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Signal Evolution (signal + evolution)

Distribution by Scientific Domains

Life Sciences	90%

Selected Abstracts

PEAK SHIFT DISCRIMINATION LEARNING AS A MECHANISM OF SIGNAL EVOLUTION

EVOLUTION, Issue 6 2005
Spencer K. Lynn
Abstract "Peak shift" is a behavioral response bias arising from discrimination learning in which animals display a directional, but limited, preference for or avoidance of unusual stimuli. Its hypothesized evolutionary relevance has been primarily in the realm of aposematic coloration and limited sexual dimorphism. Here, we develop a novel functional approach to peak shift, based on signal detection theory, which characterizes the response bias as arising from uncertainty about stimulus appearance, frequency, and quality. This approach allows the influence of peak shift to be generalized to the evolution of signals in a variety of domains and sensory modalities. The approach is illustrated with a bumblebee (Bombus impatiens) discrimination learning experiment. Bees exhibited peak shift while foraging in an artificial Batesian mimicry system. Changes in flower abundance, color distribution, and visitation reward induced bees to preferentially visit novel flower colors that reduced the risk of flower-type misidentification. Under conditions of signal uncertainty, peak shift results in visitation to rarer, but more easily distinguished, morphological variants of rewarding species in preference to their average morphology. Peak shift is a common and taxonomically widespread phenomenon. This example of the possible role of peak shift in signal evolution can be generalized to other systems in which a signal receiver learns to make choices in situations in which signal variation is linked to the sender's reproductive success. [source]

A Method for Simulating Signal Evolution Using Real Animals

ETHOLOGY, Issue 10 2000
Björn Forkman
We studied response biases to visual stimulation using a new experimental technique. The subjects (hens, Gallus gallus domesticus) were confronted with several rewarding and non-rewarding patterns on a computer screen. In contrast with standard discrimination tasks the rewarding patterns were not identical and varied in a dimension differentiating them from the non-rewarding patterns. The rewarding patterns changed in response to hens' biases in selection of patterns. The aim of the study was to examine the possibility of receivers being a driving force in signal evolution. In one of the experiments a clear-cut result was obtained. During the course of the experiment the rewarding patterns became gradually more different from the non-rewarding one, a result expected from theoretical studies of the effect of response bias in signal evolution. A second similar experiment was less conclusive, with ceiling and floor effects influencing the results. [source]

Mating signal partitioning in multi-species assemblages: a null model test using frogs

ECOLOGY LETTERS, Issue 3 2003
Andrew A. Chek
Abstract Competitive partitioning of ,community' signal space has long been suggested to underlie diversification of mating signals. Selection or competitive exclusion is expected to reduce overlap of signals, minimizing destructive interference or reducing mismating. We used null models backed by simulation of type I and II error rates to test for evidence of structuring within 11 frog advertisement call assemblages. Within three assemblages, we found significant over-dispersion and regularity-of-spacing in dominant frequency and in pulse rate, consistent with a signal interference hypothesis and signal confusion hypothesis, respectively. Observed partitioning could represent signal evolution or could result from selection on assemblage composition. Most assemblages showed no acoustic partitioning possibly because: (i) partitioning is more readily apparent in female preference, calling times or sites, rather than call attributes; (ii) assemblages have not yet accommodated recently arrived species, or are compositionally unstable so that acoustic accommodation cannot occur; and (iii) evidence of partitioning is only likely where the acoustic space is densely packed. [source]

Divergence in Female Duetting Signals in the Enchenopa binotata Species Complex of Treehoppers (Hemiptera: Membracidae)

ETHOLOGY, Issue 12 2006
Rafael L. Rodríguez
Sexual communication often involves signal exchanges between the sexes, or duetting, in which mate choice is expressed through response signals. With both sexes acting as signalers and receivers, variation in the signals of males and females may be important for mate choice, reproductive isolation, and divergence. In the Enchenopa binotata species complex , a case study of sympatric speciation in which vibrational duetting may have an important role , male signals are species-specific, females choose among males on the basis of signal traits that reflect species and individual differences, and female preferences have exerted divergent selection on male signals. Here, we describe variation in female signals in the E. binotata species complex. We report substantial species differences in the spectral and temporal features of female signals, and in their timing relative to male signals. These differences were similar in range to differences in male signals in the E. binotata complex. We consider processes that might contribute to divergence in female signals, and suggest that signal evolution in the E. binotata complex may be influenced by mate choice in both sexes. [source]

