bluuebunny/crossref_metadata_2025 huggingface dataset:
The response of benthic rhizopods to sediment disturbance does not support the intermediate disturbance hypothesis
Authors: Garstecki Tobias , Wickham Stephen A.
Published: October 2003

Disturbance is one of the mechanisms which counteract competitive exclusion of populations in resource‐limited communities, thereby facilitating coexistence and maintaining community species diversity. The intermediate disturbance hypothesis predicts maximum diversity at intermediate disturbance intensities and frequencies. This paper reports results of an experimental test of this hypothesis using a coastal benthic community of rhizopods (Protozoa: Rhizopoda), and experimental sediment resuspension as a simulated natural disturbance. We carried out two experiments of 5 d duration which focussed on the effects of resuspension intensity and frequency, respectively, on the abundance, species richness and on the Shannon‐Weaver diversity index of rhizopod communities in surface sediments of natural sediment cores from the coastal southern Baltic. Care was taken to adjust the experimental treatments to the natural disturbance regime in this area.

Twenty‐four and 28 rhizopod species were present during the intensity and frequency experiment, respectively. Small bacterivorous rhizopods of the Vannellidae, Cochliopodidae, Paramoebidae and Rhizopoda incertae sedis dominated the communities during both experiments. Rhizopod abundance, species richness and diversity increased towards the end of the intensity experiment, but they did not show effects of disturbance intensity. Similarly, no effects of disturbance frequency were found during the frequency experiment. Our results indicate that coexistence and community diversity maintenance in benthic rhizopod communities, and probably in benthic heterotrophic protistan communities in general, may rely on different mechanisms than intermediate disturbance, such as trophic niche separation and high rates of dispersal and colonisation.
Linking frequencies of acorn masting in temperate forests to long‐term population growth rates in a songbird: the veery (Catharus fuscescens)
Authors: Schmidt Kenneth A.
Published: October 2003

Many terrestrial ecosystems are characterized by intermittent production of abundant resources for consumers, termed pulsed resources. The impact of resource pulses on populations downwind of the initial pulse are only beginning to be characterized, while the relationship between the frequencies of pulses and the long‐term growth rate of affected species is unknown. I monitored the reproductive success of veeries (Catharus fuscescens) breeding in oak‐dominated forest in southeastern New York State from 1998 to 2002. During this time veeries experienced high interannual variability in growth rates as a consequence of trophic cascades stemming from pulsed production of acorns. Rodent populations that benefited from acorns also depredated veery nests, while raptors that increased in response to rodent outbreaks are major predators on adult and juvenile birds. Veeries may recoup losses following low to moderate acorn crops that lead to rodent population declines. Thus, veeries fluctuate between years of positive and negative growth rate, however, long‐term population trends, and thus true source‐sink designation, cannot be made until the frequency of various year types is characterized. I simulated long‐term growth rates using reproductive parameters estimated from field studies and survivorship data from the literature. Simulations suggest that variability in the frequency of masting events in oaks can lead to ∼10% fluctuation in long‐term growth rates in veeries. These studies suggest that temporal variability in masting dynamics has the potential to substantially influence songbird population trends. Furthermore, spatial variability in masting characteristics (e.g. the frequency of masting events and/or the size of seed crops) may greatly contribute to regional differences in songbird population trends. Because even less is known about the relationship between sizes of acorn crops and songbird populations, the influence of pulses in seed production on songbird population dynamics is likely to be underestimated.
Density dependent population growth of the two‐spotted spider mite, Tetranychus urticae, on the host plant Leonurus cardiaca
Authors: Rotem Karin A. , Agrawal Anurag A.
Published: October 2003

We observed Tetranychus urticae (Koch), a polyphagous spider mite herbivore, on Leonurus cardiaca (L.) at several sites in eastern North America at variable density, ranging from extremely dense to sparse. To understand the nature of T. urticae's population dynamics we experimentally manipulated population densities on L. cardiaca and assessed per capita growth after 1 to 2 generations in laboratory and field experiments. In particular, we took a ‘bottom‐up’ approach, manipulating both plant size and quality to examine effects on mite dynamics. Per capita growth was strongly dependent on the initial density of the mite population. Spider mite populations grew (1) in a negatively density dependent manner on small plants and (2) unhindered by density dependence on large plants. Mean per capita growth was 59% higher on small plants compared to large plants, irrespective of mite density. We also found evidence for density dependent induced susceptibility to spider mites in small plants and density dependent induced resistance in large plants. Hence, spider mite populations grew at a relatively fast rate on small plants, and this was associated with negative density dependence due to factors that depress population growth, such as food deterioration or limitation. On large plants, spider mite populations grew at a relatively slow rate, apparently resulting in herbivore densities that may not have been high enough to cause intraspecific competition or other forms of negative density dependence.
Birds have no impact on folivorous insect guilds on a montane willow
Authors: Low Candace , Connor Edward F.
Published: October 2003

