Receiver discriminability drives the evolution of complex sexual signals by sexual selection

A hallmark of sexual selection by mate choice is the evolution of exaggerated traits, such as longer tails in birds and more acoustic components in the calls of birds and frogs. Trait elaboration can be opposed by costs such as increased metabolism and greater predation risk, but cognitive processes of the receiver can also put a brake on trait elaboration. For example, according to Weber's Law traits of a fixed absolute difference will be more difficult to discriminate as the absolute magnitude increases. Here, we show that in the Emei music frog (Babina daunchina) increases in the fundamental frequency between successive notes in the male advertisement call, which increases the spectral complexity of the call, facilitates the female's ability to compare the number of notes between calls. These results suggest that female's discriminability provides the impetus to switch from enhancement of signaling magnitude (i.e., adding more notes into calls) to employing a new signal feature (i.e., increasing frequency among notes) to increase complexity. We suggest that increasing the spectral complexity of notes ameliorates some of the effects of Weber's Law, and highlights how perceptual and cognitive biases of choosers can have important influences on the evolution of courtship signals.     

Proportional processing of a visual mate choice signal in the green swordtail,Xiphophorus hellerii

During mate choice, receivers often assess the magnitude (duration, size, etc.) of signals that vary along a continuum and reflect variation in signaller quality. It is generally assumed that receivers assess this variation linearly, meaning each difference in signalling trait between signallers results in a commensurate change in receiver response. However, increasing evidence shows receivers can respond to signals non-linearly, for example through Weber's Law of proportional processing, where discrimination between stimuli is based on proportional, rather than absolute, differences in magnitude. We quantified mate preferences of female green swordtail fish, Xiphophorus hellerii, for pairs of males differing in body size. Preferences for larger males were better predicted by the proportional difference between males (proportional processing) than the absolute difference (linear processing). This demonstration of proportional processing of a visual signal implies that receiver perception may be an important mechanism selecting against the evolution of ever-larger signalling traits.     

Lifetime monogamy and the evolution of eusociality

All evidence currently available indicates that obligatory sterile eusocial castes only arose via the association of lifetime monogamous parents and offspring. This is consistent with Hamilton''s rule (br_s > r_oc), but implies that relatedness cancels out of the equation because average relatedness to siblings (r_s) and offspring (r_o) are both predictably 0.5. This equality implies that any infinitesimally small benefit of helping at the maternal nest (b), relative to the cost in personal reproduction (c) that persists throughout the lifespan of entire cohorts of helpers suffices to establish permanent eusociality, so that group benefits can increase gradually during, but mostly after the transition. The monogamy window can be conceptualized as a singularity comparable with the single zygote commitment of gametes in eukaryotes. The increase of colony size in ants, bees, wasps and termites is thus analogous to the evolution of multicellularity. Focusing on lifetime monogamy as a universal precondition for the evolution of obligate eusociality simplifies the theory and may help to resolve controversies about levels of selection and targets of adaptation. The monogamy window underlines that cooperative breeding and eusociality are different domains of social evolution, characterized by different sectors of parameter space for Hamilton''s rule.     

Scaling relative incentive value: different adjustments to incentive downshift in pigeons and rats

Previous research suggests that pigeons and rats show differences in their behavioral adjustments in spaced-trial, incentive-downshift situations. Also, Papini and Pellegrini [Papini, M.R., Pellegrini, S., 2006. Scaling relative incentive value in consummatory behavior. Learn. Motiv. 37, 357-378] and Pellegrini and Papini [Pellegrini, S., Papini, M.R., 2007. Scaling relative incentive value in anticipatory behavior. Learn. Motiv. 38, 128-154] showed that changes in the rat's lever-pressing performance, runway running, and consumption of sucrose solutions after downshifts in incentive magnitude were a function of the ratio of postshift/preshift incentive magnitudes. Here, two experiments using a Pavlovian autoshaping procedure studied the adjustment of pigeons and rats to changes in incentive magnitude. In Experiment 1, pigeons received light-food pairings, whereas in Experiment 2, rats received lever-sucrose pairings. As a result, key-pecking and lever-pressing developed in each experiment, respectively. Preshift incentive magnitudes were downshifted so as to obtain postshift/preshift ratios of 0.125 and 0.25. Pigeons responded during the postshift phase according to the preshift incentive value and independently of the ratio value. However, rats showed ratio constancy, responding during the postshift in accordance with the postshift/preshift ratio, rather than with the absolute magnitudes of either the preshift or postshift incentives. These results support the comparative hypothesis that the mechanisms underlying ratio constancy during incentive downshifts are unique to mammals.     

