Linear Discrimination,Ordination, and the Visualization of Selection Gradients in Modern Morphometrics

Linear discriminant analysis (LDA) is a multivariate classification technique frequently applied to morphometric data in various biomedical disciplines. Canonical variate analysis (CVA), the generalization of LDA for multiple groups, is often used in the exploratory style of an ordination technique (a low-dimensional representation of the data). In the rare case when all groups have the same covariance matrix, maximum likelihood classification can be based on these linear functions. Both LDA and CVA require full-rank covariance matrices, which is usually not the case in modern morphometrics. When the number of variables is close to the number of individuals, groups appear separated in a CVA plot even if they are samples from the same population. Hence, reliable classification and assessment of group separation require many more organisms than variables. A simple alternative to CVA is the projection of the data onto the principal components of the group averages (between-group PCA). In contrast to CVA, these axes are orthogonal and can be computed even when the data are not of full rank, such as for Procrustes shape coordinates arising in samples of any size, and when covariance matrices are heterogeneous. In evolutionary quantitative genetics, the selection gradient is identical to the coefficient vector of a linear discriminant function between the populations before vs. after selection. When the measured variables are Procrustes shape coordinates, discriminant functions and selection gradients are vectors in shape space and can be visualized as shape deformations. Except for applications in quantitative genetics and in classification, however, discriminant functions typically offer no interpretation as biological factors.     

Selective preying of the sphecid wasp Trachypus boharti on the meliponine bee Scaptotrigona postica: potential involvement of caste‐specific cuticular hydrocarbons

The specialist digger wasp Trachypus boharti Rubio‐Espina preys exclusively on males of the stingless bee Scaptotrigona postica Latreille 1807, although the hunting attacks involve both male and worker bees of S. postica and members of its own species. To understand the mechanism of prey selection, the cuticular hydrocarbon patterns of workers and males of S. postica are analyzed in detail, and the mandibular secretion of males is examined. The cuticular profiles of males and workers are distinctively different. The major group of cuticular compounds, heptacosene isomers, is twice as abundant in workers as in males. There is no clear distinction between worker and male mandibular secretions. Such a distinct and straightforward caste‐specific difference in cuticular hydrocarbons could function as a recognition cue by which T. boharti distinguishes between workers and males of S. postica.     

The Bacillus subtilis 168 alkaline phosphatase III gene: impact of a phoAIII mutation on total alkaline phosphatase synthesis.

The first alkaline phosphatase (APase) structural gene mutant of Bacillus subtilis 168 was constructed by using a clone identified by hybridization to a synthetic degenerative oligonucleotide. The design of the probe was based on the first 29 amino acids of the sequenced mature APase III protein, which had been isolated from the secreted fraction of vegetative, phosphate-starved cells. DNA sequencing of the clone revealed the first 80 amino acids of the APase III protein, including a typical procaryotic signal sequence of 32 amino acids preceding the start of the mature protein. The 29 amino acids encoded by the predicted open reading frame immediately following the signal sequence are identical to the first 29 amino acids of the sequenced mature protein. This region shows 80% identity to strand A of the beta sheet that is very well conserved in Escherichia coli and mammalian APases. A phoAIII structural mutant was constructed by insertional mutagenesis with a fragment internal to the coding region. The effects of this mutation on APase production in B. subtilis 168 were analyzed under both phosphate starvation and sporulation conditions. The mutation in APase III reduced the total vegetative APase specific activity by approximately 40% and sporulation APase specific activity by approximately 45%. An APase protein was isolated from sporulating cells at stage III and was identified as APase III by protein sequencing of the amino terminus and by its absence in the phoAIII mutant. The APase III gene has been mapped to approximately 50 degrees on the B. subtilis chromosome.     

The Le Fort III advancement osteotomy in the child under 7 years of age

This is a longitudinal study of 12 patients with craniofacial synostosis syndromes (Crouzon's, Apert's, Pfeiffer's) who underwent Le Fort III advancement under the age of 7 years (average age 5.1 years, range 4.0 to 6.7 years). The average follow-up was 5.0 years and included clinical, dental, and cephalometric examinations according to a prescribed protocol. The study demonstrated that the procedure could be safely performed in the younger child with an acceptable level of morbidity. There was a remarkable degree of postoperative stability of the maxillary segment. However, although vertical (inferior) growth or movement of the midfacial segment was demonstrated, there was minimal, if any, anterior or horizontal growth. Any occlusal disharmony developing during the period of follow-up could be attributed to anticipated mandibular development and could be corrected by orthognathic surgery. The roles of surgical overcorrection and anterior-pull headgear therapy after release of intermaxillary fixation are also discussed. The Le Fort III osteotomy is justifiably indicated during early childhood for psychological and physiologic reasons.