Chemical and thermal stimuli have short-lived effects on the retzius cell in the medicinal leech

During the appetitive phase of feeding, hungry leeches detect a prey by the integration of signals perceived by different sensory systems. Earlier reports suggested that chemical or thermal sensory stimulation of the lip was associated with increased afferent activity in cephalic nerves connecting the lip to the central nervous system. These authors further suggested that this activity was relayed to Retzius cells in segmental ganglia, which then released serotonin to initiate and control all aspects of feeding behavior. In this study, we show that chemosensory or thermal activation of the lip lasting for at least 5 min produces a distinct signal in the cephalic nerves consisting of action potentials of low amplitude. These small amplitude signals are clearly distinguishable from the large action potentials evoked by mechanosensory stimuli applied to the same area of the lip. Both types of sensory stimuli also evoke an increase in the firing frequency of the Retzius cells in segmental ganglia. However, the response recorded in the nerves and the Retzius cells during a maintained stimulus is not constant but decreases with an exponential time course. These results agree with our earlier observations on a semi-intact feeding preparation in which we showed that the firing frequency of the Retzius cell decreased as soon as the leech began to ingest its meal. Therefore, our data provide further evidence suggesting that it is unlikely that heat or chemical cues maintain the Retzius cell in an active state throughout the consummatory phase of feeding.     

Differential effects of serotonin depletion on sensitization and dishabituation in the leech,Hirudo medicinalis

The goal of these experiments was to test the hypothesis that serotonin (5-HT) is involved in facilitation of the shortening reflex in the leech Hirudo medicinalis. For this reason, we have used the toxin 5-hydroxytryptamine (5,7-DHT) to deplete serotonin from the nervous systems of intact leeches and have assessed the effect on early facilitation, dishabituation, and sensitization of the touch-elicited shortening reflex using behavioral procedures previously developed in our lab (Boulis and Sahley, 1988). We find that 5,7-DHT lesions completely attenuate early facilitation and sensitization but only reduce dishabituation of the touch-elicited shortening reflex. Histological analyses of the ganglia from these leeches using glyoxilic acid staining procedures revealed an absence of staining in the Retzius cell of experimental leeches. All other serotonin-containing neurons showed glyoxilic acid staining comparable to that observed in the control leeches.     

Mechanisms of postinhibitory rebound and its modulation by serotonin in excitatory swim motor neurons of the medicinal leech

Postinhibitory rebound (PIR) is defined as membrane depolarization occurring at the offset of a hyperpolarizing stimulus and is one of several intrinsic properties that may promote rhythmic electrical activity. PIR can be produced by several mechanisms including hyperpolarization-activated cation current (I_h) or deinactivation of depolarization-activated inward currents. Excitatory swim motor neurons in the leech exhibit PIR in response to injected current pulses or inhibitory synaptic input. Serotonin, a potent modulator of leech swimming behavior, increases the peak amplitude of PIR and decreases its duration, effects consistent with supporting rhythmic activity. In this study, we performed current clamp experiments on dorsal excitatory cell 3 (DE-3) and ventral excitatory cell 4 (VE-4). We found a significant difference in the shape of PIR responses expressed by these two cell types in normal saline, with DE-3 exhibiting a larger prolonged component. Exposing motor neurons to serotonin eliminated this difference. Cs⁺ had no effect on PIR, suggesting that I_h plays no role. PIR was suppressed completely when low Na⁺ solution was combined with Ca²⁺ -channel blockers. Our data support the hypothesis that PIR in swim motor neurons is produced by a combination of low-threshold Na⁺ and Ca²⁺ currents that begin to activate near –60 mV.     