Are there general laws for digit evolution in squamates? The loss and re‐evolution of digits in a clade of fossorial lizards (Brachymeles,Scincinae)

Evolutionary simplification of autopodial structures is a major theme in studies of body‐form evolution. Previous studies on amniotes have supported Morse's law, that is, that the first digit reduced is Digit I, followed by Digit V. Furthermore, the question of reversibility for evolutionary digit loss and its implications for “Dollo's law” remains controversial. Here, we provide an analysis of limb and digit evolution for the skink genus Brachymeles. Employing phylogenetic, morphological, osteological, and myological data, we (a) test the hypothesis that digits have re‐evolved, (b) describe patterns of morphological evolution, and (c) investigate whether patterns of digit loss are generalizable across taxa. We found strong statistical support for digit, but not limb re‐evolution. The feet of pentadactyl species of Brachymeles are very similar to those of outgroup species, while the hands of these lineages are modified (2‐3‐3‐3‐2) and a have a reduced set of intrinsic hand muscles. Digit number variation suggests a more labile Digit V than Digit I, contrary to Morse's law. The observed pattern of digit variation is different from that of other scincid lizards (Lerista, Hemiergis, Carlia). Our results present the first evidence of clade‐specific modes of digit reduction.     

Monitoring the social behavior of a bachelor mandrill (Mandrillus sphinx) dyad participating in touchscreen‐mediated cognitive testing

Cognitive testing of primates in zoos is becoming increasingly common. Cognition experiments are generally thought to be beneficial as they provide participants with an opportunity to engage in species‐specific cognitive functioning, perhaps more so than with traditional forms of environmental enrichment. However, testing may increase competition and aggression between conspecifics if it has monopolizable features or creates social tension within groups. The purpose of this study was to monitor the social behavior of a bachelor mandrill (Mandrillus sphinx) dyad participating in a touchscreen‐mediated cognition study. The mandrills' behavior was monitored before and after testing sessions for 8 months. Positive changes in the mandrills' affiliative behavior were observed. Rates of play, presentations, and silent bared‐teeth face increased posttesting. No change in rates of agonism were observed between pre‐ and posttesting conditions. The observed positive changes in affiliative behavior suggest cognitive testing was enriching for the mandrills and participating in testing improved their welfare. Zoos beginning cognitive studies should monitor participant behavior to ensure their welfare is not compromised and is, ideally, enhanced.     

On the challenges and mechanisms of embodied decisions

Neurophysiological studies of decision-making have focused primarily on elucidating the mechanisms of classic economic decisions, for which the relevant variables are the values of expected outcomes and action is simply the means of reporting the selected choice. By contrast, here we focus on the particular challenges of embodied decision-making faced by animals interacting with their environment in real time. In such scenarios, the choices themselves as well as their relative costs and benefits are defined by the momentary geometry of the immediate environment and change continuously during ongoing activity. To deal with the demands of embodied activity, animals require an architecture in which the sensorimotor specification of potential actions, their valuation, selection and even execution can all take place in parallel. Here, we review behavioural and neurophysiological data supporting a proposed brain architecture for dealing with such scenarios, which we argue set the evolutionary foundation for the organization of the mammalian brain.     

