Aggression and RHP in the Northern Swordtail Fish, Xiphophorus cortezi: The Relationship Between Size and Contest Dynamics in Male–Male Competition

Current theory predicts that contest outcome, as well as decisions on whether to initiate a contest, escalate during a contest or retreat are decided by asymmetries in resource holding potential (RHP) and/or expected payoffs between contestants. In this investigation, dyadic contests were staged between male swordtail fish (Xiphophorus cortezi) where individuals were paired based on cumulative fight records and were ranked at the end of the trials in order to approximate RHP. Size was the only asymmetry that I did not attempt to control for and as a result, I was able to determine the relationships between size, contest initiation, escalation and outcome. Individuals changed their contest initiation strategy based on their size relative to that of their opponents, and contrary to predictions, the smaller of the two males in each contest was more likely to initiate the conflict than was the larger male. However, the larger of the two males was more likely to win and standard length proved to be a moderate predictor of an individual's final rank. Regardless of size, initiators fared poorly, winning only 31% of the contests. In instances where the smaller males won the contests, they were no more likely to initiate the encounter than was the larger male. However, when small males did win, fights lasted longer, suggesting that in some cases smaller males may be able to outlast their opponents.     

¿I like the way you move¿: how hormonal changes across the menstrual cycle affect female perceptions of gait

ABSTRACT: BACKGROUND: Variations in hormone concentrations across the menstrual cycle affect human female mate preferences. It has been shown that around the time of ovulation human females prefer more masculine male voices, faces, and bodies while simultaneously preferring less faces that are more feminine. They prefer also displays of male dominance, males with more symmetrical faces, and the scent of males with high levels of body symmetry. The aim of the experiments reported here was to investigate whether there are changes in female preferences for walking gaits across the menstrual cycle. RESULTS: Experiment 1 showed female observers could discriminate between point-light walkers with low and high levels of fluctuating asymmetries in their gaits. Female observers were more sensitive to asymmetries in female gaits than they were for asymmetries in male gaits. Experiment 2 showed that level of gait asymmetry did not affect the abilities of observers to discriminate female from male walkers. Experiment 3 showed that female observers did not change their preference for low and high asymmetry walkers across their menstrual cycles. However, females showed a decreased preference for all female walkers at the time during which it was estimated observers were at peak fertility. That same change in preference was not observed for male walkers. CONCLUSIONS: These data suggest female observers may not value gait asymmetry, as a mate selection cue, in the same way that they value asymmetries in faces and bodies. While only "average" gaits were used in these experiments, rather than the gaits of individual walkers, the types of asymmetries in gait tested here were not used in the same way as static cues for judging the apparent healthiness of individuals. Females do discriminate well average female gait asymmetries and do change their preferences for those gaits across their menstrual cycle. Doing so may reflect the operation of processes that equip females with an advantage when competing for mates at times of peak fertility.     