We examined the impact of avian predators on the community of insects feeding on Lemmon's willow, Salix lemmonii, at Carman Valley, California. Salix lemmonii supports a diverse assemblage of insect species that feed in either a concealed or an exposed manner on leaves by mining, tying, curling, galling, skeletonizing, or chewing. We tested the hypothesis that there are guild specific differences in the effects of avian predators on concealed and exposed‐feeding folivores. We compared the feeding damage and frequency of each guild in the presence and absence of avian predators. Contrary to most studies of the effects of avian predators on folivorous insects, birds failed to reduce significantly the frequency of or feeding damage caused by exposed‐feeding insects during 1999 and 2000. Chewing insects, which accounted for the majority of foliar damage by exposed‐feeding insects, inflicted slightly more damage and skeletonizing insects slightly less damage in the presence of birds. We also observed no reduction in the frequency of concealed‐feeding insects in the presence of avian predators; rather three out of four guilds were slightly more common in the presence of avian predators. While the abundance of foliage gleaning birds at the study site was slightly lower than the average for the past nine years, we interpret our results to indicate a true lack of an effect of avian predators on the community of folivorous insects on S. lemmonii. Future inquiry into the effects of avian predators on folivorous insects should focus on determining under what circumstances birds will or will not suppress guilds of folivorous insects.
A test of host specialization by insect vectors as a mechanism for reproductive isolation among entomophilous fungal species
Authors: Bultman Thomas L. , Leuchtmann Adrian
Published: October 2003

Epichloë species are self incompatible (heterothallic) fungi that must be fertilized by spermatia from individuals of opposite mating type for successful sexual reproduction to occur. Female flies of the genus Botanophila act as vectors of the fungi by ingesting and defecating spermatia (gametes) onto fungal stromata (fruiting bodies) after oviposition. Larvae feed and develop on the stromata and thus maintain a symbiotic relationship with Epichloë fungi. We hypothesized that sole dependence on fertilized stromata as a food source would promote specialization by flies to single compatible host species and that this specialization would promote reproductive isolation among Epichloë species. Analysis of progeny of ascospores from experimental field plots in Zurich, Switzerland, indicated prevalence of specific matings between stromata of the same host, and thus was consistent with the hypothesis that flies are species‐specific in their visitation behaviour. Genetic analyses of spermatia contained in the faeces of individual flies also gave some support for this hypothesis. We recovered spermatia of 4 different Epichloë species from fly faeces. Comparison of spermatia found in fly faeces to those available from stromata showed flies avoided Epichloë clarkii and may have preferred Epichloë typhina. Interestingly, these are the only two Epichloë species known to be interfertile with one another. Individual flies tended to carry spermatia predominantly from one fungal species. Thus, flies may adopt a type of “majoring” and “minoring” behaviour when visiting fungi. Yet, Botanophila flies are not monolectic and often visited all hosts that were available within screened cages. In addition to any reproductive isolation flies may provide to some fungal species, differences in competitiveness among spermatia of different species deposited on the same stroma may favor intraspecific matings.
How litter quality affects mass loss and N loss from decomposing Sphagnum
Authors: Limpens Juul , Berendse Frank
Published: October 2003

Nitrogen (N) deposition may affect litter decomposition and may thus have an impact on the rate of carbon (C) sequestration in Sphagnum peatlands. We present results from four separate experiments aimed at delineating the effects of litter N‐enrichment, Sphagnum species, stem part of Sphagnum, and place of incubation on decomposition rate and N release. We measured mass loss and N loss from litterbags incubated at 10‐15 cm in the field for one year.

Mass loss was positively related to the N/C quotient of the litter, but depended strongly on the range in N/C quotients observed; only a distinct difference in N/C quotients affected mass loss. Although hummock species decayed at a slower rate than hollow species, the differences between the species became less pronounced for old stem parts and for N‐enriched litter. Old stem parts decayed at a slower rate than young stem parts, except for S. papillosum. Neither position of incubation (low hummock or hollow), nor the inorganic N concentration of the incubation environment affected mass loss. N loss was mainly determined by, and positively related to, the N/C quotient of the litter; species and stem part had minor effects. Above a N/C quotient of about 0.015, net N loss was observed for all species.

We conclude that decomposition of Sphagnum is stimulated by N deposition. As the latter also affects litter N concentration and thus N release, we think that positive feedbacks through changing litter quality should be taken into account when modelling the effects of N deposition on Sphagnum peatlands and C sequestration in these systems.
Are spatially correlated or uncorrelated disturbance regimes better for the survival of species?
Authors: Johst Karin , Drechsler Martin
Published: October 2003

The survival of species in dynamic landscapes (characterised by patch destruction and subsequent regeneration) depends on both the species’ attributes and the disturbance pattern. Using a spatially explicit model we explored how the mean time to extinction of a metapopulation depends on the spatial correlation of patch destruction in relation to the population growth and dispersal abilities of species. Two contrasting answers are possible. On the one hand, increasing spatial correlation of patch destruction increases the spatial correlation of population growth and this is known to decrease metapopulation persistence. On the other hand, spatially correlated patch destruction and regeneration can lead to clustered habitat patches and this is known to increase metapopulation persistence. Therefore, we hypothesised that some species are better off under spatially correlated and alternatively uncorrelated disturbance regimes. However, contrary to this hypothesis, in all kinds of cases spatial correlation reduced metapopulation persistence. We found this to be due to the fact that the spatial correlation of patch destruction causes increasing temporal fluctuations in the regional carrying capacity of the metapopulation and is hence generally disadvantageous for long‐term persistence. The main consequence for conservation biology is that reducing spatial correlation in disturbances is likely to be a reliable strategy in a dynamic landscape that will benefit practically all species with a low risk of adverse side effects.
Community assembly time and the relationship between local and regional species richness
Authors: Mouquet N. , Munguia P. , Kneitel J. M. , Miller T. E.
Published: October 2003

