bluuebunny/crossref_metadata_2025 huggingface dataset:
A field versus laboratory study of blood oxygen status in normoxic crabs at different temperatures
Authors: Massabuau J.-C. , Forgue J.
Published: May 2008

The blood oxygen status of two species of active crabs (Carcinus maenas and Necora puber) was studied in the field and compared with the results of previous laboratory experiments performed on a wide spectrum of physiologically different water-breathers. The aim was to determine whether, as in the laboratory, the functioning of the O2supply system in the field could be based on maintaining the arterial [Formula: see text] in the low range, 1–3 kPa. The O2partial pressures and concentrations in the arterial and venous blood, arterial blood pH, and blood respiratory pigment concentration were measured in normoxic water at various temperatures ranging from 10 to 20 °C and in various seasons. In the field, [Formula: see text] values in normoxic C. maenas and N. puber were in the low range, 1–3 kPa, independently of temperature, season, and blood haemocyanin concentration. It is concluded that in the field as in the laboratory, [Formula: see text] values mainly in the low range provide a head pressure sufficient to meet O2needs. The changes that appear to occur in other respiratory variables are discussed in relation to field versus laboratory conditions and temperature differences. The consequences for analysing problems of hypoxaemia in hypoxic waters or situations are discussed.
Winter concealment by subyearling rainbow trout: space size selection and reduced concealment under surface ice and in turbid water conditions
Authors: Gregory Jim S. , Griffith J. S.
Published: May 2008

The proportion of rainbow trout (Oncorhynchus mykiss) concealing themselves in simulated interstitial spaces was examined in the presence of surface ice, in turbid water, and in clear water. Tests were conducted in enclosures in a small Idaho stream with structures that provided five rectangular spaces varying in width and height, one circular space, and one triangular space. Space use was assessed each morning by trapping test fish inside the structures. Significantly more fish concealed themselves under clear water conditions than under either surface ice or turbid water conditions. Spaces narrower than the width of a test fish with extended pectoral fins and spaces taller than the height of a test fish with dorsal fin extended were used less than would be expected if space use was random. The frequency with which two or more fish occurred together in the same space was similar to that expected if fish occurred together at random. Fish rarely returned to the same space on consecutive nights.
Effect of forest patch area on population attributes of white-footed mice (Peromyscus leucopus) in fragmented landscapes
Authors: Nupp Thomas E. , Swihart Robert K.
Published: May 2008

We studied population densities, sex ratios, adult masses, reproductive activity, age structure, and over-summer recapture rates of white-footed mice (Peromyscus leucopus) in 15 woodlots of various sizes and three continuous-forest sites to ascertain the effects of forest patch area on these population attributes. Our study was conducted in west-central Indiana during spring 1992 and 1993 and autumn 1992. Densities of white-footed mice were inversely related to forested area. A survey of previous studies conducted at similar latitudes revealed a similar pattern. Extremely high densities (up to 200 adults/ha) were found in small woodlots (< 0.5 ha). Mass of adult male mice also was inversely related to forest area, and a positive relationship between proportion of adult male mice and forest area was suggested. Ratios of juveniles to adults were positively related to forest area in autumn but not in spring. The proportion of sexually active individuals in the population was not related to forest area, nor were over-summer recapture rates. Our findings indicate that patch area can have dramatic effects on the structure and dynamics of populations of white-footed mice inhabiting fragmented landscapes.
Porcupine (Erethizon dorsatum) demography in central Massachusetts
Authors: Hale Mary B. , Fuller Todd K.
Published: May 2008

From 1991 to 1993 we radio-collared and monitored 50 porcupines (Erethizon dorsatum) in central Massachusetts to obtain estimates of survival and reproduction, and applied these estimates to a model of porcupine population dynamics to estimate the annual rate of change (λ). The annual survival rate for all adult (> 1 year old) porcupines was 0.67 ± 0.07 (mean ± SE). Survival was higher, but not significantly so (P = 0.22), for adult females (0.74 ± 0.08) than for adult males (0.56 ± 0.12). Adult porcupines died of starvation (annual mortality rate 0.08), injuries (0.05), interactions with humans (0.04), and disease (0.05) but not predation. Annual survival of juveniles (< 1 year old) ranged from at least 0.37 in 1992 to at most 0.39 in 1993. Minimum birth rates of radio-collared females > 2 years old, determined by sightings of young near females, lactation, and pregnancy status as determined by ultrasound, were 0.64 in 1992 and 0.62 in 1993. Incorporation of maximum and minimum values of demographic parameters from this study and from the literature into population models indicated a decreasing porcupine population.
Morphometric discrimination among sibling species in thefulva–rudis–texanacomplex of the ant genusAphaenogaster(Hymenoptera: Formicidae)
Authors: Umphrey Gary J.
Published: May 2008

