The effect of intruded events on peak time: the role of reinforcement history during the intruded event

Pigeons were studied in an extension of a study by Aum et al. [Aum, S., Brown, B.L., Hemmes, N.S. 2004. The effects of concurrent task and gap events on peak time in the peak procedure. Behav. Process. 65, 43-56] on timing behavior under a discrete-trial fixed-interval (FI) procedure during which 6-s intruded events were superimposed on peak-interval (PI) test trials. In Aum et al., one event consisted in termination of the timing cue (gap trial); the other was a stimulus in the presence of which subjects had been trained to respond under an independent random-interval (RI) schedule of reinforcement (concurrent task trial). Aum et al. found a disruption of timing on concurrent task trials that was greater than that on gap trials. The present study investigated history of reinforcement associated with intruded events as a possible explanation of this earlier finding. After training to peck a side key on a 30-s PI procedure, discrimination training was conducted on the center key in separate sessions; red or green 6-s stimuli were associated with RI 24s or EXT (extinction) schedules. During testing under the PI procedure, three types of intruded events were presented during probe trials--the stimulus associated with the RI (S+) or EXT (S-) schedule during discrimination training, or a gap (termination of the side-keylight). Intruded events occurred 3, 9, or 15s after PI trial onset. Effects of reinforcement history were revealed as substantial disruption of timing during the S+ event and relatively little disruption during the S- event. Intermediate effects were found for the gap event. Results indicate that postcue effects are at least partially responsible for the disruptive effects of the S+ event.     

Training delays reduce the choose-short effect with keylight, but not with food, duration samples in pigeons

Pigeons were trained to match 2- and 8-s food samples. The delay on training trials was either 0s (group 0sF), 5s (group 5sF), or varied between 2 and 8s (M=5s, group 5sV). Testing at a delay that exceeded the training delay by 15s in each group revealed a robust choose-short effect in each group. The same pigeons then reacquired a previously trained matching task involving 2- and 8-s keylight samples. Different comparison stimuli were used on food-sample and keylight-sample trials. The delay on training trials was the same on both food- and keylight-sample trials. Extended-delay testing revealed a robust choose-short effect in all three groups when the durations were conveyed by food presentations, but only group 0sF revealed a choose-short effect when the durations were conveyed by keylight presentations. Hence, training with a nonzero delay, whether fixed or variable, reduces the choose-short effect with keylight durations but not with food durations. It was concluded that at least some of the psychological processes mediating performance differ as a function of the event that conveys the duration.     

Context effect in a temporal bisection task with the choice keys available during the sample

In a symbolic matching to sample task, six pigeons learned to associate different sample durations with different comparison stimuli. On “Short” trials, choice of Red and Green keylight comparisons were reinforced following 3-s and 9-s samples, respectively; on “Long” trials, Blue and Yellow keylight comparisons were reinforced following 9-s and 27-s samples, respectively. In contrast with previous studies, the comparison keys were available during the samples. After the temporal discriminations were learned, new pairs of comparison keys were presented and the preference for each was assessed during 27-s samples. One pair in particular, Green and Blue, was critical because it tested the predictions of two timing models, Scalar Expectancy Theory (SET) and the Learning-to-Time (LeT) model. The results showed that preference for Green increased during the sample, a result consistent with LeT but not with SET. Other test results, however, were predicted by neither model.     

Energetic cost of web construction and its effect on web relocation in the web-building spider Agelena limbata

Summary Although spider webs may be effective in trapping prey, they require energy for construction. The design of webs varies in complexity from species to species. I assume that the energetic cost of web construction is significantly different among web types or species. This cost may constrain foraging tactics, particularly web relocation, because web relocation also requires energy to make a new web. To clarify the effect of the cost of web construction on web relocation, the energy cost of web construction and the rate of web relocation were estimated for the spider Agelena limbata. This spider constructs a sheet-funnel web consisting of a tight mesh of silk threads. This web was costly in terms of the energy needed for construction, which ranged from 9 to 19 times the daily maintenance energy. The daily rate of web relocation was below 1%, indicating high web-site tenacity. Relocation rates of species which built different types of web were compared in relation to cost of web construction. Orbweavers, which produce less costly webs than sheet-funnel weavers, relocate webs more frequently. Sheetweavers, which make webs of intermediate cost, appear to relocate webs more frequently than sheetfunnel weavers but less frequently than orbweavers. These results suggest that the energy cost of web construction is important in determining the frequency of web relocation.     