Many previous studies have assumed that a linear relationship between local and regional species richness indicates that communities are limited by regional processes, while a saturating relationship suggests that species interactions restrict local richness. We show theoretically that the relationship between local and regional richness changes in a consistent fashion with assembly time in interacting communities. Communities show saturation in their early assembly stages because only a subset of the regional pool may colonize a locality. At intermediate assembly times, communities will appear unsaturated until significant competitive exclusion occurs. Finally, when communities reach equilibrium, we found saturation as a result of resource competition resulting in the dominance of a limited number of species. We show that habitat size and species fecundity are important in determining the time needed for the community to reach equilibrium and thus affect the relationship between local and regional species richness. Our results suggest the number of coexisting species is a function of local and regional processes whose relative influences might vary over time and that research using the relationship between local and regional species richness to infer mechanisms limiting species richness must have knowledge of the assembly time of the community.
Crowding‐induced responses in a geometrid moth revisited: a field experiment
Authors: Ruohomäki Kai , Klemola Tero , Kaitaniemi Pekka , Käär Miia
Published: October 2003

In Lepidoptera, effects of larval crowding on life history traits may manifest themselves as changes in growth rate and duration of larval period. For the outbreaking geometrid moth, Epirrita autumnata, impacts of crowding have been shown in earlier laboratory studies, and these responses were modified by diet quality. In this study, the aim was to find out the specific nature of crowding effects of E. autumnata in the field. E. autumnata larvae were reared individually and in groups in mesh bags on mountain birch, both on good and poor quality foliage. Three field experiments were carried out with different densities in the crowded treatment (12, 21 and 45 larvae per 100 short shoots of mountain birch), simulating intermediate to severe outbreaks. The study revealed the density interval (12–21) within which impacts of crowding become evident. Significant effects were mostly found with the two highest densities in the crowded treatment combined with poor foliage quality. In those treatments, crowding resulted in 8–12% and 24–33% decrease in pupal mass and larval survival, respectively. The results of the present field experiments, however, did not corroborate the results of earlier laboratory studies: duration of larval period was not substantially affected, net effects of crowding were negative and interactions between crowding and foliage quality were contrary to those obtained in earlier laboratory studies. In many other Lepidoptera as well, the knowledge on responses to crowding may be mostly qualitative since most crowding experiments have been conducted in laboratory.
Effects of light and prey availability on nocturnal, lunar and seasonal activity of tropical nightjars
Authors: Jetz Walter , Steffen Jan , Linsenmair Karl Eduard
Published: October 2003

Nightjars and their allies represent the only major group of visually hunting aerial insectivores with a crepuscular and/or nocturnal lifestyle. Our purpose was to examine how both light regime and prey abundance in the tropics, where periods of twilight are extremely short, but nightjar diversity is high, affect activity across different temporal scales. We studied two nightjar species in West African bush savannah, standard‐winged nightjars Macrodipteryx longipennis Shaw and long‐tailed nightjars Caprimulgus climacurus Vieillot. We measured biomass of potential prey available using a vehicle mounted trap and found that it was highest at dusk and significantly lower at dawn and during the night. Based on direct observations, both nightjars exhibit the most intense foraging behaviour at dusk, less intense foraging at dawn and least at night, as predicted by both prey abundance and conditions for visual prey detection. Nocturnal foraging was positively correlated with lunar light levels and ceased below about 0.03 mW m−2. Over the course of a lunar cycle, nocturnal light availability varied markedly, while prey abundance remained constant at dusk and at night was slightly higher at full moon. Both species increased twilight foraging activity during new moon periods, compensating for the shorter nocturnal foraging window at that time. Seasonally, the pattern of nocturnal light availability was similar throughout the year, while prey availability peaked shortly after onset of the wet season and then slowly decreased over the following four months. The courtship and breeding phenology of both species was timed to coincide with the peak in aerial insect abundance, suggesting that prey availability rather than direct abiotic factors act as constraints, at least at the seasonal level. Our findings illustrate the peculiar constraints on visually orienting aerial nocturnal insectivores in general and tropical nightjars in particular and highlight the resulting nocturnal, lunar and seasonal allocation of activities.
Neuropeptide Y (NPY) Delays the Oestrogen‐Induced Luteinizing Hormone (LH) Surge in the Ovariectomized Ewe: Further Evidence That NPY has a Predominant Negative Effect on LH Secretion in the Ewe
Authors: Estrada K. M. , Pompolo S. , Morris M. J. , Tilbrook A. J. , Clarke I. J.
Published: October 2003

