Nervous system development in the fairy shrimp Branchinella sp. (Crustacea: Branchiopoda: Anostraca): Insights into the development and evolution of the branchiopod brain and its sensory organs

Using immunohistochemical labeling against acetylated a‐tubulin and serotonin in combination with confocal laser scanning microscopy and 3D‐reconstruction, we investigated the temporary freshwater pond inhabitant Branchinella sp. (Crustacea: Branchiopoda: Anostraca) for the first time to provide detailed data on the development of the anostracan nervous system. Protocerebral sense organs such as the nauplius eye and frontal filament organs are present as early as the hatching stage L0. In the postnaupliar region, two terminal pioneer neurons grow from posterior to anterior to connect the mandibular neuromeres. The first protocerebral neuropil to emerge is not part of the central complex but represents the median neuropil, and begins to develop from L0+ onwards. In stage L3, the first evidence of developing compound eyes is visible. This is followed by the formation of the visual neuropils and the neuropils of the central complex in the protocerebrum. From the deutocerebral lobes, the projecting neuron tract proceeds to both sides of the lateral protocerebrum, forming a chiasma just behind the central body. In the postnaupliar region, the peripheral nervous system, commissures and connectives develop along an anterior–posterior gradient after the fasciculation of the terminal pioneer neurons with the mandibular neuromere. The peripheral nervous system in the thoracic segments consists of two longitudinal neurite bundles on each side which connect the intersegmental nerves, together with the ventral nervous system forming an orthogon‐like network. Here, we discuss, among other things, the evidence of a fourth nauplius eye nerve and decussating projecting neuron tract found in Branchinella sp., and provide arguments to support our view that the crustacean frontal filament (organ) and onychophoran primary antenna are homologous. J. Morphol. 277:1423–1446, 2016. © 2016 Wiley Periodicals, Inc.     

Some observations on the swimming and feeding of the nauplius larvae of Lepas pectinata (Girripedia: Crustacea)

Limb movements of restrained stage VI nauplii of Lepas pectinata were studied by cine-photography. Outline drawings were made of successive limb positions in both swimming and grooming activity. The antennae appeared to act as leaky paddles performing both propulsion and food gathering. Free-swimming nauplii averaged 120 limb beats min^-1 and a speed of c. 4 mm s^-1. Grooming occurred every 7–20 beats.
It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat.     

When similar beginnings lead to different ends: Constraints and diversity in cirripede larval development

Summary

Cirripedes are fascinating models for studying both functional constraints and diversity in larval development. Adult cirripedes display an amazing variation in morphology from sessile suspension feeders that still retain many crustacean characters to parasites that have lost virtually all arthropod traits. In contrast, cirripede larval development follows a common scheme with pelagic larvae comprising a series of nauplii followed by a cyprid. Variations are mostly concerned with whether or not the nauplii are feeding and the degree of abbreviation of development, culminating in species where the larvae hatch as cyprids. The cypris larvae are very similar among the ingroups of the Cirripedia, but interesting variations occur in structures used for substrate location and attachment. The cyprid is specialized to both swim through the water and actively explore the substratum by walking on the antennules and using an array of sensory organs in search for a suitable site to attach. This unique morphology and behavior of the cyprid have enabled the Cirripedia to colonize widely different habitats ranging from hard rock to soft animal tissue. Yet, the cyprid can metamorphose into juveniles as different as a setose feeding barnacle and the vermiform stages of the parasitic forms. This emphasizes the importance of the cyprid as one of the key features for the evolutionary success of the Cirripedia.     

Planktonic encounter rates in homogeneous isotropic turbulence: the case of predators with limited fields of sensory perception

It is a well-established fact that encounter rates between different species of planktonic microorganism, either swimming, or passively advected by the flow, are enhanced in the presence of turbulence. However, due to the complexity of the various calculations involved, current encounter rate theories are based on a number of simplifying approximations, which do not reflect reality. In particular, a typical planktonic predator is usually assumed to have perfect 'all round vision', i.e. it can perceive a prey particle at any relative orientation, provided it lies within some given contact radius R. Unfortunately, there is a wide body of experimental evidence that this is not the case. In this study the encounter problem for a predator with a limited field of sensory perception, swimming in a turbulent flow, is examined from first principles and a number of new modelling ideas proposed. A wide range of kinematic simulations are also undertaken to test these predictions. Particular attention is paid to the swimming strategy such a predator might undertake to enhance its encounter rate. It turns out that the predicted optimum swimming strategies differ radically from the results of previous work. Empirical evidence is also presented which appears to support these new findings.     

