Ontogeny of the Solitary Chemosensory Cells in the Zebrafish, Danio rerio

Secondary epidermal solitary chemosensory cells (SCCs) are widespreadamong the primary aquatic vertebrates. They resemble taste budsensory cells in fine structure and may be innervated from facialor spinal nerves. According to previous studies, SCCs may constitutea water sampling system in the contexts of predator avoidance,habitat recognition and, in some cases, finding food. By quantitativescanning (SEM) and transmission electron microscopy (TEM) in60 specimens (57 SEM, 3 TEM) of 16 developmental stages, frompre-hatchlings to adults, we describe the ontogenetic developmentof SCC densities and shapes of sensory apices in the zebrafish,Danio rerio. This is put into perspective with the ontogenyof external taste buds. Just prior to hatching, 3 days afterfertilization (3d AF), sensory apices of SCCs penetrate betweenthe squamous epidermal cells, whereas taste bud pores only appearat the onset of exogenous feeding (5d AF). SCC densities increasesharply from hatching shortly after metamorphosis (25d AF) upto 6 x 10³ per mm² on the head and remain relatively constantin density thereafter. Conservatively estimated, there may be     

Density and distribution of external taste buds in cyprinids

Synopsis The aim of the present qualitative and quantitative study was to survey the density and distribution of external taste buds (TB) in 10 common European cyprinid species. TB pores were stained with silver nitrate and counted in 7 sample areas on the body and 3 on the fins. TB densities decrease from rostral to caudal and from ventral to dorsal. Highest densities were encountered in the gular region of the minnow (297 per mm²), white bream (291) and vimba (285), or at the forehead, in white bream (147). Of the fins, the pectoral showed highest densities (150 per mm² in vimba,138 in the minnow). The overall TB density rank from high to low is: minnow Phoxinus phoxinus, white bream Blicca bioerkna, crucian carp Carassius carassius, vimba VVimba vimba, bream Abramis brama, roach Rutilus rutilus, bleak Alburnus alburnus, sun bleak Leucaspius delineatus, sabre carp Pelecus cultratus and bitterling Rhodeus sericeus. This is also a fair rank of life styles from benthivory to open water planktivory and surface feeding. A significant positive correlation exists between densities of external taste buds and the relative sizes of the brain stem facial lobes. An apparent compensatory relationship between vision and taste, but not lateral line, is discussed.     

Solitary chemosensory cells — taste,common chemical sense or what?

Summary Secondary solitary chemosensory cells (SCCs) occur scattered within the epidermis of lampreys, teleosts and ranid tadpoles. Counts in representative telost species revealed that SCC's outnumber chemosensory cells organized in taste buds. Therefore, SCCs may be considered the structural substrate of a basic and probably important vertebrate chemosense. However, detailed information on structure, innervation and function is only available from specialized fins in a few teleost species, where SCCs are sufficiently concentrated. The foremost research model has been the anterior dorsal fin (ADF) in rocklings, which contains millions of SCCs but no other specialized chemosensory elements. It has been shown that these ADF-SCCs are innervated from the recurrent facial nerve. Electrophysiological recordings revealed that there is virtually no overlap in stimulus spectrum between the ADF-SCCs and pelvic fin taste buds; SCC responses could only be triggered by dilutions of heterospecific fish body mucus. Results of behavioural experiments indicate that fish mucus is indeed a relevant stimulus. Therefore it is hypothesized that the biological role of the ADF-SCCs is predator avoidance rather than search for food. Whether these findings are valid for rockings only, or can be generalized for the scattered SCC systems in more than 20000 species of fish and in some amphibians, remains an open question. Further investigations on the function and biological roles of the SCC chemosense will be crucially important to improve our understanding of sensory perception and its evolution in aquatic vertebrates.     

