scholarly journals Bilateral and ipsilateral ascending tectopulvinar pathways in mammals: A study in the squirrel (spermophilus beecheyi)

2012 ◽  
Vol 520 (8) ◽  
pp. 1800-1818 ◽  
Author(s):  
Felipe Fredes ◽  
Tomas Vega-Zuniga ◽  
Harvey Karten ◽  
Jorge Mpodozis
Keyword(s):  
Spermophilus Beecheyi

Directional filter characteristics of optic nerve fibers in California ground squirrel (Spermophilus beecheyi)

1984 ◽  
Vol 52 (6) ◽  
pp. 1200-1212 ◽  
Author(s):  
M. E. McCourt ◽  
G. H. Jacobs
Keyword(s):  
Optic Nerve ◽  
Ground Squirrel ◽  
Receptive Fields ◽  
Spatial Summation ◽  
Nerve Fibers ◽  
Field Size ◽  
Image Motion ◽  
Spermophilus Beecheyi ◽  
California Ground Squirrel ◽  
Preferred Direction

Directional units in the optic nerve of the California ground squirrel (Spermophilus beecheyi) were studied with respect to their response to diffuse light, preferred directions of motion, tuning for preferred direction, the relationship between spatial and directional tuning characteristics, and receptive-field size and areal summating properties. Directional units in the ground squirrel optic nerve are of the “on-off” type. No purely on or off units were encountered in a sample of 356 directionally selective fibers. The distribution of preferred directions of image motion for 356 units was significantly anisotropic; greater than 50% of the directional units prefer motion in the direction of the superior-nasal visual quadrant. Mean directional bandwidth, measured at half-amplitude response, for 39 units was 88.5 degrees. The distribution of directional bandwidths suggests that two subpopulations of directional units may exist a broadly tuned (106.4 degrees bandwidth) group preferring image motion in the superior-nasal direction, and a narrowly tuned group (59.9 degrees bandwidth) with a uniform distribution of preferred direction. Tuning for direction of motion and for spatial frequency were significantly positively correlated in a sample of 35 directional units. Area-vs.-response measures for directional units show that they possess excitatory discharge centers with a concentric antagonistic surround, plus a larger suppressive surround activated specifically by moving luminance contours, which may be asymmetric. Critical activation areas for directional units, as measured along orthogonal orientations, were highly positively correlated. This suggests that these receptive fields possess the property of linear spatial summation, not of luminance flux, but of areas of moving luminance contours.

Disease Surveillance of California Ground Squirrels (Spermophilus beecheyi) in a Drive-through Zoo in Oregon, USA

2017 ◽  
Vol 53 (3) ◽  
pp. 667-670
Author(s):  
Julia Ter Beest ◽  
Andrew Cushing ◽  
Modesto McClean ◽  
Wendy Hsu ◽  
Robert Bildfell
Keyword(s):  
Disease Surveillance ◽  
Ground Squirrels ◽  
Spermophilus Beecheyi ◽  
California Ground Squirrels

scholarly journals Quantitative Shedding of Two Genotypes of Cryptosporidium parvum in California Ground Squirrels (Spermophilus beecheyi)

2001 ◽  
Vol 67 (6) ◽  
pp. 2840-2843 ◽  
Author(s):  
Edward R. Atwill ◽  
Sergio Maldonado Camargo ◽  
Ralph Phillips ◽  
Laura Herrera Alonso ◽  
Kenneth W. Tate ◽  
...  
Keyword(s):  
Cryptosporidium Parvum ◽  
Ground Squirrels ◽  
Spermophilus Beecheyi ◽  
California Ground Squirrels

ABSTRACT Sixteen percent of California ground squirrels (Spermophilus beecheyi) were found to be shedding an average of 53,875Cryptosporidium parvum oocysts/g of feces. Male squirrels had a higher prevalence and higher intensity of shedding than did female squirrels. The majority of C. parvum isolates matched a bovine-murine genotype, with a few isolates resembling a porcine genotype. Higher intensities of shedding by males may enhance dissemination and genotypic mixing of this protozoa given males' proclivity to disperse to nonnatal colonies.

