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Luiz Carlos L Silveira - One of the best experts on this subject based on the ideXlab platform.
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ganglion cell and displaced amacrine cell density distribution in the retina of the howler monkey Alouatta caraya
PLOS ONE, 2014Co-Authors: Jose Muniz, Luana Modesto De Athaide, Bruno Duarte Gomes, Barbara L. Finlay, Luiz Carlos L SilveiraAbstract:Unlike all other New World (platyrrine) monkeys, both male and female howler monkeys (Alouatta sp.) are obligatory trichromats. In all other platyrrines, only females can be trichromats, while males are always dichromats, as determined by multiple behavioral, electrophysiological, and genetic studies. In addition to obligatory trichromacy, Alouatta has an unusual fovea, with substantially higher peak cone density in the foveal pit than every other diurnal anthropoid monkey (both platyrrhines and catarrhines) and great ape yet examined, including humans. In addition to documenting the general organization of the retinal ganglion cell layer in Alouatta, the distribution of cones is compared to retinal ganglion cells, to explore possible relationships between their atypical trichromacy and foveal specialization. The number and distribution of retinal ganglion cells and displaced amacrine cells were determined in six flat-mounted retinas from five Alouatta caraya. Ganglion cell density peaked at 0.5 mm between the fovea and optic nerve head, reaching 40,700–45,200 cells/mm2. Displaced amacrine cell density distribution peaked between 0.5–1.75 mm from the fovea, reaching mean values between 2,050–3,100 cells/mm2. The mean number of ganglion cells was 1,133,000±79,000 cells and the mean number of displaced amacrine cells was 537,000±61,800 cells, in retinas of mean area 641±62 mm2. Ganglion cell and displaced amacrine cell density distribution in the Alouatta retina was consistent with that observed among several species of diurnal Anthropoidea, both platyrrhines and catarrhines. The principal alteration in the Alouatta retina appears not to be in the number of any retinal cell class, but rather a marked gradient in cone density within the fovea, which could potentially support high chromatic acuity in a restricted central region.
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Alouatta trichromatic color vision cone spectra and physiological responses studied with microspectrophotometry and single unit retinal electrophysiology
PLOS ONE, 2014Co-Authors: Luiz Carlos L Silveira, Cézar A. Saito, Manoel Da Silva Filho, Jan Kremers, James K. Bowmaker, Barry B LeeAbstract:The howler monkeys (Alouatta sp.) are the only New World primates to exhibit routine trichromacy. Both males and females have three cone photopigments. However, in contrast to Old World monkeys, Alouatta has a locus control region upstream of each opsin gene on the X-chromosome and this might influence the retinal organization underlying its color vision. Post-mortem microspectrophotometry (MSP) was performed on the retinae of two male Alouatta to obtain rod and cone spectral sensitivities. The MSP data were consistent with only a single opsin being expressed in each cone and electrophysiological data were consistent with this primate expressing full trichromacy. To study the physiological organization of the retina underlying Alouatta trichromacy, we recorded from retinal ganglion cells of the same animals used for MSP measurements with a variety of achromatic and chromatic stimulus protocols. We found MC cells and PC cells in the Alouatta retina with similar properties to those previously found in the retina of other trichromatic primates. MC cells showed strong phasic responses to luminance changes and little response to chromatic pulses. PC cells showed strong tonic response to chromatic changes and small tonic response to luminance changes. Responses to other stimulus protocols (flicker photometry; changing the relative phase of red and green modulated lights; temporal modulation transfer functions) were also similar to those recorded in other trichromatic primates. MC cells also showed a pronounced frequency double response to chromatic modulation, and with luminance modulation response saturation accompanied by a phase advance between 10–20 Hz, characteristic of a contrast gain mechanism. This indicates a very similar retinal organization to Old-World monkeys. Cone-specific opsin expression in the presence of a locus control region for each opsin may call into question the hypothesis that this region exclusively controls opsin expression.
Barry B Lee - One of the best experts on this subject based on the ideXlab platform.