Studies in rats suggest that neuropeptide Y (NPY) plays a stimulatory role in the generation of the preovulatory luteinizing hormone (LH) surge, via the Y1 receptor. We have investigated this issue using the oestradiol benzoate (EB)‐treated ovariectomized (OVX) ewe which is a model for the preovulatory LH surge. A Y1 receptor antagonist (BIBO3304) was infused (25 µg/h) into the third cerebral ventricle (III‐V) from 2 h before EB injection for 24 h, and had no effect on the ensuing LH surge. Using in situ hybridization, we then examined expression of NPY mRNA in the arcuate nucleus during the luteal, follicular and oestrous phases of the oestrous cycle, and found that levels were greatest during the luteal phase. Thus, reduced NPY synthesis might be an integral factor in the events leading to the cyclic preovulatory LH surge. This was tested by infusion of NPY (25 µg/h) into the III‐V (as above). The NPY infusion delayed the LH surge until the infusion was ceased. High levels of NPY expression during the luteal phase of the oestrous cycle may be caused by progesterone. Thus, we determined whether NPY cells possess progesterone receptors (PR) and whether progesterone treatment up‐regulates NPY mRNA expression in the arcuate nucleus. Immunohistochemistry for NPY and PR was performed in OVX, oestrogen‐treated ewes, but no NPY cells of the arcuate nucleus were seen to colocalize PR. In situ hybridization for NPY was performed in OVX and OVX ewes treated with progesterone. There was no significant effect of progesterone treatment on NPY mRNA expression in the arcuate nucleus. We conclude that chronically elevated levels of NPY block the preovulatory surge of gonadotropin‐releasing hormone/LH secretion in sheep, but high levels of NPY mRNA expression in the luteal phase of the oestrous cycle cannot be explained by an action of progesterone.
Neurone‐Specific Expression and Regulation of the Pufferfish Isotocin and Vasotocin Genes in Transgenic Mice
Authors: Gilligan P. , Brenner S. , Venkatesh B.
Published: October 2003

We used comparative genetics to investigate the location, structure and evolution of the oxytocin and vasopressin gene regulatory regions. The pufferfish, Fugu rubripes, is an attractive vertebrate model for comparison because of its maximal evolutionary distance from mammals and short intergenic regions. To determine whether regulatory DNA is conserved between oxytocin and vasopressin, and their Fugu homologs, isotocin and vasotocin, we generated transgenic mice bearing overlapping Fugu cosmids that contained the isotocin and/or vasotocin genes as well as short isotocin (5 kb) and vasotocin (9 kb) constructs. Our study shows that the Fugu isotocin and vasotocin genes express specifically in the mouse oxytocinergic and vasopressinergic neurones, respectively, and that the cis‐regulatory elements which mediate neurone‐specific expression are located within the short transgene constructs tested. Thus, the neurone‐specific expression of the oxytocin and vasopressin gene families, and the mechanisms mediating the cell‐specificity, evolved before the divergence of the fish and mammalian lineages. Salt‐loading of transgenic mice induced an increase in abundance of isotocin, but not vasotocin mRNA in the cognate neurones. It appears that either the vasotocin gene does not respond to osmotic perturbations or the vasotocin transgene construct tested lacks osmotic response elements. Comparisons of homologous flanking sequences of the Fugu and mouse genes identified several short matching sequences, which are candidate regulatory elements.
Food Restriction During Lactation Results in Prolonged Hyposensitivity to the Positive‐Feedback Effects of Oestradiol
Authors: Abizaid A. , Service G. , Woodside B.
Published: October 2003

Food restriction prolongs lactational infertility in rats. Here, we investigated whether an attenuated response to the positive‐feedback effects of oestrogen on luteinizing hormone release contributed to this effect. The ability of oestrogen to induce surges in luteinizing hormone in ad libitum fed and food‐restricted dams at different times of lactation was compared. The results showed that, on day 20 postpartum, ad libitum fed dams showed luteinizing hormone surges after oestrogen treatment, but food‐restricted dams did not. Ovariectomy or RU486 treatment restored the ability of oestrogen to induce luteinizing hormone surges in food‐restricted dams, and chronic progesterone exposure reduced oestrogen‐induced surges of luteinizing hormone in ad libitum fed ovariectomized dams. Food restriction also resulted in a reduced ability of oestrogen to induce progesterone receptor immunoreactivity, but did not reduce the number of oestrogen receptors (ERα) in the anteroventralperiventricular area. As with the surge in luteinizing hormone, the effects of food restriction on oestrogen induction of progesterone receptors were mediated by progesterone. Together, these results suggest that the ability of food restriction to extend the length of lactational diestrus is mediated, in part, by a decrease in sensitivity to the positive‐feedback effects of oestrogen. This results from high circulating concentrations of progesterone which apparently reduce the ability of oestrogen to induce progesterone receptor expression.
Changes in Agouti‐Related Peptide During the Ring Dove Breeding Cycle in Relation to Prolactin and Parental Hyperphagia
Authors: Strader A. D. , Buntin J. D.
Published: October 2003

