The consequences of genetic diversity in competitive communities

Several lines of evidence suggest that the species diversity and composition of communities should depend on genetic diversity within component species, but there has been very little effort to directly assess this possibility. Here I use models of competition among genotypes and species to demonstrate a strong positive effect of the number of genotypes per species on species diversity across a range of conditions. Genetic diversity allows species to respond to selection imposed by competition, resulting in both functional convergence and divergence among species depending on their initial niche positions. This ability to respond to selection promotes species coexistence and contributes to a reduction in variation in species composition among communities. These models suggest that whenever individual fitness depends on the degree of functional similarity between a focal individual and its competitors, genetic diversity should promote species coexistence; this prediction is consistent with the few relevant empirical data collected to date. The results point to the importance of considering the genetic origin and diversity of material used in ecological experiments and in restoration efforts, in addition to highlighting potentially important community consequences of the loss of genetic diversity in natural populations.     

Hidden genetic diversity in a key model species of coral

A total of 43 colonies of the scleractinian coral Pocillopora damicornis from lagoonal and reef slope sites in the western Indian Ocean (WIO) region were genetically characterised at one nuclear and two mitochondrial sequence markers and six microsatellite loci. Both mitochondrial and microsatellite data support the existence of two reciprocally monophyletic clusters (F- and NF-types) and provide evidence of the existence of two cryptic species of P. damicornis on reefs in WIO region and put current morphological delineation and geographical boundaries of P. damicornis and Pocillopora molokensis into question. The results add to ongoing studies on the phylogeny and phylogeography within the genus Pocillopora, which all point towards a range of unresolved morphological and molecular species boundaries. Nuclear phylogenies derived from the present and previously published sequences show evidence for incomplete lineage sorting and/or introgressive hybridisation between Pocillopora morphospecies. However, the two WIO types largely remain in separate clusters, further supporting the theory that these represent two different species.     

Role of food subsidies and habitat structure in influencing benthic communities of shell mounds at sites of existing and former offshore oil platforms

Mussels (Mytilus californianus, M. galloprovincialis) and other organisms sloughed from offshore oil platforms provide a food subsidy to benthic consumers and alter underlying soft bottom habitat by creating hard substrate. The removal of overlying platforms eliminates this food subsidy, but large shell mounds remain. The distribution, abundance, and population characteristics of mobile macroinvertebrates differed among shell mounds beneath existing offshore oil platforms, shell mounds at the former sites of offshore oil platforms, and soft bottom. Predatory and omnivorous echinoderm and mollusk species were more abundant and generally larger on shell mounds under platforms than on shell mounds without platforms. Omnivorous and deposit feeding echinoderms were the most abundant macroinvertebrate taxa sampled on mound-only sites. The brown rock crab (Cancer antennarius), known to have a strong preference for hard substrate, was significantly more abundant on shell mounds, with or without platforms, than adjacent soft bottom sites. Results suggest that the effects of platform removal differed among benthic species according to trophic level, degree of mobility, and substrate preference. Although the shell mound habitat persists after removal of platform structures, species abundance and the composition of the associated benthic community is altered by removal of the platform structure.Communicated by P.W. Sammarco, Chauvin     

喀斯特地区白三叶形态和遗传多样性研究

白三叶（Trifolium repens）的形态学特征随利用年限的增加而进化,单株叶数、生长点数、中叶长、中叶长宽比以及种群内个体之间变异性随着年限的增加而增加,而叶层高度、中叶宽则下降。三个不同年龄草地的平均单株叶质量、根质量、地上生物量、地上生物量与地下生物量的比值等指标数值接近,差异不显著。但是,与茎有关的指标如茎质量等差异显著,匍匐茎生物量随年限的增加而增加,以回避动物采食等干扰,并有利于占据动态空斑而增加种群的持久性。100年白三叶的等位基因数没有20年的高,意味着年限越长的种群以少数大克隆体占优势。     

The relative importance of host-plant genetic diversity in structuring the associated herbivore community

