Behavioural and neural studies of male singing and female phonotaxis behaviour in crickets

Acoustic communication in crickets is achieved by the production of calling, courtship, and rivalry songs in male crickets and the recognition of the songs by conspecifics. Male crickets sing by rhythmically opening and closing the forewings to generate sound pulses and song patterns. The central command for singing is controlled by the brain. The song structure is under control of the abdominal central pattern generator (CPG) and acts as a behavioural barrier to prevent courtship with females of closely related species. Therefore, an analysis of the song structure, the central command, and the organisation of the CPG in different cricket species could reveal how evolution shaped cricket singing behaviour. In G. bimaculatus, I recorded different song types and corresponding wing movement of individual males. I discovered a small amplitude oscillation of the forewings during courtship song that was not reported before. The similar pulse parameters and wing movements during calling and rivalry song could imply a shared neural network for the two song types in G. bimaculatus. I analysed rivalry and courtship behaviour before and after applying specific lesions to the abdominal nerve cord in G. bimaculatus. Most elements of rivalry and courtship behaviour are not affected by lesions, except for rivalry song, courtship song, and copulation. For generation of the rivalry song the central nerve cord from the brain to A4 is sufficient (same as calling song), whereas the whole nerve cord without the terminal abdominal ganglion is required for generation of courtship song. I compared the calling song before and after applying specific lesions to the abdominal nerve cord in four cricket species: G. rubens, G. assimilis, Teleogryllus oceanicus, and T. commodus. The four species show similar effects of the lesions on the generation of sound pulses besides a species-specific control of song structure, suggesting they share a conserved organisation of the CPG network for calling song. Following the discovery of the calling song command neuron in G. bimaculatus, I carried out intracellular recording in the brain of males of different species. I found the putative command neurons for calling song in G. bimaculatus, G. assimilis, and T. commodus and characterize the physiological and functional properties of these neurons. The results suggest the command neurons in the three species could be homologues by showing a similar control on generating calling song. Furthermore, based on female cricket phonotaxis preference I developed an animal acoustic selecting system, in which the females have to navigate through a complex parkour to reach the acoustic stimulus presenting speaker. I tested the system with different selecting experiments and proved the system can be applied to select females attracted to certain song pattern. Overall, these findings broaden our understanding of cricket singing in terms of neural control of different song types and evolution of singing behaviour in different species, and provide a new tool to study phonotactic behaviour.Cambridge Trust Ministry of Education in Taiwa

A conjunctive groundwater and surface water model of the upper part of the Mark Twain Watershed in northeast Missouri

The Mark Twain Lake Watershed in northeastern Missouri is the main source of water supply for 16 water districts in the region and is suffering serious water quality issues. A steady-state, analytical-element, groundwater flow model GFLOW simulation was constructed in the Mark Twain Lake watershed in claypan soils of northeastern Missouri including the Crooked Creek monitoring site. The objectives of the study were to establish a conjunctive surface water and groundwater model for central part of the Mark Twain Lake Watershed region using GFLOW. The near-field region consisted of 3,000 km² area within a domain representing approximately 6,000 km². The model was calibrated using 6 hydraulic head targets, 4 lake stage targets, and 5 baseflow flux targets by trial-and-error, UCODE, and PEST simulations. Parameters refined through the automatic technique yielded optimal values of 5 m/day for regional hydraulic conductivity for the model domain, 100 m/day for inhomogeneities (alluviual deposits along streams), and a recharge rate of 0.000195 m/yr (about 7% of mean annual precipitation). Model results indicated that Mark Twain Lake is a surface-water-dominated lake. Sixty-seven percent of the water arriving at the Mark Twain Lake is from streamflow and 22 percent from precipitation, whereas only 11 percent is from groundwater. The lake received about ten times more groundwater inflow (101,000 m³/day, 11 percent) than outflow (18,000 m³/day, 2 percent). More than ninety-eight percent of water moving out of the lake from is evapotranspiration (210,000 m³/day) and stream flow (731,000 m³/day), whereas only 2 percent (18,000 m³/day) is lost from groundwater. The groundwater flow and surface water discharge predicted by the GFLOW simulations probably reflect the strong influence of claypan soils in the study area, where overland flow comprises most of streamflow. According to the particle tracking results, NPS pollutants in groundwater are transported primarily downstream through highly permeable, alluvial channels. Groundwater inflow to the stream emanates only from a small zone immediately adjacent to the stream. These results suggest that the net effect of riparian buffers on NPS pollutants in the region could be increased by expanding buffers outward from the creek edge to the edge of the alluvial deposits along the valley

