Spelling suggestions: "subject:"biology, cology."" "subject:"biology, cacology.""
761 |
Neural pathways underlying visually guided flight control in flies (Diptera): Evolutionary implications and phylogenetic consequences of cellular architectureBuschbeck, Elke Karin Ursula, 1967- January 1996 (has links)
In dipteran brains, a motion sensitive but color insensitive, pathway consists of large diameter neurons, organized as a precise retinotopic map. Several cell classes can be uniquely identified by their shapes, projections and relative positions in the neuropil. Morphological comparisons of small-field neurons in the second visual neuropil, the medulla, in 16 dipteran taxa reveal that those neurons that are involved in elementary motion computation are conserved in aspects that are expected to contribute to the functional pathway, but vary moderately in shape and cell decorations. On the other hand large-field neurons of the third visual neuropil, the lobula plate (LP), vary considerably in their numbers, shapes and positions within the mosaic. Those are neurons that integrate information from arrays of EMDs in a taxon-specific way. Because of the map-like organization of this neuropil, differences in cell size, architecture and cell number are of major functional consequence. Character evolution studies suggest that specific LP organizations are indeed tightly connected with specific functional properties; namely, differences that influence flight behavior. For example, the comparison of isomorphic vertical cells against hovering flight reveals multiple parallel origins of these two character traits. Other characters are closely associated with phylogenetic hypothesis, and no evolutionarily associated functional characteristics have been found. A parsimony analysis based on 32 neuroanatomical characters shows close similarities with conventional literature-derived hypotheses, suggesting the systematic value of neuroanatomical characters.
|
762 |
Sexual selection and biological diversification: Patterns and processesMesnick, Sarah Lynne, 1960- January 1996 (has links)
This dissertation investigates the evolutionary consequences of three very different behavioral mechanisms by which males may bias female mating decisions in their favor, elaborate male displays (Chapters I and II) and sexual coercion and resource brokering (Chapter III). The results presented here suggest that sexual selection is an important force in evolution. In Chapters I and II, I investigate the relationship between male courtship displays and speciation. Chapter I utilizes the multiple sister-taxa comparison method to test the hypothesis that sexual dimorphism is correlated with increased species diversity in teleost fishes. In 21 of 27 sister-group comparisons, the lineage with the greater degree of sexual dimorphism was more species-rich than its hypothesized sister taxa. The pattern holds across taxonomic levels and sensory modalities, and whether the male, or the female, is the displaying sex. Additional data supporting the sexual selection-diversity hypothesis in other taxa are also discussed. Chapter II investigates how variation in the signals displayed during social and sexual interactions affect reproductive isolation and may facilitate subsequent speciation, utilizing both field and laboratory experiments with the marine fish, Acanthemblemaria crockeri, a chaenopsid blenny endemic to the Gulf of California, Mexico. The anterior portion of the body, the "signal organ", displayed during social interactions, was found not only to be the most variable but was also the most geographically informative. The behavioral responses of the fish themselves, in both male courtship discrimination trials and in female spawning trials, reinforce these geographical differences and results suggest that variation in socially selected traits may accelerate reproductive isolation. In Chapter III, I examine how, if some males in a population use force to bias female mating decisions, protection can become a valuable resource that other males can use to attract females. I term this the bodyguard hypothesis of female mate choice. I present data illustrating the effectiveness of protective males in reducing the probability of aggression from other males and suggest the importance of protective mating alliances in the evolution of a diversity of animal mating systems including mate guarding, leks, "harems", monogamy, polygyny, and pair-bonding in humans.
|
763 |
Studies of bats in southeastern Arizona with emphasis on aspects of life history of Antrozous pallidus and Eptesicus fuscusSidner, Rhonda Marie January 1997 (has links)
During 1980-1995, 42 cohorts of free-living juvenile female Antrozous pallidus and Eptesicus fuscus were banded and recaptured at three bridge roosts in Chihuahuan desertscrub in southeastern Arizona. Surviving female colony members returned each Spring to rear young. Life tables from known-age cohorts provided comparison of survivorship within and between populations sharing similar macro-environmental conditions at these maternity roosts. Mean first-year survivorship varied between and within species and roosts and was higher for E. fuscus than for A. pallidus. First-year survivorship was affected by weather, by age of mothers through indirect influence on neonate size with number of young in the litter, and by human activity. Disease, predation, inclement weather, and human vandalism caused mortality. Second and third-year survivorship was higher than juvenile year for both species. Eptesicus fuscus had higher adult survivorship than A. pallidus. Compared to A. pallidus, female E. fuscus had lower mortality rates, and females decreased their reproductive effort by litter size reduction and deferred age of first reproduction. While A. pallidus females began reproducing at yearling age, 54% of E. fuscus females deferred their first reproduction until age two. Fifty-five percent of age two A. pallidus and up to 100% of older females produced twins. By contrast, only 9% of age two E. fuscus had twins, and 28% of older females produced twins. Lower annual productivity by E. fuscus females was apparently balanced by longer life. While no more than 10% of A. pallidus reached five years of age, at least 10% of E. fuscus attained eight years. Thus, these species have evolved a life history that allows reproductive replacement with low fecundity and high survivorship. Western populations of E. f. pallidus produced smaller litters, deferred first reproduction, and had higher juvenile and adult survivorship than reported for E. f. fuscus, demonstrating intraspecific geographical differences in life history. Maximum life-span records for A. pallidus were a 10-year old male and a female that was at least 11 years old. The oldest E. fuscus were two females that were at least 14 and 15 years old.
