共查询到20条相似文献,搜索用时 15 毫秒
1.
T. A. Williams 《Development genes and evolution》1998,207(7):427-434
In Drosophila, Distalless (Dll) is critical in establishing the proximal/distal axis of the leg. Lack of proper Dll expression causes distal limb structures to be truncated or lost. Dll expression was examined through the course of development in the limbs of two crustaceans, Triops and Nebalia. Because the limbs of these two species are branched, they provide a comparison to the uniramous (unbranched) leg of Drosophila. In Triops and Nebalia, development of limb branches is not tightly coupled with Dll expression: in some cases, branches can arise prior to Dll expression and in others, certain branches never express Dll. These data suggest that, while Dll may indeed initiate overall limb outgrowth, limb branches are unlikely to be patterned by a simple iteration of the mechanism
patterning the unbranched leg of Drosophila.
Received: 14 May 1997 / Accepted: 25 September 1997 相似文献
2.
The digital airborne sensor, CASI (Compact Airborne Spectrographic Imager) has considerable potential for mapping marine
habitats. Here we present an account of one of the first coral reef applications. The CASI was flown over reefs of the Turks
and Caicos Islands (British West Indies) and set to view 1 m pixels in 8 spectral bands. In addition, reef habitats were sampled
in situ by visual assessment of percent cover in 1 m quadrats. Seagrass standing crop was assessed using a calibrated visual scale.
Benthic habitats were classified using hierarchical cluster and similarity percentage analyses of the field survey data. Two
levels of habitat discrimination were assessed: a coarse level (corals, algae, sand, seagrass) and a fine level which included
nine reef habitats. Overall accuracies of CASI-derived habitat maps were 89% and 81% for coarse and fine levels of habitat
discrimination, respectively. Accuracies were greatest once CASI data had been processed to compensate for variations in depth
and edited to take account of generic patterns of reef distribution. These overall accuracies were significantly (P<0.001) better than those obtained from satellite imagery of the same site (Landsat MSS, Landsat TM, SPOT XS, SPOT Pan, merged
Landsat TM/SPOT Pan). Results from CASI were also significantly better than those from interpretation of 1:10 000 colour aerial
photographs of reefs in Anguilla (Sheppard et al. 1995). However, the studies may not have been entirely comparable due to
a disparity in the areas mapped.
Accepted: 26 May 1997 相似文献
3.
Scleractinian coral reefs, when coexistent with siliciclastic sediments, usually occur in association with deltaic or coastal
sands. Nevertheless, Pleistocene reef limestones in southwestern Taiwan are developed in association with thick claystones
that were deposited in a deeper-water environment. These reef limestones are characterized by: (1) rapid transition from underlying
claystones upward to reefal limestones, (2) lateral interfingering with open-shelf claystones, (3) being overlain by terrestrial
deposits or exposed with no covering strata, and (4) being located in close association with anticlines. The authors propose
that these reef limestones developed on anticlinal ridges raised above the adjacent sea floor by thrust-front migration in
a foreland setting.
Accepted: 21 April 1998 相似文献
4.
Abstract . This paper assesses variation in coral species diversity within the Indonesian archipelago, and the influence of regional species pools, geomorphology and anthropogenic pollution on coral species diversity and occurrence. We obtained transects from 33 sites on 14 reefs in three regions of Indonesia: Ambon (Moluccas), South Sulawesi and the Java Sea. We determined the within‐site species richness by using species‐sampling curves. Cluster analysis and multi‐dimensional scaling showed that land‐based pollution was the primary determinant of coral species diversity and species occurrence on reefs. Relatively unaffected reference sites in eastern Indonesia were approximately 20% more diverse than Java Sea reference sites. Rare species formed a higher proportion of the coral fauna on eastern Indonesian sites, and eastern Indonesian apparent endemic species contributed approximately 25% of the total species pool sampled. Between‐site variation in species occurrence was lower on Java Sea reefs than on eastern Indonesian reefs. A larger species pool in eastern Indonesia than in the Java Sea probably accounted for most of the difference in within‐site species diversity between eastern Indonesian and Java Sea reference sites. High fishing intensity in the Java Sea, including destructive fishing practices, may have also contributed to reduced within‐site species diversity on Java Sea reference reefs. Despite the fact that the Java Sea was exposed during Pleistocene lowstands, and was recolonized by marine organisms only within the last 10 000 years, coral species diversity and assemblage composition on the Java Sea reefs was largely similar to open ocean reefs in eastern Indonesia. 相似文献
5.
