Showing papers in "The Biological Bulletin in 2002"
TL;DR: Preliminary results of the efforts to develop a modeling framework that synthesizes much of this previous work are presented, to identify relationships between behavioral parameters and group-level statistics.
Abstract: Heterogeneous, "aggregated" patterns in the spatial distributions of individuals are almost universal across living organisms, from bacteria to higher vertebrates. Whereas specific features of aggregations are often visually striking to human eyes, a heuristic analysis based on human vision is usually not sufficient to answer fundamental questions about how and why organisms aggregate. What are the individual-level behavioral traits that give rise to these features? When qualitatively similar spatial patterns arise from purely physical mechanisms, are these patterns in organisms biologically significant, or are they simply epiphenomena that are likely characteristics of any set of interacting autonomous individuals? If specific features of spatial aggregations do confer advantages or disadvantages in the fitness of group members, how has evolution operated to shape individual behavior in balancing costs and benefits at the individual and group levels? Mathematical models of social behaviors such as schooling in fishes provide a promising avenue to address some of these questions. However, the literature on schooling models has lacked a common framework to objectively and quantitatively characterize relationships between individual-level behaviors and group-level patterns. In this paper, we briefly survey similarities and differences in behavioral algorithms and aggregation statistics among existing schooling models. We present preliminary results of our efforts to develop a modeling framework that synthesizes much of this previous work, and to identify relationships between behavioral parameters and group-level statistics.
661 citations
TL;DR: It is suggested that the use of amorphous calcium carbonate might be advantageous for these storage structures, which function as reservoirs of ions during the animal molting period, and its high solubility is beneficial for temporary storage of calciumcarbonate ions that are subsequently dissolved and used elsewhere.
Abstract: Amorphous calcium carbonate (ACC) is the least stable form of the six known phases of calcium carbonate. It is, however, produced and stabilized by a variety of organisms. In this study we examined calcium storage structures from the terrestrial crustacean Orchestia cavimana, in order to better understand their formation mode and function. By using X-ray diffraction, infrared and Raman spectroscopy, thermal analysis and elemental analysis, we determined that the mineral comprising these storage structures is amorphous calcium carbonate with small amounts of amorphous calcium phosphate (5%). We suggest that the use of amorphous calcium carbonate might be advantageous for these storage structures, which function as reservoirs of ions during the animal molting period. Its high solubility is beneficial for temporary storage of calcium carbonate ions that are subsequently dissolved and used elsewhere. Stabilization of these amorphous minerals is probably due to macromolecular constituents of the organic matrix, and to the magnesium and phosphate present in the mineral phase. Amorphous minerals constitute a little less than a quarter of all known biominerals (1). When formed with no biological control, these minerals are usually metastable in comparison to their crystalline counterparts. They tend to transform into a more stable crystalline form. In contrast, biologically controlled amorphous minerals are, in most cases, stabilized by organisms for their entire lifetime. There are a few examples in which biogenic amorphous
143 citations
TL;DR: The continuing relevance of the crustacean cardiac ganglion as a relatively simple model for pacemaking and central pattern generation is confirmed by the rapidly widening documentation of intrinsic potentials such as plateau potentials in neurons of all major animal groups.
Abstract: Investigations of the electrophysiology of crustacean cardiac ganglia over the last half-century are reviewed for their contributions to elucidating the cellular mechanisms and interactions by which a small (as few as nine cells) neuronal network accomplishes extremely reliable, rhythmical, patterned activation of muscular activity-in this case, beating of the neurogenic heart. This ganglion is thus a model for pacemaking and central pattern generation. Favorable anatomy has permitted voltage- and space-clamp analyses of voltage-dependent ionic currents that endow each neuron with the intrinsic ability to respond with rhythmical, patterned impulse activity to nonpatterned stimulation. The crustacean soma and initial axon segment do not support impulse generation but integrate input from stretch-sensitive dendrites and electrotonic and chemically mediated synapses on axonal processes in neuropils. The soma and initial axon produce a depolarization-activated, calcium-mediated, sustained potential, the "driver potential," so-called because it drives a train of impulses at the "trigger zone" of the axon. Extreme reliability results from redundancy and the electrotonic coupling and synaptic interaction among all the neurons. Complex modulation by central nervous system inputs and by neurohormones to adjust heart pumping to physiological demands has long been demonstrated, but much remains to be learned about the cellular and molecular mechanisms of action. The continuing relevance of the crustacean cardiac ganglion as a relatively simple model for pacemaking and central pattern generation is confirmed by the rapidly widening documentation of intrinsic potentials such as plateau potentials in neurons of all major animal groups. The suite of ionic currents (a slowly inactivating calcium current and various potassium currents, with variations) observed for the crustacean cardiac ganglion have been implicated in or proven to underlie a majority of the intrinsic potentials of neurons involved in pattern generation.
131 citations
TL;DR: The lipid core of a biological membrane requires a certain degree of structural rigidity, but it must also be sufficiently fluid to permit lateral movement of the constituent lipids and embedded proteins, and a simple but very strong relationship between fluidity and a single polyunsaturated fatty acid is shown.
