Rapid, corticosterone-induced disruption of medullary sensorimotor integration related to suppression of amplectic clasping in behaving roughskin newts (Taricha granulosa)

Endogenously secreted or injected corticosterone (CORT) rapidly suppresses courtship clasping in male roughskin newts (Taricha granulosa) by an action on a specific neuronal membrane receptor. Previous studies, using immobilized newts, showed that CORT administration rapidly depresses excitability of reticulospinal neurons and attenuates medullary neuronal responsiveness to clasp-triggering sensory stimuli. The present study used freely moving newts to examine clasping responses and concurrently record sensorimotor properties of 67 antidromically identified reticulospinal and other medullary reticular neurons before and after CORT injection. Before CORT, reticulospinal neurons fired in close association with onset and offset of clasps elicited by cloacal pressure. Reticulospinal neurons also showed firing correlates of nonclasping motor events, especially locomotion. Neuronal activity was typically reduced during clasping and elevated during locomotion. Medullary neurons that were not antidromically invaded (unidentified neurons) usually showed sensorimotor properties that resembled those of reticulospinal neurons. Intraperitoneal CORT (but not vehicle) reduced the probability and quality of hindlimb clasping in response to cloacal pressure, especially within 5-25 min of injection. Simultaneously, responses of reticulospinal and unidentified neurons to cloacal pressure and occurrence of clasping-related activity were attenuated or eliminated. CORT effects were relatively selective, altering clasping-related neuronal activity more strongly than activity associated with nonclasping motor events. The properties of CORT effects indicate that the hormone impairs clasping by depressing processing of clasp-triggering afferent activity and by disrupting the medullary control of clasping normally mediated by reticulospinal neurons. The rapid onset of these CORT effects implicates a neuronal membrane receptor rather than genomic action of the steroid.     

A comparison of genetic variation in two sibling species pairs of haplodiploid insects

Sibling species pairs of sweat bees (Halictus confusus and H. tumulorum) and pine sawflies (Neodiprion pratti and N. maurus) were surveyed for genetic variability using enzyme electrophoresis. Levels of heterozygosity were found to be within the ranges earlier recorded for Hymenoptera. Expected heterozygosities were not significantly higher in the sawflies than in the sweat bees. Estimates of genetic identity between the sibling species were not lower than those generally found for diplodiploid insect species: no evidence was found for an increased rate of evolution in these haplodiploids. Genetic identity data among populations of H. confusus and between Halictus species were within the range expected for conspecific populations and sibling species, respectively. In Neodiprion all genetic distances were low but the two populations of N. pratti had similar genetic distances as each did to N. maurus, indicating the necessity for further systematic studies of the genus.     

Genetic variation in heterogeneous environments

A model of population structure in heterogeneous environments is described and conditions sufficient for maintaining a polymorphism are derived. The absolute fitness of any genotype is regarded as a function of location in the niche space and the population density at that location. Two modes of habitat selection are examined: (1) organisms are distributed uniformly over the environment; and (2) each organism selects to occupy that habitat in which it is most fit ("optimal habitant selection"). Sufficient conditions for maintenance of genetic polymorphisms are derived for both models. In populations which do not practice habitat selection heterozygote superiority averaged over the environment is sufficient to guarantee the existence of polymorphisms. Comparable conditions for populations which practice optimal habitat selction are much less restrictive. If the heterozygotes are superior to one homozygote in any one part of the niche and to the other homozygote in any other part of the niche then a polymorphism will be defined. A positive correlation between genetic and environmental variation follows from the model with habitat selection, but not from the other. The adaptive significance of polymorphisms thus depends on how animals behave.     

Genetic variation in the east Midlands

According to history, the population of the British Isles derives its genepool from a succession of invaders and immigrants. The settlement pattern of these invaders gave rise to a patchwork of genepools, shown in previous genetic surveys. Specimens from 1117 blood donors of regionally subdivided East Midlands (Derbyshire, Nottinghamshire and Leicestershire) were analysed for 18 conventional genetic systems (blood groups, serum proteins and red cell enzymes), according to place of residence. Significant differences exist among the five geographically defined sub-populations, and it is argued that these are derived from the historical settlement of continental European populations in the region, especially the Danes and the Vikings.     

Genetic variation in some Oxfordshire villages

The patterns of serological polymorphic variety in a group of Oxfordshire populations are related to previously made demographic predictions that the different villages and social classes might be expected to be genetically homogeneous if movement were the main factor determining genetic structure. The predictions are largely fulfilled though there remains a residual pattern of variety which is detectable when all the systems tested are considered together by "genetic distance" examination, and in the case of the geographic variation this pattern reflects the comparative magnitude of the exchanges between the different villages.     

