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The rock-paper-scissors game and the evolution of alternative male strategies

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Abstract

MANY species exhibit colour polymorphisms associated with alternative male reproductive strategies, including territorial males and 'sneaker males' that behave and look like females1-3. The prevalence of multiple morphs is a challenge to evolutionary theory because a single strategy should prevail unless morphs have exactly equal fitness4,5 or a fitness advantage when rare6,7. We report here the application of an evolutionary stable strategy model to a three-morph mating system in the side-blotched lizard. Using parameter estimates from field data, the model predicted oscillations in morph frequency, and the frequencies of the three male morphs were found to oscillate over a six-year period in the field. The fitnesses of each morph relative to other morphs were non-transitive in that each morph could invade another morph when rare, but was itself invadable by another morph when common. Concordance between frequency-dependent selection and the among-year changes in morph fitnesses suggest that male interactions drive a dynamic 'rock-paper-scissors' game7.
© 1996Nature Publishing Group
© 1996Nature Publishing Group
© 1996Nature Publishing Group
© 1996Nature Publishing Group
... During recent decades, research on colour polymorphism is increasingly focussed on whether morphs coexisting in the same population might diverge into separate, new species through sympatric speciation (Corl et al. 2010 idea is that morphs underlay a suite of morphological, physiological, and behavioural traits, including mating strategies and parasite resistance (reviewed in McKinnon and Pierotti 2010). These trait complexes represent alternative fitness optima, and allow multiple morphs to coexist in a single population in a balanced polymorphism (Maynard Smith 1996;Sinervo and Lively 1996). Polymorphic species are therefore able to occupy broader niches and spread over larger areas than monomorphic species (Galeotti and Rubolini 2004;Åberg 2008a, 2008b;McLean and Stuart-Fox 2014). ...
... Different processes have been supposed to contribute to the maintenance of colour polymorphism, including negative frequency dependent selection (Sinervo and Lively 1996), hybridisation in secondary contact zone (Roulin 2004), genetic drift (Runemark et al. 2010) and spatial-temporal variation in selection (McLean and Stuart-Fox 2014). These processes often involve sexual interactions among individuals, either among males only, or between males and females, or in both cases (reviewed in Wellenreuther et al. 2014). ...
... These processes often involve sexual interactions among individuals, either among males only, or between males and females, or in both cases (reviewed in Wellenreuther et al. 2014). For example, the three male morphs of the Sideblotched lizard (Uta stansburiana) employthree alternative tactics, and are maintained by negative frequency-dependent selection, where a morph's fitness increases when it is rare within populations, but decreases when it becomes more common (Sinervo and Lively 1996;Sinervo and Calsbeek 2006). ...
Article
Context. Among processes involved in colour polymorphism, geographic variation in morph composition and frequency has been attracting interest since it reflects morph local adaptation. A recent study in the Pyrenees associated the pattern of geographic variation in morph frequency of the common wall lizard with the divergence in climatic niches, supporting the hypothesis that morphs represent alternative local climatic adaptations. However, the Pyrenees represent only a small portion of the species range. Aims. We modelled the ecological niches of Italian morphs using the same procedure adopted for the Pyrenees to check whether the effects detected at local scales (i.e. the Pyrenees) were repeatable at regional scales (i.e. Italy). This generalisation is needed to investigate how natural selection maintains locally adapted polymorphisms. Methods. We classified each locality (120 populations) according to the presence/absence of morphs, and independent Ecological Niche Models (ENMs) against the same background were fitted. Receiver Operating Curves accounting for sampling biases, equivalency and similarity tests were used to check and compare models accounting for spatial distribution of data. Key results. Morph-specific ENMs did not reproduce any of the patterns detected in the Pyrenees. Any difference among morphs disappeared after controlling for morph spatial distribution. Since occurrence points of the rarest morphs were a subsample of the occurrence points of the most common morph, it is not possible to separate the effects of true ecological differences among morphs from the effects of the spatial distribution patterns of morph occurrence. Conclusions. Using presence data not specifically collected for ENM comparisons does not allow reliable assessments of morph niche segregation. Our analysis points out the need to be very cautious in ecological interpretations of ENMs built on presence/background or presenceonly data when occurrences are spatially nested. Implications. When dealing with data not specifically collected according to a targeted design, it is not legitimate to compare ENMs with completely nested occurrence points, because this approach can not exclude the possibility that ENM differences were the result of a spatial subsampling. This type of bias is probably largely underestimated, and it may lead to serious misinterpretations as shown in this study.
