Search results for " selection"
showing 10 items of 1271 documents
Coincidental loss of bacterial virulence in multi-enemy microbial communities.
2014
The coincidental virulence evolution hypothesis suggests that outside-host selection, such as predation, parasitism and resource competition can indirectly affect the virulence of environmentally-growing bacterial pathogens. While there are some examples of coincidental environmental selection for virulence, it is also possible that the resource acquisition and enemy defence is selecting against it. To test these ideas we conducted an evolutionary experiment by exposing the opportunistic pathogen bacterium Serratia marcescens to the particle-feeding ciliate Tetrahymena thermophila, the surfacefeeding amoeba Acanthamoeba castellanii, and the lytic bacteriophage Semad11, in all possible combi…
SEXUALLY SELECTED TRAITS EVOLVE POSITIVE ALLOMETRY WHEN SOME MATINGS OCCUR IRRESPECTIVE OF THE TRAIT
2014
Positive allometry of secondary sexual traits (whereby larger individuals have disproportionally larger traits than smaller individuals) has been called one of the most pervasive and poorly understood regularities in the study of animal form and function. Its widespread occurrence is in contrast with theoretical predictions that it should evolve only under rather special circumstances. Using a combination of mathematical modeling and simulations, here we show that positive allometry is predicted to evolve under much broader conditions than previously recognized. This result hinges on the assumption that mating success is not necessarily zero for males with the lowest trait values: for examp…
The advantage of alternative tactics of prey and predators depends on the spatial pattern of prey and social interactions among predators
2011
Individual variation in behavioral strategies is ubiquitous in nature. Yet, explaining how this variation is being maintained remains a challenging task. We use a spatially-explicit individual-based simulation model to evaluate the extent to which the efficiency of an alternative spacing tactic of prey and an alternative search tactic of predators are influenced by the spatial pattern of prey, social interactions among predators (i.e., interference and information sharing) and predator density. In response to predation risk, prey individuals can either spread out or aggregate. We demonstrate that if prey is extremely clumped, spreading out may help when predators share information regarding…
Do female leaf beetles Galerucella nymphaeae choose their mates and does it matter?
1998
The role of active female choice in sexual selection is frequently difficult to ascertain, and this is particularly the case for many insect species. Also, it is uncertain whether choosing between males would affect offspring viability. We designed an experiment to investigate the presence of female choice in a Coleoptera species (Galerucella nymphaeae). We also estimated whether mate choice would have any effect on offspring performance. Females were first placed with two males in a test arena to see which of the males copulated with the virgin female, and how quickly. Subsequently the loser male was offered a new virgin female to test for any change in latency time until mating. The two-m…
When are vomiting males attractive? Sexual selection on condition-dependent nuptial feeding in Drosophila subobscura
2009
Nuptial gifts are any nutritious items or inedible tokens transferred from the male to the female as a part of courtship or copulation. Although nuptial gift donation has been studied in a variety of taxa, this behavior has been largely overlooked in Drosophila. We studied nuptial feeding in Drosophila subobscura, where the gift is a regurgitated drop of liquid, in order to examine the importance of this behavior for male mating success and female fecundity. We varied male and female condition by dietary restriction to assess any condition dependence of male nuptial feeding ability and female feeding behavior and mate discrimination. Our results show that there was directional selection for…
Sexual signalling and viability in a wolf spider ( Hygrolycosa rubrofasciata ): measurements under laboratory and field conditions
1999
This study examined the crucial prediction of the conditional-handicap theory, the relationship between male sexual trait size and male viability, in the wolf spider Hygrolycosa rubrofasciata. In this species, males court females by drumming dry leaves with their abdomen, and males with the highest drumming rate enjoy highest mating success. We determined male drumming rate, body mass, and mobility, which reflects mate-searching activity, in relation to male survival. Because it is often difficult to know how results obtained from laboratory studies reflect the natural world, particularly when the measured variable is survival, we repeated our study in both laboratory and field conditions. …
Unbundling technology adoption and tfp at the firm level. Do intangibles matter?
2012
We use a panel of European firms to investigate the relationship between intangible assets and productivity. We distinguish between total factor productivity (tfp) and technology adoption, whereas standard estimations consider only a notion of productivity that conflates the two effects. Although we are unable to address simultaneity, we allow for the existence of multiple technologies within sectors through a mixture model approach. We find that intangible assets have nonnegligible effects that both push firms toward better technologies (technology adoption effects) and allow for more efficient exploitation of a given technology (tfp effects).
Selection by committee: Anonymity and gratitude
2018
Abstract What kind of candidate is selected into a job when the principal has to appoint a committee to measure the candidates’ ability and select a winner? We find that if the committee takes into account the candidate’s gratitude towards them, a candidate with less than first best ability will be selected. A relevant exception may occur if the first best is the overall best candidate. First best selection is always achieved if the committee is anonymous to the candidates. If the committee is not detached enough from the candidates then delegation fares even worse than random selection.
The timeline of trading frictions in the European carbon market
2012
We evaluate the quality of prices of EU-ETS, the most active European derivative market for greenhouse gas emissions allowances (EUAs). So far, this market has had two phases, a trial phase (from 2005 to 2007) and a commitment phase (from 2008 to 2012). The true value of a trial-phase EUA at the beginning of 2008 was inevitably zero because it could not be used in the commitment phase to cover emission targets. However, continued rumors of over-allocation of EUAs led to an early collapse of the market by May 2007. We study whether this market breakdown and the subsequent outbreak of the international financial crisis had a persistent effect on the quality of the commitment phase. We provide…
Variable selection in the analysis of energy consumption-growth nexus
2015
There is abundant empirical literature that focuses on whether energy consumption is a critical driver of economic growth. The evolution of this literature has largely consisted of attempts to solve the problems and answer the criticisms arising from earlier studies. One of the most common criticisms is that previous work concentrates on the bivariate relationship, energy consumption–economic growth. Many authors try to overcome this critique using control variables. However, the choice of these variables has been ad hoc, made according to the subjective economic rationale of the authors. Our contribution to this literature is to apply a robust probabilistic model to select the explanatory …