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1.
An on-going, Caribbean-wide epizootic affecting sea fan corals (Gorgonia spp.) is caused by the fungus Aspergillus sydowii (Thom et Church). We examined the role of crude extracts in resistance of two species of sea fans, Gorgonia ventalina (L.) and G. flabellum (L.), against A. sydowii and a bacterial pathogen of fish, Listonella anguillarum (MacDonell et Colwell). Sea fans were collected in January 1997 from San Salvador, Bahamas, and in June 1997 and January
1998 from Alligator Reef, Florida Keys, USA. Crude extracts from both species were tested to determine concentrations inhibiting
germination of A. sydowii spores. Crude extracts from both species inhibited spore germination at concentrations as low as 1.5 mg ml−1; most samples were active at 5 to 10 mg ml−1. These concentrations are within the range estimated in living tissue and were higher in healthy colonies suggesting their
role in mediating disease susceptibility. We also detected within-colony gradients in antifungal activity, which varied with
the disease state of the colony. In healthy sea fans, resistance was highest at colony edges and lowest in medial and central
regions of the colony. Among sea fans with lesions in the colony center, resistance in tissue from proximal and medial regions
was as high as tissue from the colony edge (i.e. distal region). The increase in antifungal activity suggests an inducible
response by the coral host to the fungal pathogen. This response is most evident among sea fans with lesions in the colony
center and not among colonies with lesions at the edge. Antibacterial activity of crude extracts against L. anguillarum was highest at the colony edge but did not vary with disease state or tissue location.
Received: 10 March 1999 / Accepted: 10 November 1999 相似文献
2.
The frequency and impact of diseases affecting corals throughout the Caribbean have been increasing but little is known about
the factors promoting the emergence and outbreak of disease. A disease caused by a fungal pathogen [Aspergillus sydowii (Thom et Church)] which affects Caribbean sea fan corals provided an opportunity to examine the efficacy of coral crude extracts
in disease resistance. Minimum inhibitory concentration (MIC) assays showed that of the 20 common gorgonian species in the
Florida Keys, extracts from 15 species had MICs < 15 mg ml−1 against A. sydowii pathogenic to sea fans. Extracts from several species in two gorgonian genera (Pseudoplexaura and Pseudopterogorgia) were among the most active, with MICs < 10 mg ml−1. Gorgonia ventalina L., one of two sea fan species known to be hosts to A. sydowii in the field, had an MIC < 10 mg ml−1, suggesting that complete disease resistance requires more active extracts. For the antifungal compounds to be effective
in situ, they must also occur in sufficiently high concentrations in living coral tissue. For example, Pseudopterogorgia americana (Gmelin) had comparatively potent extracts but did not have sufficient concentrations in the tissue to be effective. Conversely,
Plexaura homomalla Esper extracts were less potent but occurred in high enough concentrations in the tissue to be effective against A. sydowii. When potency and extract concentration are considered together (i.e. potency × concentration), several other gorgonian corals
emerge as likely hosts to A. sydowii. Crude extracts from the most active gorgonian species were also effective against two geographic variants of A. sydowii pathogenic to sea fans, a non-pathogenic terrestrial strain of A. sydowii, and three strains of A. flavus Link known to be human, plant, and insect pathogens (MIC range, 7.5 to > 15 mg ml−1). Although the potency in these assays did not attain a clinically significant level, the potency is comparable to a known
antifungal agent, hygromycin B, which had an MIC ≤7.5 mg ml−1 in our assays, highlighting the potential of these gorgonian corals for bioprospecting.
Received: 29 May 1999 / Accepted: 22 May 2000 相似文献
3.