... 非传递性竞争理论最早由May和Leonard [20] 提出 (图2(a)). 此后, 在珊瑚礁无脊椎动物群 [27] 、潮间带生 图 1 传递性竞争(a)与非传递性竞争(b) Figure 1 Transitive competition (a) and intransitive competition (b) 物 [28] 、浮游生物 [29] 、蜥蜴 [30] 、细菌 [31] 、维管植物 [32,33] 中都发现了非传递性竞争的例子. 近10年来, 生态学家 开始探究非传递性竞争的作用机制, 并归纳为资源利 用型、生活史型、行为权衡型、竞争权衡型和化感作 用型. ...
... 典例子 [30] , 该物种雄性具有不同的表型, 其雄性生殖策 略是根据不同喉咙颜色演化出3种不同的行为, 并且这 ...
... 实验发现, 大肠杆菌(Escherichia coli)能够分泌 一种大肠杆菌毒素杀死其他的大肠杆菌, 但一些大肠 杆菌产生了抗体, 剩余部分则没有变化 [31] , 这三者称为 毒素菌(表型A)、抗药菌(表型B)和敏感菌(表型C) [29] . 侧斑蜥蜴野外研究证实了这一结论 [30] , 不同喉咙颜色的蜥蜴都出现循环周期为6年的种群波 ...
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Maintaining biodiversity requires direct and indirect interspecific interactions. The study of direct interactions, including competition, predation, mutualism, commensalism, and parasitism, has greatly promoted the development of species coexistence theory. However, as a simplified method to explain community assembly, direct interactions alone cannot adequately explain the coexistence of related species in the absence of indirect interactions. Indirect interactions can be defined as the impact of one species on another that is mediated or transmitted by a third, and they are considered to be a more complex and less understood type of interspecific interaction. During the past two decades, scientists have gradually realized that a type of density-mediated indirect interaction, known as intransitive competition, is ubiquitous in nature. Intransitive competition can be described as a game of “rockpaper-scissors” in which three species A, B and C have competitive ranks A>B>C>A. In this competitive mode, competitive exclusion between relative species is counteracted by mutual restrictiveness, and there are no “invincible” species in the community. Therefore, intransitive competition is an important factor in promoting species coexistence, which affects species distribution patterns, community structure and ecosystem functions. To summarize the theory of intransitive competition, this paper discusses the definition, characteristics, and detection methods of intransitive competition and the main factors affecting intransitive competition as well. There are five formation modes of intransitive competition. Resource utilization mode occurs when species have different competitive abilities for resources. Life history mode arises if species cannot maintain an absolute competitive advantage throughout their life stages. Behavioral trade-off mode follows when species have different ways of acquiring resources. Competition trade-off mode and allelopathy mode require species to develop both aggressive and defensive survival strategies. Our paper also explores three characteristics of intransitive competition. First, the populations of species participating in intransitive competition often exhibit periodic fluctuations in their frequency. which are regulated by dynamic equilibrium. Second, intransitive competition systems involving an odd number of species can maintain community stability, whereas systems involving an even number of species will theoretically collapse. Finally, multiple intransitive competition loops may appear in the community, and intransitive competition may also be nested in other coexistence patterns. This nested feature makes intransitive competition difficult to detect and measure. Fortunately, current research methods such as competition matrix, transfer matrix and invasion growth rate model can be used to infer the existence of intransitive competition and quantify its prevalence and importance. Competitive rank has been considered as one of the most important factors affecting intransitive competition. The higher the coefficient of variation of competitive rank among species, the more negative impact on intransitive competition. At the same time, global-scale environmental changes could also be critical factors: drought increases the intransitive competition in the community, but eutrophication caused by land-use intensification reduces the intransitive competition. Functional traits are non-negligible because species traits adapted to high-productivity environments often impede the formation of intransitive competition. Finally, to promote the understanding of indirect interaction and multi-species coexistence strategies, we propose that future research on intransitive competition should focus on long-term controlled field experiments, coupled with theoretical considerations of high-order interactions, complex networks, and ecosystem function.
