Substratum adhesion and gliding in a diatom are mediated by extracellular proteoglycans

Diatoms are unicellular microalgae encased in a siliceous cell wall, or frustule. Pennate diatoms, which possess bilateral symmetry, attach to the substratum at a slit in the frustule called the raphe. These diatoms not only adhere, but glide across surfaces whilst maintaining their attachment, secreting a sticky mucilage that forms a trail behind the gliding cells. We have raised monoclonal antibodies to the major cell surface proteoglycans of the marine raphid diatom Stauroneis decipiens Hustedt. The antibody StF.H4 binds to the cell surface, in the raphe and to adhesive trails and inhibits the ability of living diatoms to adhere to the substratum and to glide. Moreover, StF.H4 binds to a periodate-insensitive epitope on four frustule-associated proteoglycans (relative molecular masses 87, 112, and >200 kDa). Another monoclonal antibody, StF.D5, binds to a carbohydrate epitope on the same set of proteoglycans, although the antibody binds only to the outer surface of the frustule and does not inhibit cell motility and adhesion. Received: 2 December 1996 / Accepted: 6 March 1997     

Modulation of trail laying in the antLasius niger (Hymenoptera: Formicidae) and its role in the collective selection of a food source

Foragers of the ant Lasius nigerexploiting a 1 Msugar source were found to lay 43 %more trail marks than those exploiting a 0.05 or a 0.1 Msource. The trail laying per forager decreased during the course of individual recruitment episodes, and the mean lifetime of the trail pheromone was estimated to be 47 min. A mathematical function describing the probability that a forager chooses one of two paths in relation to the amount of trail pheromone on them closely fitted experimental data. These results were incorporated into a model describing the recruitment dynamics of L. niger.Simulations of this model showed that the observed modulation of trail laying with respect to food source quality is sufficient in itself to account for the systematic selection of the richer source seen in the experiments.     

3种淡水布纹藻(硅藻纲)的超微结构研究

该研究利用光学和扫描电子显微镜对3种淡水布纹藻(钝布纹藻、库氏布纹藻和赛欧托布纹藻)的形态学进行了研究,以明确它们的精细结构特征;并分析讨论它们在中国的地理分布区域。结果表明：(1) 3种淡水布纹藻皆属于粗糙布纹组;从壳面观看,都具有S形和反S(S)形两种壳瓣外形。(2) 钝布纹藻具有弱的S形壳面外形、T形的外近端壳缝末稍和直的内近端壳缝末稍以及椭圆形的中央区;库氏布纹藻具有明显的S形壳面外形、略微向不同侧偏转的外近端壳缝末稍和直的内近端壳缝末稍以及椭圆形的中央区;赛欧托布纹藻具有弱的S形壳面外形、强烈钩状的外近端壳缝末稍和T形的内近端壳缝末稍以及倾斜的中央区。(3) 钝布纹藻在广东、广西、湖南、四川和云南等地有分布;库氏布纹藻在新疆和湖南等地有发现;赛欧托布纹藻分布于武陵山区,该文是其在中国淡水分布的首次报道。     

VALVE MORPHOGENESIS IN THE PENNATE DIATOM NAVICULA CUSPIDATA1

The deposition of siliceous valves during asexual reproduction of the pennate diatom, Navicula cuspidata Kütz., is described with emphasis on the cytoplasmic components involved. The events accompanying valve secretion are similar to those already known from other pennate species. After mitosis, the microtubule centre (MC) moves to the center of the cleavage furrow where silica deposition is initiated inside a tubular silicalemma, and it remains associated with the prospective central nodule during valve growth. Microtubules (MTs), emanating from the MC, run parallel to the prospective raphe and together with the raphe fibres, appear to be involved with raphe development. Multiple raphe fibres occupy the maturing raphe fissure, in contrast to the single fibre of Pinnularia viridis, P. maior and Hantzschia amphioxys. The fibers exhibit a periodic substructure and are often opposed to the silicalemma where they may inhibit silica deposition and control the shaping of the raphe fissure. In contrast with the above species, in N. cuspidata MTs are clustered strictly opposite the raphe and lose their association with the MC which degenerates before the valves are mature. The primary role of MTs may be the stabilization of the cytoplasmic region where initial silicification occurs. Mitochondria and endoplasmic reticulum are not involved in molding valve growth in this species. Evidence for vesicle involvement in silica transport and deposition was limited. The possible contributions provided by comparative studies on the ultrastructure of valve morphogenesis towards elucidating the control of valve formation and the taxonomy of diatoms are discussed briefly.     

