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PubMed1989

Maintenance and regulation of cellular handedness in Tetrahymena.

The left-handed phenotype of Tetrahymena thermophila (LH) is a global mirror image of its right-handed counterpart (RH). LH cells are 'wound' in the opposite direction from that of RH cells with respect to the placement of all structures that are asymmetrically disposed on the cell circumference. However, the local geometry of ciliary rows, including the asymmetrically placed microtubule bands and other accessory structures, is identical in RH and LH cells. Populations of LH cells grow more slowly than those of RH cells, probably because of nutritional problems due to faulty construction of the cell mouth. LH cells, like RH cells, conjugate in a homopolar configuration, while LH cells mate with RH cells in a heteropolar union which suffices to initiate the conjugal nuclear events but is insufficient to allow survival of progeny. Subclonal analyses indicate that reversion of the LH to the RH form is relatively rare. However, the frequency of reversion is greatly increased by conditions that promote the formation of doublets by fission arrest. An analysis of intermediate doublet forms in such cultures strongly suggests that reversion takes place through a specific pathway, with LH-LH doublets regulating to LH-RH forms that then may give rise to RH singlets. The origin and fate of the LH-RH intermediate forms can be explained by applying a modified polar coordinate model of positional information with the proviso that there is a preferred direction for the intercalation of new positional values.

Animals↗

PubMed2006

Reciprocation and interchange in wild Japanese macaques: grooming, cofeeding, and agonistic support.

Social primates spend a significant proportion of their time exchanging grooming with their group companions. Although grooming is mainly exchanged in kind, given its hygienic and tension-reducing functions, it is still debated whether grooming also provides some social benefits, such as preferential access to resources (e.g., food or mating partners). In this study we analyzed grooming distribution among wild female Japanese macaques living in two groups on Yakushima. We tested the tendency of monkeys to reciprocate the amount of grooming received, and to direct their grooming up the hierarchy. Then we analyzed the relation of grooming to three of its possible benefits: reduced aggression, increased tolerance over food, and agonistic support against a male aggressor. The data were analyzed by means of row-wise matrix correlations. Grooming was highly reciprocated (i.e., exchanged in kind) and directed up the hierarchy in both the study groups. No significant relationship was found between grooming and aggression. Conversely, grooming favored tolerance over food, since it was positively correlated with presence on the same food patch, close proximity, and close approaches (both within 1 m) during feeding. Grooming was also positively related to agonistic support against adult males, although this relationship became nonsignificant when we controlled for kinship. Although these results are not definitive, they suggest that monkeys may derive various social benefits from grooming. This conclusion is supported by the fact that in various primate species animals tend to prefer high-ranking individuals as grooming partners.

Aggression↗

PubMed1991

Sexual isolation in Drosophila. I. Theoretical models for multiple-choice experiments.

Several simple models are developed to calculate expected mating frequencies in ethological isolation experiments. They take into account the effect that the peculiar sexual behavior of Drosophila species can have in multiple-choice experiments. These models depend on only three basic parameters: male competitive ability (C), female receptivity (R) and the coefficient of females acceptance (A). Two types of model can be distinguished: (1) models with discrete preferences, in which A is a measure of the percentage of females accepting a particular kind of male and (2) models with continuous preferences, in which A represents the probability of acceptance for each courtship. It is demonstrated that the information rendered by just one experiment, although effective for determining whether sexual isolation exists, it is insufficient to estimate its degree or to demonstrate that it is asymmetrical. Further developments of the models under more complex conditions as well as their implications for reinforcement and founder effect theories are discussed.

Animals↗

PubMed2002

Sexual isolation between two sibling species with overlapping ranges: Drosophila santomea and Drosophila yakuba.

