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Showing papers in "The Quarterly Review of Biology in 1992"


Journal Article•DOI•
TL;DR: A conceptual model of the evolution of plant defense is concluded, in which plant physioligical trade-offs interact with the abiotic environment, competition and herbivory.
Abstract: Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: Th...

3,843 citations


Journal Article•DOI•
TL;DR: This framework for relating sex differences in mating competition to the operational sex ratio, potential reproductive rates, and parental expenditure differs from Triver's concept of the relation between parental investment and mating competition in three ways.
Abstract: In most animals, members of one sex compete more intensely for mates than members of the other sex, and show a greater development of secondary sexual traits. The relative intensity of mating competition in the two sexes depends on the operational sex ratio (OSR) (the ratio of males that are ready to mate to females that are ready to mate) at the site and times when mating occurs. The extent and direction of biases in the OSR is closely related to the potential rates of reproduction that individual males and females can achieve, although the distribution of the two sexes in space and time, sex differences in development time or life expectancy, and biases in the sex ratio at birth or hatching can also be important. The potential rates of reproduction in the two sexes are, in turn, affected by the proportion of time and energy expended by male and female parents on their progeny, though other factors may constrain reproductive rate in one or both sexes. We outline a simple model of the factors affecting th...

784 citations


Journal Article•DOI•
TL;DR: The delayed-dispersal threshold model is proposed as a guide for organizing and evaluating the ecological factors potentially responsible for this phenomenon and it is concluded that no one factor by itself causes delayed dispersal and cooperative breeding.
Abstract: Why do the young of cooperative breeders--species in which more than two individuals help raise offspring at a single nest--delay dispersal and live in groups? Answering this deceptively simple question involves examining the costs and benefits of three alternative strategies: (1) dispersal and attempting to breed, (2) dispersal and floating, and (3) delayed dispersal and helping. If, all other things being equal, the fitness of individuals that delay dispersal is greater than the fitness of individuals that disperse and breed on their own, intrinsic benefits are paramount to the current maintenance of delayed dispersal. Intrinsic benefits are directly due to living with others and may include enhanced foraging efficiency and reduced susceptibility to predation. However, if individuals that disperse and attempt to breed in high-quality habitat achieve the highest fitness, extrinsic constraints on the ability of offspring to obtain such high-quality breeding opportunities force offspring to either delay dispersal or float. The relevant constraint to independent reproduction has frequently been termed habitat saturation. This concept, of itself, fails to explain the evolution of delayed dispersal. Instead, we propose the delayed-dispersal threshold model as a guide for organizing and evaluating the ecological factors potentially responsible for this phenomenon. We identify five parameters critical to the probability of delayed dispersal: relative population density, the fitness differential between early dispersal/breeding and delayed dispersal, the observed or hypothetical fitness of floaters, the distribution of territory quality, and spatiotemporal environmental variability. A key conclusion from the model is that no one factor by itself causes delayed dispersal and cooperative breeding. However, a difference in the dispersal patterns between two closely related species or populations (or between individuals in the same population in different years) may be attributable to one or a small set of factors. Much remains to be done to pinpoint the relative importance of different ecological factors in promoting delayed dispersal. This is underscored by our current inability to explain satisfactorily several patterns including the relative significance of floating, geographic biases in the incidence of cooperative breeding, sexual asymmetries in delayed dispersal, the relationship between delayed dispersal leading to helping behavior and cooperative polygamy, and the rarity of the co-occurrence of helpers and floaters within the same population. Advances in this field remain to be made along several fronts.(ABSTRACT TRUNCATED AT 400 WORDS)

498 citations


Journal Article•DOI•
TL;DR: It is argued that adherence to conventional, narrow definitions of teaching, generally derived from observations of human adult-infant interactions, has caused many related but simpler phenomena in other species to go unstudied or unrecorded, and severely limits further exploration of this topic.
Abstract: We derive a simple operational definition of teaching that distinguishes it from other forms of social learning where there is no active participation of instructors, and then discuss the constituent parts of the definition in detail. From a functional perspective, it is argued that the instructor's sensitivity to the pupil's changing skills or knowledge, and the instructor's ability to attribute mental states to others, are not necessary conditions of teaching in nonhuman animals, as assumed by previous work, because guided instruction without these prerequisites could still be favored by natural selection. A number of cases of social interaction in several orders of mammals and birds that have been interpreted as evidence of teaching are then reviewed. These cases fall into two categories: situations where offspring are provided with opportunities to practice skills ("opportunity teaching"), and instances where the behavior of young is either encouraged or punished by adults ("coaching"). Although certain taxonomic orders appear to use one form of teaching more often than the other, this may have more to do with the quality of the current data set than with inherent species-specific constraints. We suggest several directions for future research on teaching in nonhuman animals that will lead to a more thorough understanding of this poorly documented phenomenon. We argue throughout that adherence to conventional, narrow definitions of teaching, generally derived from observations of human adult-infant interactions, has caused many related but simpler phenomena in other species to go unstudied or unrecorded, and severely limits further exploration of this topic.