The nocturnal orientation behaviour of the late pelagic stages of two reef fish families (Apogonidae and Pomacentridae) was
examined using behavioural cages deployed in the field. The behavioural cages enabled the fish to choose between swimming
towards or away from the reef in response to natural cues. Overall, 55% of fish displayed a choice in the experiments, however,
the proportion varied between the two families, with 67% of pomacentrids and 27% of apogonids displaying a choice. In both
families, of the fish which displayed a choice, the proportion of fish swimming towards the reef was significantly greater
than 50%, as random movement would predict (64% of pomacentrids and 67% of apogonids swam towards the reef). This proportion
did not vary significantly among four field sites with different current regimes and geographic locations. The results suggest
that the late pelagic stages of reef fish display nocturnal orientation behaviour, possibly in response to sound, which may
aid in their settlement on reefs.
Accepted: 18 August 1997 相似文献
6.
P. J. Edmunds 《Coral reefs (Online)》1999,18(2):133-140
Millepora species are conspicuous members of shallow coral reefs where they occupy a variety of substrata and produce morphologically
complex skeletons. This study focuses on the roles of growth on vertical and horizontal surfaces and the production of encrusting
bases and branches (a “sheet-tree” morphology) for the success of the Millepora alcicornis on coral reefs. The effects of inclination were investigated by comparing the size and growth rates of M. alcicornis on vertical and horizontal surfaces at 3–5 m depth, in St. John, US Virgin Islands. The consequences of morphological complexity
were investigated by comparing polyp density, chlorophyll content and biomass between encrusting bases and branches; the role
of branches in asexual reproduction was also quantified. Colonies on vertical surfaces had larger encrusting bases, longer
perimeters and lower densities of branches compared to those on horizontal surfaces. Growth rates also varied significantly
between surfaces, largely because colonies on horizontal surfaces shrank in area while those on vertical surfaces increased
in area, albeit slowly. Branches were not specialized in comparison to encrusting bases in terms of the density of dactylozooids
and gastrozooids, chlorophyll content and biomass, but they were effective asexual propagules. During one storm, 79% of the
branches were removed from colonies of M. alcicornis, and 4% attached to the substratum to produce new colonies at a density of ≈0.5 colonies.m-2. Anecdotal observations suggest that such storms rarely damaged encrusting bases on vertical surfaces, but often destroyed
those on horizontal surfaces. Thus, the encrusting bases on vertical surfaces are likely to be large because of greater age
rather than faster growth, while those on horizontal surfaces are likely to be small because they are relatively young and
short lived. These findings suggest that the success of M. alcicornis is a result, in part, of the beneficial consequences of their “sheet-tree” morphology, that supports: (a) slow growth and
resistance to wave damage of encrusting bases on vertical surfaces, and (b) the use of branches as asexual propagules.
Accepted: 24 November 1998 相似文献
7.
A. Angiolillo M. Mencuccini L. Baldoni 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,98(3-4):411-421
Amplified fragment length polymorphism (AFLP) analysis was used to study the genetic variation within and among populations
of genus Olea. A group of genotypes, all of them cultivated varieties of a single species, Olea europaea, was compared with wild olives and with a group of individuals belonging to different Olea species. Five primer combinations were used which produced about 290 polymorphic bands. The data obtained were elaborated
with the Nei’s genetic similarity coefficient, applying different clustering methods and the Principal Coordinate Analysis.
Cultivars, wild olives and North-West African species formed groups clustering together at a similarity level of 0.56, while
the Olea species from East Africa and Asia grouped separately. Species from the Indian Ocean and Australia showed the highest diversity.
