Energetics of reproduction and its evolutionary implications

The majority of invertebrates so far studied are more efficient converters of absorbed food energy to gametes than they are, as adults, to somatic tissues. Indeed, reproductive conversion efficiencies sometimes better the best conversion efficiencies associated with somatic production (usually in juveniles). Depending on species, this is achieved either by an increase in absorption relative to respiratory losses, or a reduction in respiratory losses relative to absorption, or by supplementing the energy absorbed from the food with that obtained from somatic stores and tissues, or by a combination of these. The fact that the metabolic processes associated with gamete production are distinct from those associated with the production of somatic tissues has implications for the theory of life-cycle evolution.     

The evolutionary maintenance of sexual reproduction: The solutions proposed for a longstanding problem

The evolutionary maintenance of mixis is one of the major unsolved problems in modern biology. This paper reviews the phenoraenon of sex, the hypotheses for its maintenance, and recent evidence bearing on the hypotheses. One elegant experiment supports the idea that bacterial transformation, an analogue and possible forerunner of eukaryolic mixis, functions as a repair mechanism. All mechanisms that produce a short-term advantage for sex in eukaryotes and that are supported by experimental results rely on strong genotype by environment interactions for fitness. While many environmental factors are involved, most prominently parasites, disease, and coarse-grained environmental heterogeneity of other sorts, each is effective only insofar as it is involved in a genotype by environment interaction for fitness.     

Phenotypic variation,sexual reproduction and evolutionary population dynamics

I studied the effects of introducing phenotypic variation into a well-known single species model for a population with discrete, non-overlapping generations. The phenotypes differed in their dynamic behaviour. The analysis was made under the assumption that the population was in an evolutionary stable state. Differences in the timing of the competitive impacts of the phenotypes on each other had a strong simplifying effect on the dynamics. This result could also be applied to competition between species. The effect of sexual reproduction on the dynamics of the population was analysed by assuming the simplest genetic model of one locus with two alleles. Sexual reproduction made the system much more stable in the (mathematical) sense that the number of attractors was reduced and their basins of attraction enlarged. In a dominant system sex tended to increase the frequency of the recessive allele, and in an overdominant system it induced gene frequencies of 1/2. Whether the attractors in the dominant system tended to be simpler or more complex than the attractors in the asexual system depended on the phenotype of the recessive homozygote. The overdominant sexual system tended to have simpler dynamics than the corresponding asexual population. A 2-locus model was used to study whether sexuals can invade an asexual population and vice versa. One locus coded for sexual and asexual reproduction, while the other coded for the dynamics. Enhanced stability through sexual reproduction seemed to be the reason why there was a clear asymmetry favouring sex in this evolutionary context.     

Ecological and evolutionary implications of dinosaur feeding behaviour

Dinosaurs had a wide variety of feeding mechanisms that strongly impacted on their ecology and evolution. Here, we show how novel application of technologies borrowed from medicine and engineering, such as CT scanning and Finite Element Analysis, have recently been combined with traditional approaches to result in significant advances in our understanding of dinosaur palaeobiology. Taxon-specific studies are providing quantitative data that can be used to generate and test functional hypotheses relating to jaw mechanics and feeding behaviour. In turn, these data form a basis for investigating larger scale patterns of ecological and macroevolutionary change, such as possible coevolutionary interactions and the influence of feeding adaptations on species richness, which are of more general interest to ecologists and evolutionary biologists.     

Ultrastructural characterization of the locomotory cytoskeletal system of the spermatozoid inGinkgo biloba

Summary The development of the locomotory cytoskeletal system of sperm is carefully coordinated with the development of the sperm inGinkgo biloba. Here we report further ultrastructural characterization of the locomotory cytoskeletal system in the developing spermatid and mature spermatozoid, particularly with respect to the initiation and early development of the flagellar apparatus. A multilayered structure (MLS) assembles from an electron-dense matrix that self-organizes after blepharoplast breakup and then further elongates. At the tail of the assembling MLS, the spline microtubules connect to an anterior beak of the nuclear envelope. Nuclear-pore complexes are found on the nuclear envelope close to this beak. The mitochondria which elongate and line up one behind the other are tightly associated with the MLS. The MLS ofG. biloba is composed of an upper layer of parallel spline microtubules and a lower layer consisting of a fibrous lamellar strip composed of paralled fibers about 9 nm in diameter. Higher-magnification images show that the fully assembled fibers of the lamellar strip consist of subunits which suggest that protofilaments are involved in the assembly processes. A unique cytoskeletal system of the spermatozoid inG. biloba is given by the anterior bundle of microtubules. This bundle, in which microtubules are arranged parallel to each other, forms between the plasmalemma and the MLS and is about 214–392 nm in cross section. These microtubules expand spirally along the MLS band. Other details of cellular fine structure of the mature spermatozoid are described.     

Ecological and evolutionary implications of immunological priming in invertebrates

Invertebrates have an immune response that differs considerably from the acquired immune response found in vertebrates. However, new studies indicate that past experience with a pathogen can provide individual invertebrates, or their descendants, with enhanced immunity. This prophylactic effect, termed immunological priming, is functionally similar to the acquired immune response in vertebrates. This newfound complexity of invertebrate immunity begs investigation into the conditions under which immunological priming should evolve, and its consequences for population dynamics.     

