The diversity of floral forms has long been considered a prime example of radiation through natural selection. However, little is still known about the evolution of floral traits, a critical piece of evidence for the understanding of the processes that may have driven flower evolution. We studied the pattern of evolution of quantitative floral traits in a group of Neotropical lianas (Bignonieae, Bignoniaceae) and used a time-calibrated phylogeny as basis to: (1) test for phylogenetic signal in 16 continuous floral traits; (2) evaluate the rate of evolution in those traits; and (3) reconstruct the ancestral state of the individual traits. Variation in floral traits among extant species of Bignonieae was highly explained by their phylogenetic history. However, opposite signals were found in floral traits associated with the attraction of pollinators (calyx and corolla) and pollen transfer (androecium and gynoecium), suggesting a differential role of selection in different floral whorls. Phylogenetic independent contrasts indicate that traits evolved at different rates, whereas ancestral character state reconstructions indicate that the ancestral size of most flower traits was larger than the mean observed sizes of the same traits in extant species. The implications of these patterns for the reproductive biology of Bignonieae are discussed. (C) 2011 The Linnean Society of London...
In industrialised countries, mortality and morbidity are dominated by age related chronic degenerative diseases. The health and health care needs of future populations will be heavily determined by these conditions of old age. Two opposite scenarios of future morbidity exist: morbidity might decrease ("compress"), because life span is limited, and the incidence of disease is postponed. Or morbidity might increase ("expand"), because death is delayed more than disease incidence. Optimality theory in evolutionary biology explains senescence as a by product of an optimised life history. The theory clarifies how senescence is timed by the competing needs for reproduction and survival, and why this leads to a generalised deterioration of many functions at many levels. As death and disease are not independent, future morbidity will depend on duration and severity of the process of senescence, partly determined by health care, palliating the disease severity but increasing the disease duration by postponing death. Even if morbidity might be compressed, health care needs will surely expand.
Ratios often lead to biased conclusions concerning the actual relationships between examined traits and comparisons of the relative size of traits among groups. Therefore, the use of ratios has been abandoned in most comparative studies. However, ratios such as body mass index and waist-to-hip ratio are widely used in evolutionary biology and medicine. One such, the ratio of the 2nd to the 4th finger (2D : 4D), has been the subject of much recent interest in both humans and animals. Most studies agree that 2D : 4D is sexually dimorphic. In men, the 2nd digit tends to be shorter than the 4th, while in women the 2nd digit tends to be of the same size or slightly longer than the 4th. Nevertheless, here we demonstrate that the sexes do not greatly differ in the scaling between the 2nd and 4th digit. Sexual differences in 2D : 4D are mainly caused by the shift along the common allometric line with non-zero intercept, which means 2D : 4D necessarily decreases with increasing finger length, and the fact that men have longer fingers than women. We conclude that previously published results on the 2D : 4D ratio are biased by its covariation with finger length. We strongly recommend regression-based approaches for comparisons of hand shape among different groups.
The poxviruses (family Poxviridae) are a family of double-stranded viruses including several species that infect humans and their domestic animals, most notably Variola virus (VARV), the causative agent of smallpox. The evolutionary biology of these viruses poses numerous questions, for which we have only partial answers at present. Here we review evidence regarding the origin of poxviruses, the frequency of host transfer in poxvirus history, horizontal transfer of host genes to poxviruses, and the population processes accounting for patterns of nucleotide sequence polymorphism.
Distributions of mutation fitness effects from evolution experiments are available in an increasing number of species, opening the way for a vast array of applications in evolutionary biology. However, comparison of estimated distributions among studies is hampered by inconsistencies in the definitions of fitness effects and selection coefficients. In particular, the use of ratios of Malthusian growth rates as ‘relative fitnesses’ leads to wrong inference of the strength of selection. Scaling Malthusian fitness by the generation time may help overcome this shortcoming, and allow accurate comparison of selection coefficients across species. For species reproducing by binary fission (neglecting cellular death), ln2 can be used as a correction factor, but in general, the growth rate and generation time of the wild-type should be provided in studies reporting distribution of mutation fitness effects. I also discuss how density and frequency dependence of population growth affect selection and its measurement in evolution experiments.
Evolutionary biology provides an essential perspective on the determinants of health and disease, believe Peter Gluckman and Carl Bergstrom. It needs to be further integrated into medical research and teaching
Rodents are important ecological components of virtually every terrestrial ecosystem. Their success is a result of their gnawing incisors, battery of grinding molars and diastema that spatially and functionally separates the incisors from the molars. Until now these traits defined all rodents. Here, we describe a new species and genus of shrew-rat from Sulawesi Island, Indonesia that is distinguished from all other rodents by the absence of cheek teeth. Moreover, rather than gnawing incisors, this animal has bicuspid upper incisors, also unique among the more than 2200 species of rodents. Stomach contents from a single specimen suggest that the species consumes only earthworms. We posit that by specializing on soft-bodied prey, this species has had no need to process food by chewing, allowing its dentition to evolve for the sole purpose of procuring food. Thus, the removal of functional constraints, often considered a source of evolutionary innovations, may also lead to the loss of the very same traits that fuelled evolutionary diversification in the past.