489 citations


Journal Article•DOI•
TL;DR: A simple two-strategy game, the cooperator's dilemma, provides a coherent framework for distinguishing the mechanisms that support cooperation in each category, which may operate, alone or together, in widely divergent taxa.
Abstract: There are three categories of cooperation among unrelated individuals: group-selected behavior, reciprocal altruism, and by-product mutualism. A simple two-strategy game, the cooperator's dilemma, which generalizes the well-known prisoner's dilemma, provides a coherent framework for distinguishing the mechanisms that support cooperation in each category. The mechanism for cooperation in group-selected behavior is deme structure; variance among trait groups allows natural selection to favor individuals in groups with a higher frequency of cooperators. A prerequisite for this mechanism to work is differential productivity of trait groups. The mechanism for cooperation in reciprocal altruism is scorekeeping, which allows cooperators to relatiate against noncooperators by conditioning their behavior on that of others. A prerequisite for this mechanism is that the expected number of interactions between individuals be sufficiently high. In nonsessile organisms, individuals must typically have a sufficiently we...

218 citations


Journal Article•DOI•
TL;DR: It is proposed here that in teleosts the brain is the initial site of sexual differentiation, and that the pattern of differentiation in the brain determines the fate of the gonads.
Abstract: Among vertebrates there is wide variation in the degree to which sexual differentiation is developmentally buffered, or canalized. In birds, and particularly in mammals, gonadogenesis occurs early in development and without a significant contribution from the environment. In contrast, sexual development in teleosts is protracted and plastic. Here I consider this lability in the context of the developmental processes underlying sex differentiation in teleosts, and contrast these processes with those in other vertebrate taxa. One fundamental difference in teleost sexual differentiation from that of letrapods may be in the developmental polarity of the brain-pituitary-gonadal axis. In mammals the gonads differentiate early and affect, through the release of steroid hormones, the sexual differentiation of the brain. It is proposed here that in teleosts the brain is the initial site of sexual differentiation, and that the pattern of differentiation in the brain determines the fate of the gonads.

210 citations


Journal Article•DOI•
TL;DR: Future studies of pollen competition and its effects on progeny fitness components should be designed to avoid confounding effects of such factors as inbreeding depression and self-incompatibility types, enabling these possibilities to be distinguished.
Abstract: The striking opportunities for competition in the pollination stage of the life cycle of flowering plants have been remarked on for many years, yet it is still not clearly known how much genetic variation for the rates of growth of pollen tubes exists in natural populations. Here we review the evidence for such variation, and discuss some of the possible mechanisms by which this thype of variation could be maintained. If faster pollen tube growth rates tend to be correlated with higher fitness of the propeny sired, then most of the variation would be expected to be due to detrimental mutations, and therefore subject to purifying selection. If, however, variation is maintained in populations, it is likely that genetic factors for fast pollen tube growth would reduce fitness at other stages of the life cycle, resulting in negative genetic correlations between pollen and progeny quality. Future studies of pollen competition and its effects on progeny fitness components should be designed to avoid confounding...

171 citations




Journal Article•DOI•
TL;DR: The Gaia concept of Lovelock and Margulis as discussed by the authors has been used to counter romanticism and what Lillie (1913) called the "biocentric" view of the universe.
Abstract: Let us understand, once for all, that the ethical progress of society depends, not on imitating the cosmic process, still less in running away from it, but in combating it (T H. Huxley, 1894:83). I AGREE with Huxley's statement, but others do not. Romantic traditions persist in finding practical lessons and moral directives in natural phenomena and, at least by implication, in urging back-tonature sentiments or in somehow imitating the cosmic process. Others prefer to run away, or at least turn their backs on nature's hostility and pretend it is not there. Their main method is to use the verbal camouflage of nice names for adverse conditions or ethically unacceptable actions. Here I will attempt to support Huxley's position, that the universe is hostile to human life and values, and to counter prevalent romanticism and what Lillie (1913) called the "biocentric" view of the universe. I am motivated by recent statements in Science (Kerr, 1988; Mann, 1991) on the Gaia concept, in opposition to Huxley's and my own view of biological principles and the human condition. The idea that the universe is especially designed to be a suitable abode for life in general and for human life in particular is, of course, an old one. It had to be abandoned in its early forms with the triumph of Copernican astronomy in the Renaissance, but some scholars still find it possible to argue that the Earth, at least, can be regarded as especially suited for human life. This idea found eloquent expression in Henderson's (1913) The Fitness of the Environment. Its main modern manifestation is in the Gaia concept of Lovelock and Margulis (1974) and Lovelock (1979, 1988).