Nancy L. Douglas Kerri M. Mullen Stephanie C. Talmage C. Drew Harvell 《Marine Biology》2007,150(6):1137-1144
Chitinases are involved in defense against chitinaceous pathogens in both invertebrates and vertebrates. This study investigated
whether sea fan corals, Gorgonia ventalina (Linnaeus) collected from the Florida Keys between the summer of 2002 and the summer of 2005 contain chitinases, and whether
these enzymes could serve an analogous protective role against the fungal pathogen, Aspergillus sydowii (Thom et Church). Crude extracts of healthy sea fans contained detectible levels of exochitinase activity in an in vitro
microplate assay using fluorogenic substrates. The exochitinase levels decreased upon injury, agitation, or manipulation of
the tissue. A concurrent, transient increase of exochitinase in the surrounding water suggests that sea fans release chitinases
as a response to these stresses. By contrast, endochitinase was detected in only 2 of 15 sea fans (13%), suggesting a high
degree of variation for this enzyme. Sea fan chitinase-containing seawater and anion exchange chromatography fractions were
both active against A. sydowii in an absorbance-based antifungal assay. The presence of chitinases in sea fan extracts, their release into the surrounding
water upon stress, and their activity against A. sydowii suggests that further study of these enzymes in coral stress responses is warranted. 相似文献
4.
Carlos Toledo-Hernández Alberto M. Sabat Anabella Zuluaga-Montero 《Marine Biology》2007,152(3):527-535
Gorgonia ventalina’s density, size structure and lesion prevalence was measured at six sites in Puerto Rico that exhibited variation in horizontal
water transparency, sedimentation rates, suspended particle matter, scleractinian and macroalgal cover. G. ventalina density varied significantly among sites (between 0.84 and 0.007 colonies/m2), and was positively correlated with water transparency. Size structure did not vary much among sites, and reflects high
mortality among the smaller size classes and high survivorship in large colonies. Prevalence of active fungi-induced lesions
(type I) did not vary significantly among sites and was density-independent. However, prevalence of old lesions of unknown
origin (type II) did vary among reefs and was negatively correlated with water transparency. Prevalence of types I or II lesions
was independent of colony size. Our results suggest that (1) turbidity and sedimentation are important abiotic factors controlling
the abundance of sea fans, (2) variation in settlement success and early survivorship of recruits has more impact on the sea
fan populations than variation in the survivorship of large colonies and (3) prevalence of aspergillosis (type I) at the studied
sites is similar to that reported for other Caribbean reefs and supports the epizootic nature of the disease and (4) lesions
with exposed skeleton are more likely to be colonized by fouling organisms at impacted reefs. The combined effects of anthropogenic
impacts and aspergillosis may cause local extinctions of sea fans, as is becoming evident in many reefs in Puerto Rico. 相似文献
5.
Environmental conditions greatly impact the dynamics of host–pathogen relationships, affecting outbreaks and emergence of new diseases. In corals, epizootics have been a main contributor to the decline of reef ecosystems and rising sea surface temperatures associated with climate change are thought to exacerbate virulence of pathogens and/or compromise the immune responses of coral hosts. Among pathogens strategies, protease secretion is a common virulence factor that promotes colonization of the host. As such, protease inhibitors play an invaluable role to the host for protection against pathogen invasion. This study describes changes in activity of proteases secreted by the fungal pathogen, Aspergillus sydowii, and protease inhibitors of Gorgonia ventalina under ambient and elevated temperatures and health conditions (disease and healthy). G. ventalina colonies were collected from Florida Keys, Florida (24° 34.138N, 81° 22.905W) or La Parguera, Puerto Rico (17° 56.091N, 67° 02.577W) in 2007 and 2012, respectively. At elevated temperatures, protease activity was significantly higher than at ambient temperatures in A. sydowii. Temperature stress did not induce a change in protease inhibitor activity, but in healthy G. ventalina colonies, inhibitor activity against proteases was higher than in diseased individuals. Healthy colonies appear capable of resisting proteolytic activity, but diseased individuals are still likely affected by pathogen infections. These data suggest that rising sea surface temperatures due to climate change may increase levels of virulence (protease activity) of A. sydowii, while immunity (protease inhibitor) of G. ventalina may not be affected. 相似文献
6.