... However, because morph cycling is a fundamentally temporal process in nature, time-series data are also needed to fully ascertain the extent that morph turnover patterns relate to concomitant climate shifts (if at all). Yet, although time-series climate data were incorporated into a study on side-blotched lizards (Uta stansburiana, a species exhibiting an ARS color polymorphism 26 ), treatment of climate was limited to an indirect measure of temperature, the hours of activity restriction 23 . Thus, the direct impact of temperature on color morph turnover, as well as any impact of other temperature or precipitation descriptors, remain unclear. ...
... Focusing on the three color components of the polymorphism in this species, I first evaluated spatial turnover in male color components among 58 localities distributed through a climatically variable portion of the species' geographic range (Fig. 1b). I then assessed the concordance of those findings with temporal patterns of climate-mediated turnover in color components across three localities surveyed over a seven-year Overlays indicate morph coding consistent with phenotypic (uppercase lettering, indicative of observed discrete badge coloration) and genotypic (lowercase italicized lettering, indicative of putative alleles underlying badge color) approaches to characterizing morph coloration 22,26,49 . Note that in some populations, the central spot color of yellow-blue and orange-blue morphs may appear green [e.g., 46 ], depending on the amount of yellow or orange pigmentation over the structural blue color underneath. ...
... For ARS color polymorphisms, morph turnover is attributed to negative frequency-dependent sexual selection that ensures persistence of all morphs within a population over time 26 . However, recent studies support that morph behavioral asymmetries interact with environmental heterogeneity, generating divergence among competing morphs in ecological traits relevant for natural selection 15,17 . ...
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Sexual selection is considered the primary driver of morph turnover in many color polymorphic taxa, yet the potential for other factors (like climate) to contribute to polymorphism maintenance and evolution remains unclear. Appreciation for a role of environmental conditions in the maintenance and evolution of color polymorphisms has grown in recent years, generating evidence suggesting that color morphs linked to sexual selection may also diverge in climate sensitivity. Focusing on the three color components contributing to the male tree lizard (Urosaurus ornatus) color morphs, I reveal a marked concordance between patterns of turnover over space and time, with a general affinity of orange- and yellow-colored males to hotter, more variable conditions, and blue colored males to wetter, cooler conditions. An assessment of long-term turnover in the blue color component in response to recent climate change over the past 60 years reinforces these findings. Overall, behavioral asymmetries attributed to sexual selection likely expose competing morphs to divergent environmental conditions in heterogeneous habitats, creating opportunity for natural selection to shape climate sensitivities that also drive turnover in morph color composition. Ultimately, these processes may favor stark asymmetries in morph persistence over the coming decades.
... In a seminal study conducted on a wild undisturbed population of side-blotched lizards (Uta stansburiana), Sinervo and Lively 19 showed that the three male head color morphs were subjected to negative frequency-dependent selection, but unlike this study, which involves predation, their observations were based upon frequency-dependent sexual selection. 13 Negative frequency-dependent predation has been recorded in several studies conducted on plants 20,21 and invertebrates. ...
... Then, tournaments are used to sample the game and to empirically evaluate agents. The empirical analysis of tournaments has a long history, in sports analytics [18,6] , ecology and animal behavior [16,25], and biology [31,28]. While the primary interest in these cases is typically in ranking agents/players, tournament graphs also reveal significant information about the nature of the game being played [32]. ...
