The effects of natural substrate discontinuities on the quadrupedal gait kinematics of free‐ranging Saimiri sciureus

Wild primates encounter complex matrices of substrates that differ in size, orientation, height, and compliance, and often move on multiple, discontinuous substrates within a single bout of locomotion. Our current understanding of primate gait is limited by artificial laboratory settings in which primate quadrupedal gait has primarily been studied. This study analyzes wild Saimiri sciureus (common squirrel monkey) gait on discontinuous substrates to capture the realistic effects of the complex arboreal habitat on walking kinematics. We collected high‐speed video footage at Tiputini Biodiversity Station, Ecuador between August and October 2017. Overall, the squirrel monkeys used more asymmetrical walking gaits than symmetrical gaits, and specifically asymmetrical lateral sequence walking gaits when moving across discontinuous substrates. When individuals used symmetrical gaits, they used diagonal sequence gaits more than lateral sequence gaits. In addition, individuals were more likely to change their footfall sequence during strides on discontinuous substrates. Squirrel monkeys increased the time lag between touchdowns both of ipsilaterally paired limbs (pair lag) and of the paired forelimbs (forelimb lag) when walking across discontinuous substrates compared to continuous substrates. Results indicate that gait flexibility and the ability to alter footfall patterns during quadrupedal walking may be critical for primates to safely move in their complex arboreal habitats. Notably, wild squirrel monkey quadrupedalism is diverse and flexible with high proportions of asymmetrical walking. Studying kinematics in the wild is critical for understanding the complexity of primate quadrupedalism.     

Levels of duplicate gene expression in armoured catfishes

Species of armoured catfishes differ significantly in their cellular DNA content and chromosome number. Starch gel electrophoresis of isozymes was used to determine whether each of 16 enzyme loci was expressed in a single or duplicate state. The percent of enzyme loci exhibiting duplicate locus expression in Corydoras aeneus, Corydoras julii, Corydoras melanistius, and Corydoras myersi was 37.5 percent, 18.75 percent, 12.5 percent, and 6.25 percent, respectively. The percentage of loci expressed in duplicate is higher in the species with higher haploid DNA contents, which are 4.4 pg, 3.0 pg, and 2.3 pg, respectively. These differences in DNA contents are also associated with differences in chromosome number. These data are consistent with the hypothesis that increases in DNA contents and enzyme loci occur both by tetraploidization and by regional gene duplication and that these increases are then followed by a partial loss of DNA and a reduction in the number of the duplicate isozyme loci expressed. Such analyses provide insight into the mechanisms of genome amplification and reduction as well as insights into the fats of duplicate genes.     

The effect of drought on the large mammal populations of Zambezi riverine woodlands

Large mammals were counted in Zambezi alluvial woodlands and on the adjacent ecotone in the north of Mana Pools National Park, Zimbabwe, from April 1981 until October 1989. Densities of all large herbivores on the alluvium in the daytime increased during the dry season. Year-to-year variation was studied by comparing end-of-dry-season densities. Flooding of the Zambezi River, controlled by Kariba Dam 100 km upstream, ceased in 1981 and the densities of all species on the alluvium declined in 1982. Rainfall was low in 1982 and very low in 1983 and 1984. The density of buffalo in the study area declined, owing to high mortality and a change in habitat utilization (buffalo herds spent more time in the south of the park). Densities of other species were high during the drought, but the densities of waterbuck, kudu, eland, bushbuck and warthog declined in 1985. Zebra density declined on the ecotone, but not on the alluvium. The densities of eland and kudu increased in 1986 and 1988, respectively, but the densities of the other species were still low in 1989. Impala density on the alluvium in October was related to rainfall during the preceding wet season and was high in drought years. Elephant density declined after a management cull. Rhinoceros density decreased by > 90% during the 1985/6 wet season, as a result of poaching and captures. The long-term decline in the densities of grazers was probably due primarily to the cessation of flooding by the Zambezi River, rather than to low local rainfall in some years. During the drought, the large grazers (e.g. buffalo) died before the smaller grazers (e.g. warthog). Waterbuck density declined less than the density of other grazers, because waterbuck could cross to vegetated sandbanks in the Zambezi River.     

Active potassium transport in reticulocytes of high-K and low-K sheep

The kinetics of active K⁺ transport were studied in immature red blood cells cells from high-K⁺ and low-K⁺ sheep, particularly with respect to the effects of varying intracellular K⁺ concentration, [K]_i. Comparison was made with active transport, or pump, activity in mature high-K⁺ and low-K⁺ red cells. Reticulocytes from both types of sheep had much higher maximal active K⁺ influxes than did mature cells. In both types of reticulocytes, and in mature high-K⁺ cells as well, the pump was relatively insensitive to increasing [K]_i. In contrast, intracellular K⁺ markedly inhibited the pump in mature low-K⁺ cells. Active K⁺ transport in low-K⁺ reticulocytes, however, as in mature low-K⁺ cells, is stimulated by specific isoimmune anti-L serum. Therefore the K⁺ pumps of high-K⁺ and low-K⁺ reticulocytes have similar kinetic properties. Maturation of the red cells, involving inactivation of most of the pump activity in both cell types, results in mature high-K⁺ and low-K⁺ cells with K⁺ pumps of very different kinetic characteristics.