Studies of the genetic basis and evolution of complex social behavior emphasize
either conserved or novel genes. To begin to reconcile these perspectives, we studied
how the evolutionary conservation of genes associated with social behavior depends on
regulatory context, and whether genes associated with social behavior exist in
distinct regulatory and evolutionary contexts. We identified modules of co-expressed
genes associated with age-based division of labor between nurses and foragers in the
ant Monomorium pharaonis, and we studied the relationship between
molecular evolution, connectivity, and expression. Highly connected and expressed
genes were more evolutionarily conserved, as expected. However, compared to the rest
of the genome, forager-upregulated genes were much more highly connected and
conserved, while nurse-upregulated genes were less connected and more evolutionarily
labile. Our results indicate that the genetic architecture of social behavior
includes both highly connected and conserved components as well as loosely connected
and evolutionarily labile components.
Flatworms number among the most diverse invertebrate phyla and represent the most biomedically significant branch of the major bilaterian clade Spiralia, but to date, deep evolutionary relationships within this group have been studied using only a single locus (the rRNA operon), leaving the origins of many key clades unclear. In this study, using a survey of genomes and transcriptomes representing all free-living flatworm orders, we provide resolution of platyhelminth interrelationships based on hundreds of nuclear protein-coding genes, exploring phylogenetic signal through concatenation as well as recently developed consensus approaches. These analyses robustly support a modern hypothesis of flatworm phylogeny, one which emphasizes the primacy of the often-overlooked ‘microturbellarian’ groups in understanding the major evolutionary transitions within Platyhelminthes: perhaps most notably, we propose a novel scenario for the interrelationships between free-living and vertebrate-parasitic flatworms, providing new opportunities to shed light on the origins and biological consequences of parasitism in these iconic invertebrates.
Historically, conceptualizations of symbiosis and endosymbiosis have been pitted against Darwinian or neo-Darwinian evolutionary theory. In more recent times, Lynn Margulis has argued vigorously along these lines. However, there are only shallow grounds for finding Darwinian concepts or population genetic theory incompatible with endosymbiosis. But is population genetics sufficiently explanatory of endosymbiosis and its role in evolution? Population genetics “follows” genes, is replication-centric, and is concerned with vertically consistent genetic lineages. It may also have explanatory limitations with regard to macroevolution. Even so, asking whether population genetics explains endosymbiosis may have the question the wrong way around. We should instead be asking how explanatory of evolution endosymbiosis is, and exactly which features of evolution it might be explaining. This paper will discuss how metabolic innovations associated with endosymbioses can drive evolution and thus provide an explanatory account of important episodes in the history of life. Metabolic explanations are both proximate and ultimate, in the same way genetic explanations are. Endosymbioses, therefore, point evolutionary biology toward an important dimension of evolutionary explanation.
Given two mutants, A and B, separated by n mutational steps, what is the evolutionary trajectory which allows a homogeneous population of A to reach B in the shortest time? We show that the optimum evolutionary trajectory (fitness landscape) has the property that the relative fitness increase between any two consecutive steps is constant. Hence, the optimum fitness landscape between A and B is given by an exponential function. Our result is precise for small mutation rates and excluding back mutations. We discuss deviations for large mutation rates and including back mutations. For very large mutation rates, the optimum fitness landscape is flat and has a single peak at type B.; Mathematics; Organismic and Evolutionary Biology
Recently, the frequency-dependent Moran process has been introduced in order to describe evolutionary game dynamics in finite populations. Here, an alternative to this process is investigated that is based on pairwise comparison between two individuals. We follow a long tradition in the physics community and introduce a temperature (of selection) to account for stochastic effects. We calculate the fixation probabilities and fixation times for any symmetric 2×2 game, for any intensity of selection and any initial number of mutants. The temperature can be used to gauge continuously from neutral drift to the extreme selection intensity known as imitation dynamics. For some payoff matrices the distribution of fixation times can become so broad that the average value is no longer very meaningful.; Mathematics; Organismic and Evolutionary Biology
Understanding the molecular details of the sequence of events in multistep evolutionary pathways can reveal the extent to which natural selection exploits regulatory mutations affecting expression, amino acid replacements affecting the active site, amino acid replacements affecting protein folding or stability, or variations affecting gene copy number. In experimentally exploring the adaptive landscape of the evolution of resistance to β-lactam antibiotics in enteric bacteria, we noted that a regulatory mutation that increases β-lactamase expression by about 2-fold has a very strong tendency to be fixed at or near the end of the evolutionary pathway. This pattern contrasts with previous experiments selecting for the utilization of novel substrates, in which regulatory mutations that increase expression are often fixed early in the process. To understand the basis of the difference, we carried out experiments in which the expression of β-lactamase was under the control of a tunable arabinose promoter. We find that the fitness effect of an increase in gene expression is highly dependent on the catalytic activity of the coding sequence. An increase in expression of an inefficient enzyme has a negligible effect on drug resistance; however...