We hypothesize that cultivars and wild plants are different forms of the same O. europaea species. The Olea from East Africa and Asia may be assigned to a different species, while the role of O. laperrini as well as that of O. maroccana as an intermediary form is confirmed.
Received: 30 April 1998 / Accepted: 13 August 1998 相似文献
8.
Matthieu Leray Alice L. Alldredge Joy Y. Yang Christopher P. Meyer Sally J. Holbrook Russell J. Schmitt Nancy Knowlton Andrew J. Brooks 《Molecular ecology》2019,28(10):2694-2710
Theories involving niche diversification to explain high levels of tropical diversity propose that species are more likely to co‐occur if they partition at least one dimension of their ecological niche space. Yet, numerous species appear to have widely overlapping niches based upon broad categorizations of resource use or functional traits. In particular, the extent to which food partitioning contributes to species coexistence in hyperdiverse tropical ecosystems remains unresolved. Here, we use a molecular approach to investigate inter‐ and intraspecific dietary partitioning between two species of damselfish (Dascyllus flavicaudus, Chromis viridis) that commonly co‐occur in branching corals. Species‐level identification of their diverse zooplankton prey revealed significant differences in diet composition between species despite their seemingly similar feeding strategies. Dascyllus exhibited a more diverse diet than Chromis, whereas Chromis tended to select larger prey items. A large calanoid copepod, Labidocera sp., found in low density and higher in the water column during the day, explained more than 19% of the variation in dietary composition between Dascyllus and Chromis. Dascyllus did not significantly shift its diet in the presence of Chromis, which suggests intrinsic differences in feeding behaviour. Finally, prey composition significantly shifted during the ontogeny of both fish species. Our findings show that levels of dietary specialization among coral reef associated species have likely been underestimated, and they underscore the importance of characterizing trophic webs in tropical ecosystems at higher levels of taxonomic resolution. They also suggest that niche redundancy may not be as common as previously thought. 相似文献
9.
This paper reports field observational evidence on the diversity-biomass production relationship from eastern Mediterranean
shrublands dominated by Cistus salviifolius. The main results are: (1) plant diversity and ecosystem primary production are positively correlated in the Cistus shrublands, which are multigrowth form systems; (2) the taxonomic and growth form diversity in Cistus shrublands suggests that there is strong differentiation along the structural niche axis, and thus functional redundancy
is weak; (3) the performance of the dominant Cistus in terms of biomass production did not affect the overall diversity-biomass production of the studied communities.
Received: 18 October 1999 / Accepted: 13 April 2000 相似文献
10.
U. Sommer 《Oecologia》2000,122(2):284-287
This study presents model experiments on the effect of the spatial pattern of herbivory on primary producer diversity. Microalgal
biofilms (periphyton) were exposed to different mixtures of two benthic herbivores, the isopod Idothea chelipes and the gastropod Littorina littorea. The herbivores are similar in their feeding selectivity but differ strongly in the spatial pattern of grazing. Idothea did not increase the spatial heterogeneity of algal cell densities beyond the level of ungrazed controls (<1 order of magnitude
between local minima and maxima at the 1 mm2 scale). Littorina grazing, in contrast, created a pronounced spatial heterogeneity with maximum:minmum ratios of almost 3 orders of magnitude.
When algae were exposed to mixtures of both gazers, the spatial heterogeneity of microalgal cell densities increased with
an increasing proportion of Littorina in the herbivore mixture. Algal species richness, diversity and evenness also increased with increasing proportions of Littorina, and was highly significantly correlated with the spatial heterogeneity of cell densities.
Received: 25 May 1999 / Accepted: 14 September 1999 相似文献
11.