Trail‐sharing among tropical ants: interspecific use of trail pheromones?

1. Trail‐sharing between different ant species is rare and restricted to a small number of species pairs. Its underlying mechanisms are largely unknown. For trail‐sharing to occur, two factors are required: (i) one or both species must recognise the other species or its pheromone trails and (ii) both species must tolerate each other to a certain extent to allow joint use of the trail. A species that follows another's trails can efficiently exploit the other's information on food sources contained in the pheromone trails. Hence, food competition and thus aggressive interactions between a species following another's trail and the species being followed, seem likely. 2. In the present study, we investigated interspecific trail following and interspecific aggression in trail sharing associations (i) among Polyrhachis ypsilon, Camponotus saundersi, and Dolichoderus cuspidatus, and (ii) among Camponotus rufifemur and Crematogaster modiglianii. We tested whether trail‐sharing species follow each other's pheromone trails, and whether the ants tolerated or attacked their trail‐sharing partners. In both associations, we confronted workers with pheromone trails of their associated species, and, for the former association, measured interspecific aggression among the trail‐sharing species. 3. In our assays, D. cuspidatus and C. rufifemur regularly followed heterospecific pheromone trails of P. ypsilon and C. modiglianii, respectively. However, only few workers of the remaining species followed heterospecific pheromone trails. Thus, shared trails of P. ypsilon and C. saundersi cannot be explained by interspecific trail‐following. 4. Interspecific aggression among P. ypsilon, C. saundersi, and D. cuspidatus was strongly asymmetric, C. saundersi being submissive to the other two. All three species differentiated between heterospecific workers from the same or another site, suggesting habituation to the respective trail‐sharing partners. We therefore hypothesise that differential tolerance by dominant ant species may be mediated by selective habituation towards submissive species and this way determines the assembly of trail‐sharing associations.     

The use of the central raphe endings as a taxonomic character

The use of the central raphe endings as a key character in the classification ofNitzschia is argued to be of doubtful validity. Some aspects of the evolution of the raphe are discussed in relation to variation in raphe structure within fibulate genera.Notes for a monograph of theBacillariaceae (Bacillariophyta) 1.     

Communication in the migratory termite-hunting ant Pachycondyla (= Termitopone) marginata (Formicidae, Ponerinae)

The Neotropical species Pachycondyla marginata conducts well-organized predatory raids on the termite species Neocapritermes opacus and frequently emigrates to new nest sites. During both activities the ants employ chemical trail communication. The trail pheromone orginates from the pygidial gland. Among the substances identified in the pygidial gland secretions, only citronellal was effective as a trail pheromone. Isopulegol elicited an increase in locomotory activity in the ants and may function as a synergist recruitment signal. The chemical signal is enhanced by a shaking display performed by the recruiting ant.     

Revisiting the trail pheromone components of the red imported fire ant,Solenopsis invicta Buren

Ants use species-specific trail pheromones to coordinate their sophisticated foraging behavior. During the past decades, many trail pheromone components with various structures have been identified in ants, including the red imported fire ant, Solenopsis invicta, a notorious invasive species worldwide. Four compounds, Z,E- (ZEF) and E,E-α-farnesene (EEF), Z,E- (ZEHF) and E,E-α-homofarnesene (EEHF), have been reported as components of S. invicta trail pheromone. However, another study reported an analog of α-farnesene, Z,Z,Z-allofarnesene, as a key trail pheromone component. These contrasting results caused some uncertainty about the trail pheromone composition in S. invicta. In this study, we synthesized ZEF and EEF, ZEHF and EEHF, and reanalyzed the chemicals in the Dufour gland extract and in the trail pheromone fraction of S. invicta worker body extract. The reported isomers of farnesene and homofarnesene were detected and showed trail-following activity, with ZEF as the major compound, while no allofarnesene was found, neither in the Dufour gland extract nor in the whole-body extract. Our results confirm ZEF and EEF, ZEHF and EEHF as trail pheromone components of S. invicta.     

