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At least 235 records · Page 13Linked to original sources
PubMed2004

Vicious circles: positive feedback in major evolutionary and ecological transitions.

Evolutionary biologists and ecologists often focus on equilibrium states that are subject to forms of negative feedback, such as optima for phenotypic traits or regulation of population sizes. However, recent theoretical and empirical studies show how positive feedback can be instrumental in driving many of the most important and spectacular processes in evolutionary ecology, including the evolution of sex and genetic systems, mating systems, life histories, complex cooperation in insects and humans, ecological specialization, species diversity, species ranges, speciation and extinction. Taken together, this work suggests that positive feedback is more common than is generally appreciated, and that its self-reinforcing dynamics generate the conditions for changes that might otherwise be difficult or impossible for selection or other mechanisms to achieve. Testing for positive feedback requires analysing each causal link in feedback loops, tracking genetic, character and population-dynamic changes across generations, and elucidating the conditions that can result in self-reinforcing change.

Journal Article↗
PubMed2003

Genetic structure of Fennoscandian populations of the threatened wood-decay fungus Fomitopsis rosea (Basidiomycota).

The genetic structure of five Fennoscandian populations of the threatened wood-decay fungus Fomitopsis rosea (Basidiomycota) was investigated using codominant PCR-RFLP, allele specific amplification (ASA) markers, inter simple sequence repeat (ISSR) markers and mating studies. Sequence analyses of a subset of single spore isolates revealed sequence variation in four target sequences; internal transcribed spacer (ITS) and intergenic spacer (IGS1) of the nuclear ribosomal DNA, the translation elongation factor 1 alpha (efa) gene and the super oxide dismutase (sod) gene. No sequence variation was found in amplified portions of the mitochondrial large and small rRNA genes. Genotype distributions were mostly (90%) in accordance with Hardy-Weinberg expectations, and the nrDNA markers (ITS/IGS1), efa and sod were in most cases (87%) in linkage equilibrium, indicating an outcrossing reproductive mode, panmictic conditions and large population sizes of the fungus. Mating tests confirmed that F. rosea exhibits an outcrossing bipolar heterothallic mating system. Mating allele richness was high in two investigated populations. Phylogenetic analyses of ITS and IGS1 sequences from the five geographic populations revealed some geographic sub-structuring of the ITS sequences, but no sub-structuring of IGS1. The nrDNA (ITS/IGS1), efa and sod markers gave a low overall FST (0.013). The ISSR markers gave no clustering of the populations in UPGMA, and the between-population variance component was very low in AMOVA (0.4%), indicating a high level of gene flow.

Alleles↗
PubMed1977

Social organization and mating success in local song populations of village indigobirds, Vidua chalybeata.

Behavioral interactions among color-marked individual Vidua chalybeata that shared common song dialects were observed for 5 years in two populations at Lochinvar National Park, Zambia. Social interactions involved males visiting and competing for mating sites and female visiting male in an apparent sampling of potential copulating partners. Differences in mating success among the polygynous males were compared with male behavior and territory resources, and criteria were developed to test the importance of intrasexual male competition and female mate choice in explaining the mating system of the populations. Song behavior best explained differences in mating success of males, with lesser effects of neighboring males and the defensible resources around the call-sites. The social organization of song populations resembles that of a dispersed lek with females visiting many males but mating with few males. We discuss the observations on indigobirds in relation to behavioral selection, sexual selection, and mating systems. Mating systems of certain populations and species are compared using statistics of individual mating success.

Aggression↗
PubMed2000

A model on female breeding dispersion and the reproductive systems of pinnipeds.

Because most mammalian mating systems ultimately depend on female dispersion, the study of habitat selection by breeding females will help in understanding the ecology of mating systems. I developed a cost-benefit model of breeding dispersion of females that is based on the concept of 'ideal free' distribution. The currency of the model is the probability of offspring survival. The cost of female grouping is the increment of female-female competition for resources, and the benefit is the reduction of male harassment. The maximal benefit depends on the resource quality of the breeding sites. I tested the qualitative predictions of the model on the female dispersion and mating system of pinnipeds. The model predicted the main differences observed between taxonomic groups of pinnipeds: higher female aggregation and polygyny in Otariidae than in Phocidae, in Otariinae than in Arctocephalinae, and in Mirounga spp. and Halichoerus sp. than in the rest of the phocids. My approach emphasises the importance of male harassment for the evolution of mammalian mating systems. I propose that the classical view of a unidirectional approach to the ecology of mammalian mating system (resource dispersion-->female dispersion-->male dispersion), should be modified to incorporate a feedback from male dispersion to the factors that regulate female dispersion.