A Method for Simulating Signal Evolution Using Real Animals

EVOLUTION OF BIRD SONG AFFECTS SIGNAL EFFICACY: AN EXPERIMENTAL TEST USING HISTORICAL AND CURRENT SIGNALS

EVOLUTION, Issue 8 2007
Elizabeth P. Derryberry
Mating signals act as behavioral barriers to gene flow in many animal taxa, yet little is known about how signal evolution within populations contributes to the formation of these barriers. Although variation in mating signals among populations is known to affect mating behavior, there is no direct evidence that the evolution of mating signals changes signal effectiveness within a natural population. Making use of historical recordings of bird song, I found that both male and female white-crowned sparrows (Zonotrichia leucophrys) respond more strongly to current than to historical songs, indicating that historical songs are less effective as signals in the current contexts of both mate choice and male,male competition. Finding that historical signals are less effective suggests that signal evolution within populations may ultimately contribute to the formation of behavioral barriers to gene flow between populations. [source]

PEAK SHIFT DISCRIMINATION LEARNING AS A MECHANISM OF SIGNAL EVOLUTION

Differentiation of morphology, genetics and electric signals in a region of sympatry between sister species of African electric fish (Mormyridae)

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2008
S. LAVOUÉ
Abstract Mormyrid fishes produce and sense weak electric organ discharges (EODs) for object detection and communication, and they have been increasingly recognized as useful model organisms for studying signal evolution and speciation. EOD waveform variation can provide important clues to sympatric species boundaries between otherwise similar or morphologically cryptic forms. Endemic to the watersheds of Gabon (Central Africa), Ivindomyrus marchei and Ivindomyrus opdenboschi are morphologically similar to one another. Using morphometric, electrophysiological and molecular characters [cytochrome b sequences and amplified fragment length polymorphism (AFLP) genotypes], we investigated to what extent these nominal mormyrid species have diverged into biological species. Our sampling covered the known distribution of each species with a focus on the Ivindo River, where the two taxa co-occur. An overall pattern of congruence among datasets suggests that I. opdenboschi and I. marchei are mostly distinct. Electric signal analysis showed that EODs of I. opdenboschi tend to have a smaller initial head-positive peak than those of I. marchei, and they often possess a small third waveform peak that is typically absent in EODs of I. marchei. Analysis of sympatric I. opdenboschi and I. marchei populations revealed slight, but significant, genetic partitioning between populations based on AFLP data (FST , 0.04). Taken separately, however, none of the characters we evaluated allowed us to discriminate two completely distinct or monophyletic groups. Lack of robust separation on the basis of any single character set may be a consequence of incomplete lineage sorting due to recent ancestry and/or introgressive hybridization. Incongruence between genetic datasets in one individual, which exhibited a mitochondrial haplotype characteristic of I. marchei but nevertheless fell within a genetic cluster of I. opdenboschi based on AFLP genotypes, suggests that a low level of recent hybridization may also be contributing to patterns of character variation in sympatry. Nevertheless, despite less than perfect separability based on any one dataset and inconclusive evidence for complete reproductive isolation between them in the Ivindo River, we find sufficient evidence to support the existence of two distinctive species, I. opdenboschi and I. marchei, even if not ,biological species' in the Mayrian sense. [source]

Proximate mechanisms of variation in the carotenoid-based plumage coloration of nestling great tits (Parus major L.)

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2003
B. Tschirren
Abstract Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoid-supplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality. [source]

T1 relaxation times for viability evaluation of the engrafted and the native liver in a rat model of heterotopic auxiliary liver transplantation: a pilot study

NMR IN BIOMEDICINE, Issue 6 2001
Ye-Dong Fan
Abstract Following a heterotopic auxiliary liver transplantation, commonly used measurements are either invasive or non-indicative of individual viability of the coexisting engrafted and native livers. Magnetic resonance imaging (MRI) was therefore tested for its potential to monitor the post-transplant hepatic viability in a rat model. Thirteen Wistar rats were systematically evaluated with MRI and serum biochemical liver parameters. Post-transplant complications and the causes of animal death were identified by autopsy and histo-pathological examinations. The data of the healthy survivors were compared with those of the rats that developed complications. On MRI, the hepatic complications could be depicted in the individual livers. A specific pattern of signal evolution was found in the livers of the healthy survivors: the mean T1 relaxation times of the engrafted livers increased immediately after transplantation (476,±,64,ms, mean,±,standard deviation, pre-operative; 730,±,48,ms, week 1) and then declined steadily to a 3 month value of 489,±,246,ms, while, following a transient first rise (476,±,64,ms, pre-operative; 589,±,28,ms, week 1), the mean T1 value of the native livers increased again 4 weeks after surgery and reached a 3 month value of 859,±,43,ms. However, in the rats with various complications, the mean T1 relaxation times of the engrafted livers continued to increase throughout the first post-operative month (760,±,48,ms, week 1; 922,±,76,ms, week 4), while that of the native liver only varied mildly (546,±,25,ms, week 1; 473,±,25,ms, week 4). After the first post-transplant week, the healthy engrafted livers could already be distinguished from those with complications by a significant decrease in T1 relaxation times. These data suggest that, besides demonstrating major complications, MRI may allow one to monitor the viability of each liver by analysing the relative signal intensity and T1 relaxation times after a heterotopic auxiliary liver transplantation. Copyright © 2001 John Wiley & Sons, Ltd. [source]