Showing papers in "The American Naturalist in 2015"
TL;DR: A theory is suggested according to which the development of isolating mechanisms follows, rather than accompanies, that of the adaptive complexes themselves, which suggests that speciation is meant the fixation of discontinuity among organisms.
Abstract: By speciation is meant the fixation of discontinuity among organisms. Discontinuity is maintained by isolating mechanisms that prevent the interbreeding of carriers of different adaptive complexes of genes. A theory is suggested according to which the development of isolating mechanisms follows, rather than accompanies, that of the adaptive complexes themselves. The development of physiological isolation takes place principally along the geographical boundaries separating the distribution areas of the incipient species. Some evidence for and against this theory is discussed.
837 citations
TL;DR: Examination of the cause-effect relationship between queen mating frequency and worker policing indicates that worker policing is caused by queen polyandry but thatworker policing is unlikely to cause polyandries, although it may help stabilize it if police workers show behavioral dominance.
Abstract: When queens of eusocial Hymenoptera mate two or more times (assuming equal sperm contributions from males and random sperm use), the workers are more closely related to the queen's sons than to the sons of a randomly chosen worker. This suggests that workers should try to prevent other workers from reproducing, and hence producing sons, in species with queens that mate two or more times. It also provides a possible reason for the absence of reproductive workers in many hymenopteran societies. Reproductive harmony may, therefore, and counterintuitively, result from lowered relatedness among workers. Evidence from the biological literature indicates that eusocial Hymenoptera have the necessary behaviors and discriminatory ability to favor queen-produced over worker-produced males, and any such behavior is referred to as "worker policing." Population-genetics simulations of the fate of a "police allele," which confers any marginal increase in policing behavior to the workers carrying it, indicate that such a...
704 citations
TL;DR: A new method is developed that infers the distribution of FST for loci unlikely to be strongly affected by spatially diversifying selection, using data on a large set of loci with unknown selective properties, which has much lower false positive rates and comparable power.
Abstract: Loci responsible for local adaptation are likely to have more genetic differentiation among populations than neutral loci. However, neutral loci can vary widely in their amount of genetic differentiation, even over the same geographic range. Unfortunately, the distribution of differentiation—as measured by an index such as FST—depends on the details of the demographic history of the populations in question, even without spatially heterogeneous selection. Many methods designed to detect FST outliers assume a specific model of demographic history, which can result in extremely high false positive rates for detecting loci under selection. We develop a new method that infers the distribution of FST for loci unlikely to be strongly affected by spatially diversifying selection, using data on a large set of loci with unknown selective properties. Compared to previous methods, this approach, called OutFLANK, has much lower false positive rates and comparable power, as shown by simulation.
362 citations
TL;DR: Predictions of population and quantitative genetic models are reviewed and individual-based simulations are used to illustrate how the architecture of local adaptation depends on the genetic redundancy of the trait, the maintenance of standing genetic variation (VG), and the susceptibility of alleles to swamping.
Abstract: Population genetic models predict that alleles with small selection coefficients may be swamped by migration and will not contribute to local adaptation. But if most alleles contributing to standing variation are of small effect, how does local adaptation proceed? Here I review predictions of population and quantitative genetic models and use individual-based simulations to illustrate how the architecture of local adaptation depends on the genetic redundancy of the trait, the maintenance of standing genetic variation (V(G)), and the susceptibility of alleles to swamping. Even when population genetic models predict swamping for individual alleles, considerable local adaptation can evolve at the phenotypic level if there is sufficient V(G). However, in such cases the underlying architecture of divergence is transient: F(ST) is low across all loci, and no locus makes an important contribution for very long. Because this kind of local adaptation is mainly due to transient frequency changes and allelic covariances, these architectures will be difficult--if not impossible--to detect using current approaches to studying the genomic basis of adaptation. Even when alleles are large and resistant to swamping, architectures can be highly transient if genetic redundancy and mutation rates are high. These results suggest that drift can play a critical role in shaping the architecture of local adaptation, both through eroding V(G) and affecting the rate of turnover of polymorphisms with redundant phenotypic effects.
278 citations
TL;DR: It is argued that empirical evidence supports a model whereby ecological factors associated with resource availability regulate species richness at continental scales, and that many purported tests of the ecological limits hypothesis are inherently weak and distract from these three core patterns.
