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PubMed1990

Koinophilia groups sexual creatures into species, promotes stasis, and stabilizes social behaviour.

In a population whose members' genomes are subject to degradation by random mutations, the heritable vigour of the most common phenotypes is unquestionable (though not necessarily optimal), and that of fringe individuals is always suspect. Natural selection will therefore support the evolution of an affinity for modal mates (i.e. koinophilia). The population's genetic make-up can then not readily be invaded by non-cryptic mutations. This imposes considerable phenotypic conservatism on sexually reproducing creatures, and inexorably canalizes them into sexually isolated, phenotypically distinct species. The model predicts, and the empiric data confirms, that the phenotypic gaps between largely monomorphic sexual species do not characterize the taxonomy of longstanding apomicts, where variation below the genus level is often continuous. The bias against the propagation of all forms of phenotypic novelty and non-conformity stabilizes social animals against selfish mutants, thus removing the barriers to the evolution of "group adaptations".

Adaptation, Biological↗
PubMed2002

Escherichia coli in disguise: molecular origins of Shigella.

Shigella, which still stands as a genus with four species today, in reality belongs to the extremely diverse species Escherichia coli. There are several lineages of Shigella strains derived through independent acquisition of the pINV virulence plasmid. The chromosomally determined phenotypic properties of Shigella result from convergent evolution during niche adaptation, most due to loss of function, some from negative selection pressure.

Adaptation, Biological↗
PubMed2003

The evolution of cursorial carnivores in the Tertiary: implications of elbow-joint morphology.

The evolution of cursorial adaptations in Tertiary (65-1.65 Myr ago) carnivores has been a contentious issue. Most such studies have focused on the relationship between hind limb proportions and running speed. Here, we show morphometrically that in extant carnivores, the elbow joint has evolved in two distinct directions with mutually exclusive implications for locomotor ability and prey procurement. Some carnivores retain supinatory ability, allowing them to manipulate prey and other items with the forepaws. Such carnivores can become very large. Other carnivores lose the ability to supinate and become cursors. This allows for only moderate size increase. Modern carnivores above ca. 20 kg body mass are committed to one or other of these strategies. This threshold coincides with a postulated threshold in carnivore physiology. The biaxial pattern mostly follows phylogenetic lines, but a strong selective regime can override this signal, as shown by the extant cheetah. Oligocene (33.7-23.8 Myr ago) and early-middle Miocene (23.8-11.2 Myr ago) carnivores follow the same pattern, though in the Miocene the pattern is shifted towards larger body mass, which may be owing to the extraordinary richness of browsing ungulates at this time.

Adaptation, Biological↗
PubMed1999

Habitat-specific genetic effects on growth rate and morphology across pH and water-level gradients within a population of the moss Sphagnum angustifolium (Sphagnaceae).

To study genetic adaptations in bryophytes on small ecological and spatial scales and to assess the adaptive significance of morphological trait variation, genotypes of Sphagnum angustifolium originating from habitats characterized by different pH and height above water table were clonally propagated and grown along the same gradients that exist in the field. Clones from ombrotrophic habitats grew consistently better ombrotrophically than clones from minerotrophic habitats and vice versa, suggesting that the genotypes were adapted to different pH levels. Genetic variation was found in several morphological traits, but habitat-specific genetic effects were detected only in length of spreading branches. Covariation between morphology and growth was generally environmentally induced. Positive and negative cross-environment genetic correlations suggested the presence of constraints on adaptive reaction norm evolution. The indications of small-scale genetic adaptations suggest either selective establishment of genotypes adapted to specific habitats, strong selective forces operating at the later stages of the life cycle, restricted gene flow over short distances, or a combination of these. In contrast to prevailing views, these results indicate that bryophytes are likely to respond genetically to small-scale environmental gradients.

Journal Article↗
PubMed1998

Coevolving predator and prey robots: do "arms races" arise in artificial evolution?

Coevolution (i.e., the evolution of two or more competing populations with coupled fitness) has several features that may potentially enhance the power of adaptation of artificial evolution. In particular, as discussed by Dawkins and Krebs [3], competing populations may reciprocally drive one another to increasing levels of complexity by producing an evolutionary "arms race." In this article we will investigate the role of coevolution in the context of evolutionary robotics. In particular, we will try to understand in what conditions coevolution can lead to "arms races." Moreover, we will show that in some cases artificial coevolution has a higher adaptive power than simple evolution. Finally, by analyzing the dynamics of coevolved populations, we will show that in some circumstances well-adapted individuals would be better advised to adopt simple but easily modifiable strategies suited for the current competitor strategies rather than incorporate complex and general strategies that may be effective against a wide range of opposing counter-strategies.

Biological Evolution↗
PubMed1996

Sexually antagonistic male adaptation triggered by experimental arrest of female evolution.

Each sex is part of the environment of the other sex. This may lead to perpetual coevolution between the sexes, when adaptation by one sex reduces fitness of the other. Indirect evidence comes from experiments with Drosophila melanogaster indicating that seminal fluid reduces the competitive ability of sperm from other males, thereby increasing male fitness. It also reduces a female's propensity to remate and increase her egg-laying rate. In contrast to these benefits to males, seminal fluid has substantial toxic side effects in females, with increasing quantity leading to decreasing female survival. Here I show that when female D. melanogaster are experimentally prevented from coevolving with males, males rapidly adapt to the static female phenotype. This male adaptation leads to a reduction in female survivorship, which is mediated by an increased rate of remating and increased toxicity of seminal fluid.

Adaptation, Physiological↗
PubMed2003

Causal belief and the origins of technology.

