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901.
902.
M. D'A. A. Le Tissier 《Marine Biology》1988,98(4):493-501
The growth and development of the tissues and skeleton of settled larvae of the reef coral Pocillopora damicornis (Linnaeus), collected in December 1983 from Ko Phuket, Thailand, were investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. The rate of development of larval skeletons was very variable, preventing the chronological sequencing of skeletal growth. However, four growth stages in the development of a complete larval skeleton from first settlement were identificd: Stage 1, deposition of the first elements of the basal plate upon settlement; Stage 2, completion of basal plate, and deposition of skeletal spines and ridges in positions corresponding to the septal cycles; Stage 3, formation of the corallite wall and septal and costal cycles; Stage 4, the complete larval skeleton which represented the maximum growth attained eight days after settlement. The configuration of the larval tissues, particularly the aboral ectoderm, mirrored the four developmental stages. The deposition of the larval skeleton was correlated with the metamorphosis of the aboral ectoderm from a columnar to a squamous morphology. The basal plate of the larval skeleton had two layers of crystals orientated perpendicular to each other. The architecture of the complete larval skeleton is described and compared to that of the adult skeleton of P. damicornis. The results are discussed with respect to previous concepts of the formation of the larval skeleton of scleractinian corals and coral calcification. 相似文献
903.
904.
Despite the importance of understanding feeding in the early stages of bivalve development, little information is available concerning the organogenesis of the bivalve gill. The present study used histological and scanning electron microscopical techniques to present a detailed account of gill development in the early stages of the scallop Pecten maximus L. (Bivalvia: Pectinidae). Live specimens from larval cultures were observed daily using light microscopy, while five scallops were sampled for electron and light microscopy every 2 to 3 d from Day 18 to 35, then weekly to Day 56, with a final sampling on Day 58. Although development was continuous, four distinct stages were identified (1-primordia, 2-homorhabdic unreflected, 3-homorhabdic reflected, 4-heterorhabdic), partially recapitulating the presumed phylogenetic evolution of this character in the Pectinidae. The absence of a ventral grcove in all stages suggests that the particle transport mechanism of pectinids evolved independently of such a structure, which is found in other bivalve families. Similarly, the absence of latero-frontal cilia in all specimens up to the largest observed (4 mm) indicates that the single row found in adults is a later development, rather than a vestige of a more abundant ciliation in ancestral forms. The anatomical data, together with in vivo observations of feeding in postlarvae, suggest that the developmental stages of the P. maximus gill correspond to critical changes in gill function. The early life of P. maximus may thus be characterized by distinct functional changes in feeding. 相似文献
905.
Mud crabs of the genus Scylla are commercially important mangrove residents that are extensively fished throughout their range in the Indo-West Pacific.
Despite this high level of exploitation very little is known about the population dynamics of any of the Scylla species. The present study concentrated on an exploited population of Scylla
paramamosain in a natural estuarine mangrove on Can Coc Island in the mouth of the Hau River, Mekong Delta, Vietnam. A total of 6,114
juvenile crabs captured on the seaward mangrove fringe were internally tagged by injection of coded microwire tags and released
over a period of 29 days. Recaptures were monitored over the following 144 days. There was little migratory movement within
the estuary; of 285 recaptured crabs, 93% were recovered within the island mangrove study area and only two individuals were
recovered from mangroves lining the opposite mainland riverbanks. A von Bertalanffy growth function was fitted to growth increment
data from recaptured crabs, with L
max = 150 mm to derive a growth constant, k = 2.39 year−1. The theoretical age at which carapace width is zero (t
0) was derived from known size at recruitment at instar 1, giving a value of −0.0095 years. Previous studies of the same population
have shown that female S. paramamosain reach maturity at a mean size of 102 mm carapace width. The present study indicates that they attain this size at around
160 days from first settlement in the mangrove fringe. Abundance of juvenile crabs in the study area was estimated by the
Petersen method as 1,101,500 (95% CI 4,17,300–1,785,800, representing 1,102 crabs ha−1 of mangrove. Estimation of mortality from tag returns and from the age-catch curves during a period of constant recruitment
were comparable (Z = 1.11 and 1.04 month−1, respectively). Fishing only accounted for 14% of total mortality, suggesting that at the time exploitation was not at a
critical level despite the apparent high level of fishing activity. 相似文献
906.
