Heartbeat control in the medicinal leech: A model system for understanding the origin,coordination, and modulation of rhythmic motor patterns

We have analyzed in detail the neuronal network that generates heartbeat in the leech. Reciprocally inhibitory pairs of heart interneurons form oscillators that pace the heartbeat rhythm. Other heart interneurons coordinate these oscillators. These coordinating interneurons, along with the oscillator interneurons, form an eight-cell timing oscillator network for heartbeat. Still other interneurons, along with the oscillator interneurons, inhibit heart motor neurons, sculpting their activity into rhythmic bursts. Critical switch interneurons interface between the oscillator interneurons and the other premotor interneurons to produce two alternating coordination states of the motor neurons. The periods of the oscillator interneurons are modulated by endogenous RFamide neuropeptides. We have explored the ionic currents and graded and spike-mediated synaptic transmission that promote oscillation in the oscillator interneurons and have incorporated these data into a conductance-based computer model. This model has been of considerable predictive value and has led to new insights into how reciprocally inhibitory neurons produce oscillation. We are now in a strong position to expand this model upward, to encompass the entire heartbeat network, horizontally, to elucidate the mechanisms of FMRFamide modulation, and downward, to incorporate cellular morphology. By studying the mechanisms of motor pattern formation in the leech, using modeling studies in conjunction with parallel physiological experiments, we can contribute to a deeper understanding of how rhythmic motor acts are generated, coordinated, modulated, and reconfigured at the level of networks, cells, ionic currents, and synapses. © 1995 John Wiley & Sons, Inc.     

GEOGRAPHIC DISTRIBUTION OF MITOCHONDRIAL DNA VARIANTS AND THE HISTORICAL BIOGEOGRAPHY OF THE SPOTTED SALAMANDER,AMBYSTOMA MACULATUM

I analyzed geographic partitioning of mitochondrial DNA (mtDNA) restriction-site variants in the spotted salamander, Ambystoma maculatum. Two highly divergent and geographically separate genetic lineages were identified that differed by a minimum of 19 restriction sites (6% sequence divergence). One of the lineages has a disjunct distribution with very closely related haplotypes occurring in Missouri, Arkansas, North Carolina, and Virginia. The other lineage is found in Michigan, Illinois, and Alabama. The geographic separation of highly divergent mtDNA haplotypes, a pattern that was predicted based on the sedentary nature of these salamanders, is evidence for long-term barriers to gene flow. In contrast, the large-scale disjunction of very similar haplotypes suggests recent, long-distance gene flow and does not match the phylogeographic expectation for a small terrestrial vertebrate. I explain this potential contradiction in the level of importance assigned to gene flow by a scenario in which historical barriers to gene flow account for the two divergent mtDNA assemblages, but stochastic sorting of ancestral polymorphism is responsible for the large-scale geographic disjunction. Ten of 16 populations collected in the Ozark Highlands were fixed for the same haplotype. I attribute this lack of detectable variation to recent colonization of this area, a hypothesis that is supported by paleoecological data and demonstrates the potential benefits of combining data from paleobotany, geology, and other disciplines to reconstruct the historical biogeography of a species.     

Nest site choice by the three-spined stickleback, Gasterosteus aculeatus (form leiurus), in spring-fed waters

The nest site characteristics of the freshwater three-spined stickleback, Gasterosteus aculeatus (form leiurus ), were quantitatively investigated in springs and the main stream of the Yamayoke and the Tsuya River system, central Japan. Most nests (93·4%) were on a muddy or sandy substratum, at depths of 10–40 cm (84·3%), in water velocities less than 15 cm s⁻¹ (76·2%) and in the temperature range of 14 to 16° C (82·7%), Spring-fed localities provided more of these conditions than the main stream channel and hence contained more potential nesting areas. Thus, they were utilized by male sticklebacks both temporally (prolonged breeding season) and spatially (more nest sites).     

Variations in stream water uptake by Eucalyptus camaldulensis with differing access to stream water

The stable isotopes ²H and ¹⁸O were used to determine the water sources of Eucalyptus camaldulensis at three sites with varying exposure to stream water, all underlain by moderately saline groundwater. Water uptake patterns were a function of the long-term availability of surface water. Trees with permanent access to a stream used some stream water at all times. However, water from soils or the water table commonly made up 50% of these trees' water. Trees beside an ephemeral stream had access to the stream 40–50% of the time (depending on the level of the stream). No more than 30% of the water they used was stream water when it was available. However, stream water use did not vary greatly whether the trees had access to the stream for 2 weeks or 10 months prior to sampling. Trees at the third site only had access to surface water during a flood. These trees did not change their uptake patterns during 2 months inundation compared with dry times, so were not utilising the low-salinity flood water. Pre-dawn leaf water potentials and leaf ¹³C measurements showed that the trees with permanent access to the stream experienced lower water stress and had lower water use efficiencies than trees at the least frequently flooded site. The trees beside the ephemeral stream appeared to change their water use efficiency in response to the availability of surface water; it was similar to the perennial-stream trees when stream water was available and higher at other times. Despite causing water stress, uptake of soil water and groundwater would be advantageous to E. camaldulensis in this semi-arid area, as it would provide the trees with a supply of nutrients and a reliable source of water. E. camaldulensis at the study site may not be as vulnerable to changes in stream flow and water quality as previously thought.     

