THE RECONSTRUCTION OF ANCESTRAL CHARACTER STATES

The problem of error in the phylogenetic reconstruction of ancestral character states is explored by developing the model of Frumhoff and Reeve (1994). Information about the evolutionary rate of change within a character is inferred from the distribution of its character states on a known phylogeny, and this information is used to impose confidence limits on the error associated with ancestral state inference. Ancestral state inference is found to be remarkably robust under the model assumptions for a wide range of parameter values; however, the probability of error increases when the number of species within a clade is small and/or state-transition probabilities are strongly skewed in favor of the non-ancestral state. The rationale for expecting such a skew, a hypothesis of parallelism, is shown to rely on assumptions of low rates of change in at least two phylogenetically inherited characters: the tendency to occupy a particular ecological niche and the tendency to respond in a particular way to selection. A means for judging the relative likelihoods of parallelism vs. straightforward homology as explanations for a given character-state distribution is suggested. General problems with the model are discussed, as are methods for making it more realistic.     

Solubility phase diagram of praziquantel enantiomeric system

The solubility behaviour of praziquantel enantiomeric system at ?15°C, 4°C, and 15°C is presented. This system exhibits both a pseudoracemate behaviour and one which leads to the formation of enantiomerically pure crystals. For solutions with lower enantiomeric purity, the pseudoracemate behaviour is more prominent. Solid solutions are formed when the mixtures of the enantiomers are crystallised. The phase diagram shows a complete absence of a eutetic. For mixtures with higher enantiomeric purity, pure crystals of the excess enantiomer are obtained when the solution is crystallised. Temperature dependency of this polymorphism is not significant. With these phase diagrams, a method is suggested to obtain enantiomerically pure isomers of praziquantel from a partially resolved mixture. © 1995 Wiley-Liss, Inc.