The effect of stimuli that isolate S-cones on early saccades and the gap effect

Disappearance of the fixation spot before the appearance of a peripheral target typically reduces average saccadic reaction times (the gap effect) and may also produce a separate population of early or express saccades. The superior colliculus (SC) is generally believed to be critically involved in generating both effects. As the direct sensory input to the SC does not encode colour information, to determine whether this input was critical in generating the gap effect or express saccades we used coloured targets which this pathway cannot distinguish. Our observers still made early saccades to colour-defined targets, but these were anticipations in response to the offset of the non-coloured fixation target. We also show that a gap effect still occurs when either the fixation target or the peripheral target is colour defined, suggesting that direct sensory input to the SC is not required and that information about the location of colour-defined targets is abstracted prior to processing within the SC.     

Predator preference for brightly colored males in the guppy: a viability cost for a sexually selected trait

Although conspicuous visual sexual signals, such as bright colors,in males serve to attract females in numerous species, theymay also attract the attention of potential predators and thusmay be costly in terms of increasing individual risk of mortalityto predation. Most models of the evolution of extravagant malesexual traits and female preferences for them assume that thesexually preferred male trait is costly to produce and maintain.However, there is surprisingly little empirical evidence fordirect fitness costs associated with sexually selected visualtraits that enhance male mating success. In the present study,we report a direct fitness cost for sexually selected, brightbody-color patterns in males in the form of an associated greaterrisk of mortality to predation. By using the guppy (Poeciliareticulata) and the blue acara cichlid fish (Aequidens pulcher)as a model prey–predator system, we demonstrate experimentallythat individual cichlids preferentially and consistently approached,attacked, and captured the more brightly colored of two size-matchedmale guppies presented simultaneously in staged encounters.This resulted in the brightly colored male incurring, on average,a significantly higher risk of mortality given an encounterwith the predator than with the drabber male in matched pairs.Our results constitute strong behavioral evidence for a directviability cost associated with bright coloration in male guppies,and they corroborate the generally accepted paradigm that directionalpredation by visual fish predators against brightly colored,adult male guppies underlies the evolution of the known divergentcolor patterns in natural guppy populations that experiencedifferent intensities of predation. The viability cost associatedwith bright conspicuous coloration in male guppies potentiallyreinforces for females the reliability of this sexually selectedtrait as an indicator trait of male quality.     

Reproduction and the energy cost of defense in a Batesian mimicry complex

Summary The amount of energy invested in reproduction and in defense was examined in a Batesian mimicry complex consisting of the modelEleodes obscura and the mimicStenomorpha marginata (both Coleoptera: Tenebrionidae). Models live up to 4 y as adults while mimic adults live only 3 mo. The energy content of the eggs of the model and mimic was determined by microbomb calorimetry. The energy content of the defensive secretions produced by the model was determined by computational chemistry and MNDO computer programming. Contrary to the predictions of some life-history theory, the long-lived model annually produces many small eggs each of low energetic content, while the short-lived mimic annually produces fewer, larger eggs each of high energetic content. However, in terms of total energy, the long-lived model has an annual investment in reproduction equal to that of the short-lived mimic. During the 3 mo of co-ocurrence of models and mimics within a year, an average individual model's cost in using defensive secretions against potential predators is 12% of the amount of energy tied up in the eggs that it produces within the year. The annual cost of defense for the model is 18% of the energy contained in the mean number of eggs produced. When the energy allocated to eggs is added to that allocated to defense, the model has an annual investiment that is greater than the annual investment in reproduction by the mimic. Although the energy invested in defense by the model is small relative to the energy invested in egg production, it buys the model considerable protection from predation. Nevertheless, the cost of defense does not explain the deviations from the predictions of life-history theory.     