The fulva–rudis–texana complex of the ant genus Aphaenogaster includes A. fulva, A. rudis, A. texana, and morphologically similar species. Morphometric and other morphological investigations were conducted on colony representatives of 10 forms (4 likely representing undescribed species) that were previously identified using cytogenetic and electrophoretic markers. In workers, most qualitative characters exhibit such a high degree of size-associated intraspecific variation relative to interspecific differences that they are not reliable for identification. Linear discriminant analysis and canonical variate analysis on 12 morphometric measurements were used to optimize classification and define a morphometric habitus for each form. Two-variable scatterplots clarify the nature of morphometric variation in the complex and provide simple characters that will reliably separate numerous pairs of forms. Indices appear to be of little taxonomic value in this complex. A preliminary key to the workers of the complex summarizes the most important taxonomic characters. This key substantially improves the ability to recognize morphologically most members of the complex, but sometimes only genetic evidence is definitive.
The development and maturation of vitellogenic oocytes, plasma steroid hormone levels, and gonadotrope activities in acid-stressed brook trout (Salvelinus fontinalis)
Authors: Tam W. H. , Zhang Xiaomin
Published: May 2008

Brook trout (Salvelinus fontinalis) were divided into a control group at neutral pH, a food-restricted control (Ph–food control) group at neutral pH, and an acid-stressed (pH 4.15) group, and were maintained under these conditions from August 14 to November 1. The food for the pH–food control group was restricted to simulate the reduced food intake of the acid-stressed fish. Throughout September, oocyte development in the acid-stressed fish was accelerated and the oocytes weighed 36–54% more than those of the pH control fish. By late September these oocytes had reached ovulatory size. Then a shift from predominantly high estrogen to high 17α,20β-dihydroxy-4-pregnen-3-one levels occurred in the circulation. Ovulation followed and by October 19 all acid-stressed trout had ovulated. The same sequence of events occurred significantly later in the pH control fish and ovulation was not complete on November 1. Although their oocytes were larger than those of pH control fish in September, hormonal changes and ovulation in pH–food control fish occurred at the same time as in pH control fish. The results suggest that while the reduced food intake during acid stress might have contributed to accelerated oocyte growth, the full effect of chronic acid exposure was responsible for advancing oocyte development, maturation, and ovulation.
Accelerated aging of giant transgenic mice is associated with elevated free radical processes
Authors: Rollo C. D. , Carlson J. , Sawada M.
Published: May 2008

Transgenic growth hormone mice lived half as long as normal on a 23% protein diet. Longevities of both transgenic and control mice on a 38% protein diet were half those on 23% protein food. We hypothesized that transgenic mice are energetically constrained by their rapid growth, so energy supplements might improve "longevity assurance investments." As predicted, sucrose supplements extended the longevity of transgenic females (from a mean of 315 to 419 d). We measured two key biomarkers of aging (in brain, heart, liver, musculature, and kidneys) to test whether aging of these mice conformed to the free radical theory. Transgenic mice showed elevated levels of both superoxide radical (SOR) and lipid peroxidation (LP) compared with controls. The pattern of SOR and LP levels across kinds of mice and diets supported a free radical interpretation of aging and suggested that energy supply (protein or sugar) may impact longevity. The brain and heart were key biomarkers of longevity. LP levels in either organ explained 89% of the variation in longevity associated with genotype, sex, and diet. If combined with dietary restriction, this system should yield an 8-fold range in longevity, representing a powerful new tool for research into life histories and gerontology.
Variation in the pteridine content in the heads of tsetse flies (Diptera: Glossinidae:GlossinaWiedemann): evidence for genetic control
Authors: Mclntyre G. S. , Gooding R. H.
Published: May 2008

The pteridine content of the head capsule of teneral flies from 11 genetically selected lines (including eye-color mutants) of Glossina morsitans morsitans Westwood and Glossina palpalis palpalis Robineau-Desvoidy was examined using fluorescence spectroscopy. Wild-type G. p. palpalis had a greater pteridine content than did wild-type G. m. morsitans. Within G. m. morsitans there was a 25% variation in fluorescence values between genetic lines. Wild-type G. p. palpalis had the same pteridine content as brick mutants but more than tan mutants; in G. m. morsitans the salmon mutants had a higher pteridine content than did wild-type flies. Pteridine content did not account for the difference in eye color between male and female brick mutants. Accumulation of pteridines was not influenced by genotype in young flies, but in older flies salmon mutants accumulated pteridines more rapidly than did wild-type flies. Young flies, both wild type and salmon, accumulated pteridines more rapidly than did old flies. The results of the analysis of head capsule fluorescence in males from the parental lines and F1and F2generations of reciprocal crosses of the G. m. morsitans lines with the highest and lowest pteridine contents revealed that genetic control of pteridine content lies on the X chromosome and on one autosome.
Den use by arctic foxes (Alopex lagopus) in a subarctic region of western Alaska
Authors: Anthony R. Michael
Published: May 2008

Distribution, abundance, and use of arctic fox dens located in coastal tundra communities of the Yukon–Kuskokwim delta were determined in studies from 1985 to 1990. Dens were denser and less complex than those described in studies conducted above the Arctic Circle. Eighty-three dens of varying complexity were found in the 52-km2study area. Nineteen dens were used by arctic foxes for whelping or rearing pups. Three females relocated litters to multiple dens; a maximum of four dens were used concurrently by pups from one litter. Although red foxes (Vulpes vulpes) were common in the region, their use of dens in the study area was minimal. Differences in vegetation at den sites and nearby unoccupied sites were minimal. Furthermore, den sites could not be distinguished from non-den sites during aerial surveys.
Distribution and abundance of Vancouver Island marmots (Marmota vancouverensis)
Authors: Bryant Andrew A. , Janz Doug W.
Published: May 2008