|
764 |
Fire frequency, nutrient concentrations and distributions, and δ¹³C of soil organic matter and plants in a southeastern Arizona grasslandBiggs, Thomas Howard, 1949- January 1997 (has links)
Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C3 Prosopis velentina (mesquite) trees, whereas the burned plots are open C4-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant-available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass 11 is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C3 shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C4 grasses to C3 shrubs in surface soil layers. δ¹³CSOM values indicate that the Holocene and Late Pleistocene were dominated by C4 grasslands, and the pre-Late Pleistocene vegetation was a C4-grass savanna with abundant C3 plants.
|
765 |
Effects of environmental heterogeneity on species diversity: A new process-based, multi-species, landscape simulation model (SHALOM)Ziv, Yaron David, 1960- January 1998 (has links)
I designed and implemented a process-based, multi-species, spatially-explicit, object-oriented landscape simulation model that analyzes how high-level ecological complexity affects species diversity patterns (SHALOM). SHALOM has physical (landscape, habitat, cell, patch) and biological classes (population, species, community). At the local scale, populations grow continuously, affected by a community-level saturation effect, a species-habitat match, and demographic stochasticity. The global-scale processes are dispersal and catastrophic stochasticity. The model uses allometric relationships and energy as a common currency to bridge differences between different body-sized species located in habitats of different productivities. The model represents a new synthetic approach to study combined ecosystem, community and population processes. I solved the model's local-scale population growth equation analytically. For a population to have a positive carrying capacity, its death-rate-to-birth-rate ratio (d/b) should be greater than its match to the habitat it occupies. Body-size dependent birth and death rates show that d/b decreases with body size for eutherian mammals. Altogether, habitat specificity negatively scales with body size. I discuss this prediction in light of two macroecological patterns--geographic range vs. body size and species abundance vs. geographic range. I simulated a simple 4-patch landscape, each patch having a unique habitat. I simulated 26 species that differed only in body size. I used allometric values of eutherian mammals. The results show that interspecific competition reduces species diversity in each habitat and in the landscape. Stochasticity depresses mean population sizes, opening opportunities for species to avoid competitive exclusion. With stochasticity, habitats have different communities determined by which large species becomes locally extinct at random. Demographic and catastrophic stochasticities differ in their effects on species diversity. Dispersing individuals move between habitats and reestablish the local populations of their species. Dispersal neutralizes the randomness of the assemblages produced by stochasticity. I simulated a 16-patch landscape. Some habitats were unsuitable for several species. The results show that body size and species abundance have a log-normal relationship, and that geographic range increases non-linearly with log body size. These patterns are highly consistent with observed data.
|
766 |
Phytosterols as neglected nutrients in grasshoppers (Orthoptera: Acrididae)Behmer, Spencer Thane, 1967- January 1998 (has links)
Grasshoppers, like most other organisms, require sterols for the production of cellular membranes and, like other animals, as precursors to steroid hormones. However, grasshoppers, like other insects, cannot synthesize sterols de novo and must acquire these essential nutrients from their diets. Survival and performance of five grasshopper species, representing three phylogenetic lineages and with different host preferences, were compared on artificial diets that varied in sterol type. Sterols used were: cholesterol (Δ⁵) sitosterol (Δ⁵) stigmasterol (Δ⁵ʼ²²) spinasterol (Δ⁷ʼ²²) and lathosterol (Δ⁷); these are the most common plant sterols. For all species studied, none survived to the adult stage on stigmasterol, spinasterol or lathosterol. Performance on the cholesterol and sitosterol diets were similar for most species. This study suggests that grasshoppers, as a group, are extremely limited with respect to the sterols they can use. Grasshoppers, however, are highly polyphagous insects, often feeding on many different host-plants. Some of these host-plants contain unsuitable sterols. The effect of sterol mixtures on survival and performance was examined by rearing the grasshopper, Schistocerca americana, on artificial diets containing sitosterol (suitable) and spinasterol (unsuitable) presented either alone or in combination. Results indicated that spinasterol, even in the presence of high levels of a sitosterol, could prevent development to the adult stage. Biochemical analysis of grasshopper tissues revealed that dietary sterols with Δ⁷ and/or Δ²²-configurations could not be metabolized to cholesterol. Unmetabolized dietary sterols tended to accumulate in the midgut tissues. Grasshoppers are known to regulate feeding in response to some nutrients in relation to need. To determine if grasshoppers could regulate intake with respect to different sterols, a series of behavioral assays was performed. The grasshopper S. americana was observed feeding on artificial diets with different sterols, in some cases up to seven hours. Results suggest that S. americana developed aversion responses to diets that contained unsuitable dietary sterols (Δ⁷ and/or Δ²²) Additional experiments suggested that the aversion response developed through a combination of post-ingestive feedbacks and associative learning. Taken together, these results suggest that sterol metabolic limitations may partially determine host-plant affiliations in grasshoppers.