The primary function of the brain is to control movement. Human interactions with the environment, unlike those of other primates, are based on a belief in cause and effect, and this led to technology. Experiments requiring simple manipulations of the environment show that chimpanzees do not have concepts of causes or forces. Children, by contrast, have causal beliefs as a developmental primitive, and these can be demonstrated even in infants. It is proposed that the evolution of causal thinking was essential for the development of tool use, as it is not possible to make a complex tool without understanding cause and effect. This was a great evolutionary adaptive advantage. The evolution of language may have been linked to the same process. It has been technology that resulted from causal beliefs, not social interaction, that has driven human evolution.

Adaptation, Physiological↗
PubMed2005

Assessing current adaptation and phylogenetic inertia as explanations of trait evolution: the need for controlled comparisons.

The determination of whether the pattern of trait evolution observed in a comparative analysis of species data is due to adaptation to current environments, to phylogenetic inertia, or to both of these forces requires that one control for the effects of either force when making an assessment of the evolutionary role of the other. Orzack and Sober (2001) developed the method of controlled comparisons to make such assessments; their implementation of the method focussed on a discretely varying trait. Here, we show that the method of controlled comparisons can be viewed as a meta-method, which can be implemented in many ways. We discuss which recent methods for the comparative analysis of continuously distributed traits can generate controlled comparisons and can thereby be used to properly assess whether current adaptation and/or phylogenetic inertia have influenced a trait's evolution. The implementation of controlled comparisons is illustrated by an analysis of sex-ratio data for fig wasps. This analysis suggests that current adaptation and phylogenetic inertia influence this trait.

Adaptation, Biological↗
PubMed2000

The Evolution of Plasticity and Nonplastic Spatial and Temporal Adaptations in the Presence of Imperfect Environmental Cues.

A model for the evolution of plasticity is considered in which the phenotype, undergoing stabilizing selection, is modeled as a linear function of an environmental cue correlated with the phenotypic optimum, with the coefficients z0 and z1 evolving according to standard quantitative genetic theory. In contrast to previous theoretical models, as the rate of migration between demes or the rate of cyclic fluctuations in the optimum increases, the amount of plasticity [Formula: see text] at equilibrium is shown to increase gradually, in part accounting for the effect of reduced nonplastic adaptation and reaching a maximum equal to the squared correlation between the environmental cue and the phenotypic optimum. Given that information available to the organism is limited, this bias of the expressed phenotype toward the global optimum is still optimal, however, in a certain decision-theoretic sense. When genetic variation in the plastic component of the trait is small so that spatial or temporal differentiation in plasticity is small, the effect of plasticity on nonplastic adaptation is to reduce the effects of variation in the phenotypic optimum by a factor [Formula: see text] only. Information acquisition costs and joint evolution of sensory systems are discussed.

environmental cues↗
PubMed1999

Quantitative variation and selection of esterase gene amplification in Culex pipiens.

Although descriptions of evolutionary mechanisms are common in the literature, very few studies focus on the possible evolution of the adaptive genes themselves, i.e. their quantitative and qualitative changes. Evolution of insecticide resistance in Culex pipiens is a suitable model for studying such processes. In this species, organophosphorous insecticide resistance can be achieved through the overproduction of esterases that sequester the insecticide, and this overproduction can be caused by gene amplification. It is generally assumed, but never verified, that esterase activity, and therefore resistance, is monotonically related to gene amplification. We have analysed resistance, esterase activity and gene amplification in different laboratory strains and natural populations in order to detect variability and to infer effects of selection on these factors. We have shown that resistance, esterase activity and amplification covary, that insecticide selection is able to increase amplification levels, and that a fitness cost is probably attached to the amplification in laboratory strains, related to the level of amplification. The importance of variation in gene amplification level is discussed and some evolutionary implications are proposed.

Animals↗
PubMed2005

Chromosome inversions, local adaptation and speciation.

We study the evolution of inversions that capture locally adapted alleles when two populations are exchanging migrants or hybridizing. By suppressing recombination between the loci, a new inversion can spread. Neither drift nor coadaptation between the alleles (epistasis) is needed, so this local adaptation mechanism may apply to a broader range of genetic and demographic situations than alternative hypotheses that have been widely discussed. The mechanism can explain many features observed in inversion systems. It will drive an inversion to high frequency if there is no countervailing force, which could explain fixed differences observed between populations and species. An inversion can be stabilized at an intermediate frequency if it also happens to capture one or more deleterious recessive mutations, which could explain polymorphisms that are common in some species. This polymorphism can cycle in frequency with the changing selective advantage of the locally favored alleles. The mechanism can establish underdominant inversions that decrease heterokaryotype fitness by several percent if the cause of fitness loss is structural, while if the cause is genic there is no limit to the strength of underdominance that can result. The mechanism is expected to cause loci responsible for adaptive species-specific differences to map to inversions, as seen in recent QTL studies. We discuss data that support the hypothesis, review other mechanisms for inversion evolution, and suggest possible tests.

Adaptation, Physiological↗
PubMed1995

A test for adaptive change in DNA sequences controlling transcription.

Spatial and temporal differences in gene expression in early development result from the interaction of transcription factors with enhancer and silencer sequences in DNA. The evolution of the developmental process thus involves changes in the DNA sequences that bind transcription factors. Here we advocate a non-parametric statistical test-comparing levels of polymorphism and fixed substitutions between species -to look for evidence of adaptive evolution in sequences controlling gene expression. The test is illustrated by DNA sequence changes in the proximal part of the 'zebra' elements in the fushi terazu gene of the Drosophila melanogaster species group, which yield significant evidence for adaptive substitutions. (This is despite highly significant evidence that all parts of the sequence have been subject to strong selective constraint). The test can be applied generally to investigate adaptive evolution in the control of gene expression.

Animals↗