A quantitative analysis of exopodite beating in the larvae of the lobster Homarus gammarus (L.).

Raw data on exopodite beating in the first three developmental stages of the lobster Homarus gammarus were collected and analysed for key beating parameters. The analysis was computer assisted and the main procedures used are described. Beating patterns are the same in all three stages and are usually very regular although perturbations do occur (figures 1, 2). When beating stops the deceleration and subsequent re-acceleration is very rapid (figure 1) and limb movement sequences usually start posteriorly and move forwards (figures 1, 2d). Ipsilateral phase relations are generally maintained at 0.4-0.6 (figures, 3,4) and while the coupling between adjacent exopodites is usually stronger than for those further apart various deviations from this are occasionally seen (figure 5). No significant correlation between the ipsilateral phase relations of adjacent exopodites and base cycle duration was detected for any of the stages (figure 6). Contralateral phase relations undergo a constant progression (figures 7, 9) and this was found to be due to a heterodyne effect (figure 8) also described as gliding coordination. The powerstroke/returnstroke ratio for all stages was approximately 0.5 (figure 10) and no significant correlation was found with cycle duration (figure 11). The only substantial difference between the three larval stages which was noted was that of cycle duration, the cycles of stage III being shorter than those of the first two stages. The exopodite beating pattern was discussed in context with other metachronously cycling systems in arthropods and the implications of the present study discussed.     

Asynchronous swimmeret beating during defense turns in the crayfish, Procambarus clarkii

Swimmeret beating was monitored in freely moving specimens of the crayfish Procambarus clarkii as they exhibited defense turn responses to tactile stimuli. Analysis of videotape records revealed alterations in swimmeret beating during turning responses compared to straight, forward walking. During turns, swimmerets beat with shorter periods and smaller amplitude power strokes than during straight walking. Coordination between swimmerets also changed. Swimmerets on the side toward which the animal turned tended to lag behind their contralateral partners, rather than beat in synchrony as in straight walking, and ipsilateral coordination was loosened relative to straight walking. Asynchronous swimmeret beating accompanied asymmetric motions of the uropods in a manner similar to that observed during statocyst-dependent equilibrium reactions in P. clarkii, but removal of the statoliths did not eliminate turn-associated responses of the swimmerets. The coordinated action of the swimmerets and uropods may contribute to the torque that rotates the animal in the yaw plane. Implications of the observed changes in swimmeret coordination for understanding the underlying neuronal control system are discussed.     

The phase of sperm flagellar beating is not conserved over a brief imposed interruption

We have studied the phase component of flagellar beating by holding the head of a sea urchin sperm in the tip of a sinusoidally vibrating micropipet and then abruptly displacing the pipet laterally at a speed of 2.5 microns/ms for various durations. This rapid displacement of the pipet delayed the initiation of the next bend for as long as the displacement continued, up to a duration of 1 beat cycle, corresponding to a delay of 0.5 beat cycle. At the end of this displacement, the movement of the pipet was stopped completely without resumption of the initial vibration. Analysis of the flagellar waveform showed that immediately when the pipet was stopped, the flagellum started to beat by spontaneously initiating the bend that had been delayed. The flagellum then continued steady-state beating, with normal waveform and a new phase that was independent of the original phase of beating. These data suggest that the information on the phase of beating is located only at the basal end of the flagellum, and not in oscillators distributed along the axoneme. After this information has been lost, the flagellum can resume beating at any arbitrary phase relative to its original phase.     

Sensory and skeletal development and growth in relation to the duration of the embryonic and larval stages in damselfishes (Pomacentridae)

Several trends were found in comparisons of rates of growth and development of larvae of four coral-reef damselfishes ( Chromis atripectoralis, Pomacentrus amboinensis, Premnas biaculeatus, Acanthochromis polyacanthus ), which were reared under constant temperature conditions in the laboratory, and which varied in their early life stage durations (respectively, egg stage durations were 2, 4, 7, 16; larval stage durations were 25, 23, 14, 0). Parameters measured included standard length, muscle area, eye diameter, and selected stages of retinal development, olfactory development, and skeletal ossification. Rates of ossification and olfactory development were inversely related to growth rate (in length and muscle area) among most species. Rates of eye growth and retinal development were also negatively correlated among all species. These results are consistent with the concept of a trade-off between growth and development. We observed a positive relationship between egg stage duration and developmental rate, and a negative correlation between larval stage duration and developmental rate. Acanthochromis developed slower than predicted by the general trends, although retinal development was very rapid. Specific retinal stages correlated with settlement, regardless of ontogenetic rates. Olfactory development was especially rapid in the anemonefish Premnas biaculeatus , which imprints to olfactory cues as an embryo. Skeletal ossification was rapid in species with pelagic larvae, and much slower in the benthic brooder. Literature-derived data on size and age at hatching and settlement from > 40 species of tropical pomacentrids were transformed into growth and developmental rates; correlations of these literature-derived parameters were mostly consistent with our controlled four-species comparison.  © 2003 The Linnean Society of London, The Biological Journal of the Linnean Society , 2003, 80 , 187−206.     