Recent studies suggest that intraspecific genetic diversity in one species may leave a substantial imprint on the surrounding community and ecosystem. Here, we test the hypothesis that genetic diversity within host-plant patches translates into consistent and ecologically important changes in the associated herbivore community. More specifically, we use potted, grafted oak saplings to construct 41 patches of four saplings each, with one, two, or four tree genotypes represented among the host plants. These patches were divided among two common gardens. Focusing first at the level of individual trees, we assess how tree-specific genotypic identity, patch-level genetic diversity, garden-level environmental variation, and their interactions affect the structure of the herbivore community. At the level of host-plant patches, we analyze whether the joint responses of herbivore species to environmental variation and genetic diversity result in differences in species diversity among tree quartets. Strikingly, both species-specific abundances and species diversity varied substantially among host-tree genotypes, among common gardens, and among specific locations within individual gardens. In contrast, the genetic diversity of the patch left a detectable imprint on local abundances of only two herbivore taxa. In both cases, the effect of genetic diversity was inconsistent among gardens and among host-plant genotypes. While the insect community differed significantly among individual host-plant genotypes, there were no interactive effects of the number of different genotypes within the patch. Overall, additive effects of intraspecific genetic diversity of the host plant explained a similar or lower proportion (7-10%) of variation in herbivore species diversity than did variation among common gardens. Combined with the few previous studies published to date, our study suggests that the impact of host-plant genetic diversity on the herbivore community can range from none to nonadditive, is generally low, and reaches its most pronounced impact at small spatial scales. Overall, our findings strengthen the emerging view that the impacts of genetic diversity are system, scale, and context dependent. As the next step in community genetics, we should then start asking not only whether genetic diversity matters, but under what circumstances its imprint is accentuated.     

Discovery of postcopulatory mate guarding in Copepoda Harpacticoida (Crustacea)

Mating behaviour of four species of Tisbe (Tisbidae) and of Paramphiascella fulvofasciata (Diosaccidae) was filmed with a videocamera during 1992 and 1993 at the University of Oldenburg. This behaviour is complex and can be divided into different phases: grasping of the female; courtship; copula and postcopulatory mate guarding. During courtship both partners lie parallel in opposite directions with their ventral sides facing each other. The male strokes the abdomen of the female with his second to fourth peracopods. As a result the female becomes motionless. The copula is a quick process of only a few seconds during which spermatophore transfer takes place. When this has happened, males do not leave the females but become inactive and are carried around by them for varying lengths of time. This pattern and the fact that only adult partners are involved in these associations prove that this behaviour is very different from the precopulatory mate guarding presumed to be ubiquitous among Harpacticoida. Cases of postcopulatory mate guarding have never been explicitly demonstrated for Harpacticoida. The minimum duration of guarding was found to match the time necessary for spermatophore discharge. Guarding is, therefore, interpreted as a strategy to secure paternity. New definitions are given for courtship, copula and postcopulatory mate guarding in Harpacticoida to help avoiding misinterpretations of associations between adult partners. Such misinterpretations abound in the literature.     

Habitat distribution and species diversity of chaetodontid and pomacentrid fishes near Bimini,Bahamas

The relative abundance of chaetodontid and pomacentrid fishes in 8 habitats, ranging in depth from 0.5 to 17 m, was determined by visual counting of free-swimming fish in the field. Habitat widths and overlaps were determined using weighting factors, developed by Colwell and Futuyma (1971), which account for the different degree of uniqueness of each habitat. The average habitat widths and the average habitat overlaps were greater for the chaetodontids than the pomacentrids. This was due, in part, to the greater use of habitat structure by the pomacentrids, and it is hypothesized that this is because they are the more vulnerable to predation. The juveniles and adults reached peak abundance in different habitats for at least some of the species, and this may further reduce the habitat-overlap values for adults of some pairs of species. It is clear, however, that the ability of the species in these families to coexist is largely due to factors operating within habitats rather than to a large degree of habitat specialization.     