Ski trail effects on a beetle (Coleoptera: Carabidae, Elateridae) community in Vermont

Beetle diversity and species composition were studied using pitfall traps placed along three parallel transects that extended from the center of a downhill ski trail, 100 m into a large, unfragmented spruce-fir forest on Mount Mansfield State Park, VT, USA. Groups of beetles showed associations with three distinct habitats: ski trail openings (Agonum cupripenne, Amara spp., Poecilus lucublandus, Hypnoidus bicolor, and H. abbreviatus), edge (Pterostichus coracinus, Agonum retractum, Sphaeroderus canadensis, and Calathus ingratus), and forest (Pterostichus adstrictus, P. punctatissimus, P. brevicornis, Platynus decentis, Trechas apicalis, T. crassiscapus, and Eanus maculipennis). Consequently, carabid and elaterid species composition in the ski trail, edge, and 5 m into the unfragmented forest showed nearly complete turnover. Most beetles within the ski trail were colonizers from lower elevations; however, one species, H. bicolor, was a tundra species that appeared to have colonized lower elevations along the ski trail opening. Of "forest" beetles, only 2 of 540 individuals (< 0.5%) were collected in the ski trail opening. Thus, ski trails are strong barriers to dispersal for forest beetles, several of which are flightless or dimorphic and primarily short-winged. Consequently, fragmentation of mountain slopes by ski trails, especially those that run perpendicular to the climatic gradient, may put isolated populations at a greater risk of local extirpation.     

The predatory snail Euglandina rosea successfully follows mucous trails of both native and non‐native prey snails

Mucous trail following is a primary means by which many predatory snails locate prey. I compared the ability of individuals of Euglandina rosea to follow mucous trails of two groups of gastropods: those found within its native habitat (southeastern USA), and those found outside its native range (Kansas). Members of E. rosea followed trails for both species found inside and outside its native range equally well. In contrast to previous studies, I found that the predatory snails consistently followed trails in the direction in which they were laid. I quantified the kinematics of trail‐following behavior using inter‐tentacle angle as the primary metric. In both prey groups, there were significant differences in the predator's inter‐tentacle angle when tracking a trail versus not, and when successfully following (in the direction the trail was laid) versus unsuccessfully following (opposite the direction that the trail was laid) trails. In addition, in both prey groups, there were significant differences in the predator's velocity when tracking a trail versus not, and when successfully versus unsuccessfully following trails. This study confirmed that members of E. rosea are robust generalist predators, capable of successfully tracking native and non‐native snails, and should not be introduced as biologic control agents. These results may be useful to managers, as they provide insight into how trail following could be used to trap members of this invasive species.     

The effect of drugs on diatom valve morphogenesis

Summary The effects of various drugs on cell wall (valve) morphogenesis was investigated in three species of diatoms (Pinnularia spp., Surirella robusta, andHantzschia amphioxys) using light microscopy (LM) and scanning electron microscopy (SEM). Treatment ofSurirella with the microtubule (MT) disrupting agent colchicine during early valve formation results in a characteristic malformation of the valve, whereby part of the normally circumferential raphe canal forms as an abnormal protruding lip on the valve surface, located up to 20 m from the edge of the valve. The position of this malformed lip coincides with the location of a microtubule center (MC) at the time of colchicine addition, suggesting that the MC may play a direct role in positioning the tip of the raphe canal during valve formation. The migration of this MC to the tip of the cell during early valve morphogenesis is reversibly inhibited by the metabolic inhibitor 2-4-dinitrophenol (DNP). The effect of colchicine onPinnularia valve formation is less severe, causing occasional malformation of the raphe, but little if any lateral displacement. InHantzschia, colchicine has no effect on the positioning of the raphe, but prolonged exposure causes fusion of the raphe canal with the valve face. Cochicine treatment also results in the absence of the normal curvature at the central interruption in the raphe, as well as abnormal pore formation in this central area. Addition of cytochalasin D during early valve formation inHantzschia causes the raphe canal to form in the center of the valve face, suggesting that the normal translocation of the raphe canal to the valve edge is actindependent. Comparison of valves from control and cytochalasintreatmentHantzschia suggest that the pore spacing within the valve is determined by the position relative to the raphe, and does not depend on whether to pores form on the side (mantle) or the face of the mature valve.Abbreviations DM diatom medium - DNP dinitrophenol - MT microtubule - MC microtubule center - PSS primary silicification site - SDV silica deposition vesicle     

Influence of Illuminance and Forager Experience on Use of Orientation Cues in Social Wasps (Vespinae)