Impact of cyprinids on zooplankton and algae in ten drainable ponds

To study the impact of cyprinids on algae, zooplankton and physical and chemical water quality, ten drainable ponds of 0.1 ha (depth 1.3 m) were each divided into two equal parts. One half of each pond was stocked with 0 + cyprinids (bream, carp and roach of 10–15 mm), the other was free of fish. The average biomass of the 0 + fish at draining of the ponds was 466 kg ha^–1, to which carp contributed about 80%.The fish and non-fish compartments showed significant differences. In the non-fish compartments the density of Daphnia hyalina was 10–30 ind. l^–1 and that of Daphnia magna 2–4 ind. l-^–1, whereas in the fish compartments densities were c. 1 ind. l^–1. Cyclopoid copepods and Bosmina longirostris, however, showed higher densities in the fish compartments. The composition of algae in the two compartments differed only slightly, but the densities were lower in the non-fish compartments. The significant difference in turbidity was probably caused by resuspension of sediment by carp. No significant difference in nutrient concentration between the compartments was found.     

Density and the commitment of apical meristems to clonal growth and reproduction in Hieracium pilosella

Summary We examined responses to population density in the commitment of apical meristems to reproduction and clonal growth in a rosette-forming, stoloniferous herb (Hieracium pilosella). Despite close physiological coupling between the evocation of the terminal inflorescence bud and the development of one or more axillary buds into stolons, the allocation of meristems was extremely plastic.Genets at the higher sowing densities showed density-dependent mortality consistent with self-thinning along a-3/2 trajectory. The probability of inflorescence evocation and associated stolon development was negatively dependent on surviving density. The proportinal distribution of primary stolons amongst genets became strikingly more unequal (expressed as the Gini coefficient) with increasing density. Clonal growth was resolved into the number of primary stolons per stoloniferous genet and the extent of stolon branching (i.e. number of apices per primary stolon); both showed strongly negative density-dependence. Reproduction, expressed as the mean number of flowering capitula per stoloniferous genet, declined 15-fold with increasing density; although theoretically expected to be unity, greater values resulted from capitulum production by attached secondary rosettes and lower values reflected the increasing abortion rate of inflorescence buds with increasing density.Both the total number of apices produced per unit area and the corresponding number of reproductive apices were maximal at intermediate surviving densities (700–1,000 m^-2). The balance between reproductive and clonal growth may be expressed as the probability of an apical meristem producing a capitulum, that also peaked sharply at intermediate density. This finding does not conform with linear models that predict a shift from vegetative growth to sexual reproduction with increasing population density.     

Solitary chemosensory cells: why do primary aquatic vertebrates need another taste system?

The taste-like system of solitary chemosensory cells (SCCs) has almost eluded scientific attention. This is particularly remarkable, since recent surveys have revealed that this system of epidermal cells is widespread and abundant among the anamniotic aquatic vertebrates. In the rocklings (Gadidae, Teleostei), high densities of SCCs occur at a specialized dorsal fin. Recent evidence from this model indicates that SCCs are narrowly tuned to dilutions of fish body mucus and bile. Thus, SCCs may sample the ambient water for the upstream presence of potential competitors or predators. However, in sea robins (Triglidae, Teleostei), SCCs seem to be involved in finding food. Information from many more species is needed to explain why SCCs and taste buds have been maintained in parallel for such a long evolutionary period of time - from the age of the agnathans to that of the most advanced teleost fishes.     

Epidermal structure of the scleractinian coral Mycetophyllia ferox: light-induced vesicles,copious mucocytes,and sporadic tentacles

Three colony fragments of the scleractinian coral Mycetophyllia ferox Wells from Florida were observed in flow-through seawater aquaria under light and dark conditions. The colonies were then anesthetized and fixed for microscopic examination. Small vesicles formed across the epidermis in response to light as gastrodermis containing approximately 1.9 × 10⁶ zooxanthellae cm⁻² migrated into them. The vesicles flattened in the dark and the gastrodermis retreated to a clumped position. The epidermis is dominated by mucus cells with more than 6300 per mm². In contrast, there are very few epidermal cnidae. The polyps lack tentacles entirely, though small tentacles do occur, albeit sporadically, along the colline walls. Colline tentacles are expanded both day and night, and there is considerable intracolonial variability in the number of cnidae within them, ranging from as few as 316 to more than 3200 per mm² tentacle. There may be several small cnidocyst batteries containing both spirocysts and nematocysts (all microbasic p-mastigophores), but the principal battery is at the tentacle tip where cnidae are much more densely packed. There is considerable variation in the ratio of the two cnidae among tentacles in the same colony. Since the tentacles occur inconsistently and do not appear to expand, their functional role is unclear. Comparisons of epidermal characters are made with other members of the genus Mycetophyllia.     