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This paper develops Principal Trade-off Analysis (PTA), a decomposition method, analogous to Principal Component Analysis (PCA), which permits the representation of any game as the weighted sum of disc games (continuous R-P-S games). Applying PTA to empirically generated tournament graphs produces a sequence of embeddings into orthogonal 2D feature planes representing independent strategic trade-offs. Each trade-off generates a mode of cyclic competition. Like PCA, PTA provides optimal low rank estimates of the tournament graphs that can be truncated for approximation. The complexity of cyclic competition can be quantified by computing the number of significant cyclic modes. We illustrate the PTA via application to a pair of games (Blotto, Pokemon). The resulting 2D disc game representations are shown to be well suited for visualization and are easily interpretable. In Blotto, PTA identifies game symmetries, and specifies strategic trade-offs associated with distinct win conditions. For Pokemon, PTA embeddings produce clusters in the embedding space that naturally correspond to Pokemon types, a design in the game that produces cyclic trade offs.
... Mate choice is a driver of the evolution and maintenance of conspicuous and exuberant traits, resulting in sexual dimorphism across many taxa (Endler 1980). Mate choice plays a major role in species with color polymorphisms (CP), as color morphs often correlate with distinct physiological and behavioral traits (Sinervo and Lively 1996;Bruinjé et al. 2019a). Maintenance of within sex CP depends on a selective balance among morphs, and female mating preferences can help to explain such maintenance (Smith and Price 1973;Eakley and Houde 2004). ...
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Sexual selection is a driver of morphological and behavioral diversity. It may also play a role in the maintenance of behavioral and morphological polymorphisms. Adaptive theory predicts that males advertise individual quality through one or more signal paths and that females choose better quality mates based on those signals. Here, we use mate choice experiments in two different signaling modes (chemical and visual), to test whether females of a color cryptic-polymorphic lizard have a preference between two co-occurring male morphs (black and yellow) with alternative behavioral types. We test whether females use visual (males’ coloration) and/or chemical cues to choose male morphs. Furthermore, we assess whether continuous costly color expression influences female choice and whether male conspicuousness in their natural background predicts female mate choice. We show that females prefer the aggressive black-morph males based on chemical cues. Females prefer more conspicuous males as mates, and coloration at polymorphic ventral part of the body also contributes to higher conspicuousness of these males. Our study adds to the knowledge of intersexual selection for multi-component signals and opens possibilities for future research to explore the roles of complementary signal modes. Significance statement Sexual selection can drive the evolution of a great diversity of behavioral and morphological features and has puzzled naturalists ever since Darwin. We studied sexual selection in the striped lava lizard (Tropidurus semitaeniatus), a species endemic to Northeast Brazil. This species is known to have two different “types” of males (yellow or black). In our study, we conducted mate choice experiments to test whether females prefer males based on chemical and/or visual cues. Black males tend to be more aggressive and dominant, and we showed that females prefer these males based on their scent. We show that females prefer males that are more conspicuous within their natural habitat, and that ventral polymorphic coloration is related to female preference. Our study highlights the complexity of animal signals and contributes to our understanding of sexual selection and the role of complementary signal modes.
... Within a single population, males may exhibit gray, yellow, or orange throat color morphs, and in the absence of the gray morph in the population, males may exhibit blue, yellow, or orange throat color morphs . Such co-occurring morphs often differ in some further attributes (McKinnon & Pierotti, 2010), for example, variations in aggressive behaviors Fuentes-D avila, 2018;San-Jos e et al., 2014;Sinervo & Lively, 1996). Therefore, to control for a potential effect of the gular morphotype on aggressive behavior, we included the identity of each individual's gular morphotype in the statistical models. ...
