Molecular criteria for determining new hybrid species--an application to the Sonneratia hybrids

The possible hybrid origin of new species can usually be corroborated by molecular means. Here, we suggest that the segregation patterns of the molecular markers be further analyzed. A true hybrid species should show the patterns under continuous breeding among its members, at least beyond the F2 generation. We applied the guidelines to the putative hybrid species of Sonneratia, a widespread mangrove genus, and concluded that all the observed hybrids in this genus are simple F1's. Thus, S. x gulngai and S. x hainanensis are not true hybrid species. The segregation patterns of molecular markers should be heeded in interpreting the existence of hybrid species.     

Tidal-Scale Hydrodynamics within Mangrove Swamps

Both the drag force and the horizontal eddy viscosity play a dominant role in the tidal-scale hydrodynamics in mangrove wetlands. Using field observations and basic fluid mechanics laws, the drag coefficient and the coefficient of dynamic eddy viscosity are found to be predictable as a function of the Reynolds Number based on the characteristic length scale of the vegetation. The characteristic length scale of the vegetation varies greatly with vegetation species, vegetation density and tidal elevation. Both these coefficients decrease with increasing values of the Reynolds Number. At the low range of the Reynolds Number both these coefficients reach much higher values than those typical of vegetation-poor estuaries and rivers. Consequently, the tidal flow within mangrove areas depends to a large degree upon the submerged vegetation density that varies with the tidal stage. These findings may be applied also in other vegetated tidal wetlands, including salt marshes.     

红树林水生动物栖息地功能及其渔业价值

红树林生长于热带、亚热带海陆交界的生态敏感带,其根系为生活于潮间带高度异质环境下的生物提供了适宜生境:藻类、双壳类、甲壳类等大量附生于红树根部;红树的呼吸根、支柱根、树干、倒落的枝条和残骸等,与沉积物形成的松软基质为大量底栖动物提供栖息地,根部结构间的空隙成为虾类、蟹类和鱼类等游泳动物的优良避难所和索饵场。红树林凋落物以碎屑形式进入食物网,连同浮游植物、附生藻类和底栖微藻等,是红树林生态系统的碳循环重要组成部分,为红树林区水生动物提供了丰富的食物来源。可见,食物来源丰富、隐蔽性强、捕食压力低等特点使得红树林成为水生动物的理想栖息地,许多水生动物选择在其中度过部分或完整生活史。另外,红树林也是重要经济动物(鱼、虾、蟹类)的育苗场,为近岸鱼类种群的补充和渔业活动提供支持。为合理开发红树林区渔业和有效保护红树林湿地生态系统,从生境价值、凋落物在红树林生态系统食物网中的贡献等方面总结了红树林栖息地功能及其渔业价值,提出今后的研究方向应将红树林的栖息地功能从其它河口、近岸栖息地中分离出来,甄别不同栖息地间的动态关系及其对渔业的影响。     

Social familiarity and shoal formation in juvenile fishes

The potential influence of social familiarity in shoal‐choice decisions was investigated in two sympatric species of north temperate fishes, juvenile banded killifish Fundulus diaphanus and juvenile bluegill sunfish Lepomis macrochirus. Groups of socially familiar and unfamiliar conspecifics were formed in the laboratory using wild‐caught fishes. Juvenile F. diaphanus demonstrated a strong preference for familiar conspecific shoalmates, whereas juvenile L. macrochirus exhibited no preference for either unfamiliar or familiar conspecific shoalmates. The differential influence of familiarity on shoalmate choice in juveniles of these two species could be due to their different ecologies, local population densities and life histories.     

INFLUENCE OF THE INDIRECT EFFECTS OF GUPPIES ON LIFE‐HISTORY EVOLUTION IN RIVULUS HARTII

Early theories of life‐history evolution predict that increased predation on young/small individuals selects for delayed maturation and decreased reproductive effort, but such theory only considers changes in mortality. Predators reduce prey abundance and increase food to survivors. Theory that incorporates such indirect effects yields different predictions. Trinidadian killifish, Rivulus hartii, inhabit communities with and without guppies. Guppies prey on young Rivulus and Rivulus densities decline and growth rates increase when guppies are present. Prior work showed that Rivulus phenotypes from communities with guppies matured earlier and had higher fecundity, consistent with theories that incorporate indirect effects. Here we examined the genetic basis of these differences by rearing 2nd generation, laboratory‐born Rivulus from sites with and without guppies under two food levels that match natural differences in growth. Many locality × food interactions were significant, often reversing the relationship between communities. Such interactions imply that there are fitness trade‐offs associated with adaptation to high or low resource environments. On high food, Rivulus from localities with guppies matured earlier, produced many small eggs, and exhibited increased reproductive investment; these differences reversed on low food. Our results suggest that indirect effects mold Rivulus evolution and thereby highlight connections between community processes and evolutionary change.     