The evolution of asymmetric genitalia in spiders and insects

Asymmetries are a pervading phenomenon in otherwise bilaterally symmetric organisms and recent studies have highlighted their potential impact on our understanding of fundamental evolutionary processes like the evolution of development and the selection for morphological novelties caused by behavioural changes. One character system that is particularly promising in this respect is animal genitalia because (1) asymmetries in genitalia have evolved many times convergently, and (2) the taxonomic literature provides a tremendous amount of comparative data on these organs. This review is an attempt to focus attention on this promising but neglected topic by summarizing what we know about insect genital asymmetries, and by contrasting this with the situation in spiders, a group in which genital asymmetries are rare. In spiders, only four independent origins of genital asymmetry are known, two in Theridiidae (Tidarren/Echinotheridion, Asygyna) and two in Pholcidae (Metagonia, Kaliana). In insects, on the other hand, genital asymmetry is a widespread and common phenomenon. In some insect orders or superorders, genital asymmetry is in the groundplan (e.g. Dictyoptera, Embiidina, Phasmatodea), in others it has evolved multiple times convergently (e.g. Coleoptera, Diptera, Heteroptera, Lepidoptera). Surprisingly, the huge but widely scattered information has not been reviewed for over 70 years. We combine data from studies on taxonomy, mating behaviour, genital mechanics, and phylogeny, to explain why genital asymmetry is so common in insects but so rare in spiders. We identify further fundamental differences between spider and insect genital asymmetries: (1) in most spiders, the direction of asymmetry is random, in most insects it is fixed; (2) in most spiders, asymmetry evolved first (or only) in the female while in insects genital asymmetry is overwhelmingly limited to the male. We thus propose that sexual selection has played a crucial role in the evolution of insect genital asymmetry, via a route that is accessible to insects but not to spiders. The centerpiece in this insect route to asymmetry is changes in mating position. Available evidence strongly suggests that the plesiomorphic neopteran mating position is a female-above position. Changes to male-dominated positions have occurred frequently, and some of the resulting positions require abdominal twisting, flexing, and asymmetric contact between male and female genitalia. Insects with their median unpaired sperm transfer organ may adopt a one-sided asymmetric position and still transfer the whole amount of sperm. Spiders with their paired sperm transfer organs can only mate in symmetrical or alternating two-sided positions without foregoing transfer of half of their sperm. We propose several hypotheses regarding the evolution of genital asymmetry. One explains morphological asymmetry as a mechanical compensation for evolutionary and behavioural changes of mating position. The morphological asymmetry per se is not advantageous, but rather the newly adopted mating position is. The second hypothesis predicts a split of functions between right and left sides. In contrast to the previous hypothesis, morphological asymmetry per se is advantageous. A third hypothesis evokes internal space constraints that favour asymmetric placement and morphology of internal organs and may secondarily affect the genitalia. Further hypotheses appear supported by a few exceptional cases only.     

Frequency-dependent physiological trade-offs between competing colour morphs

Evolutionary theory suggests that alternative colour morphs (i.e. genetically controlled phenotypes) may derive similar fitness under frequency-dependent selection. Here we experimentally demonstrate opposing effects of frequency-dependent social environments on plasma hormone levels (testosterone and corticosterone) and immune function between red- and black-headed male morphs of the Gouldian finch (Erythrura gouldiae). Red-headed males are highly sensitive to changes in the social environment, especially towards the relative density of their own aggressive morph, exhibiting high stress responses and immunosuppression in socially competitive environments. In contrast, the non-aggressive black-headed males follow a more passive strategy that appears to buffer them against social stresses. The differential effect of hormones on aggressive behaviour and immune performance reinforces the contrasting behavioural strategies employed by these colour morphs, and highlights the importance of the social environment in determining the individual basis of behavioural and physiological responses.     

先天性心脏病患者皮纹波动不对称性的研究

本文采用随机整体抽样的方法分析了先天性心脏病患者129例(男性59例, 女性70例) 和正常对照人群133例(男性69例, 女性64例) 13项皮纹波动不对称性(Fluctuating asymmetry, FA)的分布特征。结果表明: (1)先天性心脏病患者组与正常对照组在13项皮纹波动不对称性指标中均未出现显著性别差异; (2)先天性心脏病患者组与正常对照组在FAⅥ(P<0.05)和FAⅦ(P<0.01)两项有显著性差异, 表现为患者组明显增高, 提示先天性心脏病患者在胚胎发育早期易受到环境因素影响, 具有较高的发育不稳定性。     

Genetic composition of social groups influences male aggressive behaviour and fitness in natural genotypes of Drosophila melanogaster

Indirect genetic effects (IGEs) describe how an individual''s behaviour—which is influenced by his or her genotype—can affect the behaviours of interacting individuals. IGE research has focused on dyads. However, insights from social networks research, and other studies of group behaviour, suggest that dyadic interactions are affected by the behaviour of other individuals in the group. To extend IGE inferences to groups of three or more, IGEs must be considered from a group perspective. Here, I introduce the ‘focal interaction’ approach to study IGEs in groups. I illustrate the utility of this approach by studying aggression among natural genotypes of Drosophila melanogaster. I chose two natural genotypes as ‘focal interactants’: the behavioural interaction between them was the ‘focal interaction’. One male from each focal interactant genotype was present in every group, and I varied the genotype of the third male—the ‘treatment male’. Genetic variation in the treatment male''s aggressive behaviour influenced the focal interaction, demonstrating that IGEs in groups are not a straightforward extension of IGEs measured in dyads. Further, the focal interaction influenced male mating success, illustrating the role of IGEs in behavioural evolution. These results represent the first manipulative evidence for IGEs at the group level.     