Ecomorphology of solitary chemosensory cell systems in fish: a review

Synopsis Solitary chemosensory cells (SCCs) are present in the skin of a wide spectrum of lower vertebrates, such as lampreys, elasmobranchs, teleost fishes and some amphibians (Kotrschal 1991, Whitear 1992). However, due to the difficulties studying them, virtually all our present knowledge on SCCs stems from the anterior dorsal fin of two species of rocklings (Gadidae). This fin is a peculiar chemosensory organ, carrying approximately 5 million SCCs (Kotrschal et al. 1984, Kotrschal & Whitear 1988). The evidence derived from this model on the structure of SCCs, on their innervation and brain representation, on the flow dynamics at the receptors, on their electrophysiological responses and behavioral relevance indicates that this fin is actively sampling for substances leaked from other fish, such as body mucus and bile components. Possibly, the rockling anterior dorsal fin aids in predators avoidance. To generate hypotheses on the functions and biological roles of the generalized., scattered SCC systems present in most fishes, their structural parameters are put in perspective to taste bud structure and function and to the rockling results. Ecomorphological reasoning serves to establish testable hypotheses: in essence, SCC systems spread over the body surface may be designed as general water samplers, but not for the exact localization of a stimulus source. If the function of the latter is equally dependent on water flow, as the rockling fin organ, fish would have to rely either on the ambient water flow, or speed up their own swimming to optimize SCC input. If SCCs are indeed evolved in the context of predator avoidance, a comparison between life history intervals and between species should reveal, that the system varies in accordance with predation pressure. It is concluded, that in fish, SCCs are certainly an important source of environmental information. If we do not understand functions and biological roles of SCCs, it will not be possible to explain fish behavior and ecology. Evidently, further investigations are urgently needed.     

ROLE OF SETTLEMENT DENSITY ON GAMETOPHYTE GROWTH AND REPRODUCTION IN THE KELPS PTERYGOPHORA CALIFORNICA AND MACROCYSTIS PYRIFERA (PHAEOPHYCEAE)1

Laboratory studies were used to examine how variation in the density of spore settlement influences gametophyte growth, reproduction, and subsequent sporophyte production in the kelps Pterygophora californica Ruprecht and Macrocystis pyrifera (L.) C. Ag. In still (non-aerated) cultures, egg maturation in both species was delayed when spores were seeded at densities 300 · mm^?2. Although the density at which this inhibition was first observed was similar for both species, the age at which their eggs matured was not. P. californica females reached sexual maturity an average of 4 days (or ～ 30%) sooner than did M, pyrifera. As observed previously in field experiments, per capita sporophyte production was negatively density dependent for both species when seeded at spore densities of 10 · mm^?2. Total sporophyte production (i.e. number · cm^?2) for both species, however, was greatest at intermediate densities of spore settlement (～ 50 spores · mm^?2). In contrast, total sporophyte production by P. californica steadily increased with increasing spore density in aerated cultures; highest sporophyte density was observed on slides seeded at a density of 1000 spores · mm^?2. Preliminary experiments with P. californica involving manipulation of aeration and nutrients indicate that inhibition of gametophyte growth and reproduction at higher densities of spore settlement in non-aerated cultures was probably caused by nutrient limitation.     

Evidence of putative sensory receptors from snout and tongue in an upstream amphihaline migratory fish hilsa <Emphasis Type="Italic">Tenualosa ilisha</Emphasis>

Epidermal sensory structures of adults and juveniles of amphihaline migratory fish hilsa Tenualosa ilisha were studied from two habitats, i.e., freshwater (FW) and marine water (MW). Every year, adults and sexually mature hilsa migrate upstream from marine habitat to riverine freshwater habitat for breeding. This report provides evidences of chemoreception on their upstream migration through several characteristic features on their body, especially on the head and oral cavity. Scanning electron microscopy (SEM) reveals that freshwater adult hilsa (FH) has abundant solitary chemosensory cells (SCCs) on the snout epidermis (around the openings of the epidermal pit) and upper lip, whereas marine water adult hilsa (MH) moderately possesses such sensory structures. The juveniles returning to marine water completely lack SCCs. Immunohistochemical studies revealed the expression of PLC β2 on the snout of FH and tongue of both FH and MH. Further analysis (immunofluorescence, immunoblot and densitometry) of the epidermis confirms the presence of chemosensory structures through strong expression and localization of G-proteins (Gαq and Gα s/olf) from the snout as well as tongue in freshwater hilsa. The SEM also confirms the presence of two types of taste buds in FH, viz. type I (TB I) and type III (TB III). Whereas TB I and TB III are observed on the upper palatine and lips, most of the TB III are located on the tongue region of freshwater and marine hilsa. The juvenile hilsa are devoid of such structures. The presence of dense and rich SCCs and taste sensory cells in adults could be a characteristic feature for strong sensory reception to recognize odour and food-related environmental cues from habitats where they often migrate.     