76 citations








Journal Article•DOI•
TL;DR: Whereas completeness and continuity make marine records the most important baseline source of information on global change, terrestrial records serve to establish the complete range of climate variability.
Abstract: Quantitative estimates of past climates have been generated from biological data based on (1) the way in which climatic factors limit the occurrences of taxa or associations, (2) the response of characteristics of taxa (for example, tree ring widths or leaf-physiognomic characters) to climate, and (3) variance in relative frequency of taxa with climate Relative-frequency analysis has been extensively applied to marine records as old as Miocene in age, and also to pollen records from the Holocene and last glacial epoch Another approach to Quaternary climate reconstruction is based on limiting factors where taxa can be identified at the species level (as is the case for plant macrofossils) Cretaceous and Tertiary floras have generally been analyzed in terms of characteristics of taxa, mainly leaf physiognomy For older assemblages, both marine and terrestrial, interpretations are more generalized and are derived from zonation patterns and occurence of climatically sensistive forms Whereas completeness a

Journal Article•DOI•
Ernst Mayr1•
TL;DR: Certain ideas, such as the occurrence of evolution, the theory of common descent, and the descent of man from the primates were universally accepted already in Darwin's lifetime, although other aspects of evolution remained highly controversial until the evolutionary synthesis of the 1930s-1940s.
Abstract: rpHE QUESTION of how much progress science is making in advancing our understanding of the world is still being argued in the literature, particularly in that of the philosophy of science. Admittedly, the advance is not on a direct pathway, it does not follow any laws of logic, and there are occasionally what in hindsight must be considered to be retrograde steps. Yet, scientists are quite unanimous in insisting on the reality of scientific progress. The issue, of course, can be definitely decided only by a detailed analysis of the history of a particular field. And evolutionary biology is particularly suitable for such an analysis. Indeed, in this discipline an entire series of definite steps can be distinguished (Mayr, 1988:536), representing clearcut advances. Certain ideas, such as the occurrence of evolution, the theory of common descent, and the descent of man from the primates were universally accepted already in Darwin's lifetime, although other aspects of evolution remained highly controversial until the evolutionary synthesis of the 1930s-1940s.




Journal Article•DOI•
TL;DR: The G. I. Mendel Memorial Symposium in Brno to commemorate the centennial of Mendel's reports on his experiments in hybridizing various strains of garden peas was held during a time when great progress was being made in genetic investigations at the cellular and molecular levels.
Abstract: N 1965 the Czechoslovak Academy of Sciences, in cooperation with the Genetics Section of the International Union of Biological Sciences, the International Atomic Energy Agency, and other patrons, organized the G. Mendel Memorial Symposium in Brno to commemorate the centennial of Mendel's reports on his experiments in hybridizing various strains of garden peas (Sosna, 1966). His presentations to the Natural Science Society of Briinn (Brno today) were published the following year in their volume for 1865 (Mendel, 1866). The symposium was held during a time when great progress was being made in genetic investigations at the cellular and molecular levels. It was also in the period of the downfall of Trofim D. Lysenko and the end of the subordination of science to ideology in the USSR, events that also had consequences in Czechoslovakia. Among the main organizers of the symposium was Jaroslav Krizenecky, who did not live to see the opening of the Mendel museum, which he was hoping to have ready in time for the August 1965 symposium. I. Michael Lerner, in his lecture, \"Mendelism and Animal Breeding\" (1966), remembered his correspondence with Krizenecky before World War II and \"in the difficult days that followed it\" and concluded: \"it was a cruel fate that prevented him from attendance at our symposium which was so dear to his heart.\" In 1963 Krizenecky, at age 67, was appointed head of the newly established Gregor Mendel department for the history of genetics in the Moravian Museum in Brno. In developing the program of activities for the department, he built upon his early ideas first expressed in 1922, when biologists and geneticists organized a meeting in Brno on the occasion of the centennial of Mendel's birth. With satisfaction he noted in 1964 that \"in many aspects much more has been accomplished to honor Mendel in Brno than we had hoped, for all our endeavors since 1922 had not achieved any results.\" Later he added: \"It was a paradox of history that this was achieved under conditions that permitted Mendel to be humbled and discredited to an extent that only scholars of history can appreciate.\" Krirzenecky was recalling the period after 1948 when he had defended Mendel and genetics not only against the attacks of the Communist ideologists in Czechoslovakia, but also against those of some biologists who had taught Mendel's work prior to 1948. Another irony of history was when the main proponents of Lysenkoism in Czecho-