Abstract: The lipid core of a biological membrane requires a certain degree of structural rigidity, but it must also be sufficiently fluid to permit lateral movement of the constituent lipids and embedded proteins. Ectotherms can counteract the ordering effects of reduced temperature by changing the structure of their membranes, a process known as homeoviscous adaptation (1). Although the content of unsaturated fatty acids in the membranes of ectothermic animals is generally known to increase in response to cold (2), no clear and direct relationship between unsaturated fatty acids and membrane fluidity has been established in marine organisms. For example, phospholipid molecular species containing docosahexaenoic acid (22:6 3) are believed to be important in controlling finfish membrane fluidity (3–6), but a direct correlation between 22:6 3 and membrane fluidity has not been found (4, 5, 7, 8). In contrast, we show here a simple but very strong relationship between fluidity and a single polyunsaturated fatty acid, eicosapentaenoic acid (20:5 3), in gill membranes from a marine bivalve mollusc, the sea scallop Placopecten magellanicus. Phospholipids are the main structural elements of biological membranes, and their physical characteristics are key determinants of membrane structure and function. Many vital cell activities that depend on the optimal functioning of membranes are therefore sensitive to the chemistry of the membrane lipids (9) and to environmental conditions, such as temperature and pressure, that perturb the phase behavior and dynamics of lipids in membranes (10). Under extreme or variable conditions, organisms can exploit the tremendous chemical diversity among membrane lipids to defend the physical properties of the membrane (10). Thus in ectotherms, where changes in temperature cause important membrane perturbations, the usual adaptive response includes a modification of lipid composition (11). Sessile animals living in Newfoundland waters must maintain membrane structure and function in the face of extreme cold in deep waters (as low as 1.4°C) or seasonally highly variable conditions in surface waters (as much as 22°C in 6 months) (12). In the present study, we exposed sea scallops to a 10°C decrease in temperature for up to 3 weeks and then examined the relationship between the fatty acid composition of branchial phospholipids and membrane fluidity. Vesicles were prepared from the gills of scallops acclimated to temperatures of 15 and 5°C. After three weeks of thermal acclimation, the structural order of the phospholipids was measured by electron spin resonance (ESR) spectroscopy at five temperatures (0–20°C) that span the physiological range of Placopecten magellanicus (Fig. 1). The vesicles prepared from gills of 5°C-acclimated scallops were significantly (ANCOVA, P 0.03) less ordered than vesicles from 15°C-acclimated scallops. Temperature acclimation had shifted the order parameter curve 1–2°C toward lower assay temperatures, giving a homeoviscous efficacy (13) of 14%. Such a partial adjustment towards an ideal or complete homeoviscous response has also been found in crabs (14) and crayfish (15). In these invertebrates, the costs of perfect compensation may be too high, or the benefits too low. On the other hand, the ESR measurements in this study were made with the spin probe 5-doxyl stearic acid, reflecting the homeoviscous response in the outer region of the purified lipid bilayer. It is possible that the response deeper in the bilayer, in the actual region of alkenyl chain unsaturation, would have been greater (16). Received 30 November 2001; accepted 22 March 2002. 1 Present address: Department of Physiology and Experimental Medicine, The George Washington University Medical Center, Ross Hall Room 402, 2300 Eye Street, NW, Washington, DC 20037. 2 To whom correspondence should be addressed. E-mail: cparrish@ mun.ca Reference: Biol. Bull. 202: 201–203. (June 2002)
129 citations
TL;DR: Through experimental and theoretical studies, it is shown how a single behavior—the resting time—leads to a collective choice in both cockroaches and weaver ants and how this behavior is a response to the density of conspecifics and can also be modulated by heterogeneities in the environment.
Abstract: Aggregation is one of the most basic social phenomena, and many activities of social insects are linked to it. For instance, the selection of a valuable site and the spatial organization of the population are very often by-products of amplifications based on the local density of nestmates. The patterns of aggregation are very diverse, ranging from the gathering of all animals in a unique site to their splitting between several ones. One might question how these multiple patterns emerge. Do ants actively initiate the formation of such patterns by modulating the emission of an attracting signal such as the trail pheromone? Alternatively, do patterns result from quantitative changes in the duration of interaction between animals once they have reached the gathering site, without any active modulation of the communications? To discuss these questions, we present two empirical studies: the gregarious behavior of cockroaches (Blatella) and self-assembly in the weaver ant (Oecophylla). Through experimental and theoretical studies, we show how a single behavior-the resting time-leads to a collective choice in both species. This behavior is a response to the density of conspecifics and can also be modulated by heterogeneities in the environment. In weaver ants, it allows the colony to focus the formation of chains in a given area among several potential sites. In cockroaches, it allows the gathering of individuals in particular shelters, depending on the proximity between strains. These results are discussed with emphasis on the role of aggregation processes in the emergence of cooperativity and task allocation.
126 citations
TL;DR: The predominant surface circulation patterns in this part of the Atlantic Ocean favor the hypothesis that C. gasar was transported from Africa to America, and a phylogenetic tree built with seven 16S sequences from Crassostrea and Saccostrea species showed that C gasar is intermediate between the American Crassstrea species and the Asian species.
Abstract: Three species of mangrove oysters, Crass- ostrea rhizophorae, C. brasiliana,and C. gasar, have been described along the Atlantic shores of South America and Africa. Because the distribution of these molluscs is of great biological and commercial interest, their taxonomy and distribution deserve further clarification. Therefore, 15 popu- lations were sampled from both continents. Their 16S mito- chondrial polymorphism was studied by sequencing and PCR-RFLP analysis. Two haplotypes were identified. Hap- lotype a was the only one observed in Africa, but it was also observed in South America together with haplotype b. Be- cause C. gasar is the only mangrove oyster identified on the west coast of Africa, haplotype a was attributed to this species, which has thus been shown to occur in South America. Haplotype b is attributed to C. rhizophorae. The karyotypes of specimens of C. gasar, from Africa and from South America, were very similar, and both species were observed at the same location in Brazil. The occurrence of C. gasar in South America adds a third species—in addition to C. rhizophorae and C. brasiliana—to the list of species present along these coasts. The predominant surface circu- lation patterns in this part of the Atlantic Ocean favor the hypothesis that C. gasar was transported from Africa to America. Finally, a phylogenetic tree built with seven 16S sequences from Crassostrea and Saccostrea species showed that C. gasar is intermediate between the American Cras- sostrea species (C. virginica and C. rhizophorae) and the Asian species (C. gigas and C. ariakensis).
