Showing papers in "The American Naturalist in 1990"
TL;DR: This model indicates that there may be widely different hormonal responses to male-male and male-female interactions and presumably equally plastic neural mechanisms for the transduction of these signals into endocrine secretions.
Abstract: A combination of field and laboratory investigations has revealed that the temporal patterns of testosterone (T) levels in blood can vary markedly among populations and individuals, and even within individuals from one year to the next. Although T is known to regulate reproductive behavior (both sexual and aggressive) and thus could be expected to correlate with mating systems, it is clear that the absolute levels of T in blood are not always indicative of reproductive state. Rather, the pattern and amplitude of change in T levels are far more useful in making predictions about the hormonal basis of mating systems and breeding strategies. In these contexts we present a model that compares the amplitude of change in T level with the degree of parental care shown by individual males. On the basis of data collected from male birds breeding in natural or captive conditions, polygynous males appear less responsive to social environmental cues than are monogamous males. This model indicates that there may be wi...
2,098 citations
TL;DR: Improvement in the ability of the water balance to distinguish between climates similar in mean annual energy and water supplies but different in the seasonal timing of the two will help to predict the effects of changing climate on the future distribution of vegetation types.
Abstract: The water balance describes climate as it is sensed by plants, as the interaction of energy and water in the environment. Discriminant analysis showed that the distribution of North American plant formations was more highly correlated with the water balance (actual evapotranspiration and deficit) than with the more traditional measures of climate (such as temperature and precipitation) used in several studies, including those used in the well-known works of Thornthwaite, Holdridge, and Whittaker. Much of the improved correlation could be attributed to the ability of the water balance to distinguish between climates similar in mean annual energy and water supplies but different in the seasonal timing of the two. Consideration of the water balance aided in the interpretation of possible mechanisms controlling the distribution of plant formations. For example, coniferous forest occurred at low actual evapotranspiration (low simultaneous availability of energy and water), consistent with the suggestion that c...
795 citations
TL;DR: It is found that mothers keep their cubs in a creche and form highly stable maternity groups that are effective in defending the cubs against infanticidal males, and larger groups successfully repel smaller ones in territorial disputes.
Abstract: Extensive observations of foraging female lions reveal that two group sizes maximize foraging success during the season of prey scarcity: one female and five or six females. Foraging success does not vary significantly with group size when prey is abundant. Female lions live in fission-fusion social units (prides) and forage only with members of their own pride. If lion grouping patterns were primarily related to group-size-specific feeding efficiency, females in prides containing fewer than five females should forage alone when prey is scarce, whereas females in larger prides should forage alone or in groups of five or six. However, extensive data on the grouping patterns of radio-collared females show that females in small prides most commonly forage in as large a group as possible, even at the expense of foraging efficiency. Females in large prides most often forage in intermediate group sizes of four or five. However, mothers keep their cubs in a creche and form highly stable maternity groups that are...
572 citations
TL;DR: In this paper, the authors compare the expected fitness consequences of two alternative decision-making strategies: a best-of-n strategy (whereby searching individuals choose the best mate from a sample of size n) and a strategy based on sequential sampling, where the searching individual establishes a critical mate quality and continues searching until encountering a mate at or above this quality.
Abstract: Sexual selection depends on differential patterns of mate preference and choice. Little attention has been paid, however, to the manner in which individuals acquire information about the quality of potential mates and how this information is used to form mating decisions. Different decision rules for determining mating preferences often lead to different fitness consequences for the actively searching and choosy sex. In this paper, I compare the expected fitness consequences of two alternative decision-making strategies: a best-of-n strategy (whereby searching individuals choose the best mate from a sample of size n) and a strategy based on sequential sampling (whereby the searching individual establishes a critical mate quality and continues searching until encountering a mate at or above this quality). For the same distribution of potential mate qualities, the sequential-search strategy generates higher expected fitness gains than the best-of-n strategy. This is in contrast to earlier conclusions (e.g.,...