Characterizing the cost of oviposition in insects: a dynamic model

The development of a consensus model of insect oviposition has been impeded by an unresolved controversy regarding the importance of time costs versus egg costs in mediating the trade-off between current and future reproduction. Here I develop a dynamic optimization model that places time and egg costs in a common currency (opportunity costs expressed as decreased lifetime reproductive success) so that their relative magnitudes can be compared directly. The model incorporates stochasticity in host encounter and mortality risk as well as behavioral plasticity in response to changes in the age and egg load of the ovipositing female. The dynamic model's predictions are congruent with those of a simpler, static model: both time- and egg-mediated costs make important contributions to the overall cost of oviposition. Modest quantitative differences between the costs predicted by the static versus dynamic models show that plasticity of oviposition behavior modulates the opportunity costs incurred by reproducing females. The relative importance of egg-mediated costs increases substantially for oviposition events occurring later in life. I propose that the long debate over how to represent the cost of oviposition should be resolved not by advocating the pre-eminence of one sort of cost above all others, but rather by building models that represent the complementary roles of different costs. In particular, both time and egg costs must be recognized to produce a general model of insect oviposition that incorporates a realistic representation of the cost of reproduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence for a cost of immunity when the crustacean Daphnia magna is exposed to the bacterial pathogen Pasteuria ramosa

The deployment of the immune system has the obvious potential to ameliorate infection outcomes, but immune responses can also harm hosts by either damaging host tissues or monopolizing resources, leading to enhanced mortality. To gain insight into such a 'cost of immunity' when the crustacean Daphnia magna is challenged with the bacterium Pasteuria ramosa, we measured survivorship among hosts that resisted infection following exposure to various strains and doses of the parasite. In the first of two experiments, these exposures were: single exposures with relatively non-aggressive strains, double exposures with non-aggressive strains, and exposure to aggressive strains. Mortality increased across this gradient of exposure. In a second experiment, we varied the dose of the most aggressive P. ramosa strain and found that resisting infection when a large dose was applied resulted in greater mortality than when a medium or low dose was applied. Assuming that resistance is accomplished with an immune response, and that more aggressive parasites and/or larger doses of parasites are more immunostimulatory, these data are compatible with a cost of immunity. Indeed, in terms of survival, resisting parasites can be more harmful than infection.     

Environment-dependent reversal of a life history trade-off in the seed beetle Callosobruchus maculatus

Environmental manipulations have consistently demonstrated a cost of reproduction in the capital-breeding seed beetle, Callosobruchus maculatus, as females deprived of seeds or mates lay fewer eggs and thereby increase their longevity. Yet fecundity and longevity tend to be positively correlated within populations, perhaps as a consequence of individual differences in resource acquisition. We conducted a split-brood experiment that combined a manipulation of seed availability (seeds present or absent) with a quantitative-genetic analysis of fecundity and lifespan in each environment. Each trait was significantly heritable in each environment. Seed availability not only altered mean fecundity and longevity between environments, but also modified how the traits were correlated within environments. The signs of both the phenotypic and genetic correlations switched from positive when seeds were present to negative when seeds were absent. This reversal persisted even after the effect of body mass (a potential indicator of resource acquisition) was statistically controlled. Cross-environment genetic correlations were positive but significantly less than one for each trait. We suggest that the reversal of the fecundity-longevity relationship depends on a shift in the relative importance of resource-acquisition and resource-allocation loci between environments. In particular, a cost of reproduction may be apparent at the individual level only when seeds are scarce or absent because differences in reproductive effort become large enough to overwhelm differences in resource acquisition. Despite their common dependence on resources acquired during larval stages, fecundity and lifespan in C. maculatus do not appear to be tightly coupled in a physiological or genetic sense.     

