The evolution of imperfect mimicry

Examples of imperfect resemblance between Batesian mimics andtheir models appear widespread in the natural world, but sofar few quantitative models have been proposed to explain thephenomenon. I used a simple signal detection model to showthat the relationship between model—mimic similarity and mimic effectiveness is typically nonlinear. In particular, Ifound that there will be little or no further selection toimprove model—mimic resemblance beyond a certain levelif the model species is costly to attack, if the mimic speciesis not particularly profitable (e.g., hard to catch), or ifthe mimic is relatively rare. When there are two different sympatricmodel species, then mimics should usually evolve a phenotypicsimilarity to one or the other model species, but not to both.In contrast, when several model species occur in differentareas (or emerge at different times) and individual mimicsuse each of these areas, then the optimal phenotype should bea "jack-of-all-trades" intermediate phenotype that does notclosely resemble any particular model species. Somewhat surprisingly,the theory predicts that if mimics spend an equal amount oftime with each model species, then the optimal intermediatephenotype should more closely resemble the least numerous andleast noxious model. This phenomenon arises because a vague similarity to an extremely noxious species is usually sufficientto guarantee significant protection, whereas a much closerresemblance to a mildly noxious model species is necessaryto afford a similar level of benefit.     

Insulin signal mimicry as a mechanism for the insulin-like effects of vanadium

Among several metals, vanadium has emerged as an extremely potent agent with insulin-like properties. These insulin-like properties have been demonstrated in isolated cells, tissues different animal models of type I and type II diabetes as well as a limited number of human subjects. Vanadium treatment has been found to improve abnormalities of carbohydrate and lipid metabolism and of gene expression in rodent models of diabetes. In isolated cells, it enhances glucose transport, glycogen and lipid synthesis, and inhibits gluconeogenesis and lipolysis. The molecular mechanism responsible for the insulin-like effects of vanadium compounds have been shown to involve the activation of several key components of insulin-signaling pathways that include the mitogen-activated-protein kinases (MAPKs) extracellular signal-regulated kinase 1/2 (ERK1/2) and p38MAPK, and phosphatidylinositol 3-kinase (PI3-K)/protein kinase B (PKB). It is interesting that the vanadium effect on these signaling systems is independent of insulin receptor protein tyrosine kinase activity, but it is associated with enhanced tyrosine phosphorylation of insulin receptor substrate-1. These actions seem to be secondary to vanadium-induced inhibition of protein tyrosine phosphatases. Because MAPK and PI3-K/PKB pathways are implicated in mediating the mitogenic and metabolic effects of insulin, respectively, it is plausible that mimicry of these pathways by vanadium serves as a mechanism for its insulin-like responses.     

Sexually antagonistic co‐evolution: a model and an empirical test

Models reveal that sexually antagonistic co‐evolution exaggerates female resistance and male persistence traits. Here we adapt an established model by including directional sexual selection acting against persistence. We find similar equilibria to previous models showing that sexually antagonistic co‐evolution can be limited by counteracting sexual, as well as, natural selection. We tested the model using empirical data for the seaweed fly, Coelopa ursina, in which body size acts as a persistence and a resistance trait. Our model can generate continuous co‐evolutionary cycles and stable equilibria, however, all simulations using empirically derived parameter estimates reach stable equilibria. Thus, stable equilibria might be more common in nature than continuous co‐evolutionary cycles, suggesting that sexual conflict is unlikely to promote speciation. The model predicts male biased sexual size dimorphism for C. ursina, comparable with empirically observed values. Male persistence is shown to be more sensitive than female resistance to changes in model parameters.     

The evolution of ecologically important characters in Heliconius butterflies (Lepidoptera: Nymphalidae): a cladistic review

The biology of Heliconius butterflies has provided a rich source of data to test theories of ecological genetics, coevolution and community ecology. Many putatively adaptive characters have been discussed with reference to a phylogenetic hypothesis based on a variety of morphological and life-history traits interpreted from an evolutionary taxonomic perspective. Here, alternate interpretations of characters on the traditional tree and a more recent mitochondrial DNA cladogram with a substantially different topology are compared and contrasted. It is shown that many characters ostensibly providing support for the traditional phylogenetic hypothesis are almost equally parsimoniously distributed and in some cases more parsimoniously distributed on the mtDNA tree than on the tree inferred from those characters. Discussion of alternate evolutionary scenarios based on the mDNA-based topology is presented for pupal mating, pollen feeding, foodplant coevolution, and other ecologically significant features.     