559 citations
TL;DR: Homeostatic grazers appear to establish an unstable equilibrium in the N: P in the algal pool and thus, presumably, in the nutrient-limitation patterns of the algae, which predicts a role for grazers not predicted by other theoretical approaches.
Abstract: The influence of pelagic herbivores on the competitive arena of their prey is examined in three models of herbivore physiology. One hallmark of pelagic herbivory is the rapid and fight cycling of nutrients among algae, herbivores,and the dissolved phase. An implication of this cycling is that the ratio of elements released by the herbivore is a "supply ratio" as defined in resource-competition theory. The nitrogen (N)-to-phosphorus (P) supply ratio depends on the assumptions made regarding grazer physiology. Three alternative models are considered: (1) a constant, mass-specific basal metabolic release of N and P; (2) a constant efficiency of accumulating N and P in grazer biomass; and (3) an adjusting efficiency of N and P accumulation that maintains a homeostatic ratio of N to P (N:P) in the bodies of the grazers. All three models predict a positive correlation between the N:P in the algal pool and that released by the animals. Previously published data provided strong supportive evidence for this relati...
388 citations
TL;DR: Characteristics of fish assemblages from Finland and northern Wisconsin are compared on several scales to investigate community-level similarity in environmentally similar but faunistically different small lakes and suggest thatFish assemblage structures in northern forest lakes are influenced by common sets of environmental factors.
Abstract: We compared characteristics of fish assemblages from Finland and northern Wisconsin on several scales to investigate community-level similarity in environmentally similar but faunistically different small lakes. Although Finland has only half as many fishes in its regional species pool, local species richness did not differ between the two regions. Variability in species composition among assemblages was lower in Finland, suggesting that a large proportion of the fauna could maintain populations across a broad range of environmental conditions, whereas the Wisconsin fauna was composed of more specialized species. Three types of fish assemblages were identified in Wisconsin based on species' presence or absence, whereas on the same scale, Finnish assemblages presented a hierarchical continuum based on species addition. These and other patterns suggest that habitat specialization and the exclusion of small prey species from lakes with piscivores contribute to the occurrence of presence-absence assemblage ty...
371 citations
TL;DR: It is argued that, although females are expected to pay lower costs in noneconomic mating systems, this need not translate into examining fewer males or spending less time in this activity, and there may be no lek paradox.
Abstract: Mate choice in noneconomic mating systems has been considered paradoxical because, relative to economic systems, females were thought to have "highly developed" preferences, despite males' having little to offer. Efforts to resolve this paradox have generally searched for genetic benefits of choice through either "good genes" or "runaway" coevolution. In this paper, we emphasize natural selection acting directly on females and their offspring. We argue that, although females are expected to pay lower costs in noneconomic mating systems, this need not translate into examining fewer males or spending less time in this activity. Furthermore, various direct (nongenetic) benefits may accrue. In species in which males offer benefits that are more variable, such as territories or parental care, females should evolve toward greater investment in mate choice, especially when these resources cannot be shared among females. Any tendency for females to be more selective in noneconomic mating systems, despite lower be...
312 citations
TL;DR: 13 nonexclusive hypotheses that may contribute to the observed frequency distribution of fruit colors are presented and a preliminary assessment of these hypotheses is made, in a preliminary way, using existing information.
Abstract: Red and black are the most common colors of bird-dispersed fruits in all regions of the world for which information is available; other colors occur, but at lower frequencies. We present 13 nonexclusive hypotheses that may contribute to the observed frequency distribution of fruit colors and assess them, in a preliminary way, using existing information. Five hypotheses relate fruit colors directly to avian foraging: (1) birds prefer red and black (weak support at best); (2) red and black displays are more readily discovered by foraging birds (mixed evidence); (3) fruit colors indicate fruit maturity (mixed evidence); (4) fruit colors facilitate quick recognition of food (little evidence); (5) nutritionally poor fruits mimic nutrient-rich fruits (no data). Three hypotheses relate fruit colors to defense against natural enemies: (6) red fruits are inconspicuous to fruit-foraging arthropods (limited applicability); (7) fruit colors exclude poor dispersal agents (few data); (8) fruit pigments defend fruits ag...