Plasticity of the skeleton and skeletal deformities in zebrafish (Danio rerio) linked to rearing density

The teleost zebrafish (Danio rerio), an established model for human skeletal diseases, is reared under controlled conditions with defined parameters for temperature and photoperiod. Studies aimed at defining the proper rearing density have been performed with regard to behavioural and physiological stress response, sex ratio and reproduction. Studies concerning the effect of rearing density on the skeletal phenotype are lacking. This study analyses the response of the skeleton to different rearing densities and describes the skeletal deformities. Wild-type zebrafish were reared up to 30 dpf (days post-fertilization) in a common environment. From 30 to 90 dpf, animals were reared at three different densities: high density (HD), 32 fish l^–1; medium density (MD), 8 fish l^–1 and low density (LD), 2 fish l^–1. Animals at 30 and 90 dpf were collected and whole-mount stained with Alizarin red S to visualize mineralized tissues. The entire skeleton was analysed for meristic counts and 172 types of deformities. The results showed that the rearing density significantly influenced the specimens’ average standard length, which decreased with the increase in the rearing density. Differences in meristic counts among the three groups were not observed. Rearing density–independent malformations affected the ribs, neural arches and the spines of the abdominal region, as well as vertebrae of the caudal complex. The HD group showed the highest number of deformities per specimen, the highest number of observed types of deformities and, together with the MD group, the highest frequency of specimens affected by severe deformities. In particular, the HD group showed deformities affecting arches, spines and vertebral centra in the caudal region of the vertebral column. This study provides evidence of an effect of the rearing density on the development of different skeletal phenotypes.     

Dianthus caryophyllus stems and Zantedeschia aethiopica petioles/pedicels show anatomical features indicating efficient photosynthesis

The fine structure of the green stem of Dianthus caryophyllus, the leaf petiole and the flower pedicel of Zantedeschia aethiopica were studied using light and scanning electron microscopy. It was revealed that these non-foliar plant parts of both species possess epidermis with numerous stomata. Stomatal density of D. caryophyllus stem was found to be relatively high (79 vs 100 per mm² found on leaf surface). Z. aethiopica petioles and pedicels also possess numerous stomata (17 per mm²), yet stomatal density was found to be about half of that of leaves. Anatomical differences observed between petioles and pedicels were only minor. Stems of D. caryophyllus as well as petioles and pedicels of Z. aethiopica have a chlorenchyma-type tissue whose fine structure is quite similar to the leaf palisade chlorenchyma. Yet, the palisade of Z. aethiopica petioles and pedicels shows a peculiar arrangement: palisade cells are arranged with their long axis parallel to the longitudinal organ axis. Palisade tissue found in the aforementioned non-foliar plant organs in both species shows strong red chlorophyll auto-fluorescence under epi-fluorescence optics, consists of cells with abundant chloroplasts, possesses high percentage of intercellular spaces (13 and 20%, respectively) and its cells expose considerable part of their surface to the intercellular air. The fine structure of this stem palisade tissue along with the abundance of functional stomata found on the epidermis may support efficient photosynthesis.     

Evolution of miniaturization and the phylogenetic position of <Emphasis Type="Italic">Paedocypris</Emphasis>, comprising the world's smallest vertebrate

Background  

Paedocypris, a highly developmentally truncated fish from peat swamp forests in Southeast Asia, comprises the world's smallest vertebrate. Although clearly a cyprinid fish, a hypothesis about its phylogenetic position among the subfamilies of this largest teleost family, with over 2400 species, does not exist. Here we present a phylogenetic analyses of 227 cypriniform taxa, including 213 cyprinids, based upon complete mitochondrial DNA cytochrome b nucleotide sequences in order to determine the phylogenetic position of Paedocypris and to study the evolution of miniaturization among cyprinids.     