外来入侵物种的基因签名及其遗传多样性聚类分析

密码子的使用频率分布能够反映一定的生物特性,因而可作为一种基因签名。本文使用CGR方法来研究外来入侵物种不同组织序列的基因签名及遗传多样性聚类分析,首先得出了刺花莲子草(Alternanthera pungens),紫茎泽兰(Ageratina adenophora),水葫芦(Eichhornia crassipes),微甘菊(Mikania micrantha),土荆芥(Chenopodium ambrosioides),一枝黄花(Solidago canadensis)等6种外来入侵植物的31条序列核苷酸字串长k=1到k=6的情况,并选取k=3,即基因序列的密码子,作为生物特性的一个重要表达。并且构造序列间的CGR欧式距离,进而对外来入侵植物序列遗传多样性进行了聚类分析。通过对所获得的6种外来入侵植物的31条序列的基因签名,得出如下结果：CGR是一种简便且计算量小的方法,且基于CGR方法的基因签名,具有典型的生物特性;入侵植物的基因序列在密码子的使用上是非均衡的,且物种亲缘关系近的,则基因签名相似越高;而且基因签名也揭示出了密码子的第三位碱基偏好使用碱基T的现象,与一般物种密码子第三位碱基偏好G/C情况有强烈反差。此外,从获得的6个物种的31条序列聚类谱系图可以直观看出,入侵植物间存在着一定的亲缘关系,遗传多样性较丰富。由于我们所建立的基于CGR方法的基因签名,不仅能够反映植物特性和进化关系,而且能揭示序列中密码子和碱基的偏好使用情况,因而该方法有利于对外来入侵物种的遗传多样性分析、风险评估及预防控制等提供科学依据。     

Local variation of within-host clonal diversity coupled with genetic homogeneity in a marine trematode

Despite their ubiquity and importance to intertidal ecosystems, information is currently lacking regarding the genetic diversity of trematode parasites within coastal organisms and the distribution of their genetic variation among intertidal habitats. In this study, we quantified the clonal diversity of the coastal marine trematode Maritrema novaezealandensis within Zeacumantus subcarinatus snail hosts from three coastal bays in Otago Harbour, New Zealand, using five microsatellite loci to determine if differences exist in the frequency of occurrence of multi-clone infections. In addition, we examined gene flow among M. novaezealandensis collected from the three bays. The frequency of mixed-clone infections varied fourfold among bays and no genetic differentiation was detected among intertidal bays. Across the coastal bays studied, M. novaezealandensis comprises a single population that is potentially infecting multiple Z. subcarinatus populations with varying life history traits.     

Copepodid and adult Argestidae Por, 1986 (Copepoda: Harpacticoida) in the southeastern Atlantic deep sea: diversity and community structure at the species level

Drawing on the example of Argestidae Por, 1986b, community structure and large-scale distribution patterns of harpacticoid copepods at species level were examined in the three southeastern Atlantic deep-sea basins. The study was based on 30 multicorer deployments at depths from 5,035 to 5,655 m during the DIVA-2 expedition. The 1,176 adult and copepodid Argestidae from CIII onwards belong to 114 species. Some species occurred at all five stations; others appeared to be exclusive for single stations. Inclusion of copepodids revealed a higher similarity in species composition among the five stations than consideration of just adults and caused a slight shift toward dominance of single species in the sediments at most locations.     

Offspring genetic diversity increases fitness of female Atlantic salmon (Salmo salar)

Inbreeding has negative effects on individual and population performances. Therefore, enhancement of offspring genetic diversity is believed to play a major role in shaping mating systems. However, no study has clearly separated the direct effect of having multiple partners from the indirect effect of having more outbred offspring on the resulting reproductive success of individuals in the wild. In this study, we report significant associations between both multiple mating and within-individual genetic diversity of offspring, and an increased reproductive success of wild female Atlantic salmon, Salmo salar. Specifically, we found that females with a higher number of mates also have more outbred offspring (within-individuals), and that both of these characteristics increased their reproductive success expressed in terms of offspring surviving when combining all freshwater juvenile stages. Our findings also indicate that determinants of fitness are different among sexes as within-individual offspring genetic diversity was not a strong predictor of male reproductive success, while the number of mates was important. We also show that females mated with more outbred males than on average, which potentially increased their chances of producing outbred offspring. These results therefore suggest that there could be more important indirect genetic benefits of multiple mating for females than for males.Communicated by M. Abrahams     

