Skip to main content
Advanced Search

Filters: Tags: evolution (X) > Extensions: Citation (X)

18 results (85ms)   

View Results as: JSON ATOM CSV
We explore the potential for applying broad ecological theories to interactions between soil animals and micro-organisms to generate a predictive framework within which more hypothesis led research can be undertaken. The paper stems from discussions during a workshop at the XIVth International Symposium on Soil Zoology. The possible linkage between biodiversity and ecosystem functions forms a good example of how soil zoology research can be productively stimulated by addressing a broader ecological concept but also how the concept can be tested below ground at fundamentally different scales to those commonly used above ground. Other areas of theory rapidly developing above ground, which are yet to be fully tested...
thumbnail
Despite some remarkable recent discoveries, the Mesozoic fossil record of salamanders remains limited, particularly for the Jurassic. Here we describe the first articulated salamander skeleton from the Jurassic of Euramerica, recovered from Upper Jurassic deposits of the Morrison Formation, Dinosaur National Monument, USA. The specimen was studied using both conventional methods and high-resolution computed tomography. It shows a combination of primitive and derived character states that distinguish it from all known Mesozoic salamanders and which permit the erection of a new genus and species, Iridotriton hechti. The derived states (including the presence of spinal nerve foramina in the tail) suggest a position...
Our planet offers many opportunities for life on the edge: high and low temperatures, high salt concentrations, acidic and basic conditions and toxic environments, to name but a few extremes. Recent studies have revealed the diversity of fungi that can occur in stressful environments that are hostile to most eukaryotes. We review these studies here, with the additional purpose of proposing some mechanisms that would allow for the evolutionary adaptation of eukaryotic microbial life under extreme conditions. We focus, in particular, on life in ice and life at high salt concentrations, as there is a surprising similarity between the fungal populations in these two kinds of environments, both of which are characterized...
Many changes in mammalian faunas occurred across the early (Wasatchian) to middle (Bridgerian) Eocene boundary as documented in the fossil record from the Western Interior of North America. One of the more striking changes took place within the tarsiiform primate family Omomyidae. In the early Eocene, omomyids were dominated, both in abundance and diversity, by the subfamily Anaptomorphinae. In the middle Eocene, the subfamily Omomyinae dominated in abundance, while both subfamilies were nearly equally diverse. Examination of a series of paleoecological indicators including leaf-margin analysis, cenogram analysis, ecological diversity analysis of trophic structure, the distribution and development of ancient soil...
Leaf ecophysiological traits related to carbon gain and resource use are expected to be under strong selection in desert annuals. We used comparative and phenotypic selection approaches to investigate the importance of leaf ecophysiological traits for Helianthus anomalus, a diploid annual sunflower species of hybrid origin that is endemic to active desert dunes. Comparisons were made within and among five genotypic classes: H. anomalus, its ancestral parent species (H. annuus and H. petiolaris), and two backcrossed populations of the parental species (designated BC2ann and BC2pet) representing putative ancestors of H. anomalus. Seedlings were transplanted into H. anomalus habitat at Little Sahara Dunes, Utah, and...
The presence or absence of heterozygous individuals and overall genetic variation were determined for the invasive exotic annual grass Bromus tectorum from four populations in northern Nevada using seven species-specific polymorphic di-nucleotide microsatellite markers. Allelic polymorphisms were found in all populations, but not at all loci within each population. Mean genetic diversity across loci within populations ranged from 0.009 ± 0.006 to 0.551 ± 0.073, across populations x̄ = 0.234 ± 0.043. Fifteen individuals from the total sample (8.24%) were heterozygous at 1–4 loci. Two populations exhibited no heterozygosity and the remaining two populations had relative heterozygote proportions of 22.5% and...
Over the 1970s and 1980s, emissions of carbon dioxide from energy use fell in per capita, per unit GDP, and in some cases in absolute terms in 10 industrialized countries studied by LBNL. These declines were driven principally by falling end-use energy intensities and the decreasing carbon content of energy. By the early 1990s, however, a slowdown in the decline of intensities and the continued growth of GDP and energy services activity have reversed the trends in absolute emissions. LBNL concludes that CO2 emissions will continue to rise in the future unless energy intensities and/or the carbon content of energy can be decreased at an accelerated rate via policy changes, technological innovation and/or behavioural...
Wind-tunnel analyses of the behavior of airborne pollen around ovules of two Ephedra species (E. trifurca and E. nevadensis) indicate that at certain airflow speeds (0.5 m/sec and 1.0 m/sec) each species is capable of biasing pollination in favor of conspecific pollen. A computer procedure was designed to evaluate the physical basis for this aerodynamic discrimination. This procedure indicates that differences in size and density confer significantly different inertial properties to the two pollen species. Operating within the specific aerodynamic environments generated around ovules from each species, these differences are sufficient to account for the biases observed in the probability of pollination. Within natural...
Categories: Publication; Types: Citation, Journal Citation; Tags: Evolution
Mitochondrial DNA control region sequences of spotted owls (Strix occidentalis) allowed us to investigate gene flow, genetic structure, and biogeographic relationships among these forest-dwelling birds of western North America. Estimates of gene flow based on genetic partitioning and the phylogeography of haplotypes indicate substantial dispersal within three long-recognized subspecies. However, patterns of individual phyletic relationships indicate a historical absence of gene flow among the subspecies, which are essentially monophyletic. The pattern of haplotype coalescence enabled us to identify the approximate timing and direction of a recent episode of gene flow from the Sierra Nevada to the northern coastal...