311 citations
TL;DR: A model is developed that incorporates time constraints, by assuming that reproduction or some other major event, such as diapause or metamorphosis, must occur by a specified time or date, and predicts optimal strategies for pre-reproductive habitat shifts that depend on both time and body weight.
Abstract: Short-term foraging behavior is typically influenced by the needs to obtain food at a high rate and to avoid predation. There is increasing evidence that the need to balance these conflicting demands plays a role in ontogenetic habitat shifts, including the spectacular shifts characteristic of complex life cycles. Previous theory has led to rules that are independent of time to predict the size at which habitat shifts take place. We develop a model that incorporates time constraints, by assuming that reproduction or some other major event, such as diapause or metamorphosis, must occur by a specified time or date. We incorporate recent formulations of dynamic programming that allow strategies to balance conflicting behaviors by expressing them in the common currency of future reproductive output. The resulting theory predicts optimal strategies for pre-reproductive habitat shifts that depend on both time and body weight. Our theory, although derived from a single set of assumptions, leads to a synthesis of...
309 citations
TL;DR: The general success of the model in explaining patterns of tree growth suggests that competition for light is the primary factor responsible for the evolution and maintenance of the arboreal life form.
Abstract: A game-theoretical model of tree growth is developed to evaluate the adaptive significance of height growth. The model balances the advantages of height for light interception against height-related costs, such as increased maintenance respiration, that reduce the energy available for stem growth. The model predicts an evolutionarily stable strategy (ESS) for trees of even-aged stands. This ESS consists of a prolonged interval of height growth that terminates when the trees reach 87% of the theoretical break-even height, at which stem maintenance and root and leaf renewal costs require all available photosynthate, leaving none for wood production. Tests of the model with data from forest yield tables indicate that (1) averagesized trees of even-aged stands follow the predicted ESS until reaching at least 70%-90% of their maximum height; (2) trees that are larger than average have thicker-than-expected trunks to withstand disproportionately greater wind forces in the upper canopy; (3) height growth may cea...
307 citations
TL;DR: The data suggest that, immediately after reproductive isolation, most lineages diverge morphologically at approximately the neutral rate and that this rate declines over evolutionary time, which suggests that the apparently rapid rates of morphological evolution in modern manrelative to other mammals and in mammals relative to other vertebrates are artifacts of temporal scaling.
Abstract: A comparison of the evolutionary rates of cranial morphology in mammals with the neutral expectation suggests that stabilizing selection is a predominant evolutionary force keeping the long-term diversification of lineages well below its potential. The rate of morphological divergence of almost all lineages, including the great apes, is substantially below the minimum neutral expectation. The divergence of the modern races of man is slightly above the minimum neutral rate but well below the maximum rate. Therefore, there is no need to invoke extraordinary mutational mechanisms, such as regulatory gene evolution, to explain what has been perceived as rapid morphological evolution in mammals. Nor does it appear that behavioral drive needs to be invoked to explain rapid morphological evolution in hominoids. Outside of man, the long-term rate of phenotypic evolution in the great apes is actually lower than that for other mammals. The data suggest that, immediately after reproductive isolation, most lineages d...
TL;DR: It is predicted that mechanisms promoting within-group reproductive synchrony are even less likely to have evolved as a predator-swamping strategy in patchily distributed populations, in which reproduction cannot be synchronized between groups.
Abstract: The logic behind the hypothesis explaining reproductive synchrony as a strategy for reducing the predation of vulnerable offspring (predator swamping) is evaluated by means of two simple models. Predator swamping was found to be an adequate explanation for the occurrence of within-season reproductive synchrony when the predator exhibits a Holling type-II functional response (specialist predator). However, in the case of a generalist predator switching from alternative prey (Holling type-III functional response), which is expected to be a common functional-response type when particular prey are unavailable at certain times of the year, highly asynchronous reproduction may be the best reproductive strategy. In particular, when prey switching occurs at high offspring densities and/or the satiation density of the predator is high relative to the total reproduction of the prey population, the peak predation rate is expected to occur when reproduction is completely synchronous. Spatially clumped prey population...
