Habitat Use of American Alligators in East Texas

ABSTRACT The American alligator (Alligator mississippiensis) has made a remarkable recovery throughout its range during the last half-century. In Texas, USA, current inland alligator population and harvest management strategies rely on generalized and often site-specific habitat and population data generated from coastal populations, because it is assumed that habitat and demographic similarities exist between inland and coastal populations. These assumptions have not been verified, however, and no studies have specifically examined inland alligator habitat use in Texas. We quantified alligator habitat use in East Texas during 2003–2004 to address this information gap and to facilitate development of regionally specific management strategies. Although habitat was variable among study areas, alligators used habitats with >50% open water, substantial floating vegetation, and emergent vegetation close (<12 m) to dry ground and cover. Adults used habitats further from dry ground and cover, in open water (75–85%), with less floating vegetation (6–22%) than did subadults, which used habitats that were closer to dry ground and cover, with less open water (52–68%), and more floating vegetation (8–40%). Although habitat use mirrored coastal patterns, we estimated alligator densities to be 3–5 times lower than reported in coastal Texas, likely a result of inland habitat deviations from optimal coastal alligator habitat, particularly in the preponderance of open water and floating vegetation. Our findings that 1) inland habitats varied among sites and did not exactly match assumed optimal coastal habitats, 2) alligators used these inland habitats slightly differently than coastal areas, and 3) inland alligator densities were lower than coastal populations, all highlight the need for regionally specific management approaches. Because alligator populations are influenced by habitat quality and availability, any deviations from assumed optimal habitat may magnify harvest impacts upon inland populations.     

Nuclear-Transfer Studies on Induced Increases in Streptomycin Resistance of Amoeba proteus

SYNOPSIS. The responses of a strain of Amoeba proteus to conditions which could give rise to induced increases in resistance to streptomycin have been investigated. An indirect selection method, based on survival time in high concentrations of streptomycin, was devised. All attempts to obtain substrains with enhanced sensitivity or enhanced resistance by indirect methods were unsuccessful. It was therefore concluded that increases in resistance observed as a result of other treatments were likely to be the result of adaptation of a majority of individuals, rather than selection of pre-existing resistant variants. Direct treatment with regularly increased concentrations of streptomycin led to a 10-fold increase in resistance of large cultures. Nuclear transfers were made by the de Fonbrune technique to produce resistant nucleus/normal cytoplasm, and normal cytoplasm/resistant nucleus combinations. Examination of the descendants of these 'crosses' showed that the resistance was nuclear dependent and not influenced by the cytoplasm. The resistance proved transitory, disappearing slowly during continued culture without further contact with streptomycin.
These results are discussed with reference to possible mechanisms responsible for the increase in streptomycin resistance and its mode of origin.     

Factors affecting the production of caffeoylquinic acid levels in germinating carrot seedlings and its estimation by u.v. epifluorescence microscopy

Conditions for obtaining reproducible estimates of caffeoylquinic acids in carrot seedlings, by fluorescence intensity determined using epifluorescent microscopy were investigated. The optimum germination conditions for the test were established as 9–10 days at 20 °C. Factors such as the presence of microflora on seed material and the environment of the seed during production were found to influence the mean radicle fluorescence.     

Powdery mildew of tabacco (Erysiphe cichoracearum DC.)

The natural spread of Erysiphe cichoracearum was assessed weekly on alternate leaves of irrigated and non-irrigated tobacco plants of Kutsaga 51 variety, grown in field plots in 1962-63. Leaf area, air temperature and humidity within the plots, relative turgidity of the leaves and soil moisture were also measured. Leaves emerged over a period of 37 days. A minimum of 29 days elapsed between leaf emergence and infection; irrigation lengthened this period by 2–6 days for leaves 2–6 and shortened it by 2–10 days for leaves 10–18. The duration of the initial resistant phase, in leaves at comparable stalk positions, appeared to be directly proportional to the eventual size of the leaves at reaping. Leaves were not infected until they were almost fully expanded. The longest dry period, when most irrigation water was applied, occurred when most lower leaves (2–8) were fully expanded and already infected; upper leaves (10–18)w ere then still expanding and not yet infected. Irrigation increased infection in all leaves; it increased the growth of the pathogen during dry weather and the subsequent susceptibility of leaves that were still actively expanding but not yet infected. Irrigation increased the percentage of susceptible leaf area infected, of intact plants, threefold and that of topped plants ninefold. Topped plants had less infection than intact ones.     

