Deconstructing the long-standing a priori assumption that serial homology generally involves ancestral similarity followed by anatomical divergence

It has long been assumed that serial homologues are ancestrally similar—polysomerism resulting from a “duplication” or “repetition” of forms—and then often diverge—anisomerism, for example, as they become adapted to perform different tasks as is the case with the forelimb and hind limbs of humans. However, such an assumption, with crucial implications for comparative, evolutionary, and developmental biology, and for evolutionary developmental biology, has in general not really been tested by a broad analysis of the available empirical data. Perhaps not surprisingly, more recent anatomical comparisons, as well as molecular knowledge of how, for example, serial appendicular structures are patterned along with different anteroposterior regions of the body axis of bilateral animals, and how “homologous” patterning domains do not necessarily mark “homologous” morphological domains, are putting in question this paradigm. In fact, apart from showing that many so-called “serial homologues” might not be similar at all, recent works have shown that in at least some cases some “serial” structures are indeed more similar to each other in derived taxa than in phylogenetically more ancestral ones, as pointed out by authors such as Owen. In this article, we are taking a step back to question whether such assumptions are actually correct at all, in the first place. In particular, we review other cases of so-called “serial homologues” such as insect wings, arthropod walking appendages, Dipteran thoracic bristles, and the vertebrae, ribs, teeth, myomeres, feathers, and hairs of chordate animals. We show that: (a) there are almost never cases of true ancestral similarity; (b) in evolution, such structures—for example, vertebra—and/or their subparts—for example, “transverse processes”—many times display trends toward less similarity while in many others display trends toward more similarity, that is, one cannot say that there is a clear, overall trend to anisomerism.     

Tree species regeneration in a mid-elevation,temperate rain forest in Isla de Chiloé, Chile

The regeneration of canopy and subeanopy species in a mid-elevation, primary rain forest in the Coastal Range of Isla de Chiloé (42°30S), in the cold-temperate region of Chile, was studied by comparing seedling and sapling abundances under the forest canopy, and within 36 tree-fall gaps. The forest was dominated byAmomyrtus luma andLaurelia philippiana (33 and 32% of the main canopy individuals), and two subcanopy species (Myrceugenia ovata, andMyrceugenia planipes) were also important. Uncommon species in the canopy wereDrimys winteri, Amomyrtus meli, andRaphithamnus spinosus. Tree-fall gaps were created generally by the fall of several trees, and the main canopy species were the principal gap-makers. Gap sizes varied between 28 and 972 m², with a mean of 197 m². Seedling and sapling abundances indicate that the dominant species are capable of regenerating below the canopy, but they also germinate and show enhanced growth within small light gaps. For one of the common subcanopy species (M. planipes) and the two infrequent canopy species (D. winteri, andA. meli) regeneration seems to depend entirely on tree-fall gaps. Thus, in this forest, light gaps allow the persistence of infrequent canopy species, but seem less important for the regeneration and maintenance of dominant canopy species.     

Klebsiella pneumoniae in orange juice concentrate.

Fecal coliform-positive, capsule-forming Klebsiella pneumoniae cells were observed in high densities (10(4) to 10(8) CFU/100 ml) in two commercial batches of frozen orange juice concentrate at a cannery in Puerto Rico. Contamination of both lots was gross and included off colors and odors. Isolates of K. pneumoniae from these concentrates revealed growth at 4, 25, and 34 degrees C with generation times from 0.39 to 1.84 h.     

Colonization factors of diarrheagenicE. coli and their intestinal receptors

WhileEscherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains ofE. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. EnterotoxigenicE. coli (ETEC) is the most extensively studied of the five categories ofE. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenicE. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three, additional categories ofE. coli diarrheal disease, their colonization factors and their host cell receptors are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and thatE. coli is part of these biofilms as both commensals and pathogens.Abbreviations CF colonization factor - CFA Colonization Factor Antigen - CS coli-surface-associated antigen - EAggEC enteroaggregativeE. coli - ECDD E. coli diarrheal disease - EHEC enterohemorrhagicE. coli - EIEC enteroinvasiveE. coli - EPEC enteropathogenicE. coli - ETEC enterotoxigenicE. coli - Gal galactose - GalNAc N-acetyl galactosamine - LT heat-labile toxin - NeuAc N-acetyl neuraminic acid - PCF Putative colonization factor - RBC red blood cells - SLT Shiga-like toxin - ST heat-stable toxin     