Genetic variation in the free-living amoeba Naegleria fowleri

In this study, 30 strains of the pathogenic free-living amoeba Naegleria fowleri were investigated by using the randomly amplified polymorphic DNA (RAPD) method. The present study confirmed our previous finding that RAPD variation is not correlated with geographical origin. In particular, Mexican strains belong to the variant previously detected in Asia, Europe, and the United States. In France, surprisingly, strains from Cattenom gave RAPD patterns identical to those of the Japanese strains. In addition, all of these strains, together with an additional French strain from Chooz, exhibited similarities to South Pacific strains. The results also confirmed the presence of numerous variants in Europe, whereas only two variants were detected in the United States. The two variants found in the United States were different from the South Pacific variants. These findings do not support the previous hypothesis concerning the origin and modes of dispersal of N. fowleri.     

Genetic variation of pancreatic esterase isozyme in Japanese quail

A genetic variation was found in pancreatic esterases of Japanese quail which appeared to be arylesterase. It was found on the cathode side in the agar gel electrophoresis. Three phenotypes, A,B and AB, were observed. These phenotypes were shown to be controlled by one autosomal locus, designated as Es-4, with co-dominant alleles Es-4A and Es-4B. Es-4 esterase isozymes were detected in all the individuals from about 4 days of age, but the activity was very weak. However, it gradually increased to reach a level almost the same as that of a mature quail from about 15 days of age.     

Genetic basis of variation in carotid artery wall thickness

BACKGROUND AND PURPOSE: Other than the documented associations of risk factors and carotid artery wall thickness, the genetic basis of variation in carotid artery intimal-medial thickness (IMT) is unknown. The purpose of this study was to examine the extent to which variation in common carotid artery (CCA) IMT and internal carotid artery (ICA) IMT are under genetic control. METHODS: The sibship data used for this analysis were part of an epidemiological survey in Mexico City. The CCA and ICA analyses were based on 46 and 44 sibships of various sizes, respectively. The CCA and ICA IMTs were measured with carotid ultrasonography. Using a robust variance decomposition method, we performed genetic analyses of CCA IMT and ICA IMT measurements with models incorporating several cardiovascular risk factors (eg, lipids, diabetes, blood pressure, and smoking) as covariates. RESULTS: After accounting for the effects of covariates, we detected high heritabilities for CCA IMT (h2 = 0.92 +/- 0.05, P = .001) and ICA IMT (h2 = 0.86 +/- 0.13, P = .029). Genes accounted for 66.0% of the total variation in CCA IMT, whereas 27.7% of variation was attributable to covariates. For ICA IMT, genes explained a high proportion (74.9%) of total phenotypic variation. The covariates accounted for 11.5% of variation in ICA IMT. CONCLUSIONS: Our results suggest that substantial proportions of phenotypic variance in CCA IMT and ICA IMT are attributable to shared genetic factors.     

Genetic variation on chromosome 1 associated with variation in body fat distribution in men

BACKGROUND: Interindividual variation in fat deposition in swine is determined by loci on porcine chromosome 4, which are contained in a region that is syntenic with part of the long arm of human chromosome 1. We hypothesized that genomic variation of chromosome 1q would be associated with variation in the ratio of waist-to-hip circumference in male North American Hutterites, a genetic isolate characterized by significant relatedness and sharing of environmental factors. METHODS AND RESULTS: In 316 male Hutterites, we tested for phenotype-genotype association of two DNA polymorphisms on chromosome 1q and the ratio of waist-to-hip circumference. We included control loci on 10 other chromosomes in the multivariate model. We observed that DNA variation on chromosome 1q was significantly associated with variation in the ratio of waist-to-hip circumference in men (P = .0029). CONCLUSIONS: The association of DNA variation chromosome 1q with the ratio of waist-to-hip circumference in male Hutterites suggests that there are important structural elements in this genomic region that have a functional impact on body fat distribution.     

Isozyme variation within and among populations of Microsporum species

Isozyme variation among 54 isolates of Microsporum canis, 18 Microsporum cookei isolates and two Diheterospora isolates were studied using starch gel electrophoresis. Of eight enzymes examined, four were polymorphic (EST, G6P, MDH and PEP), having from two to four electrophoretic forms. Within each species, consistent and reproducible isozyme patterns of the eight enzyme systems were obtained. Phenotypic diversity (H) in M. canis was higher than in M. cookei (H = 0.459 and H = 0.408 respectively), but phenotypic differentiation of M. canis isolates from different geographical regions (Auckland, Wellington and Palmerston North, New Zealand) was low, with a proportion of total diversity (Gst) of 0.151 found among the localities. The results suggest that the isolates of M. canis from different geographical regions are closely related, supporting the theory of a common lineage.     