We examine whether Species Abundance Distribution models (SADs) and diversity indices can describe how species colonization status influences species community assembly on oceanic islands. Our hypothesis is that, because of the lack of source-sink dynamics at the archipelago scale, Single Island Endemics (SIEs), i.e. endemic species restricted to only one island, should be represented by few rare species and consequently have abundance patterns that differ from those of more widespread species. To test our hypothesis, we used arthropod data from the Azorean archipelago (North Atlantic). We divided the species into three colonization categories: SIEs, archipelagic endemics (AZEs, present in at least two islands) and native non-endemics (NATs). For each category, we modelled rank-abundance plots using both the geometric series and the Gambin model, a measure of distributional amplitude. We also calculated Shannon entropy and Buzas and Gibson's evenness. We show that the slopes of the regression lines modelling SADs were significantly higher for SIEs, which indicates a relative predominance of a few highly abundant species and a lack of rare species, which also depresses diversity indices. This may be a consequence of two factors: (i) some forest specialist SIEs may be at advantage over other, less adapted species; (ii) the entire populations of SIEs are by definition concentrated on a single island, without possibility for inter-island source-sink dynamics; hence all populations must have a minimum number of individuals to survive natural, often unpredictable, fluctuations. These findings are supported by higher values of the α parameter of the Gambin mode for SIEs. In contrast, AZEs and NATs had lower regression slopes, lower α but higher diversity indices, resulting from their widespread distribution over several islands. We conclude that these differences in the SAD models and diversity indices demonstrate that the study of these metrics is useful for biogeographical purposes. 相似文献
12.
Investigation of the life history of corals is hampered by an inability to identify early recruits. In this study, the pattern
of formation and morphology of the juvenile skeletons of three laboratory-reared pocilloporids, Seriatopora hystrix, Stylophora pistillata and Pocillopora damicornis, were compared to determine whether they could be reliably distinguished. The pattern of skeleton formation, including the
origin and structure of the septa, columella and corallite wall was similar in all species. Following the completion of the
primary corallite wall after 4–5 days, these species could be identified by differences in the diameter of the primary corallite.
The mean diameter (±SE) of each species differed markedly: S. hystrix 400 ± 2.7 μm, range 325–450 μm; S. pistillata 505 ± 3.5 μm, range 400–550 μm; P. damicornis 697 ± 7.5 μm, range 492–885 μm. Values for the primary corallite diameter overlapped in only 3% of samples, demonstrating
the potential utility of this feature as a tool for classifying recruits obtained from the field.
Accepted: 4 January 2000 相似文献
13.
S. K. Wilson A. M. Dolman A. J. Cheal M. J. Emslie M. S. Pratchett H. P. A. Sweatman 《Coral reefs (Online)》2009,28(1):3-14
Habitat perturbations play a major role in shaping community structure; however, the elements of disturbance-related habitat
change that affect diversity are not always apparent. This study examined the effects of habitat disturbances on species richness
of coral reef fish assemblages using annual surveys of habitat and 210 fish species from 10 reefs on the Great Barrier Reef
(GBR). Over a period of 11 years, major disturbances, including localised outbreaks of crown-of-thorns sea star (Acanthaster planci), severe storms or coral bleaching, resulted in coral decline of 46–96% in all the 10 reefs. Despite declines in coral cover,
structural complexity of the reef framework was retained on five and species richness of coral reef fishes maintained on nine
of the disturbed reefs. Extensive loss of coral resulted in localised declines of highly specialised coral-dependent species,
but this loss of diversity was more than compensated for by increases in the number of species that feed on the epilithic
algal matrix (EAM). A unimodal relationship between areal coral cover and species richness indicated species richness was
greatest at approximately 20% coral cover declining by 3–4 species (6–8% of average richness) at higher and lower coral cover.
Results revealed that declines in coral cover on reefs may have limited short-term impact on the diversity of coral reef fishes,
though there may be fundamental changes in the community structure of fishes. 相似文献
14.
Macroalgae, nutrients and phase shifts on coral reefs: scientific issues and management consequences for the Great Barrier Reef 总被引:26,自引:13,他引:13
L. J. McCook 《Coral reefs (Online)》1999,18(4):357-367
Degradation of coral reefs often involves a “phase shift” from abundant coral to abundant macroalgae. This paper critically
reviews the roles of nutrient increases in such phase shifts. I conclude that nutrient overloads can contribute to reef degradation,
but that they are unlikely to lead to phase shifts simply by enhancing algal growth rates and hence allowing overgrowth of
corals, unless herbivory is unusually or artificially low. Concentrations of dissolved inorganic nutrients are poor indicators
of reef status, and the concept of a simple threshold concentration that indicates eutrophication has little validity. I discuss
the significance and consequences of these assessments for reef management, focusing on the Great Barrier Reef, and conclude
with some specific recommendations, including protection of herbivorous fishes, minimisation of terrestrial runoff, and protection
of coastal reefs.