TL;DR: Four replicates of all 16 combinations of the presence and absence of two predators and adult salamanders and two anuran prey in an array of artificial temporary ponds found that Anax caused an even greater reduction in survival but not as strong an acceleration of metamorphosis.
Abstract: We performed four replicates of all 16 combinations of the presence and absence of two predators (larvae of the dragonfly Anax junius and adult salamanders Notophthalmus viridescens) and two anuran prey (Bufo americanus and Rana palustris larvae) in an array of artificial temporary ponds. The two species of anurans were introduced at densities high enough to cause density-dependent reductions in survival and body size at metamorphosis and to increase larval period. The two species were in competition when raised together. Notophthalmus reduced the density of Bufo and caused the survivors to metamorphose early and at a small size. Anax caused an even greater reduction in survival but not as strong an acceleration of metamorphosis. Newts also reduced the density of Rana, but survivors benefited by growing rapidly. The effects of Anax were even stronger; the only Rana tadpoles that were able to metamorphose in the 2 mo of the experiment were from ponds in which Anax reduced densities enough to permit rapid g...
TL;DR: It is shown that the correct weights to use are the class reproductive values, and, using these, a covariance equation for allele-frequency change is formed that provides the classical inclusive-fitness formulation if benefits are calculated by weighting each offspring by the individual reproductive value that pertains to his class.
Abstract: Suppose that in a population with a class structure, we wish to calculate the change in frequency of an allele under the action of selection. If the allele affects the behavior of individuals in different classes differently and if parents of different classes have different class distributions of offspring, then the allele frequencies in different classes may be different, and any overall calculation of allele-frequency change must decide how to weight the different class frequencies. I show that the correct weights to use are the class reproductive values, and, using these, I formulate a covariance equation for allele-frequency change. This equation also provides the classical inclusive-fitness formulation if benefits (increased numbers of offspring) are calculated by weighting each offspring by the individual reproductive value that pertains to his class.
TL;DR: In this paper, a community is judged most stable when the absolute abundance of each species remains constant over time, while the abundance of individual species fluctuates, but abundance rankings remain constant.
Abstract: Community persistence exists within a hierarchical framework wherein the numerical scale of analysis can influence judgments about the stability of assemblages. Numerical resolution refers to whether data are analyzed in terms of the absolute abundances of species, abundance rankings, or species' presence and absence. A community would be judged most stable when the absolute abundance of each species remains constant over time. At a lower level of stability, the abundance of individual species fluctuates, but abundance rankings remain constant over time. An even lower level of stability would involve assemblages in which both the absolute abundances and the abundance rankings of species fluctuate, but the same species are always present. The least stable condition would occur when even the presence and absence of species are unpredictable over time. Analysis of simulated communities showed that assemblages may be judged stable at some levels within this hierarchy but not at others; thus, statements about ...
TL;DR: The model predicts the conditions under which changes in the availability of male-derived nutrients to individual females will be accompanied by changes in female fecundity, in adult female feeding, and/or in the allocation of the total nutrient pool to egg production and can be used to predict associations of reproductive and foraging traits within a species or population.
Abstract: Male insects of many species donate nutrients to their females at mating, and the females can use these nutrients for egg production and somatic maintenance. These male-derived nutrients represent male investment in reproduction. The relative investment by each sex in reproduction has been postulated to be a determinant of the mating system and possible operation of sexual selection. However, the effect of male nutrient donations on female fitness is not well understood. I examine the effect on female fitness of male nutrients donated at mating in terms of the role of male nutrients in the female's nutrient budget for egg production. Nonnutritional constraints on total egg mass, the timing of egg production, the quality and quantity of adult female feeding, and alternative functions of male nutrient donations are incorporated into a model describing the role of male-derived nutrients. The model predicts the conditions under which changes in the availability of male-derived nutrients to individual females ...