Ring doves (Streptopelia risoria) exhibit marked increases in food consumption and decreases in body weight when they are provisioning their young. This study examined changes in hypothalamic immunostaining for agouti‐related peptide (AGRP), an endogenous melanocortin receptor antagonist and appetite stimulant, during the ring dove breeding cycle. Because prolactin is orexigenic in doves, and is elevated in blood at the onset of parental hyperphagia, we also explored the possibility that prolactin‐induced hyperphagia is associated with AGRP changes. The numbers of AGRP‐immunoreactive (ir) cells within the tuberal hypothalamus were maximal during the prelaying period of the breeding cycle but decreased dramatically during early incubation. AGRP‐ir cell numbers began to increase again during late incubation and reached a peak during the early and late posthatching stages. Because posthatching elevations in AGRP‐ir were temporally associated with marked elevations in parental food intake, and because AGRP is orexigenic in doves, these findings suggest that increased AGRP activity in the dove tuberal hypothalamus may contribute to parental hyperphagia. Rising prolactin secretion during late incubation and early posthatching may initiate this increase in AGRP‐ir, since intracerebroventricular administration of prolactin significantly elevated food intake and AGRP‐ir cell numbers in the tuberal hypothalamus of nonbreeding doves. Prolactin‐induced elevations in AGRP‐ir cell numbers persisted when the confounding effects of weight gain that accompany prolactin‐induced hyperphagia in nonbreeding doves were eliminated by a food restriction procedure, thereby suggesting that prolactin can directly influence AGRP activity under neutral energy state conditions.
Enhanced Up‐Regulation of Corticotropin‐Releasing Hormone Gene Expression in Response to Restraint Stress in the Hypothalamic Paraventricular Nucleus of Oxytocin Gene‐Deficient Male Mice
Authors: Nomura M. , Saito J. , Ueta Y. , Muglia L. J. , Pfaff D. W. , Ogawa S.
Published: October 2003

The neuropeptide oxytocin is released not only into the blood, but also within the brain in response to various stressors. Accumulating evidence suggests that central oxytocin may play a major role in the regulation of neuroendocrine responses to stress. In the present study, using the oxytocin knockout mouse model, we tested whether oxytocin might act to attenuate stress‐induced up‐regulation of corticotropin‐releasing hormone (CRH) mRNA expression in the brain. The expression of CRH mRNA in the paraventricular nucleus (PVN) after 4 h of restraint stress was examined in oxytocin gene‐deficient (OTKO), wild‐type and heterozygous male mice using in situ hybridization histochemistry. We found that basal levels of CRH mRNA were not different among the three genotypes. Although restraint stress resulted in a significant increase of CRH mRNA expression in the PVN regardless of genotype, the degree of stress induced‐up‐regulation was significantly higher in OTKO mice than in wild‐type mice. The effects of restraint stress on the expression of the arginine vasopressin (AVP) and the oxytocin genes were also examined. Unlike CRH mRNA, basal expression (in nonstressed control groups) of AVP mRNA in OTKO mice, as well as oxytocin mRNA in heterozygous mice, was significantly lower in the PVN and the supraoptic nucleus than in wild‐type mice. After restraint stress, the expression of AVP mRNA was significantly increased in the PVN of OTKO mice compared to the nonstressed control group, whereas the expression of both AVP and oxytocin mRNA were unchanged in the PVN and the supraoptic nucleus of wild‐type and heterozygous mice. Finally, in a separate set of mice, restraint stress‐induced Fos expression was also examined in several brain regions involved in stress response, including the lateral septum, the bed nucleus of the stria terminalis (BNST), the medial preoptic area, the PVN, the medial and central amygdala using immunohistochemistry. After 90 min of restraint stress, the number of Fos‐expressing cells significantly increased in all brain regions examined regardless of genotype. However, the number of stress‐induced Fos‐expressing cells in the BNST and the medial amygdala of OTKO mice was significantly lower than in wild‐type mice. Collectively, the findings in the present study suggest that oxytocin may regulate stress‐induced CRH gene expression in the PVN. Furthermore, neuronal activity in the BNST and the medial amygdala may be involved in this neuroendocrine regulatory system.
Corticotropin‐Releasing Hormone Immunoreactivity in Human T and B Cells and Macrophages: Colocalization With Arginine Vasopressin
Authors: Baker C. , Richards L. J. , Dayan C. M. , Jessop D. S.
Published: October 2003

Corticotropin‐releasing hormone (CRH) and arginine vasopressin (AVP) are expressed in cells of the immune system where they exert immunomodulatory roles, but these neuropeptides are poorly characterized in human immune tissues. The aim of this study was to determine concentrations and distribution of CRH and AVP in nonactivated human peripheral blood mononuclear cells (PBMC). PBMC from normal human subjects were separated into enriched subpopulations of T and B cells and monocytes/macrophages by a magnetic bead/monoclonal antibody technique. CRH and AVP were measured in cell extracts by radioimmunoassay (RIA). CRH‐immunoreactivity (ir) ranged 0.24–0.8 fmol/million cells (n = 6 subjects) in T cell extracts, 0.4–2.7 fmol/million cells (n = 4) in B cells and 0.63–2.16 fmol/million cells (n = 4) in macrophages. AVP‐ir ranged 0.2–0.95 fmol/million cells in T cell extracts, <0.1–0.8 fmol/million cells in B cells and 0.14–3.19 fmol/million cells in macrophages. Reversed‐phase high‐performance liquid chromatography (HPLC) of T and B cell extracts revealed a peak of CRH‐ir which coeluted with synthetic CRH‐41; this peak was not present in macrophages. A second peak of CRH‐ir which eluted in a more hydrophobic position was observed in extracts of T and B cells and macrophages. This unidentified form of CRH‐ir is the predominant form of CRH‐ir in nonactivated human PBMC. This is the first study to demonstrate that CRH‐ir and AVP‐ir are colocalized within human T cells, B cells and monocytes/macrophages. We have confirmed observations of a variant form of CRH‐ir in human PBMC and show that this is the predominant form in macrophages and B cells whereas CRH‐ir, which coelutes with CRH(1–41) on HPLC, is present in significant amounts only in T cells. These data also confirm that CRH‐ir in human PBMC is not urocortin because the antiserum used in the CRH RIA does not bind to urocortin.
Acute Glucocorticoid Pretreatment Suppresses Stress‐Induced Hypothalamic‐Pituitary‐Adrenal Axis Hormone Secretion and Expression of Corticotropin‐Releasing Hormone hnRNA but Does Not Affect c‐fos mRNA or Fos Protein Expression in the Paraventricular Nucleus of the Hypothalamus
Authors: Ginsberg A. B. , Campeau S. , Day H. E. , Spencer R. L.
Published: October 2003

