Survival,Growth and Reproduction of Cryopreserved Larvae from a Marine Invertebrate,the Pacific Oyster (Crassostrea gigas)

This study is the first demonstration of successful post-thawing development to reproduction stage of diploid cryopreserved larvae in an aquatic invertebrate. Survival, growth and reproductive performances were studied in juvenile and adult Pacific oysters grown from cryopreserved embryos. Cryopreservation was performed at three early stages: trochophore (13±2 hours post fertilization: hpf), early D-larvae (24±2 hpf) and late D-larvae (43±2 hpf). From the beginning (88 days) at the end of the ongrowing phase (195 days), no mortality was recorded and mean body weights did not differ between the thawed oysters and the control. At the end of the growing-out phase (982 days), survival of the oysters cryopreserved at 13±2 hpf and at 43±2 hpf was significantly higher (P<0.001) than those of the control (non cryopreserved larvae). Only the batches cryopreserved at 24±2 hpf showed lower survival than the control. Reproductive integrity of the mature oysters, formely cryopreserved at 13±2 hpf and 24±2 hpf, was estimated by the sperm movement and the larval development of their offspring in 13 crosses gamete pools (five males and five females in each pool). In all but two crosses out of 13 tested (P<0.001), development rates of the offspring were not significantly different between frozen and unfrozen parents. In all, the growth and reproductive performances of oysters formerly cryopreserved at larval stages are close to those of controls. Furthermore, these performances did not differ between the three initial larval stages of cryopreservation. The utility of larvae cryopreservation is discussed and compared with the cryopreservation of gametes as a technique for selection programs and shellfish cryobanking.     

Adaptations by Invertebrate Larvae for Nutrient Acquisition from Seawater

Unlike life on land, animals that live in seawater are surroundedby a medium that contains organic nutrients in dilute solution.Larval forms of soft-bodied marine invertebrates are adaptedto take advantage of the fact that most of the organic carbonin their environment is in solution as dissolved organic material(DOM). New evidence for the importance of DOM to metazoans ispresented by showing that larval forms can increase in biomass,even in the absence of paniculate foods. Such increases occurredonly in those species capable of transporting DOM. The physiologicalbasis for using DOM as an energy source is dependent upon anincreased transport capacity for DOM as growth proceeds. Usingbivalve larvae, mass coefficients and exponents were determinedfor (i) alanine transport rates and (ii) metabolic rates. Thesecoefficients were not statistically different when determinedover the life span of a larva. Thus, as growth proceeds, theselarvae increase their ability to obtain a potential supply ofmetabolic fuel (DOM) in direct proportion to the increase intheir metabolic demand. The percent of this increased transportcapacity that larvae could actually utilize in nature will dependupon the substrate concentrations in their environment. Currentviews on what these concentrations are in seawater may be alteredas more attention is given to the fine scale distributions oforganic chemicals in the ocean. After DOM has been transportedby the animal, its metabolic fate can now be rigorously studiedusing bacteria-free larvae. Measurements of amino acid synthesisin larvae cultured under axenic conditions suggest that a muchgreater plasticity may exist in the biochemical requirementsof larvae for dietary amino acids.     

Reproduction and Development in Chondrichthyan Fishes

Patterns of chondrichthyan reproduction and development arediverse. Species either are reproductively active throughoutthe year, or have a poorly defined annual cycle with one ortwo peaks of activity, or have a well defined annual or biennialcycle. Based on embryological origin and adult morphology, theirreproductive system is more similar to tetrapods than to teleosts.Primordial germ cells are of endodermal origin. The Wolffianducts in males and Mullerian ducts in females become the functionalurogenital ducts. Differentiation is under hormonal control.Unusual features of the reproductive system include an epigonalorgan in males and females. It contains lymphoid and hemopoietictissue. Leydig's gland, a modified region of the kidney, producesseminal fluid. In some species, sperm passing through the vasdeferens, is enclosed in spermatophores. Rotating about theirlong axis, helical spermatozoa can move forward or reverse direction.Spermatogenesis often occurs in bicellular units, spermatocysts.These consist of a spermatogonium enclosed in a Sertoh cell.Fertilization is internal. Claspers, modified portions of thepelvic fins act as intromittent organs. In many viviparous sharksand rays, the female reproductive system is asymmetrical. Eggsof some sharks are the largest known cells. Yolk platelets containlipovitellin. Oocytes have lampbrush chromosomes. Eggs releasedfrom the ovary into the body cavity are transported by ciliaryaction to the ostium of the oviduct. There they are fertilized.Physiological polyspermy is normal. The shell gland, a specializedregion of the anterior oviduct, functions both in long termsperm storage and in egg case production. Egg cases of sharksand skates consist of unique collagenous protein with a 400Å period, organized as a cholesteric liquid crystal. Chimaeroidegg cases contain 550 Å pseudotubules in orthogonal lattices.In small sharks, males copulate by coiling around the female.A parallel position is assumed by large sharks. Skates and rayscopulate with ventral surfaces apposed or by a dorsal approach.Biting is a pre-copulatory release mechanism. Parental care,except for selective oviposition, is lacking. Heavily yolkedeggs undergo meroblastic, discoidal cleavage. Development islengthy, shortest (2–4 months) in rays, longer in skates(3–8 months) and longest (9–22 months) in sharksand chimaeras. Most sharks and all rays are viviparous. Chimaeras,skates, and some sharks are oviparous. Viviparity either involvesa yolk sac placenta or is aplacental. If aplacental, the embryoderives nutrients either from yolk reserves, or by intra-uterineembryonic cannibalism, or from placental analogues which secrete"uterine milk." Phylogenetic position, geographical distribution,benthic vs. pelagic habitat, adult size, egg-embryo size, feedingecology, and embryonic osmoregulation are factors in the retentionof oviparity or the evolution of viviparity.     