Abstract: Explaining variation in species richness among provinces and other large geographic regions remains one of the most challenging problems at the intersection of ecology and evolution. Here we argue that empirical evidence supports a model whereby ecological factors associated with resource availability regulate species richness at continental scales. Any large-scale predictive model for biological diversity must explain three robust patterns in the natural world. First, species richness for evolutionary biotas is highly correlated with resource-associated surrogate variables, including area, temperature, and productivity. Second, species richness across epochal timescales is largely stationary in time. Third, the dynamics of diversity exhibit clear and predictable responses to mass extinctions, key innovations, and other perturbations. Collectively, these patterns are readily explained by a model in which species richness is regulated by diversity-dependent feedback mechanisms. We argue that many p...
218 citations
TL;DR: The key perceptual principles, namely, retinal photoreception, sensory channels, opponent processing, color constancy, and receptor noise, are discussed, to inform an analytical framework driven by the research question in relation to identifiable viewers and visual tasks of interest.
Abstract: The world in color presents a dazzling dimension of phenotypic variation. Biological interest in this variation has burgeoned, due to both increased means for quantifying spectral information and heightened appreciation for how animals view the world differently than humans. Effective study of color traits is challenged by how to best quantify visual perception in nonhuman species. This requires consideration of at least visual physiology but ultimately also the neural processes underlying perception. Our knowledge of color perception is founded largely on the principles gained from human psychophysics that have proven generalizable based on comparative studies in select animal models. Appreciation of these principles, their empirical foundation, and the reasonable limits to their applicability is crucial to reaching informed conclusions in color research. In this article, we seek a common intellectual basis for the study of color in nature. We first discuss the key perceptual principles, namely, retinal photoreception, sensory channels, opponent processing, color constancy, and receptor noise. We then draw on this basis to inform an analytical framework driven by the research question in relation to identifiable viewers and visual tasks of interest. Consideration of the limits to perceptual inference guides two primary decisions: first, whether a sensory-based approach is necessary and justified and, second, whether the visual task refers to perceptual distance or discriminability. We outline informed approaches in each situation and discuss key challenges for future progress, focusing particularly on how animals perceive color. Given that animal behavior serves as both the basic unit of psychophysics and the ultimate driver of color ecology/evolution, behavioral data are critical to reconciling knowledge across the schools of color research.
211 citations
TL;DR: It is argued that biotas at scales from local communities to entire continents are nearly always open to new species and that their diversities are far from any ecological limits.
Abstract: We argue that biotas at scales from local communities to entire continents are nearly always open to new species and that their diversities are far from any ecological limits. We show that the fossil, phylogenetic, and morphological evidence that has been used to suggest that ecological processes set limits to diversity in evolutionary time is weak and inconsistent. At the same time, ecological evidence from biological invasions, experiments, and diversity analyses strongly supports the openness of communities to new species. We urge evolutionary biologists to recognize that ecology has largely moved beyond simple notions of equilibrium at a carrying capacity and toward a richer view of communities as highly dynamic in space and time.
175 citations
TL;DR: This work used an individual-based model to quantify the effects of operative environmental temperatures, as well as their heterogeneity and spatial structure, on the thermoregulation, movement, and energetics of ectotherms and showed that the heterogeneity andatial structure of a thermal landscape are as important as its mean temperature.
Abstract: In recent years, ecologists have stepped up to address the challenges imposed by rapidly changing climates. Some researchers have developed niche-based methods to predict how species will shift their ranges. Such methods have evolved rapidly, resulting in models that incorporate physiological and behavioral mechanisms. Despite their sophistication, these models fail to account for environmental heterogeneity at the scale of an organism. We used an individual-based model to quantify the effects of operative environmental temperatures, as well as their heterogeneity and spatial structure, on the thermoregulation, movement, and energetics of ectotherms. Our simulations showed that the heterogeneity and spatial structure of a thermal landscape are as important as its mean temperature. In fact, temperature and heterogeneity interact to determine organismal performance. Consequently, the popular index of environmental quality (de), which ignores variance and spatial structure, is inherently flawed as a ...
159 citations
TL;DR: The model shows that the passing of maternal cues and the transgenerational integration of sources of information readily evolve, and factors such as the degree of temporal autocorrelation, the predictive accuracy of different environmental cues, and the level of gene flow strongly influence the expression of adaptive maternal cues.