Endoparasites of plethodontid salamanders from Paradise Brook, New Hampshire

Totals of 52 dusky salamanders Desmognathus fuscus, 51 two-lined salamanders Eurycea bislineata, 54 red-backed salamanders Plethodon cinereus, and 3 spring salamanders Gyrinophilus porphyriticus (Plethodontidae) collected in June and August 1995 from Paradise Brook, a tributary to Hubbard Brook, New Hampshire, were examined for parasites. Parasites found were Brachycoelium storeriae, Brachycoelium sp., Bothriocephalus rarus, Falcaustra sp., Omeia sp., Batracholandros magnavulvaris, and Cepedietta michiganensis. Eighty-six percent of the red-backed salamanders, a terrestrial species, harbored 1 or more parasites. Among the aquatic and semiaquatic species, 27% of the dusky and 45% of the two-lined salamanders were infected with 1 or more parasites.     

Genetic variation and bill size dimorphism in a passerine bird, the reed bunting Emberiza schoeniclus

In passerine birds morphological differentiation in bill size within species is not commonly observed. Bill size is usually associated with a trophic niche, and strong differences in it may reflect the process of genetic differentiation and, possibly, speciation. We used both mitochondrial DNA (mtDNA) and nuclear microsatellites to study genetic variation between two subspecies of reed bunting, Emberiza schoeniclus schoeniclus and E.s. intermedia, along their distributional boundary in western Europe. These two subspecies are characterized by a high dimorphism in bill size and, although breeding populations of the two subspecies are found very close to each other in northern Italy, apparently no interbreeding occurs. The observed morphological pattern between the two subspecies may be maintained by geographically varying selective forces or, alternatively, may be the result of a long geographical separation followed by a secondary contact. MtDNA sequences of cytochrome b and ND5 (515 bp) showed little variation and did not discriminate between the two subspecies, indicating a divergence time of less than 500 000 years. The analysis of four microsatellite loci suggested a clear, although weak, degree of genetic differentiation in the large- and small-billed populations, as indicated by FST and RST values and genetic distances. The correlation between bill size and genetic distance between populations remained significant after accounting for the geographical distances between sampling localities. Altogether, these results indicate a very recent genetic differentiation between the two bill morphs and suggest that a strong selection for large bills in the southern part of the breeding range is probably involved in maintaining the geographical differentiation of this species.     

Genetic variation within the Hereford breed of cattle

Genetic differentiation among Hereford populations from Britain, Ireland, Sweden, Canada and New Zealand together with six other beef breeds was assessed using blood type polymorphisms. Changes in the genetic structure of the British Hereford population over time were also examined. Loci surveyed were seven red cell antigen systems (A, B, C, F, L, S, Z), and two serum protein loci (transferrin and albumin). Within group variation was measured by the average expected heterozygosity, and between group relationships by genetic distance. There was significant genetic differentiation among Hereford populations from different countries. Differences between Hereford groups, however, were not as large as differences between breeds. There were also significance differences among British herds. The proportion of Canadian genes in the British 'hybrid' population was estimated to have increased from 0.42 (+/- 0.34) in the 1970s to 0.98 (+/- 0.11) in the 1990s. Canadian Hereford groups were found to be less heterozygous than other groups, and replacement of the British population with Canadian animals may lead to loss of variation. Breeding strategies that preserve original native genes in British Hereford populations should be considered by commercial breeders, in order to prevent the long-term loss of genetic variation within the breed.     

Genetic and environmental components of thyroxine variation in Mennonites from Kansas and Nebraska

Thyroxine is an endocrine hormone that regulates cellular and organismic metabolism. Current research on thyroxine has primarily examined its adaptive potential and genetic inheritance patterns. To date, no studies have attempted to investigate the interaction between the genetic and environmental components of thyroxine variation. This approach is useful because hormones are on feedback regulation; thus interaction occurs between the environment and gene expression. The purposes of this research are to characterize the genetic and environmental components of thyroxine variation using univariate statistics and to estimate the genetic and cultural heritabilities through path analysis. For univariate analyses, analyses of variance are used to determine whether or not age, sex, or community affiliation are covariates of thyroxine level. Significant differences existed in thyroxine level based on sex and community affiliation (p < 0.05). The genetic and environmental components of thyroxine variation were partitioned through path analysis. Heritability was estimated at 0.317 +/- 0.109 for the genetic component and at 0.060 +/- 0.029 for the environmental component. The environmental variables that contributed to the variation in thyroxine level were caffeine consumption, blood calcium level, and biceps skinfold thickness.     