Recovery Deficiency Following Tree Mortality in Mangroves of Two Caribbean Islands: Field Survey and Statistical Classification

Mangrove species are well adapted to the harsh ecological conditions of their environment throughout the tropics. However, in the islands of Guadeloupe and Martinique (Lesser Antilles), deficient forest recovery was evidenced in 43 mangrove sites (>1000 m²) affected by apparently natural tree mortality. Such sites were recorded from four chronological sets of aerial photographs between 1950 and 1995, and field-investigated in terms of environment and vegetation characteristics. Given the speculative relationship between the slow-regenerating vegetation and its present environment within non-steady state, disturbed sites, statistical analyses arbitrarily matching physicochemical and biological data were primarily avoided. On one hand, principal component analysis (PCA), combined with an agglomerative hierarchical classification, was performed on environmental, rank-ordered data; on the other hand, multidimensional scaling (MDS) was implemented on vegetation data. Discriminant analyses (DA) further characterized the environment/vegetation interrelationships for each site type. Ultimately, three main types of mortality sites have been distinguished among the study areas. One type clustered the sites showing the lowest salinity values and the highest surge vulnerability whose dominant mangrove species is Rhizophora. Another type presented highly saline sites having clayey soils with pure, stunted, Avicennia stands. The last type consisted of peculiar forest gaps on deep, compact, peat soils. During the rainy season, these sites turned into shallow ponds scattered with living, young Rhizophora and large, standing, dead Avicennia. The authors suggest that this classification may serve as a comprehensive framework to test subsequent hypotheses (hurricanes, droughts…) on the origins of natural massive tree mortality and the causes of recovery deficiency in mangroves of the Caribbean.     

Distribution and Characteristics of Dissolved Organic Matter in Mangrove Sediment Pore Waters along the Coastline of French Guiana

Mangroves represent a major environment of tropical coasts. They are highly productive, and act both as a source and a sink of organic carbon. Concentrations and characteristics (fluorescence and hydrophobic–hydrophilic fractions) of dissolved organic matter (DOM) were investigated in relation to the organic content of sediments and to the chemistry of pore waters along the coastline of French Guiana. The pore waters studied were extracted (centrifugation, soil moisture sampler) from sediments cored beneath A. germinans mangrove stands representative of development stages: pioneer, mature and senescent. In order to asses the effects of seasonal changes, two cores were performed in each location, just after dry and wet seasons, respectively. Dissolved organic carbon (DOC) concentrations in pore waters of the upper sediment were found to increase, from 0.7 mmol l⁻¹ under the pioneers to 9 under senescent mangroves. The evolution of sedimentary organic carbon (SedOC) in the same sediment paralleled that of DOC, increasing from 0.7 to 28%. On the contrary, in the lower parts of sediment cores SedOC and DOC displayed contrasting vertical trends: SedOC decreased sharply with depth while DOC increased, reaching concentrations up to 30 mmol l⁻¹ at 50 cm in the older, senescent mangroves. In addition, the Fluorescence/DOC ratios and the hydrophobic contents of DOC were higher at greater depths in most cores, expressing changes in the DOC composition. These results suggest that the DOC of the upper layers originated directly from the SedOC of the enclosing sediment, while the hydrophobic and fluorescent DOC accumulated in the anoxic bottom layer. The mechanisms responsible for this accumulation at depth requires additional research to be fully understood. However, the anoxic conditions and high pH values prevailing in the lower sediment, by lessening DOM sorption and enhancing SedOC dissolution, may be partly responsible for the high DOC concentrations and fluorescences at depth. In addition, seasonal variation may be involved. During the rainy season, water sources were mixed resulting in lower DOC concentrations in the upper sediment, whereas during the dry season, increased evapotranspiration concentrate salts and DOC, which are transported vertically with percolating water.     

Molecular cloning and functional expression of a multifunctional triterpene synthase cDNA from a mangrove species Kandelia candel (L.) Druce

Homology based PCRs with degenerate primers designed from the conserved sequences among the known oxidosqualene cylases (OSCs) have resulted in cloning of a triterpene synthase (KcMS) from the young roots of Kandelia candel (L.) Druce (Rhizophoraceae). KcMS consists of a 2286 bp open reading frame, which codes for 761 amino acids. The deduced amino acid sequence showed 79% homology to a lupeol synthase from Ricinus communis suggesting it to be a lupeol synthase of K. candel. KcMS was expressed in a lanosterol synthase deficient yeast with the expression vector pYES2 under the control of GAL1 promoter. GC-MS analysis showed that the transformant accumulated a mixture of lupeol, beta-amyrin and alpha-amyrin in a 2:1:1 ratio, indicating that KcMS encodes a multifunctional triterpene synthase, although it showed high sequence homology to a R. communis lupeol synthase. This is the first OSC cloning from mangrove tree species.     

1株裂殖壶菌(Schizochytrium sp.)的分离鉴定

采用松树花粉诱集法从乐清湾红树林分离到一株纯培养物,其特点为：营养菌体为椭圆球形,单核;营养菌体的细胞壁由许多紧压在一起的致密鳞片层构成,在细胞壁不连续处可分辨鳞片;营养菌体形成外质网,它产生于外质网形成体;营养菌体以产生游动孢子行无性繁殖,游动孢子为双鞭毛;无性繁殖过程中形成四分体结构。据此鉴定为裂殖壶菌（Schizochytrium sp．）。