Changes in the resistance of tobacco leaf to Erysiphe cichoracearum DC. induced by topping,cytokinins and antibiotics*

Treatments that produced different rates of growth in attached tobacco leaves and leaf discs, also affected the growth of powdery mildew on them. Topping (removal of flower head) increased the resistance of upper leaves, and attached leaves of topped and intact plants were more susceptible than leaf discs from them incubated on water. Hyphal growth increased on leaf discs incubated on water at increasing light intensities, as did dry and fresh mass of healthy discs. On kinetin, dry and fresh mass also increased with light intensity but hyphal growth decreased slightly. Discs incubated at all light intensities on kinetin had less hyphal growth than those on water at the lowest intensity (< 50 lx). Floating leaf discs on chloramphenicol at 500 μ/ml restricted fungal growth but not quite as much as kinetin (10 μ/ml); kinetin inhibited the fungus in the presence of chloramphenicol. Actinomycin D (2.μ5 μ/ml) and puromycin (5.0 μml) had little effect on the fungus.     

Enzyme polymorphisms in the House Sparrow, Passer domesticus

Methods are described for the visualization of 20 enzymes from the house sparrow, Passer domesticus, in starch gels and by iso-electric focussing. Many of the methods are applicable to other avian species. Two samples of sparrows from the east midlands of England have been analysed. The patterns that are manifest in the gels can be ascribed to between 33 and 35 loci, of which the same nine are polymorphic in both samples. The level of heterozygosity in these birds is about 15%, which at first sight is higher than an introduced population in Australia. However, this difference disappears when homologous loci are compared.     

Machine vision automated species identification scaled towards production levels

Computer‐automated identification of insect species has long been sought to support activities such as environmental monitoring, forensics, pest diagnostics, border security and vector epidemiology, to name just a few. In order to succeed, an automated identification programme capable of addressing the needs of the end user should be able to classify hundreds of taxa, if not thousands, and is expected to distinguish closely related and hence morphologically similar species. However, it remains unknown how automated identification methods might handle an increase in data quantity, be it in reference imagery or taxonomic diversity. We sought to test the scalability of an automated identification method in terms of the number of reference specimens used to train the classifier and the number of taxa into which the classifier should assign unknown specimens. Is there an optimal number of reference images, where the cost of acquiring more images becomes greater than the marginal increase in identification success? Does increasing taxonomic diversity affect identification success, whether negatively or positively? In order to test the scalability of the automated insect identification enterprise, we used a sparse processing technique and support vector machine to test the largest dataset to date: 72 species of fruit flies (Diptera: Tephritidae) and 76 species of mosquitoes (Diptera: Culicidae). We found that: (i) machine vision methods are capable of correctly classifying large numbers of closely related species; (ii) when the misclassification of a specimen occurs at the species level, it is often classified in the correct genus; (iii) classification success increases asymptotically as new training images are added to the dataset; (iv) broad taxon sampling outside a focal group can increase classification success within it.     

Evolution of intrinsic reproductive isolation among four North American populations of Rhagoletis pomonella (Diptera: Tephritidae)

Across its range in North America, four geographically separated, ecologically and genetically diverged populations of hawthorn (Crataegus)‐infesting Rhagoletis pomonella (Diptera: Tephritidae) flies inhabit the Eje Volcánico Trans Mexicano (EVTM), the Sierra Madre Oriental (SMO), the Chiapas Highlands (CHIS) and the USA. Here, we tested whether these four populations are reproductively isolated by any intrinsic, nonhost‐related, pre‐ or postmating barriers to gene flow. Crossing experiments suggested that a low level of host‐independent prezygotic isolation may exist between hawthorn flies from EVTM and the three other populations, but only with respect to a slight reduction in copulation duration in EVTM matings. Some evidence for postmating isolation was found, again primarily involving EVTM crossed to SMO, CHIS and US flies. Certain crosses produced no (SMO male × EVTM female) or few (EVTM male × CHIS female; CHIS male × SMO female) F1 hybrid offspring. F2 crosses were generally fertile, except for US male × CHIS female matings. Inherent reproductive isolation therefore appears to be quantitative rather than absolute between populations, as the possibility for gene flow exists through at least some combinations of mating among EVTM, SMO, CHIS and US flies. Our results are consistent with a recently advanced hypothesis that episodic introgression from Mexico into the USA has played a role in providing genetic variation, facilitating sympatric host race formation and the adaptive radiation of the R. pomonella sibling species' complex in the USA. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 213–223.