Asymmetric Forceps Increase Fighting Success among Males of Similar size in the Maritime Earwig

Extreme asymmetric morphologies are hypothesized to serve an adaptive function that counteracts sexual selection for symmetry. However, direct tests of function for asymmetries are lacking, particularly in the context of animal weapons. The weapon of the maritime earwig, Anisolabis maritima, exhibits sizeable variation in the extent of directional asymmetry within and across body sizes, making it an ideal candidate for investigating the function of asymmetry. In this study, we characterized the extent of weapon asymmetry, characterized the manner in which asymmetric weapons are used in contests, staged dyadic contests between males of different size classes, and analyzed the correlates of fighting success. In contests between large males, larger individuals won more fights and emerged as the dominant male. In contests between small males, however, weapon asymmetry was more influential in predicting overall fighting success than body size. This result reveals an advantage of asymmetric weaponry among males that are below the mean size in the population. A forceps manipulation experiment suggests that asymmetry may be an indirect correlate of a morphologically independent factor that affects fighting ability.     

Geography of fluctuating asymmetry in the greenfinch, Carduelis chloris

Levels of fluctuating asymmetry (FA) in 12 bilateral skeletal traits were estimated from 12 populations of greenfinches (Carduelis chloris) collected along a north‐south gradient across Europe. Average FA of measured traits was positively correlated with latitude indicating that the younger and genetically less diverse northern European populations are developmentally less stable than the older and genetically more diverse southern populations. Levels of FA differed significantly between different traits being lowest for functionally important traits (limb and wing bones) and highest for functionally less important traits such as foramina (apertures through bones)– a pattern that was highly concordant across different populations. Males tended to exhibit higher levels of FA than females, a finding consistent with the suggestions that males are more prone to developmental perturbations than females. Age differences in levels of FA were relatively clear, but inconsistent across traits with different degree of functionality. Individual heterozygosity – as enumerated from variation in allozyme loci – was unrelated to individual FA. No evidence for existence of individual asymmetry parameter (IAP) was found although traits related to locomotion indicated some degree of integration, which was expressed by correlations in the signed asymmetry. Nevertheless, an individual's overall asymmetry was poorly predicted by asymmetry of individual characters. Evidence for existence of population asymmetry parameter (PAP) was clear since all traits exhibited a similar degree of association with latitude. That the latitudinal cline of increasing FA towards north coincided with decreasing levels of genetic variability across the cline could be indicative of break down of developmental stability in the recently established and genetically impoverished populations. To what extent a reduced heterozygosity, the break up of co‐adapted gene complexes and/or environmental differences contributed to this process cannot be distinguished from our data.     

Androgenesis is a maternal trait in the invasive ant Wasmannia auropunctata

Androgenesis is the production of an offspring containing exclusively the nuclear genome of the fathering male via the maternal eggs. This unusual mating system is generally considered a male trait, giving to androgenetic males a substantial fitness advantage over their sexually reproducing relatives. We here provide the first empirical study of the evolutionary outcomes of androgenesis in a haplo-diploid organism: the invasive ant Wasmannia auropunctata. Some of the populations of this species have a classical haplo-diploid sexual mating system. In other populations, females and males are produced through parthenogenesis and androgenesis, respectively, whereas workers are produced sexually. We conducted laboratory reciprocal-cross experiments with reproductive individuals from both types of populations and analysed their progenies with genetic markers, to determine the respective contribution of males and females to the production of androgenetic males. We found that androgenesis was a parthenogenetic female trait. A population genetic study conducted in natura confirmed the parthenogenetic female origin of androgenesis, with the identification of introgression events of sexual male genotypes into androgenetic/parthenogenetic lineages. We argue that by producing males via androgenesis, parthenogenetic queen lineages may increase and/or maintain their adaptive potential, while maintaining the integrity of their own genome, by occasionally acquiring new male genetic material and avoiding inbreeding depression within the sexually produced worker cast.     