Influence of walking on swimmeret beating in the lobster Homarus gammarus

Influence of walking on swimmeret beating in intact lobsters, Homarus gammarus, has been analyzed using a treadmill experimental device. Belt movement activates both leg stepping and swimmeret beating. The simultaneity of the onset of the two motor systems in this situation is demonstrated to be the result of a startle response initiated when the belt begins to move. This reaction consists of a non-specific motor activity involving several antagonist postural and dynamic muscles. Abdominal extension and vigorous swimmeret beating are the main featurs of this reaction. The main characteristics of the swimmeret beating as defined by Davis (1969) has been observed here in sequences without walking. However during long walking sequences a very different swimmeret beating pattern occurs. It is suggested that this slow swimmeret beating is completely subordinate to the walking rhythm during sequences of absolute coordination. In more rapid swimmeret beating a relative coordination with leg stepping is very common. The functional meaning of this linkage between legs and swimmerets is discussed.     

Larval and post-larval development of the branchiopod clam shrimp Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Conchostraca, Spinicaudata)

The larval and post-larval development of Cyclestheria hislopi is examined by SEM. There are at least nine stages (excluding the adult) – six larval and three post-larval stages. The first four stages are passed within the egg-membrane. The larval and the post-larval phase are separated by a profound change in morphology that takes place between stages VI and VII. The larva shifts from a dorso-ventrally flattened 'larval' appearance up to stage VI to a laterally flattened, more 'adult' appearance from stage VII. New morphological data have been revealed by this study, including (1) a large and globular larval dorsal organ; (2) the carapace starts its development from the segments of the first and second maxillae; (3) the anterior ramus of the second antenna in adult Cyclestheria hislopi is the endopod, and the posterior ramus the exopod. Direct development of the brood in Cyclestheria hislopi – unique among conchostracans – is compared with that of the Cladocera. If Cyclestheria is the sister group to the Cladocera, as favoured in this work, the classical neoteny theory of the Cladocera must be reconsidered, as there is no particular similarity between any adults of the Cladocera and any of the larval stages of Cyclestheria . It is suggested that Cyclestheria displays the type of development present in a cladoceran ancestor. A comparison between Cyclestheria and the Upper Cambrian 'Orsten' fossil Rehbachiella kinnekullensis reveals a remarkable similarity in the endite morphology of the trunk limbs.     

Larval retention and dynamics of the prawns Palaemon longirostris H. Milne Edwards and Crangon crangon Linnaeus (Decapoda,Caridea) in the Mira estuary,Portugal

Summary

Palaemon longirostris and Crangon crangon larval and post-larval stages were collected intensively in two 24-h cycles during neap and spring tidal periods in a fixed station located in the mid-Mira estuary (southwest Portugal). In each case, on the previous day, horizontal distribution of larval stages was studied in a series of 20 stations from the mouth of the estuary to near freshwater. Horizontal distribution of the discrete instars of both species were similar, suggesting larval retention. Results from the 24-h cycles indicate a semilunar cycle of larval release activity, and an initial displacement of the larvae from the parental stock, as newly-hatched larvae concentrate in the surface layer of the water column on post-crepuscular ebbing tides. The sequence of larval stages tends to be progressively more dependent of the bottom layers, and the whole larval and post-larval development is accomplished within the estuarine boundaries. Larval release cycles, coupled with duration of development and progressive change in vertical position, induce mutual exclusion of different aged larvae, which may minimise cannibalistic behaviour and competition between larvae with different capabilities.     

Tactile stimulation of the swimmeret alters motor programs for abdominal posture in the lobsterHomarus americanus

The influence of mechanosensory stimulation of a second segment swimmeret upon the abdominal postural program was examined in an isolated abdominal nerve cord-swimmeret preparation. The swimmeret was stimulated in several different ways to assess the extent of influence exerted on abdominal positioning. Localized tactile stimulation of the swimmeret surface with a mechanical probe usually generated flexion inhibition where the flexor inhibitor (f5) was activated while the small and medium flexor excitors were inhibited. Flexion inhibition was much stronger in females than males. In 50% of the animals a weak flexion excitation was seen. After 3-6 hours the response of one-third of these preparations changed to flexion inhibition. Strong manual stimulation of the swimmeret surface inhibited all of the flexor excitors (f1, f2, f3, f4, and f6) while exciting the inhibitor f5 and increasing extensor activity. Similar extension responses were observed in both sexes. Repeated tactile stimulation of the swimmeret surface elicited a response similar to that evoked during manual stimulation. The strongest extension response was produced at 2 Hz which falls within the normal range of swimmeret beating in intact lobsters. Similar extension responses were also obtained during spontaneous swimmeret beating and rhythmic manual movement of the swimmeret.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variation in the level of free amino acids during larva development of Penaeus japonicus (Crustacea, Decapoda, Penaeidae]