Demography and research with high altitude populations

Abstract

This report compares the 1977 genetic demographies of Colonsay and Jura, adjacent yet isolated islands of the Scottish Inner Hebrides. Completed family analyses demonstrated that the residents of Colonsay have higher fertility, shorter generation length, and longer female reproduction span than those of Jura. Based on oral genealogies of five to six generations, the natives of Jura had a higher inbreeding coefficient (f= 0.0044) than did those of Colonsay (f= 0.0023). Each set of natives mainly derives from small groups of “founding” ancestors. Founder effects in the populations are transitory phenomena dependent upon population decline and the periodic emigration of native families. With their small sizes, the maximum sampling errors due to random genetic drift are ±0.063 for Colonsay and ±0.059 for Jura per generation. An unusual finding was that the effective sizes of Colonsay and Jura exceed their respective breeding sizes. Today Colonsay and Jura are former geographical isolates in dissolution through an increasing marital admixture with immigrants. Human migration dictated in large part by Hebridean economics dominates the mi‐croevolutions of Colonsay and Jura.     

Animal evolution during domestication: the domesticated fox as a model

We review the evolution of domestic animals, emphasizing the effect of the earliest steps of domestication on its course. Using the first domesticated species, the dog (Canis familiaris), for illustration, we describe the evolutionary peculiarities during the historical domestication, such as the high level and wide range of diversity. We suggest that the process of earliest domestication via unconscious and later conscious selection of human‐defined behavioral traits may accelerate phenotypic variations. The review is based on the results of a long‐term experiment designed to reproduce early mammalian domestication in the silver fox (Vulpes vulpes) selected for tameability or amenability to domestication. We describe changes in behavior, morphology and physiology that appeared in the fox during its selection for tameability, which were similar to those observed in the domestic dog. Based on the data of the fox experiment and survey of relevant data, we discuss the developmental, genetic and possible molecular genetic mechanisms underlying these changes. We ascribe the causative role in evolutionary transformation of domestic animals to the selection for behavior and to the neurospecific regulatory genes it affects.     

Animal visual systems and the evolution of color patterns: sensory processing illuminates signal evolution

Abstract Animal color pattern phenotypes evolve rapidly. What influences their evolution? Because color patterns are used in communication, selection for signal efficacy, relative to the intended receiver's visual system, may explain and predict the direction of evolution. We investigated this in bowerbirds, whose color patterns consist of plumage, bower structure, and ornaments and whose visual displays are presented under predictable visual conditions. We used data on avian vision, environmental conditions, color pattern properties, and an estimate of the bowerbird phylogeny to test hypotheses about evolutionary effects of visual processing. Different components of the color pattern evolve differently. Plumage sexual dimorphism increased and then decreased, while overall (plumage plus bower) visual contrast increased. The use of bowers allows relative crypsis of the bird but increased efficacy of the signal as a whole. Ornaments do not elaborate existing plumage features but instead are innovations (new color schemes) that increase signal efficacy. Isolation between species could be facilitated by plumage but not ornaments, because we observed character displacement only in plumage. Bowerbird color pattern evolution is at least partially predictable from the function of the visual system and from knowledge of different functions of different components of the color patterns. This provides clues to how more constrained visual signaling systems may evolve.     

Cultural transmission and the evolution of cooperative behavior

Sociobiological theory predicts that humans should not cooperate with large groups of unrelated individuals. This prediction is based on genetic models that show that selection acting on variation between large unrelated groups will generally be much weaker than selection acting on variation between individuals. Recently, several authors have presented related models of human evolution that integrate cultural and genetic transmission of behavior. We show that in such models group selection is potentially a strong force. Data on ethnocentrism is examined in the context of these results.     

基于红外相机技术的白冠长尾雉集群行为研究

白冠长尾雉(Syrmaticus reevesii)生性机警,行为隐蔽,在野外研究其集群行为较为困难。红外相机技术为解决这一问题提供了有益的工具。为研究白冠长尾雉集群行为及其地理变异,采用红外相机技术在湖北广水平靖关村和河南董寨自然保护区两个地点对其集群行为进行了调查。依据前期无线电遥测的结果,在两个研究地点分别设置了1 km×1 km的样地,在样地中分别放置了25台红外相机进行监测,野外累计放置了12412个相机日,获得视频24374段,其中有白冠长尾雉的视频有1361段。以有集群行为的独立视频数量(m)与独立视频数量(M)的比表示集群率,以拍摄到的白冠长尾雉个体数量(n)与有集群行为的独立视频数量(m)的比代表集群强度。结果表明,平靖关和董寨两地均是数量为2只的群体占比最大,在平靖关和董寨分别占68.23%、72.79%,Pearson卡方检验的结果表明群体大小在两地之间无显著差异(Pearson χ~2=6.522,df=5,P=0.259),而集群方式在两地之间则差异显著(Pearson χ~2=46.415,df=4,P0.001),两地均以单性集群为主要集群方式。单因素方差分析结果表明,集群率在季节间差异不明显。Neu方法分析发现,在平靖关,白冠长尾雉对灌丛和竹林显著偏好,对针阔混交林、杉木林和乔灌丛显著回避;而在董寨,其对针阔混交林和针叶林明显偏好,对杉木林和阔叶林明显回避。     