Drosophila yakuba is widespread in Africa, whereas D. santomea, its newly discovered sister species, is endemic to the volcanic island of São Tomé in the Gulf of Guinea. Drosophila santomea probably formed after colonization of the island by a D. yakuba-like ancestor. The species presently have overlapping ranges on the mountain Pico do São Tomé, with some hybridization occurring in this region. Sexual isolation between the species is uniformly high regardless of the source of the populations, and, as in many pairs of Drosophila species, is asymmetrical, so that hybridizations occur much more readily in one direction than the other. Despite the fact that these species meet many of the conditions required for the evolution of reinforcement (the elevation of sexual isolation by natural selection to avoid maladaptive interspecific hybridization), there is no evidence that sexual isolation between the species is highest in the zone of overlap. Sexual isolation is due to evolutionary changes in both female preference for heterospecific males and in the vigor with which males court heterospecific females. Heterospecific matings are also slower to take place than are homospecific matings, constituting another possible form of reproductive isolation. Genetic studies show that, when tested with females of either species, male hybrids having a D. santomea X chromosome mate much less frequently with females of either species than do males having a D. yakuba X chromosome, suggesting that the interaction between the D. santomea X chromosome and the D. yakuba genome causes behavioral sterility. Hybrid F1 females mate readily with males of either species, so that sexual isolation in this sex is completely recessive, a phenomenon seen in other Drosophila species. There has also been significant evolutionary change in the duration of copulation between these species; this difference involves genetic changes in both sexes, with at least two genes responsible in males and at least one in females.

Animals↗

PubMed2005

Speciation: more likely through a genetic or through a learned habitat preference?

A problem in understanding sympatric speciation is establishing how reproductive isolation can arise when there is disruptive selection on an ecological trait. One of the solutions that has been proposed is that a habitat preference evolves, and that mates are chosen within the preferred habitat. We present a model where the habitat preference can evolve either by means of a genetic mechanism or by means of learning. Employing an adaptive-dynamical analysis, we show that evolution proceeds either to a single population of specialists with a genetic preference for their optimal habitat, or to a population of generalists without a habitat preference. The generalist population subsequently experiences disruptive selection. Learning promotes speciation because it increases the intensity of disruptive selection. An individual-based version of the model shows that, when loci are completely unlinked and learning confers little cost, the presence of disruptive selection most probably leads to speciation via the simultaneous evolution of a learned habitat preference. For high costs of learning, speciation is most likely to occur via the evolution of a genetic habitat preference. However, the latter only happens when the effect of mutations is large, or when there is linkage between genes coding for the different traits.

Adaptation, Biological↗

PubMed2000

Sexual selection and the evolution of costly female preferences: spatial effects.

Models of Fisher's runaway process show that if there is a cost to female preference, no preference or male trait exaggeration will evolve. Surprisingly, this is true no matter how small the cost, which reveals that these models of Fisher's process are structurally unstable (Bulmer 1989). Here a model of Fisher's runaway process is presented to demonstrate that costly female preference evolves very easily when space is explicitly included in the model. The only requirement is that the optimal male phenotype changes across the species' range. The model shows that the spatial average of the female preference and male trait reach an evolutionary equilibrium that is identical to those of nonspatial models, but that the preference and male trait can deviate greatly from these averages at any point in space. For example, if random mating results in the lowest cost to females, then at equilibrium the spatial average preference will be zero. Nevertheless, there will be some locations at which females prefer males with larger ornaments and others where they prefer males with smaller ornaments. Results also show that the structural instability of nonspatial models of Fisher's process is less of a problem in spatial models. In particular, many of the main qualitative features of cost-free spatial models of Fisher's process remain valid even when there are small costs of female preference. Finally, the model shows that abrupt changes in the optimal male phenotype across space can result in an amplification of this pattern when preference has a small cost, but it can also result in a pattern similar to reproductive character displacement. Which of these occurs depends on the magnitude of the cost of female preference. This suggests that some patterns of reproductive character displacement in nature might be explained simply by sexual selection rather than by hybrid dysgenesis and reinforcement.

Animals↗

PubMed1996

Concurrent androgenic stimulation of the ventral tegmental area and medial preoptic area: synergistic effects on male-typical reproductive behaviors in house mice.

