Receiver bias for exaggerated signals in honeybees and its implications for the evolution of floral displays

Mechanistic models of animal signals posit the occurrence of biases on the part of receivers that could be potentially exploited by signallers. Such biases are most obvious when animals are confronted with exaggerated versions of signals they normally encounter. Signalling systems operating in plant-pollinator interactions are among the most highly coevolved, with plants using a variety of floral signals to attract pollinators. A number of observations suggest that pollinators preferentially visit larger floral displays although the benefit of this to either the plant or the pollinator is not always clear. We use a standard dual-choice experimental protocol to show that honeybees display a receiver bias for exaggerated size and colour contrast--two important components of floral signals--even when such signals do not indicate quality. We discuss the implications of this receiver bias for the evolution of floral displays and its possible exploitation by invading alien plants.     

Living with observational data in biological anthropology

The establishment of cause and effect relationships is a fundamental objective of scientific research. Many lines of evidence can be used to make cause–effect inferences. When statistical data are involved, alternative explanations for the statistical relationship need to be ruled out. These include chance (apparent patterns due to random factors), confounding effects (a relationship between two variables because they are each associated with an unmeasured third variable), and sampling bias (effects due to preexisting properties of compared groups). The gold standard for managing these issues is a controlled randomized experiment. In disciplines such as biological anthropology, where controlled experiments are not possible for many research questions, causal inferences are made from observational data. Methods that statisticians recommend for this difficult objective have not been widely adopted in the biological anthropology literature. Issues involved in using statistics to make valid causal inferences from observational data are discussed.     

Evidence of an emerging female preference for an artificial male trait and the potential for spread via mate choice copying in Poecilia latipinna

The initial purpose of the project described herein was to assess the preference of female Poecilia latipinna for an artificial novel male trait—an orange‐colored distal fringe added to the caudal fin of an otherwise wild‐type conspecific. Analysis of the preliminary data revealed consistent individual differences in the strength of female preference for either orange‐tailed or wild‐type males. This finding inspired the study's second aim—to evaluate whether the preference for orange‐tailed males observed among a subset of females could spread via mate choice copying to others in the population that initially preferred wild‐type males. Two experiments and a control were conducted wherein females were simultaneously presented with an orange‐tailed and a wild‐type dummy male using a standard dichotomous choice design. In the first experiment, female preference was assessed on two separate occasions in order to characterize the variability and consistency in preference for orange‐tailed versus wild‐type males. The second experiment addressed mate choice copying: Female preference was again assessed on two separate occasions, but involved pairing a model female with the non‐preferred male for a period of time between preference tests. A third set of control tests were conducted using the same protocol as the copying experiment except that subject females were unable to see the model paired with the non‐preferred male. Results showed that, although females collectively preferred neither the orange‐tailed nor the wild‐type dummy male in the first round of preference tests, the majority showed relatively strong individual preferences. The subset of females that preferred the orange‐tailed over the wild‐type male in the first round of testing all maintained their preferences in the second round whether or not they had observed a model in association with the non‐preferred wild‐type male between tests. However, females that preferred the wild type over the orange male in the first round of testing copied the model's choice of the non‐preferred orange‐tailed male in their second round of preference testing. These results highlight the importance of recognizing the likelihood that only a subset of females will express a preference as it first emerges within a population. In such instances, the preference may not be detected at the population level—a point frequently overlooked in studies of mate choice. Additionally, these data highlight the importance of assessing the preferences of individual females and their capacity to drive evolutionary change within populations. Lastly, this study offers evidence of a possible mechanism by which a novel male trait might spread via mate choice copying by exploiting an emerging sensory bias within a subset of females in the population.     

What are we measuring? Novices agree amongst themselves (but not always with experts) in their assessment of dog behaviour

Humans differ in how they perceive, assess, and measure animal behaviour. This is problematic because strong observer bias can reduce statistical power, accuracy of scientific inference, and in the worst cases, lead to spurious results. Unfortunately, reports and studies of measurement reliability in animal behaviour studies are rare. Here, we investigated two aspects of measurement reliability in working dogs: inter‐observer agreement and criterion validity (comparing novice ratings with those given by experts). Here, we extend for the first time a powerful framework used in human psychological studies to investigate three potential aspects of (dis)agreement in nonhuman animal behaviour research: (a) that some behaviours are easier to observe than others; (b) that some subjects are easier to observe than others; and (c) that observers with different levels of experience with the subject animal give the same or different ratings. We found that novice observers with the same level of experience agreed upon measures of a wide range of behaviours. We found no evidence that age of the dogs affected agreement between these same novice observers. However, when observers with different levels of experience (i.e., novices vs. a working dog expert) assessed the same dogs, agreement appeared to be strongly affected by the measurement instrument used to assess behaviour. Given that animal behaviour research often utilizes different observers with different levels of experience, our results suggest that further tests of how different observers may measure behaviour in different ways are needed across a wider variety of organisms and measurement instruments.     