Exchange of serine residues 263 and 266 reduces the function of mouse gap junction protein connexin31 and exhibits a dominant-negative effect on the wild-type protein in HeLa cells

To characterize the role of Cx31 phosphorylation, serine residues 263 and 266 (Cx31Delta263,266) or 266 (Cx31Delta266) alone were exchanged for amino acids that cannot be phosphorylated. HeLa cells, which were stably transfected with wild type and the two different mutant Cx31-cDNA constructs, were analyzed for expression, phosphorylation, localization, formation of functional gap junction channels, and degradation of mutant Cx31 protein. Both mutant proteins showed similar reduced phosphorylation levels compared to Cx31 wild type, indicating a pivotal role of serine residue 266 for Cx31 phosphorylation. None of these mutations did interfere with correct intracellular trafficking of gap junction proteins. Pulse chase experiments with the different transfectants revealed an increased turnover of both mutated Cx31 proteins. They showed decreased intercellular communication as shown by dye transfer to neighboring cells and measurement of total conductance (mutant Cx31Delta263,266). Mutated Cx31 protein (Cx31Delta263,266) diminished the function of the Cx31 wild-type protein dependent on the amount of the mutated protein, indicating a dominant-negative effect of the mutated protein in HeLa cells.     

Molecular-size corrections to the strength of the hydrophobic effect: a critical review

Large increases in the strength of the hydrophobic effect and, consequently, in the estimates of the hydrophobic contribution to the thermodynamics of protein folding (and other biologically-relevant processes), have been recently advocated on the basis of the application, to model transfer thermodynamic data, of corrections for the solute/solvent size disparity. In this work we first examine the effect of molecular-size corrections on the values calculated from several types of model transfer data. For the transfer of a solute from an organic solvent to water, the above increase is exclusively associated with the application of a solute/water molecular-size correction. Secondly, we critically review and assess the several theoretical arguments that lead to these corrections. In particular, we show that, contrary to previous claims in the literature, the analysis of dissolution processes in terms of ideal-gas, intermediate states does not lead to the molecular-size correction term, but only to expressions equivalent (although not strictly identical) to those derived from the well-known Ben-Naim's statistical-mechanical approach. In general, the several analyses offered or discussed in this work disfavor the application of the solute/water molecular-size corrections.     

Evidence of a maternal effect that protects against water stress in larvae of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

We report that the ability to absorb water vapor from the air in larvae of the American dog tick, Dermacentor variabilis, changes depending upon moisture conditions where the eggs develop. When development occurs at lower relative humidities, resultant larvae can replenish water stores, maintain water balance, and survive at relative humidities as low as 75-85% RH, a range that agrees with previously published values for the critical equilibrium humidity or CEH. In contrast, exposure to high relative humidity conditions during development elevates the CEH to 93-97% RH. These larvae can survive only at relative humidities that are close to saturation, as 93% RH is a dehydrating atmosphere. For these larvae, absorption at 97% RH can be prevented by blocking the mouthparts with wax, indicating that an upward shift has occurred in the moisture threshold where the active mechanism for water vapor absorption operates. Based on transfer experiments between low and high relative humidities, the CEH of larvae is determined by the relative humidity experienced by the mother rather than the moisture conditions encountered by eggs after they are laid. The fact that no changes in body water content, dehydration tolerance limit and water loss rate were observed implies that adjustments to the CEH conferred by the mother have the adaptive significance of enabling larvae to maintain water balance by limiting the range of hydrating atmospheres.     

Restricted dispersal reduces the strength of spatial density dependence in a tropical bird population

Spatial processes could play an important role in density-dependent population regulation because the disproportionate use of poor quality habitats as population size increases is widespread in animal populations-the so-called buffer effect. While the buffer effect patterns and their demographic consequences have been described in a number of wild populations, much less is known about how dispersal affects distribution patterns and ultimately density dependence. Here, we investigated the role of dispersal in spatial density dependence using an extraordinarily detailed dataset from a reintroduced Mauritius kestrel (Falco punctatus) population with a territorial (despotic) breeding system. We show that recruitment rates varied significantly between territories, and that territory occupancy was related to its recruitment rate, both of which are consistent with the buffer effect theory. However, we also show that restricted dispersal affects the patterns of territory occupancy with the territories close to release sites being occupied sooner and for longer as the population has grown than the territories further away. As a result of these dispersal patterns, the strength of spatial density dependence is significantly reduced. We conclude that restricted dispersal can modify spatial density dependence in the wild, which has implications for the way population dynamics are likely to be impacted by environmental change.     

