Serotonin immunoreactivity in the nervous system of the free‐swimming larvae and sessile adult females of Stephanoceros fimbriatus (Rotifera: Gnesiotrocha)

Unlike most rotifers (Rotifera), which are planktonic and direct developers, many gnesiotrochan rotifers (Monogononta: Gnesiotrocha) are sessile and have indirect development. Few details exist on larval metamorphosis in most gnesiotrochans, and considering the drastic transformation that takes place at metamorphosis—the replacement of the ciliated corona with a new head that bears ciliated tentacles (the infundibulum)—it is perhaps surprising that there are limited data on the process. Here, we document part of this metamorphosis by examining the presence and distribution of neurons with serotonin immunoreactivity in the nervous system of both planktonic larvae and sessile adult females. Using antibodies against serotonin combined with confocal laser‐scanning microscopy (CLSM) and 3D reconstruction software, we mapped the immunoreactive cell bodies and neurites in both life stages and found that relatively few changes occurred during metamorphosis. The larvae possessed a total of eight perikarya with serotonergic immunoreactivity (5HT‐IR) in the brain, with at least two pairs of perikarya outside the brain in the region of the corona. Cells with 5HT‐IR in the brain innervated the larval corona and also sent neurites to the trunk via the nerve cords. During metamorphosis, the corona was replaced by the infundibulum, which emerged from the larval mouth to become the new functional head. This change led to a posterior displacement of the brain and also involved the loss of 5HT‐IR in the lateral brain perikarya and the gain of two perikarya with 5HT‐IR in the anterior brain region. The innervation of the anterior end was retained in the adult; neurites that extended anteriorly to the mouth of the larva formed a distinct neural ring that encircled the infundibulum after metamorphosis. Significantly, there was no innervation of the infundibular tentacles by neurites with 5HT‐IR, which suggests that ciliary control is unlikely to be modulated by serotonin within the tentacles themselves.     

Neuromuscular organization of the freshwater colonial rotifer, Sinantherina socialis, and its implications for understanding the evolution of coloniality in Rotifera

Coloniality among rotifers is rare, and while the adaptive significance of the lifestyle has been explored previously, there are few details about how it may have influenced the morphology of colony members. In this study, we use confocal laser scanning microscopy combined with cyto- and immunohistochemistry to determine if the colonial rotifer, Sinantherina socialis, differs in neuromuscular organization relative to other colonial and solitary forms. Our observations indicate that the patterns of serotonergic neurons and somatic muscles in S. socialis are broadly similar to other rotifers. At the neuronal level, the distribution of serotonergic (5HT-IR) neurons in S. socialis is most similar to colony-forming species of Conochilus: (1) paired nerve cords extend the length of the body; (2) the cerebral ganglion innervates the corona with paired neurites that form a neuronal ring; and (3) a single pair of neurites innervates the ventral sensory antennae. Unique to S. socialis is the presence of two additional neuronal rings that supply the corona and may function to modulate ciliary beat. At the muscular level, S. socialis displays a typical pattern of somatic muscle organization similar to other rotifers, but diverges from the pattern in three significant ways: (1) somatic circular muscles form complete rings; (2) circular muscles are distinguishable based on their size and position in the body; and (3) transverse muscles are present within the corona and presumably function to modify its shape for feeding and defensive purposes. These differences in neuromuscular organization may be adaptations to the colonial and/or sessile lifestyle, both of which are characteristic of S. socialis.     

Analysis of the aggregation behavior in the larvae ofHarmonia axyridis Pallas (Coleoptera: Coccinellidae) to prey colony

Summary The searching and handling behaviors ofHarmonia axyridis larvae to the colony ofRhopalosiphum padi were experimentally examined and the processes of their aggregation to the prey colony was analyzed. All the instar larvae searched for the prey at random and they have no preference to the prey colony, but except the 1st instar they tend to aggregate to the plants with prey colonies. The 1st instar larvae tend to stay on the plants they once located. The 2nd to 4th instar larvae often emigrate from the plants without prey colony but seldom emigrate from the plants with prey colonies, and consequently, they aggregate to the plants with prey colonies. The expense of time to eat prey (in the 2nd and 3rd instars) and the change of searching behavior for the prey after feeding (in the 3rd and 4th instars) are responsible for the larval concentration to prey colony as a trapping effect for predators to prey colony.     