Marc Slattery 《Chemoecology》1999,9(3):97-104
Summary. Fungal pathogenesis of the sea fan Gorgonia ventalina has developed on the Belize barrier reef during 1997 and 1998. The disease incidence (= percent of infected sea fans) remained
unchanged at two sites along the barrier reef crest between years. However, the incidence increased significantly at an offshore
atoll during that time, as did the virulence (= percent tissue loss). Grazing by the gorgonian specialist mollusc Cyphoma gibbosum increased on infected sea fans. Sea fan responses to fungal infection included significant decreases in a furano-germacrene
compound with antifeedant activity and significant increases in the concentration of sclerites at the site of infection. Feeding
assays utilizing C. gibbosum and a natural assemblage of reef fishes indicated sclerites are an effective deterrent, to both consumers, at both pre- and
post-infected concentrations. In contrast, the compound was only deterrent to the fish, and only at concentrations found in
pre-infected sea fans. These data indicate that sea fan pathogenesis can directly and indirectly affect population health
via virulent tissue necrosis and pathogen-mediated reductions in grazer resistance, respectively.
Received 4 November 1998; accepted 5 April 1999. 相似文献
7.
Aspergillosis is a widespread disease that has impacted the demography of the Caribbean sea fan coral, Gorgonia ventalina. The innate coral immune defenses can be measured as constitutive levels of immune proteins (peroxidase [POX], prophenoloxidase
[PPO], lysozyme-like activity [LYS], exochitinase [EXOC]), antioxidant (superoxide dismutase [SOD]), and antimicrobial (antibacterial
[AB] and antifungal [AF]) activity. Therefore, variations in these parameters across a geographic region could provide clues
to the role of environment in disease. This study examined healthy sea fans collected in July 2005 from six offshore sites
in the Florida Keys lying between 24.569°N and 25.220°N, a distance of ~145 km. Contrary to expectations, small (<15 cm) colonies
did not differ significantly from large colonies (>15 cm) in the protein-based levels of activity in any of the measured parameters.
However, there were significant differences in many of the parameters among sites, and Molasses Reef and Looe Key Reef were
the most different in POX, PPO, SOD, and AF activity. This suggests that there are potential site-specific environmental factors
that shape the immune physiology of colonies. Several proxies of environmental stress were also regressed against levels of
the immune parameters. The proxies included 10 year averages of benthic community composition, 5 year averages of water quality,
and historic aspergillosis disease prevalence and severity. Generality about environmental drivers was limited by assaying
only six sites, but several patterns did emerge. SOD, EXOC, and AF activity were all correlated with percent bare substrate
cover, suggesting that certain immune components may be activated in low coral environments. LYS and EXOC activity were positively
correlated with dissolved inorganic nitrogen (DIN), one proxy of water quality. There were no relationships between any of
the measured immune parameters and previous disease prevalence and severity. This study is a first step in evaluating levels
of within- and between-site variation in coral immunity and investigating possible environmental drivers. 相似文献
8.
Expansion of a central California kelp forest following the mass mortality of sea urchins 总被引:3,自引:0,他引:3
The mass mortality by disease of a localized population of sea urchins, Strongylocencrotus franciscanus, on the seaward side of a kelp forest was followed by the rapid seaward expansion of 4 species of brown algae, Macrocystis pyrifera, Laminaria dentigera, Pterygophora california, and to a lesser extent, Nereocystis leutkeana. One other brown alga, Cystoseira osmundacea, failed to become established in the newly available area. Competition among M. pyrifera, L. dentigera, P. californica, and N. Leutkeana apparently was severe, and within 1 year after the demise of the sea urchins, M. pyrifera formed a dense, nearly monospecific stand. Experimental removal of M. pyrifera demonstrated that the canopy of these plants limited light penetration to levels below that necessary for the growth and survival of other brown and red algae. 相似文献
9.
Heterogeneity in the photoprotective capacity of three Antarctic diatoms during short-term changes in salinity and temperature 总被引:1,自引:0,他引:1
The Antarctic marine ecosystem changes seasonally, forming a temporal continuum of specialised niche habitats including open
ocean, sea ice and meltwater environments. The ability for phytoplankton to acclimate rapidly to the changed conditions of
these environments depends on the species’ physiology and photosynthetic plasticity and may ultimately determine their long-term
ecological niche adaptation. This study investigated the photophysiological plasticity and rapid acclimation response of three
Antarctic diatoms—Fragilariopsis cylindrus, Pseudo-nitzschia subcurvata and Chaetoceros sp.—to a selected range of temperatures and salinities representative of the sea ice, meltwater and pelagic habitats in the
Antarctic. Fragilariopsis cylindrus displayed physiological traits typical of adaptation to the sea ice environment. Equally, this species showed photosynthetic
plasticity, acclimating to the range of environmental conditions, explaining the prevalence of this species in all Antarctic
habitats. Pseudo-nitzschia subcurvata displayed a preference for the meltwater environment, but unlike F. cylindrus, photoprotective capacity was low and regulated via changes in PSII antenna size. Chaetoceros sp. had high plasticity in non-photochemical quenching, suggesting adaptation to variable light conditions experienced in
the wind-mixed pelagic environment. While only capturing short-term responses, this study highlights the diversity in photoprotective
capacity that exists amongst three dominant Antarctic diatom species and provides insight into links between ecological niche
adaptation and species’ distribution. 相似文献
10.
