Fires enhance flammability in Ulex parviflorus

6 páginas, 2 figuras, 2 tablas.This work was financed by the VIRRA project (CGL2009-12048 ⁄ BOS) from the Spanish Government. G.A.A. is supported by a Juan de la Cierva scholarship (JDC 2009-5067; Spanish Government) and B.M. by an FCT grant (SFRH ⁄BD⁄ 41343 ⁄ 2007; Portuguese Government). CIDE is supported by the Spanish National Research Council (CSIC), Generalitat Valenciana and the University of Valencia. We thank R. Bossi (CEAM, GRACCIE project, CONSOLIDERINGENIO 2010), E. Beltran, S. Paula, J. Chofre and O. González-Pelayo for their collaboration in the field and laboratory work, M. C. Castellanos for comments on an early version of the manuscript, and Fundación Caja Castellón-Bancaja for permission to work in Barranc dels Horts (Ares del Maestrat).Peer reviewe

Morphological Evolution of Spiders Predicted by Pendulum Mechanics

[Background] Animals have been hypothesized to benefit from pendulum mechanics during suspensory locomotion, in which the potential energy of gravity is converted into kinetic energy according to the energy-conservation principle. However, no convincing evidence has been found so far. Demonstrating that morphological evolution follows pendulum mechanics is important from a biomechanical point of view because during suspensory locomotion some morphological traits could be decoupled from gravity, thus allowing independent adaptive morphological evolution of these two traits when compared to animals that move standing on their legs; i.e., as inverted pendulums. If the evolution of body shape matches simple pendulum mechanics, animals that move suspending their bodies should evolve relatively longer legs which must confer high moving capabilities.[Methodology/Principal Findings] We tested this hypothesis in spiders, a group of diverse terrestrial generalist predators in which suspensory locomotion has been lost and gained a few times independently during their evolutionary history. In spiders that hang upside-down from their webs, their legs have evolved disproportionately longer relative to their body sizes when compared to spiders that move standing on their legs. In addition, we show how disproportionately longer legs allow spiders to run faster during suspensory locomotion and how these same spiders run at a slower speed on the ground (i.e., as inverted pendulums). Finally, when suspensory spiders are induced to run on the ground, there is a clear trend in which larger suspensory spiders tend to run much more slowly than similar-size spiders that normally move as inverted pendulums (i.e., wandering spiders).[Conclusions/Significance] Several lines of evidence support the hypothesis that spiders have evolved according to the predictions of pendulum mechanics. These findings have potentially important ecological and evolutionary implications since they could partially explain the occurrence of foraging plasticity and dispersal constraints as well as the evolution of sexual size dimorphism and sociality.This paper has been written under a Ramón y Cajal research contract from the Spanish Ministry of Science and Culture (MEC) to JML and a FPI scholarship (BES-2005-9234) to GC. This work has been funded by MEC grants CGL2004-03153 and CGL2007-60520 to JML and GC, as well as CGL2005-01771 to EMPeer reviewe

Implicaciones de la capacidad de movimiento en arañas (Araneae) para la evolución adaptativa del tamaño y la forma según el sexo, hábitat y modo de vida

Tesis Univ. Granada. Departamento de Ecología. Leída el 21 de julio de 201

The Role of ultraviolet colour in the assessment of mimetic accuracy between Batesian mimics and their models : a case study using ant-mimicking spiders

The use of ultraviolet (UV) cues for intra-and interspecific communication is common in many animal species. Still, the role of UV signals under some predator-prey contexts, such as Batesian mimicry, is not clear. Batesian mimicry is a defensive strategy by which a palatable species (the mimic) resembles an unpalatable or noxious species (the model) to avoid predation. This strategy has evolved independently in many different taxa that are predated by species capable ofUV perception. Moreover, there is considerable variation in how accurately Batesian mimics resemble their models across species. Our aimwas to investigate how UV colour contributed to mimetic accuracy using several ant-mimicking spider species as a case study. We measured the reflectance spectrum (300-700 nm) for several species of mimics and models, and we tested whether they differ in visible and UV colour. We modelled whether two different predators could discriminate between mimics and models using colour information. We found that generally, ant-mimicking spiders differed significantly from their ant models in UV colour and that information from the visible range of light cannot be extrapolated into the UV. Our modelling suggested that wasps should be able to discriminate between mimics and models combining information from visible and the UV light, whereas birds may not discriminate between them. Thus, we show that UV colour can influence mimic accuracy and we discuss its potential role in Batesian mimicry. We conclude that colour, especially in the UVrange, should be taken into account when measuring mimetic accuracy.11 page(s

Long term effects of aversive reinforcement on colour discrimination learning in free-flying bumblebees.