We analysed historic records and annual counts to assess the population status of Vancouver Island marmots (Marmota vancouverensis). Since 1972, marmots have been found at 47 sites on 15 mountains. All but 2 colonies were located within 5 adjacent watersheds on south-central Vancouver Island. Counts underestimated actual marmot abundance. For most site–year combinations, observers probably counted 66–78% of adults and 75–89% of juveniles. Reproductive colonies typically contained fewer than 5 adults ([Formula: see text], SE = 0.61, n = 34). Most animals were found at elevations above 1000 m (81%), on south- to west-facing slopes (74%). After 1981, marmots colonized 11 habitats created by logging of forests above 700 m. Numbers of adults were above average (134–147%) during the early 1980s and have been near or below average since 1990 (58–99%). The current (1995) population contains 100–200 animals, including 50–100 animals in logged habitats. Marmota vancouverensis is rare primarily because of the small size and patchy distribution of natural subalpine meadows on Vancouver Island. The species is apparently adapted to a metapopulation life-style, in which a network of small colonies exhibit population fluctuations, local extinctions and recolonizations over time.
Effects of substrate on prey use by belted kingfishers (Ceryle alcyon): a test of the prey abundance – availability assumption
Authors: Kelly Jeffrey F.
Published: May 2008

Foraging trials were conducted using belted kingfishers (Ceryle alcyon) to examine relationships among prey abundance, availability, and use. Because these relationships are affected by the preference of the predator, I also determined the prey preference of belted kingfishers. Fish (Pimephales promelas and Catostomus commersoni) and crayfish (Orconectes spp.) were exposed to predation by 12 wild belted kingfishers under 4 treatments in which prey availability was manipulated by altering habitat structure. The preferred prey of belted kingfishers were relatively large fish (11–13 cm long). In structurally simple habitats, prey use by belted kingfishers reflected this preference. Complex habitat structure reduced the availability of preferred prey items and resulted in prey use that did not differ from the initial prey abundance distribution. These experiments demonstrated that prey abundance was not equivalent to availability and that habitat structure and prey preference had important effects on the relationships among prey abundance, availability, and use. Thus, evaluating the importance of prey resources to predators on the basis of prey abundance–use comparisons, while ignoring prey availability and the dynamic factors that influence it, may lead to erroneous conclusions.
Variable levels of immunity to experimental Eimetia arizonensis infections in natural, seminatural, and laboratory populations of deer mice (Peromyscus maniculatus)
Authors: Fuller Claire A.
Published: May 2008

Acquired immunity to parasites may affect both host and parasite population dynamics. Although immunity has been studied experimentally in laboratory-reared hosts, less attention has focused on free-living animals. I examined acquired immunity of free-living deer mice (Peromyscus maniculatus) to naturally occurring and experimental infections of Eimeria arizonensis (Protozoa: Coccidia). In a mark – recapture study, I found evidence of complete immunity to natural infections in only 1 of 3 years and evidence of partial immunity in all years. I subsequently examined partial immunity to experimental infections by giving laboratory-reared, free-living, and enclosure populations of deer mice two or three consecutive E. arizonensis infections. Greater than 90% (13 of 14) of laboratory-reared animals developed immunity after only one exposure, suggesting that E. arizonensis is immunogenic. However, significantly fewer animals living under natural and seminatural conditions developed immunity after one exposure in two of three experiments. These observational and experimental results suggest that immunocompetence of free-living deer mice to E. arizonensis may be variable and may differ with respect to that of laboratory-reared animals.
Intrinsic and extrinsic factors influencing coyote predation of small mammals in Yellowstone National Park
Authors: Gese Eric M. , Ruff Robert L. , Crabtree Robert L.
Published: May 2008

We examined the intrinsic (age, sex, and social status) and extrinsic factors (snow depth and hardness, temperature, cloud cover, wind speed, and habitat) influencing coyote (Canis latrans) predation of small mammals in Yellowstone National Park, Wyoming. We observed 54 coyotes (49 residents from 5 packs, plus 5 transients) for 2507 h from January 1991 to June 1993. We observed 6433 prey detections by coyotes during which coyotes made 4439 attempts to capture prey, resulting in 1545 successful prey captures. The age of the coyote influenced prey-detection rates, predation attempts, and capture rates, plus the proportions of prey attacked after being detected and capture success. Pups had higher prey-detection rates and higher attempt rates than alphas and betas, but capture rates were similar. Snow depth and hardness and habitat type were factors influencing detection rates, predation attempt rates and capture rates. Coyotes hunted mainly in mesic meadows and shrub–meadows, where prey-detection rates, predation attempt rates, and capture rates were highest. Snow depth influenced coyote predation on small mammals, prey-detection rates, predation attempt rates, and capture rates being highest in low snow cover and lower in deeper snow. Our findings indicated that young, inexperienced coyotes detected and attacked small mammals at a higher rate than older coyotes. Yearlings and adults were more selective, and thus detected and attempted to capture prey at a lower rate than pups. Overall, however, pups and older coyotes captured similar numbers of prey per hour.
Prey choice of Tengmalm's owls (Aegolius funereus funereus): preference for substandard individuals?
Authors: Koivunen Vesa , Korpimäki Erkki , Hakkarainen Harri , Norrdahl Kai
Published: May 2008