TL;DR: A general model for the effects of variation in reproductive success on gene-frequency change and phenotypic evolution is developed and applied to patterns of developmental homeostasis, the evolution of iteroparity, and the effect of variability in resource acquisition under nonlinear gains.
Abstract: We develop a general model for the effects of variation in reproductive success on gene-frequency change and phenotypic evolution. Our approach is based on distinguishing among individual, genotypic, and population-level reproductive success and on relating these three levels through correlations. For example, the variance of genotypic reproductive success can be expressed by individual-level variance and by the correlations among individuals. We use these correlations to show the simple relationship among earlier models of selection on the variance of reproductive success, of temporal variation in selection, of spatial variation in selection, and of variation in behavioral traits. Our approach also applies to diploid individuals by regarding diploidy as a way to induce correlations in reproductive success between pairs of alleles. We apply our method to patterns of developmental homeostasis, the evolution of iteroparity, and the effects of variability in resource acquisition under nonlinear gains. Finall...
TL;DR: The morphological traits, flight speeds, and temperatures of 54 species of common Neotropical rain-forest butterflies in Corcovado National Park, Costa Rica, correlate with their palatabilities, and body shape correlates most closely with flight and temperature measures of butterflies and with the responses of jacamars.
Abstract: The morphological traits, flight speeds, and temperatures of 54 species of common Neotropical rain-forest butterflies in Corcovado National Park, Costa Rica, correlate with their palatabilities. Bu...
TL;DR: The results show that long-term studies in the field are capable of demonstrating a cost of reproduction in plants, and the pink lady's slipper orchid, Cypripedium acaule, is well suited to this design.
Abstract: The cost of current reproduction on future growth, survival, and reproduction is a central concept in evolutionary ecology, but the field evidence in plants for a cost of reproduction is weak because the appropriate experimental protocol (manipulation of the level of reproduction in an experimental group of individuals) has rarely been carried out. The pink lady's slipper orchid, Cypripedium acaule, is well suited to this design because naturally occurring flowering plants only rarely fruit, whereas virtually all hand-pollinated flowers develop into fruits. In two eastern Massachusetts populations, plants were randomly assigned to be hand-pollinated or left as controls, with the treatments repeated in four successive years. After 2 yr, treatment effects were weak at one site and absent from the other site. By the third and fourth years, the high cost of reproduction was clearly demonstrated in a lower growth and flowering rate of hand-pollinated plants in comparison with the control plants. An average-siz...
TL;DR: Mate-choice experiments allowing a female red jungle fowl (Gallus gallus) to choose between two roosters showed female preferences for several male secondary sex characters.
Abstract: Mate-choice experiments allowing a female red jungle fowl (Gallus gallus) to choose between two roosters showed female preferences for several male secondary sex characters. In 1987, male comb length was most strongly related to mating success, with eye color and the color of some ornamental feathers also being important in choice. In 1988, males with darker, redder eyes were again chosen more frequently, but comb color explained a significant portion of mating-success variation, whereas comb length was unimportant. Females did not choose older males over younger ones, but, in our sample, older and younger roosters did not differ on the basis of traits used in making choices. Male courtship behavior was generally not significantly different between chosen and unchosen males, and behavior was not correlated with morphological characters. Comb characteristics are facultative and are probably good indicators of individual condition, suggesting that females using these traits to distinguish among males could ...
TL;DR: This work provides the first detailed comparison of survival rates of tropical and temperate forest birds based on extensive data bases and modern capture-recapture models and finds no support for the conventional wisdom.
Abstract: Survival rates of tropical forest birds are widely assumed to be high relative to the survival rates of temperate forest birds. Much life-history theory is based on this assumption despite the lack of empirical data to support it. We provide the first detailed comparison of survival rates of tropical and temperate forest birds based on extensive data bases and modern capture-recapture models. We find no support for the conventional wisdom. Because clutch size is only one component of reproductive rate, the frequently assumed, simple association between clutch size and adult survival rates should not necessarily be expected. Our results emphasize the need to consider components of fecundity in addition to clutch size when comparing the life histories of tropical and temperate birds and suggest similar considerations in the development of vertebrate life-history theory.