Effects of transition metal ions on spontaneous electrical activity and chemical synaptic transmission of neurons in the medicinal leech

Leech neurons exposed to salines containing inorganic Ca²⁺-channel blockers generate rhythmic bursts of impulses. According to an earlier model, these blockers unmask persistent Na⁺ currents that generate plateau-like depolarizations, each triggering a burst of impulses. The resulting increase in intracellular Na⁺ activates an outward Na⁺/K⁺ pump current that contributes to burst termination. We tested this model by examining systematically the effects of six transition metal ions (Co²⁺, Ni²⁺, Mn²⁺, Cd²⁺, La³⁺, and Zn²⁺) on the electrical activity of neurons in isolated leech ganglia. Each ion induced bursting activity, but the amplitude, form, and persistence of bursting differed with the ion used and its concentration relative to Ca²⁺. All ions tested suppressed chemical synaptic transmission between identified motor neurons, consistent with block of voltage-dependent Ca²⁺ currents in these cells. In addition, a strong correlation between suppression of synaptic transmission and burst amplitudes was obtained. Finally, burst duration was increased and the rate of repolarization decreased in reduced K⁺ saline, as expected for pump-dependent repolarization. These results provide further support for the hypothesis that a novel form of oscillatory electrical activity driven by persistent Na⁺ currents and the Na⁺/K⁺ pump occurs in leech ganglia exposed to Ca²⁺-channel blockers. Accepted: 15 May 1997     

Variation in parental rearing expenditure triggers short‐term physiological effects on offspring in a long‐lived seabird

Parental care in long‐lived bird species involves a trade‐off between the benefits of increasing the effort expended on current offspring and the costs that this represents for future reproductive output. Under regimes of high environmental variability, long‐lived seabirds can adjust their breeding effort to buffer the negative effects of this variability on their offspring. However, the potential impacts of variation in breeding effort on offspring physiology in the short term and on longer‐term survival are poorly understood. In this study, we manipulated brood age through a cross‐fostering experiment to assess whether increasing or decreasing parental reproductive expenditure led to costs in Blue‐footed Booby Sula nebouxii chicks. Specifically, we tested the consequences of altered parental reproductive expenditure on the offspring's physiological condition (plasma metabolites, heterophil to lymphocyte ratio (H/L) and body condition index (BCI)) and survival. Offspring from broods in which parental investment was experimentally increased showed a lower BCI and lower alkaline phosphatase levels and higher H/L ratios than controls. Conversely, offspring showed the opposite pattern when reproductive expenditure was experimentally decreased. We observed no effects of manipulation of parental investment on triglyceride levels or on survival rates. Although our findings suggest that Blue‐footed Booby parents have the ability to adjust their breeding effort according to the demands of their offspring, parental effort could influence the effect of hatching order by suppressing the aggressive tendency of the senior chick.     

Immediate and delayed life history effects caused by food deprivation early in life in a short‐lived lizard

Detailed studies of the mechanisms driving life history effects of food availability are of prime importance to understand the evolution of phenotypic plasticity and the capacity of organisms to produce better adapted phenotypes. Food availability may influence life history trajectories through three nonexclusive mechanisms: (i) immediate and long‐lasting effects on individual quality, and indirect delayed effects on (ii) intracohort and (iii) intercohort interactions. Using the common lizard (Zootoca vivipara), we tested whether a food deprivation during the two‐first months of life influence life history (growth, survival, reproduction) and performance traits (immunocompetence, locomotor performances) until adulthood. We investigated the underlying mechanisms and their possible interactions by manipulating jointly food availability in a birth cohort and in cohorts of older conspecifics. Food deprivation had direct immediate negative effects on growth but positive long‐lasting effects on immunocompetence. Food deprivation had also indirect delayed effects on growth, body size, early survival and reproduction mediated by an interaction between its direct effects on individual quality and its delayed effects on the intensity of intercohort social interactions combined with density dependence on body size. These results demonstrate that interactions between direct and socially mediated effects of past environments influence life history evolution in size‐structured and stage‐structured populations.     