Journal Article↗
PubMed2005

Plant population dynamics, pollinator foraging, and the selection of self-fertilization.

Many flowering plants rely on pollinators, self-fertilization, or both for reproduction. We model the consequences of these features for plant population dynamics and mating system evolution. Our mating systems-based population dynamics model includes an Allee effect. This often leads to an extinction threshold, defined as a density below which population densities decrease. Reliance on generalist pollinators who primarily visit higher density plant species increases the extinction threshold, whereas autonomous modes of selfing decrease and can eliminate the threshold. Generalist pollinators visiting higher density plant species coupled with autonomous selfing may introduce an effect where populations decreasing in density below the extinction threshold may nonetheless persist through selfing. The extinction threshold and selfing at low density result in populations where individuals adopting a single reproductive strategy exhibit mating systems that depend on population density. The ecological and evolutionary analyses provide a mechanism where prior selfing evolves even though inbreeding depression is greater than one-half. Simultaneous consideration of ecological and evolutionary dynamics confirms unusual features (e.g., evolution into extinction or abrupt increases in population density) implicit in our separate consideration of ecological and evolutionary scenarios. Our analysis has consequences for understanding pollen limitation, reproductive assurance, and the evolution of mating systems.

Animals↗
PubMed1997

Interpreting hominid behavior on the basis of sexual dimorphism.

Numerous studies use estimates of sexual dimorphism in canine tooth size and body weight to support speculation about the behavior of australopithecines. However, the range of mating systems inferred for australopithecines encompasses virtually the entire spectrum of mating systems seen among extant anthropoid primates, from monogamy to polygyny characterized by intense male male competition. This variety of opinion can be attributed partly to the unusual combination of high body size dimorphism and reduced canine dimorphism in australopithecines. Here we provide a joint comparison of recent models for the behavioral correlates of both canine dimorphism and body size dimorphism, and apply this to published estimates of dimorphism in body size and canine tooth size in hominids. Among extant species, body weight dimorphism and canine dimorphism are strongly correlated with estimates of intrasexual competition. Canine crown height dimorphism provides the best discrimination between taxa that show high degrees of male-male competition, and those that do not. Relative male maxillary canine tooth size offers additional evidence about male-male competition. On the other hand, canine occlusal dimorphism offers little discrimination among species of different male-male competition levels. Estimates of canine dimorphism, relative canine size, and body weight dimorphism in australopithecines provide little definitive information about male-male competition or mating systems. Dimorphism of Australopithecus africanus and Australopithecus robustus can be reconciled with a mating system characterized by low-intensity male-male competition. The pattern of dimorphism and relative canine size in Australopithecus afarensis and A. robustus provides contradictory evidence about mating systems and male-male competition. We review a number of hypotheses that may explain the unusual pattern of dimorphism of A. afarensis and Australopithecus boisei, but non-satisfactorily resolves the problem given current data.

Animals↗
PubMed2004

Estimation of genetically effective breeding numbers using a rejection algorithm approach.

Polygynous mating results in nonrandom sampling of the adult male gamete pool in each generation, thereby increasing the rate of genetic drift. In principle, genetic paternity analysis can be used to infer the effective number of breeding males (Nebm). However, this requires genetic data from an exhaustive sample of candidate males. Here we describe a new approach to estimate Nebm using a rejection algorithm in association with three statistics: Euclidean distance between the frequency distributions of maternally and paternally inherited alleles, average number of paternally inherited alleles and average gene diversity of paternally inherited alleles. We quantify the relationship between these statistics and Nebm using an individual-based simulation model in which the male mating system varied continuously between random mating and extreme polygyny. We evaluate this method using genetic data from a natural population of highly polygynous fruit bats (Cynopterous sphinx). Using data in the form of mother-offspring genotypes, we demonstrate that estimates of Nebm are very similar to independent estimates based on a direct paternity analysis that included data on candidate males. Our method also permits an evaluation of uncertainty in estimates of Nebm and thus facilitates inferences about the mating system from genetic data. Finally, we investigate the sensitivity of our method to sample size, model assumptions, adult population size and the mating system. These analyses demonstrate that the rejection algorithm provides accurate estimates of Nebm across a broad range of demographic scenarios, except when the true Nebm is high.

Algorithms↗