Release of planula larvae, settlement and development of Siderastrea stellata Verrill, 1868 (Anthozoa, Scleractinia)

We herein provide the first observations on planulation, larval development, and metamorphosis of Siderastrea stellata, an endemic reef-building species that occurs along the northeastern and southeastern coasts of Brazil. The release and settlement of larvae were observed in two distinct periods. The first started 3 days after collection on January 28 during the last quarter, whereas the second started 2 months later, on April 10 during the change from new moon to the first quarter. Planulation continued throughout approximately 48 h. Brooded larvae released from the mouth contained zooxanthellae, and underwent settlement after 48 h. Newly extruded larvae stayed in close contact with parental polyps. Fusion was observed among larvae from the same colony. The first septal cycle was formed by day 2–3, while the third cycle of exosepta became evident 15 days after protosepta development. The development of the corallite of primary polyp was slow, and after 9 months of analyses no evidence of budding was obtained, this indicating that colonial development is likely to be a late event in the S. stellata life history.     

Prey availability and eclosion-help of callow workers in the formicine ant Camponotus mus

Summary In the ant Camponotus mus the eclosion of imagines from the cocoons was shown to be controlled by nurse workers, which broke the cocoons and assisted the callows to energe. Short-term colony prey deprivation modified the eclosion-help behavior resulting in a delay in cocoon opening times. During long-term prey deprivation, no new cocoons were spun; the starved larvae grew and pupated when prey was again available. These findings as a colony strategy adapted to the changing condition of prey availabitity in a temperate habitat are discussed.     

Morphology of Floscularia ringens (Rotifera, Monogononta) from egg to adult

Abstract. Floscularia ringens is a cosmopolitan, sessile rotifer (class Monogononta) that lives inside a tube it constructs from numerous small, rounded pellets. Adults of F. ringens produce parthenogenetic eggs that are retained within the tube. Upon hatching, juveniles remain within the maternal tube for a short time completing their development before swimming away. The free-swimming juvenile has a conical body, short foot, small corona, and mastax with trophi, but appears unable to feed. After a short time (<1 day), the young rotifer attaches permanently to a substrate and its morphology changes radically: the corona develops 4 wide lobes and the foot elongates, becoming slender and retractable. Once the corona has developed, the young animal begins to feed by producing filtering currents, and also starts to build its own tube. Here we report 4 new morphological details regarding this species. (1) A specialized epidermal groove is present on the trunk in front of the cloaca. (2) A small hole is located in the center of the inner surface of each pellet of the tube. (3) The muscles inside the foot are U-shaped in transverse section. (4) The size of the trophi remains unchanged during growth of the juvenile into an adult.     

Early collapse of Vespa simillima (Hymenoptera, Vespidae) colonies in central Japan

During the past 15 years in the Ina Valley, Japan, mature fifth instar larvae of the yellow hornet, Vespa simillima, have been occasionally ejected from colonies during September. During 2005, this unusual behavior was particularly widespread, and collection of several V. simillima colonies confirmed that very few fifth instar larvae were present. When compared with an average colony, constructed from 41 colonies collected 20 years previously, colonies in 2005 had 80% fewer fifth instar larvae, despite queen egg‐laying rates remaining similar. It may be that the amount of food provided to the larvae by workers is less than the amount of larval secretions received by workers, which is causing the larvae to become emaciated and preventing them from pupating. This phenomenon normally occurs naturally at the end of the colony cycle in November, when prey abundance decreases and larval secretions or other sources of carbohydrates, for example from ripe fruit, tree sap, or aphid secretions, are needed by sexuals to build up fat reserves. However, another possibility is that the unexplained appearance of this phenomenon in September, which is causing colonies to collapse without producing any or very few sexuals, is due to foragers feeding the larvae prey that are contaminated with insect growth regulators, via pesticides, which are known to prevent successful pupation.     

Predatory behavior of Cupelopagis vorax (Rotifera; Collothecacea; Atrochidae) on protozoan prey