Conte Yves Le Sreng Leam Sacher Nelly Trouiller Jérôme Dusticier Georges Poitout Serge Henri 《Chemoecology》1994,5(1):6-12
Summary Honey bee workers are able to nurse or to destroy and thus to recognize the capped queen cells containing a pupa. Fatty acid esters, especially methyl oleate, methyl palmitate and ethyl oleate were found in significant amounts on the queen pupal cuticle. Methyl oleate, the major component, along with smaller amounts of methyl linoleate and methyl linolenate, were involved in the recognition of queen cells by workers. In natural conditions of the colony, queen cells containing a paraffin pupal lure with methyl oleate were accepted 5.9 days by workers, releasing about 1.8 queen pupa equivalents during that period, when control cells (without ester) were kept only 2.1 days. Although these esters are non specific to honey bees, they are of great importance in social regulation of the honey bee colony. 相似文献
907.
Zooplankton of tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter 总被引:2,自引:0,他引:2
The standing stock and taxonomic composition of zooplankton (>200 m) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals >200 m comprised 50% of the total biomass of all organisms from 35 to >2000 m. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy periods. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for April 1985 and April 1986. Using the C:N:P ratio method, net growth efficiencies, K
2, were calculated for total mesozooplankton, mixed copepods, and two planktonic species, Undinula vulgaris and Thalia democratica. Combined with nitrogen and phosphorus excretion rates, these K
2 values enabled the assessment of production rates. On a 24 h basis, P:B ratios (%) were close to 100 for the total zooplankton and 54, 34 and 800 for mixed copepods, U. vulgaris and T. democratica, respectively. These ratios are 5.7 times lower than that recorded for phytoplankton. High productivity may be ascribable to the high density of seston, the high temperature (29.5°C), and the kind of organisms present. Zooplankton production equalled 38 and 30% of 14C uptake during April 1985 and April 1986, respectively. Ingestion of animals >35m was calculated by means of assimilation efficiencies and amounted to 17 and 7% of particulate organic carbon, 100 and 38% of living carbon, and 64 and 140% of primary production during the two periods, respectively. Finally, inorganic exduring was 32 and 18% of phytoplankton nitrogen and phosphorus requirements. A model based on the dimensional structure of the pelagic food-web, has been drawn to illustrate the biomass and carbon, nitrogen and phosphorus fluxes in the study area. The lagoon appears to export part of its planktonic biomass, which is 4.2 times lower one sea mile outside the main pass connecting the lagoon to the open ocean. 相似文献
908.
M. Salvy Y. Capowiez Y. Le Conte M. Salvy J.-L. Clément 《Die Naturwissenschaften》1999,86(11):540-543
Varroa jacobsoni is an ectoparasite of honey bees which reproduces in capped brood cells. Multi-infestation is frequently observed in worker
brood and can be interpreted as an aggregative phenomenon. The aim of this study was to determine whether the distribution
of V. jacobsoni in worker brood cells relies on a random or an aggregative process. We studied the distribution of Varroa females in capped worker brood at similar age by comparing, by a Monte Carlo test, the observed frequency distribution of
mites per cell to simulated distributions based on a random process. A complementary approach, using the "nearest neighbor
distances" (NND) with Monte Carlo tests, was investigated to study the spatial distribution (a) between mites in different
cells and (b) between infested cells in brood. The observed distributions did not differ significantly from that expected
by a random process, and we conclude that there is no aggregation during invasion of V. jacobsoni in worker brood.
Received: 29 April 1999 / Accepted in revised form: 26 August 1999 相似文献
909.
910.
保护和恢复阿拉善梭梭生态林的探讨 总被引:2,自引:0,他引:2
本文分析了近 40年来阿拉善盟梭梭生态林退化的原因 ,并提出了今后保护与恢复这片梭梭生态林的对策和建议。 相似文献