Evidence for a female‐produced,long range pheromone of Anoplophora glabripennis (Coleoptera: Cerambycidae)

Abstract Volatiles from female Asian longhorned beetle (ALB), Anoplophora glabripennis, were evaluated as candidate sex pheromone components. Previous studies on ALB have revealed several antennally active compounds from virgin females; however the origins and activity of these compounds were not apparent and require further investigation. We tested the hypothesis that one or more of the ALB contact sex pheromones is a precursor that undergoes abiotic oxidation to yield volatile pheromone components, and evaluated the activity of these compounds using laboratory and field bioassays. Gas chromatography coupled electroantennography detection (GC‐EAD) analysis indicated the presence of three antennally active aldehydes (heptanal, nonanal, and hexadecanal) in female cuticular extracts exposed to ozone or UV and visible light. In laboratory bioassays using a Y‐tube olfactometer, males were preferentially attracted to ozonized female body washes over crude body washes. Similarly, synthetic formulations of these compounds were preferred over controls in the olfactometer. Field trapping experiments conducted from 2006 to 2008 in Ningxia, China showed that synthetic lures of the three aldehydes formulated in a ratio simulating that of virgin females attracted more beetles compared to controls, and that combinations of these aldehydes, linalool oxide, and host kairomones captured more beetles than controls, and captured significantly more males.     

Response of bee-flies to the shape and pattern of model flowers: implications for floral evolution in a Mediterranean herb

1. The functional significance of floral traits in Linum pubescens (Linaceae), a Mediterranean annual that is pollinated almost exclusively by the bee-fly Usia bicolor (Bombyliidae), was investigated. The flies feed on both pollen and nectar, and use the flowers as mating rendezvous sites in the afternoon.
2. Choice experiments with model flowers were used to determine the response of U. bicolor to visual cues, such as shape, size, colour and pattern.
3. Bee-flies strongly preferred models with a dissected outline over models with a simple outline. They also preferred pink models over other colours, and larger models over smaller models.
5. Flies landing on models with converging lines ('nectar guides') tended to follow the lines to the point where they meet in the centre of the model, while flies landing on plain models showed undirected behaviour, often moving to the edge of the model.
6. Flies were strongly attracted to flowers of L. pubescens which had a fly glued on to one of the petals, as well as flowers with a dark spot painted onto one of the petals. In addition, models with a dark spot were strongly preferred over plain models during the afternoon when flies exhibit mating behaviour. This evidence suggests that the dark centre of the L. pubescens flower may function as an attractant to mate-seeking bee-flies.     

Development of a colorimetric colony‐screening assay for detection of defluorination by micro‐organisms

Aims: To develop a colorimetric colony‐screening assay to facilitate the isolation of micro‐organisms capable of defluorination. Methods and Results: A metal‐dye chelate, zirconium‐xylenol orange was used to detect fluoride ions released from a fluorinated substrate through microbial metabolism. Depolymerised zirconium reagent gave the greatest visual contrast for the presence of fluoride compared to more polymerised forms of zirconium reagent. The sensitivity of the assay was greatest when the molar ratio of depolymerised zirconium to xylenol orange was 1 : 2. Using depolymerised zirconium and xylenol orange (150 and 300 nmol l^?1 respectively), the assay could detect a fluoride application spot (5 mmol l^?1) containing 50 nmoles of fluoride ions. Most media constituents were well tolerated by the assay, although phosphate ions needed to be restricted to 0·1 g l^?1 and some proteins digest to between 1 and 5 g l^?1. A microbial enrichment culture growing on solidified medium containing 20 mmol l^?1 fluoroacetate was screened using the assay, and defluorinating bacteria belonging to the genus Burkholderia isolated. Conclusions: A method was developed that is sensitive, rapid and reliable for detecting defluorination by micro‐organisms growing on solidified medium. Significance and Impact of the Study: This method can be used to facilitate the isolation of micro‐organisms capable of defluorination.     