Cytogenetics of two species of Euceraphis (Homoptera, Aphididae)

The mechanism of electrical coupling between cells of early Xenopus embryos has been studied by examination of the nonjunctional membrane resistances and capacitances as a function of cleavage stage, the junctional and nonjunctional membrane resistances as functions of time during the first cleavage, and the electrical properties of the primitive blastocoel. The changes in membrane resistances and capacitances during the first two cleavages may be completely explained by the addition of new membrane, identical in specific resistance and capacitance to the original membrane, at a constant rate to furrows which are electrically connected to the perivitelline space. Microelectrode recording from the primitive blastocoel indicates that there is no electrical difference detectable between it and the perivitelline space. These results are discussed in the context of current theories of the mechanism of intercellular electrotonic coupling.     

Primary and secondary somatosensory projections in direct-developing plethodontid salamanders

In three species of plethodontid salamanders (Plethodon jordani, Hydromantes italicus, and Bolitoglossa subpalmata), primary and secondary somatosensory pathways were investigated by means of tract-tracing in vivo and in vitro using biocytin, horseradish peroxidase, and neurobiotin. Afferent sensory fibers of cranial nerves V, VII, and X and the brachial nerve run in the dorsal funiculus of the medulla oblongata and spinal cord. Fibers ascend to the level of, but do not enter, the cerebellum. In the caudal medulla oblongata, sensory tracts of the cranial nerves descend in a dorsal and a dorsolateral bundle and reach the level of the fourth spinal nerve. Two bundles are likewise formed by spinal afferent fibers, which descend to the level of the seventh spinal nerve. Secondary somatosensory projections ascend in contralateral ventral, contralateral lateral, and ipsilateral lateral tracts, the latter two corresponding to the spinal lemniscal tracts of Herrick. These tracts reach the cerebellum, mesencephalic, and diencephalic targets (tegmentum, torus, tectum, tuberculum posterius, pretectum, and ventral thalamus) ipsi- and contra-laterally. The projection to the tectum is confined to fiber layer 4. Fibers of the ascending tracts cross in the cerebellar and tectal commissure. Our study demonstrates that the ascending secondary somatosensory pathways of plethodontid salamanders differ remarkably from those of other amphibians.     

Genetic differentiation within and between two habitats

We investigate the usefulness of analyses of population differentiation between different ecological types, such as host races of parasites or sources and sink habitats. To that aim, we formulate a model of population structure involving two classes of subpopulations found in sympatry. Extensions of previous results for Wright's F-statistics in island and isolation-by-distance models of dispersal are given. It is then shown that source and sinks cannot in general be distinguished by F-statistics nor by their gene diversities. The excess differentiation between two partially isolated classes with respect to differentiation within classes is shown to decrease with distance, and for a wide range of parameter values it should be difficult to detect. In the same circumstances little differentiation will be observed in "hierarchical" analyses between pools of samples from each habitat, and differences between levels of differentiation within each habitat will only reflect differences between levels of gene diversity within each habitat. Exceptions will indicate strong isolation between the different classes or habitat-related divergent selection.     

Comparative biology of sperm storage in female salamanders

Females in seven of the ten families of salamanders possess cloacal glands called spermathecae that store sperm. The annual cycle of sperm storage has been studied by light and electron microscopy in eight species representing five families. In these taxa, we recognized 14 characters associated with the spermathecae and traced their evolution on a phylogeny of salamanders based upon other characters. The plasticity and phyletic significance of the spermathecal characters varied greatly. Plethodontids have complex spermathecae while other families possess simple spermathecae; thus, this character has phyletic value as well as being highly conserved within the Salamandroidea. Other characters, such as carbohydrate histochemistry, are highly plastic and show no obvious phyletic trends. The significance of some of these variable characters, such as duration of sperm storage, is apparent only after including in the analysis other aspects of the reproductive cycle, such as length of the mating season. Additional comparative studies, employing the protocol used in this paper, will help further clarify the relationships between phyletic and functional variability in sperm storage mechanisms in salamanders.     

Concentric bodies in two species of he loculoascomycetes

Concentric bodies were found in vegetative and pycnidial cells of Podoxythium tricothecium and in ascostromal paraphyses of Rhytidhysterium rufulum, two representatives of the Loculoascomycetes. They averages 185 nm in diameter in P. trichothecium and 255 nm in R. rufulum and consisted of three zones.