斑须蝽三代卵块的空间分布和田间抽样技术研究

通过田间调查和计算,明确了斑须蝽三代卵块呈聚集分布,且以负二项分布为主。理论抽样数当t＝1．00,D＝0．3时,n＝13．091/＋63．878,如果防治指标定为百株虫卵块12块时,则最大抽样数为173株,序贯抽样的累积虫卵块数量界限为：T0（N）＝0.12N±0．4735。田间随机取样以平行线和Z字形为最佳。     

Food mixing by generalist grasshoppers: Plant secondary compounds structure the pattern of feeding

Plant secondary compounds can prevent feeding by phytophagous insects or, if ingested, can be poisonous to them. Less attention has been paid to the additional effects they have on feeding behavior when they are only weakly deterrent or not deterrent at all. Experiments were carried out on the generalist grass-hopperSchistocerca americana. Individuals were presented either with two cakes of high-quality artificial food with a single deterrent compound added or with two cakes, each with a different added deterrent compound. The deterrents consisted of single plant secondary compounds that were either marginally or strongly deterrent. There were profound differences in feeding behavior between those individuals given identical and those given different cake types, including longer feeding bouts on single cakes when a choice of different cake types was available. The behavioral effects demonstrate that the presence of secondary compounds in one food can influence the patterns of feeding on other available foods and suggest that such chemicals could impact foraging activities in a complex manner.     

Morphometric analysis of the genusHemerocallis L. (Liliaceae) in Korea

To better understand the patterns of variability and distributions ofHemerocallis in Korea, 53 locations were visited and measurements of 19 morphological and phenological characters were taken on plants directly from their natural habitats. For morphometric analysis, 10 plants from each of 34 populations and five herbarium specimens ofH. middendorffii were used and the data from 12 quantitative characters was analyzed using univariate analysis. Except the littoral populations of Cheju, Hong, Taehuksan, and Sohuksan Islands (H. hongdoensis M. Chung & S. Kang), three peninsular KoreanHemerocallis species can be recognized mainly in South Korea:H. hakuunensis Nakai (=H. micrantha Nakai, growing on southern, central, and northwestern Korea);H. thunbergii Baker (=H. coreana Nakai, found on southeastern and central Korea); andH. middendorffii Tr. et Mey. (central and northeastern Korea). Morphological and phenological features contributing to recognition of the three groups were; color of perianth, shape of roots, shape of inflorescence, flowering time, odor, length of inflorescence, width of the lowest bracts, length of perianth tube enclosing a ovary, width of the inner perianth lobes. Natural hybridization seems to be rare in KoreanHemerocallis. It appears that the KoreanHemerocallis species are relatively well characterized by their distribution patterns, phenology, and habitats compared with the JapaneseHemerocallis species.     

Demography and social structure of one group of muriquis (Brachyteles arachnoides)

We monitored one group of muriquis, or woolly spider monkeys (Brachyteles arachnoides), over a 9-year period at Fazenda Montes Claros, Minas Gerais, Brazil. The group grew from 22 to 42 individuals due to the births of 21 surviving infants. Eight immigrations involving immature females were offset by emigrations and disappearances. The home range of the group expanded as the group size increased. The group traveled as a cohesive unit during the first 6 years of the study, but recently it has begun to show greater tendencies to fission temporarily into smaller subgroups. Six adult males from the other muriqui group at this site have simultaneously increased their associations with the main study group. These observations indicate that the group is in a state of transition which may lead, ultimately, either to its division into two smaller units or to a more fluid social structure.     

Ontogenetic patterns of volatiles identified in Dufour's gland extracts from queens and workers of the primitively eusocial halictine bee,Lasioglossum malachmum (Hymenoptera: Halictidae)

Summary Ontogenetic patterns of volatile compounds identified in Dufour's gland extracts from queens and workers of the primitively eusocial sweat beeLasioglossum malachurum (K.) were compared. Only young unmated queens showed high proportions of isopentenyl esters, while macrocyclic lactones were dominant in old breeding queens, spring queens, and workers. In young queens the relative and absolute amounts of volatiles changed one day after mating. A discriminant analysis revealed significant differences in odor patterns of unmated and mated young queens. The fat body was the largest in young females, while eggs could be recorded only in breeding queens. Possible functions of different odor components in the investigated female groups are discussed.     

Flow patterns and endothelial cell morphology in a simplified model of an artificial ventricle

The aim of this study was to delineate the flow patterns in a non-unidirectional flow field inside a ventricle-shaped cell culture chamber, and examine the resulting morphology and integrity of the endothelium in select regions of the monolayer. The chamber was perfused by pulsatile flow, and the coherent motion of the fluid was studied using flow visualization aided by image analysis. Four distinct flow patterns were discerned and examined: central jet, flow impingement, flow separation, and recirculating eddies. The influence of these patterns on endothelial cell morphology was assessed after 20 h of exposure to flow. There were no signs of damage to the endothelium in the jet region nor was there evidence of cell alignment with the flow. Yet, there were changes in cell morphology and cytoskeletal architecture as compared to control. By contrast, within the eddies where the flow was highly disturbed, there was apparent damage to the endothelium. Thus, exposure of cells to random velocity fluctuations in regions of quasi-static flow compromises the integrity of the monolayer. Identification of such sites and acquisition of the knowledge necessary to protect the cells from denudation will be valuable for the endothelialization efforts of cardiac prostheses.