Abstract: An organism’s phenotype can be influenced by maternal cues and directly perceived environmental cues, as well as by its genotype at polymorphic loci, which can be interpreted as a genetic cue. In fluctuating environments, natural selection favors organisms that efficiently integrate different sources of information about the likely success of phenotypic alternatives. In such situations, it can be beneficial to pass on maternal cues that offspring can respond to. A maternal cue could be based on environmental cues directly perceived by the mother but also partly on cues that were passed on by the grandmother. We have used a mathematical model to investigate how the passing of maternal cues and the integration of different sources of information evolve in response to qualitatively different kinds of temporal and spatial environmental fluctuations. The model shows that the passing of maternal cues and the transgenerational integration of sources of information readily evolve. Factors such as the degr...
150 citations
TL;DR: This work presents a general statistical framework for assessing the adequacy of phylogenetic trait models and uses this approach to evaluate the statistical performance of commonly used trait models on 337 comparative data sets covering three key angiosperm functional traits.
Abstract: Making meaningful inferences from phylogenetic comparative data requires a meaningful model of trait evolution. It is thus important to determine whether the model is appropriate for the data and the question being addressed. One way to assess this is to ask whether the model provides a good statistical explanation for the variation in the data. To date, researchers have focused primarily on the explanatory power of a model relative to alternative models. Methods have been developed to assess the adequacy, or absolute explanatory power, of phylogenetic trait models, but these have been restricted to specific models or questions. Here we present a general statistical framework for assessing the adequacy of phylogenetic trait models. We use our approach to evaluate the statistical performance of commonly used trait models on 337 comparative data sets covering three key angiosperm functional traits. In general, the models we tested often provided poor statistical explanations for the evolution of the...
145 citations
TL;DR: The expansion load process in models where population growth depends on the population’s fitness is studied, showing that expansion load can severely slow down expansions and limit a species’ range, even in the absence of environmental variation.
Abstract: Expanding populations incur a mutation burden, the so-called expansion load. Using a mixture of individual-based simulations and analytical modeling, we study the expansion load process in models where population growth depends on the population’s fitness (i.e., hard selection). We show that expansion load can severely slow down expansions and limit a species’ range, even in the absence of environmental variation. We also study the effect of recombination on the dynamics of a species range and on the evolution of mean fitness on the wave front. If recombination is strong, mean fitness on front approaches an equilibrium value at which the effects of fixed mutations cancel each other out. The equilibrium rate at which new demes are colonized is similar to the rate at which beneficial mutations spread through the core. Without recombination, the dynamics is more complex, and beneficial mutations from the core of the range can invade the front of the expansion, which results in irregular and episodic ...
TL;DR: The problem of organic diversity must now be studied in a new aspect, namely, as a general property of living matter, for such it truly is.
Abstract: THE boundless diversity of organic forms is impressive even to a casual observer. Reducing this seemingly chaotic multiformity to some sort of rational system was a prerequisite for a scientific study of living things; hence taxonomy and morphology were in the past the most active branches, description and generalizing induction the main methods of biology. Later the main trend of thought has turned from morphology to physiology, from description to experiment, and from peculiarities of single species to properties common to large groups or to all of them. The problem of organic diversity must now be studied in a new aspect, namely, as a general property of living matter, for such it truly is. The difference between any two individuals or species may be attributed to the differences between their gene complexes, and in a few cases between their cytoplasms. Assuming this statement to be correct (and it is not universally accepted), one must nevertheless admit that it does not represent an adequate solution of the problem of organic diversity, for it disregards the fundamental fact that the living world is subdivided into discrete groups of forms which we call species. The living world is not an array of individuals embodying all the possible combinations of the existing genes; it is certain that only an infinitesimal fraction of the possible gene combinations has been ever realized. Organisms are more or less adapted to their environment, and the gene patterns each of them carries must represent at least a tolerably liarmonious whole. With the sexual process being the predominatineg mode of reproduction, an unlimited inter-
TL;DR: Shifts in the supply function indicate that there is a proximate effect of food abundance on feeding rate, but these shifts do not support the hypothesis that the food supply in the environment places an absolute evolutionary constraint on clutch size by limiting the ability of parents to feed their broods.
