Showing papers in "Annual Review of Ecology, Evolution, and Systematics in 1993"
TL;DR: The effects of genetic drift, inbreeding, and gene flow on genetic diversity and fitness in rare plants and small populations and those circumstances that are likely to put these plant species and populations at genetic risk are identified.
Abstract: Although the potential genetic risks associated with rare or endangered plants and small populations have been discussed previously, the practical role of population genetics in plant conservation remains unclear. Using theory and the available data, we examine the effects of genetic drift, inbreeding, and gene flow on genetic diversity and fitness in rare plants and small populations. We identify those circumstances that are likely to put these plant species and populations at genetic risk. Warning signs that populations may be vulnerable include changes in factors such as population size, degree of isolation, and fitness. When possible, we suggest potential management strategies.
2,485 citations
TL;DR: Phenotypic plasticity is the change in the expressed phenotype of a genotype as a function of the environment, and is likely due both to differences in allelic expression across environments and to changes in interactions among loci.
Abstract: To achieve a coherent evolutionary theory, it is necessary to account for the effects of the environment on the process of development. Phenotypic plasticity is the change in the expressed phenotype of a genotype as a function of the environment. Various measures of plasticity exist, many of which can be united within the framework of a polynomial function. This function is the norm of reaction. For the special case of a linear reaction norm, genetic variation can be partitioned into portions that are independent and dependent on the environment. From this partition two heritability measures are derived which can be used, alternatively, to compare populations or make predictions about the response to selection. Genetically, plasticity is likely due both to differences in allelic expression across environments and to changes in interactions among loci; plasticity is not a function of heterozygosity. Plasticity responds to both artificial and natural selection. The evolution of plasticity is modeled in thre...
1,702 citations
TL;DR: A large number of abundant, well-studied, or economically important taxa have recently been shown to be complexes of sibling species, and the broad habitat and geographic distributions characteristic of many marine species require reevaluation.
Abstract: Sibling species are common in all major marine groups and habitats. Their abundance reflects both inadequate study of morphological features of living organisms ("pseudo-sibling species") and divergence in habitat, life history, and chemical recognition systems without parallel divergence in morphology. Many marine sibling species are quite distinct genetically. Others, however, exhibit slight genetic differences whose significance is only clear in sympatry and in combination with other subtle but concordant patterns of differentiation. A large number of abundant, well-studied, or economically important taxa have recently been shown to be complexes of sibling species. The broad habitat and geographic distributions characteristic of many marine species require reevaluation in this context.
1,238 citations
TL;DR: The idea that plant species can reduce predation by synchronizing their phenological activity has the best support, because biotic factors are often arbitrary with respect to the timing of these peaks, it is essential also to consider abiotic influences.
Abstract: Most tropical woody plants produce new leaves and flowers in bursts rather than continuously, and most tropical forest communities display seasonal variation in the presence of new leaves, flowers, and fruits. This patterning suggests that phenological changes represent adaptations to either biotic or abiotic factors. Biotic factors may select for either a staggering or a clustering of the phenological activity of individual plant species. We review the evidence for several hypotheses. The idea that plant species can reduce predation by synchronizing their phenological activity has the best support. However, because biotic factors are often arbitrary with respect to the timing of these peaks, it is essential also to consider abiotic influences. A review of published studies demonstrates a major role for climate. Peaks in irradiance are accompanied by peaks in flushing and flowering except where water stress makes this impossible. Thus, in seasonally dry forests, many plants concentrate leafing and flowering around the start of the rainy season; they also tend to fruit at the same time, probably to minimize seedling mortality during the subsequent dry season. Phenological variation at the level of the forest community affects primary consumers who respond by dietary switching, seasonal breeding, changes in range use, or migration. During periods of scarcity, certain plant products, keystone resources, act as mainstays of the primary consumer community.