Molecular drift of the bride of sevenless (boss) gene in Drosophila

DNA sequences were determined for three to five alleles of the bride-of- sevenless (boss) gene in each of four species of Drosophila. The product of boss is a transmembrane receptor for a ligand coded by the sevenless gene that triggers differentiation of the R7 photoreceptor cell in the compound eye. Population parameters affecting the rate and pattern of molecular evolution of boss were estimated from the multinomial configurations of nucleotide polymorphisms of synonymous codons. The time of divergence between D. melanogaster and D. simulans was estimated as approximately 1 Myr, that between D. teissieri and D. yakuba as approximately 0.75 Myr, and that between the two pairs of sibling species as approximately 2 Myr. (The boss genes themselves have estimated divergence times approximately 50% greater than the species divergence times.) The effective size of the species was estimated as approximately 5 x 10(6), and the average mutation rate was estimated as 1-2 x 10(-9)/nucleotide/generation. The ratio of amino acid polymorphisms within species to fixed differences between species suggests that approximately 25% of all possible single-step amino acid replacements in the boss gene product may be selectively neutral or nearly neutral. The data also imply that random genetic drift has been responsible for virtually all of the observed differences in the portion of the boss gene analyzed among the four species.      

Monandrous social organization of pigtailed langurs ( Simias concolor ) in the Pagai Islands, Indonesia

Between June 1986 and October 1992, in 3 periods totaling 12 months, we studied social organization of pigtailed langurs (Simias concolor)in the Pagai Islands, Indonesia. With one possible exception, all of 20 family groups contained only 1 adult male each. Nine of them contained only 1 adult female,and 11 contained ≥2 adult females. Mean group size is 4.1 individuals. Home ranges varied from 7 to 20 ha, and population density averages 21 animals/km ² . Simias concoloris sexually dimorphic⤖n a museum sample males average 29% heavier than females, and their canine teeth are on average nearly twice the length of female canines. Combined data from several studies indicate that 60% of S. concolorgroups contain an adult pair plus young,and 40% are multifemale groupings. We sggest that any 1-male mating system that comprises a mixture of 1-female and multifemale groups in the same population should be termed monandry.     

Serine protein kinase activity associated with rotavirus phosphoprotein NSP5.

The rotavirus nonstructural protein NSP5, a product of the smallest genomic RNA segment, is a phosphoprotein containing O-linked N-acetylglucosamine. We investigated the phosphorylation of NSP5 in monkey MA104 cells infected with simian rotavirus SA11. Immunoprecipitated NSP5 was analyzed with respect to phosphorylation and protein kinase activity. After metabolic labeling of NSP5 with 32Pi, only serine residues were phosphorylated. Separation of tryptic peptides revealed four to six strongly labeled products and several weakly labeled products. Phosphorylation at multiple sites was also shown by two-dimensional polyacrylamide gel electrophoresis (PAGE), where several isoforms of NSP5 with different pIs were identified. Analysis by PAGE of protein reacting with an NSP5-specific antiserum showed major forms at 26 to 28 and 35 kDa. Moreover, there were polypeptides migrating between 28 and 35 kDa. Treatment of the immunoprecipitated material with protein phosphatase 2A shifted the mobilities of the 28- to 35-kDa polypeptides to the 26-kDa position, suggesting that the slower electrophoretic mobility was caused by phosphorylation. Radioactive labeling showed that the 26-kDa form contained additional phosphate groups that were not removed by protein phosphatase 2A. The immunoprecipitated NSP5 possessed protein kinase activity. Incubation with [gamma-32P]ATP resulted in 32P labeling of 28- to 35-kDa NSP5. The distribution of 32P radioactivity between the components of the complex was similar to the phosphorylation in vivo. Assays of the protein kinase activity of a glutathione S-transferase-NSP5 fusion polypeptide expressed in Escherichia coli demonstrated autophosphorylation, suggesting that NSP5 was the active component in the material isolated from infected cells.