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PubMed1993

Chaotic population dynamics can result from natural selection.

The question of whether animal populations display chaotic dynamics has motivated a thriving body of research for two decades. Yet unambiguous evidence for chaos in the wild remains scarce. Accordingly, it has been proposed that evolutionary forces act to preserve populations from chaos as well as oscillations. We have tested for this hypothesis by considering the dynamics associated with evolutionarily stable life histories (including age of maturity, adult survivorship and recruitment to adulthood) in a simple, but general, demographic model. Contrary to expectation, individual selection operating on demographic traits should often lead to oscillatory or chaotic dynamics for species with late feasible ages of maturity and many age classes. Also, the optimality of chaos is more likely whenever trade-offs constrain recruitment to rapidly decrease with increasing adult survival or decreasing age of maturity. Our results bring evolutionary support to the possibility that chaotic population dynamics might be much more widespread than inferred until now from data analyses. Furthermore, these findings provide novel support for the view that chaos could be an optimal regime for several biological systems.

Aging↗
PubMed2004

How predation risk affects the temporal dynamics of avian leks: greater sage grouse versus golden eagles.

Leks often attract predators as well as mates, yet most evolutionary models have assumed that sexual selection, not predation, drives lekking behavior. We explored the influence of predation on lek dynamics using a stochastic dynamic game model based on the lek-breeding greater sage grouse (Centrocercus urophasianus) and its principal avian predator, the golden eagle (Aquila chrysaetos). The model predicts time-dependent male lek attendance as a function of factors affecting both mating success (female arrival rate, male numbers, and social status) and predation risk (eagle arrival rate and group size). Dominant males are predicted to arrive sooner and leave later than subordinates, especially if mating skew is high, predation risk is low, or the relationship between lek size and female arrival rate is weak. Both high mean levels of predation risk and small lek size should reduce lek attendance, but the relative tendency of predators to attack large versus small leks has little influence on predicted lekking behavior. Field observations confirmed the predicted effects of female arrival rate, lek size, male dominance, and weather-dependent predator arrival rates on lek departure times. Predicted effects of female arrival rates and male dominance on seasonal lek attendance were also supported. Our model provides an empirically supported adaptive explanation for short-term lek dynamics. It also suggests alternative interpretations for phenomena previously invoked to support the hotshot and skew models of lek formation.

Animals↗
PubMed1993

Lateral transfer in natural populations of eukaryotes.

Although there are several likely instances of trans-kingdom lateral transfer of genomic sequences involving eukaryotes and prokaryotes, almost all well-documented cases of eukaryote to eukaryote transfer seem to involve mobile elements or other parasitic sequences. Consistent with general observations of phylogenetic regularity, the limited molecular evidence suggests that lateral transfer of eukaryotic genomic sequences is at best very rare. However, due to limited data, the possibility of rare transfers that could have considerable evolutionary significance cannot be ruled out. A possible propensity for lateral transfer by mobile elements may reflect their innate capacity for genomic wandering. In addition, occasional cross-species mobility may play a critical role in the long-term evolutionary survival of these elements and have been subject to natural selection. Much work is needed to fully understand the dynamics of TEs and other multigene families. Problems of paralogy, recombination, and variation in evolutionary rates currently present important difficulties in distinguishing conclusively between occasional lateral transfer and strictly vertical transfer. The importance of lateral transfers for host organisms must await answers to more general questions about the long-term evolutionary significance of mobile elements and the extent to which they can act as vectors for host genomic sequences.

Animals↗
PubMed1999

Frontiers of finance: evolution and efficient markets.

In this review article, we explore several recent advances in the quantitative modeling of financial markets. We begin with the Efficient Markets Hypothesis and describe how this controversial idea has stimulated a number of new directions of research, some focusing on more elaborate mathematical models that are capable of rationalizing the empirical facts, others taking a completely different tack in rejecting rationality altogether. One of the most promising directions is to view financial markets from a biological perspective and, specifically, within an evolutionary framework in which markets, instruments, institutions, and investors interact and evolve dynamically according to the "law" of economic selection. Under this view, financial agents compete and adapt, but they do not necessarily do so in an optimal fashion. Evolutionary and ecological models of financial markets is truly a new frontier whose exploration has just begun.

Economics↗
PubMed1990

[Where do the parasites of man come from?].

