Catecholamines and dihydroxyphenylalanine in metamorphosing larvae of the nudibranch Phestilla sibogae Bergh (Gastropoda: Opisthobranchia)

The content of catecholamines and dihydroxyphenylalanine in larvae of the nudibranch Phestilla sibogae was analyzed by high-performance liquid chromatography with electrochemical detection. Dihydroxyphenylalanine, norepinephrine and dopamine were identified in larvae of all ages examined (5 through 12 days post-fertilization). Dihydroxyphenylalanine could be accurately quantified only in larvae of ages 8 through 12 days, when its average concentration increased from 0.62 to 6.71 × 10⁻² pmol μg protein⁻¹. Between ages 5 and 12 days dopamine rose from 0.081 to 0.616 pmol μg protein⁻¹, and norepinephrine from 0.45 to 2.17 × 10⁻² pmol μg protein⁻¹. Dihydroxyphenylalanine, dopamine and norepinephrine were also measured at different stages of metamorphic progress in 10- to 12-day larvae. Dihydroxyphenylalanine increased by a factor of 2.4 between the onset and completion of metamorphosis, but levels of dopamine and norepinephrine remained stable. One millimolar alpha-methyl-dl-m-tyrosine, an inhibitor of catecholamine synthesis, inhibited natural metamorphosis and depleted endogenous norepinephrine and especially dopamine, respectively, to 75% and 35% of control values. The existence of unexpectedly high levels of catecholamines in metamorphically competent larvae, and the association of catecholamine depletion with inhibition of metamorphosis, indicate that these compounds may participate in the control of gastropod development. Accepted: 18 April 1997     

Observations on the ecology of Membranipora (bryozoa) and a major predator Doridella steinbergae (nudibranchiata) along the fronds of Laminaria saccharina at Friday Harbor,washington

The distribution of the bryozoan Membranipora and one of its major predators, the nudibranch Doridella steinbergae (Lance) along the fronds of Laminaria saccharina (L.) Lamour. at Friday Harbor, Washington were studied during the summer (July–August) 1975. Whilst the fronds are most heavily encrusted by the bryozoan in the middle and distal regions, settlement occurs principally in the younger more basal regions of the plants. The distribution pattern of the nudibranch closely parallels that of its prey though there is a tendency for the most distal regions, especially in older plants, to be avoided. An average density of 240 Doridella/plant was found for plants of mean length 91.0 cm. Despite the severe predation pressure imposed by this nudibranch, evidence tends to suggest that these extensive and highly productive Membranipora populations could probably support even higher densities of Doridella than those presently found — at least over that period of the year during which this investigation was made.     

Larval development and metamorphosis in Pleurobranchaea maculata, with a review of development in the notaspidea (Opisthobranchia)

Pleurobranchaea maculata is a carnivorous notaspidean that is common in New Zealand. This species produces small eggs (diameter 100 microm) and planktotrophic veligers that hatch in 8 d and are planktonic for 3 weeks before settling on biofilmed surfaces (14 degrees C). Larval development is known in detail for only two other notaspidean species, P. japonica and Berthellina citrina. In all three species of pleurobranchids, mantle and shell growth show striking differences from veligers of other opisthobranch taxa. In young veligers of pleurobranchids, the shell is overgrown by the mantle, new shell is added by cells other than those of the mantle fold, and an operculum does not form. Thus some "adult" traits (e.g., notum differentiation, mechanism of shell growth, lack of operculum) are expressed early in larval development. This suggests that apomorphies characteristic of adult pleurobranchids evolved through heterochrony, with expression in larvae of traits typical of adults of other clades. The protoconch is dissolved post-settlement and not cast off as occurs in other opisthobranch orders, indicating that shell loss is apomorphic. P. maculata veligers are atypical of opisthobranchs in having a field of highly folded cells on the lower velar surface, a mouth that is posterior to the metatroch, and a richly glandular, possibly chemodefensive mantle. These data indicate that notaspidean larvae are highly derived in terms of the novel traits and the timing of morphogenic events. Phylogenetic analysis must consider embryological origins before assuming homology, as morphological similarities (e.g., shell loss) may have developed through distinct mechanisms.     