97 citations
TL;DR: It is argued that a biological system will be self-organized when it possesses a large number of subunits, and these subunits lack either the communicational abilities or the computational abilities, or both, that are needed to implement centralized control.
Abstract: Self-organization, or decentralized control, is widespread in biological systems, including cells, organisms, and groups. It is not, however, the universal means of organization. I argue that a biological system will be self-organized when it possesses a large number of subunits, and these subunits lack either the communicational abilities or the computational abilities, or both, that are needed to implement centralized control. Such control requires a well informed and highly intelligent supervisor. I stress that the subunits in a self-organized system do not necessarily have low cognitive abilities. A lack of preadaptations for evolving a system-wide communication network can prevent the evolution of centralized control. Hence, sometimes even systems whose subunits possess high cognitive abilities will be self-organized.
96 citations
TL;DR: The results demonstrate the presence of a host-symbiont recognition mechanism, and possibly competition among potential algal symbionts in the Aiptasia-Symbiodinium association.
Abstract: To understand the flexibility of symbiotic associations in coral reefs, we investigated the specificity of the Aiptasia (cf. insignis)-Symbiodinium association in the laboratory by rendering the anemones aposymbiotic and inoculating them with different isolates of SYMBIODINIUM: Infective algal symbionts were monitored over 3 months by re-isolation and identification using denaturing-gradient gel electrophoresis and sequence comparison of their amplified 18S rRNA hypervariable V1 + V2 gene region. Despite similarity in their external morphology, the algal isolates differed in their infectivity towards the host. Within days of single-isolate inoculation, aposymbiotic anemones formed associations with fresh or cultured isolates (clade B) from the anemones Aiptasia sp. or A. tagetes, respectively. They associated to a limited extent with cultured isolates (clade A) from the tridacnids Tridacna crocea or Hippopus hippopus, and not at all with a cultured isolate (clade C) from the stony coral Montipora verrucosa, nor with a free-living isolate (clade A) from subtidal sands. Aposymbiotic anemones inoculated with a mixture of all isolates had only the anemone taxon as their detectable symbionts. Re-inoculation of induced symbioses with a mixture of all isolates and incubation with wild anemones showed that the initial induced symbioses with the anemone taxon were stable. Anemones originally infected with tridacnid isolates either additionally acquired the anemone taxon or had the former outgrown by the latter. These results demonstrate the presence of a host-symbiont recognition mechanism, and possibly competition among potential algal symbionts in the Aiptasia-Symbiodinium association. Here we present a method that may be useful in monitoring the algal population dynamics in symbiotic corals in the field, along with an efficient method of rendering Aiptasia aposymbiotic for further laboratory investigation of Aiptasia-Symbiodinium symbioses.
92 citations
TL;DR: Findings indicate that spicule concentration is a plastic morphological trait that can be induced by damage, and that A. varians may be able to reduce spicules concentrations when environmental conditions change (e.g., in the absence of predators).
Abstract: The goal of the research presented here was to examine phenotypic plasticity exhibited by three morpho- types of the common Caribbean sponge Anthosigmella vari- ans (Duchassaing & Michelotti). We were interested in examining the biotic (and, to a lesser extent, abiotic) factors responsible for branch production in this species. We also tested the hypothesis that the skeleton may serve an anti- predator function in this sponge, focusing on vertebrate fish predators (i.e., angelfish) in this work. In transplant and caging experiments, unprotected forma varians replicates were immediately consumed by angelfish, while caged rep- licates persisted on the reef for several months. These find- ings support the hypothesis that predators (and not wave energy) restrict forma varians to lagoonal habitats. Branch production was not observed in A. varians forma incrustans when sponges were protected from predators or placed in predator-free, low-wave-energy environments. It is not clear from our work whether forma incrustans is capable of producing branches (i.e., whether branch production is a plastic trait in this morph). Additional field experiments demonstrated that A. varians forma varians increased spi- cule concentrations, compared to uninjured sponges, in re- sponse to artificial predation events, and A. varians forma rigida reduced spicule concentrations, compared to uncaged controls, when protected from predators. These findings indicate that spicule concentration is a plastic morphologi- cal trait that can be induced by damage, and that A. varians may be able to reduce spicule concentrations when envi- ronmental conditions change (e.g., in the absence of pred- ators). The potential significance of inducible defenses and structural anti-predator defenses in sponges is discussed in relation to recent work on sponge chemical defenses.
89 citations
TL;DR: The species that undergo DVM have peak photobehavioral responses at wavelengths corresponding to those available during twilight in coastal water, although the range of wavelengths to which they respond is variable.
Abstract: Light is a critical factor in the proximate basis of diel vertical migration (DVM) in zooplankton. A photobehavioral approach was used to examine the spectral sensitivity of four coastal species of calanoid copepod, representing a diversity of DVM patterns, to test whether species that migrate (nocturnal or reverse DVM) have response spectra that differ from non-migratory surface dwellers. The following species were given light stimuli at wavelengths from 350 to 740 nm, and their photoresponses were measured: Centropages typicus (nocturnal migrator), Calanopia americana (nocturnal migrator), Anomalocera ornata (reverse migrator), and Labidocera aestiva (non-migrator). Centropages typicus and A. ornata had peak responses at 500 and 520 nm, respectively, while Calanopia americana had maximum responses at 480 and 520 nm. Thus, the species that undergo DVM have peak photobehavioral responses at wavelengths corresponding to those available during twilight in coastal water, although the range of wavelengths to which they respond is variable. Non-migratory surface-dwelling L. aestiva had numerous response peaks over a broad spectral range, which may serve to maximize photon capture for vision in their broad-spectrum shallow-water habitat.