Cannulae containing testosterone proprionate (T) were bilaterally implanted into the medial preoptic area (MPO), the ventral tegmental area (VTA), or both areas concurrently (MPO/VTA) of castrated male house mice. A fourth group of castrates in which the intracranial implants missed their targets (MIMP) served as controls. In addition, other castrates were implanted subcutaneously with empty silastic capsules (BSIL) or silastic capsules containing T (TSIL). All subjects were examined for the following male-typical behaviors: mounting, attraction to female urine, ultrasonic mating vocalizations and urinary scent marking. In addition, the males were tested for activity levels to insure that they were not motorically impaired. In general, TSIL implants restored all male-typical behaviors to normal levels, whereas BSIL and MIMP implants were generally ineffective. Similar to previous findings, MPO implants alone completely restored ultrasonic vocalizations, partially restored urine marking, and had little or no effect upon mounting or urine preference. In contrast, VTA implants alone were ineffective at restoring any of these male-typical behaviors. However, the combined MPO/VTA implants were the most effective in restoring male-typical behaviors. In fact, a synergism between concurrent hormone action in the MPO and VTA was seen for mounting and urine preference. We interpret these data to indicate that androgen may act simultaneously in the MPO and VTA for more complete expression of some male-typical reproductive behaviors.

Animals↗

PubMed2001

Autoparasitism, interference, and parasitoid-pest population dynamics.

Autoparasitoids ("heteronomous hyperparasitoids") are parasitoids that lay female eggs on homopteran hosts and male eggs on juvenile parasitoids of either the same species or another species. Males develop as hyperparasitoids and eventually kill the juvenile parasitoid. We present a series of stage-structured models that investigate the effects of autoparasitism on population dynamics. Autoparasitism causes density-dependent mortality on juvenile parasitoids and therefore has a stabilizing effect. This also leads to an increase in host population abundance. In most cases an autoparasitoid leads to higher host equilibrium densities than a comparable primary parasitoid (except when the primary parasitoid is arrhenotokous (sexual) and the autoparasitoid has a low preference for attacking parasitized hosts or can attack the parasitized host for only a small portion of its development). When male autoparasitoids are followed explicitly in the models, mate limitation reduces the stabilizing effect of autoparasitism and leads to a further increase in host abundance. Coexistence of an autoparasitoid with a nonprimary parasitoid or second autoparasitoid is possible when the level of conspecific autoparasitism is greater than the level of heterospecific autoparasitism. When an autoparasitoid coexists with a primary parasitoid, the resulting host density is always greater than that with only the primary parasitoid. Therefore, autoparasitoids have the potential to disrupt control achieved by primary parasitoids. When two autoparasitoids coexist, the resulting host density is always lower than that attained by either autoparasitoid alone. The effects of autoparasitism are compared with those of other forms of interference competition.

Animals↗

PubMed2006

Gender differences in smiling: An evolutionary neuroandrogenic theory.

Studies have found that, under a wide variety of social circumstances, females are more likely than males to smile. The present article offers a theoretical explanation for this difference based on the premise that testosterone (along with other sex hormones) has evolved the tendency to alter brain functioning in ways that inhibit male smiling, especially during their most reproductively active years. Underlying the theory are the assumptions that (a) females have been naturally selected for preferring to mate with males who have the ability to assist in long-term child rearing primarily by provisioning resources, that (b) males partially accommodate this female preference by competing with rival males who are also vying for resources with which to attract mates, and that (c) male smiling interferes with their ability to most effectively intimidate rivals. If this reasoning is correct, genes must be involved in promoting the tendency to compete for resources, the most likely location for which would be on the Y-chromosome. According to the present theory, these genes operate in part by inhibiting social signals of fear and submissiveness. An additional element of the theory asserts that testosterone alters brain functioning in ways that shift the neocortex away from the left (more "prosocial and friendly") hemisphere toward the right (less "prosocial and friendly") hemisphere. Current evidence bearing on the theory is reviewed and a number of largely untested hypotheses are derived from the theory for future assessment of its predictive power.

