The Occurence and Properties of Uric Acid Decomposing Anaerobic Bacteria in the Avian Caecum

S ummary . Anaerobic bacteria which decompose uric acid have been found in the caeca of chickens, turkeys, ducks, pheasants and guinea-fowl at levels between 5.4 × 10⁸ and 1.8 × 10¹⁰/g of caecal material (wet weight). A study has been made of the properties and identity of 35 strains which were present in high numbers in the chicken caecum. The isolates included strains of Bacteroides clostridiiformis var. clostridiiformis, Fusobacterium plauti, Clostridium malenominatum, Peptostreptococcus productus and a number of types which could not be identified with known species. Of these 3 were Bacteroides spp., 3 Eubacterium spp., 2 Peptostreptococcus spp. and 1 was an anaerobic Streptococcus . None of the strains had an absolute requirement for uric acid.     

Identification of Enterobacteriaceae in the Clinical Microbiology Laboratory

A total of 5,137 enterobacterial clinical isolates were examined with three series of biochemical tests. The data were analyzed with respect to the use of economical and practical procedures for the accurate identification of lactose-fermenting and -nonfermenting Enterobacteriaceae within 24 hr after isolation.     

Genetic and morphological evidence of a geographically widespread hybrid zone between two crocodile species,Crocodylus acutus and Crocodylus moreletii

Hybrid zones represent natural laboratories to study gene flow, divergence and the nature of species boundaries between closely related taxa. We evaluated the level and extent of hybridization between Crocodylus moreletii and Crocodylus acutus using genetic and morphological data on 300 crocodiles from 65 localities. To our knowledge, this is the first genetic study that includes the entire historic range and sympatric zone of the two species. Contrary to expectations, Bayesian admixture proportions and maximum‐likelihood estimates of hybrid indexes revealed that most sampled crocodiles were admixed and that the hybrid zone is geographically extensive, extending well beyond their historical region of sympatry. We identified a few geographically isolated, nonadmixed populations of both parental species. Hybrids do not appear to be F₁s or recent backcrosses, but rather are more likely later‐generation hybrids, suggesting that hybridization has been going on for several to many generations and is mostly the result of natural processes. Crocodylus moreletii is not the sister species of C. acutus, suggesting that the hybrid zone formed from secondary contact rather than primary divergence. Nonadmixed individuals from the two species were distinguishable based on morphological characters, whereas hybrids had a complex mosaic of morphological characters that hinders identification in the wild. Very few nonadmixed C. acutus and C. moreletii populations exist in the wild. Consequently, the last nonadmixed C. moreletii populations have become critically endangered. Indeed, not only the parental species but also the naturally occurring hybrids should be considered for their potential conservation value.     

Metamorphosis of the olfactory organ of the sea lamprey (Petromyzon marinus L.): Morphological changes and morphometric analysis

In larval sea lampreys (Petromyzon marinus), a small, relatively inconspicuous olfactory organ sac contains small, densely packed olfactory receptor neurons and sustentacular cells. During metamorphosis, the larval organ transforms into a prominent lamellar structure with large distinct olfactory epithelial cells that is characteristic of the adult lamprey. In the present study, scanning electron microscopy and light microscopy are used to examine changes during the seven stages (1–7) of metamorphosis. The magnitude of growth over the course of metamorphosis is evident from the doubling of the relative weight of the nasal sac. During early metamorphosis (stages 1 and 2), the larval olfactory organ enlarges, and by stage 3 specific adult structures begin to form, namely a nasal valve between the nasal tube and the organ, lamellar folds, and diverticuli of the accessory olfactory organ. Subsequent development involves widening of the cells lining the lamellar folds to the form characteristic of postmetamorphic lampreys. Although the cells in the troughs initially retain numerical density values that are significantly higher than those on the lamellar surfaces, by stage 7 values decline both in troughs and along lamellar surfaces to those observed in adults. These results show that although expansion of the olfactory organ is ongoing throughout metamorphosis, remodeling occurs early (by stage 3). This timing provides space for extensive olfactory receptor neuron neurogenesis and differentiation and correlates with the transformation of some organs that were previously examined. This is the first report in any species of olfactory receptor neuron zonation based on morphometric characteristics. J. Morphol. 231:41–52, 1997. © 1997 Wiley-Liss, Inc.     

Intricate evolutionary histories in montane species: a phylogenetic window into craniodental discrimination in the Peromyscus mexicanus species group (Mammalia: Rodentia: Cricetidae)

Mountain‐associated species, which exhibit allopatric distributions associated with elevation, endemisms and complex evolutionary histories, pose challenging evolutionary scenarios in which to discern the diversification of species. The Peromyscus mexicanus mice group, distributed along mountains in southern Mexico and Central America, is morphometrically variable, a key rationale for the ongoing controversy regarding its species delimitation. Based on the recognized 15 mitochondrial lineages for the group, we analysed external and craniodental morphometric variables to test whether lineages can be differentiated morphometrically and allow for the delimitation of species. We also aimed to test the prediction that the phylogenetic structure of the morphometric data is concordant with that of the molecular information. Based on 19 craniodental measurements from 521 specimens, multivariate and discriminant analyses showed that lineages are morphometrically discernible, representing distinct phenotypes, and that overall size and mandible measurements are significant features that discriminate lineages, supporting hypotheses about differences in feeding habits between species. Also, a pattern of increasing size with elevation was observed, further supported by specific morphological differences exhibited between highland and lowland lineages inhabiting the same mountain. Our results demonstrate that P. mexicanus is both genetically and morphometrically variable, where most highland montane species are differentiated from lowland species; also, a significant correlation between mitochondrial and morphometric information is indicative of phenetic concordance, altogether in agreement with a recent taxonomic proposal for the group. We suggest that the group's intricate diversification responds to ecological diversification and adaptation to a variety of mountain habitats and Pleistocene biogeographic climatic dynamics.     

Mitochondrial fragmentation in neurodegeneration

Mitochondria are remarkably dynamic organelles that migrate, divide and fuse. Cycles of mitochondrial fission and fusion ensure metabolite and mitochondrial DNA mixing and dictate organelle shape, number and bioenergetic functionality. There is mounting evidence that mitochondrial dysfunction is an early and causal event in neurodegeneration. Mutations in the mitochondrial fusion GTPases mitofusin 2 and optic atrophy 1, neurotoxins and oxidative stress all disrupt the cable-like morphology of functional mitochondria. This results in impaired bioenergetics and mitochondrial migration, and can trigger neurodegeneration. These findings suggest potential new treatment avenues for neurodegenerative diseases.