88 citations
TL;DR: If groups were nonpermanent units, often fusing and splitting up, then any increase of the distance at which animals perceive one another could increase the rate of group fusion and thus mean group size, changing the way in which the history of gregariousness in large herbivores during the Tertiary is envisaged.
Abstract: In large mammalian herbivores, the increase of group size with habitat openness was first assumed to be an adaptive response, encoded in the individual. However, it could, alternatively, be an emergent property: if groups were nonpermanent units, often fusing and splitting up, then any increase of the distance at which animals perceive one another could increase the rate of group fusion and thus mean group size. Dynamical models and empirical data support this second hypothesis. This is not to say that adaptive modifications of mean herd size cannot occur. However, this changes the way in which we can envisage the history of gregariousness in large herbivores during the Tertiary.
TL;DR: To understand the molecular basis of osmotic stress responses in vivo, homologous cDNA probes were used to characterize the mRNA patterns of lobster HSP70, HSP90, and polyubiquitin during hypo- and hyper-osmotic stress in abdominal muscle and hepatopancreas.
Abstract: The American lobster, Homarus americanus, encounters osmotic stress throughout its life cycle. To understand the molecular basis of osmotic stress responses in vivo, we used homologous cDNA probes to characterize the mRNA patterns of lobster HSP70 (=70-kDa heat-shock protein), HSP90 (=90-kDa heat-shock protein), and polyubiquitin during hypo- and hyper-osmotic stress in abdominal muscle and hepatopancreas (a digestive tissue) at 30, 60, and 120 min of osmotic stress. Hypo- and hyper-osmotic stress significantly increased the levels of the mRNAs encoding HSP70 and HSP90 in abdominal muscle. Hyper-osmotic stress increased HSP90 mRNA levels in hepatopancreas, but hypo-osmotic stress did not. Both abdominal muscle and hepatopancreas exhibited significant changes in polyubiquitin gene expression during osmotic stress. In abdominal muscle, polyubiquitin mRNA levels increased during both hypo- and hyper-osmotic stress. Hepatopancreas, however, showed a significant elevation in polyubiquitin mRNA only during hypo-osmotic stress.
TL;DR: The difference between adhesive and non-adhesive mucus suggests that relatively small proteins are important for controlling the mechanics of periwinkle mucus.
Abstract: The composition of the adhesive form of marsh periwinkle mucus was compared to the trail mucus used during locomotion. The trail mucus consists primarily of large, carbohydrate-rich molecules with some relatively small proteins. In contrast, the adhesive mucus has 2.7 times as much protein with no significant difference in carbohydrate concentration. The resulting gel has roughly equal amounts of protein and carbohydrate. This substantial increase in protein content is due to the additional presence of two proteins with molecular weights of 41 and 36 kD. These two proteins are absent from the trail mucus. Both proteins are glycosylated, have similar amino acid compositions, and have isoelectric points of 4.75. This change in composition corresponds to an order of magnitude increase in tenacity with little clear change in overall concentration. The difference between adhesive and non-adhesive mucus suggests that relatively small proteins are important for controlling the mechanics of periwinkle mucus.
TL;DR: A much stronger block to cross-species fertilization of E. lucunter eggs than was previously shown at fixed sperm concentrations is demonstrated, and mild incompatibility of the other two species’ eggs where previous crosses between species were not distinguishable from within-species controls are presented.
Abstract: Species of the sea urchin genus Echinometra found on the two coasts of Panamaare recently diverged and only partially isolated by incomplete barriers to inter- specific fertilization. This study confirms previous work that revealed incompatibility between the eggs of the Atlantic E. lucunter and the sperm of the other two neotropical species, whereas eggs of its sympatric congener E. viridis and allo- patric E. vanbrunti are largely compatible with heterospe- cific sperm. Here we quantify fertilization using a range of sperm dilutions. We demonstrate a much stronger block to cross-species fertilization of E. lucunter eggs than was previously shown at fixed sperm concentrations, and mild incompatibility of the other two species' eggs where previ- ous crosses between species were not distinguishable from within-species controls. Additionally, we present evidence for intraspecific variation in egg receptivity towards het- erospecific sperm. Our findings here again discount the "reinforcement model" as a viable explanation for the pat- tern of prezygotic isolation. Gamete incompatibility in these Echinometra has appeared recently—within the last 1.5 million years— but is weaker in sympatry than in allopatry. Accidents of history may help explain why incompatibility of eggs emerged in one species and not in others. Compen- satory sexual selection on sperm in this species could fol- low, and promote divergence of proteins mediating sperm- egg recognition.
TL;DR: The findings indicate that the complements of the four major MAAs in these species of Anthopleura broadly reflect phylogenetic differences among the anemones rather than the taxon of endosymbionts, presence or absence of symbionts or environmental factors.