Breeding and recruitment in a population of the New Zealand starfish Stichaster australis (Verrill)

The annual reproductive cycle of the New Zealand starfish Stichaster australis (Verrill) was determined at Maori Bay on the west coast of Auckland. S. australis has a clearly defined summer breeding season, closely repeated from year to year. Changes in the gonad shown by histological sections confirmed this cycle.S. australis juveniles reared in the laboratory were maintained on Mesophyllum insigne (Foslie) Adey substrata and the growth rates and feeding behaviour of individual starfish were determined. Settlement on the shore was from May to July each year. When the time of spawning is considered this implies a planktotrophic larval life of ≈ 6 months. This is considerably longer than laboratory studies on larval development would suggest.Growth of yearly settlement cohorts on a nursery site on the shore used in conjunction with laboratory results gave a fairly clear picture of growth after settlement. Growth rates followed a typical sigmoid curve, growth being slow initially and becoming more rapid later. The numbers of juveniles recruited to nursery areas vary from year to year but mortality following settlement appears to be low. It was found that juvenile Stichaster australis graze Mesophyllum insigne exclusively until they reach ≈ 0.8 cm in diameter (7–8 months old) when they may occasionally predate juvenile Perna canaliculus (Gmelin). The incidence of carnivorous feeding gradually increases until juveniles are ≈ 2.0–2.5 cm in diameter (15–18 months old) by which time they are exclusively carnivorous on small P. canaliculus. As growth continues juvenile starfish gradually migrate from nursery areas to adjacent reefs where there are dense beds of adult P. canaliculus. Starfish of this species become sexually mature when they reach ≈ 5–8 cm in diameter.     

Nudibranch-sponge feeding dynamics: Benefits of symbiont-containing sponge to Archidoris montereyensis (Cooper, 1862) and recovery of nudibranch feeding scars by Halichondria panicea (Pallas, 1766)

Selected interactions between the encrusting sponge Halichondria panicea and its primary predator, the dorid nudibranch Archidoris montereyensis, were investigated in a high-latitude rocky intertidal community spatially dominated by H. panicea. Feeding experiments were conducted in which A. montereyensis pairs were provided with sponge containing symbiotic zoochlorellae or sponge in which the zoochlorellae population had been reduced or removed by shading. Nudibranchs consuming H. panicea with symbiotic zoochlorellae had higher feeding, growth, and egg production rates than individuals eating aposymbiotic sponge. We simulated A. montereyensis predation on H. panicea by creating typically sized feeding grooves in the sponge. H. panicea's response was high linear growth rates into the experimental feeding grooves, generally recovering most of the groove area within 4 weeks. Overall, the sponge's rapid response to tissue damage minimizes grazing impacts and substrate loss and reduces susceptibility to wave removal.     

Activities of natural methyl farnesoids on pupariation and metamorphosis of Drosophila melanogaster

Methyl farnesoate (MF) and juvenile hormone (JH III), which bind with high affinity to the receptors USP and MET, respectively, and bisepoxy JH III (bisJH III) were assessed for several activities during Drosophila larval development, and during prepupal development to eclosed adults. Dietary MF and JH III were similarly active, and more active than bisJH III, in lengthening larval development prior to pupariation. However, the order of activity was changed (JH III > bisJH III > MF) with respect to preventing prepupae from eclosing as normal adults, whether administered in the larval diet or as topically applied at the white puparium stage. If endogenous production of all three larval methyl farnesoids was suppressed by a strongly driven RNAi against HMGCR in the corpora allata cells, most larvae did not attain pupariation. Farnesol (which has no demonstrated life-necessary function in larval life except in corpora allata cells as a precursor to methyl farnesoid biosynthesis) when incorporated into the diet rescued attainment of pupariation in a dose-dependent manner, presumably by rescuing endogenous production of all three hormones. A more mild suppression of endogenous methyl farnesoid production enabled larval attainment of pupariation. However, in this background dietary MF had increased activity in preventing puparia from attaining normal adult eclosion. The physiological relevance of using exogenous methyl farnesoids to block prepupal development to normally eclosed adults was tested by, instead, protecting in prepupae the endogenous titer of methyl farnesoids. JH esterase normally increases during the mid-late prepupal stage, presumably to clear endogenous methyl farnesoids. When JH esterase was inhibited with an RNAi, it prevented attainment of adult eclosion. Cultured adult corpora allata from male and female Aedes aegypti released both MF and JH III, and the A. aegypti nuclear receptor USP bound MF with nanomolar affinity. These A. aegypti data support the use of Drosophila as a model for mosquitoes of the binding of secreted MF to USP.     

