Marine hydroids are commonly thought to be defended by stinging organelles called nematocysts that penetrate predator tissues
and inject proteinaceous venoms, but not all hydroids possess these nematocysts. Although an increasing number of bioactive
secondary metabolites have been isolated from marine hydroids, ecological roles of these compounds are poorly known. To test
the hypothesis that nematocysts and noxious secondary metabolites represent alternative defenses against predation, we examined
hydroids from North Carolina, United States for: (1) the palatability of whole polyps before and after nematocysts had been
deactivated; (2) the palatability of their chemical extracts; and (3) their nutritional value in terms of organic content,
protein content, and levels of refractory structural material (chitin). All hydroids were avoided by a generalist predator,
the pinfish Lagodon rhomboides, compared with palatable control foods. Two of these (Halocordyle disticha and Tubularia crocea) became palatable after being treated with potassium chloride to discharge their nematocysts, suggesting that these species
rely on nematocysts for defenses against predators. Chemical extracts from nematocyst-defended species had no effect on fish
feeding. The four species that remained unpalatable after nematocysts had been discharged (Corydendrium parasiticum, Eudendrium carneum, Hydractinia symbiolongicarpus, Tridentata marginata) possessed chemical extracts that deterred feeding by pinfish. We have isolated and characterized the structures of the deterrent
metabolites in two of these species. We found no differences in nutritional content or levels of chitin between nematocyst-defended
and chemically defended species, and no evidence that either of these played a role in the rejection of hydroids as prey.
Our results suggest that, among hydroids, chemical defenses may be at least as common as nematocyst-based defenses and that
the two may represent largely alternative defensive strategies. The four hydroid species with deterrent extracts represent
four families and both sub-orders of hydroids, suggesting that chemical defenses in this group may be widespread and have
multiple origins.
Received: 25 May 1999 / Accepted: 1 February 2000 相似文献
Increasingly, studies of community assembly and ecosystem function combine trait data and phylogenetic relationships to gain novel insight into the ecological and evolutionary constraints on community dynamics. However, the key to interpreting these two types of information is an understanding of the extent to which traits are phylogenetically conserved. In this study, we develop the necessary framework for community phylogenetics approaches in a system of marine crustacean herbivores that play an important role in the ecosystem functioning of seagrass systems worldwide. For 16 species of amphipods and isopods, we (1) reconstructed phylogenetic relationships using COI, 16S, and 18S sequences and Bayesian analyses, (2) measured traits that are potentially important for assembling species between and within habitats, and (3) compared the degree to which each of these traits are evolutionarily conserved. Despite poor phylogenetic resolution for the order Amphipoda as a whole, we resolved almost all of the topology for the species in our system, and used a sampling of ultrametric trees from the posterior distribution to account for remaining uncertainty in topology and branch lengths. We found that traits varied widely in their degree of phylogenetic signal. Body mass, fecundity, and tube building showed very strong phylogenetic signal, and temperature tolerance and feeding traits showed much less. As such, the degree of signal was not predictable based on whether the trait is related to environmental filtering or to resource partitioning. Further, we found that even with strong phylogenetic signal in body size, (which may have large impacts on ecosystem function), the predictive relationship between phylogenetic diversity and ecosystem function is not straightforward. We show that patterns of phylogenetic diversity in communities of seagrass mesograzers could lead to a variety of interpretations and predictions, and that detailed study of trait similarities and differences will be necessary to interpret these patterns. 相似文献
Field studies of community assembly patterns increasingly use phylogenetic relatedness as a surrogate for traits. Recent experiments appear to validate this approach by showing effects of correlated trait and phylogenetic distances on coexistence. However, traits governing resource use in animals are often labile. To test whether feeding trait or phylogenetic diversity can predict competition and production in communities of grazing amphipods, we manipulated both types of diversity independently in mesocosms. We found that increasing the feeding trait diversity of the community increased the number of species coexisting, reduced dominance and changed food availability. In contrast, phylogenetic diversity had no effect, suggesting that whatever additional ecological information it represents was not relevant in this context. Although community phylogenetic structure in the field may result from multiple traits with potential for phylogenetic signal, phylogenetic effects on species interactions in controlled experiments may depend on the lability of fewer key traits. 相似文献
Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr−1) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.
Intraspecific variation in habitat-forming species can have important ecological consequences at the population, community,
and ecosystem level. However, the contribution of genetic variation among individuals to these effects is seldom documented.
We quantified morphological and physiological variation among genotypes of a marine foundation species, the seagrass Zostera marina. We grew replicate shoots of eight genetically distinct Zostera individuals collected from Bodega Bay, California, in a common garden environment and then quantified shoot production and
morphology, nutrient uptake, and key photosynthetic parameters. We found that genotypes differed in shoot production, biomass,
and both root and shoot nutrient uptake rates, even when corrected for genotype-specific biomass differences. In addition,
the rank order of uptake ability differed for ammonium and nitrate, indicating that genotypes may exhibit resource partitioning
of different forms of nutrients. Our results suggest that both niche complementarity among genotypes and the sampling/selection
effect could contribute to previously observed positive effects of seagrass clonal diversity on resource utilization and biomass
production. Further, they highlight that genotypic variation in key traits of habitat-forming species could have measurable
effects on community structure and function. 相似文献