Dynamics of choice during estimation of subjective value

This study characterized preferential choice in binary trials and investigated intra-session variations in response time (RT). In Experiment 1, participants (N = 77) were asked to choose the preferred of two images of body wash; all unique combinations of 19 images were presented. The results showed: (a) marked and consistent individual preferences for specific stimuli; (b) RT decreased monotonically with increasing exposure to each stimulus; (c) RT decreased exponentially as a function of relative preference ranking of the 2 images in a trial; and (d) a regression model efficiently predicted trial RT as a function of exposure and relative preference. Experiment 2 (N = 112) explored the effect of amount of exposure on RT, and relative preference as a function of the type of choice task (a previously completed vs. a new choice task). The results showed that: (a) within a single choice task, amount of exposure and relative preference between the stimuli predicted the systematic changes in RT observed in Exp. 1; and (b) when the choice task changed, the effects of previous amount of exposure, and relative stimulus preference did not transfer to the new task.     

Increased landscape heterogeneity supports the conservation of European rollers (Coracias garrulus) in southern Hungary

European rollers (Coracias garrulus) were almost extinct from large parts of Hungary in the 1970–1980s. However up till now their population size increased considerably, mainly due to a nature conservation campaign, supplying artificial nest-boxes for breeding. We studied which factors affected rollers’ occurrences at the landscape scale in southern Hungary, under natural circumstances and when artificial nest-boxes were supplied. We analyzed the composition and the configuration of the landscape at two spatial scales. We found that beside the presence of natural grasslands, heterogeneous landscape provided high quality breeding and hunting sites favorable for rollers. Even though habitat characteristics of roller territories with natural holes or nest-boxes were similar, breeding sites without artificial nest-boxes harbored higher coverage of forests and heterogeneous agricultural areas. Sites with occupied and unoccupied nest-boxes considerably overlapped, suggesting that the available habitats were not saturated. Nest-box supplementation proved to be an effective tool for rollers’ conservation in areas where natural nesting sites were limited, but prey resources were available. Consequently, the preservation of landscape heterogeneity is a key factor which should be taken into consideration in the conservation management of roller populations.     

Variation between and within the sexes in body size preferences

Although it is often assumed that males and females have mating preferences for larger individuals of the other sex, potential underlying differences between male and female preferences for body size are not commonly investigated. Here, sexual differences in body size preferences are examined in the poeciliid fish, Brachyrhaphis rhabdophora. Females preferred larger males to smaller males, but preference did not appear to be affected by female size. One population-level analysis for males did not indicate an overall preference for larger females. A closer examination, however, revealed an effect of male size on preference; larger males preferred larger females, while smaller males preferred smaller females. It appears then that females, regardless of size, share a preference for large males, but males differ in their behaviour, depending on their body size. In addition, while the degree of difference in size between paired females did not appear to affect male preference, the degree of difference in size between paired males strongly affected female preference; the greater the difference, the more strongly females preferred the larger male. Thus, intersexual selection is found to operate in both sexes, but how it operates appears to differ. Intrasexual and intersexual differences in mating behaviour may be missed when evaluating population-wide preferences. That is, there can be underlying differences in how the sexes respond and the consequences of such differences should be considered when investigating mate choice. The results are considered in terms of the evolution of mating preferences, alternative mating strategies, assortative mating, the maintenance of trait variation in a population, and current methods to evaluate mating preferences.     

Field preferences of the Social Wasp Vespula germanica (Hymenoptera: Vespidae) for Protein-rich Baits

Food preferences displayed by foraging insects are important from a fundamental perspective and in pest control. We studied the preference of an invasive wasp, V. germanica, for protein foods in field conditions. Preferences were evaluated by placing baits in a paired design in different habitats and analyzing wasp visits, using a Bayesian approach to the Thurstone model. V. germanica workers display a clear rating of preferences, but were affected by the presence of competitors at the bait. These results contribute knowledge aimed at toxic baiting protocols for this wasp and suggest that food choice is a complex process subject to the influence of diverse factors. We emphasize the importance of on-site paired comparisons in preference studies to fully understand the drivers of food choice by insects.     