Androgens↗

PubMed2003

It's not just average faces that are attractive: computer-manipulated averageness makes birds, fish, and automobiles attractive.

Average faces are attractive. We sought to distinguish whether this preference is an adaptation for finding high-quality mates (the direct selection account) or whether it reflects more general information-processing mechanisms. In three experiments, we examined the attractiveness of birds, fish, and automobiles whose averageness had been manipulated using digital image manipulation techniques common in research on facial attractiveness. Both manipulated averageness and rated averageness were strongly associated with attractiveness in all three stimulus categories. In addition, for birds and fish, but not for automobiles, the correlation between subjective averageness and attractiveness remained significant when the effect of subjective familiarity was partialled out. The results suggest that at least two mechanisms contribute to the attractiveness of average exemplars. One is a general preference for familiar stimuli, which contributes to the appeal of averageness in all three categories. The other is a preference for averageness per se, which was found for birds and fish, but not for automobiles, and may reflect a preference for features signaling genetic quality in living organisms, including conspecifics.

Adult↗

PubMed2004

The evolution of female preferences for multiple indicators of quality.

In a variety of species, females exhibit preferences for multiple male ornaments. Several hypotheses have been proposed to explain this phenomenon. Which, if any, of these hypotheses is the most plausible in general remains largely unresolved based on the available empirical data. Yet theoretical studies conclude that the evolution of preferences for multiple signals of male quality is unlikely, especially when the use of an additional cue in mate choice strongly increases the overall cost of choice. This would imply that most male courtship characters do not reflect the male's genetic quality but instead evolved through Fisherian sexual selection. However, the existing models focus on ornaments that signal overall genetic quality and do not address the possibility that different ornaments provide information about different aspects of quality. Therefore, we develop a model in which the ornaments act as signals for distinct quality components. When the ornaments provide overlapping information about these quality components, we retrieve the results of earlier models. However, when the ornaments provide independent information, preferences for multiple ornaments may evolve, even when exhibiting multiple preferences is costly. We discuss our results in relation to the multiple-message and redundant-signal hypotheses for ornament diversity and identify parallels between Fisherian and good-genes mechanisms for the evolution of multiple ornaments.

Animal Communication↗

PubMedDate not supplied

[The hypothesis of immune testing of partners--coordinated adaptations and changes in mating preferences].

Reproductive isolation plays the key role in speciation. According to the prevailing ideas, the main speciation mechanism is gradual accumulation of genetic differences in isolated populations (allopatric phase of speciation) based on mutations, selection, and genetic drift. In this case, reproductive isolation emerges as an occasional byproduct of adaptation to different conditions (ecological speciation) or accumulation of random changes in the gene pool resulting from long-term isolation. Pure sympatric speciation assumes isolation as a direct product of selection (divergent or disruptive selection) that favors individuals selectively mating with their likes. A third possibility is substantiated below. We believe that isolation can be a regular and determined product rather than occasional byproduct of divergence. It can rely on the friend/foe discrimination mechanisms, some of which can be "immune-based" and compare the partner's and own properties (signaling molecules, pheromones, and other antigens in a broad sense). Antigens of the major histocompatibility complex (MHC) can play a substantial role in such testing of potential mates.

Adaptation, Psychological↗

PubMed2001

Sexual selection of multiple handicaps in the red-collared widowbird: female choice of tail length but not carotenoid display.