We tested the influence of illuminance and level of forager experience on nest orientation behavior of the social wasps Vespula vulgaris, Vespa crabro, and Dolichovespula saxonica in an artificial laboratory tunnel system. The number of wasps which oriented themselves chemically via a terrestrial trail or used visual orientation were determined at different illuminance levels for foragers which were naïve or experienced with the tunnel system. In V. vulgaris and D. saxonica, mainly the young and naïve foragers used the chemical trail for orientation in brightness. Experienced foragers used visual cues for nest orientation. In V. crabro, naïve and experienced foragers followed the chemical trail in a similar intensity. In darkness, when visual orientation was limited, the relative importance of the chemical trail increased dramatically in all species and all experience classes.     

The trail of the african urticating antTetramorium aculeatum: Source,potency, and workers' behavior (Hymenoptera: Formicidae)

This paper studies the production of and the response to the trail in the African urticating ant,Tetramorium aculeatum under a variety of laboratory conditions. The trail was found to contain a complex mix of substances. Two of these components are secreted by the poison gland: The most volatile one is an attractant and increases the ants' linear speed; the other is the trail pheromone, which may act for days on a dry substrate. A third component is present on the last abdominal sternite. It acts as an attractant and a locostimulant and is synergistic of the trail pheromone. The activity of these substances increases with the age of the workers. While following a trail, foragers, even unrewarded, reinforce it with both the poison gland contents and the synergistic compound. The ants follow trails better in darkness than in light. A wetted trail rapidly loses its activity. The article suggests an explanation for the functioning ofT. aculeatum's natural trails, including the role of its different components.     

管壳缝类硅藻中国新记录属种——非洲南氏藻

利用光学和电子显微镜对采自黄海水域的1个管壳缝类硅藻——非洲南氏藻进行了形态学研究,并对其地理分布进行了讨论。结果表明:(1)该种壳体带面呈矩形,壳面窄椭圆形,具有钝圆的末端。(2)壳缝居中,由两条等长的分支组成。(3)管壳缝由复杂、接合的肋突支撑,但无龙骨。(4)每条线纹仅有1个孔纹,壳套上最多有1列孔纹。(5)目前本种仅发现于南非萨尔达尼亚湾和中国黄海。非洲南氏藻是该属在中国的第一个报道种类,因此,该属也是在中国第一次报道。     

Sex pheromones and trail‐following pheromone in the basal termites Zootermopsis nevadensis (Hagen) and Z. angusticollis (Hagen) (Isoptera: Termopsidae: Termopsinae)

In the context of an evolutionary study of the chemical communication in termites, sex pheromones and trail‐following pheromones were investigated in two Termopsidae, Zootermopsis nevadensis and Z. angusticollis. In these species, in which the presence of sex‐specific pheromones has been demonstrated previously, the chemical structure of the female sex pheromone has now been identified as (5E)‐2,6,10‐trimethylundeca‐5,9‐dienal and the male sex pheromone as (+)‐ or (?)‐syn‐4,6‐dimethyldodecanal. The amount of sex pheromone was estimated at 5–10 ng per individual in females and 2–5 ng in males. Because these two sympatric species do not differ in their pheromonal chemical composition, reproductive isolation is probably mediated chiefly by differences in dispersal flight chronology. The trail‐following pheromone was shown to be composed of the same compound as the male sex pheromone, that is syn‐4,6‐dimethyldodecanal. The compound syn‐4,6‐dimethyldodecanal was 10 times more active than the racemic (+/?)‐syn + (+/?)‐anti‐4,6‐dimethyldodecanal in eliciting trail‐following. The amount of syn‐4,6‐dimethyldodecanal was estimated at 0.1–0.5 ng per pseudergate. Regarding the phylogenetic aspects, the nature of the female sex pheromone of Zootermopsis is structurally akin to the trail‐following pheromone of Mastotermes darwiniensis of Mastotermitidae and Porotermes adamsoni and Stolotermes victoriensis of Termopsidae. Interestingly, the nature of the trail‐following pheromone of the Termopsinae Zootermopsis is clearly different from that of the Porotermitinae P. adamsoni and the Stolotermitinae S. victoriensis, which mirrors recent molecular data on the paraphyly of Termopsidae. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 519–530.     