Bumblebees occupy: when foragers do and do not use the presence of others to first find food

The aim of this study was to determine whether an unlearned preference by bumblebees for flowers that are occupied by other bees is frequency dependent and whether it depends on the size of the flower. In three experiments, bees leaving their colony for the first time were given 20 unrewarded choices of occupied versus unoccupied floral patterns in a radial arm maze. In Experiment 1, the relative frequency of occupiers was manipulated. In Experiment 2, a variety of large (≥6 cm diameter) artificial flowers was used. In Experiment 3, floral patterns were eliminated in an effort to reduce the similarity between “occupied” and “unoccupied”. A significant unlearned preference was found only under the combination of conditions in which occupied flowers were comparatively rare and the occupier to flower size ratio was relatively high. Otherwise, the preferences were non-significant, though the stimuli were discriminable because control groups given prior discrimination training acquired a preference. Our results narrow down the conditions under which foragers respond to the presence of others when making their first floral choices.     

Unabhängigkeit der bewertung zweier musterparameter von deren unterschiedlichkeitsgrad bei der Dressur

Bees were trained on a black disc (rewarded) against a smaller grey disc (unrewarded). Thus the bees had the choice of distinguishing between the two training figures by relying on the difference in size or on the difference in greyness or on both parameters. The aim of the present investigation was whether the relative weight of these parameters depended upon the differences in size and greyness presented during the training phase. 1. During the first two days of training the relative rating of these parameters changed in some, though not all individuals. In these cases the size of the discs rose in importance while the greyness was rated uniformly high (Fig. 3). Later, from the third day of training onwards the parameters were rated constantly. 2. Whenever size and greyness of the two training figures differed noticeably the bee relied on both parameters. The bee rated both parameters independently of the quantity of the differences in size and greyness presented during the training (Fig. 5). Thus the bee's analysis of the tested patterns cannot be attributed solely to the training paradigm, but seems to rely also on given (innate) “analyzers” (cf. Sutherland and Mackintosh, 1971). The type of training patterns only determines which “analyzers” influence the choice reaction. 3. The bee's “analyzer for size” had an influence on the choice reaction only if there was a noticeable size-difference between the training figures. The “analyzer for shades of grey”, however, strongly influenced the choice reactions also in those cases where the training figures showed no difference in greyness but only differences in size (Fig. 2).     

Review of the September 30, 2002 Symposium on the "Evolving Legal Status of Chimpanzees"-Harvard Law School

A survey was conducted to assess decisions people make when acquiring dogs, including what sources they consider, the importance of the variety of dogs available, and their willingness to travel to adopt dogs of their choice. A conjoint design was used to ask each respondent to rate his or her likelihood of acquiring a dog based on a “profile” that included attributes such as age, size, and color as well as where the dog came from and euthanasia risk. Overall, these results showed that people preferred variety and would drive distances to get dogs of their choice. The findings revealed that no single attribute drove choice, indicating that people have complex preferences and these vary widely across individuals. Nonhuman animal shelters may be able to increase their adoption rates by providing more variety and not just dogs typically thought of as “in demand” but those who represent a range of diversity through the utilization of animal relocation programs.     

Fruit choice by red howler monkeys (Alouatta seniculus) in a tropical rain forest