Development of Antisnake Defenses in California Ground Squirrels (Spermophilus Beecheyi): II. Microevolutionary Effects of Relaxed Selection From Rattlesnakes

Behaviour ◽  
1993 ◽  
Vol 124 (1-2) ◽  
pp. 137-162 ◽  
Author(s):  
Richard G. Coss ◽  
Naomie S. Poran ◽  
Kevin L. Gusé ◽  
David G. Smith
Keyword(s):  
Population Level ◽  
Ground Squirrels ◽  
Species Discrimination ◽  
Spermophilus Beecheyi ◽  
Relaxed Selection ◽  
Virtual Absence ◽  
Rare Site ◽  
California Ground Squirrels ◽  
Two Populations

AbstractNonvenomous Pacific gopher snakes (Pituophis melanoleucus catenifer) and venomous northern Pacific rattlesnakes (Crotalus viridis oreganus) have coexisted in a predator-prey relationship with California ground squirrels (Spermophilus beecheyi) for many thousands of generations. This long-term relationship has fostered in ground squirrels the evolution of antisnake defenses that consist of physiological resistance to rattlesnake venom and behavioral tactics of probing and harassing that might facilitate snake-species discrimination. Snake harassment by adults might also protect pups by interfering with snake hunting activities. Some ground squirrel populations have colonized habitats where rattlesnakes, but not gopher snakes, are rare or absent. Initial research indicates that squirrels experiencing relaxed selection from rattlesnakes are very aggressive toward their remaining nonvenomous snake predator, the gopher snake. Two experiments investigated the effects of relaxed selection from rattlesnakes by examining: 1) changes in level of venom resistance, 2) the reorganization of antisnake behaviors in lab-born pups and wild-caught adults from different sites, and 3) the role of natural experiences on the development of antisnake behavior in a rattlesnake-adapted population. Level of venom resistance was examined by an in vitro radioimmunoassay of serum-to-venom binding of two populations of Douglas ground squirrels (S. b. douglasii). The ancestors of one population are estimated to have experienced relaxed selection from rattlesnakes for about 9,000 years based on genetic distance and radiocarbon analyses. The antisnake behavior of 60-73 day-old lab-born pups from these two populations was video taped during presentations of a caged rattlesnake or gophcr snake for alternate 5-min trials in a seminatural laboratory setting. Two groups of wild-caught adult Beechey groundsquirrels (S. b. beecheyi) were studied using the same protocol for examining antisnake behavior. One group was obtained from a population that recently colonized a rattlesnake-rare site and exhibits moderate venom resistance. The second group came from a population that exhibits very low venom resistance and inhabits a rattlesnake-free site; relaxed selection from rattlesnakes for this population is estimated to span approximately 60,000 years. Comparisons of Douglas ground squirrels from rattlesnake-abundant and rettlesnakerare sites revealed that venom resistance declined approximately 59% after an estimated 9,000 years of relaxed selection from rattlesnakes. Lab-born Douglas pups from the same rattlesnake-rare site were more aggressive toward the gopher snake than toward the rattlesnake whereas pups from the population experiencing predation from both species of snake treated both snakes as similarly dangerous. Unlike pups, wild-caught adults from the rattesnake-adapted population harassed the rattlesnake more intensely than the gopher snake, a phenomenon that may reflect their experience with snakes in nature and larger body size that reduces their vulnerability to envenomation. Wild-caught Beechey ground squirrels that recently colonized a rattlesnake-rare site did not differentiate the rattlesnake and gopher snake whereas Beechey ground squirrels whose ancestors have experienced prolonged relaxed selection from rattlesnakes were more aggressive toward the gopher snake. Consistent with previous findings, prolonged relaxed selection from rattlesnakes, but not gopher snakes, appears to have reduced the inhibition to harass large gopher snakes. This microevolutionary shift in increased aggressiveness toward the gopher snake could result from the virtual absence of any risk in misidentifying rattlesnakes from gopher snakes.

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