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Alouatta trichromatic color vision cone spectra and physiological responses studied with microspectrophotometry and single unit retinal electrophysiology
PLOS ONE, 2014Co-Authors: Luiz Carlos L Silveira, Cézar A. Saito, Manoel Da Silva Filho, Jan Kremers, James K. Bowmaker, Barry B LeeAbstract:The howler monkeys (Alouatta sp.) are the only New World primates to exhibit routine trichromacy. Both males and females have three cone photopigments. However, in contrast to Old World monkeys, Alouatta has a locus control region upstream of each opsin gene on the X-chromosome and this might influence the retinal organization underlying its color vision. Post-mortem microspectrophotometry (MSP) was performed on the retinae of two male Alouatta to obtain rod and cone spectral sensitivities. The MSP data were consistent with only a single opsin being expressed in each cone and electrophysiological data were consistent with this primate expressing full trichromacy. To study the physiological organization of the retina underlying Alouatta trichromacy, we recorded from retinal ganglion cells of the same animals used for MSP measurements with a variety of achromatic and chromatic stimulus protocols. We found MC cells and PC cells in the Alouatta retina with similar properties to those previously found in the retina of other trichromatic primates. MC cells showed strong phasic responses to luminance changes and little response to chromatic pulses. PC cells showed strong tonic response to chromatic changes and small tonic response to luminance changes. Responses to other stimulus protocols (flicker photometry; changing the relative phase of red and green modulated lights; temporal modulation transfer functions) were also similar to those recorded in other trichromatic primates. MC cells also showed a pronounced frequency double response to chromatic modulation, and with luminance modulation response saturation accompanied by a phase advance between 10–20 Hz, characteristic of a contrast gain mechanism. This indicates a very similar retinal organization to Old-World monkeys. Cone-specific opsin expression in the presence of a locus control region for each opsin may call into question the hypothesis that this region exclusively controls opsin expression.
Leslie A Knapp - One of the best experts on this subject based on the ideXlab platform.
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comparing the selective landscape of tlr7 and tlr8 across primates reveals unique sites under positive selection in Alouatta
Molecular Phylogenetics and Evolution, 2020Co-Authors: Nicole S Torosin, Hernan Argibay, Timothy H Webster, Patrice Showers Corneli, Leslie A KnappAbstract:Abstract Among primates, susceptibility to yellow fever (YFV), a single-stranded (ss) RNA virus, ranges from complete resistance to high susceptibility. Howler monkeys (genus Alouatta) are the most susceptible to YFV. In order to identify Alouatta-specific genetic factors that may be responsible for their susceptibility, we collected skin samples from howler monkey museum specimens of the species A. caraya and A. guariba clamitans. We compared the rate of nonsynonymous to synonymous ( dN / dS ) changes of Toll-like receptor (TLR) 7 and TLR8, the two genes responsible for detecting all ssRNA viruses, across the Primate order. Overall, we found that the TLR7 gene is under stronger purifying selection in howler monkeys compared to other New World and Old World primates, but TLR8 is under the same selective pressure. When we evaluated dN / dS at each codon, we found six codons under positive selection in Alouatta TLR8 and two codons under positive selection in TLR7. The changes in TLR7 are unique to A. guariba clamitans and are found in functionally important regions likely to affect detection of ssRNA viruses by TLR7/TLR8, as well as downstream signaling. These amino acid differences in A. guariba clamitans may play a role in YFV susceptibility. These results have implications for identifying genetic factors affecting YFV susceptibility in primates.
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positively selected variants in functionally important regions of tlr7 in Alouatta guariba clamitans with yellow fever virus exposure in northern argentina
American Journal of Physical Anthropology, 2020Co-Authors: Nicole S Torosin, Ilaria Agostini, Hernan Argibay, Timothy H Webster, Hebe Ferreyra, Marcela Uhart, Candelaria Sanchez Fernandez, Leslie A KnappAbstract:BACKGROUND In 2007-2009, a major yellow fever virus (YFV) outbreak in Northern Argentina decimated the local howler monkey (Alouatta) population. AIMS To evaluate whether the surviving howler monkeys possess advantageous genetic variants inherited from monkeys alive prior to the YFV outbreak, we explored the relationship between Toll-like receptor (TLR) 7 and TLR8 gene variation and YFV susceptibility. METHODS We used samples from Alouatta individuals in Misiones, Argentina alive before the YFV outbreak, individuals that died during the outbreak, and individuals that survived the outbreak and are alive today. We measured genetic divergence between Alouatta YFV exposure groups and evaluated Alouatta-specific substitutions for functional consequences. RESULTS We did not find different allele frequencies in the post-YFV exposure Alouatta group compared to the pre-exposure group. We identified three nonsynonymous variants in TLR7 in Alouatta guariba clamitans. Two of these substitutions are under positive selection in functionally important regions of the gene. DISCUSSION AND CONCLUSIONS Our results did not indicate that surviving howler monkey spossess advantageous genetic variants at greater frequency than those alive before the YFV outbreak. However, the positively selected unique coding differences in A. guariba clamitans are in the region important in pathogen detection which may affect YFV resistance. Morework is necessary to fully explore this hypothesis.