Article
Aggressive behavior is performed in the context of intraspecific competition for gaining access to mates, food, or suitable territories. However, aggressive confrontations may divert time and energy from other important activities and increase the likelihood of suffering physical injury or predation. Aggressive behavior is particularly costly for ectotherms because it may reduce the time available for thermoregulation, which is a time‐consuming activity but indispensable for adequate maintenance of metabolic processes. In this study, we analyzed the long‐term effect of the thermal quality (i.e. the degree of discrepancy between the temperatures available in a given environment and temperatures that animals prefer) on the aggressive behavior of the mesquite lizard Sceloporus grammicus. Our hypothesis was that time allocated to aggressive behavior in low thermal quality environments is diverted from time spent on the acquisition and maintenance of an adequate body temperature. Accordingly, we found that lizards from the low thermal quality location (i.e. low environmental temperature) exhibited less aggressive behavior than those captured in middle and high thermal quality locations. Our results show that in the low thermal quality location aggressive behavior was almost absent, suggesting that this behavior may interfere with the acquisition and maintenance of an adequate body temperature. Therefore, it is likely that the benefits of thermoregulation outweigh those of aggressive behavior at low thermal quality locations. Aggressive behavior is performed in the context of intraspecific competition, however, aggressive confrontations may divert time and energy from other important activities and increase the likelihood of suffering physical injury or predation. Aggressive behavior is particularly costly for ectotherms because it may reduce time available for thermoregulation. In this study, we analyzed the long‐term effect of the thermal quality (i.e. the degree of discrepancy between the temperatures available in a given environment and temperatures that animals prefer) on the aggressive behavior of the mesquite lizard Sceloporus grammicus. Our results show that in the low thermal quality location aggressive behavior was almost absent, suggesting that this behavior may interfere with the acquisition and maintenance of an adequate body temperature.
... NFDS can also be driven by sexual selection, and among these scenarios, we find sexual conflict (Gosden & Svensson, 2007;Svensson et al., 2005), mate competition (Rios-Cardenas et al., 2018;Sinervo & Lively, 1996), and mate choice (Takashi & Hori, 2008). ...
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Marine gastropods are characterized by an incredible variation in shell color. In this review, we aim to introduce researchers to previous studies of shell color polymorphism in this group of animals, trying to provide an overview of the topic and highlighting some potential avenues for future research. For this, we tackle the different aspects of shell color polymorphism in marine gastropods: its biochemical and genetic basis, its patterns of spatial and temporal distribution, as well as its potential evolutionary causes. In particular, we put special emphasis on the evolutionary studies that have been conducted so far to reveal the evolutionary mechanisms responsible for the maintenance of shell color polymorphism in this group of animals, as it constitutes the least addressed aspect in existing literature reviews. Several general conclusions can be drawn from our review: First, natural selection is commonly involved in the maintenance of gastropod color polymorphism; second although the contribution of neutral forces (gene flow-genetic drift equilibrium) to shell color polymorphism maintenance do not seem to be particularly important, it has rarely been studied systematically; third, a relationship between shell color polymorphism and mode of larval development (related to dispersal capability) may exist. As for future studies, we suggest that a combination of both classical laboratory crossing experiments and -Omics approaches may yield interesting results on the molecular basis of color polymorphism. We believe that understanding the various causes of shell color polymorphism in marine gastropods is of great importance not only to understand how biodiversity works, but also for protecting such biodiversity, as knowledge of its evolutionary causes may help implement conservation measures in those species or ecosystems that are threatened.
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Competitive systems can exhibit both hierarchical (transitive) and cyclic (intransitive) structures. Despite theoretical interest in cyclic competition, which offers richer dynamics, and occupies a larger subset of the space of possible competitive systems, most real-world systems are predominantly transitive. Why? Here, we introduce a generic mechanism which promotes transitivity, even when there is ample room for cyclicity. Consider a competitive system where outcomes are mediated by competitor attributes via a performance function. We demonstrate that, if competitive outcomes depend smoothly on competitor attributes, then similar competitors compete transitively. We quantify the rate of convergence to transitivity given the similarity of the competitors and the smoothness of the performance function. Thus, we prove the adage regarding apples and oranges. Similar objects admit well ordered comparisons. Diverse objects may not. To test that theory, we run a series of evolution experiments designed to mimic genetic training algorithms. We consider a series of canonical bimatrix games and an ensemble of random performance functions that demonstrate the generality of our mechanism, even when faced with highly cyclic games. We vary the training parameters controlling the evolution process, and the shape parameters controlling the performance function, to evaluate the robustness of our results. These experiments illustrate that, if competitors evolve to optimize performance, then their traits may converge, leading to transitivity.