Variations of free amino-acids (FAA) content during the larval development of Penaeus japonicus have been studied. FAA content increases from 83 to 687 mumoles/g dry weight from egg to post-larval (20 days old: P20) development. There is a sharp increase between zoe and mysis stages, and another one between one day post-larvae (P1) and P20. After the mysis stage, free essential and non essential amino-acids evolve in a different way: the non essential FAA content, mainly glycine, increases continuously, whereas essential FAA content decreases (about 40%) from the mysis stage to metamorphosis in post-larvae (P1). FAA content evolution during larval development exhibits the same trend as the variation of the digestive enzyme activity.     

Early innervation of abdominal swimmeret muscles in developing lobsters.

The swimmerets in the abdomen of the lobster Homarus americanus are paired external appendages whose back and forth propulsive movements are brought about largely by a group of power and return stroke muscles located in the lateral abdominal cavity. We find functional innervation of these muscles by several excitatory axons and a single inhibitor in embryonic and stage 1 larval lobsters before the external appendages are even formed. This early innervation is via a few nerve bundles in which branches of the motor axons are intertwined in a complex manner. As the swimmerets develop to maturity in later larval and juvenile stages, the innervation consisting usually of several excitor and a single inhibitor synaptic terminals becomes localized to individual muscles. Patterned synaptic activity in these muscles was not seen in the embryonic and larval stages but has been shown in early juvenile stages, when it coincides with the onset of rhythmic movement of the swimmerets. Consequently, such early innervation of the swimmeret muscles may be influential in establishing the central circuitry for the generation of patterned activity, a possibility that was discounted in a previous study (Proc. Natl. Acad. Sci. USA, 70:954-958).     

A Large-Scale Pattern of Ontogenetic Shape Change in Ray-Finned Fishes

Fishes exhibit a remarkable diversity of body shape as adults; however, it is unknown whether this diversity is reflected in larval stage morphology. Here we investigate the relationship between larval and adult body shape as expressed by body elongation. We surveyed a broad range of ray-finned fish species and compared body shape at larval and adult stages. Analysis shows that the vast majority of fish are more elongate at the larval stage than at the adult stage, and that adults display greater interspecies variation than larvae. We found that the superorder Elompomorpha is unique because many species within the group do not follow the observed elongation trends. These results indicate that much of the diversity observed in adults is achieved in post-larval stages. We suggest that larval morphology is subject to common constraints across the phylogeny.     

Hyperactivation is the mode conversion from constant-curvature beating to constant-frequency beating under a constant rate of microtubule sliding

Flagellar beating of hyperactivated golden hamster spermatozoa was analyzed in detail using digital image analysis and was compared to that of nonhyperactivated (activated) spermatozoa in order to understand the change in flagellar beating during hyperactivation and the active microtubule sliding that brought about the change in flagellar beating. Hyperactivated flagellar beating, which was characterized by a sharp bend in the proximal midpiece and low beat frequency, was able to alter the waveform with little change in beat frequency (constant-frequency beating), whereas activated flagellar beating, which was characterized by a slight bend in the proximal midpiece and high beat frequency, was able to alter beat frequency with little change in the waveform (constant-curvature beating). These results demonstrate that flagellar beating of hyperactivated and activated spermatozoa were essentially different modes and that hyperactivation was the mode conversion from constant-curvature beating to constant-frequency beating. Detailed analysis of flagellar bends revealed that the increase in curvature in the proximal midpiece during hyperactivation was due to the increase in total length of microtubule sliding in a nearly straight region between bends, while the rate of microtubule sliding remained almost constant.     