Corticosterone regulates both basal and stress‐induced hypothalamic‐pituitary‐adrenal (HPA) axis activity in a negative‐feedback fashion. However, the cellular and molecular mechanisms of this negative feedback have yet to be explicitly characterized. By comparing stress‐induced c‐fos and corticotropin‐releasing hormone (CRH) expression in the paraventricular nucleus (PVN), we may be able to determine whether acute glucocorticoid treatment affects the net neural excitatory input to the PVN (represented primarily by c‐fos mRNA expression) or directly affects the ability of cells in the PVN to respond to that input (represented primarily by CRH hnRNA expression). In the following studies, we observed the effect of acute glucocorticoid (RU28362) treatment on subsequent HPA axis reactivity by measuring stress‐induced plasma hormone concentration [corticosterone and adrenocorticotropic hormone (ACTH)] and gene expression (c‐fos and CRH) in the PVN. First, we examined the dose–response relationship between systemically administered RU28362 (1–150 µg/kg, i.p) and suppression of the stress‐induced corticosterone response. We then confirmed central nervous system access of the maximally suppressive dose of RU28362 (150 µg/kg) by an ex vivo radioligand binding assay. RU28362 selectively occupied the majority of glucocorticoid receptors in the hippocampus and hypothalamus while having no effect on mineralocorticoid receptors. In separate studies, RU28362 (150 µg/kg) and corticosterone (5 mg/kg) were injected i.p. 1 h before restraint stress. Compared to vehicle‐treated controls, rats treated with RU28362 and corticosterone had substantially blunted stress‐induced corticosterone and ACTH production, respectively. Furthermore, treatment with RU28362 significantly blunted stress‐induced CRH hnRNA expression in the PVN. By contrast, neither RU28362 nor corticosterone treatment had an effect on stress‐induced neuronal activation as measured by c‐fos mRNA and its protein product in the PVN. This dissociation between c‐fos and CRH gene expression suggests that glucocorticoid suppression of HPA activity within this time‐frame is not a result of decreased excitatory neural input to the PVN, but instead depends on some direct effect of RU28362 on cells intrinsic to the HPA axis.
Melatonin Implants Disrupt Developmental Synchrony Regulated By Flexible Interval Timers
Authors: Gorman M. R.
Published: October 2003

Siberian hamsters born into short daylengths near the end of the breeding season are reproductively inhibited from birth and delay gonadal maturation until the following spring. This vernal transition to a reproductive phenotype coincides with an abrupt increase in body weight, and both processes are triggered by an interval timing mechanism that becomes insensitive, or refractory, to short‐day inhibition. It was previously demonstrated that hamsters born into simulated natural photoperiods in early August became photorefractory at later ages than hamsters born into September photoperiods. As a consequence of flexibility in the duration programmed by the interval timer, development of seasonal birth cohorts was synchronous with respect to the calendar date simulated by laboratory photoperiod. In the present study, hamsters were born into simulated August or September photoperiods. Hamsters from each cohort were given removable constant release melatonin implants to reversibly obscure the neuroendocrine representation of daylength between 3 and 9 weeks or 9–15 weeks of age. When control hamsters were given beeswax capsules throughout, August‐born males were approximately 6 weeks older than September males at the onset of photorefractoriness as assessed by accelerated increases in body weight and testicular size. Females exhibited the same pattern in body weight. These measures were synchronized with respect to calendar date. Synchronization of cohorts was disrupted by melatonin capsules from 3–9 weeks of age but not by later implants. Melatonin implants altered synchronization by influencing the developmental trajectory of September‐born hamsters without influencing the August cohort. These results demonstrate that the function of the interval timer underlying photorefractoriness is influenced by photoperiod and by melatonin. The endogenous pattern of melatonin signals adjusts the duration measured by the interval timer to insure that developmental milestones of seasonal cohorts are synchronized with environmental conditions.
Genetic evidence for female‐biased dispersal in the bullfrog, Rana catesbeiana (Ranidae)
Authors: Austin James D. , Dávila José A. , Lougheed Stephen C. , Boag Peter T.
Published: October 2003