Abstract: We examine the occurrence of UV-absorbing, mycosporine-like amino acids (MAAs) in four sympatric species of sea anemones in the genus Anthopleura, all collected from intertidal habitats on the Pacific Coast of temperate North America. We compare patterns of MAAs in A. elegantissima of several types: specimens having predominately zooxanthellae (dinoflagellates comprising at least two species) or zoochlorellae as symbionts; those containing algal endosymbionts of both kinds, and naturally occurring aposymbiotic specimens that lack the endosym- bionts typically found in most specimens. We also compare MAAs in zooxanthellate specimens of A. sola and A. xan- thogrammica, and specimens from the asymbiotic species A. artemisia. Our findings indicate that the complements of the four major MAAs in these species of Anthopleura (mycosporine-taurine, shinorine, porphyra-334, and myco- sporine-2 glycine) broadly reflect phylogenetic differences among the anemones rather than the taxon of endosymbi- onts, presence or absence of symbionts, or environmental factors. An exception, however, occurs in A. elegantissima, where mycosporine-2 glycine increases in concentration with the density of zooxanthellae. Our evidence also shows that A. elegantissima can accumulate MAAs from its food, which may explain the occasional occurrence of minor MAAs in some individuals.
TL;DR: A classification scheme is proposed based upon three aspects: whether the stimuli to which individuals respond are quantitative or qualitative, whether positive feedback is involved, and whether interindividual interactions are direct or indirect (stigmergic).
Abstract: Self-organization is a concept and phenomenon whereby system-level patterns spontaneously arise solely from interactions among subunits of the system. Focusing on self-organization at the organismal level, I ask the ques- tion: are the boundaries to self-organization indistinct? Af- ter reviewing a number of published definitions of self- organization, I explore the conceptual boundaries among self-organization and two similar concepts, stigmergy and self-assembly. I highlight borderline cases that may blur the distinction among these and suggest that they may indeed be conceptually indistinct and difficult to separate in practice. Consequently, I propose a classification scheme based upon three aspects: whether the stimuli to which individuals respond are quantitative or qualitative, whether positive feedback is involved, and whether interindividual interac- tions are direct or indirect (stigmergic). In addition, I con- sider several other issues about self-organization, including (1) could a self-organized system use global information? (2) what is the role of the degree of correlation of activity among individuals? and (3) what is the role of positive feedback?
TL;DR: Exposing larvae of C. fornicata to excess K+ leads to a shutdown of nitric oxide synthesis via a dopaminergic pathway, a pathway that can be blocked by some dopamine antagonists, and the largely latent inductive effects of chlorpromazine, an inhibitor of Nitric oxide synthase, suggest that endogenousNitric oxide may play a natural role in inhibiting metamorphosis in this species.
Abstract: The signal transduction pathway through which excess potassium ion stimulates the larvae of many marine invertebrates to metamorphose is incompletely understood. Recent evidence suggests that dopamine plays important roles in the metamorphic pathway of Crepidula fornicata. Therefore, we asked whether blocking dopamine receptors might prevent excess potassium ion from stimulating metamorphosis in this species. Surprisingly, the effects of the three putative dopamine antagonists tested (all at 10 μM) varied with exposure duration and the age of competent larvae. Chlorpromazine, a nonspecific dopamine antagonist known to have a number of other pharmacological effects, blocked the inductive action of excess potassium ion during the initial 5–8-h exposure periods in most assays, particularly for younger or smaller competent larvae. However, chlorpromazine in the absence of excess potassium ion also stimulated metamorphosis, particularly over the next 18 h, and worked faster on older competent larvae than on yo...
TL;DR: Time to first swimming correlated significantly with time from first to second cleavage (first cell cycle) in analyses of all embryos sampled and separately within the Spiralia and Echinodermata, and suggests that allocation of time to multiplication of cells versus differentiation of cells is resolved differently in species with different types of locomotion.
Abstract: Planktonic embryos of marine animals swim at an early stage and age. Although natural selection has apparently favored rapid development of structures for swimming, taxa have not converged on the same, minimal time from first cell division to first swimming. Comparisons of 34 species with planktonic embryos in 10 phyla revealed factors that account for variation in time to swimming. Time to first swimming correlated significantly with time from first to second cleavage (first cell cycle) in analyses of all embryos sampled and separately within the Spiralia and Echinodermata. Time to first swimming also correlated sig- nificantly with egg diameter in some clades, but not in all. Correlations between egg diameter and cell cycle duration were low except for the three species of Urochordata. De- velopment to a feeding or nonfeeding larva did not affect time to first swimming beyond effects attributable to egg size. Time to first swimming did not correlate with type of locomotion developed (uniciliated cells, multiciliated cells, or muscle). Nonetheless, differences in locomotion are as- sociated with changes in cell cycle durations prior to swim- ming. The ratios of time to first swimming and time for first cell cycle suggests that allocation of time to multiplication of cells versus differentiation of cells is resolved differently in species with different types of locomotion.
TL;DR: The aim of this study was to investigate spatial and social distribution of female zebrafish in a large aquarium where they could choose between different localities and partners, and indicates that under more normal conditions femaleZebrafish might live with one or two males but separated from other females.
