Temporal and spatial genetic variability in white-tailed deer (Odocoileus virginianus).

Starch-gel electrophoresis was used to assess temporal and spatial genetic variation in populations of white-tailed deer (Odocoileus virginianus) in western Tennessee. Samples of liver and kidney obtained from animals at five localities during 1985-1992 were analyzed at 11 loci known to be polymorphic in white-tailed deer. There were minimal significant differences in allelic frequencies between sexes and among age groups for each year at each locality and among years at each locality with ages and sexes combined. No significant difference occurred among mean values of heterozygosity. A heterozygote deficiency was detected in white-tailed deer populations from western Tennessee and could reflect limited inbreeding but was more likely due to Wahlund effects. Limited temporal variation occurred among years within a locality and indicated a stasis in terms of minimal genetic drift and harvest effects on genetic structure of the populations. Herd origin, stocking history of populations, and gene flow were probable causes of spatial heterogeneity in deer populations in western Tennessee.

Ultrashort laser pulse bioeffects and safety.

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.

A potential model for early stages of chromosomal evolution via concentric Robertsonian fans: a large area of polymorphism in southern short-tailed shrews (Blarina carolinensis).

Western Tennessee contains unusually highly polymorphic populations of southern short-tailed shrews (Blarina carolinensis). We previously documented eight Robertsonian translocations (ROBs) accounting for a variation in diploid number from 46 in most of this species' range to 34-40 in western Tennessee. We have now expanded our study to include data from adjacent areas in Tennessee and Mississippi, 10 localities in all. The new data show a variation in diploid number ranging from 31 to 41, four new ROBs (for a total of 12), and the novel finding of monobrachial translocations in this group. All animals collected from this large area (extending over 12, 000 km(2)) had some level of ROBs, and none represented the 2n = 46 form seen in other parts of the range of this species. Because other species of shrews (genus Sorex) are not affected in the same area, the factors and/or selective forces causing this extensive polymorphism in B. carolinensis must be unique to this species and to this geographic area. Some ROBs were found throughout this large area of over 12,000 km(2). Other translocations (including those with monobrachial homology) were located in one or two localities in this large area, and still other translocations were intermediate in their distribution. There was a concentric pattern to the evolution and presumed spreading of the ROBs. This allowed us to expand the concept of a Robertsonian "fan," introduced by Matthey (1970), to that of concentric evolution of multiple fusion fans: ROBs likely arose independently, separated temporally and geographically, and radiated into surrounding populations to create this complex zone of polymorphism. This is an active process in its infancy, and it is not as mature as that seen in European studies of Mus and Sorex.

Comparative study of laser damage threshold energies in the artificial retina.

Laser damage threshold energies produced from ultrashort (i.e., ⩽1 ns) laser pulses are investigated as a function of both pulse width and spot size for an artificial retina. A piece of film acts as the absorbing layer and is positioned at the focus of a variant on the Cain artificial eye [C. Cain, G. D. Noojin, D. X. Hammer, R. J. Thomas, and B. A. Rockwell, "Artificial eye for in vitro experiments of laser light interaction with aqueous media," J. Biomed. Opt.2, 88-94 (1997)]. Experiments were performed at the focal point and at two and ten Rayleigh ranges (RR) in front of the focus with the damage end point being the presence of a bubble imaged at the film plane. Pulse energy thresholds were determined for wavelengths of 1064, 580, and 532 nm with pulse durations ranging from the nanosecond (ns) to the femtosecond (fs) regime. For the at-focus data in the visible regime, the threshold dropped from 0.25 µJ for a 532 nm, 5 ns pulse to 0.11 µJ for a 580 nm, 100 fs pulse. The near-infrared (NIR) threshold changed from 5.5 µJ for a 5 ns pulse to 0.9 µJ for a 130 fs pulse at a distance two RR in front of the focus. The experiment was repeated using the same pulse widths and wavelengths, except the water path was removed to determine the impact of nonlinear self-focusing in water. A vertical microscope imaging system was employed in order to observe the threshold event. The NIR fluence threshold of 0.5 J/cm2 remained constant within an experimental uncertainty for all pulse widths, which corresponds to values in the literature [C. P. Lin and M. W. Kelly, "Ultrafast time-resolved imaging of stress transient and cavitation from short pulsed laser irradiated melanin particles," SPIE Laser-Tissue Interactions VI, Proc. SPIE2391, 294-299 (1995)]. The visible data also demonstrated a nearly constant fluence of 0.07 J/cm2. The disparity in thresholds between the two techniques arises from nonlinear optical phenomena related to propagation differences in the ocular fluid. © 1999 Society of Photo-Optical Instrumentation Engineers.

Robertsonian chromosomal rearrangements in the short-tailed shrew, Blarina carolinensis, in western Tennessee.

We report significant heterozygosity for numerous Robertsonian translocations in the southern short-tailed shrew (Blarina carolinensis) in western Tennessee. Eight Robertsonian rearrangements were documented using G-banding techniques that explain the variability in diploid numbers from 46 throughout most of the range of the species to 34-40 in western Tennessee. These fusions resulted in the loss of telomere sequences and were not associated with nucleolar organizer regions. When heterozygocity is considered, the lowest diploid number possibly present would be 30. Four localities with distances of over 180 km apart were sampled, and 80-90% of the collected animals were heterozygous for at least one rearrangement. No putative parental type was found in western Tennessee. Heterozygosity for the same rearrangements was found in these different localities, and no monobrachial fusions were noted. Thus, this is a very wide hybrid zone with rare or absent parental types in the areas sampled or is an evolutionary stage preceding establishment of Robertsonian races. Selective forces, if any, were minimal, as evidenced by the wide area of polymorphism, significant heterozygosity, and the fact that the Robertsonian translocations were in Hardy-Weinberg equilibrium. The origin of such extensive polymorphism in western Tennessee is discussed, especially in light of putative effects of the New Madrid seismic activity. Similarities and differences are noted between the Blarina model and the well-documented variation in the European common shrew (Sorex araneus) and Mus musculus groups.

Retinal damage and laser-induced breakdown produced by ultrashort-pulse lasers.

BACKGROUND: In vivo retinal injury studies using ultra-short-pulse lasers at visible wavelengths for both rabbit and primate eyes have shown that the degree of injury to the retina is not proportional to the pulse energy, especially at suprathreshold levels. In this paper we present results of calculations and measurements for laser-induced breakdown (LIB), bubble generation, and self-focusing within the eye. METHODS: We recorded on video and measured the first in vivo LIB and bubble generation thresholds within the vitreous in rabbit and primate eyes, using external optics and femtosecond pulses. These thresholds were then compared with calculations from our LIB model, and calculations were made for self-focusing effects within the vitreous for the high peak power pulses. RESULTS: Results of our nonlinear modeling and calculations for self-focusing and LIB within the eye were compared with experimental results. The LIB ED50 bubble threshold for the monkey eye was measured and found to be 0.56 microJ at 120 fs, compared with the minimum visible lesion (MVL) threshold of 0.43 microJ at 90 fs. Self-focusing effects were found to be possible for pulsewidths below 1 ps and are probably a contributing factor in femtosecond-pulse LIB in the eye. CONCLUSIONS: Based on our measurements for the MVL thresholds and LIB bubble generation thresholds in the monkey eye, we conclude that in the femtosecond pulsewidth regime for visible laser pulses, LIB and self-focusing are contributing factors in the lesion thresholds measured. Our results may also explain why it is so difficult to produce hemorrhagic lesions in either the rabbit or primate eye with visible 100-fs laser pulses even at 100 microJ of energy.