Operational sex ratio and resource defence as predictors of the mating system in European bitterling

Operational sex ratio (OSR), the ratio of sexually active males to fertilizable females in a population, plays a central role in the theory of mating systems by predicting that the intensity of male–male competition and the degree of sexual selection increases as the OSR becomes increasingly male biased. At high values of OSR, however, resource defence theory predicts the breakdown of territoriality and a shift towards scramble competition with a decrease in sexual selection. The direction that correlations between OSR and resource competition and variance in mating success will take depends on the biology of the species of interest. We investigated the effects of male population density and male‐biased operational sex ratio on male mating tactics shown by a freshwater fish, the European bitterling, Rhodeus sericeus . This species spawns inside living unioneid mussels. Large males defended territories, were aggressive towards conspecifics under equal sex ratios and monopolized pair spawnings with females. The mating tactic, however, changed at high male density where large males ceased to be territorial and instead competed with groups of smaller males to release sperm when females spawned. This change in male behaviour from pair to group spawning has two ramifications for sexual selection. The intensity of sexual selection and variance in male mating success decrease, and the form of sexual competition changes from resource‐ to sperm competition. Thus, the use of alternative mating tactics renders the OSR unable to predict the direction of resource competition and variance in male mating success at high densities.     

Evolution of ungulate mating systems: Integrating social and environmental factors

Ungulates exhibit diverse mating systems that range from monogamous pair territories to highly polygynous leks. We review mating systems and behaviors across ungulates and offer a new approach synthesizing how interacting factors may shape those mating systems. Variability exists in mating systems among and within species of ungulates and likely is affected by predation risk, availability of resources (food and mates), habitat structure, and sociality. Ungulate mating systems may be labile as a consequence of the varying strength of those interacting factors. In addition, degree of polygyny and sexual dimorphism in size are associated with the evolution of mating systems. Neither male–male combat nor paternal care, however, can completely explain differences in sexual size dimorphism for ungulates, a necessary component in understanding the development of some mating systems. Whatever the evolutionary pathway, sexual segregation limits paternal care allowing more intense male–male competition. Selection of habitat structure, because it modifies risk of predation, is a major determinant of sociality for ungulates. Likewise, ruggedness and steepness of terrain limit the types of mating systems that can occur because of limitations in group size and cohesiveness, as well as the ability of males to herd even small groups of females effectively. The quality and defensibility of resources affect mating systems, as does the defensibility of females. Population density of females also may be a critical determinant of the types of mating systems that develop. Size of groups likewise constrains the types of mating tactics that males can employ. Our aim was to use those relationships to create a broad conceptual model that predicts how various environmental and social factors interact to structure mating systems in ungulates. This model provides a useful framework for future tests of the roles of both ecological and social conditions in influencing the social systems of ungulates.     

Costs of inducible defence along a resource gradient

In addition to having constitutive defence traits, many organisms also respond to predation by phenotypic plasticity. In order for plasticity to be adaptive, induced defences should incur a benefit to the organism in, for example, decreased risk of predation. However, the production of defence traits may include costs in fitness components such as growth, time to reproduction, or fecundity. To test the hypothesis that the expression of phenotypic plasticity incurs costs, we performed a common garden experiment with a freshwater snail, Radix balthica, a species known to change morphology in the presence of molluscivorous fish. We measured a number of predator-induced morphological and behavioural defence traits in snails that we reared in the presence or absence of chemical cues from fish. Further, we quantified the costs of plasticity in fitness characters related to fecundity and growth. Since plastic responses may be inhibited under limited resource conditions, we reared snails in different densities and thereby levels of competition. Snails exposed to predator cues grew rounder and thicker shells, traits confirmed to be adaptive in environments with fish. Defence traits were consistently expressed independent of density, suggesting strong selection from predatory molluscivorous fish. However, the expression of defence traits resulted in reduced growth rate and fecundity, particularly with limited resources. Our results suggest full defence in predator related traits regardless of resource availability, and costs of defence consequently paid in traits related to fitness.     

Female‐biased dispersal in a bat with a female‐defence mating strategy

The ultimate causes for predominant male‐biased dispersal (MBD) in mammals and female‐biased dispersal (FBD) in birds are still subject to much debate. Studying exceptions to general patterns of dispersal, for example, FBD in mammals, provides a valuable opportunity to test the validity of proposed evolutionary pressures. We used long‐term behavioural and genetic data on individually banded Proboscis bats (Rhynchonycteris naso) to show that this species is one of the rare mammalian exceptions with FBD. Our results suggest that all females disperse from their natal colonies prior to first reproduction and that a substantial proportion of males are philopatric and reproduce in their natal colonies, although male immigration has also been detected. The age of females at first conception falls below the tenure of males, suggesting that females disperse to avoid father–daughter inbreeding. Male philopatry in this species is intriguing because Proboscis bats do not share the usual mammalian correlates (i.e. resource‐defence polygyny and/or kin cooperation) of male philopatry. They have a mating strategy based on female defence, where local mate competition between male kin is supposedly severe and should prevent the evolution of male philopatry. However, in contrast to immigrant males, philopatric males may profit from acquaintance with the natal foraging grounds and may be able to attain dominance easier and/or earlier in life. Our results on Proboscis bats lent additional support to the importance of inbreeding avoidance in shaping sex‐biased dispersal patterns and suggest that resource defence by males or kin cooperation cannot fully explain the evolution of male philopatry in mammals.     