|
767 |
Cell surface hydrophobicity of Pseudomonas aeruginosa: Effects of monorhamnolipid and substrate on fatty acid and lipopolysaccharide contentAl-Tahhan, Ragheb Abdel-Razzak January 1998 (has links)
Cell surface hydrophobicity is a biosurfactant inducible parameter associated with increased biodegradation rates of hydrocarbons. Little is known about the types of physiological changes that are induced by a biosurfactant to change cell surface hydrophobicity. The objective of this study was to investigate the rhamnolipid-induced chemical and structural changes that cause the increase in cell surface hydrophobicity of two P. aeruginosa strains; P. aeruginosa ATCC 27853 and P. aeruginosa ATCC 9027. Both fatty acid and lipopolysaccharide content of cells were measured during growth on a soluble substrate; glucose, and a slightly soluble substrate; hexadecane in the presence and absence of monorhamnolipid. Cell surface hydrophobicity is a dynamic surface property that changes depending on strain, growth stage, substrate, and rhamnolipid addition. Results showed a general decline in the readily extractable lipid content that was correlated with increase in cell surface hydrophobicity. This decline took place only when growing cultures was supplied with rhamnolipid. In addition, rhamnolipid treatment caused a partial release of lipopolysaccharides (LPS) from the cells. This was indicated by KDO analysis and by SDS-PAGE analysis of LPS from culture supernatant. Also, LPS release from both strains was rhamnolipid concentration-dependent. Rates of LPS release from suspensions prepared from cells of both strains were highest at low rhamnolipid concentrations. Although increase in cell surface hydrophobicity was associated with LPS release, the amount of LPS released did not correlate with cell surface hydrophobicity. Rather the amount of LPS release was strain dependent. Cell surface ultrastructure revealed by scanning electron microscopy showed that the cells studied have a naturally rough surface. Cells grown in the presence of rhamnolipid had a smooth surface indicating a loss of the LPS from the outer membrane. Cells grown on hexadecane in the presence of rhamnolipid had deep pits on the cell surface which may act as hydrophobic sites that allow increased hexadecane absorption. These data suggest that biosurfactant addition caused LPS loss resulting in development of cell surface hydrophobicity.
|
768 |
Purple nutsedge (Cyperus rotundus L.) competition with cotton: Species biology and effects of proportion, density, and moistureCinco-Castro, Ramon-Antonio, 1958- January 1999 (has links)
Greenhouse and field experiments were conducted to determine how proximity factors and water stress interact to influence competition between purple nutsedge and upland cotton. Purple nutsedge produced more total dry weight than cotton in wet conditions but produced less or similar total dry weight in dry conditions. Cotton's ability to extract water from greater soil depth and maintain a high rate of photosynthesis during water stress enabled it to maintain higher RGR (relative growth rate), LAR (leaf area ratio), and leaf expansion than nutsedge. Absolute growth rate (AGR), initial propagule weight, and early shoot production were important parameters for purple nutsedge competition with cotton. Moisture stress affected the relative importance of intraspecific and interspecific competition between species in both greenhouse and field experiments. intraspecific competition was more important than interspecific competition in determining cotton biomass production in wet conditions but drier conditions further reduced the relative importance of interspecific competition. The results of all experiments indicate that greenhouse addition series competition experiments can be applicable to field conditions provided the experimental design takes into account the biological characteristics of the species being studied. Pot size had a large influence on intra- and interspecific competition between purple nutsedge and cotton. In greenhouse experiments, physiological measurements were initiated one hour after irrigation and repeated every 2 h throughout the day. One hour after the cessation of water stress, the photosynthetic rates of both species increased, but photosynthesis recovered faster in cotton than in purple nutsedge. The faster recovery of photosynthesis in cotton was probably due to the osmotic adjustment that occurred in cotton leaves that protected enzymes and other cellular components during water stress. In additive field experiments, seed cotton yield was reduced because the number of harvestable bolls m⁻¹ was reduced as purple nutsedge density increased. Yield was also reduced by cotton seedling death at the highest nutsedge density. The interference of purple nutsedge with cotton cannot be reduced through water management alone. But, based on the growth characteristics of indeterminate cotton varieties, we suggest that delaying the first post-planting irrigation of some cotton varieties could reduce the competition of purple nutsedge with cotton without affecting final seed cotton yield.