1,185 citations
TL;DR: C4 and CAM photosynthesis are evolutionarily derived from C3 photosynthesis, with a tendency toward ecological adaptation of C4 plants into warm, monsoonal climates and CAM plants into water-limited habitats and in an anthropogenically altered CQ2 environment, C 4 plants may lose their competitive advantage over C3 plants.
Abstract: C4 and CAM photosynthesis are evolutionarily derived from C3 photosynthesis. The morphological and biochemical modifications necessary to achieve either C4 or CAM photosynthesis are thought to have independently arisen numerous times within different higher plant taxa. It is thought that C4 photosynthesis evolved in response to the low atmospheric CO2 concentrations that arose sometime after the end of the Cretaceous. Low CO2 concentrations result in significant increases in photorespiration of C3 plants, reducing productivity; both C3-C4 intermediate and C4 plants exhibit reduced photorespiration rates. In contrast, it may be argued that CAM arose either in response to selection of increased water-use efficiency or for increased carbon gain. Globally, all three pathways are widely distributed today, with a tendency toward ecological adaptation of C4 plants into warm, monsoonal climates and CAM plants into water-limited habitats. In an anthropogenically altered CQ2 environment, C4 plants may lose their competitive advantage over C3 plants. 411
758 citations
TL;DR: This work uses sensitive dependence on initial conditions as the best heuristic definition of chaos, which forms the common theme for the review of approaches for demonstrating the importance of chaos in ecology.
Abstract: We review the role of chaos and the study of chaos in ecology. We use sensitive dependence on initial conditions as the best heuristic definition of chaos. This definition forms the common theme for our review of approaches for demonstrating the importance of chaos in ecology. We emphasize that this
499 citations
TL;DR: The house mouse is the most recent phylogenetic offshoot of the genus Mus.
Abstract: In the light of available paleontological, genetic, and ecological data, we attempt to reconstruct the natural history of the house mouse (Mus musculus) and to justify a systematics. The house mouse is the most recent phylogenetic offshoot of the genus Mus. Its present components result from a radiation that took place most probably in the north of the Indian subcontinent about 0.5 MYA. The different colonization paths into the rest of Eurasia led to the present day subspecies: M. m. domesticus in western Europe and the Mediterranean basin, M. m. musculus from central Europe to northern China, and M. m. castaneus in southeast Asia. The central populations remain very polymorphic and are not attributable to any of these subspecies; the status of M. m. bactrianus is unclear. This radiation led to a mosaic evolution of the different parts of the genome in these subspecies. The expansion to the periphery of the Eurasian range, and more recently to the rest of the world, is related to human activity. In the case of M. m. domesticus commensalism apparently started with human sedentism in the Fertile Crescent, but its extension to the western Meditteranean basin occurred only after Neolithic times. The recent expansion has produced zones of secondary contact at the perip hery of the cont inent. For instance, in Europe M. m. domesticus and M. m. musculus have formed a narrow hybrid zone where selection prevents the introgression of sex chromosomes. M. m. musculus and M. m. castaneus have
479 citations
TL;DR: The occurrence of selfing and mechanisms for its avoidance, in functionally hermaphrodite animal and plants and theories for the advantages and disadvantages are reviewed.
Abstract: Selfing, the fusion of male and female gametes from a single genetic individual or colony, is possible in many plants and also in hermaphrodite animals. We review the occurrence of selfing and mechanisms for its avoidance, in functionally hermaphrodite animal and plants. We discuss means by which selfing can be detected and briefly review techniques for estimation of selfing frequencies in natural populations. Although many functionally hcmaphrodite species are probably almost complete outcrossers or inbreeders, mixed mating systems are also found in both plant and animal populations. We review theories for the advantages and disadvantages of selfing, and for the maintenance of mixed mating systems, together
454 citations
TL;DR: Tropical rainforest plants produce seeds showing a wide range of sizes, shapes, structures, chemical composition, water content, dormancy mechanisms, and patterns of longevity.