Synergistic effects of olfactory and tactile cues in short‐range mate finding of Ophraella communa

Sensory signals between individuals are important in short‐range mate finding. The purpose of our experiments was to verify the roles of different sensory cues in mate orientation and discrimination in Ophraella communa LeSage (Coleoptera: Chrysomelidae) adults. Sex discrimination and sensory deprivation tests (i.e., depriving the olfactory and/or visual senses of either or both sexes by coating with paint) were conducted in the laboratory. Male O. communa were able to locate and recognize conspecifics using olfactory cues prior to physical contact, but could not discriminate the opposite sex prior to physical contact. When the olfaction of male O. communa was deprived by painting antennae, males spent significantly longer times seeking mates in the arena. Copulation duration did not differ significantly among treatments. Thus, the mating process of O. communa adults was mediated by contact cues, but not by olfactory cues. The percentages of successful mating, searching duration, and copulation duration were all unaffected by visual deprivation, i.e., when the eyes of either or both sexes were covered by black paint. The function of visual cues was thus negligible in the mate‐finding process of O. communa adults. Overall, these results suggested that orientation and discrimination of the opposite sex by O. communa is dependent on the synergy between olfactory and tactile cues.     

Long‐term fertilizer regimes have both direct and indirect effects on arthropod community composition and feeding guilds

Vegetation species composition and structure are known to affect taxonomic composition and life‐history characteristics of arthropod communities. Soil conditions alter vegetation composition and structure, and thus, soils have indirect effects on arthropods. Whilst grassland management affects soil properties, and hence vegetation, the direct effects of soil on arthropod communities within the sward are less clear. We used a long‐term hay meadow experiment to assess both direct and indirect effects of various fertilizer regimes on arthropod community composition and feeding guilds. Arthropods were sampled via pitfall traps and sweep nets and then analysed using principal components and redundancy analyses (RDA) to determine relationships between soil properties, vegetation community, forage quality and arthropod community. Vegetation community composition, measured by the first vegetation principal component, was used as a constraining variable in partial RDA, to estimate direct effects of soil on the arthropods. Variance partitioning quantified the relative roles of vegetation and soil on the arthropod community. Our results indicate that available soil nitrogen and carbon–nitrogen ratios are important determinants of arthropod community composition. Once the effects of the vegetation were removed, it was found the soil acidity and the available potassium altered arthropod community composition. Further research is required to determine the mechanisms by which these soil properties affect arthropod communities.     

Serine proteases in the spiny lobster olfactory organ: Their functional expression along a developmental axis,and the contribution of a CUB‐serine protease

Several serine proteases and protease inhibitors have been identified in the crustacean olfactory organ, which is comprised of the lateral flagellum of the antennule and its aesthetascs sensilla that house olfactory receptor neurons and their supporting cells. The function of these proteases in the olfactory organ is unknown, but may include a role in perireception (e.g., odor activation or inactivation) or in the development or survival of olfactory receptor neurons. To examine directly the function of proteases in the olfactory organ of the Caribbean spiny lobster Panulirus argus, we used different tissue fractions from the lateral flagellum in an enzyme activity assay with a variety of protease substrates and inhibitors. Trypsin‐like serine protease activity occurs throughout the lateral flagellum but is enriched in the cell membranes from aesthetascs. Cysteine‐ and metalloprotease activities also occur in olfactory tissue, but are more abundant in tissue fractions other than aesthetascs. To assess the contribution of one of the olfactory serine proteases—CUB‐serine protease (Csp)—Csp was immunoprecipitated using an antibody; results with the remaining fraction suggest that Csp accounts for at least 40% of the total serine protease activity in the olfactory organ. The amount of total serine protease activity follows a developmental axis in the lateral flagellum. Total protease activity is lowest in the proximal zone, which lacks aesthetascs, and the proliferation zone, where olfactory receptor neurons and associated cells are born, and highest in aesthetascs of the distally‐located senescence zone, which has the oldest olfactory tissue. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2004     

Faunal response to sea‐level and climate change in a short‐lived seaway: Jurassic of the Western Interior,USA