Cypris morphology in the barnacles Ibla and Paralepas (Crustacea: Cirripedia Thoracica) implications for cirripede evolution

We used scanning electron microscopy (SEM) to describe cypris morphology in species of the barnacles Ibla and Paralepas, both of which are pivotal in understanding cirripede evolution. In Ibla, we also studied late naupliar stages with video and SEM. Special emphasis was put on the lattice organs, the antennules and the thorax and telson. In Paralepas we had settled specimens only and could therefore only investigate the carapace with the lattice organs. Cyprids of Ibla quadrivalvis and Paralepas dannevigi have five sets of lattice organs, grouped as two anterior and three posterior pairs. The organs are of the pore‐field type and the terminal pore is situated anteriorly in the first pair, just as in the Rhizocephala and the Thoracica. In Ibla the armament of antennular sensilla resembles that found in the Thoracica but differs from the Rhizocephala. The absence of setules on the A and B setae sited terminally on the fourth antennular segment is a similarity with the Acrothoracica. The attachment disc is angled rather than facing distally and is encircled by a low cuticular velum. The thoracopods have two‐segmented endopods and exopods as in the Thoracica, but the number, shape, and position of thoracopodal setae differ somewhat from other species of that superorder. Both Ibla and Paralepas cyprids have a deeply cleaved telson, but no independent abdominal part. In cypris morphology, Ibla and Paralepas show several synapomorphies with the clade comprising Rhizocephala and Thoracica and there are no specific apomorphies with either the Acrothoracica, the Rhizocephala or any particular subgroup within the Thoracica. This is in agreement with recent molecular evidence that Ibla (Ibliformes) is the sister taxon to all other Thoracica and the ibliforms therefore become the outgroup of choice for studying character evolution within the superorder. Paralepas, and other pedunculated barnacles without shell plates, are apparently not primitive but are secondarily evolved and nested within the Thoracica. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

Functional artificial luciferases as an optical readout for bioassays

This study elucidates functional artificial luciferases (ALucs) wholly synthesized for bioassays and molecular imaging. The ALucs bearing epitopes were newly created by amending the sequences of our previously reported ALucs in light of a multi-sequence alignment and hydrophobicity search. The synthesized ALucs are survived in live cells and stable in culture media for 25 days after secretion. The epitopes in ALucs are exposed during the secretion process and indeed valid for column purification and immunological assays. The ALucs exerted a 9400-times stronger optical intensity with a coelenterazine derivative (CTZ i), when compared with Renilla reniformis luciferase 8.6–535. A supersecondary structure of ALuc30 was predicted with respect to the X-ray crystallographic information of the coelenterazine-binding protein (CBP). The structure revealed that ALuc30 has a room for accommodating the iodide of CTZ i. This study guides on how to create functional artificial luciferases and predicts the structural details with the current bioinformatics technologies.     

Axogenesis in the stomatopod crustacean Gonodactylaceus falcatus (Malacostraca)

Abstract. The formation of the central nervous system of the stomatopod crustacean Gonodactylaceus falcatus is described by means of antibody stainings against synapsin and α-tubulin. It is shown that the longitudinal fiber tracts of the ventral nervous system are formed by two centers of origin comprising a number of pioneer neurons, one at the posterior part of the forming brain, the other in the area of the telson anlage at the posteriormost region of the embryo. In addition to the lateral anlagen of the connectives, a median longitudinal nerve is formed beginning in the mandibular segment neuromere. In contrast to those of other segments, the mandibular ganglia are connected by a single commissure. The brain forms a circumoral ring. There is evidence that the deutocerebrum possesses praestomodeal and poststomodeal commissural fibers. The anlage of the nauplius eye reveals a specific pattern of pigment and sensory cells with the two pigment cells expressing synapsin. Clear differences between the expression patterns of synapsin and α-tubulin recommend the combination of a variety of antibodies to gain a complete picture of embryonic neuroanatomy. Our results show overall similarities to other malacostracan and non-malacostracan crustaceans. The comparisons with other crustaceans and arthropods indicate homology of crustacean nauplius eyes, a circumoral deutocerebrum, and a more widespread occurrence of posterior pioneer neurons forming the axon scaffold of the ventral central nervous system than previously thought.     

Effects of Karenia brevis diet on RNA:DNA ratios and egg production of Acartia tonsa

Karenia brevis is a harmful alga associated with deleterious effects on zooplankton, but the exact cause (e.g. toxin, nutritional inadequacy or starvation) of these adverse effects is not clear. RNA:DNA ratios, fecundity and fecal pellet production of Acartia tonsa were measured on mono-algal and mixed-algal culture diets of K. brevis and Peridinium foliaceum to examine the usefulness of RNA:DNA ratios as an indicator of nutrition and to determine if adverse effects of K. brevis are due to the presence of toxins, poor nutritional quality or starvation. RNA:DNA ratios and egg production values were significantly higher for 100% P. foliaceum diet compared to 100% K. brevis diet. Significant differences in egg production, but not RNA:DNA ratios, were found between the various mixed diets, suggesting egg production is a more sensitive indicator of nutritional quality than RNA:DNA ratios. Changes in RNA:DNA ratios, fecundity and fecal pellet production of copepods fed two different toxic K. brevis strains were nearly identical, indicating that the presence of brevetoxins has little affect on A. tonsa. The similarity in RNA:DNA ratios, egg production, percent hatching and fecal production between the 100% K. brevis diet and starved copepods suggests that A. tonsa does not consume K. brevis when offered as its sole food source.     