Fluctuating asymmetry, call structure and the risk of attack from phonotactic parasitoids in the bushcricket Sciarasaga quadrata (Orthoptera: Tettigoniidae)

The acoustically orienting parasitoid Homotrixa alleni (Diptera: Tachinidae) is a significant mortality factor of calling male Sciarasaga quadrata (Orthoptera: Tettigoniidae), with less than 10% of males escaping parasitism within the duration of the calling season. This study examined fluctuating asymmetry (FA) (small, random deviations from perfect symmetry) in five morphological traits in S. quadrata and its relation to the survival of calling males in the field. A significant relationship was demonstrated in only a single trait; across three consecutive field seasons and among each of the collections per season, parasitised males were shown to have significantly more asymmetric hind tibia than unparasitised males. Since the morphological development of males is complete prior to parasitoid attack, this relationship is not caused by the activities of the parasitoid. Further experimentation revealed that there was no relationship between the level of FA in the hind tibia and the success of parasitism, with males artificially parasitised in the laboratory showing no difference in FA from those where parasitism was unsuccessful. Instead, FA was shown to be negatively related to chirp length, an aspect of call structure that significantly affects the survival of calling males under parasitism risk in the field. We explore the possible reasons why more asymmetric males produce calls of shorter chirp length and hypothesise that the difference in hind tibia asymmetry seen between parasitised and unparasitised males in the field is related to host location in H. alleni rather than the inability of S. quadrata to defend itself against parasitoid attack. Received: 14 November 1997 / Accepted: 20 April 1998     

Explicit Mentalizing Mechanisms and Their Adaptive Role in Memory Conformity

Memory conformity occurs when an individual endorses what other individuals remember about past events. Research on memory conformity is currently dominated by a ‘forensic’ perspective, which views the phenomenon as inherently undesirable. This is because conformity not only distorts the accuracy of an individual''s memory, but also produces false corroboration between individuals, effects that act to undermine criminal justice systems. There is growing awareness, however, that memory conformity may be interpreted more generally as an adaptive social behavior regulated by explicit mentalizing mechanisms. Here, we provide novel evidence in support of this emerging alternative theoretical perspective. We carried out a memory conformity experiment which revealed that explicit belief-simulation (i.e. using one''s own beliefs to model what other people believe) systematically biases conformity towards like-minded individuals, even when there is no objective evidence that they have a more accurate memory than dissimilar individuals. We suggest that this bias is functional, i.e. adaptive, to the extent that it fosters trust, and hence cooperation, between in-group versus out-group individuals. We conclude that memory conformity is, in more fundamental terms, a highly desirable product of explicit mentalizing mechanisms that promote adaptive forms of social learning and cooperation.     

Persistence of subtle departures from symmetry over multiple molts in individual brachyuran crabs: Relevance to developmental stability

Fluctuating asymmetry (FA) is generally viewed as a population-level character. It is described by some measure of the variance of the difference between the right and left sides for a collection of individuals. Very little is known of the developmental origins of FA, despite the fact that FA is widely used to estimatedevelopmental stability. We present a novel technique for examining the growth trajectory of the asymmetries that give rise to FA, and we explore two sample data sets for the brachyuran crabHemigrapsus nudus. We have traced the fate of these small, random deviations from perfect symmetry through three successive molts of individual crabs. Invertebrates that molt, and hence grow in discrete steps, provide an easily preserved record of their growth. Model II regressions of measurements from one molt versus the previous molt can help describe the stability of subtle departures from symmetry over time. Although any number of different patterns may occur, we identify four general cases: a) asymmetries vary at random throughout growth (random determination), b) asymmetries remain unchanged in sign and magnitude (constant asymmetries), c) asymmetries increase in proportion to character size and hence increase with growth (size-dependent asymmetries), and d) asymmetries persist, but are reduced in magnitude (damped asymmetries). Data from tenHemigrapsus nudus, measured for between 21 and 28 metrical, limb-segment characters over three successive molts, yielded associations most similar to our pattern ‘b’, although some subtle departures in the direction of pattern ‘c’ were also observed. Persistent asymmetries accounted for 26% and 20% of the variance among asymmetries between molts 1 and 2, and molts 2 and 3 respectively. Thus, in spite of large and rapid increments in the external size of the crab, these subtle asymmetries tended to persist in both direction and magnitude, from molt to molt. This result suggests either i) that individual crabs have a genetic predisposition towards asymmetry in a particular direction but contribute to a continuous and normal distribution ofR-L differences at the population level, or ii) that these subtle asymmetries arose at some earlier ontogenetic stage and were preserved through growth. Either interpretation has important ramifications for the study of FA. The first suggests that under some circumstances FA may not provide a valid measure of developmental instability, because subtle departures from symmetry in an individual may have a genetic basis. The second implies that subtle departures from bilateral symmetry are not ‘corrected’ as an individual grows.     