Optimum signal in a diffusion leaky integrate-and-fire neuronal model

An optimum signal in the Ornstein-Uhlenbeck neuronal model is determined on the basis of interspike interval data. Two criteria are proposed for this purpose. The first, the classical one, is based on searching for maxima of the slope of the frequency transfer function. The second one uses maximum of the Fisher information, which is, under certain conditions, the inverse variance of the best possible estimator. The Fisher information is further normalized with respect to the time required to make the observation on which the signal estimation is performed. Three variants of the model are investigated. Beside the basic one, we use the version obtained by inclusion of the refractory period. Finally, we investigate such a version of the model in which signal and the input parameter of the model are in a nonlinear relationship. The results show that despite qualitative similarity between the criteria, there is substantial quantitative difference. As a common feature, we found that in the Ornstein-Uhlenbeck model with increasing noise the optimum signal decreases and the coding range gets broader.     

Protein kinase‐mediated signalling in priming: Immune signal initiation,propagation, and establishment of long‐term pathogen resistance in plants

“Priming” in plant phytopathology describes a phenomenon where the “experience” of primary infection by microbial pathogens leads to enhanced and beneficial protection of the plant against secondary infection. The plant is able to establish an immune memory, a state of systemic acquired resistance (SAR), in which the information of “having been attacked” is integrated with the action of “being prepared to defend when it happens again.” Accordingly, primed plants are often characterized by faster and stronger activation of immune reactions that ultimately result in a reduction of pathogen spread and growth. Prerequisites for SAR are (a) the initiation of immune signalling subsequent to pathogen recognition, (b) a rapid defence signal propagation from a primary infected local site to uninfected distal parts of the plant, and (c) a switch into an immune signal‐dependent establishment and subsequent long‐lasting maintenance of phytohormone salicylic acid‐based systemic immunity. Here, we provide a summary on protein kinases that contribute to these three conceptual aspects of “priming” in plant phytopathology, complemented by data addressing the role of protein kinases crucial for immune signal initiation also for signal propagation and SAR.     

Courtship in long-legged flies (Diptera: Dolichopodidae): function and evolution of signals

Analyzing the courtship behavior of long-legged flies (Diptera:Dolichopodidae), we focus on the evolutionary development ofcourtship signals. Long-legged flies may serve as a model forthis evolutionary process, because males of some species presentsexually dimorphic badges during courtship, whereas others donot exhibit such conspicuous signals but present lavish courtshipbehavior, including dynamic flight maneuvers. A comparison ofthese two groups within a single taxonomic family provides insightinto the evolution of courtship signals and the correspondingbehavior. Males of the closely related Empididae do not possesssuch badges. Within the super-family Empidoidea, we proposean evolutionary shift from dynamically courting and mating onthe wing (in Empididae) to courting and mating on ground (inDolichopodidae), accompanied by signaling through badge-waving.By comparing previously published data and observations on courtshipbehavior in Dolichopodidae, we present the hypothesis that thelatter replaced the former energetically expensive behavioras a case of automimicry and sensory trap.     

The evolution of punishment and apology: an iterated prisoner's dilemma model

Recently, behaviors that seem to function as punishment or apology have been reported among non-human primates as well as humans. Such behaviors appear to play an important role in maintaining cooperation between individuals. Therefore, the evolution of these behaviors should be examined from the viewpoint of the evolution of cooperation. The iterated prisoner's dilemma (IPD) game is generally considered to be a standard model for the evolution of cooperation. In the present study, strategies accompanied by punishment-like attacks or apology-like behavior were introduced into the common IPD simulation. Punishment and apology were represented by the P signal and the AS signal given immediately after defection. A strategy with the P and AS signals, named the pPAS strategy, was proved to be an evolutionarily stable strategy under certain conditions. Numerical simulations were carried out according to different assigned values of the costs of punishment and apology. The simulations showed that pPAS could dominate the population (1) when the cost of giving P is relatively small, (2) when the cost of receiving P is relatively large, or (3) when the cost of giving AS is relatively large. The relative cost of giving AS had the clearest effect on the success of pPAS. pPAS can dominate the population even when a dominance asymmetry of the costs between two players was introduced. The present results suggest the possible evolution of social behaviors like punishment or apology as a means of maintaining cooperation. This revised version was published online in November 2006 with corrections to the Cover Date.