This paper presents and discusses aspects of fruit selectivity by red howler monkeys (Alouatta seniculus) in relation with morphological characteristics of fruits. These data are used to provide an answer to the following questions: which are the fruit characteristics that lead fruit choice of howler monkeys and to what extent fruit characteristics play a role in seed dispersal by monkeys? The frugivorous diet of a troop of red howler monkeys was determined during a 2-year field study in French Guiana. The selection of fruit by howler monkeys was analyzed in relation to the fruit availability. Results showed that, although consumption followed availability, fruit species could be classified in three categories according to their selection ratio (percentage of consumption/percentage of abundance) as “high ranking,” “middle ranking,” and “low ranking” species. Also, the 97 species of fruit eaten by the monkeys were grouped according to the morphological characteristics thought to influence the monkeys' choice. This showed that howler monkeys consumed essentially fruits with juicy pulp, bright color, and a small number of well-protected seeds. Most of high ranking species had medium-sized fruits with yellow color, and low ranking species often had small fruits. However, howler monkeys are associated with the dispersal of seeds from fruit with a hard and indehiscent pericarp and/or large seeds, like those of the Sapotaceae family. Consequently, they can be considered as “specialized” frugivores for this fruit syndrome. © l996 Wiley-Liss, Inc.     

Computer animation as a tool to study preferences in the cichlid Pelvicachromis taeniatus

Four choice experiments were conducted with both sexes of the cichlid Pelvicachromis taeniatus using computer-manipulated stimuli of digital images differing in movement, body shape or colouration. The results show that computer animations can be useful and flexible tools in studying preferences of a cichlid with complex and variable preferences for different visual cues.     

Conspecific attraction and shelter selection in gregarious insects

During habitat selection, the presence of conspecifics can frequently drive a nonuniform distribution of animals across habitats of equivalent quality. In group-living species, subgroups of individuals might display mutual attraction while differing in their preferences for environmental resources. The final decision to settle requires individuals to integrate both environmental and social cues. This raises the question of the relative importance of sociality and resources preferences in determining habitat choice. In this study, we examined the interactive influence of conspecific attraction on individual resource preferences on refuge choice in groups of cockroaches. Shelters scaled to the sizes of nymphs and adult males were offered to groups of only nymphs and only males and to mixed groups. The choices of males were consistent across social conditions. Conversely, the preferences of nymphs shifted depending on the social context; the presence of males overrode the affinity nymphs had for scaled-size shelters. We developed a numerical model implementing parameters derived from these experiments to test whether the final spatial distribution of individuals originated from a differential attraction between nymphs and males that was associated with their relative body size. Finally, we propose a general framework for understanding how similar mechanisms can promote the skewed distribution of organisms at different spatial scales.     

Substrate selection and assortative mating in Gammarus pulex L.

We reject the published proposition that assortative mating for size in Gammarus is brought about purely as a result of spatial heterogeneity in substrate particle size. We confirm that, in general, large Gammarus prefer substrates with larger particle size than small Gammarus. However, in artificial streams in the laboratory, in choice experiments Gammarus males and females showed positive assortative mating for size in each of three substrates differing in mean particle size. We propose an explanation for assortative mating based on sexual selection.     

Rational mate choice decisions vary with female age and multidimensional male signals in swordtails

Biologists have long been interested in intransitive preferences: circular preferences in which options cannot be ranked and no single option dominates, similar to a game of rock‐paper‐scissors. Intransitive preferences violate rational decision‐making, an assumption made by models of evolution by mate choice. Despite its potential importance in the study of sexual selection, few studies have tested for intransitive preferences. Even fewer have asked whether females differ in whether they choose mates transitively or intransitively and what factors might predict (in)transitive choice. Though intransitive choice is thought to be more common as options become more complex, this prediction is untested in animals. To fill this gap, we tested whether female Xiphophorus nigrensis swordtails can rank digitally animated males differing in size, courtship intensity, or both size and courtship intensity, and whether female responses were predicted by a female's age. Females choosing among males that varied only in size showed higher than expected levels of intransitivity, whereas females choosing among males that varied in their courtship or both properties did not. Older females were more likely to be irrational than younger females when evaluating male size, suggesting that experience modifies transitive decision‐making processes. These results show that mate choice irrationality may vary by a female's experience and the signal characteristics during decision‐making.     