Habitat and the evolution of social and reproductive behavior in callitrichidae

The numerous remarkable traits characterizing the ecology and behavior of callitrichids have inspired considerable research and discussion of the flexible mating system (cases of monogamy, polygyny, and polyandry), cooperative breeding, reproductive inhibition by dominant females, rapid reproductive rate, significance of dietary differences (gum feeding, frugivory, and insectivory), and demographics and social characteristics of the four genera, Cebuella, Callithrix, Saguinus, and Leontopithecus. The majority of functional explanations evaluate costs, benefits, and alternative strategies but do not address the critical selective forces that led to the behaviors in the first place. In this paper, it is argued that Callithrix and Saguinus evolved to occupy a small insectivore/frugivore niche in secondary growth forest patches (gaps arising from tree falls), and other successional forests and edge habitats; that Cebuella evolved to occupy a gum-feeding/insectivore niche in inundated forest; and that Leontopithecus is above all a small animal predator/frugivore and a mature forest genus. The keys to explanations concerning the evolution of the social and reproductive systems of these animals lie in an understanding of the resource base in these different habitats. Finally, it should be remembered that studies of callitrichids have in the main part been carried out in habitats highly altered by human activities (especially the Brazilian Atlantic forest, home to marmosets and lion tamarins) and are not the environments in which their social and breeding behavior evolved. © 1996 Wiley-Liss, Inc.     

Mimicry and the evolution of premating isolation in Heliconius melpomene Linnaeus

Ecological divergence can cause speciation if adaptive traits have pleiotropic effects on mate choice. In Heliconius butterflies, mimetic patterns play a role in mate detection between sister species, as well as signalling to predators. Here we show that male butterflies from four recently diverged parapatric populations of Heliconius melpomene are more likely to approach and court their own colour patterns as compared with those of other races. A few exceptions, where males were more attracted to patterns other than their own, suggest that some mimetic patterns are sub-optimal in mate choice. Genotype frequencies in hybrid zones between races of H. melpomene suggest that mating is random, so reinforcement is unlikely to have played a role in intra-specific divergence. In summary, co-evolved divergence of colour pattern and mate preference occurs rapidly and is likely the first step in Heliconius speciation.     

A moving topic: control and dynamics of animal locomotion

Animal locomotion arises from complex interactions among sensory systems, processing of sensory information into patterns of motor output, the musculo-skeletal dynamics that follow motor stimulation, and the interaction of appendages and body parts with the environment. These processes conspire to produce motions and forces that permit stunning manoeuvres with important ecological and evolutionary consequences. Thus, the habitats that animals may exploit, their ability to escape predators or attack prey, their capacity to manoeuvre and turn, or the use of their available energy all depend upon the processes that determine locomotion. Here, we summarize a series of 10 papers focused on this integrative research topic.     

蜜蜂采集及其信息传递的行为机制研究进展

蜜蜂的采集行为是蜜蜂众多社会行为中一种较复杂的行为,涉及信息评估、信息传递、学习记忆及能量代谢等不同的行为过程。研究蜜蜂采集及信息交流系统的分子机制,不仅利于蜜蜂的理论研究和蜂产业的发展,还为人类语言及信息交流系统的研究提供借鉴。本文从行为、感觉基础及分子机制等不同研究层面,综述了近年来对蜜蜂采集及信息传递行为的研究进展,并提出了研究设想,以期为深入研究蜜蜂的采集行为及其信息传递行为的分子机制提供参考。