Sebastián P. Luque John P. Y. Arnould Edward H. Miller Yves Cherel Christophe Guinet 《Marine Biology》2007,152(1):213-224
The duration of periods spent ashore versus foraging at sea, diving behaviour, and diet of lactating female Antarctic (Arctocephalus gazella, AFS) and subantarctic (A. tropicalis, SFS) fur seals were compared at Iles Crozet, where both species coexist. The large disparity in lactation duration (SFS:
10 months, AFS: 4 months), even under local sympatry, has led to the expectation that AFS should exhibit higher foraging effort
or efficiency per unit time than SFS to allow them to wean their pups in a shorter period of time. Previous evidence, however,
has not supported these expectations. In this study, the distribution of foraging trip durations revealed two types of trips:
overnight (OFT, <1 day) and long (LFT, >1 day), in common with other results from Macquarie Island. However, diving behaviour
differed significantly between foraging trip types, with greater diving effort in OFTs than in LFTs, and diving behaviour
differed between fur seal species. OFTs were more frequent in SFS (48%) than in AFS (28%). SFS performed longer LFTs and maternal
attendances than AFS, but spent a smaller proportion of their foraging cycle at sea (66.2 vs. 77.5%, respectively). SFS dove
deeper and for longer periods than AFS, in both OFTs and LFTs, although indices of diving effort were similar between species.
Diel variation in diving behaviour was lower among SFS, which foraged at greater depths during most of the night time available
than AFS. The diving behaviour of AFS suggests they followed the nychthemeral migration of their prey more closely. Concomitant
with the differences in diving behaviour, AFS and SFS fed on the same prey species, but in different proportions of three
myctophid fish (Gymnoscopelus fraseri, G. piabilis, and G. nicholsi) that represented most of their diet. The estimated size of the most important fish consumed did not vary significantly between
fur seal species, suggesting that the difference in dive depth was mostly a result of changes in the relative abundance of
these myctophids. The energy content of these fish at Iles Crozet may thus influence the amount and quality of milk delivered
to pups of each fur seal species. These results contrast with those found at other sites where both species coexist, and revealed
a scale of variation in foraging behaviour which did not affect their effort while at sea, but that may be a major determinant
of foraging efficiency and, consequently, maternal investment. 相似文献
11.
Coral diseases have increased in frequency over the past few decades and have important influences on the structure and composition of coral reef communities. However, there is limited information on the etiologies of many coral diseases, and pathways through which coral diseases are acquired and transmitted are still in question. Furthermore, it is difficult to assess the impacts of disease on coral populations because outbreaks often co-occur with temperature-induced bleaching and anthropogenic stressors. We developed spatially explicit population models of coral disease and bleaching dynamics to quantify the impact of six common diseases on Florida Keys corals, including aspergillosis, dark spots, white band, white plague, white patch, and Caribbean yellow band. Models were fit to an 8-year data set of coral abundance, disease prevalence, and bleaching prevalence. Model selection was used to assess alternative pathways for disease transmission, and the influence of environmental stressors, including sea temperature and human population density, on disease prevalence and coral mortality. Classic disease transmission from contagious to susceptible colonies provided the best-fit model only for aspergillosis. For other diseases, external disease forcing, such as through a vector or directly from pathogens in the environment, provided the best fit to observed data. Estimates of disease reproductive ratio values (R0) were less than one for each disease, indicating coral colonies were below densities required for diseases to become established through contagious spread alone. Incidences of white band and white patch disease were associated with greater susceptibility or slower recovery of bleached colonies, and no disease outbreaks were associated with periods of elevated sea temperatures alone. Projections of best-fit models indicated that, atleast during the period of this study, disease and bleaching did not have substantial impacts on populations and impaired rates of population growth appeared to be attributable to other stressors. By applying epidemiological models to field data, our study gives qualitative insights into the dynamics of coral diseases, relative stressor impacts, and directions for future research. 相似文献
12.