Although sexual selection through female choice explains exaggerated male ornaments in many species, the evolution of the multicomponent nature of most sexual displays remains poorly understood. Theoretical models suggest that handicap signaling should converge on a single most informative quality indicator, whereas additional signals are more likely to be arbitrary Fisherian traits, amplifiers, or exploitations of receiver psychology. Male nuptial plumage in the highly polygynous red-collared widowbird (Euplectes ardens) comprises two of the commonly advocated quality advertisements (handicaps) in birds: a long graduated tail and red carotenoid coloration. Here we use multivariate selection analysis to investigate female choice in relation to male tail length, color (reflectance) of the collar, other aspects of morphology, ectoparasite load, display rate, and territory quality. The order and total number of active nests obtained are used as measures of male reproductive success. We demonstrate a strong female preference and net sexual selection for long tails, but marginal or no effects of color, morphology, or territory quality. Tail length explained 47% of male reproductive success, an unusually strong fitness effect of natural ornament variation. Fluctuating tail asymmetry was unrelated to tail length, and had no impact on mating success. For the red collar, there was negative net selection on collar area, presumably via its negative relationship with tail length. None of the color variables (hue, chroma, and brightness) had significant selection differentials, but a partial effect (selection gradient) of chroma might represent a color preference when tail length is controlled for. We suggest that the red collar functions in male agonistic interactions, which has been strongly supported by subsequent work. Thus, female choice targets only one handicap, extreme tail elongation, disregarding or even selecting against the carotenoid display. We discuss whether long tails might be better indicators of genetic quality than carotenoid pigmentation. As regards the evolution of multiple ornaments, we propose that multiple handicap signaling is stable not because of multiple messages but because of multiple receivers, in this case females and males.

Animals↗

PubMed1978

[Possible methods of control of virus disease in swine today and in the future. II. Specific applications (author's transl)].

The four alternatives discussed in the previous paper (5), are applied to a number of virus infections which are common in pigs. The enzootic state of SMEDI enteroviruses, vomiting and wasting virus and parvovirus should be promoted by bringing the young gilts into close contact with the older sow population at a sufficiently early stage. There should preferably not be a change of herd for primiparous sows during pregnancy. In parvovirus infection, maternal immunity may be so prolonged that gilts will only be infected after the time of breeding. Therefore, mating should preferably be postponed until they are nine months of age, unless previous serological tests have shown that they are in a state of active immunity. Considering the present disease situation of swine fever in several continental West European countries and consequently they high number of existing virus sources, compulsory vaccination of sows and fattening piglets is recommended against this virus on an international scale for at least three years. This vaccination can be omitted only after the number of outbreaks has been reduced to a very low level. Vaccination is the only possible alternative left in the combat against Aujezky's disease. Caution is undoubtedly indicated in using live vaccines in these cases. So far, methods have not become available for the effective control of transmissible gastroenteritis and prospects are not encouraging. The possibility of eradication of transmissible gastroenteritis is discussed.

Animals↗

PubMed2001

Castration in Gambel's and Scaled Quail: ornate plumage and dominance persist, but courtship and threat behaviors do not.

During the breeding season, testosterone in male birds is often linked to some secondary sexual ornaments, courtship behaviors, and intrasexual aggression. I examined the effect of castration on plumage expression in Gambel's Quail (Callipepla gambelii), a species in which males are highly ornate, and in Scaled Quail (C. squamata), an unornamented species. Using male pairs, each consisting of a castrate and a control, I also assessed whether castration affected (1) the behavior of males, (2) the mating decisions of females, or (3) the outcome of male-male competition. Castration did not alter the plumage of male Gambel's or Scaled Quail. In these species, and some other members of the avian order Galliformes, production of ornate plumage appears to be independent of testosterone. In contrast, castration reduced or eliminated courtship behaviors. Females almost never preferred castrated individuals. During male-male competition, castrates also exhibited lower rates of threat behaviors, which appear to be identical to those used during courtship. Castration did not, however, influence the outcome of male-male competition. Castrates of both species exhibited overt aggression (pecks, chases, displacement) and frequently won male contests. Such results suggest that certain types of aggressive behavior may be testosterone-independent. In both Gambel's and Scaled Quail, male body size correlated positively with dominant individuals.