The Hominids have come in contact, over the last few million years, with the infective stages of many parasites which had up to then evolved in non Primate hosts; this is because Hominids have occupied multiple environments and acquired diversified behaviour. The high number of these lateral transfers explains the multiplicity of current human parasitic diseases whereas their youth on an evolutionary scale accounts for the seriousness of most of these diseases. The basic questions arising from the exceptional opportunities offered to parasites by the evolution of the human lineage concern: the precise role played by human behaviour, the mechanisms of alterations in specificity, the identity of the original host phyla, the dynamic and genetic consequences for parasites, the relationship with the evolutionary history of the ancestors of Homo sapiens sapiens; for instance, it is suggested that man's mastery of fire, allowing him to cook his food, dramatically reduced his contamination by certain parasites and that this contributed to the subsequent success of Hominids.

Animals↗
PubMed2004

Adaptive changes in harvested populations: plasticity and evolution of age and size at maturation.

We investigate harvest-induced adaptive changes in age and size at maturation by modelling both plastic variation and evolutionary trajectories. Harvesting mature individuals displaces the reaction norm for age and size at maturation toward older ages and larger sizes and rotates it clockwise, whereas harvesting immature individuals has the reverse qualitative effect. If both immature and mature individuals are harvested, the net effect has approximately the same trend as when harvesting immature individuals only. This stems from the sensitivity of the evolutionary response, which depends on the maturity state of harvested individuals, but also on the type of harvest mortality (negatively or positively density dependent, density independent) and the value of three life-history parameters (natural mortality, growth rate and the trade-off between growth and reproduction). Evolutionary changes in the maturation reaction norm have strong repercussions for the mean size and the density of harvested individuals that, in most cases, result in the reduction of biomass--a response that population dynamical models would overlook. These results highlight the importance of accounting for evolutionary trends in the long-term management of exploited living resources and give qualitative insights into how to minimize the detrimental consequences of harvest-induced evolutionary changes in maturation reaction norms.

Adaptation, Biological↗
PubMed1997

Spatial and density effects in evolutionary game theory.

Two models are considered for the study of game dynamics in a spatial domain. Both models are continuous in space and time and give rise to reaction-diffusion equations. The spatial domain is homogeneous but the mobility of the individuals is allowed to depend upon the strategy. The models are analysed for spatial patterns (via a Turing instability) and also for the direction of the travelling wave that replaces one strategy by another. It is shown that the qualitative behaviour of the two models is quite different. When considering the existence of spatial patterns and deciding whether increased mobility is helpful or not, it is shown that the answers depend crucially upon the model equations. Since both models (in the absence of spatial variation) are quite standard, it is clear that considerable care has to be exercised in the formulation of spatial models and in their interpretation.

Animals↗
PubMedDate not supplied

Centromere dynamics and chromosome evolution in marsupials.

The eukaryotic centromere poses an interesting evolutionary paradox: it is a chromatin entity indispensable to precise chromosome segregation in all eukaryotes, yet the DNA at the heart of the centromere is remarkably variable. Its important role of spindle attachment to the kinetochore during meiosis and mitosis notwithstanding, recent studies implicate the centromere as an active player in chromosome evolution and the divergence of species. This is exemplified by centromeric involvement in translocations, fusions, inversions, and centric shifts. Often species are defined karyotypically simply by the position of the centromere on certain chromosomes. Little is known about how the centromere, either as a functioning unit of chromatin or as a specific block of repetitive DNA sequences, acts in the creation of these types of chromosome rearrangements in an evolutionary context. Macropodine marsupials (kangaroos and wallabies) offer unique insights into current theories expositing centromere emergence during karyotypic diversification and speciation.

Animals↗
PubMed1999

[The clinico-evolutionary neuro-ophthalmological aspects in multiple sclerosis].

The paper presents the dynamic of the more important neuro-ophthalmologic signs in 112 patients with multiple sclerosis from the first attack to the second one using an interdisciplinary methodology. The existence of ocular signs at the first attack as well as the fortuitous association of the signs of the disease make doubtfully the utility of defining a neuro-ophthalmologic clinical form of the disease. The more significant dominance of the ocular signs at the first attack points out the importance of the ophthalmologic examination for the early diagnosis of the multiple sclerosis.

Diplopia↗
PubMedDate not supplied

Mutationism and the dual causation of evolutionary change.