J. Kohlmeyer 《Marine Biology》1971,8(4):344-350
Fungi inhabiting Sargassum spp. from the Sargasso Sea were examined. Three ascomycetes were found, two of which are new records for this environment. Haloguignardia oceanica (Ferdinandsen et Winge) Kohlm. comb. nov. was collected only once before, over 50 years ago. Haloguignardia tumefaciens (Cribb et Herbert) Cribb et Cribb was known only from Australia and New Zealand. Imperfect states of these ascomycetes and fruiting bodies (acervuli) of a hyperparasitic deuteromycete (cf. Sphaceloma sp.) were found for the first time in the galls of the two species. Lindra thalassiae
Orpurt et al., previously known only from the sea grass Thalassia testudinum
Köngig, develops in air bladders of Sargassum sp., causing a shedding of infested vesicles. Possible reasons for the rarity of fungal species and diseased plants in the Sargasso Sea are diseussed.Dedicated respectfully to my teacher, Professor Dr. H Drawert (Universität Famburg), on the occasion of his 60th birthday. 相似文献
13.
Studies conducted on the distribution, fate and metabolism of DDT in a model ecosystem simulating a tropical marine environment of fish, Gobious nudiceps, Lethrinus harak, Gobious keinesis, Gobious nebulosis and white shrimp (Panaeus setiferus), show that DDT concentration in the water decreases rapidly within the first 24?h. Rapid accumulation of the pesticide in the biota also reaches a maximum level in 24?h before gradually declining. The bioaccumulation factors calculated for the fish species (G. keinesis) and white shrimp (P. Setiferus) were 270 and 351, respectively, after 24?h. There was a steady build up of DDT residues in the sediment during the first 24?h which continued to a maximum concentration of 6.66?ng/g in the seawater/fish/sediment ecosystem after 3 weeks and 5.27?ng/g in the seawater/shrimps/sediment ecosystem after 2.7 days. The depuration of the accumulated pesticide was slow with only 54% lost in G. nudiceps within 3 days of exposure in fresh sea water. By contrast, depuration was fast in the white shrimp, which lost 97% of the accumulated pesticide under the same conditions. DDT was found to be toxic to two of the fish species (G. nebulosis and L. harak) and to white shrimp, and the degree of toxicity was dependent on the particular species. The 24?h LC50 at room temperature for the fish species G. nebulosis and white shrimp was found to be 0.011 and 0.116?mg/kg, respectively. These levels are comparable to the ones recorded for the temperate organisms. Degradation of DDT to its primary metabolites, DDE and DDD, was found in all the compartments of the ecosystem with DDE being the major metabolite in the fish, shrimps and sediment, while in seawater, DDD dominated as the major metabolite. 相似文献
14.
Population divergence in the sinistral whelks of North America,with special reference to the east Florida ecotone 总被引:4,自引:0,他引:4
This study evaluated models of species relationships among sinistral whelks in the genus Busycon in the Atlantic and Gulf of Mexico. Gene frequencies at eight polymorphic allozyme loci, shell morphology, anatomy, and partial DNA sequences for the cytochrome c oxidase I (COI) mitochondrial gene were examined in eight populations, ranging from New Jersey to the Yucatan peninsula, and from the dextrally coiled sister taxon Busycon carica (Gmelin, 1791). Whelks were collected in 1997 and 1998. The maximum COI sequence divergence recorded among 32 sinistral individuals was 1.96%, which together with the absence of any gross or qualitative morphological differences, suggested all eight populations should be considered conspecific. High levels of divergence between the allopatric western Atlantic and Gulf of Mexico populations, as revealed by fixed or nearly fixed differences at several allozyme-encoding loci were interpreted as evidence that the east Florida ecotone constitutes a significant barrier to gene flow. Size trimming also revealed several significant quantitative differences in shell and radular morphology between the three pooled Atlantic populations and five pooled Gulf populations. The Yucatan sample was the most distinctive conchologically, with heavy spines and tumid ridges, possibly related to stone crab predation. Based on the evidence all left-handed whelks of North America should be referred to the oldest available nomen, Busycon perversum (Linné, 1758), with three subspecies, B. perversum perversum along the Yucatan peninsula, B. perversum sinistrum (Hollister, 1958) in the northern and eastern Gulf of Mexico, and B. perversum laeostomum (Kent, 1982) in the Atlantic.Communicated by J.P. Grassle, New Brunswick 相似文献
15.