|
769 |
Population genetics of incipient speciation in two species of jumping spiders (Salticidae: Habronattus) on the sky islands of southeast ArizonaMasta, Susan Elaine January 1999 (has links)
The population genetic forces that promote speciation, although well understood theoretically, are poorly known in nature. This dissertation focuses on the population genetics of allopatric speciation, using a system of jumping spiders (Araneae: Salticidae) whose populations are subdivided among the disjunct patches of mountain woodland habitat called "sky islands" in southeastern Arizona. I studied two species of salticids that apparently share similar histories of range fragmentation but differ greatly in their amount of intraspecific phenotypic divergence. Using sequence data from neutrally evolving mitochondrial genes, I investigated the population genetic factors influencing divergence. Analyses of gene trees for Habronattus oregonensis and H. pugillis revealed that neither gene flow, effective population size, mutation rate, nor differences in divergence time can explain the interspecific difference in phenotypic divergence. Instead, selection--in these animals, presumably sexual selection--must have acted differentially on traits encoded by nuclear loci to produce the discrepancy. A phylogeographic study of populations of H. pugillis may help clarify the influence of post-Pleistocene vegetational change on organisms dependent upon montane woodlands. Gene trees suggest limited migration between mountain ranges, but offer stronger evidence for incomplete lineage sorting. The trees provide no clear indication of the chronological sequence of woodland fragmentation, but suggest an old geographic division between northern and southern populations. Dates estimated for population divergence range from 26,000 to 291,000 years ago, but rely on molecular clock estimates from non-arachnid arthropods. Divergence estimates based on vegetation change data would require that the mutation rate be considerably faster in these spiders than in non-arachnid arthropods. Whereas there is no fossil-based molecular clock calibration for arachnids to judge whether this is likely, analyses of mitochondrial sequences from three Habronattus species do reveal other highly unusual features. For example, secondary structures that were inferred from DNA sequences of tRNA genes lack the TPsiC arm, and therefore are predicted not to form the standard tRNA cloverleaf. In addition, the 3' half of the gene encoding ribosomal 16S RNA appears to fold to a normal arthropod-like secondary structure, but the 5' half is extremely divergent and truncated with respect to other arthropods.
|
770 |
Genetic differentiation in Gulf of California blennioid fishesRiginos, Cynthia January 2000 (has links)
Marine organisms inhabit an environment where there are few absolute barriers to movement. In addition, a planktonic larval stage is common to most marine fishes and invertebrates. Consequently, marine organisms are often characterized by little genetic differentiation over large geographic distances, and the factors that might generally promote genetic divergence are not well understood. Here, contributions to population structure from both intrinsic and extrinsic factors were investigated in Gulf of California blennioid fishes. In Appendix A, population structure was estimated from mtDNA control region sequences for three species, Axoclinus nigricaudus, Malacoctenus hubbsi, and Ophioblennius steindachneri, that differ in predicted dispersal patterns (based on ichthyoplankton distribution and abundance patterns relative to rock reefs). FST ranged widely among low to high predicted dispersal species, in the same rank order predicted by larval distribution patterns. In A. nigricaudus (low predicted dispersal), phylogenetic, population genetic, and general linear model analyses of mtDNA (Appendix B) showed that variation was significantly partitioned between two biogeographic regions, and that geographic distance and unsuitable habitat also contributed to mtDNA differentiation. In contrast, allozyme variation in A. nigricaudus showed less partitioning than mtDNA and there was no break between biogeographic regions (Appendix C). In Gulf of California blennies, I find that population structure varies among fishes that have a planktonic larval stage in a manner that can be predicted from larval distribution patterns. The correlation between larval distribution and population structure suggests that some fish larvae, such as A. nigricaudus, actively maintain a position close to their natal reef, preventing substantial gene flow among many populations. In addition, patterns of population subdivision in A. nigricaudus (low dispersal) indicate that when dispersal is restricted, substantial population subdivision due to a combination of factors can occur, despite having a planktonic larval stage. The discordance between mtDNA and allozymes in A. nigricaudus is consistent with non-equilibrium conditions following a population perturbation, selection on allozymes or mtDNA, or some combination of these factors. These results emphasize that multiple genetic markers should be examined when making inferences about the genetic structures of natural populations.
|
Page generated in 0.0888 seconds