ABSTRACT
Ant protection of extrafloral nectar (EFN)-secreting plants is a common form of mutualism found in most habitats around the world. However, very few studies have considered these mutualisms from the ant, rather than the plant, perspective. In particular, a whole-colony perspective that takes into account the spatial structure and nest arrangement of the ant colonies that visit these plants has been lacking, obscuring when and how colony-level foraging decisions might affect tending rates on individual plants. Here, we experimentally demonstrate that recruitment of Crematogaster opuntiae (Buren) ant workers to the EFN-secreting cactus Ferocactus wislizeni (Englem) is not independent between plants up to 5 m apart. Colony territories of C. opuntiae are large, covering areas of up to 5,000 m(2), and workers visit between five and 34 EFN-secreting barrel cacti within the territories. These ants are highly polydomous, with up to 20 nest entrances dispersed throughout the territory and interconnected by trail networks. Our study demonstrates that worker recruitment is not independent within large polydomous ant colonies, highlighting the importance of considering colonies rather than individual workers as the relevant study unit within ant/plant protection mutualisms.
Subject(s)
Ants/physiology , Behavior, Animal , Symbiosis , Animals , Plant NectarABSTRACT
Electric birefringence imaging (EBI) maps stresses in agarose electrophoresis gels. Both DNA and gel alignment can be monitored using this technique. Previously, we have reported birefringence images associated with resolved small (< 48 kbp) and partially resolved large 48 kb-(2 Mbp) DNA fragments oriented with relatively short electric field pulses. In this paper, differences between images acquired using short and long (DC) voltage pulses are presented. It is shown that stress signals distribute over long distances when exposed to prolonged electric fields. Resolution also affects band shapes. Refinements in instrumental design and evaluation of limiting noise sources of the technique are also described.
Subject(s)
Birefringence , DNA/isolation & purification , Electromagnetic Fields , Electrophoresis, Agar Gel , Electricity , Linear Models , Nephelometry and Turbidimetry , Temperature , Time FactorsABSTRACT
Local temperatures inside a 75-microns-i.d. capillary under electrophoresis conditions are measured noninvasively with a Raman microprobe. The method is based on the temperature dependence of the water O-H stretch equilibrium between weakly bent and strongly bent hydrogen bonded species. With calibration against a known temperature standard, this technique is shown to be capable of obtaining spatially resolved intracapillary temperature measurements with an accuracy of +/- 1.0 degree C and a precision of +/- 0.1 degree C. Intracapillary temperatures ranging from 25 to 70 degrees C are observed over the range of buffer compositions and electric fields used. Differences between local temperatures and average capillary temperatures are observed at all operating conditions. The difficulty of an accurate theoretical description of heat dissipation under CE conditions is discussed.
Subject(s)
Electrophoresis/instrumentation , Spectrum Analysis, Raman/instrumentation , TemperatureABSTRACT
Image processing techniques which separate the DNA Kerr effect and induced electrokinetic distortion contributions to electric birefringence images of agarose nucleic acid electrophoresis gels are described. Under standard electrophoresis conditions, detection limits of 10 ng of DNA per well are obtained in hydroxyethylated agarose without signal averaging or 7.5 ng with averaging of four measurements. Maintaining constant gel temperature is shown to improve the quality of the images. Monochromatic light (589 nm) is shown to give a small increase in sensitivity compared to polychromatic (650 +/- 20 nm) light.
Subject(s)
DNA/analysis , Electrophoresis, Agar Gel , MicrochemistryABSTRACT
Multilinear regression analysis is used to test a model (Lanan et al., 1991) for electric birefringence imaging (EBI) of DNA fragment bands in agarose electrophoresis gels. EBI signals attributed to localized electro-kinetic gel distortion and to intrinsic DNA birefringence are studied by fitting ethidium bromide fluorescence profiles to EBI results. Fluorescence polarization imaging (FPI) is used to assess the influence of localized gel distortion on nucleic acid orientation across a fragment band. It is shown that DNA aligns parallel, on average, with an applied electric field independent of its location within a band. DNA orientation varies as the 1.2 power in electric field strength under the conditions tested.
Subject(s)
DNA/isolation & purification , Electrophoresis, Agar Gel , Birefringence , DNA/chemistry , Electrochemistry , Ethidium , Evaluation Studies as Topic , Fluorescence Polarization , Regression AnalysisABSTRACT
Time-resolved and steady-state electric birefringence imaging with a slow-scan video camera is used to study orientation during DNA agarose gel electrophoresis. The hydrodynamically induced gel distortion is shown to be the major source of birefringence under electrophoresis running conditions and to generate a birefringence image that approximates the image of the DNA concentration gradient in the electric field direction. A fluid kinematic model is presented to describe the spatial distribution of steady-state birefringence and is verified with fluorescence measurements of DNA distribution. The stress-optic coefficient of 1% agarose gel is measured by mechanical compression and used to evaluate the magnitude of the induced strain on the gel during electrophoresis.