Errington proposed that predators mainly kill substandard prey, because dominant individuals force subordinate ones into poor habitats, where the predation risk is higher. We studied the prey choice of breeding male Tengmalm's owls (Aegolius funereus funereus) in 1992, when vole densities crashed. We trapped small mammals in the main habitat types in 21 owl territories, and simultaneously identified prey items cached by the same owls in their nest boxes. The main prey of owls in western Finland are the common vole (Microtus epiroticus), field vole (M. agrestis), bank vole (Clethrionomys glareolus), and common shrew (Sorex araneus). Common voles were the preferred prey of owls, followed by field voles, bank voles, and common shrews. Prey captured by owls tended to be lighter and smaller than those available in the field. This tendency was significant for field voles and common shrews. Field voles, common voles, and female common shrews captured by owls tended to have more internal fat than those available in the field. This tendency was significant for male field voles and female common shrews. Owls appeared to choose small individuals of some, but not all, prey species, and that these prey items were not in poor physiological condition.
Touch sensitivity in oligochaete giant fibers is transiently enhanced by a single spike
Authors: Turnbull David E. , Drewes Charles D.
Published: May 2008

Weak tactile stimulation of posterior segments in the freshwater oligochaete Lumbriculus variegatus evokes a single lateral giant fiber (LGF) spike but no overt escape shortening. After initiation of a single spike, giant-fiber excitability is increased, as reflected by a period of enhanced conduction velocity for a second LGF spike that follows 5–50 ms after the first. Using non-invasive recordings from intact worms and a biofeedback arrangement for stimulus delivery, it was shown that the period of enhanced velocity is associated with a marked increase in sensitivity to a second touch stimulus. Enhanced touch sensitivity is distributed within the LGF sensory field to loci remote from the original site of stimulation, leading to an increased likelihood that a second, weak stimulus will elicit rapid escape withdrawal.
Overripening as the cause of low survival to hatch in Lake Erie coho salmon (Oncorhynchus kisutch) embryos
Authors: Flett P. A. , Kraak G. Van Der , Munkittrick K. R. , Leatherland J. F.
Published: May 2008

We investigated the cause of the low survival to hatch of embryos of coho salmon (Oncorhynchus kisutch) from the Fairview, Pennsylvania, stock in Lake Erie. In 1988, survival to hatch of this stock was only 42%, whereas another Great Lakes coho salmon stock of similar genetic origin had an 84% survival to hatch. Laboratory cross-fertilization studies between the Fairview stock and a reference Lake Erie stock from Simcoe, Ontario, showed that eggs from the Fairview stock were the probable source of the low fertility. The presence of overripe eggs in Fairview females was associated with poor fertilization and low survival to hatch. Plasma gonadotropin II levels were similar in preovulatory females taken from the Fairview and Simcoe stocks, but testosterone and 17α, 20β-dihydroxy-4-pregnen-3-one levels were significantly lower in the Fairview females. Increasing the triiodo-L-thyronine (T3) content of the eggs by the administration of T3 to the preovulatory females did not enhance egg fertility. We propose that the low survival to hatch of the Fairview embryos is due to delayed oocyte maturation and ovulation and vent maturation, which may have been caused by exposure of the Fairview salmon to warmer water during the period of late ovarian maturation and migration.
Characteristics of ringed seal,Phoca hispida, subnivean structures and breeding habitat and their effects on predation
Authors: Furgal C. M. , Kovacs K. M. , Innes S.
Published: May 2008

Characteristics of ringed seal (Phoca hispida) subnivean structures and breeding habitat were quantified and their potential influence on predation success by polar bears (Ursus maritimus), arctic foxes (Alopex lagopus), and humans on ringed seals was investigated in Admiralty Inlet and Strathcona Sound, Northwest Territories. A total of 237 ringed seal structures were located between April and June 1991–1993 using trained dogs. Ringed seal lairs and breathing holes were concentrated in areas of deep snow, and were associated with large, thick ice ridges. Only a small percentage of the available fast-ice habitat had sufficient snow depth for lair construction each year. A discriminant function analysis used to classify structures located in 1992, using a combination of structural and habitat measurements, correctly classified 70% of structures located in 1991 and 1993 into functional groups. The length, width, internal height, and level of "tiggak," the odour of rutting male ringed seals, associated with structures were the most important descriptors separating structure types. Seventy-three percent of structures located in the study were undisturbed by predators. The mean length and width of structures entered by predators were significantly greater than those of undisturbed structures. Polar bear success decreased as snow depth and the thickness of the roof covering the structures increased. The conditions necessary for successful arctic fox predation are unclear. Inuit hunters attacked structures close to ice ridges, and ridge height and snow depth influenced their success. All predators attacked lairs having the odour of rutting male ringed seals less often than structures with no male odour.
The breeding behavior of Atlantic walruses,Odobenus rosmarus rosmarus, in the Canadian High Arctic
Authors: Sjare B. , Stirling I.
Published: May 2008