西藏东达山3种嵩草属植物气孔特征沿海拔的变化

嵩草属(Kobresia)植物是藏东南高山草甸的优势种和建群种,对该区畜牧业发展和维持生态系统平衡起着重要作用。选择西藏左贡县东达山为研究地点,从林线开始,海拔每升高约100m设置1个样带直至高山草甸分布边缘,共8个样带,调查各样带中物种的组成及盖度,并依据相对盖度和相对频度计算3种嵩草植物矮生嵩草(K.humilis)、线叶嵩草(K.capillifolia)和大花嵩草(K.macrantha)在群落中的重要值,同时取样观察它们叶片远、近轴面表皮细胞形态,测量气孔长度及保卫细胞宽度,计算气孔密度,探讨嵩草属植物对海拔梯度的适应性。结果表明:(1)3种嵩草属植物叶表皮细胞均呈波浪状,气孔器仅分布于远轴面,近轴面无气孔器分布。(2)3种嵩草属植物气孔密度沿海拔梯度的变化均呈单峰曲线分布格局,且在海拔4 537m样带处达到最大值,并表现为矮生嵩草(777.6个/mm2)线叶嵩草(476.4个/mm2)大花嵩草(414.3个/mm2)。(3)随海拔的增加,矮生嵩草和线叶嵩草气孔长度显著增大(P0.05),而保卫细胞宽度显著减小;但大花嵩草气孔长度随海拔的升高而显著减小,保卫细胞宽度基本保持不变。(4)矮生嵩草和线叶嵩草气孔密度、长度和保卫细胞宽度与海拔梯度均显著相关,气孔特征对海拔梯度变化的敏感程度高,与其在群落中重要值高的分布特征一致;而大花嵩草仅气孔密度和长度与海拔梯度显著相关,气孔特征对海拔梯度变化的敏感性低,与其在群落中重要值低的分布特征一致;嵩草属植物气孔密度、长度和保护细胞宽度与海拔梯度之间的相关性,反映出它们在海拔梯度上对生境的适应程度。可见,3种嵩草属植物气孔特征对海拔梯度上生境变化的适应性不同,从而影响它们在群落中的分布范围和物种优势度,其中矮生嵩草和线叶嵩草对环境变化敏感,而大花嵩草对环境变化相对不敏感;保卫细胞宽度与气孔长度同样对植物适应环境变化起重要作用。     

Microvascular and biochemical compensation during ventricular hypertrophy in male rainbow trout

We investigated whether there are compensatory changes in the coronary microvasculature, cardiac lipid metabolism, and myocyte ultrastructure associated with ventricular enlargement in male rainbow trout. Epicardial tissue was sampled at different stages of sexual maturation, and we estimated arterial capillary density, intercapillary diffusion distance, and applied a diffusion model to predict PO₂ at different workloads. We also measured biochemical indices of lipid metabolism and estimated fractional volumes of mitochondria and myofibrils in myocytes. Immature fish with nonenlarged ventricles had the highest capillary length densities (1620±158 mm mm⁻³). Maturing trout with moderate ventricular hypertrophy had lower capillary length densities (1103±58 mm mm⁻³) and similar diffusion distances (13.9±0.7 μm) compared with immature fish (11.7±0.9 μm). The largest ventricles had intermediate capillary length densities (1457±288 mm mm⁻³) and diffusion distances (12.8±0.8 μm). Modelling predicted that enlarged ventricles would not become anoxic even at maximal workloads. Biochemical markers of fatty acid metabolism and aerobic capacity were unchanged with hypertrophy. Volume densities of mitochondria and myofibrils were also not influenced by cardiac growth. In summary, ventricle hypertrophy results in expansion of the coronary capillary bed and the maintenance of the epicardial capacities for fat and oxidative metabolism.     