Over the 1970s and 1980s, emissions of carbon dioxide from energy use fell in per capita, per unit GDP, and in some cases in absolute terms in 10 industrialized countries studied by LBNL. These declines were driven principally by falling end-use energy intensities and the decreasing carbon content of energy. By the early 1990s, however, a slowdown in the decline of intensities and the continued growth of GDP and energy services activity have reversed the trends in absolute emissions. LBNL concludes that CO2 emissions will continue to rise in the future unless energy intensities and/or the carbon content of energy can be decreased at an accelerated rate via policy changes, technological innovation and/or behavioural...
Previous field studies of squamate reptiles have shown that many life history traits show a significant amount of phenotypic plasticity, especially in response to prey availability. These results were recently supported by laboratory studies on a viviparous garter snake, which showed that clutch size and clutch mass were plastic in response to changes in energy intake, but that relative clutch mass and offspring size were relatively canalized. To determine if these results extend to oviparous reptiles, we conducted an experimental study of phenotypic plasticity in the corn snake, Elapheguttata. Female corn snakes on a high energy diet produced larger clutch sizes, larger clutch masses, and larger relative clutch...
We used variation in a portion of the mitochondrial DNA control region to examine phylogeography of Tamiasciurus hudsonicus, a boreal-adapted small mammal in the central Rocky Mountain region. AMOVA revealed that 65.66% of genetic diversity was attributable to variation within populations, 16.93% to variation among populations on different mountain ranges, and 17.41% to variation among populations within mountain ranges. Nested clade analysis revealed two major clades that likely diverged in allopatry during the Pleistocene: a southern clade from southern Colorado and a northern clade comprising northern Colorado, Wyoming, eastern Utah, and eastern Idaho. Historically restricted gene flow as a result of geographic...
thumbnail
The extent and impact of introgressive hybridization was examined in the Gila robusta complex of cyprinid fishes using mitochondrial DNA (mtDNA) sequence variation. Lower Colorado River basin populations of G. robusta, G. elegans, and G. cypha exhibited distinct mtDNAs, with only limited introgression of G. elegans into G. cypha. The impact of hybridization was significant in upper Colorado River basin populations; most upper basin fishes sampled exhibited only G. cypha mtDNA haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence. Analysis...
Male calling effort and mitochondrial DNA (mtDNA) variation were examined in a breeding chorus of toads from a hybrid zone between Bufo microscaphus and B. woodhousii in central Arizona. The chorus comprised 50 B. microscaphus and 17 hybrids, identified on the basis of morphology and advertisement calls; no pure B. woodhousii were observed. Males produced advertisement calls throughout the early evening, even when relatively large numbers of males (>50) were present at the chorus; active searching and satellite tactics were not observed. Calling efforts (call duration X call rate) of hybrids (23.9%, n= 8) and B. microscaphus (24.9%, n= 19) were similar and comparable to call efforts of B. woodhousii (21.9%, n= 10)...
This paper is based on the marshalling of a wide variety of evidence in an effort to understand the origins and evolutionary deployment of a faunal unit, namely the species of toads of the genus Buf o that occur in North America. Another purpose is to learn the mechanisms of speciation in this group Published in Evolution, volume 17, issue 1, on pages 1 - 16, in 1963.
Categories: Publication; Types: Citation, Journal Citation; Tags: Evolution
Since the beginning of the Cenozoic period several hundreds of metres of the sedimentary cover have been removed from the Colorado Plateau. Palaeoclimatic considerations show that the Colorado Plateau has been dominated by dry climates throughout the Cenozoic with the possible exception of the early Palaeocene. Today in the still prevailing arid climate, which strongly accentuates differences in rock resistance, the relief shows a structurally controlled cuesta scarp topography in the slightly deformed strata of alternating resistance. In examining whether the denudational efficiency of scarp retreat was sufficient to account for the wide erosional gaps in the sedimentary cover, rates of scarp retreat were determined...
Geographic variation in selection pressures may result in population divergence and speciation, especially if sexual selection varies among populations. Yet spatial variation in targets and intensity of sexual selection is well studied in only a few species. Even more rare are simultaneous studies of multiple populations combining observations from natural settings with controlled behavioral experiments. We investigated how sexual selection varies among populations of the chuckwalla, Sauromalus obesus. Chuckwallas are sexually dimorphic in color, and males vary in coloration among populations. Using field observations and multiple regression techniques, we investigated how sexual selection acts on various male traits...
We explore the potential for applying broad ecological theories to interactions between soil animals and micro-organisms to generate a predictive framework within which more hypothesis led research can be undertaken. The paper stems from discussions during a workshop at the XIVth International Symposium on Soil Zoology. The possible linkage between biodiversity and ecosystem functions forms a good example of how soil zoology research can be productively stimulated by addressing a broader ecological concept but also how the concept can be tested below ground at fundamentally different scales to those commonly used above ground. Other areas of theory rapidly developing above ground, which are yet to be fully tested...
    map background search result map search result map The role of introgressive hybridization in the evolution of the Gila robusta complex (Teleostei: Cyprinidae) A Late Jurassic salamander (Amphibia: Caudata) from the Morrison Formation of North America A Late Jurassic salamander (Amphibia: Caudata) from the Morrison Formation of North America The role of introgressive hybridization in the evolution of the Gila robusta complex (Teleostei: Cyprinidae)