By rotating on a short, flexible, pedal stalk, Cupelopagis vorax captures prey that traverse the substratum to which this sessile rotifer attaches. Microvideographic analysis (including slow motion and freeze-frame) permitted us to examine some of the details of Cupelopagis foraging behavior. When undisturbed, Cupelopagis usually faces forward in a resting or neutral position (NP) with its unciliated infundibulum (corona) directed parallel to the surface of the substratum. However, vibrations produced by artificial means (fine pins) or small prey (protists) evoke unique behaviors in Cupelopagis. Our analysis of Cupelopagis foraging on two protozoan prey (Paramecium bursaria and a small, unidentified flagellate, SUF) indicates that this predator possesses a 360 ° encounter field (EF) biased towards the NP Size of the EF appears to be a function of both predator and prey size, but it extends at least 650 µm, as measured from the point of attachment of the predator's pedal stalk to the substratum. When a prey comes close to Cupelopagis, this predator can lean toward the organism, stretching forward on its pedal stalk and extending its corona over the prey in a swift motion (< 0.5 s). Probability of capture after attack was a function of prey type (61.6% for P. bursaria and 41.5% for the SUF). Analysis of prey capture by Cupelopagis indicates that this predator has a handling time ranging from a few seconds to several minutes: 24.6 ± 16.8 s for P. bursaria (n= 274) and 34.6 ± 25.4 s for the SUF (n=111). Occasionally Cupelopagis sweeps part of the EF by retracting its corona, turning to the right or left (mean angle subtended 63 ° ± 42 °), unfolding the corona, and slowly returning to the original resting position. This behavior, termed surveillance, occurs in the presence or absence of prey. While not unique in its ability to detect water movements, Cupelopagis is the only rotifer known to exhibit specific behaviors to vibrations produced by potential prey.     

Induction of Settlement and Metamorphosis of the Veliger Larvae of the Nudibranch,Onchidoris bilamellata

Summary

Onchidoris bilamellata veligers were reared in the laboratory on a combination of phytoñagellates and diatoms. They attained metamorphic competence after a period of 28 to 32 days at 11°C, or 60 to 80 days at a temperature averaging 7.5° C.

Experimental evidence suggests that settlement is stimulated by a diffusible chemical emanating from living barnacles, whereas metamorphosis is induced by a chemical or mechanochemical cue, which is also associated with barnacles. Settlement and metamorphosis are considered to be separable events in O. bilamellata. The settlement response is reversible and can be repeated; it involves a characteristic behavioral repertoire including descent to the bottom, foot contortions and crawling on the pedal sole. Settlement occurs only in seawater that contains, or had previously contained, living barnacles. Metamorphosis is irreversible and involves the resorption of the velum, loss of the larval shell, and incorporation of the visceral mass into the cephalopedal mass. Metamorphosis is triggered only when physical contact with living or dead barnacles is made (dead barnacles refers to shell and tissue fragments which are only effective in inducing metamorphosis when they are used in combination with seawater that had previously contained living barnacles).

Settlement and metamorphosis in O. bilamellata is compared with that of other nudibranch species, and its unique settlement response is discussed.     

Preliminary data on size composition and settlement ofDreissena polymorpha (Pallas) (Mollusca: Bivalvia) in lakes differing in trophic state

Size composition of colonies and settlement of larvae on nylon substrates as function of depth inDreissena polymorpha demonstrated differences in three lakes of different trophic state. In one lake, the data on size distribution in the colony and of the settled larvae also differed. The explanation requires further research.     

Cooperation during prey digestion between workers and larvae in the ant, Pheidole spadonia

Digestion and distribution of nutrients are central to the growth and reproduction of social insect colonies, just as they are to individual organisms. In the case of eusocial insect species, different components of food handling and processing can be distributed among castes. This paper reports on an ant species, Pheidole spadonia, in which the adult workers butcher prey and 4^th instar larvae dissolve prey for distribution among other colony members including workers, larvae and queens. To characterize the process, six groups, each composed of twenty-five workers and thirty larvae, were provisioned with a fruit fly carcass, and then video-taped continuously for 24 hours. On average, five adult workers and twenty-two 4^th instar larvae invested 12.8 labor hours into butchering and predigesting one fly carcass. Workers contributed a mean total of 3.3 labor hours to butcher the carcass into small fragments. Fourth instar larvae contributed a mean total of 9.5 labor hours to pre-orally dissolve the solid fragments. Surprisingly, larvae did not ingest during the dissolving process. Instead, workers ingested the dissolved prey tissue into their crops and then regurgitated it to colony members, larvae and workers, that solicited for feedings. The cooperative interactions reported here between workers and larvae extend the mechanistic and evolutionary explanations for eusociality. Received 13 January 2005; revised 22 April 2005; accepted 25 April 2005.     