Abstract: A supply-and-demand model was developed to describe parent-offspring food-provisioning interactions in nidicolous birds. The supply function represents the feeding response of the parents to the hunger signals of the brood, and the demand function describes the hunger-signaling response of the brood to the feeding rate. The intersection of the two functions is an equilibrium point representing the feeding rate and hunger-signaling level observed in the real world. The model was tested for broods of six tree swallows at 13 days of age. It was shown that the supply function shifts in response to changes in food abundance in the environment and that compensating shifts in the demand function occur in accordance with the nutritional condition of the young. The resulting feeding rates are relatively stable over wide ranges of food abundance and hunger-signal level, indicating that the behavioral system enables parents to adjust feeding rates to the needs of the young, in spite of variations in their environmen...
TL;DR: It is suggested that the effects of large carnivores on scavengers depend on attributes of both carnivores and scavengers (including size) and that competition for carcasses may result in intraguild predation as well as mesocarnivore release.
Abstract: Pumas (Puma concolor) and black bears (Ursus americanus) are large carnivores that may influence scavenger population dynamics We used motion-triggered video cameras deployed at deer carcasses to determine how pumas and black bears affected three aspects of carrion acquisition by scavengers: presence, total feeding time, and mean feeding-bout duration We found that pumas were unable to limit acquisition of carrion by large carnivores but did limit aspects of carrion acquisition by both birds and mesocarnivores Through their suppression of mesocarnivores and birds, pumas apparently initiated a cascading pattern and increased carrion acquisition by small carnivores In contrast, black bears monopolized carrion resources and generally had larger limiting effects on carrion acquisition by all scavengers Black bears also limited puma feeding behaviors at puma kills, which may require pumas to compensate for energetic losses through increasing their kill rates of ungulates Our results suggest that
TL;DR: This study reveals how simple morphological traits and prey-handling ability can profoundly influence individual space use, which underpins broader-scale patterns in the spatial ecology of vertebrates.
Abstract: Daily animal movements are usually limited to a discrete home range area that scales allometrically with body size, suggesting that home-range size is shaped by metabolic rates and energy a...
TL;DR: The loss of larger predators will have greater consequences on trophic control and biomass structure in food webs than the loss of smaller predators.
Abstract: Trophic cascades are indirect positive effects of predators on resources via control of intermediate consumers. Larger-bodied predators appear to induce stronger trophic cascades (a greater rebound of resource density toward carrying capacity), but how this happens is unknown because we lack a clear depiction of how the strength of trophic cascades is determined. Using consumer resource models, we first show that the strength of a trophic cascade has an upper limit set by the interaction strength between the basal trophic group and its consumer and that this limit is approached as the interaction strength between the consumer and its predator increases. We then express the strength of a trophic cascade explicitly in terms of predator body size and use two independent parameter sets to calculate how the strength of a trophic cascade depends on predator size. Both parameter sets predict a positive effect of predator size on the strength of a trophic cascade, driven mostly by the body size dependence...
TL;DR: The observed assemblies are those showing minimum separation and hence maximum utilization of resource space, and the pattern of niche separation and diversity demonstrates niche dimensionality in this fauna.
Abstract: Current ecological theory predicts limits to the closeness of species packing. Increased competition from more competitors should result in greater average niche separation. This idea was tested for locally sympatric heteromyid rodents in part of the Sonoran Desert of Arizona, and the predictions were verified. As a consequence of diffuse competition, niche separation increases with species diversity, and rodent species show separation on both niche dimensions quantified in this study (seed-size collection and habitat utilization). However, when local diversity is low (Dipodomys merriami-Perognathus penicillatus), rodents are very similar in their overall utilization of both dimensions. As diversity increases, first seed-size differences then subsequently both seed-size and habitat differences are apparent. Therefore, the pattern of niche separation and diversity demonstrates niche dimensionality in this fauna. The pattern of niche separation and diversity also accounts for the occurrence of specific comb...
TL;DR: It is shown that bats invest more per young than do other mammals and hypothesize that this results from a fundamental, proximate constraint acting on flying vertebrates in general that restricts the number of offspring they can raise at one time.