Agonistic Behavior↗

PubMed1999

Phylogenetic influence on mating call preferences in female túngara frogs, Physalaemus pustulosus.

We evaluated how various phylogenetic models for estimating ancestral characters can influence studies of behavioural evolution. Previously we used a single model of evolution to estimate the values of call characters at ancestral nodes for the Physalaemus pustulosus species group and some close relatives (Ryan & Rand 1995, Science, 269, 390-392). We then synthesized these ancestral calls and measured the females' responses to such calls in phonotaxis experiments. We repeated the above procedure to determine the sensitivity of these results and conclusions to various models used to estimate the ancestral call characters. We asked whether: (1) different models gave different call estimates for the same nodes; (2) different call estimates at the same node were perceived as different by females; and (3) differences in female responses influenced previous conclusions. We used seven different models that varied in at least one of the following parameters: tree topology (bifurcating versus pectinate in-group trees), algorithms (local squared-change versus squared-change parsimony), tempo (gradual or punctuated evolution), and outgroups (two or three outgroup taxa used). Although different models often gave different call estimates for the same node, these different estimates often were not perceived as different by the females. These data reinforce our previous conclusions that: (1) the range of female preferences exceeds the known variation of the conspecific call; (2) females do not discriminate between the conspecific call and the call of their most recent ancestor; and (3) female responses may be context dependent, given that females differ in their responses to the same signal variation in discrimination and recognition experiments. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1993

A role for central vasopressin in pair bonding in monogamous prairie voles.

Monogamous social organization is characterized by selective affiliation with a partner, high levels of paternal behaviour and, in many species, intense aggression towards strangers for defence of territory, nest and mate. Although much has been written about the evolutionary causes of monogamy, little is known about the proximate mechanisms for pair bonding in monogamous mammals. The prairie vole, Microtus ochrogaster, is a monogamous, biparental rodent which exhibits long-term pair bonds characterized by selective affiliation (partner preference) and aggression. Here we describe the rapid development of both selective aggression and partner preferences following mating in the male of this species. We hypothesized that either arginine-vasopressin (AVP) or oxytocin (OT), two nine-amino-acid neuropeptides with diverse forebrain projections, could mediate the development of selective aggression and affiliation. This hypothesis was based on the following observations: (1) monogamous and polygamous voles differ specifically in the distribution of forebrain AVP and OT receptors; (2) AVP innervation in the prairie vole brain is sexually dimorphic and important for paternal behaviour; (3) central AVP pathways have been previously implicated in territorial displays and social memory; and (4) central OT pathways have been previously implicated in affiliative behaviours. We now demonstrate that central AVP is both necessary and sufficient for selective aggression and partner preference formation, two critical features of pair bonding in the monogamous prairie vole.

Aggression↗

PubMed2004

Song learning accelerates allopatric speciation.

The songs of many birds are unusual in that they serve a role in identifying conspecific mates, yet they are also culturally transmitted. Noting the apparently high rate of diversity in one avian taxon, the songbirds, in which song learning appears ubiquitous, it has often been speculated that cultural transmission may increase the rate of speciation. Here we examine the possibility that song learning affects the rate of allopatric speciation. We construct a population-genetic model of allopatric divergence that explores the evolution of genes that underlie learning preferences (predispositions to learn some songs over others). We compare this with a model in which mating signals are inherited only genetically. Models are constructed for the cases where songs and preferences are affected by the same or different loci, and we analyze them using analytical local stability analysis combined with simulations of drift and directional sexual selection. Under nearly all conditions examined, song divergence occurs more readily in the learning model than in the nonlearning model. This is a result of reduced frequency-dependent selection in the learning models. Cultural evolution causes males with unusual genotypes to tend to learn from the majority of males around them, and thus develop songs compatible with the majority of the females in the population. Unusual genotypes can therefore be masked by learning. Over a wide range of conditions, learning therefore reduces the waiting time for speciation to occur and can be predicted to accelerate the rate of speciation.

Animals↗