Abstract: Tropical rainforest plants produce seeds showing a wide range of sizes, shapes, structures, chemical composition, water content, dormancy mechanisms, and patterns of longevity. Prompt germination seems to be the most common behavior, although there are many cases where germination is delayed by a hard coat or endogenous or enforced dormancy mechanisms. Some gap colonizers show sophisticated light or temperature regulated dormancy. Most rainforest seeds remain alive for a short time in the soil, even those that form part of the soil seed bank.
417 citations
TL;DR: Evaluation of causes and consequences of miniaturization should consider obvious feattires of physical size as well as less obvious, but biologically important, features such as genome and cell size.
Abstract: Miniaturization, or the evolution of extremely small adult body size, is a widespread phenomenon in animals. It has important consequences for both organismal biology and phyletic diversification above the species level. The miniaturized phenotype is a complex combination of ancestral and derived traits, including reduction and structural simplification, increased variability, and morphological novelty. Many features likely represent secondary consequences of size decrease, which may be the result of selection primarily for small body size or some related attribute such as life history characteristics. In some cases, miniaturization has resulted in novel bauplans associated with the origin of higher taxa. Evaluation of causes and consequences of miniaturization should consider obvious feattires of physical size as well as less obvious, but biologically important, features such as genome and cell size.
411 citations
TL;DR: The global trop ical forest type of ecosystem of the early Tertiary was disrupted by Late Eocene climatic changes, with the extinction of most archaic mammalian lineages and the appearance of most modem famil ies.
Abstract: Evolutiona ry trends among mammals over the past 66 Myr have been profou ndly influenced by changing climat es, in tum the result of tectonic events. The global trop ical forest type of ecosystem of the early Tertiary was disrupted by Late Eocene climatic changes, with the extinction of most archaic mammalian lineages and the appearance of most modem famil ies. Later Tertiary trends reflect increasing aridity, with the appearance of open-habitat mammals such as grazing ungulate s, although true grasslands probably did not appear until the Late Miocene in the New World and the Pliocene in the Old World. Patterns of mammalian diversity track paleote mperature curves for the northern latitudes, with maxima in the early Mid dle Eocene and early Middle Miocene. Major dispersals occurred at times of sea level lows, resulting in loss of endemism in originally isolated continents such as South America and Afr ica, and changes in faunal composition across Holarctica. Dispersal in con junction with climatic changes accounted for maj or extinction events in the Late Eocene to Early Oligoce ne, at the end of the Miocene , and in the mid Pliocene. Outstanding problems include the origin and dispersal routes of many extant orders that appeared at the start of the Eocene and the
TL;DR: Already existing treatments in dynamic models of energy allocation are reviewed, and the expected evolutionary outcome is an optimal allocation pattern, but this depends on the environment experienced during the evolution and on the fitness costs and benefits incurred by allocating resources in different ways.
Abstract: In dynamic models of energy allocation, assimila ted energy is alloc ated to reproduction, somatic growth , maintenance or storage, and the allocation pattern can change with age . The expected evolutionary outcome is an optimal allocation patte rn, but this depends on the environment experienced during the evolutiona ry pro cess and on the fitness costs and benefits incurred by allocating resources in dif ferent ways. Here we review existing treatments
TL;DR: Most types of feeding larvae evolved at most once, are in clades that diverged early, and are therefore of ancient origin and direction of evolutionary transitions of larval traits are indicated by distribution of traits within clades and by vestigial structures.