Fitness consequences for copepods feeding on a red tide dinoflagellate: deciphering the effects of nutritional value, toxicity, and feeding behavior

Phytoplankton exhibit a diversity of morphologies, nutritional values, and potential chemical defenses that could affect the feeding and fitness of zooplankton consumers. However, how phytoplankton traits shape plant–herbivore interactions in the marine plankton is not as well understood as for terrestrial or marine macrophytes and their grazers. The occurrence of blooms of marine dinoflagellates such as Karenia brevis suggests that, for uncertain reasons, grazers are unable to capitalize on, or control, this phytoplankton growth—making these systems appealing for testing mechanisms of grazing deterrence. Using the sympatric copepod Acartia tonsa, we conducted a mixed diet feeding experiment to test whether K. brevis is beneficial, toxic, nutritionally inadequate, or behaviorally rejected as food relative to the palatable and nutritionally adequate phytoplankter Rhodomonas lens. On diets rich in K. brevis, copepods experienced decreased survivorship and decreased egg production per female, but the percentage of eggs that hatched was unaffected. Although copepods showed a 6–17% preference for R. lens over K. brevis on some mixed diets, overall high ingestion rates eliminated the possibility that reduced copepod fitness was caused by copepods avoiding K. brevis, leaving nutritional inadequacy and toxicity as remaining hypotheses. Because egg production was dependent on the amount of R. lens consumed regardless of the amount of K. brevis eaten, there was no evidence that fitness costs were caused by K. brevis toxicity. Copepods limited to K. brevis ate 480% as much as those fed only R. lens, suggesting that copepods attempted to compensate for low food quality with increased quantity ingested. Our results indicate that K. brevis is a poor food for A. tonsa, probably due to nutritional inadequacy rather than toxicity, which could affect bloom dynamics in the Gulf of Mexico where these species co-occur.     

A new genus of monstrilloid copepods (Crustacea) with anteriorly pointing ovigerous spines and related adaptations for subthoracic brooding

Maemonstrilla gen. nov. , known exclusively from females, is proposed for Monstrilla longipes A. Scott, 1909, M. turgida A. Scott, 1909, and five new species from coral reef plankton in the Ryukyu Islands, Japan: Maemonstrilla hyottoko sp. nov. (type species), M. polka sp. nov. , M. spinicoxa sp. nov. , M. simplex sp. nov. and M. okame sp. nov. A syntype of M. turgida was examined, but the holotype of M. longipes is lost; the latter species, being similar to several of the new species, is regarded as unidentifiable, and the identity of specimens assigned to it by several authors is put in doubt. Until now, all known female monstrilloids have had posteriorly trailing ovigerous spines, but in Maemonstrilla gen. nov. these spines point anteriorly and hold the egg mass between the legs beneath the thorax. This is the first known instance of subthoracic brooding in a planktonic copepod; its functional significance is discussed, and brooding habits of non‐planktonic copepods are briefly reviewed. The intercoxal sclerites of legs 1–4 in Maemonstrilla gen. nov. are very wide, making room for the eggs. In all species except M. turgida comb. nov. , the inner seta of the proximal segment of each leg ramus is either absent or reduced to a nub; this may lessen interference of the egg mass with leg movement. All species have a uniramous leg 5 with two setae, except M. turgida comb. nov. (biramous with setae on both rami); M. turgida comb. nov. is evidently the sister‐group of its congeners, each sister‐group in the genus being defined by additional autapomorphies. Scanning electron micrographs of all the Ryukyuan species except M. simplex sp. nov. are provided; these constitute a preliminary survey of monstrilloid integumental organs and cuticular ornamentation. Among the unusual features are two lobes at the base of the coxa in legs 1–4 of M. polka sp. nov. and M. spinicoxa sp. nov. and two pairs of posterodorsal spine‐like scales on the first and second free pedigers of M. turgida comb. nov. Newly hatched nauplii of M. okame sp. nov. , examined by scanning electron microscopy, are generally similar to those of Monstrilla hamatapex Grygier & Ohtsuka, 1995, but with a different mandibular structure in which the distal hook and seta clearly represent the endopod, not enditic armament of the basis. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 152 , 459–506.