Horizontal gene transfer as a possible evolutionary predecessor of sexual reproduction

Computer modeling shows that high rates of lateral gene transfer (LGT), combined with homologous recombination, enhance selection efficiency, thus making it possible for organisms to acquire larger genomes without irreversible growth of mutation load. In prokaryotes, the optimal (high) rate of LGT cannot evolve because of the “suicidal effect” of modifiers, i.e., alleles that enhance LGT are systematically replaced by alleles that hinder LGT and never vice versa. Therefore, the latter alleles spread despite the fact that they reduce fitness of organisms and populations. This “conflict of interests” can be resolved via evolution of whole-genome reciprocal recombination, which effectively removes the basis for propagation of “selfish” modifiers. Eukaryotic sexual reproduction (amphimixis) probably appeared as the final result of evolution of mechanisms of LGT driven by selection for high interindividual recombination rate. Such selection could have been facilitated at the early stages of eukaryogenesis due to an increase in genome size and high mutation rate caused by higher O₂ concentration and invasion of group II introns.     

Ecological and evolutionary responses in complex communities: implications for invasions and eco‐evolutionary feedbacks

It is easier to predict the ecological and evolutionary outcomes of interactions in less diverse communities. As species are added to communities, their direct and indirect interactions multiply, their niches may shift, and there may be increased ecological redundancy. Accompanying this complexity in ecological interactions, is also complexity in selection and subsequent evolution, which may feed back to affect the ecology of the system, as species with different traits may play different ecological roles. Drawing from my own work and that of many others, I first discuss what we currently understand about ecology and evolution in light of simple and diverse communities, and suggest the importance of escape from community complexity per se in the success of invaders. Then, I examine how community complexity may influence the nature and magnitude of eco‐evolutionary feedbacks, classifying eco‐evolutionary dynamics into three general types: those generating alternative stable states, cyclic dynamics, and those maintaining ecological stasis and stability. The latter may be important and yet very hard to detect. I suggest future directions, as well as discuss methodological approaches and their potential pitfalls, in assessing the importance and longevity of eco‐evolutionary feedbacks in complex communities. Synthesis The ecology, evolution and eco‐evolutionary dynamics of simple and diverse communities are reviewed. In more diverse communities, direct and indirect interactions multiply, species’ niches often shift, ecological redundancy can increase, and selection may be less directional. Community complexity may influence the magnitude and nature of eco‐evolutionary dynamics, which are classified into three types: those generating alternative stable states, cyclic dynamics, and those maintaining ecological stasis and stability. Strengths and pitfalls of approaches to investigating eco‐evolutionary feedbacks in complex field communities are discussed.     

The requirements for sexual reproduction

Summary Sexual reproduction requires controls for gonadogenesis, genital differentiation, and sexuality. The initiating event is induction of testicular differentiation by an effect of the H-Y locus or a combination of X- and Y-borne genes. This paper reviews the evidence that testosterone, either directly or via regulated conversion to other steroids, controls sexuality as it does male genital differentiation. The point is also stressed that, despite their difference, sexual reproduction and individual homcostasis are intimately linked.     

The evolution of meiosis and sexual reproduction

It has been argued that because intermediate states would not be advantageous, it is impossible for natural selection to account for the evolution of meiosis and sexual reproduction. The argument is invalid because a reasonable hypothesis is presented. The hypothesis is developed from a consideration of unicellular eukaryotes and prokaryotes and is that the ancestral eukaryote had a form of parasexual cycle with 'somatic' or 'mitotic' recombination. Later mitosis, then meiosis evolved. In multicellular organisms genetic recombination then usually became restricted to meiosis. Several predictions are made that could be tested in the near future. A conclusion is that we have been misled by treating meiosis and genetic recombination as more or less synonomous. The question of the ultimate origin of recombination is more obscure but it is pointed out that recombination could give the most immediate advantage early in the origin of life, particularly with a hypercycle model. It could result in the combination of advantageous quasi-species (short nucleotidc sequences) into one genome, and it could eliminate ineffective combinations. There are discussions of the scientific role of hypotheses for the origin of complex biological features and on the biological success of cooperative units of DNA.     

The evolutionary significance of sexual selection

A model for the joint evolution of a secondary sexual male trait Z and a female mating preference Y is discussed. Recurrence relations for the moments of (Z, Y) are given under the assumption that the traits are binormally distributed. It is shown that female preference for a male character can lead to an equilibrium distribution of the male trait with non-zero variances. The conditions under which the distribution is stable, are given. Unstable situations, in which a continued exaggeration of the male trait occurs, are described. It is demonstrated that the effect of sexual selection on the evolution of the male trait depends on the intensity of natural selection, i.e. the effect of the sexual selection increases when the intensity of natural selection is reduced. The effect of the female preference on the male trait also increases with increasing availability of males. This provides a link to several ecological conditions which have generally been known to be correlated with the degree of sexual selection. Furthermore, it is demonstrated that perturbations away from the equilibrium may cause rapid evolution of the male character, eventually leading to speciation.     