Abstract: Among mammals, many life-history traits correlate with body size (Millar 1977, 1981; Wooton 1987; Harvey and Read 1988; Read and Harvey 1989). In general, large mammals live long lives during which they produce litters of few, large, slow-growing, late-maturing offspring. Small mammals live short lives and have litters of many, small, rapidly growing, early-maturing offspring. Even when body size is factored out, however, life-history traits correlate with one another (Read and Harvey 1989). Some mammals produce litters of few, large, slow-growing offspring and live long lives for their body size, whereas others produce large litters of fast-growing young and die at an early age. In the debate over the evolution of mammalian life-history variation, the second largest group of mammals, bats, has been either completely ignored (Sacher and Staffeldt 1974; Western 1979; Millar 1981; Western and Ssemakula 1982) or severely underrepresented (Millar 1977; Blueweiss et al. 1978; Wooton 1987; Promislow and Harvey 1990). Bats can be used to argue against a simple allometric constraint on life-history variation. Despite their small size (most have body masses under 100 g; Barclay and Brigham 1991), bats are long-lived (Tuttle and Stevenson 1982) and have uniformly small litters. Most species produce only a single young, and only eight are known to regularly produce more than two young (Tuttle and Stevenson 1982). The purpose of this note is to propose a physiological nd evolutionary explanation for the consistently small litter size of bats. I show that bats invest more per young than do other mammals and hypothesize that this results from a fundamental, proximate constraint acting on flying vertebrates in general that restricts the number of offspring they can raise at one time. Although such costs of reproduction are typically measured in terms of energy, I suggest hat calcium for offspring skeletal growth is a more critical constraint. Finally, I propose that birds and bats are influenced to different degrees by this constraint because of basic differences in their parental care systems and foraging abilities. One hypothesis for why bats have small itters is that flight constrains reproductive output. Litter mass may be constrained, which limits the number of viable neonates that can be produced (Millar 1977). The mass of a near-term litter influ-
TL;DR: Only a few of the more than one hundred patterns that are known to occur in the species of the genera Coecinella, Semiadalia, Adonia and Hippodamia are restricted to a single species.
Abstract: THE coleopterous family Coccinellidae presents very favorable material for studies on variation. The colorpattern of the elytra and of the pronotum is very widely variable in many species. The variations may be arranged in series beginning with entirely light (yellow or red) elytra, ranging through light elytra with a number of dark (black or brown) spots, dark elytra with light spots, and ending with dark, unspotted elytra. The intraspecific variability is not infrequently discontinuous, the intergrades between the different patterns being rare or absent. Large groups of related species and genera exhibit parallel series of patterns, upholding the rule of homologous series in variation, formulated by Vavilov (1922). Thus, only a few of the more than one hundred patterns that are known to occur in the species of the genera Coecinella, Semiadalia, Adonia and Hippodamia are restricted to a single species. A large majority of these patterns reappear in several or in many species. The similarity of the homologous patterns in different species is often striking (compare Figs. 2 E and 3 H, Figs. 2 L, 4 D and 4 G. Figs. 2 I, 4 J and 5 D). Homologous varieties of different species may appear even more similar to each other than do different varieties of the same species. However, the different varieties of the same species, at
TL;DR: Analysis of sequences from 130 families of angiosperms shows that variation in the synonymous substitution rate is correlated among genes from the mitochondrial, chloroplast, and nuclear genomes and linked to differences in traits among families (average height and genome size).
Abstract: A new view is emerging of the interplay between mutation at the genomic level, substitution at the population level, and diversification at the lineage level. Many studies have suggested that rate of molecular evolution is linked to rate of diversification, but few have evaluated competing hypotheses. By analyzing sequences from 130 families of angiosperms, we show that variation in the synonymous substitution rate is correlated among genes from the mitochondrial, chloroplast, and nuclear genomes and linked to differences in traits among families (average height and genome size). Within each genome, synonymous rates are correlated to nonsynonymous substitution rates, suggesting that increasing the mutation rate results in a faster rate of genome evolution. Substitution rates are correlated with species richness in protein-coding sequences from the chloroplast and nuclear genomes. These data suggest that species traits contribute to lineage-specific differences in the mutation rate that drive both synonymous and nonsynonymous rates of change across all three genomes, which in turn contribute to greater rates of divergence between populations, generating higher rates of diversification. These observations link mutation in individuals to population-level processes and to patterns of lineage divergence.
TL;DR: An integrated model that predicts life-cycle phenology in complex environments by integrating across life stages demonstrates how genetic variation in one transition can influence subsequent transitions and the geographic distribution of life cycles more generally.