The breeding behavior of Atlantic walruses, Odobenus rosmarus rosmarus, overwintering at the Dundas Island polynya (76 °09′N, 94 °52′W) in the Canadian High Arctic was studied from 1981 to 1990. Approximately 25–65 walruses frequented the polynya area each winter; their distribution was determined by sea-ice features (e.g., thin annual ice, cracks) that ensured easy access to open water. The mating system of walruses breeding in the area is best described as female-defense polygyny. A large mature male had exclusive access to a herd of walruses containing several females for 1–5 days at a time. Although there were numerous males in the polynya capable of attending a herd during the breeding season, one or two males spent significantly more time with a herd. It was not evident that female preference was important in determining which male became the attending male. When attending a herd, a male continuously repeated a complex, stereotyped underwater song. Other sexually mature males in the area behaved as silent herd members, vocal satellite males, or, in some cases, both. The small number of walruses at the polynya, the sedentary nature of the population due to ice conditions, and the inherent gregariousness of female walruses appear to be important factors influencing the evolution of social behavior and the mating system in walruses
Demography, sex ratio, and sexual size dimorphism in a northern population of common musk turtles (Sternotherus odoratus)
Authors: Edmonds Jonathan H. , Brooks Ronald J.
Published: May 2008

A population of common musk turtles (Sternotherus odoratus) was studied in Georgian Bay, Ontario, near the northern limit of the species' range, during the summers of 1991–1994. A total of 314 (229 adult males, 68 adult females, and 17 juveniles) turtles were captured, marked, measured, and released. Over the geographic range of S. odoratus there was a positive relationship between body size and latitude, the musk turtles of the Georgian Bay population being significantly larger than those in any of the more southerly populations. The sex ratio was significantly male-biased, and the study population was unique in having sexual size dimorphism, with significantly larger males. We have hypothesized that this dimorphism has arisen through sexual selection that is being driven by the male-biased sex ratio. Male–male competition for mates is intensified and thereby selects for larger males. Proximately, biased sex ratios and sexual size dimorphism in turtles have been attributed to differential ages and sizes at sexual maturity. However, we found no support for this hypothesis in our population. We have attributed sexual size dimorphism to either differential growth rates after maturity or differential mortality of adults. The male-biased sex ratio may be due to differential movement patterns, differential mortality of the sexes, or the effects of ambient temperature on sex determination.
Origins of endemic stickleback from the Queen Charlotte Islands: mitochondrial and morphological evidence
Authors: Deagle B. E. , Reimchen T. E. , Levin D. B.
Published: May 2008

Recently, two divergent mitochondrial lineages were described in a survey of 12 scattered populations of the threespine stickleback (Gasterosteus aculeatus) on the Queen Charlotte Islands (QCI), western Canada, one of which, possibly a relict lineage, was subsequently shown to characterize stickleback from the western Pacific near Japan. In the present study, we assayed 985 fish from 85 QCI populations for mitochondrial lineage using a restriction enzyme test. Our data indicate that the relict lineage was largely limited (18 of 20 populations) to adjacent watersheds in the northeast corner of the QCI close to a suspected glacial refugium, but we also found the lineage in two remote lakes on the west coast of the QCI, distant from any known refugia. We obtained a sample of 33 stickleback from the mid-Pacific and found both mitochondrial DNA (mtDNA) lineages, strongly suggesting ongoing dispersal of these fish across the Pacific, and inconsistent with previous suggestions of relict status for one of the lineages. Morphologically derived traits, such as loss of armour and loss of spines, occurred in both lineages, but these were more prevalent in the Japanese lineage. Surprisingly, 19 localities had both lineages, and within each of these there were no significant univariate or multivariate associations between lineages and morphology, suggesting few if any reproductive barriers between the divergent mtDNA lineages.
Conventional and isotopic determinations of shorebird diets at an inland stopover: the importance of invertebrates andPotamogeton pectinatustubers
Authors: Alexander Stuart A. , Hobson Keith A. , Gratto-Trevor Cheri L. , Diamond Antony W.
Published: May 2008

We used gut-content and stable-isotope techniques to determine diets of shorebirds staging at a prairie wetland complex. Stable-isotope ratios for carbon (13C/12C) and nitrogen (15N/14N) varied greatly within and among prey types and shorebirds, depending on location within the complex. Both dietary techniques suggested that Long-billed Dowitchers (Limnodromus scolopaceus) and Stilt Sandpipers (Calidris himantopus) ate mostly invertebrates, whereas Hudsonian (Limosa haemastica) and Marbled godwits (Limosa fedoa) ate mainly Potamogeton pectinatus tubers. In comparison, the stable-isotope technique indicated that godwits, especially juvenile Marbled Godwits, ate more invertebrates than is indicated by the gut-content analysis. The discrepancies between methods reflect the potential for bias in the application of these techniques. Researchers using stable isotopes to assess migratory shorebird diets should be aware of possible complications arising from isotopic variability within prey types, even over small geographic ranges. High isotopic variability at inland agro-wetland complexes might preclude reliable isotopic assessment of shorebird diets, especially long term. Rhizivory in godwits may be more common than is generally recognized, especially at inland stopovers during autumn migration in both North America and Eurasia, and should be factored into conservation initiatives for these species.
First-year survival of great horned owls during a peak and decline of the snowshoe hare cycle
Authors: Rohner Christoph , Hunter D. Bruce
Published: May 2008