Participatory Development and Community-Based Conservation: Opportunities Missed for Lessons Learned?

This paper traces the evolution as well as key elements, and provides examples of implementation of participatory development and community-based conservation, two concepts that resemble distant cousins in the intersecting worlds of development assistance and environmental conservation. The paper examines the connections between the concepts, the implications of participatory development for community-based conservation, and the reasons for the differences in their conceptualization and implementation. The paper is based on a review of the literature in both fields and on the authors' research and experience with participatory development and community-based conservation. Several keys to understanding the disconnection between the concepts emerge; intellectual and pragmatic origins of and impetus for the concepts, the expertise and interests of their promoters, and the differing emphasis on participation as means versus end. Results may inform our understandings of why many participatory approaches to conservation have failed to achieve meaningful participation in practice.     

Morphological and Molecular Characterization of Dietary-Induced Pseudo-Albinism during Post-Embryonic Development of Solea senegalensis (Kaup, 1858)

The appearance of the pseudo-albino phenotype was investigated in developing Senegalese sole (Solea senegalensis, Kaup 1858) larvae at morphological and molecular levels. In order to induce the development of pseudo-albinos, Senegalese sole larvae were fed Artemia enriched with high levels of arachidonic acid (ARA). The development of their skin pigmentation was compared to that of a control group fed Artemia enriched with a reference commercial product. The relative amount of skin melanophores, xanthophores and iridophores revealed that larval pigmentation developed similarly in both groups. However, results from different relative proportions, allocation patterns, shapes and sizes of skin chromatophores revealed changes in the pigmentation pattern between ARA and control groups from 33 days post hatching onwards. The new populations of chromatophores that should appear at post-metamorphosis were not formed in the ARA group. Further, spatial patterns of distribution between the already present larval xanthophores and melanophores were suggestive of short-range interaction that seemed to be implicated in the degradation of these chromatophores, leading to the appearance of the pseudo-albino phenotype. The expression profile of several key pigmentation-related genes revealed that melanophore development was promoted in pseudo-albinos without a sufficient degree of terminal differentiation, thus preventing melanogenesis. Present results suggest the potential roles of asip1 and slc24a5 genes on the down-regulation of trp1 expression, leading to defects in melanin production. Moreover, gene expression data supports the involvement of pax3, mitf and asip1 genes in the developmental disruption of the new post-metamorphic populations of melanophores, xanthophores and iridophores.     

Alternative Concepts of Reproductive Effort, Costs of Reproduction, and Selection in Life-History Evolution

An outline for an organismic theory of reproductive tacticsis presented to develop the demographic theory of optimal reproductivetactics into a more realistic theory of life-history evolution.Reproductive effort—denned as the proportion of resourcesinvested in reproduction—and the costs in somatic investmentdo not automatically result in survival costs. Both the conditionswhere survival costs are produced and the conditions where reproductioncan take place without survival costs are specified. Compensationand threshold hypotheses are put forward to allow weaker correlationsbetween reproduction and survival than the trade-off hypothesis,which assumes direct impacts by reproductive effort on survival.Furthermore, reproductive tactics are unlikely to be mouldedby the demographic forces of selection only. An empirical exampleis shown where residual reproductive value played no significantrole in the evolution of reproductive tactics. Selection probablyoperates not on separate life-history traits but on whole organismsthrough their entire life-history. The structural and physiologicalintercouplings between separate traits can result in phenotypicopportunity sets where selection can mould life-history traitsonly within the constraints of the opportunity sets. Optimizationtheory has provided an efficient technique for modelling andmaking predictions. However, organismic selection does not necessarilyoptimize adaptive strategies but eliminates unfit strategies.Life-history theory, and evolutionary theory in general, canbe developed along alternative logical lines when differenthypotheses are generated on how selection operates.     