Do females preferentially associate with males given a better start in life?

A poor start in life owing to a restricted diet can have readily detectable detrimental consequences for many adult life-history traits. However, some costs such as smaller adult body size are potentially eliminated when individuals modify their development. For example, male mosquitofish (Gambusia holbrooki) that have reduced early food intake undergo compensatory growth and delay maturation so that they eventually mature at the same size as males that develop normally. But do subtle effects of a poor start persist? Specifically, does a male''s developmental history affect his subsequent attractiveness to females? Females prefer to associate with larger males but, controlling for body length, we show that females spent less time in association with males that underwent compensatory growth than with males that developed normally.     

精神分裂症患者皮纹a-b嵴线数波动性不对称的研究

本文分析了精神分裂症患者134例(男性70例,女性64例)和正常对照人群331例(男性170例,女性161例)皮纹a-b嵴线数波动性不对称的分布特征。结果表明:⑴精神分裂症患者双手皮纹a-b嵴线数明显低于正常对照组(P<0.01),表现出明显增高。     

Quantitative-genetic analysis of wing form and bilateral asymmetry in isochromosomal lines ofDrosophila subobscura using Procrustes methods

Fluctuating asymmetry (FA) is often used as a measure of underlying developmental instability (DI), motivated by the idea that morphological variance is maladaptive. Whether or not DI has evolutionary potential is a highly disputed topic, marred by methodological problems and fuzzy prejudices. We report here some results from an ongoing study of the effects of karyotype, homozygosity and temperature on wing form and bilateral asymmetry using isochromosomal lines ofDrosophila subobscura. Our approach uses the recently developed methodologies in geometric morphometrics to analyse shape configurations of landmarks within the standard statistical framework employed in studies of bilateral asymmetries, and we have extended these methods to partition the individual variation and the variation in asymmetries into genetic and environmental causal components. The analyses revealed temperaturedependent expression of genetic variation for wing size and wing shape, directional asymmetry (DA) of wing size, increased asymmetries at suboptimal temperature, and a transition from FA to DA in males as a result of increase in the rearing temperature. No genetic variation was generally detected for FA in our samples, but these are preliminary results because no crosses between lines were carried out and, therefore, the contribution of dominance was not taken into account. In addition, only a subset of the standing genetic variation was represented in the experiments.     

Non-genomic transmission of paternal behaviour between fathers and sons in the monogamous and biparental California mouse

Maternal behaviour has profound, long-lasting implications for the health and well-being of developing offspring. In the monogamous California mouse (Peromyscus californicus), care by both parents is critical for offspring survival. We tested the hypothesis that similar to maternal care in rodents, paternal huddling and grooming (HG) behaviour can be transmitted to future generations via behavioural mechanisms. In California mice, testosterone maintains paternal HG behaviour. In the present study, we randomly assigned a group of male California mice to castration or sham-operated conditions and allowed them to raise their offspring normally. Adult sons of these males were paired with a female, and they were observed interacting with their own offspring. We found that like their fathers, the sons of castrated males huddled and groomed their young at lower levels than the sons of sham-operated fathers. The sons of castrates also retrieved pups more frequently. When both parents were present, the sons of castrates also showed a trend towards engaging in less exploratory behaviour. These data support the hypothesis that paternal behaviour, like maternal behaviour, can be transferred to future generations via epigenetic mechanisms and suggest that in a biparental species both parents contribute to offspring behavioural development.     