The effects of the excretory-secretory products of fouling organisms on settlement of larvae of the sponge Halichondria panicea (Pallas, 1766) (Porifera: Demospongiae)

The effects of the excretory-secretory products (ESPs) of several fouling organisms on the larvae of the sponge Halichondria panicea were assessed in laboratory experiments. The ESPs of the brown alga Laminaria saccharina significantly stimulated larval settlement and metamorphosis, while the metabolites excreted by conspecific adult colonies were harmful to H. panicea larvae. The ESPs of the ascidians Styela rustica and Molgula citrina and the blue mussel Mytilus edulis impeded both the settlement and metamorphosis of the sponge larvae to varying degrees. The chemical cues of the bivalve Hiatella arctica had no significant effect on the number of settled larvae of H. panicea but retarded their metamorphosis.     

Chemical induction of settlement and metamorphosis of Capitella capitata Sp. I (Polychaeta) larvae by juvenile hormone-active compounds

Summary

The influence of juvenile hormone (JH)-active chemicals on the settlement and metamorphosis of metatrochophore larvae of the polychaete annelid Capitella sp. I of the Capitella complex has been investigated. These studies demonstrate that JH-active chemicals are able to induce settlement and metamorphosis of Capitella larvae, and that these effects may possibly be mediated by protein kinase C induction. Evidence for the presence of JH-active compounds in marine sediments is also presented, suggesting that these chemicals may serve a natural role as chemical cues for settlement and metamorphosis for Capitella larvae in the marine environment.     

Intraspecific variation in Gape–prey size Relationships and Feeding Success During Early Ontogeny in Red Drum, Sciaenops Ocellatus

The relationship between predator gape and prey consumption in laboratory-reared larva and field-caught early juvenile red drum, Sciaenops ocellatus, was investigated in light of the hypothesis that feeding success varies throughout the early life history intervals of marine fishes. We expected the feeding ability of red drum to be more strongly constrained by mouth gape in smaller fish and expected this ability to improve with gape size. To test this hypothesis, field-caught, early juvenile red drum were examined to determine the relationship between gape size and prey size consumed. In field-caught early juveniles, gape (height and width) and prey size consumed (length and width) increased linearly with standard length (SL); however, mean width of prey consumed was only 20–47% of gape width. Furthermore, when regressed on SL, gape width yielded a higher slope than prey width. To further test this hypothesis on less developed, pre-metamorphic fish, age-specific differences in gape, number of prey and size of prey consumed prior to metamorphosis were determined from laboratory-reared red drum larvae. Similar patterns were observed for gape height– and gape width–SL relationships in laboratory-reared red drum larvae. Size of consumed prey increased from three days from hatching (dfh) to 18dfh. The percentage of feeding larvae also increased from 3% at 3dfh to 97% at 18dfh. In both field-caught, early juvenile red drum and laboratory-reared larvae, there was little evidence that the size of prey consumed was constrained by mouth gape. It is hypothesized that besides gape size, the development of other features of the feeding mechanism (e.g., hyoid and opercular series) influences prey-capture performance prior to settlement in marine fishes.     

Growth-related changes in predation behavior in incipient colonies of the ponerine antEctatomma tuberculatum (Olivier)

Summary We traced the development in the laboratory of 18 young colonies of the arboricolous ponerine antEctatomma tuberculatum. Colony foundation is of the partially-claustral type. During the early stages, when the colony is entirely dependent on the queen's behavior, the growth of the colony in terms of number of workers produced over time was relatively predictable. Afterwards, divergence in colony growth in function of the time increases as fast as the number of workers influences the efficiency of colony provisioning.Comparative analysis indicated clear changes in the predation behavior of foundresses and workers as colonies developed. For any stage of colony growth, all individuals provisioned the nest with dead prey or sugar-rich substances in the same way. However, prey hunting involves two different strategies. Foundresses and nanitic workers (originating from colonies with 9–15 workers) foraged actively, catching prey as the result of random encounters. Post-nanitic foragers (originating from colonies with 20–30 workers) and those from nature colonies developed an ambush strategy. Workers in these colonies gained experience at catching and handling prey during a period when they acted as nest guards, and so tended to be more efficient hunters than poorly experienced foundresses or nanitic foragers. The change in strategy was also positively correlated with an increase in the size of workers as the colony matured. A stable maximum in workers size is apparently reached only after the appearance of efficiently hunting foragers, presumably in numbers sufficient to provide adequate quantity and quality of larval food. Such a correlation between worker size and colony growth, assumed general for all ants, has not been demonstrated for Ponerinae before this work.     