To understand the variation in aggressiveness and factors important for contest outcome, we quantified and compared agonistic
interactions of four field cricket species in eastern North America: Gryllus fultoni (Orthoptera; Gryllidae), G. vernalis, G. pennsylvanicus, and G. rubens. The most aggressive behavior that we observed, the grapple, was frequently displayed in agonistic trials of G. pennsylvanicus and G. rubens. By contrast, we never observed this behavior in trials involving G. fultoni and G. vernalis. Consequently, species was the only significant variable affecting the variation in aggressiveness, whereas size difference,
age difference, and contest duration had no significant effect. In species with high levels of aggressiveness, G. pennsylvanicus and G. rubens, the factors that might be indicative of resource holding potential such as size or age difference seemed to be significant
for contest outcome. In species with low levels of aggressiveness, G. fultoni and G. vernalis, however, there were indications that contest outcomes were determined by aggressiveness itself rather than the size and
age differences between opponents. Markov chain analyses revealed that the difference in aggressiveness between species with
high and low levels of aggressiveness lay in a sequence of escalating behaviors: antennal fencing, mandible flare, and grapple.
The escalated state of aggressiveness characterized by this behavioral sequence in G. pennsylvanicus and G. rubens seems to be the ancestral state in the North American Gryllus phylogeny. We argue that the loss of a tendency to use burrows in G. fultoni and G. vernalis might be related to low levels of aggressiveness in these species. 相似文献
16.
We examined the location of squuestered secondary metabolites in three species of sea hares, Stylocheilus longicauda, Dolabella auricularia, and Aplysia californica (Opisthobranchia: Anaspidea). The sea hares ate a natural diet or were fed an artificial diet containing secondary metabolites in the laboratory. In all three species, sequestered secondary metabolites were located almost exclusively in the digestive gland, an internal organ, rather than in the exterior parts of the body, in eggs, or in ink (released when sea hares are disturbed). S. longicauda, a specialist sea hare, was able to sequester measur-able amounts of all six algal metabolites offered (caulerpenyne, halimedatetraacetate, pachydictyol A, malyingamides A and B, and ochtodene) and two (luffariellolide and Dysidea spp. brominated diphenyl ether) of three sponge metabolites offered (chondrillin was not sequestered). Malyngamides A and B, found in the host plant of S. longicauda, were sequestered at high, but not unique concentrations. D. auricularia, a generalist sea hare, was fed caulerpenyne, pachydictyol A and malyngamide B; patterns of sequestration of these three compounds did not differ markedly between S. longicauda and D. auricularia. S. longicauda did not lose measurable amounts of malyngamides after 18 d on a malyngamide-free diet. These results suggest that sea hares have generic mechanisms for sequestering algal metabolites rather than mechanisms that are tightly linked to particular compounds, that these mechanisms do not differ dramatically between species, and that sequestered secondary metabolites are not located optimally for defense. 相似文献
17.
E. Sala 《Marine Biology》1997,129(3):531-539
Direct observations of predation on 436 individuals of the sea urchin Paracentrotus lividus (Lamarck) were carried out in infralittoral rocky bottoms (between 5 and 20 m deep) in three Mediterranean marine reserves.
The predator guild was composed of six fish species, the sparids Diplodus sargus and D. vulgaris being the main predators, and the labrid Coris julis a major predator of juvenile sea urchins. Four species attempted but failed to open sea urchins. The scavenger guild was
most rich in species, with 17 species observed. Predation was size-dependent; the size of predators increased with increasing
size of the sea urchins. The presence of two feeding guilds is suggested, one composed of sparids (Diplodus spp.), able to kill juvenile and adult sea urchins, and the other composed of labrids (mainly C. julis), which feed on juvenile sea urchins. To avoid the extension of overgrazed, barren areas created by P. lividus populations, fisheries' regulations should focus on major sea-urchin predators, chiefly D. sargus, D. vulgaris and C. julis.