Accepted: 13 August 1999 相似文献
15.
M. J. Iqbal N. Aziz N. A. Saeed Y. Zafar K. A. Malik 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):139-144
Random amplified polymorphic DNA (RAPD) analysis was used to evaluate the genetic diversity of elite commercial cotton varieties.
Twenty two varieties belonging to Gossypium hirsutum L. and one to G. arboreum L. were analyzed with 50 random decamer primers using the polymerase chain reaction (PCR). Forty nine primers detected polymorphism
in all 23 cotton varieties, while one produced monomorphic amplification profiles. A total of 349 bands were amplified, 89.1%
of which were polymorphic. Cluster analysis by the unweighted pair group method of arithmetic means (UPGMA) showed that 17
varieties can be placed in two groups with a similarity ranging from 81.51% to 93.41%. G. hirsutum L. varieties S-12, V3 and MNH-93 showed a similarity of 78.12, 74.46 and 69.56% respectively with rest of the varieties. One
variety, CIM-1100, showed 57.02% similarity and was quite distinct. The diploid cotton G. arboreum L. var. Ravi was also very distinct from rest of its tetraploid counterparts and showed only 55.7% similarity. The analysis
revealed that the intervarietal genetic relationships of several varieties is related to their center of origin. As expected,
most of the varieties have a narrow genetic base. The results obtained can be used for the selection of possible parents to
generate a mapping population. The results also reveal the genetic relationship of elite commercial cotton varieties with
some standard “Coker” varieties and the diploid G. arboreum L. var. Ravi (old world cotton).
Received: 12 July 1996 / Accepted: 26 July 1996 相似文献
16.
There is limited information on the validity and reproducibility of estimates of benthic cover from manta tow surveys. To
address this, benthic cover estimates from the same reef area were compared (i) among observers and (ii) with an independent
assessment using under-water video. Benthic cover was classified into 11 categories. There was generally unbiased agreement
within one cover category, both among observers (89%) and for comparisons between manta tow and video (86%). While estimates
of dead coral cover were reproducible, they were not valid because the concordance between observer estimates and video estimates
was not greater than would be expected by chance. Manta tow estimates of the cover of sand and rubble were biased in that
they consistently overestimated sand and rubble cover in comparison with estimates from video. The results indicate that manta
towing is generally effective for the broadscale estimation of live coral cover, providing observers receive adequate training.
Accepted: 25 June 1999 相似文献
17.
Limb development in a primitive crustacean,Triops longicaudatus: subdivision of the early limb bud gives rise to multibranched limbs 总被引:2,自引:2,他引:0
Recent advances in developmental genetics of Drosophila have uncovered some of the key molecules involved in the positioning and outgrowth of the leg primordia. Although expression
patterns of these molecules have been analyzed in several arthropod species, broad comparisons of mechanisms of limb development
among arthropods remain somewhat speculative since no detailed studies of limb development exist for crustaceans, the postulated
sister group of insects. As a basis for such comparisons, we analysed limb development in a primitive branchiopod crustacean,
Triops longicaudatus. Adults have a series of similar limbs with eight branches or lobes that project from the main shaft. Phalloidin staining
of developing limbs buds shows the distal epithelial ridge of the early limb bud exhibits eight folds that extend in a dorsal
ventral (D/V) arc across the body. These initial folds subsequently form the eight lobes of the adult limb. This study demonstrates
that, in a primitive crustacean, branched limbs do not arise via sequential splitting. Current models of limb development
based on Drosophila do not provide a mechanism for establishing eight branches along the D/V axis of a segment. Although the events that position
limbs on a body segment appear to be conserved between insects and crustaceans, mechanisms of limb branching may not.