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When a genetically determined polymorphism is selectively maintained in a population, the different morphs should have equal fitnesses at equilibrium. We empirically examined this prediction for the size polymorphism of the swordtail Xiphophorus nigrensis, in which a single locus on the Y chromosome controls male size. Small males mature earlier and chase females, whereas large males mature later and court females. We analyze our data with a model that uses the differential mating success and the ages at sexual maturity of the two morphs to calculate the per capita death rate necessary for them to have equal fitness. We demonstrate how female fecundity data can be used to determine whether the estimated death rate is biologically realistic. Our data support the hypothesis that morph fitnesses are equal, and the model is fairly robust to changes in population growth rate and differential death rates of morphs. However, the confidence intervals for our estimates are large, which suggests that the null hypothesis only be accepted with caution. We show that in many circumstances very large sample sizes will be needed to distinguish between alternative hypotheses concerning the relative fitnesses of the two morphs. We emphasize that despite the popularity of alternative mating behaviors, specifically, and mixed evolutionarily stable strategies, in general, there is almost no empirical evidence that alternative behavioral morphs have equal fitnesses. Also, the conclusion that morph fitnesses are equal does not address the hypothesis that frequency-dependent mating success is the mechanism maintaining the equilibrium of fitnesses. This requires additional evidence directly demonstrating the fitness effect of changes in morph frequency.
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THREE genetically discrete male morphs coexist in Paracerceis sculpta, a Gulf of California marine isopod1-5. The large α males defend harems within intertidal sponges, the smaller β males mimic female behaviour and morphology, and the tiny γ males invade and sequester themselves within large harems. If selection is responsible for maintaining this polymorphism, then the mean fitness of each male morph must be equal over time6-9. Here we report that average reproductive success is equivalent among the three male morphs in monthly population samples collected over two years. We have investigated the total opportunity for sexual selection within and among morphs, and find that < 0.10% of the total opportunity for sexual selection occurs among morphs. Furthermore, alleles responsible for the expression of this polymorphism conform to the Hardy-Weinberg equilibrium, indicating the absence of differential natural selection among morphs. Conditions necessary for stable coexistence of three alternative male reproductive strategies seem to exist in nature.
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Multivariate statistical methods are derived for measuring selection solely from observed changes in the distribution of phenotypic characters in a population within a generation. Selective effects are readily detectable in characters that do not change with age, such as meristic traits or adult characters in species with determinate growth. Ontogenetic characters, including allometric growth rates, can be analyzed in longitudinal studies where individuals are followed through time. Following an approach pioneered by Pearson (1903), this analysis helps to reveal the target(s) of selection, and to quantify its intensity, without identifying the selective agent(s). By accounting for indirect selection through correlated characters, separate forces of directional and stabilizing (or disruptive) selection acting directly on each character can be measured. These directional and stabilizing selection coefficients are respectively the parameters that describe the best linear and quadratic approximations to the selective surface of individual fitness as a function of the phenotypic characters. The theory is illustrated by estimating selective forces on morphological characters influencing survival in pentatomid bugs and in house sparrows during severe weather conditions.