TL;DR: Influence du risque du a la presence de predateurs and a au jeune subit sur le taux d'accouplement and sur sa duree.
Abstract: Influence du risque du a la presence de predateurs et a au jeune subit sur le taux d'accouplement et sur sa duree
TL;DR: Studies in ecology, behavior, and conservation could be significantly enhanced by using acoustic tomography, especially when monitored by several acoustic receivers.
Abstract: When monitored by several acoustic receivers, the sounds emitted by terrestrial and marine animals can be used to localize their positions The localization can proceed quickly and automatically with the use of computers when cross-correlation of the acoustic records is used to optimally estimate the travel-time difference between signals at different receivers The time-bandwidth product (call duration x acoustic bandwidth) of the call is an important parameter When the time-bandwidth product of the acoustic call equals or exceeds 10 (which is the case for many animals), localization is possible even when the signal-to-noise ratios of the call are below the noise level, as long as cross-correlation is used to estimate the travel-time difference Use of cross-correlation significantly increases the range at which a calling animal may be detected over that possible by visual inspection of acoustic records The error maps for the localization can be improved by factors from 2 to 100 if tomographic techniqu
TL;DR: The difference in the application of the model and two of its assumptions to these two major forest biomes is indicative of a fundamental difference in their strategies of pollination.
Abstract: A model is developed to demonstrate how mast years increase the effectiveness of wind pollination. The model is based on seven assumptions relating to the timing and distribution of reproductive effort. Field data from reproduction in lodgepole pine (Pinus contorta) demonstrate how relaxing some of the assumptions influences the effectiveness of wind pollination. Relaxing five of the assumptions raises or lowers, but does not eliminate, the advantage of increased fecundity resulting from having the extreme variation in annual reproduction characteristic of species with mast years, If two of the assumptions are relaxed, the model quickly loses relevance. These assumptions are that (1) both male and female reproductive efforts vary synchronously and (2) the cost of producing a female is nearly the same whether she is fertilized or not. These two assumptions tend to be true for both the gymnosperms and angiosperms of boreal forests and false for the wind-pollinated angiosperms and one gymnosperm of temperate...
TL;DR: Goats learned to avoid condensed tannins from blackbrush current season's growth by associating the flavor of foods containing CTs with aversive postingestive consequences, which suggest several areas of inquiry related to the interaction between CTs and herbivores.
Abstract: It has been hypothesized that herbivores instinctively avoid tannin-containing plant parts in response to the adverse effects of tannins on forage digestion. However, we found that goats learned to avoid condensed tannins (CTs) from blackbrush current season's growth by associating the flavor of foods containing CTs with aversive postingestive consequences. The aversive consequences experienced by goats apparently are not related to digestion inhibition and may depend on the structure of CTs and on how CTs are bound with other cell constituents. These observations suggest several areas of inquiry related to the interaction between CTs and herbivores. A better understanding of the physiological effects of CTs and how herbivores perceive these effects is essential to our knowledge of chemically mediated interactions between plants and mammalian herbivores. With few exceptions, the effects of food flavor have not been separated from those associated with postingestive consequences, even though our data show ...
TL;DR: Results in T. castaneum and a reexamination of published studies reveal a high degree of intraspecific variation in sperm precedence, suggesting that mean values are insufficient to adequately characterize sperm-precedence patterns.