Compositional dynamics and codon usage pattern of BRCA1 gene across nine mammalian species

The BRCA1 gene is located on the human chromosome 17q21.31 and plays important role in biological processes. The aminoacyl-tRNA synthetases (AARS) are a family of heterogenous enzymes responsible protein synthesis and whose secondary functions include a role in autoimmune myositis. Our findings reveal that the compositional constraint and the preference of more A/T –ending codons determine the codon usage patterns in BRCA1 gene while more G/C-ending codons influence the codon usage pattern of AARS gene among mammals. The codon usage bias in BRCA1 and AARS genes is low. The codon CGC encoding arginine amino acid and the codon TTA encoding leucine were uniformly distributed in BRCA1 and AARS genes, respectively in mammals including human. Natural selection might have played a major role while mutation pressure might have played a minor role in shaping the codon usage pattern of BRCA1 and AARS genes.     

Evaluating food availability and nest predation risk as sources of bias in aural bird surveys

ABSTRACT The use of aural surveys to estimate population parameters is widespread in avian studies. Despite efforts to increase the efficacy of this method, the potential for ecological context to bias population estimates remains largely unexplored. For example, food availability and nest predation risk can influence singing activity independent of density and, therefore, may bias aural estimates where these ecological factors vary systematically among habitats or other categories of ecological interest. We used a natural fire event in a mixed‐conifer forest that experienced variation in fire severity (low, intermediate, and high) to determine if aural surveys produce accurate density estimates of Dark‐eyed Juncos ( Junco hyemalis) independent of ecological context. During the first 2‐yr postfire, we censused junco populations in each burn type with intensive spot‐mapping and nest searching, locating 168 nests. Simultaneously, we conducted fixed‐radius point‐count surveys and estimated food availability and nest predation risk in each burn type to test whether ecological context may influence aural detection probability independent of actual density. We found no difference in nesting densities among patches burned at different severity. Arthropod food availability was inversely related to fire severity during the first postfire breeding season, but increased to higher levels across all severities during the second. In both years, aural detections were significantly greater in intermediate severity patches that consistently represented the habitat with the lowest nest predation risk. These results suggest that nest predation risk may significantly bias aural estimates of avian populations. Although traditional aural survey methods such as the Breeding Bird Survey measure habitat attributes, our findings highlight the difficulty in assessing relevant covariates in estimates of avian population. Future research must consider the potential for nest predation and other ecological factors to drive interannual or interhabitat variation in avian population estimates independent of true changes in population size.     

Why are translationally sub-optimal synonymous codons used in Escherichia coli?

Natural selection favors certain synonymous codons which aid translation in Escherichia coli, yet codons not favored by translational selection persist. We use the frequency distributions of synonymous polymorphisms to test three hypotheses for the existence of translationally sub-optimal codons: (1) selection is a relatively weak force, so there is a balance between mutation, selection, and drift; (2) at some sites there is no selection on codon usage, so some synonymous sites are unaffected by translational selection; and (3) translationally sub-optimal codons are favored by alternative selection pressures at certain synonymous sites. We find that when all the data is considered, model 1 is supported and both models 2 and 3 are rejected as sole explanations for the existence of translationally sub-optimal codons. However, we find evidence in favor of both models 2 and 3 when the data is partitioned between groups of amino acids and between regions of the genes. Thus, all three mechanisms appear to contribute to the existence of translationally sub-optimal codons in E. coli. Received: 18 July 2000 / Accepted: 17 April 2001     

Mutability of microsatellites developed for the ant Camponotus consobrinus

Five highly polymorphic (GA)n microsatellite loci are reported for the formicine ant Camponotus consobrinus. The occurrence of many nests with a simple family structure enabled a search for new mutations, 11 of which were found from 3055 informative typings. These mutations were not randomly distributed across loci, 10 of them occurring at the locus Ccon70. The spectrum of mutations across alleles at Ccon70 was also nonrandom, with all of them occurring in alleles in the upper half of the allele size distribution. Six of the Ccon70 mutations decreased allele size. The mutations observed fit the stepwise mutation model well, i.e. mutations could always be assigned to an allele which differed in size from them by one repeat unit. The parental origins of the Ccon70 mutations were established and appear more female biased than vertebrate mutations, significantly so compared with human haemophilia A and primate intron mutations. This result may indicate that the lack of meiosis in males (which are haploid in ants) reduces the mutation rate in that sex relative to species in which both sexes are diploid.     

Generalized estimating equations for ordinal categorical data: arbitrary patterns of missing responses and missingness in a key covariate

We propose methods for regression analysis of repeatedly measured ordinal categorical data when there is nonmonotone missingness in these responses and when a key covariate is missing depending on observables. The methods use ordinal regression models in conjunction with generalized estimating equations (GEEs). We extend the GEE methodology to accommodate arbitrary patterns of missingness in the responses when this missingness is independent of the unobserved responses. We further extend the methodology to provide correction for possible bias when missingness in knowledge of a key covariate may depend on observables. The approach is illustrated with the analysis of data from a study in diagnostic oncology in which multiple correlated receiver operating characteristic curves are estimated and corrected for possible verification bias when the true disease status is missing depending on observables.     

Codon Bias and Mutability in HIV Sequences

A survey of the patterns of synonymous codon preference in the HIV env gene reveals a correlation between the codon bias and the mutability requirements of different regions of the protein. At hypervariable regions in gp120 one finds a greater proportion of codons that tend to mutate nonsynonymously, but to a target that is similar in hydrophobicity and volume. We argue that this strategy results from a compromise between the selective pressure placed on the virus by the induced immune response, which favors amino acid substitutions in the complementarity determining regions, and the negative selection against missense mutations that violate structural constraints of the env protein. Received: 9 June 1997 / Accepted: 25 May 1998