Sex‐biased dispersal is an important but unexplored area of amphibian ecology. We predicted female‐biased dispersal in the bullfrog (Rana catesbeiana) based on aspects of their mating system and tested this prediction using data from seven polymorphic DNA microsatellite loci. Allelic (F‐statistics) and genotypic [assignment index, (AIc)] frequencies from nine Ontario populations support our prediction, although significant sex differences in inbreeding and variance of AIc were not detected. The diversity of mating systems found in amphibians represents an important avenue for investigating the relationship between reproductive systems, dispersal and phylogeny.
Genetic structure of Mesoamerican populations of Big‐leaf mahogany (Swietenia macrophylla) inferred from microsatellite analysis
Authors: Novick Rachel Roth , Dick Christopher w. , Lemes Maristerra R. , Navarro Carlos , Caccone Adalgisa , Bermingham Eldredge
Published: October 2003

While microsatellites have been used to examine genetic structure in local populations of Neotropical trees, genetic studies based on such high‐resolution markers have not been carried out for Mesoamerica as a whole. Here we assess the genetic structure of the Mesoamerican mahogany Swietenia macrophylla King (big‐leaf mahogany), a Neotropical tree species recently listed as endangered in CITES which is commercially extinct through much of its native range. We used seven variable microsatellite loci to assess genetic diversity and population structure in eight naturally established mahogany populations from six Mesoamerican countries. Measures of genetic differentiation (FST and RST) indicated significant differences between most populations. Unrooted dendrograms based on genetic distances between populations provide evidence of strong phylogeographic structure in Mesoamerican mahogany. The two populations on the Pacific coasts of Costa Rica and Panama were genetically distant from all the others, and from one another. The remaining populations formed two clusters, one comprised of the northern populations of Mexico, Belize and Guatemala and the other containing the southern Atlantic populations of Nicaragua and Costa Rica. Significant correlation was found between geographical distance and all pairwise measures of genetic divergence, suggesting the importance of regional biogeography and isolation by distance in Mesoamerican mahogany. The results of this study demonstrate greater phylogeographic structure than has been found across Amazon basin S. macrophylla. Our findings suggest a relatively complex Mesoamerican biogeographic history and lead to the prediction that other Central American trees will show similar patterns of regional differentiation.
Disparate patterns of population genetic structure and population history in two sympatric penaeid shrimp species (Farfantepenaeus aztecusandLitopenaeus setiferus) in the eastern United States
Authors: Mcmillen‐Jackson A. L. , Bert T. M.
Published: October 2003

Analysing the population genetic structures of sympatric species provides opportunities to compare patterns of population genetic structure and phylogeography in order to gain insight into the factors that influence the development of the observed patterns. In this study, we compared the population genetic structures and phylogeographies of brown shrimp (Farfantepenaeus aztecus) and white shrimp (Litopenaeus setiferus), two sympatric penaeid shrimp species that inhabit the waters of the eastern USA, using sequence analysis of the mitochondrial DNA control region. Brown shrimp showed no significant phylogenetic structure or population subdivision, and closely related haplotypes were geographically dispersed. Mismatch analysis indicated that brown shrimp experienced a late‐Pleistocene era sudden population expansion. In contrast, white shrimp had a complex haplotype phylogeny consisting of two distinct lineages and two less well‐defined sublineages, and the haplotypes and lineages were geographically structured. Mismatch analysis for white shrimp also showed evidence of sudden population expansion, albeit for each lineage separately and more recently than in the brown shrimp. These disparate patterns may have developed as a result of species‐specific differences in physiological tolerances and habitat preferences that caused greater fluctuations in white shrimp population sizes and reductions in long‐term effective population size relative to that of the brown shrimp, and thereby increased the susceptibility of the white shrimp populations to stochastic genetic change.
mtDNA perspective of chromosomal diversification and hybridization in Peters’ tent‐making bat (Uroderma bilobatum: Phyllostomidae)
Authors: Hoffmann Federico G. , Owen James G. , Baker Robert J.
Published: October 2003

We compared sequence variation in the complete mitochondrial cytochrome‐bgene with chromosomal and geographical variation for specimens of Peters’ tent‐making bat (Uroderma bilobatum). Three different chromosomal races have been described in this species: a 2n = 42 race from South America east of the Andes, a 2n = 44 from NW Central America and 2n = 38 from the rest of Central America and NW South America. The deepest nodes in the tree were found within the South American race (42 race), which is consistent with a longer history of this race. Average distance among races ranged from 2.5 to 2.9%, with the highest amount of intraracial variation found within the 2n = 42 race (1.7%), intermediate values within the 2n = 38 race (0.9%) and lowest within the 2n = 44 race (0.5%). Variation among chromosomal races accounted for over 55% of molecular variance, whereas variation among populations within races accounted for 6%. The 2n = 38 and 2n = 44 races hybridize in the coastal lowlands of Honduras, near the Gulf of Fonseca. Introgression between these two races is low (two introgressed individuals in 45 examined). Clinal variation across the hybrid zone for the cytochrome‐bofU. bilobatum,is similar to clinal variation reported for chromosomes and isozymes of this species. Mismatch distribution analyses suggests that geographical isolation and karyological changes have interplayed in a synergistic fashion. Fixation of the alternative chromosomal rearrangements in geographical isolation and secondary contact is the most likely mechanism accounting for the hybrid zone between the 2n = 38 and 2n = 44 races. If a molecular clock is assumed, with rates ranging from 2.3 to 5.0% per million years, then isolation between these races occurred within the last million years, implying a relatively recent origin of the extant diversity inUroderma bilobatum. None the less, the three chromosomal races probably represent three different biological species.
Hybridization and introgression betweenCallicarpa japonicaandC. mollis(Verbenaceae) in central Japan, as inferred from nuclear and chloroplast DNA sequences
Authors: Tsukaya Hirokazu , Fukuda Tatsuya , Yokoyama Jun
Published: October 2003