Abstract: Organisms develop through multiple life stages that differ in environmental tolerances. The seasonal timing, or phenology, of life-stage transitions determines the environmental conditions to which each life stage is exposed and the length of time required to complete a generation. Both environmental and genetic factors contribute to phenological variation, yet predicting their combined effect on life cycles across a geographic range remains a challenge. We linked submodels of the plasticity of individual life stages to create an integrated model that predicts life-cycle phenology in complex environments. We parameterized the model for Arabidopsis thaliana and simulated life cycles in four locations. We compared multiple “genotypes” by varying two parameters associated with natural genetic variation in phenology: seed dormancy and floral repression. The model predicted variation in life cycles across locations that qualitatively matches observed natural phenology. Seed dormancy had larger effects ...
TL;DR: The results suggest that intercolonial recognition is the most plausible means by which recognition itself can generate genetic odor-cue diversity, and that low diversity of odor cues may facilitate the evolution of highly cooperative worker behavior by making queen-rearing discrimination less worthwhile.
Abstract: Recognition in many taxa is mediated by genetic-cue diversity. The present study investigates the likely effects of two recognition contexts on genetic odor-cue diversity in social Hymenoptera by means of single-locus, two-allele, and multiple-allele population-genetics models. Full-sister versus half-sister discrimination in polyandrous societies, as in queen-rearing discrimination in the honey bee, leads to reduced allelic diversity when queens mate with more than two males. In doubly mated species, discrimination may raise or lower allelic diversity, depending on the rules used by workers in discrimination, but most plausibly it results in a reduction in allelic diversity to two alleles. In contrast, colony recognition based on genetic odors can increase allelic diversity, if colonies with rare odors produce more reproductives. This assumption seems likely for social insects that use genetic cues for nest-mate recognition. This result is the reverse of one obtained earlier in an analysis of genetic rec...
TL;DR: It is found that nest visit synchrony responded directly to the brood manipulation and increased with brood size, suggesting that parental coordination could indeed play an important role in partners’ investment decisions, underpinning the evolution of the most prominent mating system in birds.
Abstract: Sexual conflict over parental care relies on the fundamental assumption that parents do not share the cost of their partner’s effort on future reproduction. However, this is unlikely to be true whenever partners breed together more than once. In that case, individuals should try to optimize the cost and benefits for the pair, rather than only for themselves. Here we seek to establish whether the synchronization of parents’ provisioning visits to the nest could fulfill this function. We conducted a brood-size manipulation experiment on wild zebra finches to test whether nest visit synchrony was flexible and beneficial for nestlings’ growth, while controlling for the confounding effects of pair “quality” and synchrony away from the nest during foraging. Using a network of readers to track parents at nests and feeding stations, we found that nest visit synchrony responded directly to the brood manipulation and increased with brood size. Synchrony at the nest and while foraging were correlated, but th...
TL;DR: A simple model of self-organized coordination and leadership in groups is recreated, including the apparent consensus behavior among naive individuals, which requires informed individuals to appropriately balance goal-oriented and socially oriented behavior.
Abstract: Leadership is widespread across the animal kingdom. In self-organizing groups, such as fish schools, theoretical models predict that effective leaders need to balance goal-oriented motion, such as toward a known resource, with their tendency to be social. Increasing goal orientation is predicted to increase decision speed and accuracy, but it is also predicted to increase the risk of the group splitting. To test these key predictions, we trained fish (golden shiners, Notemigonus crysoleucas) to associate a spatial target with a food reward (“informed” individuals) before testing each singly with a group of eight untrained fish who were uninformed (“naive”) about the target. Informed fish that exhibited faster and straighter paths (indicative of greater goal orientation) were more likely to reach their preferred target and did so more quickly. However, such behavior was associated with a tendency to leave untrained fish behind and, therefore, with failure to transmit their preference to others. Eit...
TL;DR: It was found that birds which received ten, 30, and even 60 per cent mimics rejected about 80 per cent of the mimics by associating their color band with that of the unpalatable model, indicating that mimicry is effective when mimics are more frequent than models.
Abstract: 1. Experiments were carried out to test the effectiveness of mimicry at different proportions of models and mimics with Starlings (Sturnus vulgaris) as predators and mealworms (Tenebrio molitor) as artificial models and mimics. 2. A band of green cellulose paint was used to mark the "model" mealworms which were made unpalatable by being dipped into a 66 per cent solution of quinine dihydrochloride. "Mimic" mealworms were identically banded, but dipped into distilled water, as were orange-banded "edible" mealworms. 3. It was found that birds which received ten per cent, 30 per cent, and even 60 per cent mimics (the balance being models) rejected about 80 per cent of the mimics by associating their color band with that of the unpalatable model. Mimicry is thus effective when mimics are more frequent than models. 4. Two birds which were given 90 per cent mimics (only ten per cent models) nevertheless rejected 17 per cent of the mimics, indicating that when a model is highly unpalatable, and a mimic relativel...