An electro-optic monitor of the behavior of Chlamydomonas reinhardtii cilia

The unicellular green alga Chlamydomonas reinhardtii steers through water with a pair of cilia (eukaryotic flagella). Long-term observation of the beating of its cilia with controlled stimulation is improving our understanding of how a cell responds to sensory inputs. Here we describe how to record ciliary motion continuously for long periods. We also report experiments on the network of intracellular signaling that connects the environment inputs with response outputs. Local spatial changes in ciliary response on the time scale of the underlying biochemical dynamics are observed. Near-infrared light monitors the cells held by a micropipette. This condition is tolerated well for hours, not interfering with ciliary beating or sensory transduction. A computer integrates the light stimulation of the eye of Chlamydomonas with the ciliary motion making possible long-term correlations. Measures of ciliary responses include the beating frequency, stroke velocity, and stroke duration of each cilium, and the relative phase of the cis and trans cilia. The stationarity and dependence of the system on light intensity was investigated. About 150,000,000 total beat cycles and up to 8 h on one cell have been recorded. Each beat cycle is resolved so that each asynchronous beat is detected. Responses extend only a few hundred milliseconds, but there is a persistence of momentary changes that last much longer. Interestingly, we see a response that is linear with absolute light intensity as well as different kinds of response that are clearly nonlinear, implying two signaling pathways from the cell body to the cilia.     

Induction of reverse development in two marine Hydrozoans

Cnidarians are unique organisms in the animal kingdom because of their unequalled potential to undergo reverse development (RD). The life cycle of some species can temporarily shift ordinary, downstream development from zygote to adult into the opposite ontogenetic direction by back-transformation of some life stages. The potential for RD in cnidarians offers the possibility to investigate how integrative signalling networks operate to control directionality of ontogeny (reverse vs. normal development). Striking examples are found in some hydrozoans, where RD of medusa bud or liberated medusa stages leads to rejuvenation of the post-larval polyp stage. Artificial stress may determine ontogeny reversal. We describe here the results of experimental assays on artificial induction of RD by different chemical and physical inducers on two marine hydrozoans, Turritopsis dohrnii and Hydractinia carnea, showing a different potential for RD. A cascade of morphogenetic events occurs during RD by molecular mechanisms and cellular patterns recalling larval metamorphosis. For the first time, we show here that exposure to cesium chloride (CsCl), an inducer of larval metamorphosis, may also induce RD, highlighting similarities and differences between these two master ontogenetic processes in cnidarians.     

Mechanosensory afferents innervating the swimmerets of the lobster

The mechanosensory innervation of the lobster (Homarus americanus) swimmeret was examined by electrophysiologically recording afferent spike responses initiated by localized mechanical stimulation of the caudal surface of the swimmeret. Two functional groups of subcuticular hypodermal mechanoreceptors innervate the swimmeret. Afferents of one group innervate the small discrete "ridges" of calcified cuticle lining the margins of both swimmeret rami. Putative ridge receptors are bipolar sensory neurons responding phasically to deformation of the ridge cuticle with the number and frequency of impulses produced dependent on stimulus strength and velocity. Afferents of the second group, which innervate substantial areas of hypodermis underlying the soft, flexible cuticular regions of the swimmeret, were designated "wide-field" hypodermal mechanoreceptors. These neurons have multiterminal receptive fields and respond phaso-tonically to cuticular distortion. The response properties of both types of hypodermal mechanoreceptors imply that they are activated during the characteristic beating movements of the swimmerets.     

Epimorphosis and repair processes of schistomelic pedipalps and walking appendages in <Emphasis Type="Italic">Tegenaria atrica</Emphasis> (Araneae,Agelenidae)

Experimental studies of regeneration and repair processes of schistomelic walking legs and pedipalps in the early postembryonal stages of Tegenaria atrica were carried out in two parts. In the first part changes in the structure of appendages were produced by exposing the developing embryos to alternating temperatures (14 and 32°C, changing every 12 hours) as teratogenic factor. In the second, principal, part of studies after amputating a given fragment of a larval schistomelic appendage the appearance, then the growth and development of the external regenerates were observed. The completion of epimorphosis of the pedipalps followed at nymph IV stage (after four post-larval moults) that of the walking appendages in most cases at nymph V stage (after five post-larval moults). In control spiders repair processes were noted, which proceeded at a rate comparable to regeneration processes.     

Coexistence of Competing Parasitoid Species on a Host with a Variable Life Cycle

Several special cases of a general model in which two parasitoid species attack different developmental stages of a single host species are presented. The inclusion of different mathematical forms of a maturation weighting function allows us to investigate the effect of several aspects of variation in immature stage durations on the outcome of competitition between the parasitoids. The two parasitoid species cannot coexist if the host developmental stages are fixed in duration. The outcome of competition depends in part on the relative duration of the two stages attacked by the parasitoid species. However, coexistence is possible if there is sufficient variation in the time that different host individuals remain in each stage. Distributed host developmental delays promote coexistence because they cause the host population to be composed of a mixture of host types with different relative egg versus larval stage durations. Each host type is thus largely available to only one of the parasitoid species.