Callicarpa × shirasawanais a natural hybrid betweenC.japonicaandC.mollis, and has a morphology that is intermediate between those of the parent species. Characterization of naturalCallicarpapopulations in the Atsumi Peninsula of central Japan, which all three of the above species inhabit sympatrically, revealed hybrids with various morphologies. Molecular analysis revealed a high occurrence of introgression of theC.japonicagenome into that ofC.mollis. Moreover, all individuals examined with morphology similar to that ofC.mollishad genetic traces of hybridization withC.japonica. Molecular analysis of individualC.mollisandC.japonicafrom five other areas of Japan showed that introgression ofC.japonicaintoC.mollisoccurs widely. Molecular data also strongly suggested that the previously recognizedC. × shirasawanaindividuals with intermediate morphology are not F1hybrids betweenC.japonicaandC.mollis, but instead are progeny ofC. × shirasawanabackcrossed withC.japonica. Moreover, it was revealed that individuals with F1‐type genotypes are indistinguishable morphologically from pureC.mollis. The results of the present study point to the need for re‐evaluation of natural populations ofC.mollisandC. × shirasawana.
Cytoplasmic composition in Pinus densata and population establishment of the diploid hybrid pine
Authors: Song Bao‐Hua , Wang Xiao‐Quan , Wang Xiao‐Ru , Ding Kai‐Yu , Hong De‐Yuan
Published: October 2003

Sequence and restriction site analyses of the paternally inherited chloroplast rbcL gene and maternally inherited mitochondrial nad1 fragments from the same set of populations and individuals were used to investigate cytoplasmic composition and population establishment of Pinus densata, a diploid pine that originated through hybridization between P. tabuliformis and P. yunnanensis. Two variable sites and three chlorotypes (TT, TC and GC) were detected on the rbcL gene of the three pines. P. densata harboured the three chlorotypes, two of which (TT, GC) were characteristic of the parental species, respectively. The third chlorotype (TC) was distributed extensively in seven of the 10 P. densata populations analysed, and might represent a mutation type or have been derived from an extinct parent. The distribution of chlorotypes, together with that of mitotypes, indicated that significant founder effect and backcross happened during the population establishment of the hybrid pine. P. tabuliformis and P. yunnanensis had acted as both mother and father donors, i.e. bi‐directional gene flow existed between the two parental species in the past. Population differentiation of P. densata is high, as detected from the cytoplasmic genomes: GST = 0.533 for cpDNA and GST = 0.905 for mtDNA. The differences in cytoplasmic composition among the hybrid populations suggest that the local populations have undergone different evolutionary histories.
Relationships of Palearctic and Nearctic ‘glacial relict’Myoxocephalussculpins from mitochondrial DNA data
Authors: Kontula Tytti , Väinölä Risto
Published: October 2003

The relationships amongMyoxocephalus quadricorniscomplex fish from Arctic coastal waters and from ‘glacial relict’ populations in Nearctic and Palearctic postglacial lakes were assessed using mtDNA sequence data (1978 bp). A principal phylogeographical split separated the North American continental deepwater sculpin (M. q. thompsonii) from a lineage of the Arctic marine and North European landlocked populations of the fourhorn sculpin (M. q. quadricornis). The North American continental invasion took place several glaciation cycles ago in the Early‐to‐Middle Pleistocene (0.9% sequence divergence); the divergence of the European and Arctic populations was somewhat later (0.5% divergence). The Nearctic‐Palearctic freshwater vicariance inMyoxocephalus, however, appears clearly younger than in similarly distributed ‘glacial relict’ crustacean taxa; the phylogeographical structure is more similar to that in other northern Holarctic freshwater fish complexes.
Lack of mitochondrial genetic structure in hamlets (Hypoplectrusspp.): recent speciation or ongoing hybridization?
Authors: Ramon Marina L. , Lobel Phillip S. , Sorenson Michael D.
Published: October 2003

Species in the genusHypoplectrus(hamlet fish) have been recognized primarily on the basis of colour morphology, which varies substantially. Limited differentiation in other morphological characters, however, has led to ongoing debate about their taxonomy. Our analysis of mtDNA sequences demonstrates neither reciprocal monophyly nor significant genetic differentiation among hamlet colour morphs. These data are potentially consistent with a model of recent speciation due to sexual selection on colour morphology. The presence within hamlets of two divergent mtDNA clades, however, suggests a longer history during which hybridization and gene flow have prevented the differentiation of hamlet colour morphs, at least in neutral genetic markers.