Plant Development and Reproduction: Advances and Prospectives

Plant development and reproduction research has been moving very rapidly in the past 10 years due to the progress of molecular biology, the analysis of various developmental mutants, and the cloning of the genes with important function in different stages of plant development. This review focuses on apical mefistem, flower initiation and development, fertilization and embryogenesis. Recent advances and the prospects in the future are discussed.     

Development and Cancer: Lessons Learned in the Pancreas

Cancer progression and organ development are similar phenomena. Both involve rapid bursts of proliferation, angiogenesis, tissue remodeling, and cell migration. Therefore, it is not surprising that both processes utilize similar signaling machinery. In fact, many recent studies have suggested that cancer is a disease triggered by the erroneous re-activation of signaling pathways that are typically down-regulated after the completion of embryonic development. This link between embryonic development and cancer is particularly exciting because it suggests that we might be able to exploit the knowledge gained in studies of Developmental Biology to obtain novel insights into tumor biology. Our evolving understanding of pancreatic adenocarcinoma is an excellent example of this relationship between development and cancer. Here we discuss recent studies have indicated important roles for two major developmental signaling pathways in pancreatic cancer: Notch and Hedgehog (Hh).     

Temperature, Food Availability, and the Development of Marine Invertebrate Larvae

SYNOPSIS. Marine invertebrates develop in waters that extendfrom the poles to the equator, experiencing the full range ofenvironmental temperature and food conditions. How selectionhas modified their development under the influence of thesetwo factors has been a matter of debate. In this paper we arguethat the primary influence on developmental rate is temperature,while other factors such as food availability are much lessimportant. From existing literature we demonstrate that (1)developmental rates of both lecithotrophic and planktotrophicasteroids decrease in a similar way from the tropics to thepoles, as they do also in other groups of invertebrates (echinoids,molluscs, crustaceans), and (2) rates of development at anyone temperature cluster around the function describing the effectof temperature, without any relationship to egg size, suggestingthat developmental rates are near the maximum for a given temperatureregardless of other variables such as nutrition. We also investigatedthe response of development to temperature in four species ofplanktotrophic asteroids, one tropical, one temperate, two polar.There was limited temperature compensation among these fourspecies, but little or no apparent ability to compensate forthe retarding effects of reduced temperature within species.Arrhenius analysis of the data suggests that Q₁₀ values forthe upper region of each species' tolerance range are approximately2, indicating that enzyme-based reactions have evolved to beclosely integrated with uncatalyzed, temperature-dependent,physicalchemical processes. Values of Q₁₀ at lower regions ofthe tolerance range, on the other hand, range between 9.5 and14.7, indicative of abrupt temperature-dependent shifts in reactionequilibria, or in the organization of macromolecules and membranes.We conclude that temperature itself, rather than egg size, food,or other variables, best explains observed latitudinal differencesin developmental rates in marine invertebrates.     

Structural Complexity and Distance from Source Habitat Determine Invertebrate Abundance and Diversity

The structural complexity of habitats and the distance from the dispersion source are considered important determinants of species diversity. The fractal dimensions of substrates are a strong alternative measure for quantifying the structural complexity. In this paper, we tested the hypothesis that structural complexity and distance from a dispersion source affect the density and diversity of macro‐invertebrates on submersed macrophytes. To test this hypothesis, we used artificial substrates with different fractal dimensions, which were incubated at different distances from a dispersion source (a stand of macrophytes) in a Neotropical floodplain lake. The relationship between the structural complexity of macrophytes and the density and diversity of invertebrates attached to artificial substrates was positive and significant. On the other hand, distance from the dispersion source negatively affected both the density and diversity of the attached invertebrates. For Oligochaeta, however, there was a significant effect of structural complexity for the artificial plants positioned further away, but it was not significant in the plants positioned closer to the dispersion source. Thus, the effects of complexity depended on the distance from the dispersion source, at least for this specific group of macro‐invertebrates. These results suggest that both structural complexity and distance from the dispersion source should be considered together to explain the diversity of invertebrates in river–floodplain systems. In addition, our results show that there is great potential for using fractal dimensions as a tool to quantify structural complexity in aquatic habitats, especially at the small spatial scales perceived by macro‐invertebrates. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

Unifying and distinguishing diversity ordering methods for comparing communities

Diversity indices have been widely used in ecological research, but they remain problematic in that different indices may rank communities inconsistently. This problem can be solved by using diversity ordering methods, the output of which is a diversity profile in graphical form for each community being compared. In this paper, we demonstrate that existing diversity ordering methods can be classified into four groups and that within-group methods are essentially equivalent, while among-group methods are not. We find that the intrinsic diversity-related methods—i.e., the group containing the right tail-sum method, the logarithmic dominance plot, the majorization method, and the k-dominance plot—provide the most stringent test of diversity ordering, and we recommend the right tail-sum method as the method of preference for practical purposes.