The rediscovery of Mendel's laws a century ago launched the science that William Bateson called "genetics," and led to a new view of evolution combining selection, particulate inheritance, and the newly characterized phenomenon of "mutation." This "mutationist" view clashed with the earlier view of Darwin, and the later "Modern Synthesis," by allowing discontinuity, and by recognizing mutation (or more properly, mutation-and-altered-development) as a source of creativity, direction, and initiative. By the mid-20th century, the opposing Modern Synthesis view was a prevailing orthodoxy: under its influence, "evolution" was redefined as "shifting gene frequencies," that is, the sorting out of pre-existing variation without new mutations; and the notion that mutation-and-altered-development can exert a predictable influence on the course of evolutionary change was seen as heretical. Nevertheless, mutationist ideas re-surfaced: the notion of mutational determinants of directionality emerged in molecular evolution by 1962, followed in the 1980s by an interest among evolutionary developmental biologists in a shaping or creative role of developmental propensities of variation, and more recently, a recognition by theoretical evolutionary geneticists of the importance of discontinuity and of new mutations in adaptive dynamics. The synthetic challenge presented by these innovations is to integrate mutation-and-altered-development into a new understanding of the dual causation of evolutionary change--a broader and more predictive understanding that already can lay claim to important empirical and theoretical results--and to develop a research program appropriately emphasizing the emergence of variation as a cause of propensities of evolutionary change.

Animals↗
PubMed1981

The genetic dynamics of disease.

The notional principles of the genetics of disease are broadly discussed. Disease is an intrinsically vague term that represents the incongruity between the inner milieu of the organism and the environment. Its dynamics, then, cannot be reduced to naive statements about selection which may operate, and operate conflictingly, on several different levels or organization. Evolutionary selection results from the advantage of complexity, and the fundamental theorem of genetic dynamics - that mutational debts must eventually be paid in full-may be false or, at best approximate. The traditional models (mendelian, galtonian, and threshold) are set in a context that identifies certain features of disease that hitherto have been totally ignored. Neither invention nor traditional analysis has been adequate. Models should be made individually adequate for the study of diseases; the diseases should not be trimmed to fit the models.

Biological Evolution↗
PubMed2006

Evolution of dispersal in a structured metapopulation model in discrete time.

In this article, a structured metapopulation model in discrete time with catastrophes and density-dependent local growth is introduced. The fitness of a rare mutant in an environment set by the resident is defined, and an efficient method to calculate fitness is presented. With this fitness measure evolutionary analysis of this model becomes feasible. This article concentrates on the evolution of dispersal. The effect of catastrophes, dispersal cost, and local dynamics on the evolution of dispersal is investigated. It is proved that without catastrophes, if all population-dynamical attractors are fixed points, there will be selection for no dispersal. A new mechanism for evolutionary branching is also found: Even though local population sizes approach fixed points, catastrophes can cause enough temporal variability, so that evolutionary branching becomes possible.

Algorithms↗
PubMed2003

Within-host parasite dynamics, emerging trade-off, and evolution of virulence with immune system.

Virulence is an evolutionary paradox because parasites never benefit from their host's death. The adaptive explanation of virulence is classically based upon the existence of physiological constraints that create a trade-off between parasites' epidemiological traits (virulence, transmissibility, and clearance). Here we develop an epidemiological model where infections are dynamic processes and we demonstrate how these dynamics generate a trade-off between emerging epidemiological parameters. We then study how host's immune strength modifies this trade-off and hence influences virulence evolution. We found that in acute infections, where parasites are engaged in a race with immune cells, immunity restrains more the duration of the infection than its intensity. As a consequence parasites evolve to provoke more virulent but shorter infections in strongly immunized hosts.

Biological Evolution↗
PubMed1998

Behavioral genetics and evolutionary psychology: unified perspective on personality research.