Most bird species have low survival rates in their first year of life, and the highest losses occur when juveniles become independent and disperse. Young great horned owls (Bubo virginianus), monitored by telemetry in the southwestern Yukon, Canada, survived well during the peak of the population cycle of snowshoe hares (Lepus americanus). Subsequently, juvenile survival collapsed parallel to the decline in hare densities. The proportion of starving owls did not increase, but there was a significant increase in mortalities involving parasitism and predation, probably as an interaction with food shortage. The mortality rates of juvenile great horned owls peaked before, not during, dispersal. We propose that extended parental care makes the postfledging stage safe during optimal conditions, but that the relatively slow development during this stage incurs the cost of increased susceptibility to disease and other mortality factors under environmental stress.
Spatial analysis of microgeographic genetic structure in Richardson's ground squirrels
Authors: Staaden Moira J. van , Michener Gail R. , Chesser Ronald K.
Published: May 2008

Local genetic structure has a sound theoretical basis, yet empirical demonstration in animal species has proved elusive, even in apparently ideal candidate species. Techniques based on the distribution of individual genotypes may offer a more complete picture of population structure than traditional measures focusing on isolation by distance and dispersal behavior. We used spatial autocorrelation and contiguous clustering to identify structure in a population of Richardson's ground squirrel (Spermophilus richardsonii) for which deviation from Hardy–Weinberg expectations indicated population subdivision. Nonrandom aggregates of genotypes were detected at five of six enzyme loci examined and selection at one locus. Genetic structuring was highly sex-dependent, being prominent only among females. Isolation by distance cannot account for the patterns of gene diversity observed, but Mantel matrix procedures of inter-individual distance based on demographic–behavioral characteristics and geographic distance were significantly associated. Social and breeding systems of S. richardsonii lead to significant local substructure. While philopatry alone may not account for fine-scale genetic structure in small mammals with sex-biased dispersal, nonrandom aggregates will be detected if appropriate social models and rigorous sampling criteria are adopted. Identification of such localized structure remains fundamental to understanding evolutionary models of population genetic structure and sociality.
Comparative body measurements, fecundity, oxygen uptake, and ammonia excretion inCambarus robustus(Astacidae, Crustacea) from an acidic and a neutral site in northeastern Ontario, Canada
Authors: Daveikis Victor F. , Alikhan M. A.
Published: May 2008

Cambarus robustus (Astacidae, Crustacea) females from acidic, metal-contaminated Wavy Lake and circumneutral, uncontaminated, fast-flowing Pike Creek showed significant allometric differences (relationships between total body length and wet mass, total body length and chela length, and carapace length and carapace width), as well as differences in their fecundity (relationships between total body length and numbers of eggs per ovary and numbers of eggs per ovary and diameter of eggs). Whereas crayfish from Pike Creek showed linear relationships between total body length, wet mass, and chela length (= isometry), decapods from Wavy Lake showed isometry only between total body length and chela length. Females from Pike Creek produced significantly more but smaller ovarian eggs than did those from Wavy Lake. Oxygen consumption was significantly lower and ammonia excretion significantly higher in crayfish from Wavy Lake than in those from Pike Creek.
Effects of sodium nitroprusside on blood circulation and acid–base and ionic balance in rainbow trout: indications for nitric oxide induced vasodilation
Authors: McGeer J. C. , Eddy F. B.
Published: May 2008

The effects of the nitric oxide (NO) releasing antihypertensive agent sodium nitroprusside (SNP) on rainbow trout (Oncorhynchus mykiss) were investigated using either waterborne exposures of up to 1.3 mM SNP over 60 and 90 min or injections via the dorsal aorta, and cardiovascular responses were compared. Doses of up to 40 μg∙kg−1into the blood stream resulted within 5 min in significantly reduced blood pressure and pulse pressure with tachycardia. Waterborne SNP below 0.53 mM had no effect, but concentrations above this level (to 1.3 mM) after 30–60 min produced significant tachycardia and vasodilation, resulting in dose- and time-dependent reductions in dorsal aorta pulse pressure, with maximum decreases of 50–57%. At and above 0.4 mM SNP waterborne exposure, blood [Formula: see text] was significantly increased, plasma Na+, K+, and Cl−values were unchanged, and there was a mild alkalosis. The cardiovascular effects of waterborne isosorbide dinitrate at 40 μM were similar to those of SNP. Exposure of fish to waterborne potassium ferricyanide (0.67 mM), which is structurally similar to SNP but does not release NO, produced only minor cardiovascular effects compared with those of SNP. Pretreatment of fish with propranolol (1.9 mg∙kg−1via the dorsal aorta) followed by exposure to 1 mM waterborne SNP showed that adrenergic responses were unlikely to be involved in the vasodilation. The results of pretreatment with methylene blue (1.5 mg∙kg−1via the dorsal aorta) followed by 1 mM waterborne SNP suggested that the vasodilation was induced by NO activation of soluble guanylyl cyclase. This study demonstrates that NO-releasing compounds cause vasodilation in rainbow trout in vivo and provides a novel way of studying the effects of altered vascular resistance in fish.
The Harderian gland of the northern grasshopper mouse,Onychomys leucogaster
Authors: Coulson Jennifer O. , Pinter Aelita J.
Published: May 2008

