Phylogeny and character behavior in the family Lemuridae.

A phylogenetic analysis of the family Lemuridae was accomplished using multiple gene partitions and morphological characters. The results of the study suggest that several nodes in the lemurid phylogeny can be robustly resolved; however, the relationships of the species within the genus Eulemur are problematically nonrobust. The genus Varecia is strongly supported as the basal genus in the family. Hapalemur and Lemur catta are strongly supported as sister taxa and together are the sister group to the genus Eulemur. E. mongoz is the most basal species in the genus Eulemur. E. fulvus subspecies form a monophyletic group with three distinct lineages. E. coronatus is strongly supported as the sister taxon to E. macaco. The relationships of E. rubriventer, E. fulvus, and the E. macaco-E. coronatus pair are unresolved. Our combined molecular and morphological analysis demonstrates the lack of influence that morphology has on the simultaneous analysis tree when these two kinds of data are given equal weight. The effects of several extreme weighting schemes (removal of transitions and of third positions in protein-coding regions) and maximum-likelihood analysis were also explored. We suggest that these other forms of inference add little to resolving the problematic relationships of the species in the genus Eulemur.

Disfluency and time perception.

Stuttering is manifested as a disruption in speech timing, but it may stem from a more basic temporal disorder (R. D. Kent, 1984). We compared the ability of stuttering and nonstuttering adults to estimate protensity and to distinguish the relative lengths of short tones. We also examined whether there is a correlation between a person's degree of disfluency and the ability to measure protensity or judge the relative lengths of short tones. Twenty stuttering and 20 nonstuttering adults were given the Duration Pattern Sequence Test. They were also asked to estimate the lengths of 8 tones and silent intervals. A negative correlation was found between degree of disfluency and ability to determine the relative lengths of short tones. A positive correlation was found between degree of disfluency and length of protensity estimates.

The response of the flexion-relaxation phenomenon in the low back to loading.

Fick hypothesized in 1911 that the erector spinae muscles are not active when the trunk is in the fully flexed position. This effect was later called the flexion-relaxation phenomenon (FRP) and is believed to be the result of the ligaments and other passive elements of the spine taking over the load of the muscles. This study examined the effect of loading on the EMG activity of five males and five females during postures of standing at 45 degrees, 90 degrees, and full flexion. The results showed major differences in the relationship between the electromyographic signal (EMG) of the erector spinae and loading for the four postures. The erector spinae muscles did not activate in positions of full flexion (or even 90 degrees for some subjects) for loading as high as 50% of their maximum voluntary contraction, suggesting that alternative muscles are being activated and that the passive tissues may be put under higher loads than originally thought in these positions. The results suggested that the FRP could be used as a biofeedback tool to illustrate to workers that their muscles are not turning on in the fully flexed positions, and therefore, these positions should be avoided.

Computational problems in molecular systematics.

The development of extremely powerful computer programs and the ready availability of microcomputers has revealed several computational problems with data analysis. These problems occur in the handling of systematic data in general and molecular systematic data in particular. This paper examines three areas of controversy in molecular systematics resulting from increased computer power. We start by examining the first step in DNA sequence analysis, the establishment of homology via sequence alignment. Next we examine several problems in phylogenetic analysis that have arisen in the last few years due to use of the PAUP (Swofford, 1991), HENNIG86 (Farris, 1988), and PHYLIP programs. These problems include limitations on the number of taxa examined in a given analysis and the accuracy of the parsimony trees in such analyses. The final subject is an examination of programs used for assessing tree robustness. We concentrate on certain programs (such as MALIGN (Wheeler and Gladstein, 1993), PAUP (Swofford, 1991), HENNIG86 (Farris, 1988), PHYLIP (Felsenstein, 1990), CLADOS (Nixon, 1993), MacClade (Maddison and Maddison, 1993), etc.), but similar comments about other programs could also be made.

mtDNA diversity in rhesus monkeys reveals overestimates of divergence time and paraphyly with neighboring species.

Reconstructions of the human-African great ape phylogeny by using mitochondrial DNA (mtDNA) have been subject to considerable debate. One confounding factor may be the lack of data on intraspecific variation. To test this hypothesis, we examined the effect of intraspecific mtDNA diversity on the phylogenetic reconstruction of another Plio-Pleistocene radiation of higher primates, the fascicularis group of macaque (Macaca) monkey species. Fifteen endonucleases were used to identify 10 haplotypes of 40-47 restriction sites in M. mulatta, which were compared with similar data for the other members of this species group. Interpopulational, intraspecific mtDNA diversity was large (0.5%-4.5%), and estimates of divergence time and branching order incorporating this variation were substantially different from those based on single representatives of each species. We conclude that intraspecific mtDNA diversity is substantial in at least some primate species. Consequently, without prior information on the extent of genetic diversity within a particular species, intraspecific variation must be assessed and accounted for when reconstructing primate phylogenies. Further, we question the reliability of hominoid mtDNA phylogenies, based as they are on one or a few representatives of each species, in an already depauperate superfamily of primates.

Context-US learning in Aplysia californica.

Two experiments explored learning about the relation between an unconditioned stimulus (US) and the context in which that US was delivered in Aplysia californica. Subjects were exposed to 2 different contexts. They received a series of moderate electric shock USs in one context but not in the other. Experiment 1 revealed that the context-shock pairings were sufficient to establish an association between that context and the shock. That association was demonstrated by the ability of the reinforced context to enhance a defensive reflex and to reduce learning about a conditioned stimulus (CS) that was subsequently paired with the shock US. Experiment 2 provided evidence that the context-US association could be extinguished by simple nonreinforced exposure to the reinforced context. These results show that context conditioning is not unique to vertebrate learning. We argue that this learning is difficult to accommodate within current contiguity-based neuronal models of learning.

Conditional discrimination learning in Aplysia californica.

Two experiments examined whether the relation between a conditioned stimulus (CS) and an unconditioned stimulus (US) might be brought under the control of contextual stimuli in the invertebrate Aplysia californica. Subjects received exposure to 2 different contexts. In both experiments, a tactile CS was paired with a shock US in one of those contexts. In the other context, that tactile CS was either nonreinforced (Experiment 1) or explicitly unpaired with the shock US (Experiment 2). Responding to the CS during a subsequent test was greater in the context in which that CS had been paired with the US compared with the context in which it had been nonreinforced or unpaired. These findings are discussed in terms of theories of conditional discrimination learning.

Time-lapse cinemicrophotographic studies of cell division patterns of human diploid fibroblasts (WI-38) during their in vitro lifespan.

Genealogies of human diploid embryonic lung fibroblasts, WI-38 were prepare from analysis of filmed sequences of clones at passages 20, 28 and 53. The results indicate heterogeneity in cell division patterns, interdivision time and migration activity. The relationship of the cell division patterns to age of culture is difficult to assess at this time because of the heterogeneity of the clones, however, the late passage culture appeared to be more variable in terms of sister-sister, and mother-daughter relationships. The passage 28 culture was representative of a highly proliferating clone, exhibiting short interdivision times and a synchronous division pattern. The passage 20 and 53 clones exhibited longer interdivision times and less synchronous division pattern than the passage 28 clone. A gradual lengthening of average interdivision time with successive generations has been observed in all genealogies regardless of passage level of the donor culture. A portion of daughter cells in the fifth and sixth generation exhibited lower interdivision time than the mother cell. The effects of nutrients, space, and mitotic inhibitors or stimulators on interdivision time of the cells within the clones is discussed.