Abstract: The zebrafish (Danio rerio) is native to freshwater streams and rice paddies in the Ganges River of East India, Bangladesh, and Burma. Although this species is widely used as a genetic model and for developmental research, little is known about its natural behavior (e.g., spatial distribution and social interactions). In the laboratory, zebrafish are usually kept in small aquaria under high densities. The mating behavior of the zebrafish seems to be influenced by the exposure of mating partners to one another several to 24 h before spawning begins at sunrise; female gonadal hormones apparently stimulate males to perform courtship behavior (1, 2). Our preliminary experiments (unpubl. data) showed reproductive suppression of female zebrafish kept together for 4 days before they were separated and mated with a single male overnight. On average, each of these females (n 52) laid only 45 12 (SE) eggs, in comparison to 200 12 (SE) eggs of a female kept isolated for 4 days and then mated with one male (n 15; 150 12 (SE) eggs) or two males (n 30; 180 12 (SE) eggs) overnight. Females kept together in a aquarium behaved aggressively toward each other and developed a dominance hierarchy. These results led us to assume that females would avoid other females if they could. The aim of this study was to investigate spatial and social distribution of female zebrafish in a large aquarium where they could choose between different localities and partners. We observed wild-type zebrafish, aged 10 months, which were kept in 30-l aquaria under a day/night cycle of 14/10 h with light on at 9:00 am before the experiments were started. Four males and four females were selected for each experiment. The eight fish were tagged individually behind the dorsal fin with Floy fish tags, all bearing a different color. These tags did not seem to affect the behavior of the fish. The fish were placed in a large 195-cm 195-cm aquarium filled with 600 l (water height: 16 cm) of formulated freshwater. A grid system of 16 equal squares was drawn on the bottom of the aquarium. In 7 of the 16 squares, artificial plants were placed in order to imitate zebrafish habitat. The fish were left to adjust to their new environment for about 3 h. Each of the five experiments lasted for 5 days. Half-hour observations were made twice daily, with at least 1 h between observation sessions. The observation sessions were split into 1-min intervals (31 intervals per observation), and the location of each fish was noted at every time interval. Newly released fish showed a strong tendency for shoaling, but after about 2–3 h they dispersed to different parts of the aquarium. Thereafter, they spent 99% of their time in one of the seven squares containing artificial plants. We evaluated how often each female was seen either alone or in the presence of only males (1 or 2 males) or with other females without any males (Fig. 1). In addition, we calculated how often females were expected to be found either alone or in these groups, assuming a random distribution (expected values). The comparison of observed and expected values showed that females avoided staying alone ( 2 4.8, df 1, P 0.05), but they preferred to stay with a single male ( 2 3.9, df 1, P 0.05) or with two males ( 2 142, df 1, P 0.001) when no other females were around. They spent only 5% of the observation time with femaleonly groups ( 2 5.7, df 1, P 0.05). Females showed no pairing with specific males. On average, each female was observed with 1.6 males per observation period. Our study indicates that under more normal conditions female zebrafish might live with one or two males but separated from other females. Males seemed to change female partners on a daily basis. We assume that they were probably attracted by female pheromones indicating female reproductive stage. Bloom and Perlmutter (3) showed that zebrafish, when placed in a T-maze, demonstrated either a preference for or an avoidance of donor water produced when specified numbers of conspecifics of either sex were kept in holding systems for set lengths of time. Their results and ours are consistent with the higher egg production we observed in females kept with one or two males. The conditions under which zebrafish are often kept in laboratories seem to conflict with their natural preferences. Egg production could be increased by considering these observed behavioral patterns.
TL;DR: The results presented here suggest that the occurrence of large MPs from the fall to early spring is better explained by abiotic proximate factors related to breeding than by socially mediated sex change in different demographic environments.
Abstract: Hypotheses on delayed sex change in the protandric simultaneous hermaphrodite Lysmata wurdemanni were tested with observations from population samples, mating experiments, and experiments on sex change under optimal and suboptimal breeding conditions. Male-phase individuals (MPs) much larger than the minimum size of sex change were most frequent in a natural population from fall through early spring. The hypothesis was tested that some MPs delay sex change to the simultaneous hermaphrodite female-phase (FP) because MPs are more competitive in obtaining copulations with parturial FPs than are FPs mating as males (MFPs). In different experiments, parturial FPs were maintained with two potential male mating partners (large MP and MFP, small MP and MFP, large MP and small MP) through the parturial molt and spawning; activities were recorded with time-lapse video. MFPs gained the single copulation with the parturial FP as frequently as MPs, large or small, but large MPs copulated with more FPs than small MPs. The hypothesis of FP reversion to large MP was tested experimentally and rejected. Rate of change of MP to FP was much lower in large MPs maintained under suboptimal (fall/winter) than optimal (spring/summer) breeding conditions. The results presented here suggest that the occurrence of large MPs from the fall to early spring is better explained by abiotic proximate factors related to breeding than by socially mediated sex change in different demographic environments.
TL;DR: The venom duct and its connection to the pharynx, along with the radular sac and teeth, were examined using light and transmission electron microscopy and the presence of putative peptides in material derived from the tooth lumen was demonstrated.
Abstract: Like all members of the genus, Conus californicus has a specialized venom apparatus, including a modified radular tooth, with which it injects paralyzing venom into its prey. In this paper the venom duct and its connection to the pharynx, along with the radular sac and teeth, were examined using light and transmission electron microscopy. The general anatomy of the venom apparatus resembles that in other members of the genus, but several features are described that have not been previously reported for other species. The proximal (posterior) quarter of the venom duct is composed of a complex epithelium that may be specialized for active transport rather than secretion. The distal portion of the duct is composed of a different type of epithelium, suggestive of holocrine secretion, and the cells display prominent intracellular granules of at least two types. Similar granules fill the lumen of the duct. The passageway between the lumen of the venom duct and pharynx is a flattened branching channel that narrows to a width of 10 micro m and is lined by a unique cell type of unknown function. Granular material similar to that in the venom duct was also found in the lumen of individual teeth within the radular sac. Mass spectrometry (MALDI-TOF) demonstrated the presence of putative peptides in material derived from the tooth lumen, and all of the more prominent species were also evident in the anterior venom duct. Radular teeth thus appear to be loaded with peptide toxins while they are still in the radular sac.
TL;DR: In this paper, the influence of gamete age on fertilization and development success in several marine invertebrates was investigated. And the results indicated that longer-lived sperm and eggs are central to the fertilization strategy of this species.