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This study provides empirical evidence in a wild population for frequency-dependent sexual selection between alternative male reproductive strategies. The bluegill sunfish (Lepomis macrochirus) has two male reproductive strategies, cuckolder or parental, used by different males to compete in fertilizing the same eggs. As the density of cuckolders in colonies of parental males increases, the average mating success of cuckolders initially peaks but then declines. The cuckolder density at which their success peaks is determined by ecological characteristics of each colony. A theoretical analysis assuming random and omniscient cuckolder distributions among ecologically different colonies shows that cuckolders will fertilize decreasing proportions of eggs, relative to parental males, as cuckolders increase in frequency in the population. This supports evolutionary models that assume negative frequency-dependent selection between the competing strategies. Cuckolder and parental strategies may therefore have evolved as an Evolutionarily Stable State (ESSt).
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Males of many species exhibit strongly dimorphic reproductive behavior and morphology associated with alternative reproductive tactics. Little is known about the physiological control of these individual differences. The relative plasticity hypothesis proposes that such within-sex differences arise from either organizational or activational actions of sex steroid hormones depending on whether adults can switch tactics or not. This hypothesis predicts that differences between individuals in a species where adults cannot switch between tactics (are "fixed") should be organized by early actions of hormones. Three experiments explored the possible organizational role of testosterone (T) on the development of male alternatives in the tree lizard (Urosaurus ornatus), which has two fixed male morphs. Orange (O) males have a mostly orange throat fan (dewlap), are non-territorial nomads, and are larger than orange-blue (OB) males which have an orange dewlap with a central blue patch and are territorial. In the first experiment intact males on the day of hatching were (1) sham-operated and implanted with empty capsules, (2) castrated, or (3) testosterone-implanted. As adults, the castration group had more O males than the control and the T-implanted group had more OB males than the control. Adult body size in castrated and T-implanted groups paralleled naturally occurring morph differences but both were smaller than controls. A second experiment with a lower dose yielded similar results for dewlap type and growth. In a third experiment, intact males were given an empty capsule or a T-implant at 30 days posthatching. Again, the frequency of OB males in the T-implanted group was significantly greater than that in the empty implant group, indicating that either the critical period extends past Day 30 or there is no well-defined critical period. Together, these results support the hypothesis that the organizational action of T or one of its metabolites contributes to the differentiation of these within-sex differences.
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Male bluegill (Lepomis macrochirus) display a complex reproductive behavior involving two alternative life history pathways: delay of sexual maturation to become “parentals” or precocious maturation as “cuckolders.” The purpose of our study was to investigate the association of two androgens, 11-ketotestosterone (11KT) and testosterone (T), with reproduction in these two types of males. Radioimmunoassay techniques were used to measure daily levels of the two androgens in the blood serum of parental male bluegill captured during the prespawning, spawning, and nesting periods throughout the reproductive season. Dramatic changes in the levels of 11KT and T were observed among parental males during these periods. Peaks occurred at the onset of spawning activity during each breeding bout. Compared to spawning parental males, spawning cuckolder males had significantly lower serum levels of 11KT. In contrast, the serum levels of T among parental and cuckolder males were not significantly different. These findings suggest that the elevated levels of 11KT are associated with the behaviors displayed by spawning parental males. The levels of T, however, seem to be associated with the occurrence of a phenomenon common to both parental and cuckolder males, such as development of gonads and/or spermiation.
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I want in this article to trace the history of an idea. It is beginning to become clear that a range of problems in evolution theory can most appropriately be attacked by a modification of the theory of games, a branch of mathematics first formulated by Von Neumann and Morgenstern in 1944 for the analysis of human conflicts. The problems are diverse and include not only the behaviour of animals in contest situations but also some problems in the evolution of genetic mechanisms and in the evolution of ecosystems. It is not, however, sufficient to take over the theory as it has been developed in sociology and apply it to evolution. In sociology, and in economics, it is supposed that each contestant works out by reasoning the best strategy to adopt, assuming that his opponents are equally guided by reason. This leads to the concept of a ‘minimax’ strategy, in which a contestant behaves in such a way as to minimise his losses on the assumption that his opponent behaves so as to maximise them. Clearly, this would not be a valid approach to animal conflicts. A new concept has to be introduced, the concept of an ‘evolutionary stable strategy’.