Short-term population dynamics of Tisbe cucumariae (Copepoda: Harpacticoida)

Population dynamics of a benthic harpacticoid copepod (Tisbe cucumariae) were studied in a seawater-system holding tank during fall-spring, 1979/1980, and January, 1981. These populations were opoortunistic scavengers, especially on the dead bodies of Ciona intestinalis, a solitary tunicate. Copepod population densities, life-history stage structures, sex ratio and percentages of females with egg sacs were determined in the absence or in the presence of dead tunicates (from death through dissolution to final disappearance). Taken together, all the data are consistent with a hypothesis for food-dependent cycling of populations of T. cucumariae through the following 4 density states: (1) a maintenance state of low density, which is the usual condition during the absence of a concentrated food source; (2) a colonization state of moderate density, which results from attraction and immigration to a new food source; (3) a bloom state at the food source, where a high density results from intensive reproduction combined with a tendency of all life stages to remain at the site; (4) a dispersal state of moderate density as the copepods emigrate from the site of the consumed food. Evidence is also presented for a facultative slowing of naupliar development in T. cucumariae in the absence of a concentrated food source such as a dead tunicate. Possible advantages afforded by delayed development are discussed in terms of risk-spreading in a stochastically hostile environment.     

Meta-analysis of susceptibility of woody plants to loss of genetic diversity through habitat fragmentation

Shrubs and trees are assumed less likely to lose genetic variation in response to habitat fragmentation because they have certain life-history characteristics such as long lifespans and extensive pollen flow. To test this assumption, we conducted a meta-analysis with data on 97 woody plant species derived from 98 studies of habitat fragmentation. We measured the weighted response of four different measures of population-level genetic diversity to habitat fragmentation with Hedge's d and Spearman rank correlation. We tested whether the genetic response to habitat fragmentation was mediated by life-history traits (longevity, pollination mode, and seed dispersal vector) and study characteristics (genetic marker and plant material used). For both tests of effect size habitat fragmentation was associated with a substantial decrease in expected heterozygosity, number of alleles, and percentage of polymorphic loci, whereas the population inbreeding coefficient was not associated with these measures. The largest proportion of variation among effect sizes was explained by pollination mechanism and by the age of the tissue (progeny or adult) that was genotyped. Our primary finding was that wind-pollinated trees and shrubs appeared to be as likely to lose genetic variation as insect-pollinated species, indicating that severe habitat fragmentation may lead to pollen limitation and limited gene flow. In comparison with results of previous meta-analyses on mainly herbaceous species, we found trees and shrubs were as likely to have negative genetic responses to habitat fragmentation as herbaceous species. We also found that the genetic variation in offspring was generally less than that of adult trees, which is evidence of a genetic extinction debt and probably reflects the genetic diversity of the historical, less-fragmented landscape.     

High genetic diversity of the symbiotic dinoflagellates in the coral Pocillopora meandrina from the South Pacific

Symbioses between dinoflagellates in the genus Symbiodinium (commonly referred to as zooxanthellae) and scleractinian corals are an essential feature for the maintenance of coral reefs. The fine-scale diversity and population structure of the zooxanthellae inhabiting the coral Pocillopora meandrina, a major reef building species in Polynesia, was examined. We used two polymorphic microsatellites to study seven populations from the South Pacific, whose host structuring has been previously investigated. The symbionts of P. meandrina showed high levels of diversity, with more than one zooxanthella genotype being identified in most of the host individuals. Genetic differentiation between symbiont populations was detected at a large scale (2,000 km) between the Tonga and the Society Archipelagos. Within the Society Archipelago, the two most remote populations (Tahiti and Bora-Bora; 200 km apart) were only weakly differentiated from each other. Statistical tests demonstrated that the symbiont genetic structure was not correlated with that of its host, suggesting that dispersal of the symbionts, whether they are transported within a host larva or free in the water, depends mainly on distance and water currents. In addition, the data suggests that hosts may acquire new symbionts after maternal transmission, possibly following a disturbance event. Lastly, the weak differentiation between symbiont populations of P. verrucosa and P. meandrina, both from Moorea, indicated that there was some host-symbiont fine-scale specificity detectable at the genetic resolution offered by microsatellites.     