The Harderian gland of the northern grasshopper mouse, Onychomys leucogaster, consists of glandular tubuloalveolar endpieces with secretory cells (small- and large-droplet cells) surrounding a wide lumen. Lumina from adjacent endpieces join repeatedly, forming progressively wider channels. Ultimately, a single secretory duct opens at the anterior canthus of the eye. Abundant sudanophilic materials secreted into the lumina of the tubuloalveoli drain into the orbit of the eye. The presence of amber–brown concretions in, and the intense fluorescence of, the Harderian gland suggest that in O. leucogaster the secretory materials also include porphyrins. Fluorescence of these secretions demonstrates that they drain from the orbit into the nasal passages; grooming spreads these materials from the nares onto other parts of the body. Although the Harderian gland of O. leucogaster shows no sexual dimorphism, there are age-related changes. Small-droplet cells are present at 1 week of age and large-droplet cells appear by 2 weeks. By 4 weeks the gland is comparable to that of adults. Glands of a few adults exhibit two features rarely reported in other rodents: (1) clusters of degenerated tubules characterized by a loss of the secretory epithelium and (2) large aggregations of lymphoid cells.
Patterns of neonatal mortality of elk in northwest Wyoming
Authors: Smith Bruce L. , Anderson Stanley H.
Published: May 2008

During May and June of 1990–1992, 164 newborn elk (Cervus elaphus) of the Jackson elk herd in northwest Wyoming were captured, weighed, aged, and fitted with expandable radio collars. Calves were subsequently monitored twice daily to determine locations and causes of mortality. All neonatal mortality had occurred by 15 July and totaled 15%, 68% of which resulted from predation by black bears (Ursus americanus) and coyotes (Canis latrans). Mortality of individual elk calves was male-biased but unrelated to birth mass. Early-born calves suffered lower mortality from causes other than predation than late-born calves. However, predation was greater upon early-born calves. Mortality rate of neonatal elk and recruitment rates, measured in early August, were not spatially density-dependent.
Species composition, distribution, and summer emergence phenology of stoneflies (Insecta: Plecoptera) from Catamaran Brook, New Brunswick
Authors: Giberson Donna J. , Garnett Heather L.
Published: May 2008

Stonefly (Plecoptera) emergence was investigated between May and September of 1993 and 1994 in Catamaran Brook, New Brunswick, as part of a base-line study to evaluate the effects of timber harvest on Atlantic salmon habitat in Atlantic Canada. Thirty-one stonefly species representing seven families were identified from Catamaran Brook, of which 8 were new provincial records. Eight species, all in the families Chloroperlidae and Leuctridae, were common in both years. The cone-type emergence traps used in this study appeared to adequately sample most stonefly species except the Perlidae. There was a pronounced seasonal progression of species emerging from the brook that was generally constant for both years. However, the abundance and timing of stonefly emergence were related to both temperature and discharge patterns. Generally earlier emergence in 1994 than 1993 was probably related to warmer water in 1994 than 1993, and lower abundance in 1994 was probably related to a reduction in habitat due to unusually low water in that year.
Organization of a taxonomically diverse lizard assemblage in Amazonian Ecuador
Authors: Vitt Laurie J. , Zani Peter A.
Published: May 2008

Of 22 lizard species studied in eastern Ecuador, 21 were diurnal. Ten were active foragers and 12 were sit-and-wait foragers. Considerable variation existed in habitat and microhabitat distribution and body temperatures among species. Body size varied over an order of magnitude (20–270 mm snout–vent length). Most morphological (size-free) variation among species (77%) was accounted for by two principal component axes and appears tied to phylogeny. Prey size was correlated with lizard size and species were separated by prey size. Low overlaps in microhabitat, habitat, and prey type also separated species. Pseudocommunity analysis indicated structure in the consumer–resource matrix. In some comparisons, prey overlaps among species were greater within than between higher taxa, and closely related species tended to be found in similar habitat patches and microhabitats, suggesting that resource-use patterns are determined to some extent by phylogeny. Ecology, morphology, and phylogeny appear tied together in a complex manner, with resource partitioning contributing to maintenance of structure. Historical interactions among closely related species may have been important in determining which species within particular clades invaded and persisted within local assemblages in lowland forest.
Settlement patterns and nest-site selection of Cliff Swallows, Hirundo pyrrhonota: males prefer to clump but females settle randomly
Authors: Meek Susan B. , Barclay Robert M. R.
Published: May 2008

We assessed the settlement pattern of colonial Cliff Swallows (Hirundo pyrrhonota) to examine whether they avoid settling near to each other or prefer to nest in close proximity. Male Cliff Swallows occupied and defended nests before females paired with them, and males settled next to other males significantly more often than expected by chance. In contrast to that of males, female settlement was not significantly different from random: females neither preferred nor avoided settling next to other Cliff Swallows, nor did females select old nests on the basis of nest stability. Neither males nor females chose nests in the same order from year to year, suggesting that quality of old nests was not an important factor affecting settlement patterns. Male arrival date is related to quality in some species, but female Cliff Swallows did not select the earliest arriving males. There was also no correlation between the order in which females chose mates and male traits. All nest sites may have offered females an equal probability of success, leading to random settlement with respect to other females, nests, and males.
Ultrastructure of uterine trophonemata, accommodation for uterolactation, and gas exchange in the southern stingray, Dasyatis americana
Authors: Hamlett William C. , Musick John A. , Eulitt Allison M. , Jarrell Robert L. , Kelly Matthew A.
Published: May 2008