Competitor density influences resource defence in a Poeciliid fish

The concept of economic defendability states that individuals will only defend resources when the benefits outweigh the costs. Competitor density is one factor that influences resource defence among fishes, resource defence being predicted to be highest at intermediate competitor densities and reduced at higher and lower densities, producing a dome shaped relationship. We investigated the effects of competitor density using male swordtails, which form dominance hierarchies and have already been demonstrated to defend a food resource. We found that both aggression (F_2,32 = 5.392; P = 0.010) and time at a food resource (F_2,32 = 3.574; P = 0.040) vary with differences in competitor density, and that the frequency of aggression significantly predicts time at the food resource only at an intermediate density (P = 0.033; r²adj = 0.219). The ability to vary the level of defence with respect to the immediate environment may result in fitness benefits to male swordtails. Further studies examining changes in behaviour over time and examining interacting influencing factors would be beneficial.     

Interactions leading to persistence in predator-prey systems with group defence

In previous work (Freedman and Wolkowicz, 1986;Bull. math. Biol. 48, 493–508) it was shown that in a predator-prey system where the prey population exhibits group defence, it is possible that enrichment of the environment could lead to extinction of the predator population. In this paper a third population is introduced and criteria are derived under which persistence of all populations will occur. In particular, criteria for a superpredator and for a competitor to stabilize the system in the sense of persistence are analyzed. Research partially supported by the Natural Sciences and Engineering Research Council of Canada, Grant No. NSERC A 4823. This research was carried out while the author was a visiting scholar at the University of Alberta.     

Individual optimization efforts and population dynamics: a mathematical model for the evolution of resource allocation strategies, with applications to reproductive and mating systems

We develop a formal framework for the optimal allocation of limited resources that includes and clarifies the interplay between individual optimization and the resulting effects at the population level. As an example, in regard to the evolution of sexual recombination, the paradox of the twofold cost of sex is avoided by distinguishing between the evolution of recombination and the subsequent emergence and stability of different mating types as a result of individual optimization within a population that benefits from recombination.

Integrating ecology and developmental biology to explain the timing of frog metamorphosis

Amphibian metamorphosis has long intrigued ecologists and developmental biologists, yet the two research programs have progressed separately and toward different goals. Plasticity in metamorphic timing has profound effects on fitness, which has prompted ecologists to develop and test models for predicting how environmental factors affect the size and age of metamorphosis. These models rely upon untested assumptions about the mechanisms for regulating growth and development. Whereas developmental biologists explicitly investigate these mechanisms at the hormonal and genetic levels, they largely ignore the role of environmental input. Recent developments in our understanding of the molecular biology of frog metamorphosis are revealing how these two research programs could be integrated. Here, I review these developments to test ecologists' assumptions about frog metamorphosis, and to present strategies for both research fields to investigate the mechanistic basis of metamorphic plasticity.     

Integrating systems biology with clinical research

A report on the conference 'Systems Genomics 2008', Heidelberg, Germany, 2-3 May 2008.     

A resource budget model to explain intraspecific variation in mast reproductive dynamics

Rowan, Sorbus aucuparia L., exhibits conspicuous geographic variation in its inter-annual patterns of reproduction across southern Norway. Along the southern west coast, trees flower and produce clusters of succulent berries every other year, while in the east, trees mast every 3 years. We investigate two hypotheses for this variation: local adaptation to environmental conditions that favors different reproductive schedules at different locations or variation arising from single stereotyped reproductive strategy in the face of a geographic variation in productivity. To assess the theoretical plausibility of each of these hypotheses, we develop a refined resource budget model for mast reproduction. The refined model assumes that there is a lower bound on the amount of resource that may be allocated to reproduction, which allows the prediction of the relation between reproductive schedules and productivity. From the analysis of the model, we find that the observed geographic transition in rowan mast is caused if either productivity in the east is lower than that in the west or if plants in the eastern populations have evolved to pause reproduction until energy reserves are replenished to higher levels. The prediction by the productivity gradient hypothesis match with the empirical finding that the productivity is, in fact, likely to be lower in the east than the west, although we lack empirical data to test the likelihood of the local adaptation hypothesis. There is a need for experimental studies to clarify the validity of the local adaptation hypothesis. Akiko Satake is the recipient of the 11th Denzaburo Miyadi Award.     

Coalescent theory for a completely random mating monoecious population

Consider a large random mating monoecious diploid population that has N individuals in each generation. Let us assume that at time 0 a random sample of ninfinity. It is then possible to obtain a generalization of coalescent theory for haploid populations if the distribution of G1 has a finite second moment and E[G(1)(3)]/N-->0 as N-->infinity.     