TL;DR: This work presents a conceptual framework for classifying multihost sharing, and develops a generalized technique to quantify each species’ contribution to parasite persistence, allowing natural systems to be located within the framework.
Abstract: Many parasites circulate endemically within communities of multiple host species. To understand disease persistence within these communities, it is essential to know the contribution each host species makes to parasite transmission and maintenance. However, quantifying those contributions is challenging. We present a conceptual framework for classifying multihost sharing, based on key thresholds for parasite persistence. We then develop a generalized technique to quantify each species' contribution to parasite persistence, allowing natural systems to be located within the framework. We illustrate this approach using data on gastrointestinal parasites circulating within rodent communities and show that, although many parasites infect several host species, parasite persistence is often driven by just one host species. In some cases, however, parasites require multiple host species for maintenance. Our approach provides a quantitative method for differentiating these cases using minimal reliance on system-specific parameters, enabling informed decisions about parasite management within poorly understood multihost communities.
TL;DR: Rearing-group size and the time juveniles spent in these groups interactively influenced the development of social skills and the relative sizes of four main brain regions, and the results suggest continuous plastic behavioral changes over time.
Abstract: Social animals can greatly benefit from well-developed social skills. Because the frequency and diversity of social interactions often increase with the size of social groups, the benefits of advanced social skills can be expected to increase with group size. Variation in social skills often arises during ontogeny, depending on early social experience. Whether variation of social-group sizes affects development of social skills and related changes in brain structures remains unexplored. We investigated whether, in a cooperatively breeding cichlid, early group size (1) shapes social behavior and social skills and (2) induces lasting plastic changes in gross brain structures and (3) whether the development of social skills is confined to a sensitive ontogenetic period. Rearing-group size and the time juveniles spent in these groups interactively influenced the development of social skills and the relative sizes of four main brain regions. We did not detect a sensitive developmental period for the shaping of social behavior within the 2-month experience phase. Instead, our results suggest continuous plastic behavioral changes over time. We discuss how developmental effects on social behavior and brain architecture may adaptively tune phenotypes to their current or future environments.
TL;DR: For species in which males contribute only sperm to reproduction, the question of whether male displays are indicative of male genetic quality can be addressed by combining behavioral observations with quantitative-genetic procedures, illustrated by an analysis of chemical communication in the red flour beetle.
Abstract: For species in which males contribute only sperm to reproduction, the question of whether male displays are indicative of male genetic quality can be addressed by combining behavioral observations with quantitative-genetic procedures. This approach is illustrated by an analysis of chemical communication in the red flour beetle (Tribolium castaneum Herbst). First, the attractiveness of male pheromone to females was evaluated in behavioral tests. Then the same males were bred and various components of fitness measured in their offspring. Males were considered different in genetic quality if significant heritability of a component of fitness was found. To test the "good genes" hypothesis, the correlation between attractiveness of males and fitness of their progeny was computed. In flour beetles no significant correlations were found. Theoretical and practical limitations of good-genes models are discussed in relation to this experiment.
TL;DR: It is suggested that early adversity carries lifelong costs, which is consistent with the developmental constraints hypothesis, and individuals that experienced at least one high-quality early environment—either ecological or social—were more resilient to ecological stress in later life.
Abstract: Early-life experiences can dramatically affect adult traits. However, the evolutionary origins of such early-life effects are debated. The predictive adaptive response hypothesis argues that adverse early environments prompt adaptive phenotypic adjustments that prepare animals for similar challenges in adulthood. In contrast, the developmental constraints hypothesis argues that early adversity is generally costly. To differentiate between these hypotheses, we studied two sets of wild female baboons: those born during low-rainfall, low-quality years and those born during normal-rainfall, high-quality years. For each female, we measured fertility-related fitness components during years in adulthood that matched and mismatched her early conditions. We found support for the developmental constraints hypothesis: females born in low-quality environments showed greater decreases in fertility during drought years than females born in high-quality environments, even though drought years matched the early c...