The southern stingray, Dasyatis americana, displays aplacental viviparity, embryos being retained in the maternal uterus throughout gestation and initially nourished by the yolk sac contents. During gestation the uterus develops vascularized appendages, trophonemata, that secrete viscous nutrient histotroph that is subsequently ingested by the embryo as it grows to term. There is a 3750% increase in wet mass from the egg to the term fetus. Trophonemata are 1.5 cm long, narrower at the base, and spatulate at the tip. Surface epithelial cells form a pattern of surface cables, each with a small blood vessel at its core. In females containing fertilized eggs, the epithelium is simple and cuboidal. In contrast, in uteri containing late-term fetuses, the epithelium is squamous. Epithelial cells, with periodic acid – Schiff positive cytoplasmic vesicles, form invaginated crypts. Epithelial cells produce proteinaceous, mucous, and lipid secretions, thus we have coined the term uterolactation to describe this phenomenon.
Ultrastructure of fetal alimentary organs: stomach and spiral intestine in the southern stingray, Dasyatis americana
Authors: Hamlett William C. , Musick John A. , Eulitt Allison M. , Jarrell Robert L. , Kelly Matthew A.
Published: May 2008

In the fetal southern stingray, Dasyatis americana, both the stomach and spiral intestine function early in development to digest and absorb nutrient histotroph elaborated by uterine villi termed trophonemata. The gastric mucosa consists of a surface columnar mucous epithelium that is confluent with gastric pits or foveolae. Gastric glands are populated by oxynticopeptic and enteroendocrine cells. The surface mucous cells are pyramidal with apical microvilli. Oxynticopeptic cells are low columnar with a distinct and elaborate tubulovesicular system in the apical cytoplasm. Microvilli line the lumen of the gastric glands and cells have elaborate interdigitating lateral folds. Enteroendocrine cells are characterized by basal granules and a prominent rough endoplasmic reticulum. The fetal intestine is filled with bile-tinged viscous fluid. A core of submucosa supports spiral intestinal plicae that form the spiral valve from which villi project. The most prominent characteristic of the cells are enormous supranuclear vesicles formed by coalescence of smaller endocytotic vesicles. The apical cytoplasm has a profusion of smooth tubules, endoplasmic reticulum, and lysosomes. The large vesicles are interpreted as storage depots for continually ingested histotroph. Small vesicles may then bud off to be digested via the lysosomal system.
Diet of the lowland tapir (Tapirus terrestrisL.) in the Tabaro River valley, southern Venezuela
Authors: Salas Leonardo A. , Fuller Todd K.
Published: May 2008

In this study we document the diet, determine diet selection, and evaluate the seed-dispersal role of lowland tapirs (Tapirus terrestris L.) in the Tabaro River valley of southern Venezuela. The diet was assessed by checking treefall gaps and closed-canopy areas of equal size for browsing signs, examining droppings for seeds and fruit remains, and casually asking experienced Ye'kwana Indian hunters. Plants browsed by tapirs were identified and counted. The abundance of each plant species at the study site was determined using 25-m2quadrats and compared with its abundance in the diet to determine selectivity. Because tapirs defecate in water, their role as seed dispersers was examined by analyzing the distribution of diet species using a data base of the locations of trees at the study site. Information from the 25-m2quadrats was used for lianas and shrubs. Results show that tapirs selectively browse on 88 out of at least 256 plant species, consistently avoiding more species in closed-canopy areas. Some species occur significantly more frequently in the diet than their relative abundance in the forest. Tapirs eat fruits of 33 species; 2 of these are mainly found near the water and 9 away from the water.
Habitat use by lowland tapirs (Tapirus terrestrisL.) in the Tabaro River valley, southern Venezuela
Authors: Salas Leonardo A.
Published: May 2008

This study presents an analysis of habitat use by lowland tapirs (Tapirus terrestris L.) in the Tabaro River valley of southern Venezuela. Five different habitat types were recognized in the study area and their proportions determined. Treefall gaps within these habitats were also analyzed as a distinctive type. The presence of tapirs was determined by following fresh tracks, counting tracks found by walking along transects and creeks, and checking gaps and closed-canopy areas of equal size for browsing signs. The numbers of tracks and sightings recorded near to and away from the water were compared for two periods of the year to assess changes in habitat use due to the availability of fruits of one food-plant species. Assessment of habitat use by counting or following tracks in each habitat type was biased toward moist soils. Tapirs forage preferentially in gaps and use all areas of the forest, but a significantly larger number of signs was found in lower elevation areas. A preference for lower elevation areas is correlated with the abundance of the commonest food-plant species. Tapirs may change their foraging behavior and habitat use to ingest more fruits of plant species in season.