Determinate growth and the scaling of photosynthetic energy intake in the solitary coral Fungia concinna (Verrill)

For many marine invertebrates, the maximum size of an individual is influenced heavily by environmental factors and may be limited by energetic constraints. In this study, an energetic model developed originally for anemones was applied to the free-living scleractinian Fungia concinna (Verrill) from Moorea (French Polynesia) to test the hypothesis that energetic constraints limit the size of this solitary coral. The modified model assumed that photosynthesis was the primary source of metabolic energy, and that metabolic costs were represented by aerobic respiration; these sources and sinks of energy were compared using daily energy budgets that were analyzed using double logarithmic regressions of energy against coral size. With this approach, energy limitation is characterized by a scaling exponent for energetic cost (b_cost) that is larger than the scaling exponent for energy intake (b_intake). For the size range of F. concinna studied, b_intake = 0.73 ± 0.09 and b_cost = 0.46 ± 0.10, thereby demonstrating that large individuals accumulated an energetic surplus, even when the expenditure associated with host tissue and symbiont growth was included in the model. The surplus of energy that this coral acquires as it grows appears to be driven by the scaling of traits associated functionally with the scaling of respiration and photosynthesis. Specifically, tissue biomass displayed a strong positive allometry with respect to surface area (i.e., b > 1), and this constraint on surface area may be the mechanistic basis of the low scaling exponent for metabolic cost. In contrast, the capacity for autotrophy - defined indirectly as Symbiodinium population density and chlorophyll content - increased isometrically with surface area, and likely contributed to the higher scaling exponent for intake relative to cost. Our results suggest that growth in F. concinna is not limited strictly by energy, but instead maximum size must be determined by alternative physiological or ecological constraints.     

Computer-based 3-dimensional reconstruction of major organ systems of a new aeolid nudibranch subspecies, Flabellina engeli lucianae, from Brazil (Gastropoda: Opisthobranchia)

Obtaining accurate and comprehensive anatomical informationfrom small opisthobranch specimens has been a major problem.Computer-based 3-dimensional reconstruction from serial histologicalslides applying AMIRA (TGS Graphics) software is shown to bean efficient and fully reproducible way to analyse tiny andcomplex organ systems in their true relative positions and proportions;this method is herein applied to nudibranchs for the first time.We used Flabellina engeli lucianae n. subsp., a small aeolid(up to 8 mm body preserved length) from subtropical southernBrazil, to illustrate all major organ systems including nervoussystems, and discuss them comparatively. Flabellina engeli lucianaediffers externally from congeners by having a translucent bodywith opaque white and iridescent blue spots, orange ceratalbands, and by the special branching of cerata forming distinctgroups on common peduncles. External and internal differencesfrom the apparently geographically and hydrographically separatedCaribbean specimens of F. engeli engeli Marcus & Marcus,1968 are discussed in detail. (Received 9 January 2006; accepted 10 July 2007)     

Prey selection and the functional response of sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say) preying on juvenile sea scallops (Placopecten magellanicus (Gmelin)) and blue mussels (Mytilus edulis Linnaeus)

Predators in nature include an array of prey types in their diet, and often select certain types over others. We examined (i) prey selection by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) when offered two prey types, juvenile sea scallops (Placopecten magellanicus) and blue mussels (Mytilus edulis), and (ii) the effect of prey density on predation, prey selection, and component behaviours. We quantified predation rates, behavioural components (proportion of time spent searching for prey, encounter probabilities) and various prey characteristics (shell strength, energy content per prey, handling time per prey) to identify mechanisms underlying predation patterns and to assess the contribution of active and passive prey selection to observed selection of prey. Sea stars strongly selected mussels over scallops, resulting from both active and passive selection. Active selection was associated with the probability of attack upon encounter; it was higher on mussels than on scallops. The probability of capture upon attack, associated with passive selection, was higher for mussels than for scallops, since mussels can not swim to escape predators. Sea stars consumed few scallops when mussels were present, and so did not have a functional response on scallops (the target prey). Rock crabs exhibited prey switching: they selected mussels when scallop density was very low, did not select a certain prey type when scallop density was intermediate, and selected scallops when scallop density was high relative to mussel density. The interplay between encounter rate (associated with passive selection) and probability of consumption upon capture (associated with both active and passive selection) explained observed selection by crabs. Scallops were encountered by crabs relatively more often and/or mussels less often than expected from random movements of animals at all scallop densities. However, the probability of consumption varied with scallop density: it was lower for scallops than mussels at low and intermediate scallop densities, but tended to be higher for scallops than mussels at high scallop densities. When mussels were absent, crabs did not have a functional response on scallops, but rather were at the plateau of the response. When mussels were present with scallops at relatively low density, crabs exhibited a type II functional response on scallops. Our results have implications for the provision of protective refuges for species of interest (i.e., scallops) released onto the sea bed, such as in population enhancement operations and bottom aquaculture.     