Permeation of organic compounds through ductile iron pipe gaskets

Ductile iron (DI) pipes have been used for the conveyance of drinking water in drinking water distribution systems over the past several decades. It has been estimated that almost half of all new water mains installed in North America are DI pipes. Although DI pipe itself is resistant to chemical permeation, the polymeric gaskets that join and seal the pipe segments are reported to be susceptible to permeation by organic contaminants. Pipe-drum, diffusion cell experiments, and numerical simulations were conducted in this research to obtain a faster mean to evaluate possible permeations through DI gaskets. Of the five types of gasket materials tested using the gravimetric sorption test, ethylene-propylene-diene monomer (EPDM) had the highest sorption of gasoline, while fluoroelastomer rubber (FKM) exhibited very low sorption of gasoline. The sorption test results suggested that the least to most resistance to permeation of premium gasoline for the five gasket materials were EPDM, styrene-butadiene rubber (SBR), chloroprene rubber (CR; neoprene), acrylonitrile butadiene rubber (NBR), and FKM. A typical gasket was found to be made of two portions, the heel and the bulb, of the same polymer but different formulation. Gravimetric sorption tests suggested that the heel portion of all gaskets may be more resistant to permeation than the bulb making it the limiting step for permeation of organic compounds in gasoline. Pipe-drum experiments showed that SBR gasket had the highest permeation rates of benzene, toluene, ethylbenzene, and xylenes (BTEX), followed by CR, EPDM, and NBR. With regards to threats to drinking water under water stagnation conditions in the pipe, the 5 μg/L maximum contaminant level (MCL) for benzene will likely be exceeded during an 8-hour stagnation period for SBR gaskets in contact with free-product premium gasoline. NBR gaskets were found to be sufficiently resistant to permeation by benzene or other BTEX compounds in gasoline and the benzene concentration is unlikely to exceed EPA MCLs. Assessment based on data from the pipe-drum experiments suggested that when there is flow of water in the pipe, benzene and other BTEX compounds in gasoline will not exceed EPA MCLs. A diffusion cell device was developed to obtain diffusion coefficients of BTEX compounds for various gasket materials under controlled conditions. Using curve fitting of the permeation data by numerical modeling, the diffusion coefficients of BTEX compounds through SBR and NBR gasket materials was found to range from 10-7 to 10-8 cm2/s. The steady-state permeation rates were found to correlate in a linear relationship with thickness while the diffusion coefficients were found to be invariable to the thickness of the polymer tested (2 mm to 5 mm). The diffusion cell provided a rapid, inexpensive, and relatively well-controlled means to study permeation of polymeric gasket materials for DI pipes and the data obtained were used to model benzene permeation of the pipe-drum experiments. The permeation of benzene through a 4-inch SBR gasket of a pipe joint was modeled using Multiphysics diffusion module. The simulations showed that the heel portions as well as part of the bulb portions of a gasket were likely to be in contact with the contaminants. Model simulation predicted that a 4-inch SBR gasket under hydrostatic pressure would permeate more organic chemicals than a pipe without hydrostatic pressure, posing greater risk to organic chemical permeations. Increase in the length/size of the bulb portion of a 4-inch SBR gasket by compression or swelling from 10% to 30%, reduced the permeated mass of benzene by about 29% to 71% within 150 days of exposure to gasoline. In summary, SBR and NBR gaskets are compatible with any level of gasoline contamination in groundwater. NBR gasket is the most effective choice when a gasket material resistant to gasoline is desired. Diffusion cell experiments in combination with numerical simulations can be used in evaluating possible BTEX permeations effectively. Gasket exposure area and its orientation in the socket after pipe joint assembly are likely to affect permeation path and permeated mass of contaminants. Results from this study can be used as a basis for crisis management for DI pipes exposed to gasoline and for development of a better gasket to improve the reliability of infrastructure of development of water distribution system

Lesions of abdominal connectives reveal a conserved organization of the calling song central pattern generator (CPG) network in different cricket species.

Although crickets move their front wings for sound production, the abdominal ganglia house the network of the singing central pattern generator. We compared the effects of specific lesions to the connectives of the abdominal ganglion chain on calling song activity in four different species of crickets, generating very different pulse patterns in their calling songs. In all species, singing activity was abolished after the connectives between the metathoracic ganglion complex and the first abdominal ganglion A3 were severed. The song structure was lost and males generated only single sound pulses when connectives between A3 and A4 were cut. Severing connectives between A4 and A5 had no effect in the trilling species, it led to an extension of chirps in a chirping species and to a loss of the phrase structure in two Teleogryllus species. Cutting the connectives between A5 and A6 caused no or minor changes in singing activity. In spite of the species-specific pulse patterns of calling songs, our data indicate a conserved organisation of the calling song motor pattern generating network. The generation of pulses is controlled by ganglia A3 and A4 while A4 and A5 provide the timing information for the chirp and/or phrase structure of the song