Pigeons’ (Columba livia) hierarchical organization of local and global cues in touch screen tasks

Redundant encoding of local and global spatial cues is a common occurrence in many species. However, preferential use of the each type of cue seems to vary across species and tasks. In the current study, pigeons (Columba livia) were trained in three experiments on a touch screen task which included redundant local positional cues and global spatial cues. Specifically, pigeons were required to choose the middle out of three choice squares, such that the position within the array provided local information and the location on the screen provided global information. In Experiment 1, pigeons were trained and tested on vertically aligned arrays. In Experiment 2, pigeons were trained and tested on horizontally aligned arrays, and in Experiment 3, pigeons were trained and tested with vertical, horizontal and diagonally aligned arrays. The results indicate that preference for cue type depends upon the type of spatial information being encoded. Specifically, on vertical and diagonally aligned arrays, pigeons preferred global cues, whereas on horizontally aligned arrays, pigeons preferred local cues.     

Colour preferences of flower-naive honeybees

Flower-naive honeybees Apis mellifera L. flying in an enclosure were tested for their colour preferences. Bees were rewarded once on an achromatic (grey, aluminium or hardboard), or on a chromatic (ultraviolet) disk. Since naive bees never alighted on colour stimuli alone, a scent was given in combination with colour. Their landings on twelve colour stimuli were recorded. Results after one reward (“first test”) were analysed separately from those obtained after few rewards (“late tests”).

1. After pre-training to achromatic signals, bees preferred, in the first test, bee-uv-blue and bee-green colours. With increasing experience, the original preference pattern persisted but the choice of bee-blue and bee-green colours increased.
2. Neither colour distance of the test stimuli to the background or to the pre-training signal, nor their intensity, nor their green contrast, accounted for the colour choice of bees. Choices reflected innate preferences and were only associated with stimulus hue.
3. Bees learned very quickly the pre-trained chromatic stimulus, the original colour preferences being thus erased.
4. Colour preferences were strongly correlated with flower colour and its associated nectar reward, as measured in 154 flower species.
5. Colour preferences also resemble the wavelength dependence of colour learning demonstrated in experienced bees.

     

Capuchin monkeys (Cebus apella) fail to show inequality aversion in a no-cost situation

Although humans show robust equality concerns across a variety of situations, there is ongoing debate regarding the extent to which any nonhuman species is inequality averse. In the current research, we test nonhuman primates' reactions to conspecifics receiving equal and unequal payoffs using a “no-cost” method in which subjects can respond to inequality without rejecting food. Specifically, we gave capuchin monkeys (Cebus apella) the opportunity to trade with one of two experimenters, each of whom offered the subject an identical reward, but had different histories of trading with the subject and a conspecific partner. An “equal” experimenter had previously given a conspecific the same reward that the subject had received, whereas the other experimenter was either an “advantageous trader” for the subject (giving the conspecific an inferior reward) or a “disadvantageous trader” for the subject (giving the conspecific a superior reward). By offering subjects a choice between experimenters, we removed several competing demands that may have masked the expression of robust equality preferences in previous studies. Even though there was no cost associated with expressing an equality preference, we found no evidence that capuchins differentiated between equal and unequal experimenters.     

Mutagenesis during transformation of Bacillus subtilis I. An increase in “selfing” resulting from hybrid donor DNAs

Reverse mutations increase when competent Baciilus subtilis cells are transformed with high concentrations of homologous “selfer” DNA. A high proportion of the mutants were also transformants of linked genes. A stimulation in the appearance of reversed mutations occurred when homoduplex and heteroduplex “selfer” DNAs were used as donors. Digestions of native and hybrid DNAs with nuclease S1 from Aspergillus oryzae resulted in the preferential decrease of mutations as compared to a much smaller inactivation of single marker tranformation. Among various repair-deficient strains of B. subtilis, only polyA mutants showed a preferential effect of either suppressing or stimulating the frequency of reverse mutation induced by “selfer” DNA. The results are consistent with mutagenic errors occurring during gap-filling steps in the process of either mismatch repair or recombinational strand exchanges.     