Chemoreception, symmetry and mate choice in lizards

Research on fluctuating asymmetry (FA)-mediated sexual selection has focused almost exclusively on visual signals and ignored chemical communication despite the fact that many species rely on chemical signals for attracting mates. Female mate choice based on visual traits appears to be rare in lizards. However, the femoral glands of male lizards produce pheromones which might transmit chemical information about an individual's developmental stability. Therefore, we hypothesized that mate choice may be based on chemical cues. We analysed the effect of the developmental stability levels of males on the attractiveness of males' scents to females in a laboratory experiment with the lizard Lacerta monticola. When we offered two males of similar body size, females preferentially associated with the scents of males with low FA in their femoral pores and also with the scents of males with a higher number of femoral pores. This suggested that the females were able to discriminate the FA of the males by chemical signals alone and that the females preferred to be in areas marked by males of high quality, thus increasing their opportunities of mating with males of high quality. We suggest that the quality and/or amount of male pheromones could communicate the heritable genetic quality of a male to the female and thereby serve as the basis for adaptive female choice in lizards.     

Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons

Animals commonly use their limbs as signals and weapons during territorial aggression. Asymmetries of limb performance that do not relate to asymmetries of limb size (cryptic asymmetry) could substantially affect disputes, but this phenomenon has not been considered beyond primates. We investigated cryptic asymmetry in male crayfish (Cherax dispar), which commonly use unreliable signals of strength during aggression. Although the strength of a chela can vary by an order of magnitude for a given size, we found repeatable asymmetries of strength that were only weakly related to asymmetries of size. Size-adjusted strength of chelae and the asymmetry of strength between chelae were highly repeatable between environmental conditions, suggesting that asymmetries of strength stemmed from variation in capacity rather than motivation. Cryptic asymmetry adds another dimension of uncertainty during conflict between animals, which could influence the evolution of unreliable signals and morphological asymmetry.     

Acceptance threshold theory can explain occurrence of homosexual behaviour

Same-sex sexual behaviour (SSB) has been documented in a wide range of animals, but its evolutionary causes are not well understood. Here, we investigated SSB in the light of Reeve''s acceptance threshold theory. When recognition is not error-proof, the acceptance threshold used by males to recognize potential mating partners should be flexibly adjusted to maximize the fitness pay-off between the costs of erroneously accepting males and the benefits of accepting females. By manipulating male burying beetles'' search time for females and their reproductive potential, we influenced their perceived costs of making an acceptance or rejection error. As predicted, when the costs of rejecting females increased, males exhibited more permissive discrimination decisions and showed high levels of SSB; when the costs of accepting males increased, males were more restrictive and showed low levels of SSB. Our results support the idea that in animal species, in which the recognition cues of females and males overlap to a certain degree, SSB is a consequence of an adaptive discrimination strategy to avoid the costs of making rejection errors.     

Sickness behaviour acting as an evolutionary trap? Male house finches preferentially feed near diseased conspecifics

Host behaviour towards infectious conspecifics is a crucial yet overlooked component of pathogen dynamics. Selection is expected to favour individuals who can recognize and avoid infected conspecifics in order to reduce their own risk of infection. However, evidence is scarce and limited to species employing chemical cues. Here, we experimentally examine whether healthy captive house finches (Carpodacus mexicanus) preferentially forage near a same-sex, healthy conspecific versus one infected with the directly transmissible pathogen Mycoplasma gallisepticum (MG), which causes lethargy and visible conjunctivitis. Interestingly, male house finches strongly preferred feeding near diseased conspecifics, while females showed no preference. This sex difference appeared to be the result of lower aggression rates in diseased males, but not in females. The reduced aggression of diseased males may act as an ‘evolutionary trap’ by presenting a historically beneficial behavioural cue in the context of a new environment, which now includes a recently emerged, potentially fatal pathogen. Since MG can be directly transmitted during feeding, healthy males may inadvertently increase their risk of contracting MG. This behaviour is likely to significantly contribute to the continued persistence of MG epidemics in wild populations.