Limited contribution of predation by zooplanktivorous cyprinids to 0+ fish mortality

Predation by zooplanktivorous cyprinids was hypothesized as substantially contributing to larval fish mortality. To test this assumption, potential predators were sampled by electric fishing at sites and times of high fish larvae densities in the lower Oder River, Germany, in 2002 and 2003. At ten sites with high prey fish densities, all fishes ≥1+ and 0+ pike – all considered potentially predating on fish larvae – were captured, anaesthetised, and fixed. In the laboratory, 982 guts, respectively, stomachs were dissected and checked for fish larvae and larvae remains. Predation on 0+ fish was detected in the primary piscivorous fishes Esox lucius L. and Aspius aspius (L.), and facultative piscivorous Perca fluviatilis L., whilst none of the other nine species examined consumed fish. These findings implicate that predation by planktivorous cyprinids did not explain the typically strong decline in larval fish densities in the first weeks after hatching.     

Angiosperm leaf vein evolution was physiologically and environmentally transformative

The veins that irrigate leaves during photosynthesis are demonstrated to be strikingly more abundant in flowering plants than in any other vascular plant lineage. Angiosperm vein densities average 8 mm of vein per mm² of leaf area and can reach 25 mm mm⁻², whereas such high densities are absent from all other plants, living or extinct. Leaves of non-angiosperms have consistently averaged close to 2 mm mm⁻² throughout 380 million years of evolution despite a complex history that has involved four or more independent origins of laminate leaves with many veins and dramatic changes in climate and atmospheric composition. We further demonstrate that the high leaf vein densities unique to the angiosperms enable unparalleled transpiration rates, extending previous work indicating a strong correlation between vein density and assimilation rates. Because vein density is directly measurable in fossils, these correlations provide new access to the physiology of extinct plants and how they may have impacted their environments. First, the high assimilation rates currently confined to the angiosperms among living plants are likely to have been unique throughout evolutionary history. Second, the transpiration-driven recycling of water that is important for bolstering precipitation in modern tropical rainforests might have been significantly less in a world before the angiosperms.     

葛(豆科)叶的解剖学研究

利用光学显微镜和扫描电镜观察了葛(Pueraria lobata)叶的解剖学特征。结果表明,葛叶片的上、下表皮都只有一层表皮细胞,上表皮比下表皮厚。上、下表皮都有腺毛和非腺毛。气孔主要分布在下表皮,下表皮的气孔密度为(261±17)mm-2,上表皮只有(6±3)mm-2。叶肉由两层栅栏组织细胞和一层海绵组织细胞构成。叶肉细胞中有丰富的叶绿体。在栅栏组织和海绵组织之间有一层平行于叶脉的薄壁细胞。叶脉中含有大量的草酸钙晶体。葛叶的这些形态特征与其喜阳、耐旱的特点相适应。     

Relationship between stomatal frequencies,yield components and morphological characters in collections of winter wheat cultivars

Genotypes on the Belgian national list as well as about 120 genotypes of winter wheat from the world collection were examined for the relationships of their stomatal frequencies in the flag leaf with yield, yield components and other morphological characters. Stomata were in rows, with a higher density in adaxial leaf surface. Cultivars differed significantly in both stomatal density and number of rows of stomata per unit of leaf width. Yield and morphological characters in general showed no significant correlation with stomatal frequencies. Densities in all series examined ranged from 46 to 78 stomata per mm² in the adaxial leaf epidermis and from 32 to 93 in the abaxial one.     

Ontogeny of vision in the Antarctic fish Pagothenia borchgrevinki (Nototheniidae)

Summary Pagothenia borchgrevinki ranging in size from 63 to 245 mm were captured from beneath sea ice in McMurdo Sound by fishing and diver collection. Changes in ocular morphology with increasing body size were measured, and assessed in relation to ingested prey. Relative eye size was highest among smaller fish (<100mm total length), and declined with increasing fish size. This was accompanied by a decrease in cone density in the retina from a maximum of 14,200 mm^–2 in the smallest fish examined (63 mm), to 1000 mm^–2 in a 220 mm long fish. Theoretical acuity was lowest among fish at either end of the size range examined (minimum separable angle 40–50) but approximately constant over the remainder of the size range (25–40). Rod density also decreased with increasing body size but rod numbers per unit visual arc were relatively constant, except in the smallest fish, where angular rod density was low. The same prey taxa occurred in fish of all sizes; however, prey items smaller than about 1.5 mm were not taken by fish of any body size.