Abstract: (i) Varied origins of larval forms and metamorphoses are indicated by comparisons among extant animals. (ii) Size-specific and stage-specific constraints on survival and growth may result in distinctive larval traits, but to explain larval origins, sizeor stage-specific advantages must be extrapolated to ancient environments and ancestral traits. Adaptations for habitat selection or dispersal do not account for evolution of long precompetent periods of larval feeding and growth or for larvae in holoplanktonic life histories. (iii) Transverse bands of cilia on ridges or posterior edges of larvae meet a common functional requirement for propulsion, are expected to be convergently similar, and may have arisen numerous times. (iv) Biases imposed by ancestral larval or juvenile traits might result in convergent similarity of derived larval traits with a result resembling homology. (v) Some extant feeding larvae persist with unusually simple structures or low performance. These larvae suggest possible intermediate steps in the evolution of feeding larvae. (vi) Direction of evolutionary transitions of larval traits are indicated by distribution of traits within clades and by vestigial structures. Feeding larval stages have been lost often and gained rarely. (vii) Most types of feeding larvae evolved at most once, are in clades that diverged early, and are therefore of ancient origin. Other evidences of antiquity are fossil traces of larval molluscs and brachiopods from the Ordovician and fossils of crustacean nauplii from the Upper Cambrian. (viii) Inferred combinations of ancestral traits can differ from combinations known from extant descendants. Examples are external fertilization combined with a feeding larva or small adult size. (ix) In some clades, feeding larval forms that originated earlier
TL;DR: Phylogenies based on molecular sequence data and on morphology are surveyed and compared within animals and within plants and it is found that incongruence between molecular trees (generated from different data sets or by different analytical methods) is as striking or pervasive as is incongrience between trees generated by morphologists in the long history of their discipline.
Abstract: Phylogenies based on molecular sequence data and on morphology are surveyed and compared within animals (concentrating on vertebrates, mammals, and hominids in particular) and within plants (concentrating on Asterales, angiosperms, seed plants, and major groups of "green plants"). The theoretical problem of assessing congruence between trees generated from different data sets is still unsolved. However, in practice, we find that incongruence between molecular trees (generated from different data sets or by different analytical methods) is as striking or pervasive as is incongruence between trees generated by morphologists in the long history of their discipline. Morphologists achieved much during that time, and none of their well-supported phylogenies is overthrown by molecular data. So far, molecular sequences have contributed most significantly in areas where morphological data are inconclusive, deficient, nonexistent, or poorly analyzed. The interrelationships of extant hominines (Gorilla, Homo, Pan), where morphology is inconclusive, are exemplary. The pattern [Gorilla [Homo, Pan]] is significantly favored by nucleotide sequence data, but the effort necessary to achieve resolution in that simple case (ca. 30 kb of aligned sequences, sampling all four extant species) may foreshadow the workload that lies ahead.
TL;DR: This review outlines the need for including informatipn on the phyletic relationships among taxa in ecological and evolutionary analyses and describes how an historical approach not only refines the definition and recognition of adaptations, but also provides an objective definition of "phylogenetic constraints."
Abstract: Hypotheses about the adaptive significance of a trait have long been tested by making comparisons among species. Many recent studies emphasized that conclusions about the origin and maintenance of adaptations as well as the underlying selective processes derived from comparative tests may be strengthened with the inclusion of a phylogenetic hypothesis. Major advances in the comparative approach have therefore occurred with the coincident developments in numerical methods available for phylogenetic inference. In this review, we outline the advantages and possible disadvantages of adopting an historical approach in ecological and evolutionary studies. We begin by discussing the need for including informatipn on the phyletic relationships among taxa in ecological and evolutionary analyses. Next we describe how an historical approach not only refines the definition and recognition of adaptations, but also provides an objective definition of "phylogenetic constraints." Because conceptual and analytical advances in comparative methods are occurring quite rapidly, we provide a brief summary of the goals,
TL;DR: It is suggested that much of evolution may be interpretable through an integrated theory of constraint, and any result or component of the phylogenetic history of a lineage that prevents an anticipated course of evolution in that lineage is defined.
Abstract: The notion of constraints is a central one in evolutionary biology. That limits may exist in the patterns resulting from diverse evolutionary processes, and the possibility that these limits can be discovered and explained mechanistically, suggests that much of evolution may be interpretable through an integrated theory of constraint. Phylogenetic constraint has been invoked in a variety of contexts but as yet there is no consensus on its definition. It is defined here as any result or component of the phylogenetic history of a lineage that prevents an anticipated course of evolution in that lineage. Hypotheses of constraint can be tested within a phylogenetic framework;
TL;DR: By measuring the associations of cytoplasmic genes with nuclear genes and genotypes within a hybrid zone, cytonuclear disequilibria provide fresh insights into levels of gene flow, age of rep roductive barriers, and directionality of crosses between hybridizing taxa.