The evolutionary outcome of sexual conflict

Inter-locus sexual conflict occurs by definition when there is sexually antagonistic selection on a trait so that the optimal trait value differs between the sexes. As a result, there is selection on each sex to manipulate the trait towards its own optimum and resist such manipulation by the other sex. Sexual conflict often leads additionally to the evolution of harmful behaviour and to self-reinforcing and even perpetual sexually antagonistic coevolution. In an attempt to understand the determinants of these different outcomes, I compare two groups of traits-those related to parental investment (PI) and to mating-over which there is sexual conflict, but which have to date been explored by largely separate research traditions. A brief review suggests that sexual conflict over PI, particularly over PI per offspring, leads less frequently to the evolution of manipulative behaviour, and rarely to the evolution of harmful behaviour or to the rapid evolutionary changes which may be symptomatic of sexually antagonistic coevolution. The chief determinants of the evolutionary outcome of sexual conflict are the benefits of manipulation and resistance, the costs of manipulation and resistance, and the feasibility of manipulation. All three of these appear to contribute to the differences in the evolutionary outcome of conflicts over PI and mating. A detailed dissection of the evolutionary changes following from sexual conflict exposes greater complexity than a simple adaptation-counter-adaptation cycle and clarifies the role of harm. Not all of the evolutionary changes that follow from sexual conflict are sexually antagonistic, and harm is not necessary for sexually antagonistic coevolution to occur. In particular, whereas selection on the trait over which there is conflict is by definition sexually antagonistic, collateral harm is usually in the interest of neither sex. This creates the opportunity for palliative adaptations which reduce collateral harm. Failure to recognize that such adaptations are in the interest of both sexes can hinder our understanding of the evolutionary outcome of sexual conflict.     

Commentary: The ecological and evolutionary implications of allometry

Evolutionary Ecology - Allometry—the study of proportional growth of body parts, and the relationship of body size to an organism’s morphology, physiology and behaviour—is a...     

泥炭藓及其孢子萌发和有性生殖

将泥炭藓孢子萌发为配子体和有性生殖及精子形态等细节,用作者拍摄的活体照片,介绍给读者,以期对植物教学有所补充。     

Ecological and evolutionary conditions for fruit abortion to regulate pollinating seed-eaters and increase plant reproduction

Coevolved mutualisms, such as those between senita cacti, yuccas, and their respective obligate pollinators, benefit both species involved in the interaction. However, in these pollination mutualisms the pollinator's larvae impose a cost on plants through consumption of developing seeds and fruit. The effects of pollinators on benefits and costs are expected to vary with the abundance of pollinators, because large population sizes result in more eggs and larval seed-eaters. Here, we develop the hypothesis that fruit abortion, which is common in yucca, senita, and plants in general, could in some cases have the function of limiting pollinator abundance and, thereby, increasing fruit production. Using a general steady-state model of fruit production and pollinator dynamics, we demonstrate that plants involved in pollinating seed-eater mutualisms can increase their fecundity by randomly aborting fruit. We show that the ecological conditions under which fruit abortion can improve plants fecundity are not unusual. They are best met when the plant is long-lived, the population dynamics of the pollinator are much faster than those of the plant, the loss of one fruit via abortion kills a larva that would have the expectation of destroying more than one fruit through its future egg laying as an adult moth, and the effects of fruit abortion on pollinator abundance are spatially localized. We then use the approach of adaptive dynamics to find conditions under which a fruit abortion strategy based on regulating the pollinator population could feasibly evolve in this type of plant-pollinator interaction.     

The glutamine synthetases of rhizobia: phylogenetics and evolutionary implications

Glutamine synthetase exists in at least two related forms, GSI and GSII, the sequences of which have been used in evolutionary molecular clock studies. GSI has so far been found exclusively in bacteria, and GSII has been found predominantly in eukaryotes. To date, only a minority of bacteria, including rhizobia, have been shown to express both forms of GS. The sequences of equivalent internal fragments of the GSI and GSII genes for the type strains of 16 species of rhizobia have been determined and analyzed. The GSI and GSII data sets do not produce congruent phylogenies with either neighbor-joining or maximum-likelihood analyses. The GSI phylogeny is broadly congruent with the 16S rDNA phylogeny for the same bacteria; the GSII phylogeny is not. There are three striking rearrangements in the GSII phylograms, all of which might be explained by horizontal gene transfer to Bradyrhizobium (probably from Mesorhizobium), to Rhizobium galegae (from Rhizobium), and to Mesorhizobium huakuii (perhaps from Rhizobium). There is also evidence suggesting intrageneric DNA transfer within Mesorhizobium. Meta-analysis of both GS genes from the different genera of rhizobia and other reference organisms suggests that the divergence times of the different rhizobium genera predate the existence of legumes, their host plants.     

The origination events of gametic sexual reproduction and anisogamy

Journal of Ethology - The evolution of gametic sex (meiosis and fertilization) and subsequent transition from isogamy (fusion between two equal-sized gametes) to anisogamy (dimorphism into eggs and...