Abstract: Gamete age has been postulated to be unimportant to the fertilization ecology of marine invertebrates. However, recent research suggests that, for some species at least, it may have a direct impact upon fertilization success. We present comparative data on the influence of gamete age on fertilization and development success in several marine invertebrates: the polychaetes Arenicola marina and Nereis virens and the asteroid echinoderm Asterias rubens. Oocytes are much longer lived in the polychaetes than in the echinoderm, with A. marina oocytes still capable of fertilizing and developing normally 96 h post-spawning. Developmental abnormalities and failure to reach blastula tend to occur well before the fertilizable life of the oocytes has expired. Sperm are similarly longer lived in the polychaetes; however, fertilizing capacity is markedly reduced following incubation in conspecific egg-conditioned seawater. These results are discussed in terms of the fertilization strategies of the three species. We further suggest that, for A. marina at least, longer-lived sperm and eggs are central to the fertilization strategy of this species.
TL;DR: The results suggest that the test of the neomenioid larvae is an enlarged pre-oral sphere of a trochophore, and the homology and evolution of molluscan larval tests is discussed.
Abstract: Neomenioid aplacophorans (= Solenogastres) constitute one of the main lineages of molluscs. Developmental data of early embryogenesis and larval development of neomenioids are available for some species based on histological sections. I used other techniques to study the development of Epimenia babai Salvini-Plawen, 1997, and here I report new data on neomenioid development. The embryos of E. babai are lecithotrophic and cleavage is spiral, unequal, and holoblastic. Two polar lobes are formed, one at the first cleavage stage and one at the second cleavage stage. No evidence of external metameric iteration is visible through scanning electron microscopy or histology at any stage. A ciliated foot, a pedal pit, and aragonitic spicules develop from the definitive ectoderm. A spicule begins as a solid tip, continues to an open-ended hollow spicule, and finally becomes a closed-ended hollow spicule. The free-swimming trochophore larvae of E. babai have been considered unusual in lacking the characteristic neomenioid cellular test, an outer locomotory structure within which the entire definitive adult body develops. However, through the use of scanning electron and light microscopy, semithin sections, Hoechst nuclear staining, and programmed cell death staining to study the ontogeny and fate of the apical cells, I show that the entire pre-oral sphere (the apical cap) of the larvae is similar to the test of the other neomenioids. The results suggest that the test of the neomenioid larvae is an enlarged pre-oral sphere of a trochophore. The test morphologies of neomenioid larvae are compared to those of pericalymma larvae of protobranch bivalves, and the homology and evolution of molluscan larval tests is discussed.
TL;DR: Each environmental factor that alters the dynamics of information transfer in group-living animals should be reconsidered not simply as a constraint but also as a part of the decision-making process and as a agent that shapes the collective pattern.
Abstract: This paper shows how colonies of social insects process information and solve problems in a complex en- vironment, while keeping some parsimony at the level of the individuals' decision rules. Two studies on ant foraging reveal the diversity of adaptive colony-level patterns that can be generated through self-organization, based on the same individual-level recruitment rules. Regarding prey scavenging, the "ability to retrieve the prey" rule accounts for changes in foraging patterns, with increasing prey size, that show all stages intermediate between an individual and a mass exploitation of food resources. Regarding liquid food foraging, the "ability to ingest a desired volume" rule enables a colony to adjust the number of tending ants to the honeydew production of aphids. In both cases, decision rules are based on intelligent criteria that intrinsically inte- grate information on multiple variables that are relevant to the ants. Furthermore, the environment can contribute di- rectly to the emergence of collective patterns, independently of any individual behavioral changes. Each environmental factor, including abiotic ones, that alters the dynamics of information transfer in group-living animals should be re- considered not simply as a constraint but also as a part of the decision-making process and as a agent that shapes the collective pattern.
TL;DR: The apical sensory organ in veliger larvae of a patellogastropod, a basal clade of gastropod molluscs, was studied using ultrastructural and immunohistochemical techniques and a tripartite arrangement of sensory dendrites can be recognized in T. scutum after loss of the apical ciliary tuft cells.
Abstract: The apical sensory organ in veliger larvae of a patellogastropod, a basal clade of gastropod molluscs, was studied using ultrastructural and immunohistochemical techniques. Immediately before veligers of Tectura scutum undergo ontogenetic torsion, the apical sensory organ consists of three large cells that generate a very long apical ciliary tuft, two cells that generate a bilateral pair of shorter ciliary tufts, and a neural ganglion (apical ganglion). Putative sensory neurons forming the ganglion give rise to dendrites that extend to the apical surface of the larva and to basal neurites that contribute to a neuropil. The ganglion includes only one ampullary neuron, a distinctive neuronal type found in the apical ganglion of other gastropod veligers. Serotonin immunoreactivity is expressed by a medial and two lateral neurons, all having an apical dendrite, and also by neurites within the neuropil and by peripheral neurites that run beneath the ciliated prototrochal cells that power larval swimming. The three cells generating the long apical ciliary tuft are lost soon after ontogenetic torsion, and the medial serotonergic cell stops expressing serotonin antigenicity in late-stage veligers. The lateral ciliary tuft cells of T. scutum may be homologs of lateral ciliary tuft cells in planktotrophic opisthobranch veligers. A tripartite arrangement of sensory dendrites, as described previously for veligers of other gastropod clades, can be recognized in T. scutum after loss of the apical ciliary tuft cells.
TL;DR: Direct measurements of energy dissipation rates are used to show that fertilization success can exceed 80% even when dissipation is as high as 2200 W/m 3 , higher than the dissipation likely to be found.