Received: 23 April 1997 / Accepted: 30 May 1997 相似文献
18.
C. Bonaviri T. Vega Fernández G. Fanelli F. Badalamenti P. Gianguzza 《Marine Biology》2011,158(11):2505-2513
Sympatric sea urchin species are usually considered to belong to the same grazer guild. Nevertheless, their role in community
dynamics may vary due to species-specific morphological traits, feeding preferences and foraging behavior. In the Mediterranean
Sea, the two species Paracentrotus lividus and Arbacia lixula co-occur in barren areas. Whereas P. lividus is usually considered responsible for creating a barren ground, the roles of the two sea urchin species in its maintenance
are currently unclear. The relative and combined effects of P. lividus and A. lixula on maintaining the benthic community in the barren state were tested experimentally, using orthogonal exclusion of the two
species. Results show that exclusion of A. lixula, regardless of the presence of P. lividus, led to a significant decrease in the surface of bare rock and a significant change of the algal assemblages, thus demonstrating
the major role of this species in maintaining the barren state. 相似文献
19.
Hookworms in otariids are considered to meet the conditions and to fulfill the predictions set forth in the theoretical literature to define a likely case of host coexistence mediation by a shared pathogen. The intensity of infections, the prevalence of skin lesions and the morphometry of hookworms Uncinaria spp. were examined in South American sea lions and fur seals sampled along the Chilean and the Uruguayan coasts in spring and summer 1981 to 1991. In sympatric host populations from Uruguay, there were clear differences in intensity of infections, prevalence of skin lesions, and body size of the hookworms from the two host species. Sea lions from Chile, allopatric to fur seal populations, are less intensively infected and hookworms found in these sea lions have the smallest body size reported in otariids, while those from South American fur seals are the largest. Hookworms found in sea lion pups from populations sympatric to fur seals revealed intermediate values in intensity and in body size, and the sea lion pups had the highest prevalence of skin lesions. Other reports of hookworms in otariids show intermediate morphometry, following a general linear trend of differentiation in size. Consequently, they are considered to belong to the same, widely distributed species Uncinaria lucasi Stiles, 1901. 相似文献
20.
Spatial and temporal patterns of gene-enzyme variation were estimated in the sibling species Gammarus zaddachi Sexton and G. salinus Spooner by starch gel electrophoresis. Twenty-one G. zaddachi and 18 G. salinus populations from coastal and estuarine areas in the Baltic Sea, North Sea and other localities of north-western Europe were surveyed. Both amphipods display similar electrophoresis patterns of the enzyme systems studied. Considerable interspecific and interpopulational differences were detected in allele frequencies at three highly polymorphic loci, phosphoglucose isomerase (PGI), glutamate oxalacetate transaminase (GOT) and arginine phosphokinase (APK). G. zaddachi exhibits a pronounced genetic heterogeneity in most areas of the sampled range. Populations from northern French and western English coasts differ significantly from the other samples in allele frequencies at the PGI or APK locus, respectively. Baltic populations are widely uniform in their genetic composition but can be distinguished from samples taken at North Sea sites in allele frequencies at the APK locus. The latter reveal a clinal variation, ranging from the Danish to the French coast. In contrast to G. zaddachi, a low degree of genetic differentiation was observed among the G. salinus populations examined. This indicates that migration and interregional mixing may be more important in maintaining the genetic structure than in G. zaddachi which, compared to G. salinus, prefers habitats of lower salinity levels. Evidently, less extensive dispersal capabilities owing to the confinement of G. zaddachi to brackish waters of dilute salt concentrations may account for a diminished gene flow and considerable genetic separation of local populations. This assumption is supported by the genetic homogeneity documented in Baltic G. zaddachi populations. In view of the low and constant salinities in wide areas of this brackish-water sea such barriers do not exist. Survey studies performed with selected populations over a 3-yr period demonstrated a general pattern of temporal constancy in the allozyme variation observed. 相似文献