Abstract: Cytonuelear disequilibria provide a new array of conceptual tools for the analysis of hybrid zone data By measuring the associations of cytoplasmic genes with nuclear genes and genotypes within a hybrid zone, cytonuclear disequilibria provide fresh insights into: (i) levels of gene flow; (ii) age of rep roductive barriers, (iii) directionality of crosses between hybridizing taxa; (iv) levels of assortative mating; (v) and mechanisms of selcction on hybrids The application of these cytonuclear disequilibria are illustrated in several hybrid zone studies
TL;DR: Evaluated studies that employ paternity analysis to examine how specific plant traits affect male reproductive success in both natural and artificial populations illustrate the risks of assuming that male RS is correlated with female RS or with components of male fitness, such as the amount of pollen produced per plant.
Abstract: Within-population variability in plant reproductive traits can influence both male and female fitness, but research on the male function of flowers has been hindered by the difficulty of measuring male fertility. Here we evaluate studies that employ paternity analysis to examine how specific plant traits affect male reproductive success (RS) in both natural and artificial populations. These studies illustrate the risks of assuming that male RS is correlated with female RS or with components of male fitness, such as the amount of pollen produced per plant. In some studies, paternity was assigned by simple genetic exclusion using unique multilocus allozyme profiles. More powerful methods involve statistical procedures that assign paternity to the most likely father of each offspring. Lack of genetic markers is a common problem in paternity analysis, and we discuss the types of molecular markers that may soon become more widely used in small, natural populations.
TL;DR: It is concluded that biological processes may be more important at smaller scales where behavior such as vertical migration and predation may control the plankton production, whereas physical processes might be moreImportant at larger scales in structuring biological communities.
Abstract: The interaction of physical and biological processes is extremely important in structuring the biological communities in all marine environments, yet the complexity of this interaction at all scales is just beginning to be appreciated. We review the patterns of plankton biomass and the processes that influence plankton production, and in particular emphasize the importance of different processes at different time and space scales (small-scale, mesoscale, and large-scale). Examples of two different systems (the Southern Ocean and the subarctic North Pacific and North Atlantic Oceans) are given to illustrate the complexity and strength of the interactions. We conclude that biological processes may be more important at smaller scales where behavior such as vertical migration and predation may control the plankton production, whereas physical processes may be more important at larger scales in structuring biological communities. An understanding of both, however, is critical to an understanding of the distribution of plankton and the processes governing production in the ocean.
TL;DR: Phylogenetic relationships among eutherian mammal orders are discussed in light of previous work on phylogenetic relationships between mammal orders.
Abstract: mammals, Abstract Phylogenetic relationships among eutherian mammal orders are discussed in light of previous
TL;DR: It is found that few areas of higher-level avian phylogeny are well supported and, hence, well understood.
Abstract: We assessed the current state of avian molecular systematics by (i) considering some of the historical factors that have shaped the field in the last 20 years, (ii) reviewing the most commonly used molecular methods, and (iii) comparing higher-level phylogenies via congruence analysis. This three-pronged approach permitted us to identify strongly supported aspects of avian phylogeny and to propose technological and methodological explanations when congruence was low. We found, in general, that few areas of higher-level avian phylogeny are well supported and, hence, well understood. One main reason for this is that, despite a great deal of effort, few studies of higher-level avian phylogenetic relationships have been well planned and executed. Some investigations, for example, have gone astray because of preconceptions about rates of molecular evolution and monophyly, and others suffer from such problems as failure to find the shortest tree, lack of an outgroup, use of a nonmetric distance measure, and sim...