Chromosome number in ten species of the genus Tisbe (Copepoda: Harpacticoida)

Of 10 species of the genus Tisbe, 9 were shown to possess the same haploid number of 12, whereas only 1 has a haploid number of 8. The hypothesis is advanced that n=12 is the primitive condition in the genus Tisbe and that T. biminiensis with n=8, is a recent form.     

Effect of crowding on larval viability in Tisbe holothuriae (Copepoda: Harpacticoida)

Larval Tisbe holothuriae Humes exposed to anionic detergent (0.5 mg l^-1 sodium dodecyl benzene sulphonate) were found to survive better than control larvae. The detergent appears to enhance viability by relaxing inhibitory interactions between nauplii. This conclusion is inferred from the following experimental observations: (1) crowding depresses larval viability; (2) the effect of crowding on viability is indirect, and results from behavioural changes which reduce contact with food; (3) detergent exposure delays or suppresses the behavioural response to crowding. The nature of the interactions which modify behaviour is unknown, but evidence suggests that close encounters between nauplii are important, and that they may lead to the impairment of distance-chemoreception. Naupliar antagonism could have evolved as a mechanism for staggering larval development or as a means of reducing the relative fitness of neighbouring individuals.     

Extreme genetic diversity and temporal rather than spatial partitioning in a widely distributed coral reef fish

Mitochondrial control region (HVR-1) sequences were used to identify patterns of genetic structure and diversity in Naso vlamingii, a widespread coral reef fish with a long evolutionary history. We examined 113 individuals from eight locations across the Indo-Pacific Ocean. Our aims were to determine the spatial scale at which population partitioning occurred and then to evaluate the extent to which either vicariance and/or dispersal events have shaped the population structure of N. vlamingii. The analysis produced several unexpected findings. Firstly, the genetic structure of this species was temporal rather than spatial. Secondly, there was no evidence of a barrier to dispersal throughout the vast distribution range. Apparently larvae of this species traverse vicariance barriers that inhibit inter-oceanic migration of other widespread reef fish taxa. Thirdly, an unusual life history and long evolutionary history was associated with a population structure that was unique amongst coral reef fishes in terms of the magnitude and pattern of genetic diversity (haplotype diversity, h = 1.0 and nucleotide diversity π = 13.6%). In addition to these unique characteristics, there was no evidence of isolation by distance (r = 0.458, R ² = 0.210, P = 0.078) as has also been shown for some other widespread reef species. However, some reductions in gene flow were observed among and within Ocean basins [Indian–Pacific analysis of molecular variance (AMOVA), Φ _st = 0.0766, P < 0.05; West Indian–East Indian–Pacific AMOVA Φ _st = 0.079, P < 0.05]. These findings are contrasted with recent studies of coral reef fishes that imply a greater degree of spatial structuring in coral reef fish populations than would be expected from the dispersive nature of their life cycles. We conclude that increased taxon sampling of coral reef fishes for phylogeographic analysis will provide an extended view of the ecological and evolutionary processes shaping coral reef fish diversity at both ends of the life history spectrum.     

A new generation of coastal monitoring platforms

The need for new instruments and systems for environment monitoring encouraged the development of a network of coastal platforms combining a high versatility with ease of use and affordability. Almost every instrument can be fitted on the platforms, thanks to the large amount of available power provided by both solar panels and wind generators. All the platforms host a pumping system that pumps water from five depths into a measurement chamber where a multiparametric probe is fitted and from where other devices (e.g. samplers or analysers) can draw samples. In situ temperature measurements are provided at the same pumping depths. A colorimetric nutrient analyser and a meteorological station complete the basic equipment. On one of the platforms, a remotely controlled water sampler and an ADCP are also fitted. The data-acquisition and transmission system enables the platform to be controlled remotely using a special macro-commands set. Several examples of use are presented.