Understanding how regional ecosystems respond to sea‐level and environmental perturbations is a main challenge in palaeoecology. Here we use quantitative abundance estimates, integrated within a sequence stratigraphic and environmental framework, to reconstruct benthic community changes through the 13 myr history of the Jurassic Sundance Seaway in the western United States. Sundance Seaway communities are notable for their low richness and high dominance relative to most areas globally in the Jurassic, and this probably reflects steep temperature and salinity gradients along the 2000 km length of the Seaway that hindered colonization of species from the open ocean. Ordination of samples shows a main turnover event at the Middle–Upper Jurassic transition, which coincided with a shift from carbonate to siliciclastic depositional systems in the Seaway, probably initiated by northward drift from subtropical latitudes to more humid temperate latitudes, and possibly global cooling. Turnover was not uniform across the onshore–offshore gradient, but was higher in offshore environments. The higher resilience of onshore communities to third‐order sea‐level fluctuations and to the change from a carbonate to a siliciclastic system was driven by a few abundant eurytopic species that persisted from the opening to the closing of the Seaway. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species. Such increased onshore stability in community composition contrasts with the well‐documented onshore increase in taxonomic turnover rates, and this study underscores how ecological analyses of relative abundance may contrast with taxonomically based analyses. We also demonstrate the importance of a stratigraphic palaeobiological approach to reconstructing the links between environmental and faunal gradients, and how their evolution through time produces local stratigraphic changes in community composition.     

Effects of site fidelity and breeding performance on mate retention in a short‐lived passerine,the tree swallow Thachycineta bicolor

We studied the relationship among re‐mating, site fidelity and breeding performance in the tree swallow Tachycineta bicolor using 16 y of data on reproductive biology in a population breeding in nest boxes near Ithaca, New York. Of 217 pairs for which both members survived the non‐breeding season, 76% mated with a new partner and 24% reunited with their previous mate. Pairs did not increase their breeding success by breeding together for more than one breeding season. Males produced fewer fledglings after breeding with a new partner, but females neither increased nor decreased their success when breeding with a new mate. Females who bred with a new partner were younger than females that reunited with their previous mates, and they were more likely to move to a different nest box. Males that bred with a new mate were of similar age to males that reunited, and they did not move more often. The probability of breeding with a new partner was better predicted by female age than by previous breeding success, suggesting that re‐mating was not strongly affected by past breeding performance. Because younger females change breeding sites more frequently than do older females and females that mated with a new partner were younger than females that reunited with their previous mates, we suggest that the tendency of tree swallows to change partners between years is a by‐product of lower site fidelity of younger females rather than a strategy for increasing breeding success.     

Radio‐tags have no behavioral or physiological effects on a migratory songbird during breeding and molt

ABSTRACT Radio‐tags are commonly used in studies of avian behavior and ecology, even though many studies have revealed negative impacts of radio‐tags. Other studies of songbirds have revealed no negative effects of radio‐tags on parental care, nesting success, or annual return rates. However, such studies have not addressed the potential physiological costs of carrying radio‐tags or determined if such costs affect birds during the energetically costly molt period. Simultaneously investigating the behavioral, physiological, and fitness consequences of radio‐tags is important for evaluating possible costs. We studied Wood Thrushes (Hylocichla mustelina) in northwestern Pennsylvania and used a repeated‐measures design to determine if radio‐tags affected parental care behavior and nesting success, and measured levels of plasma lipid metabolites (β‐hydroxybutyrate, free glycerol, and triglycerides) to evaluate physiological condition. We also examined the possible physiological effects of radio‐tags during the energetically demanding period of molt in late summer. Radio‐tags did not affect male or female feeding rates, nesting success, number of nesting attempts, number of eggs laid, fledging success, or hatching success, and we found no significant effects of radio‐tag use on levels of plasma lipid metabolites of nesting females. During molt, Wood Thrushes with radio‐tags had lower levels of β‐hydroxybutyrate and higher levels of trigylcerides, suggesting they were in better, not worse, energetic condition. Our results suggest that radio‐tags do not have negative effects on the behavior or physiology of Wood Thrushes. Similar studies on a wider range of songbirds are needed before concluding radio‐tags have little or no impact during the molting period.     