The impact of plasticity and maternal effect on the evolution of leaf resin production in Diplacus aurantiacus

Our previous quantitative genetic study of leaf resin production in Diplacus aurantiacus revealed large environmental and maternal effects on variation in resin production, which suggests the possibility of a genotype×environment interaction for this trait when plants grow in heterogeneous environments. Our objectives in this study were to observe the genetic variation in plasticity of resin production under field and chamber conditions, compare phenotypic correlations of resin content with growth traits under these two environmental conditions, and distinguish the possible basis of the maternal effect on resin production using parents and half-sib progeny. A significant genotype×environment interaction (P<0.0001) in leaf resin production was found, which suggests a potential for the evolution of plasticity of these secondary metabolites under heterogeneous environments. The phenotypic correlation between resin content and growth rate also exhibited plasticity. In addition, the resin content of dam half-sib families grown in the chamber had a closer relationship with their maternal parents in the field (r=0.65, P=0.059) than in the chamber (r=0.39, P=0.34), suggesting an environmentally based maternal effect on the secondary chemicals. We suggest that the maternal environmental effect may act as a contributor to plasticity of resin production and, while it may not diminish the appearance of the genotype×environment interaction, the heritable variation of plasticity of resin production may be confounded.     

Communally breeding Bechstein's bats have a stable social system that is independent from the postglacial history and location of the populations

Investigating macro-geographical genetic structures of animal populations is crucial to reconstruct population histories and to identify significant units for conservation. This approach may also provide information about the intraspecific flexibility of social systems. We investigated the history and current structure of a large number of populations in the communally breeding Bechstein's bat ( Myotis bechsteinii ). Our aim was to understand which factors shape the species' social system over a large ecological and geographical range. Using sequence data from one coding and one noncoding mitochondrial DNA region, we identified the Balkan Peninsula as the main and probably only glacial refugium of the species in Europe. Sequence data also suggest the presence of a cryptic taxon in the Caucasus and Anatolia. In a second step, we used seven autosomal and two mitochondrial microsatellite loci to compare population structures inside and outside of the Balkan glacial refugium. Central European and Balkan populations both were more strongly differentiated for mitochondrial DNA than for nuclear DNA, had higher genetic diversities and lower levels of relatedness at swarming (mating) sites than in maternity (breeding) colonies, and showed more differentiation between colonies than between swarming sites. All these suggest that populations are shaped by strong female philopatry, male dispersal, and outbreeding throughout their European range. We conclude that Bechstein's bats have a stable social system that is independent from the postglacial history and location of the populations. Our findings have implications for the understanding of the benefits of sociality in female Bechstein's bats and for the conservation of this endangered species.     

Evidence for a wahlund effect in a unique breton community,the bigoudens

A random sample of the Bigoudens community was tested for 16 genetic markers. The existence of silent alleles had to be postulated more often than usual although no minus-minus phenotype was observed. Four explanations may be put forward for this apparent contradiction: selection pressure for homozygosity, inbreeding, true silent alleles and random genetic drift between and within the villages. The degree of inbreeding is unlikely to be high enough to account for our data and some of the silent alleles postulated are not thought to exist. We therefore favour the explanation of genetic differentiation and the so-called Wahlund effect.     

A high-throughput screen for inhibitors of the prolyl isomerase,Pin1, identifies a seaweed polyphenol that reduces adipose cell differentiation

The peptidyl prolyl cis/trans isomerase Pin1 enhances the uptake of triglycerides and the differentiation of fibroblasts into adipose cells in response to insulin stimulation. Pin1 downregulation could be a potential approach to prevent and treat obesity-related disorders. In order to identify an inhibitor of Pin1 that exhibited minimal cytotoxicity, we established a high-throughput screen for Pin1 inhibitors and used this method to identify an inhibitor from 1,056 crude fractions of two natural product libraries. The candidate, a phlorotannin called 974-B, was isolated from the seaweed, Ecklonia kurome. 974-B inhibited the differentiation of mouse embryonic fibroblasts and 3T3-L1 cells into adipose cells without inducing cytotoxicity. We discovered the Pin1 inhibitor, 974-B, from the seaweed, E. kurome, and showed that it blocks the differentiation of fibroblasts into adipose cells, suggesting that 974-B could be a lead drug candidate for obesity-related disorders.