The results of behavioural experiments provide important information about the structure and information-processing abilities of the visual system. Nevertheless, if we want to infer from behavioural data how the visual system operates, it is important to know how different learning protocols affect performance and to devise protocols that minimise noise in the response of experimental subjects. The purpose of this work was to investigate how reinforcement schedule and individual variability affect the learning process in a colour discrimination task. Free-flying bumblebees were trained to discriminate between two perceptually similar colours. The target colour was associated with sucrose solution, and the distractor could be associated with water or quinine solution throughout the experiment, or with one substance during the first half of the experiment and the other during the second half. Both acquisition and final performance of the discrimination task (measured as proportion of correct choices) were determined by the choice of reinforcer during the first half of the experiment: regardless of whether bees were trained with water or quinine during the second half of the experiment, bees trained with quinine during the first half learned the task faster and performed better during the whole experiment. Our results confirm that the choice of stimuli used during training affects the rate at which colour discrimination tasks are acquired and show that early contact with a strongly aversive stimulus can be sufficient to maintain high levels of attention during several hours. On the other hand, bees which took more time to decide on which flower to alight were more likely to make correct choices than bees which made fast decisions. This result supports the existence of a trade-off between foraging speed and accuracy, and highlights the importance of measuring choice latencies during behavioural experiments focusing on cognitive abilities

Implicaciones de la capacidad de movimiento en las arañas (Araneae) para la evolución adaptativa del tamaño y la forma según el sexo, hábitat y modo de vida

Peer reviewe

Introducing the refined gravity hypothesis of extreme sexual size dimorphism

<p>Abstract</p> <p>Background</p> <p>Explanations for the evolution of female-biased, extreme Sexual Size Dimorphism (SSD), which has puzzled researchers since Darwin, are still controversial. Here we propose an extension of the Gravity Hypothesis (i.e., the GH, which postulates a climbing advantage for small males) that in conjunction with the fecundity hypothesis appears to have the most general power to explain the evolution of SSD in spiders so far. In this "Bridging GH" we propose that bridging locomotion (i.e., walking upside-down under own-made silk bridges) may be behind the evolution of extreme SSD. A biomechanical model shows that there is a physical constraint for large spiders to bridge. This should lead to a trade-off between other traits and dispersal in which bridging would favor smaller sizes and other selective forces (e.g. fecundity selection in females) would favor larger sizes. If bridging allows faster dispersal, small males would have a selective advantage by enjoying more mating opportunities. We predicted that both large males and females would show a lower propensity to bridge, and that SSD would be negatively correlated with sexual dimorphism in bridging propensity. To test these hypotheses we experimentally induced bridging in males and females of 13 species of spiders belonging to the two clades in which bridging locomotion has evolved independently and in which most of the cases of extreme SSD in spiders are found.</p> <p>Results</p> <p>We found that 1) as the degree of SSD increased and females became larger, females tended to bridge less relative to males, and that 2) smaller males and females show a higher propensity to bridge.</p> <p>Conclusions</p> <p>Physical constraints make bridging inefficient for large spiders. Thus, in species where bridging is a very common mode of locomotion, small males, by being more efficient at bridging, will be competitively superior and enjoy more mating opportunities. This "Bridging GH" helps to solve the controversial question of what keeps males small and also contributes to explain the wide range of SSD in spiders, as those spider species in which extreme SSD has not evolved but still live in tall vegetation, do not use bridging locomotion to disperse.</p

Flight arena used in this study.

<p>Photograph showing how stimuli were presented in association with the artificial flowers and distributed throughout the flight arena, as well as a marked bumblebee (marked with a numbered yellow tag) visiting a flower.</p

Experimental design.

<p>Combinations of unconditioned (US) and conditioned (CS) stimuli experienced by the bees during training. Each rectangular box indicates the contents of the flight arena at the beginning of each trial, for bees in the different treatments (represented by columns) in each experimental phase (top and bottom rows for phases 1 and 2, respectively). We studied the effect on learning of four reinforcement schedules, characterized by different choices of the US-. The US- could be water (W) or quinine (Q) during the whole experiment, or change from one to the other halfway through the experiment, accounting for the four experimental treatments: WW, WQ, QW and QQ. Regardless of the treatment, bees entering the arena encountered eight distractor flowers (US- column in each rectangular box), each one containing ca. 25 µl of the US- (represented by “filled cups”), and eight target flowers (US+ column). Four target flowers were empty (empty cups) and the other four contained ca. 25 µl of the US+ (sucrose solution – filled cups). Note that, in the experiment, distractor and target flowers were haphazardly distributed throughout the arena. Distractor and target flowers were identified by the colour squares (CS+ and CS-) on which they were set (represented by the cream and reddish parallelograms in the figure). The squares were cut from Canson Mi-Teintes cardboard (refs. 133 and 336). Forty bees were allocated to the different treatments, 10 bees per treatment. Within each experimental group, colour #133 was the CS+ for five of the bees and the CS- for the other five.</p

Relationship between choice latency and performance during phase 1.

<p>Each dot represents the choice latency and performance for an individual bee. Latencies are calculated as the averages of those measured in trials 14 and 29. Performance is the proportion of correct choices over a block, for (A) block 1 (trials 1–5), (B) block 2 (trials 6–10) and (C) block 3 (trials 11–14). Symbol type indicates whether bees experienced water (red squares) or quinine (blue circles) as negative reinforcer during phase 1. Note the increase in the slope of the regression line as we move from A to C.</p