Behavioral geneticists and evolutionary psychologists have generally pursued human behavioral analyses with little theoretical or methodological exchange. However, significant benefits might accrue from increased communication between these disciplines. The primary goals of this article are (1) to identify meaningful junctures between behavioral genetics and evolutionary psychology, (2) to describe behavioral genetic research designs and their applications to evolutionary analyses, and (3) to reassess current personality research in light of behavioral genetic and evolutionary concepts and techniques. The five-factor model of personality is conceptualized as subsuming variation in normative species-typical systems with adaptive functions in the human environment of evolutionary adaptation. Considered as universal evolved mechanisms, personality systems are often seen in dynamic conflict within individuals and as highly compartmentalized in their functioning between settings. However, genetically influenced individual differences in personality may also be understood within an evolutionary framework. Studies of the heritability of personality traits indicate broad-sense heritabilities in the 0.40-0.50 range with evidence of substantial nonadditive genetic variation and nonshared environmental influences. Evidence indicates that evolutionary theory (e.g., inclusive fitness theory) predicts patterns of social interaction (e.g., cooperation and bereavement) in relatives. Furthermore, variation in personality may constitute a range of viable strategies matching the opportunities available in the complex niche environment of human societies. Within this wide range of viable strategies, personality variation functions as a resource environment for individuals in the sense that personality variation is evaluated according to the interests of the evaluator (e.g., friendships, coalitions, or mate choice).

Biological Evolution↗
PubMed2001

Recent duplication, domain accretion and the dynamic mutation of the human genome.

An estimated 5% of the human genome consists of interspersed duplications that have arisen over the past 35 million years of evolution. Two categories of such recently duplicated segments can be distinguished: segmental duplications between nonhomologous chromosomes (transchromosomal duplications) and duplications mainly restricted to a particular chromosome (chromosome-specific duplications). Many of these duplications exhibit an extraordinarily high degree of sequence identity at the nucleotide level (>95%) and span large genomic distances (1-100 kb). Preliminary analyses indicate that these same regions are targets for rapid evolutionary turnover among the genomes of closely related primates. The dynamic nature of these regions because of recurrent chromosomal rearrangement, and their ability to create fusion genes from juxtaposed cassettes suggest that duplicative transposition was an important force in the evolution of our genome.

Biological Evolution↗
PubMed2006

Dynamical advantages of scale-free networks.

A dynamical analysis of common network topologies is given and it is reported that a scale-free structure has two vital and distinctive features. First, complex but nevertheless reproducible states exist and, second, single-site induced state switching reminiscent of gene-expression control exists also. This indicates that scale-free networks have key dynamical advantages over other network topologies that could have contributed to their evolutionary success and thus may provide another reason for their prevalence in nature.

Models, Biological↗
PubMed2006

Microtubule plus end: a hub of cellular activities.

Microtubules (MTs) are highly dynamic polymers, which control many aspects of cellular architecture. Growing MT plus ends accumulate a specific set of evolutionary conserved factors, the so-called MT plus-end-tracking proteins (+TIPs). +TIPs regulate MT dynamics and the reciprocal interactions of MTs with the cell cortex, mitotic kinetochores or different cellular organelles. Most +TIPs can directly bind to MTs, but the molecular mechanisms of their specific targeting to the growing plus ends remain poorly understood. Recent studies suggest that the members of one particular +TIP family, EB1 and its homologues, are present in all eucaryotic kingdoms, interact directly with the majority of other known plus-end-associated proteins and may be responsible for their specific accumulation at the MT tips.

Animals↗
PubMed2003

[Dynamic observation on ultrasonographic image during chemotherapy of hepatic cystic echinococcosis and a proposal for ultrasonic classification].

OBJECTIVE: To submit a proposal for the classification of ultrasonographic image in patients with hepatic cystic echinococcosis, on the basis of characteristic and distribution of ultrasonic image of hydatid cysts in cases and systematic observation on dynamic changes of sonographic image under treatment with emulsion albendazole and in relation to clinical efficacy. METHODS: The ultrasonic image of 645 cysts in 497 cases with liver cystic echinococcosis was classified. The distribution of different types of image in patients was analyzed. A comparative analysis of correspondence between the sonographic type and clinical efficacy was made in association with the rule of changes in ultrasonic features during chemotherapy. RESULTS: The ultrasonographic image of hydatid cysts was divided into six types. The distribution of ultrasonic types in patients reflected the process of natural evolution of cysts in human bodies. The dynamic change of ultrasonic image during treatment was identical with the natural evolution process of hydatid cysts. CONCLUSION: The proposal for ultrasonographic classification submitted reflects a long evolutionary process from growth to death of hydatid cysts in human body. The dynamic change of hydatid cysts during chemotherapy indicated that the effect of drug has accelerated this process. Therefore this classification may be applied in diagnosis and to judge the chemotherapeutic efficacy of cystic echinococcosis.

Adolescent↗