Habitat selection by two Mediterranean species of Aplysia: A. fasciata poiret and a. depilans Gmelin (Mollusca : Opisthobranchia)

Factors influencing habitat selection were examined in two species of Mediterranean Aplysia. Animals and egg masses were found in four types of habitats that varied in degree of exposure to wave action. Both species were frequently found in groups. Neither species was common in areas cut off from the surge of the sea. No difference in food preference was observed. A. depilans Gmelin were primarily found in areas subject to greater wave action, while A.fasciata Poiret dominated the calmer habitats. Both species were common in intermediate environments. In late summer, when A. depilans are absent, A. fasciata penetrated some environments previously dominated by the former. Morphological and behavioural features of A. depilans and A.fasciata are consistent with adaptation to rough and calm habitats, respectively.     

Development of Amphioplus abditus (Verrill) (Echinodermata: Ophiuroidea): I. Larval biology

A fraction rich in secretory granules was prepared from the pyloric caeca of Asterias amurensis by sucrose density gradient centrifugation. The freshly prepared fraction exhibited no casein-hydrolyzing activity- but showed nine times as much specific activity as that of tissue homogenates after incubation at 37 degrees C for thirty minutes. Electron microscopy showed that the secretory granules were membrane-bound granules measuring 0.5-290 mu in diameter and contained dense and/or light amorphous substances.     

Dietary nitrogen availability in macroalgae enhances growth of the sea hare Aplysia californica (Opisthobranchia: Anaspidea)

Evidence suggests that marine herbivores select for prey items with elevated nitrogen content. We tested this hypothesis with experimental growth studies of the herbivorous gastropod Aplysia californica offered diets of the rhodophyte Gracilaria ferox with varying nitrogen content. A. californica had a sevenfold feeding preference by weight for G. ferox with higher tissue % N and % protein, and lower % C, % carbohydrate and carbon-to-nitrogen ratio (C/N) as compared to treatments with lower nitrogen and protein content. A. californica provided treatment diets of varying nitrogen availability (high, medium and low) also had significantly different growth rates within 30 days. The high N diet supported a two-fold higher growth rate than that of the medium N diet and four-fold higher than the low N treatment, with mean weights over the experiment reaching 20.4, 9.8, and 5.6 g, respectively. The evolutionary value of this dietary preference may facilitate faster growth to reproductive size, outgrowth of predators and sequestration of organic compounds from nitrogen-enriched macroalgae to deter predators. Despite recent attention, the importance of diet-derived compounds as anti-predatory chemical defenses in Aplysiids remains equivocal. Nitrogen-enriched macroalgal diets, however, may provide “primary metabolites” that serve as alternative defenses for Aplysiids.     

The role of kleptoplasts in the survival rates of Elysia timida (Risso, 1818): (Sacoglossa: Opisthobranchia) during periods of food shortage

The importance of photosynthetic products derived from kleptoplasts in several sacoglossan species is being investigated in different fields, such as chemistry, biomolecular genetics and ecology. This study analyzes the effect of kleptoplasts on the survival rates of Elysia timida by evaluating the development of chlorophyll concentration, total length and survival rates of starved E. timida specimens kept in the light and in the dark. Although chlorophyll concentration values were similar in both cases, after 28 days specimens kept in the dark showed a greater size decrease and a lower survival rate (up to 30% lower) than those kept in the light. It is evident that kleptoplasts provide the mollusc with extra energy at the primary metabolism level to compensate for a shortage in food.     