Gynoecium development inRubiaceae-Vanguerieae,with particular reference to the “stylar head”-complex and secondary pollen presentation

Gynoecium development in taxa of the tribeVanguerieae (Rubiaceae, subfam.Antirheoideae) was studied, using primarily a 2- and a 5-carpellate genus (Keetia andVangueria) as examples. All investigated taxa, characterized by ovaries with a solitary, ± apically inserted, pendulous anatropous ovule per locule/carpel, showed a very similar gynoecium development. Comparisons with other uniovulateRubiaceae (taxa of subfam.Rubioideae) revealed that notwithstanding the place of insertion and orientation of the solitary ovules (apically vs. basally inserted, pendulous vs. erect, anatropous ovules) the gynoecium development follows the same pattern; differing ovule insertion and orientation can easily be explained by the principle of variable proportions. — Since secondary pollen presentation is characteristic for the tribe, particular attention was paid to the development of the conspicuous “stylar head”-complex, defined here as structural unit comprised of pollen presenting organ, “receptaculum pollinis”, plus stigmatic (i.e., receptive) surfaces. It was found that their morphological differentiation, following the same pattern in all investigated taxa, starts at very early stages of floral development. They already had their final shape at a stage when the ovule development in the ovary had just barely started. The fully developed, actual “receptaculum pollinis” is made up of enormously enlarged, ± cylindrical epidermis cells which have peculiar ring-like thickenings in vicinity of and parallel to the outer tangential walls (a “mechanical barrier” preventing pollen tubes from entering?) and a much smaller-celled subepidermal tissue. With regard to shape, size, and exposure of the stigmatic surfaces, the investigated taxa exhibited certain morphological differences. These were found to be correlated with differences in androecium structure (and, ultimately, pollen presentation).     

Adaptive,but not condition‐dependent,body shape differences contribute to assortative mating preferences during ecological speciation

Assortative mating is critical for reproductive isolation during speciation; however, the mechanisms underlying mating preferences are often unknown. Assortative mating can be mediated through preferences for condition‐dependent and adaptive (“magic”) traits, but rigorously testing these hypotheses has been impeded by trait covariation in living organisms. We used computer‐generated models to examine the role of body shape in producing association preferences between fish populations undergoing ecological speciation in different habitat types. We demonstrate that body shape can serve as an adaptive trait (variation in head size between populations) and a condition‐dependent signal (variation in abdominal distention among individuals). Female preferences for stimuli varying in only one aspect of body shape uncovered evidence for body shape as a magic trait across population pairs, but no evidence for body shape serving as a condition‐dependent signal. Evolution of preferences only in females from one habitat type as well as stronger preferences in sympatric nonsulfidic as opposed to allopatric nonsulfidic populations suggests that reinforcement may have played a role in producing the observed patterns.     

Origins of female genital diversity: Predation risk and lock‐and‐key explain rapid divergence during an adaptive radiation

The study of male genital diversity has long overshadowed evolutionary inquiry of female genitalia, despite its nontrivial diversity. Here, we identify four nonmutually exclusive mechanisms that could lead to genital divergence in females, and potentially generate patterns of correlated male–female genital evolution: (1) ecological variation alters the context of sexual selection (“ecology hypothesis”), (2) sexually antagonistic selection (“sexual‐conflict hypothesis”), (3) female preferences for male genitalia mediated by female genital traits (“female‐choice hypothesis”), and (4) selection against inter‐population mating (“lock‐and‐key hypothesis”). We performed an empirical investigation of all four hypotheses using the model system of Bahamas mosquitofish inhabiting blue holes that vary in predation risk. We found unequivocal support for the ecology hypothesis, with females exhibiting a smaller genital opening in blue holes containing piscivorous fish. This is consistent with stronger postmating female choice/conflict when predators are present, but greater premating female choice in their absence. Our results additionally supported the lock‐and‐key hypothesis, uncovering a pattern of reproductive character displacement for genital shape. We found no support for the sexual conflict or female choice hypotheses. Our results demonstrate a strong role for ecology in generating female genital diversity, and suggest that lock‐and‐key may provide a viable cause of female genital diversification.