Abstract: Turbulent water motion can either aid or hinder external fertilization in aquatic organisms. On one hand, turbulence provides the mixing necessary to bring eggs and sperm together; on the other, the forces imposed by turbulent eddies may interfere with the attachment of sperm to eggs and may even damage zygotes. Mead and Denny (1) explored this dichotomy by measuring the efficacy of fertilization in the purple sea urchin(Strongylocentrotus purpuratus) while gametes were subjected to sheared flow in a Couette cell. When calculated rates of turbulent energy dissipation exceeded 100 W/m 3 , fertilization and early development were severely affected. Dissipation rates of this magnitude are common in breaking waves, and Mead and Denny therefore concluded that turbulent flow could be a substantial environmental hindrance to sexual reproduction in nearshore urchins. However, the rates of energy dissipation calculated by Mead and Denny for the Couette cell were erroneously small. Here we use direct measurements of energy dissipation rates to show that fertilization success can exceed 80% even when dissipation is as high as 2200 W/m 3 , higher than the dissipation likely to be found
TL;DR: It is suggested that the filter-feeding pharynx is not an innovation of the chordates, but evolved prior to the evolutionary divergence of the hemichordate-echinoderm clade from the chordATEs.
Abstract: An investigation of the feeding behavior of the acorn worm Harrimania planktophilus suggests a novel form of enteropneust feeding with significant phylogenetic implications. H. planktophilus is a holoinfaunal worm that feeds on deposited sediments, and filter feeds on suspended particles in interstitial pore water. To visualize the particle retention behavior involved in filter feeding, adult animals were held in chilled seawater under low light and fed food coloring and fluorescent particles. The behavior was recorded by videography. Most particles ingested were drawn into the mouth by an incurrent flow created by cilia on the pharyngeal bars and without the aid of mucus. Particles that passed freely through the gill pores averaged 3.04 μm, whereas particles retained in the gut and defecated in the feces averaged 13.9 μm. Food coloring entered the mouth and was pumped through the pharynx at a rate of 0.5–2.0 mm/s. There is no evidence of an endostyle or mucus-net capture mechanism in H. planktophilus, bu...
TL;DR: The results support the hypothesis that LAFpro is a peptide that resembles a molt-inhibiting hormone, and inhibit molting by suppressing the Y-organs from secreting ecdysone.
Abstract: Molting and limb regeneration are tightly cou- pled processes, both of which are regulated by ecdysteroid hormone synthesized and secreted by the Y-organs. Regen- eration of lost appendages can affect the timing and duration of the proecdysial, or premolt, stage of the molt cycle. Autotomy of all eight walking legs induces precocious molts in various decapod crustacean species. In the land crab Gecarcinus lateralis, autotomy of a partially regener- ated limb bud before a critical period during proecdysis (regeneration index 17) delays molting so that a second- ary limb bud (2° LB) forms and the animal molts with a complete set of walking legs. It is hypothesized that 2° LBs secrete a factor, termed limb autotomy factor-proecdysis (LAF pro ), that inhibits molting by suppressing the Y-organs from secreting ecdysone. Molting was induced by autotomy of eight walking legs; autotomy of primary (1°) LBs re- duced the level of ecdysteroid hormone in the hemolymph 73% by one week after limb bud autotomy (LBA). Injection of extracts from 2° LBs, but not 1° LBs, inhibited 1° LB growth in proecdysial animals, thus having the same effect on molting as LBA. The inhibitory activity in 2° LB extracts was stable after boiling in water for 15 min, but was destroyed by boiling 15 min in 0.1 N acetic acid or incu- bation with proteinase K. These results support the hypoth- esis that LAFpro is a peptide that resembles a molt-inhibiting hormone.
TL;DR: This paper discusses in this paper how related species, which differ in many respects, may evolve by a combination of individual selection, self-organization, and group-selection, requiring an evolutionary adaptation of only a single trait.
Abstract: Differences between related species are usually explained as separate adaptations produced by individual selection I discuss in this paper how related species, which differ in many respects, may evolve by a combination of individual selection, self-organization, and group-selection, requiring an evolutionary adaptation of only a single trait In line with the supposed evolution of despotic species of macaques, we take as a starting point an ancestral species that is egalitarian and mildly aggressive We suppose it to live in an environment with abundant food and we put the case that, if food becomes scarce and more clumped, natural selection at the level of the individual will favor individuals with a more intense aggression (implying, for instance, biting and fierce fighting) Using an individual-centered model, called DomWorld, I show what happens when the intensity of aggression increases In DomWorld, group life is represented by artificial individuals that live in a homogeneous world Individuals are extremely simple: all they do is flock together and, upon meeting one another, they may perform dominance interactions in which the effects of winning and losing are self-reinforcing When the intensity of aggression in the model is increased, a complex feedback between the hierarchy and spatial structure results; via self-organization, this feedback causes the egalitarian society to change into a despotic one The many differences between the two types of artificial society closely correspond to those between despotic and egalitarian macaques in the real world Given that, in the model, the organization changes as a side effect of the change of one single trait proper to an egalitarian society, in the real world a despotic society may also have arisen as a side effect of the mutation of a single trait of an egalitarian species If groups with different intensities of aggression evolve in this way, they will also have different gradients of hierarchy When food is scarce, groups with the steepest hierarchy may have the best chance to survive, because at least a small number of individuals in such a group may succeed in producing offspring, whereas in egalitarian societies every individual is at risk of being insufficiently fed to reproduce Therefore, intrademic group selection (selection within an interbreeding group) may have contributed to the evolution of despotic societies