The natural occurrence of Pandora heteropterae (Zygomycetes: Entomophthorales) infecting Lygus lineolaris (Hemiptera: Miridae)

An unknown fungal pathogen was recovered from Lygus lineolaris (Palisot de Beauvois) during a survey of parasitic and pathogenic natural enemies conducted in Franklin County, Arkansas. The pathogen was identified as Pandora heteropterae (Ba?azy) Keller based on characteristics of the morphology, as well as growth and sporulation on hosts. The fungus infected 11 of the 3405 (0.32%) wild L. lineolaris collected. In a laboratory host-range bioassay, five of seven hemipteran species from the families Miridae, Coreidae, Lygaeidae, and Pentatomidae were successfully infected. P. heteropterae was previously reported only once, from an unidentified host species in Poland. Here we describe the morphology and growth of P. heteropterae and discuss its potential impact on L. lineolaris in the field.     

Comparative studies on the life history of Angiostrongylus mackerrasae Bhaibulaya, 1968 and Angiostrongylus cantonensis (Chen, 1935)

The life history of A. mackerrasae was found to differ from that of A. cantonensis as follows: (1) the moulting times of A. cantonensis in the definitive host occurred a few days earlier than those of A. mackerrasae; (2) the growth rate of A. cantonensis was more rapid than that of A. mackerrasae. However, there were no differences in the migratory pattern of the third-stage larvae of both species in experimentally-infected definitive hosts. It is concluded that Mackerras & Sandars (1955) described the life history of A. mackerrasae and not A. cantonensis.     

Effects of temperature on carbon fixation and carbon budget partitioning in the zooxanthellal symbiosis of Aiptasia pallida (Verrill)

Effects of temperature on carbon fixation rates and partitioning between Aiptasia pallida (Verrill) and its symbiotic alga Symbiodinium microadriaticum Freudenthal were examined by ¹⁴C incubation studies. Total fixation varied strongly with temperature, with an optimum of 32 °C. More photosynthate was translocated to the host at 12 °C (82%) than at 27 °C (63%). Partitioning among three fractions (alcohol soluble, ether soluble, and alcohol/ether insoluble) varied with temperature in Aiptasia pallida, but not in the alga. Relative partitioning between host and alga increased with time in favor of A. pallida when maintained at 12 °C, but absolute levels of translocation to the host did not change; however, photosynthate retention by the alga did decline substantially. Total fixation declined by ≈ 80% after 10 days at 12 °C. Turnover rates of fixed carbon also varied with temperature, as determined by pulse-chase studies, and the effect varied for the different fractions.These results suggest that zooxanthellae are less thermally adaptable than their hosts, and may be especially susceptible to low temperatures. Thermal effects on biochemical partitioning may have great importance in relation to growth and reproduction of animal hosts of zooxanthellae and the viability of the symbiotic relationship. These effects, combined with the pronounced effect of temperature on total photosynthate production, probably play a major role in limitation of zooxanthellal symbioses to warm waters.     

Fine structure of muscle insertions on the larval shell and operculum of the nudibranch Phestilla sibogae (Mollusca: Gastropoda) before and during metamorphosis

In Phestilla, the attachment of the larval body to shell and operculum occurs at muscle insertion sites. Attachment zones are specialized areas of squamous epithelium wherein the cells contain structures considered to be cytoplasmic anchors. The anchors are intracellular organelles consisting of apical and basal hemidesmosomal plaques connected by bundles of tonofilaments which traverse the cells. Muscle-to-epithelium and epithelium-to-shell adhesion is probably due to an extracellular cement. At metamorphosis, both shell and operculum are lost. Electron microscopic investigation of shell and opercular attachment sites during metamorphosis has demonstrated that apical hemidesmosomes lose their integrity and tonofilament bundles pull away from the apical plasmalemma of the epithelial cells as the cells lose contact with the shell or operculum.     

Luthrobium (Tetartopeus): natural history, phylogeny and revision of the nearctic species (Coleoptera, Staphylinidae)

Abstract. The eleven species of Lathrobium subgenus Tetartopeus from the Nearctic Region are revised. Thirteen specific names are placed in synonymy, Lconvolutum sp.n. is described, and Deratopeus Casey is synonymized with Tetartopeus . A cladistic analysis suggests that Tetartopeus is monophyletic, and that five monophyletic species-groups are represented in the Nearctic Region.