined by the ability to cope with variation in water flow, such as differences in the assemblage of fish species found in a given water flow environment being linked to swimming ability (based on fin shape and mode of locomotion). It remains unclear, however, whether similar assembly rules apply within a species. Here we show phenotypic variation among sites in traits functionally linked to swimming ability in the damselfish Acanthochromis polyacanthus. These sites differ in wave energy and the observed patterns of phenotypic differences within A. polyacanthus closely mirrored those seen at the interspecific level. Fish from high-exposure sites had more tapered fins and higher maximum metabolic rates than conspecifics from sheltered sites. This translates to a 36 % larger aerobic scope and 33 % faster critical swimming speed for fish from exposed sites. Our results suggest that functional relationships among swimming phenotypes and water flow not only structure species assemblages, but can also shape patterns of phenotypic divergence within species. Close links between locomotor phenotype and local water flow conditions appear to be important for species distributions as well as phenotypic divergence across environmental gradients.     

Effects of substratum and conspecific adults on the metamorphosis of Chasmagnathus granulata (Dana) (Decapoda: Grapsidae) megalopae

The ability of marine invertebrate larvae to delay their metamorphosis in the absence of adequate environmental cues has been reported for numerous sedentary and sessile species. In the present study, the effect of various substrata and the presence of conspecific adults on the metamorphosis of a mobile species, the crab Chasmagnathus granulata, was evaluated. The duration of the megalopa stage in experiments with six different substrata and in the presence or absence of conspecific adults was compared in a laboratory study. In addition, the influence of natural substrata was compared with that of artificial substrata of similar grain size or texture. In a further experiment, the two most effective cues (natural mud and conspecific adults) were tested as single vs. combined factors. Natural mud and unidentified chemical cues from conspecific adults had the strongest accelerating effects on development duration to metamorphosis. With the exception of nylon threads (artificial filamentous substratum), none of the artificial substrata had a significant effect on the duration of the megalopa stage. Simultaneous exposure to natural mud and water containing chemical cues from conspecific adults accelerated metamorphosis more than each of these factors separately. Megalopae that were reared without a substratum (control) delayed their metamorphosis by 29% (about 3 days) compared with those in simultaneous contact with natural mud and rearing water of adult conspecifics. The results indicate that the metamorphosis of the megalopa of C. granulata is influenced by the presence or absence of environmental stimuli that are associated with the preferred adult habitat.     

Schistosoma mansoni: Electron probe X-ray microanalysis of the elemental composition of the tegument and subtegumental tissues of adult worms

The elementary composition [Na, Mg, P, S, Cl, K, Ca and Fe] of the tegument, tegumental spines, and subtegumental tissues of adult male and female Schistosoma mansoni have been determined by electron probe X-ray microanalysis of unfixed, freeze-dried cryosections. Statistical analysis of the results suggests that there are distinct differences in the elemental composition of the tissues both between and within individual male and female worms, and between male and female worms in general. In particular, there were significant variations in the elemental contents of the tissues between individual male and female worms, which may reflect differences in the physiology and/or metabolic state of the worms. Significant differences in the elemental composition of the various tissues examined within individual worms were also found. In general, in both male and female worms, there were significantly higher elemental levels in the tegument, as opposed to the subtegumental tissues. The elemental composition of the tegumental spines in both male and female worms differed from that of the tegumental cytoplasm, although the differences in the elemental composition between spines from male and female worms reflected the differences in the elemental content between the teguments themselves. Differences in the elemental composition of the tissues between male and female worms were also found, with the female tegument containing significantly higher elemental levels (with the exception of Cl) than the male tegument. In particular, the tegument of female worms contained higher levels of calcium and, in relatively small areas, isolated calcium-containing granules. This higher tegumental calcium level in female worms may reflect a higher calcium demand by sexually mature female worms due to the presence, within the mature vitelline cells, of calcium-containing corpuscles and the production of large numbers of eggs.