Received: 28 February 1996/Accepted: 24 June 1996 相似文献
18.
The rate of terrigenous sediment supply to the central Great Barrier Reef (GBR) coastline has probably increased in the last
200 years due to human impact on the catchments of central Queensland. This has led some researchers and environmental managers
to conclude that corals within the GBR are under threat from increased turbidity and sedimentation. Using geological data
and information on sedimentary processes, we show that turbidity levels and sediment accumulation rates at most coral reefs
will not be increased, because these factors are not currently limited by sediment supply.
Accepted: 15 January 1999 相似文献
19.
S. A. Khan D. Hussain E. Askari J. McD Stewart K. A. Malik Y. Zafar 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,101(5-6):931-938
Total genomic DNA from 31 available Gossypium species, three subspecies and one interspecific hybrid, were analysed to evaluate genetic diversity by RAPD, using 45 random
decamer primers. A total of 579 amplified bands were observed, with 12.9 bands per primer, of which 99.8% were polymorphic.
OPJ-17 produced the maximum number of fragments while the minimum number of fragments was produced with primer OPA-08. Cluster
analysis by the unweighted paired group method of arithmetic means (UPGMA) showed six main clusters. Cluster ’A’ consisted
of two species and one subspecies of the A-genome, with a 0.78–0.92 Nei’s similarity range. Cluster B, composed of all available
tetraploid species and one interspecific hybrid, showed the same sister cluster. Nei’s similarity ranged from 0.69 to 0.84.
The B-genome formed the UPGMA sister cluster to the E-genome species. Cluster ’C’ consisted of five Gossypium species of which three belong to the B-genome, with Nei’s similarity values of 0.81 to 0.86. Although there was considerable
disagreement at lower infra-generic ranks, particularly among the D- genome (diploid New World species) and C-genome (diploid
Australian species) species. The sole F-genome species Gossypium longicalyx was resolved as a sister group to the D-genome species. Gossypium herbaceum and G. herbaceum Africanum showed the maximum Nei’s similarity (0.93). Minimum similarity (0.29) was observed between Gossypium trilobum and Gossypium nelsonii. The average similarity among all studied species was 50%. The analysis revealed that the interspecific genetic relationship
of several species is related to their centre of origin. As expected, most of the species have a wide genetic base range.
The results also revealed the genetic relationships of the species Gossypium hirsutum to standard cultivated Gossypium barbadense, G. herbaceum and Gossypium arboreum. These results correspond well with previous reported results. The level of variation detected in closely related genotypes
by RAPD analysis indicates that it may be a more efficient marker than morphological marker, isozyme and RFLP technology for
the construction of genetic linkage maps.
Received: 2 January 2000 / Accepted: 12 February 2000 相似文献
20.
C. T. Perry 《Coral reefs (Online)》1998,17(3):277-287
Macroboring organisms are recognised as key agents of reef framework modification and destruction, and while recent studies
in the Pacific have improved understanding of spatial variations in macroboring community structure, and rates of macroboring
within individual reefs, comparable studies from the Caribbean are largely lacking. This study assesses the distribution of
macroboring species and the degree of framework infestation across the reefs at Discovery Bay, north Jamaica. Although individual
species of borers exhibit variable distributions across the reef, relative abundances of the main groups of macroborers (sponges,
bivalves, worms) illustrate clear distributional trends. Sponges are dominant at fore-reef sites, while sipunculan and polychaete
worms are only of importance at back-reef/lagoon and shallow fore-reef sites. Bivalves are locally important within back-reef
and lagoon patch reef framework. Average percentages of internal bioerosion (macroboring) vary between sites, but are highest
at back-reef and deep fore-reef sites. No systematic pattern of variation occurs within back-reef/lagoon samples, but a significant
trend of increased macroboring is recognised with increased water depth on the fore-reef. In addition, significant differences
in terms of the susceptibility of individual coral species are recognised. These factors are likely to result in biasing of
the fossil record, with variable styles of preservation evident both between sites (i.e. with depth/environment) and within
sites (i.e. between coral species).
Accepted: 1 June 1998 相似文献