5-HT和DA对虾蟹打斗行为影响的研究进展

5-羟色胺(5-HT)和多巴胺(DA)是两种神经递质,可与众多不同类型的受体结合发挥多种重要的生理功能.现已证明其广泛分布于多种动物的不同组织中,在动物的打斗行为活动中起着重要的调节作用.目前,在虾蟹中已被报道的5-HT受体主要有5种,分别是5-HT1A、5-HT1B、5HT2A、5HT2B和5-HT7;DA受体主要为DA1A、DA1B、DA2和DA4.5-HT和DA及其受体分布存在明显的种属和组织特异性.5-HT和DA参于了虾蟹打斗行为的调节过程并有不同的调节机理.5-HT可以调节环磷酸腺苷(cAMP)或高血糖激素(CHH)的释放,促进或抑制虾蟹打斗行为;而DA同样能够通过调节cAMP及COMT等物质的释放来调节虾蟹打斗行为.     

Mitochondrial mutations and aging: random drift is insufficient to explain the accumulation of mitochondrial deletion mutants in short‐lived animals

Mitochondrial DNA deletions accumulate over the life course in post‐mitotic cells of many species and may contribute to aging. Often a single mutant expands clonally and finally replaces the wild‐type population of a whole cell. One proposal to explain the driving force behind this accumulation states that random drift alone, without any selection advantage, is sufficient to explain the clonal accumulation of a single mutant. Existing mathematical models show that such a process might indeed work for humans. However, to be a general explanation for the clonal accumulation of mtDNA mutants, it is important to know whether random drift could also explain the accumulation process in short‐lived species like rodents. To clarify this issue, we modelled this process mathematically and performed extensive computer simulations to study how different mutation rates affect accumulation time and the resulting degree of heteroplasmy. We show that random drift works for lifespans of around 100 years, but for short‐lived animals, the resulting degree of heteroplasmy is incompatible with experimental observations.     

Edge effects on ground beetles at the woodlot–field interface are short‐range and asymmetrical

• 1 Boundaries between woodlots and agricultural habitats are numerous in temperate agricultural landscapes and influence ecological processes in both woodlots and agricultural habitats.
• 2 We aimed to determine how far the species assemblage of ground beetles in woodlot and open habitats was influenced by the presence of the woodlot–field boundary.
• 3 We studied the distribution of ground beetles on both sides of the boundaries of four woodlots along transects of pitfall traps (n = 140). The depth of edge influence (i.e. the distance from the boundary at which the presence of the boundary has no more significant influence) on the species assemblage of ground beetles in each woodlot and in each agricultural habitat was determined with nonlinear canonical analysis of principal coordinates, an ordination method that is followed by nonlinear regression of the principal coordinates on distance from the boundary.
• 4 The depth of edge influence on the species assemblages of ground beetles was asymmetrical relative to the boundary: it was generally higher and had higher variability in open habitats (14.4 ± 12.3 m) than in woodlots (4.9 ± 2.3 m). Species assemblages of ground beetles in edges were a mix between both adjacent species assemblages. Edge effects in woodlots were deeper in the woodlots exhibiting a deeper penetration of open habitat species. Symmetrically, edge effects in open habitat were deeper in the open habitats with a deeper diffusion of forest species into the open habitat.
• 5 Forest ground beetles were not threatened by edge effects. Rather, edge effects are likely to benefit agriculture, mostly through the dispersal of predatory forest species into agricultural fields.

     

The contrasting effects of short‐ and long‐term habitat drainage on the population dynamics of freshwater turtles in a human‐dominated landscape

相似文献