Genealogical theory for random mating populations with two sexes

Consider a random mating population that has N(m) males and N(f) females in each generation. Let us assume that at time 0 a random sample of n copies of a gene is taken from this population. Then, for models introduced by Wright [Evolution in Mendelian populations, Genetics 16 (1931) 97; Inbreeding and homozygosis, Proc. Nat. Acad. Wash. 19 (1933) 420; Evolution and the Genetics of Populations, The Theory of Gene Frequencies, vol. II, The University of Chicago, Chicago and London, 1969.], it is possible to obtain generalizations of the haploid theory of genealogical processes developed by Felsenstein . It is conjectured that these hold generally, regardless of the effective population size, if n相似文献   

Nuclear fusion during yeast mating occurs by a three-step pathway

In Saccharomyces cerevisiae, mating culminates in nuclear fusion to produce a diploid zygote. Two models for nuclear fusion have been proposed: a one-step model in which the outer and inner nuclear membranes and the spindle pole bodies (SPBs) fuse simultaneously and a three-step model in which the three events occur separately. To differentiate between these models, we used electron tomography and time-lapse light microscopy of early stage wild-type zygotes. We observe two distinct SPBs in ~80% of zygotes that contain fused nuclei, whereas we only see fused or partially fused SPBs in zygotes in which the site of nuclear envelope (NE) fusion is already dilated. This demonstrates that SPB fusion occurs after NE fusion. Time-lapse microscopy of zygotes containing fluorescent protein tags that localize to either the NE lumen or the nucleoplasm demonstrates that outer membrane fusion precedes inner membrane fusion. We conclude that nuclear fusion occurs by a three-step pathway.     

A new hypothesis to explain the coexistence of n species in the presence of a single resource

This paper presents a hypothesis allowing us to explain the coexistence of several species (here micro-organisms) in competition on a single resource (called a substrate) in a chemostat. We introduce a new class of kinetics that does not only depend on the substrate concentration in the medium, but also on the biomass concentration. From the study of elementary interactions (i) between micro-organisms, (ii) between micro-organisms and their environment in which they grow and from simulations, we show that this modelling approach can be interpreted in terms of substrate diffusion phenomena. A rigorous study of this new class of models allows us to hypothesize that abiotic parameters can explain the fact that an arbitrarily large number of species can coexist in the presence of a unique substrate.     

Sexual dimorphism and mating systems: jumping to conclusions

Previous studies have suggested that there is a strong relationship between a high degree of aggressive competition among males for access to fertile females and large body and canine size in males. It has further been suggested that such a relationship among living primates can be used to infer the social organization of extinct primate species from the degree of sexual dimorphism exhibited. Our field studies of patas (Erythrocebus patas) and blue monkeys (Cercopithecus mitis), two species which had previously been characterized as having one-male ‘harem’ group structures, indicate considerable variability in mating systems. We suggest, on the basis of our observations of these species, that factors other than male-male competition (e.g., predation) may also have influenced the degree of dimorphism in primates.     

Quality coding by neural populations in the early olfactory pathway: analysis using information theory and lessons for artificial olfactory systems

In this article, we analyze the ability of the early olfactory system to detect and discriminate different odors by means of information theory measurements applied to olfactory bulb activity images. We have studied the role that the diversity and number of receptor neuron types play in encoding chemical information. Our results show that the olfactory receptors of the biological system are low correlated and present good coverage of the input space. The coding capacity of ensembles of olfactory receptors with the same receptive range is maximized when the receptors cover half of the odor input space - a configuration that corresponds to receptors that are not particularly selective. However, the ensemble's performance slightly increases when mixing uncorrelated receptors of different receptive ranges. Our results confirm that the low correlation between sensors could be more significant than the sensor selectivity for general purpose chemo-sensory systems, whether these are biological or biomimetic.     

Signaling of human frizzled receptors to the mating pathway in yeast

Frizzled receptors have seven membrane-spanning helices and are considered as atypical G protein-coupled receptors (GPCRs). The mating response of the yeast Saccharomyces cerevisiae is mediated by a GPCR signaling system and this model organism has been used extensively in the past to study mammalian GPCR function. We show here that human Frizzled receptors (Fz1 and Fz2) can be properly targeted to the yeast plasma membrane, and that they stimulate the yeast mating pathway in the absence of added Wnt ligands, as evidenced by cell cycle arrest in G1 and reporter gene expression dependent on the mating pathway-activated FUS1 gene. Introducing intracellular portions of Frizzled receptors into the Ste2p backbone resulted in the generation of constitutively active receptor chimeras that retained mating factor responsiveness. Introducing intracellular portions of Ste2p into the Frizzled receptor backbone was found to strongly enhance mating pathway activation as compared to the native Frizzleds, likely by facilitating interaction with the yeast Galpha protein Gpa1p. Furthermore, we show reversibility of the highly penetrant G1-phase arrests exerted by the receptor chimeras by deletion of the mating pathway effector FAR1. Our data demonstrate that Frizzled receptors can functionally replace mating factor receptors in yeast and offer an experimental system to study modulators of Frizzled receptors.