Abstract: Sperm precedence, defined as nonrandom differential fertilization success among mating males, is likely to play a fundamental role in mediating male reproductive success in species with multiply mating females (Parker 1970a) The phenomenon of differential sperm usage from consecutive matings has now been documented across an extraordinary diversity of animal groups, including insects, spiders, birds, fish, reptiles, bats, and primates (review in Smith 1984) These studies typically have measured species-specific sperm precedence as mean P2 values, calculated as the mean proportion of eggs fertilized by the second of two mates (Boorman and Parker 1976; Gwynne 1984) However, nearly all species show an extremely wide, and as yet unexplained, range of variation around these mean P2 values (table 3; see also, eg, Schlager 1960; Fincke 1984; Nakano 1985) This intraspecific variability may be due to random variation, to differences among males in the competitive ability of their sperm, or to female sperm preference Further examination of such variation may contribute substantially to our understanding of the evolutionary significance of sperm precedence Our intent in this study was to examine the sources of variation in sperm precedence by sequentially mating pairs of males with replicate females We used the red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae), measuring P2 values and several behavioral and morphological traits in an attempt to understand the mechanisms underlying differences in sperm precedence
TL;DR: This article reviewed the considerable body of research into the sea urchin phenomenon responsible for the alternation between macroalgal beds and coralline barrens in the northwestern Atlantic and identified problems with both the scientific approach and the interpretation of results.
Abstract: We have reviewed the considerable body of research into the sea urchin phenomenon responsible for the alternation between macroalgal beds and coralline barrens in the northwestern Atlantic. In doing so, we have identified problems with both the scientific approach and the interpretation of results. Over a period of approximately 20 years, explanations for the phenomenon invoked four separate scenarios, which changed mainly as a consequence of extraneous events rather than experimental testing. Our specific concerns are that results contrary to the keystone-predator paradigm for the American lobster were circumvented, system components of the various scenarios became accepted without testing, and modifications of some components appeared arbitrary. Our review illustrates dilemmas that, we suggest, have hindered ecological progress in general. We argue for a more rigorous experimental approach, based on sound natural-history observations and strong inference. Moreover, we believe that the scientific communi...
TL;DR: The hypothesis that variation in parental investment controls the numbers of males and females available for mating in katydids is tested and data suggest that male parental investment in the spermatophore increases in its relative importance when diet is low in quality.
Abstract: Theory predicts that relative parental investment by the sexes controls the ratio of the numbers of fertilizable females and sexually active males (the operational sex ratio, OSR) and thus sexual selection and sexual differences. This paper tests the hypothesis that variation in parental investment controls the numbers of males and females available for mating. In katydids, males and females invest parentally by providing material investment to eggs, with the male donation derived from spermatophore materials eaten by the female. Previous work with katydids in nature has shown intraspecific variation in sexual selection acting on females; only certain populations show a courtship role reversal in which females compete for access to males. These observations led to the hypothesis that the availability of food in nature determines the frequency of spermatophore production and thus the number of males available for mating. In the present study, male and female katydids were maintained on diets that differed ...
TL;DR: Etude theorique des mecanismes susceptibles d'expliquer la difference de taille entre mâles et femelles chez certaines especes animales.
Abstract: Etude theorique des mecanismes susceptibles d'expliquer la difference de taille entre mâles et femelles chez certaines especes animales
TL;DR: A population of the polyphagous mite Tetranychus urticae that had been selected for adaptation to tomato plants was used to determine whether tradeoffs between fitness on tomato and fitness on lima bean occur in this species.
Abstract: Trade-offs, or negative genetic correlations, in fitness on different hosts have been hypothesized to restrict evolutionary expansion of host range in phytophagous arthropods. I used a population of the polyphagous mite Tetranychus urticae that had been selected for adaptation to tomato plants to determine whether tradeoffs between fitness on tomato and fitness on lima bean occur in this species. Two lines established from the tomato-adapted population and reared on lima bean showed significant declines in ability to survive on tomato after more than 10 generations on bean. The most likely explanation for this result is that tomato-adapted genotypes were selected against on bean. The tomato-adapted population did not have detectably lower survival or fecundity on bean than a control population kept on bean, however, suggesting that tomato-adapted genotypes were at only a slight disadvantage on bean. This study and a similar previous experiment with T. urticae using cucumber and bean provide the only evide...