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positively selected variants in functionally important regions of tlr7 in Alouatta guariba clamitans with yellow fever virus exposure in northern argentina
bioRxiv, 2019Co-Authors: Nicole S Torosin, Ilaria Agostini, Hernan Argibay, Timothy H Webster, Hebe Ferreyra, Marcela Uhart, Leslie A KnappAbstract:1 Abstract In 2007-2009, a ma jor yellow fever virus (YFV) outbreak in Northern Argentina decimated the local howler monkey (Alouatta) population. We explored the relationship between Toll-like receptor (TLR) 7 and TLR8 gene variation and YFV susceptibility using samples from Alouatta individuals alive before the YFV outbreak, individuals that died during the outbreak, and individuals that survived the outbreak and are alive today. We measured genetic divergence between Alouatta YFV exposure groups and evaluated Alouatta-specific substitutions for functional consequences. We did not find different allele frequencies in the post-YFV exposure Alouatta group compared to the pre-exposure group. However, we identified three nonsynonymous variants in TLR7 in A. guariba clamitans. Two of these substitutions are under positive selection in functionally important regions of the gene. These unique coding differences in A. guariba clamitans may affect YFV resistance, but more work is necessary to fully explore this hypothesis.
Linde E T Ostro - One of the best experts on this subject based on the ideXlab platform.
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shifts in social structure of black howler Alouatta pigra groups associated with natural and experimental variation in population density
International Journal of Primatology, 2001Co-Authors: Scott C Silver, Linde E T Ostro, R Horwich, Fred W Koontz, Robin C BrockettAbstract:We examined variation in the group structure of black howlers (Alouatta pigra) using the adult composition of 48 social groups. We compared the structure of groups at 5 sites with different population densities and variation in group structure over time with rising population density. In addition, we examined changes in the group structure of monkeys that were translocated from an area of high population density to an area with a much lower population density. We found at low population densities, groups comprised either heterosexual pairs or a single male with two females. At high population densities groups tended to be multimale and often contained >2 adult females. We suggest the relative costs and benefits of dispersal by maturing adults varies with population density, and in Alouatta pigra results in a shift from single to multimale groups of larger size with increasing population density.
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feeding ecology of the black howler monkey Alouatta pigra in northern belize
American Journal of Primatology, 1998Co-Authors: Scott C Silver, Linde E T Ostro, C P Yeager, R HorwichAbstract:We studied the feeding ecology of the black howler monkey (Alouatta pigra) from March 1994 to April 1995 in the Community Baboon Sanctuary in northern Belize, Central America. Activity and diet composition were recorded using continuous focal animal sampling. Diet composition was compared with the relative abundance of plant parts eaten by the howlers within the study site. The study animals spent an average of 24.4% of their time feeding, 61.9% resting, and approximately 9.8% traveling. In contrast to previously published reports on A. pigra, we found the diet composition to be similar to that of other Alouatta species (conforming to the folivore/frugivore profile), with 41% of feeding time spent eating fruit, 45% foliage, and 11% flowers. This contrast may indicate a wide degree of dietary flexibility that allows A. pigra to inhabit a variety of habitat types. We suggest that a high level of resource abundance throughout the year makes the Community Baboon Sanctuary excellent habitat for Alouatta pigra.
Scott C Silver - One of the best experts on this subject based on the ideXlab platform.
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shifts in social structure of black howler Alouatta pigra groups associated with natural and experimental variation in population density
International Journal of Primatology, 2001Co-Authors: Scott C Silver, Linde E T Ostro, R Horwich, Fred W Koontz, Robin C BrockettAbstract:We examined variation in the group structure of black howlers (Alouatta pigra) using the adult composition of 48 social groups. We compared the structure of groups at 5 sites with different population densities and variation in group structure over time with rising population density. In addition, we examined changes in the group structure of monkeys that were translocated from an area of high population density to an area with a much lower population density. We found at low population densities, groups comprised either heterosexual pairs or a single male with two females. At high population densities groups tended to be multimale and often contained >2 adult females. We suggest the relative costs and benefits of dispersal by maturing adults varies with population density, and in Alouatta pigra results in a shift from single to multimale groups of larger size with increasing population density.
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feeding ecology of the black howler monkey Alouatta pigra in northern belize
American Journal of Primatology, 1998Co-Authors: Scott C Silver, Linde E T Ostro, C P Yeager, R HorwichAbstract:We studied the feeding ecology of the black howler monkey (Alouatta pigra) from March 1994 to April 1995 in the Community Baboon Sanctuary in northern Belize, Central America. Activity and diet composition were recorded using continuous focal animal sampling. Diet composition was compared with the relative abundance of plant parts eaten by the howlers within the study site. The study animals spent an average of 24.4% of their time feeding, 61.9% resting, and approximately 9.8% traveling. In contrast to previously published reports on A. pigra, we found the diet composition to be similar to that of other Alouatta species (conforming to the folivore/frugivore profile), with 41% of feeding time spent eating fruit, 45% foliage, and 11% flowers. This contrast may indicate a wide degree of dietary flexibility that allows A. pigra to inhabit a variety of habitat types. We suggest that a high level of resource abundance throughout the year makes the Community Baboon Sanctuary excellent habitat for Alouatta pigra.