Size dependence of composition, photosynthesis and growth in the colony-forming freshwater ciliate, Ophrydium versatile

1. Ophrydium versatile is a symbiotic ciliate which forms gelatinous colonies up to several centimetres in diameter in transparent temperate lakes. The ciliates are evenly spaced at the colony surface and constitute a small proportion of the surface area (7%) and volume (3.1%) of the colony, but a large proportion of organic carbon (74%) and nitrogen content (82%) (exemplified for 1 cm³ colonies). The majority of the colony volume is formed by the jelly. The biomass proportion of ciliates scales inversely with colony size, following the decline of surface area to colony volume. The largest colonies found in Danish lakes in early summer contain almost 1 million ciliates, and assuming they derive from a single ciliate undergoing exponential division, they need twenty generations and, presumably, almost a year to reach maximum size. 2. The ciliates contain numerous symbiotic zoochlorellae that constitute about 10% of ciliate volume and more than half of the carbon content. Zoochlorellae dominate oxygen metabolism of the assemblage, resulting in low light compensation points, a large diel photosynthetic surplus, and a marked dependence on light for sustained growth and ciliate metabolism. Estimated gross photosynthesis (7ng C ciliate^?1 day^?1) of Ophnrydium from shallow, clear waters in June greatly exceeded the estimated carbon contained in filtered bacteria and small algae (1.9ng C cilicate^?1 day^?1). Nitrogen and phosphorus content of the prey, however, may provide the main nutrient source consistent with the correspondence between mass-specific rates of nutrient uptake and measured relative growth rates (average 0.067 day^?1, generation time 10 days). 3. The large Ophrydium colonies require increased allocation of photosynthetic carbohydrates with increasing colony size to maintain the jelly. The large colonies tend to become gas-filled, floating, mechanically destroyed and their ciliate inhabitants abandon them as swarmers. Colony formation, however, should offer protection against predators which may be more important for the natural abundance than the costs of growing in a colony.     

Larval behaviour and choice of settlement site: Correlation with environmental distribution pattern in an erect bryozoan

Summary This paper concerns the preferred environmental conditions for settlement and metamorphosis of larvae of the erect, rigidly calcified cheilostome bryozoanSchizotheca serratimargo and compares the settlement preferences with in situ distribution of adult colonies. A review of bryozoan larval behaviour and responses to environmental parameters is given in order better to understand larval settlement and metamorphosis in this species. Release of larvae ofS. serratimargo (Hincks) was induced so that each travelled down a path with a limited set of microenvironments in which it could choose to settle. Four different flow velocities, three different depths below the water surface, two different light intensities, three different orientations of plexiglas surfaces, and subdivision of distance of travel into three segments, yielded 216 microenvironments. 466 larvae successfully settled and metamorphosed within the experimental chamber. They metamorphosed in significantly higher numbers in microenvironments with low flow velocity, in the shallowest of the three possible depths, in darker areas, and on nonoverhanging surfaces with little or no sediment. The most important stimulus for settlement was darkness, especially where there was a strong gradient in light intensity.S. serratimargo grows as erect bilaminate bushes on protected flanks of boulders, in small caves, and just within the entrances of larger caves at depths of 5–30 m, as well as on hard debris on open muddy sand floors at 30–35 m depth in the Adriatic and Mediterranean Seas. The experimentally-determined settlement patterns suggest that recruitment is more important than post-settlement interactions or exposure to physical damage in determining local distribution of the species.     

Processes affecting newly-settled juveniles and the consequences to subsequent community development

Summary

Processes affecting the growth and mortality of the juvenile benthic life-stages that immediately follow larval metamorphosis and settlement are as important as those processes controlling the supply of settling larvae or later interactions among established adults. In addition, the ecology of juveniles is of ten distinctly different from that of other life-stages, including differences in interactions with predators and competitors and responses to the physical environment. In particular, newly-settled stages of ten experience quantitatively or qualitatively different predation than older life-stages. We have documented this in a New England hard substrate community where the wrasse, Tautogolabrus adspersus, and two species of tiny gastropods, Mitrella lunata and Anachis lafresnayi, prey on newly-settled andjuvenile ascidians but not on adults. An extensive series of field experiments was conducted using artificial pilings placed subtidally. Results demonstrated that (1) the predators were extremely active and fairly specific in their prey, (2) predators could eliminate prey species regardless of settlement densities, (3) predation varied drastically with life-stage, and (4) predators control community structure and composition by altering the number of settling larvae that survived their first several weeks to become identifiable recruits. Because of differences in predator abundances the development and species dominance within the community varied drastically between sites.