Mate Finding Via a Trail Sex Pheromone by <Emphasis Type="Italic">Aphytis melinus</Emphasis> DeBach (Hymenoptera: Aphelinidae) Males

Finding mates is frequently problematic for parasitoid wasps. In some parasitoid species, males rely on volatile, airborne sex pheromones for locating mates, while in others they rely on contact, trail sex pheromones. This study sought to shed light on the mate finding mechanism of males of Aphytis melinus. Specifically, the goal was to determine whether A. melinus males use airborne or contact pheromones, or both, for locating mates. The study showed that A. melinus males rely on a contact, trail sex pheromone for locating mates: A. melinus males responded to substrate-borne cues left by virgin females, while they did not respond to airborne cues from virgin females. Specifically, males more frequently encountered virgin females when the females walked across an arena to a fixed encounter point compared to when they were manually placed at the encounter point, and spent greater than expected time on surfaces previously visited by virgin females compared to control surfaces not visited by females. In contrast, males did not respond to airborne cues from virgin females in an airflow olfactometer nor to traps baited with virgin females in the field, and spent similar lengths of time on surfaces visited by newly-mated or 24-h mated females versus control surfaces not visited by females. The main effect of the trail sex pheromone on the behavior of A. melinus males was to direct their search and, so, increase the likelihood of encountering mates. This effect apparently is not preceded by longer-range attraction of males via an airborne female sex pheromone. Overall, the results of this study support a hypothesis in which A. melinus males searching on substrates on which females may be present rely exclusively on a trail sex pheromone to locate mates.     

Pheromone trail decay rates on different substrates in the Pharaoh's ant, Monomorium pharaonis

Abstract. Many ants use pheromone trails to organize collective foraging. This study investigated the rate at which a well‐established Pharaoh's ant, Monomorium pharaonis (L.), trail breaks down on two substrates (polycarbonate plastic, newspaper). Workers were allowed to feed on sucrose solution from a feeder 30 cm from the nest. Between the nest and the feeder, the trail had a Y‐shaped bifurcation. Initially, while recruiting to and exploiting the feeder, workers could only deposit pheromone on the branch leading to the feeder. Once the trail was established (by approximately 60 ants per min for 20 min), the ants were not allowed to reinforce the trail and were given a choice between the marked and unmarked branches. The numbers of ants choosing each branch were counted for 30 min. Initially, most went to the side on which pheromone had been deposited (80% and 70% on the plastic and paper substrates, respectively). However, this decayed to 50% within 25 min for plastic and 8 min for paper. From these data, the half‐life times of the pheromone are estimated as approximately 9 min and 3 min on plastic and paper, respectively. The results show that, for M. pharaonis, trail decay is rapid and is affected strongly by trail substrate.     

THE “PARADOX” DIATOM BACILLARIA PAXILLIFER (BACILLARIOPHYTA) REVISITED1

Defined by its unique colonial locomotion, Bacillaria paxillifer (O. F. Müll.) Hendey was recognized as a single, pandemic species by many phycologists. However, reinvestigation of colonies from different habitats revealed three distinct groups: (A) brackish/freshwater, (B) marine littoral, and (C) marine planktonic taxa. Groups differed in colony and cell form, raphe flanges (RFs), shape and position of transapical ribs (Tr's), and morphogenesis. Linear‐shaped species were restricted to group A: Tr's thickened principally to the interior. Lanceolate forms were confined to groups B and C: valve formation proceeded from an internal base layer to the exterior. The planktonic species differed in the shape of its raphe slit, and the transformation of girdle bands (GBs) into “winglets.” Taxa also differed in chloroplast shape and number. All species formed motile colonies. Siblings adhered via elastic fibrils secreted through their raphe. Raphe ribs were held in position by siliceous clamps (fibulae), anchored in an extra pair of axial ribs (fibular ribs) parallel to the raphe ribs. This raphe system resembled that of Cylindrotheca rather than the “canal raphe” of Nitzschia. Many valves were asymmetric along the apical axis due to protruding RFs shuttling in a 1:1 ratio within a colony, but raphe slits were mirror images, as were the growth direction of fibulae and position of plastids, with pyrenoids tilted in the same direction. Species possessed four open GBs per epitheca; the third band invariably bore an internal, organic ridge to aid in adhesion of the plasmalemma during cleavage. The results suggested that these taxa are a natural phylogenetic group, requiring precise determination of their taxonomic position.