All mammals thus far studied sleep, yet important questions remain concerning the ecological factors that influence sleep patterns. Here, we developed an evolutionary individual-based model to investigate the effect of predation pressure on prey sleep. We investigated three ecological conditions, including one that assumed a dynamic interaction between predator and prey behaviour. In condition 1, we found that monophasic predators (i.e. with one sleep bout per 24 h) select for monophasic prey that sleep perfectly out of phase with predators. In condition 2, predators were monophasic but the safety of prey varied as a function of their activity (sleeping versus awake). In this condition, the prey adjusted their sleeping behaviour to lower the risk of predation. Finally, in condition 3, we modelled a more dynamic interaction between predator and prey, with predator activity dependent on prey activity in the previous hour. In this scenario, the prey adjusted their behaviour relative to one another, resulting in either greater or lesser synchrony in prey as a function of predator searching behaviour. Collectively, our model demonstrates that predator behaviour can have a strong influence on prey sleep patterns, including whether prey are monophasic or polyphasic (i.e. with many sleep bouts per 24 h). The model further suggests that the timing of sleep relative to predator behaviour may depend strongly on how other potential prey partition the activity period.; Human Evolutionary Biology
Studies of the genetic basis and evolution of complex social behavior emphasize either conserved or novel genes. To begin to reconcile these perspectives, we studied how the evolutionary conservation of genes associated with social behavior depends on regulatory context, and whether genes associated with social behavior exist in distinct regulatory and evolutionary contexts. We identified modules of co-expressed genes associated with age-based division of labor between nurses and foragers in the ant Monomorium pharaonis, and we studied the relationship between molecular evolution, connectivity, and expression. Highly connected and expressed genes were more evolutionarily conserved, as expected. However, compared to the rest of the genome, forager-upregulated genes were much more highly connected and conserved, while nurse-upregulated genes were less connected and more evolutionarily labile. Our results indicate that the genetic architecture of social behavior includes both highly connected and conserved components as well as loosely connected and evolutionarily labile components.; It was funded by University of Pennsylvania with grant name: University Research Foundation
Background: Standard epidemiological theory claims that in structured populations competition between multiple pathogen strains is a deterministic process which is mediated by the basic reproduction number (R0) of the individual strains. A new theory based on analysis, simulation and empirical study challenges this predictor of success. Principal Findings: We show that the quantity is a valid predictor in structured populations only when size is infinite. In this article we show that when population size is finite the dynamics of infection by multi-strain pathogens is a stochastic process whose outcome can be predicted by evolutionary entropy, S, an information theoretic measure which describes the uncertainty in the infectious age of an infected parent of a randomly chosen new infective. Evolutionary entropy characterises the demographic stability or robustness of the population of infectives. This statistical parameter determines the duration of infection and thus provides a quantitative index of the pathogenicity of a strain. Standard epidemiological theory based on as a measure of selective advantage is the limit as the population size tends to infinity of the entropic selection theory. The standard model is an approximation to the entropic selection theory whose validity increases with population size. Conclusion: An epidemiological analysis based on entropy is shown to explain empirical observations regarding the emergence of less pathogenic strains of human influenza during the antigenic drift phase. Furthermore...
Designing a photometric system to best fulfil a set of scientific goals is a
complex task, demanding a compromise between conflicting requirements and
subject to various constraints. A specific example is the determination of
stellar astrophysical parameters (APs) - effective temperature, metallicity
etc. - across a wide range of stellar types. I present a novel approach to this
problem which makes minimal assumptions about the required filter system. By
considering a filter system as a set of free parameters it may be designed by
optimizing some figure-of-merit (FoM) with respect to these parameters. In the
example considered, the FoM is a measure of how well the filter system can
`separate' stars with different APs. This separation is vectorial in nature, in
the sense that the local directions of AP variance are preferably mutually
orthogonal to avoid AP degeneracy. The optimization is carried out with an
evolutionary algorithm, which uses principles of evolutionary biology to search
the parameter space. This model, HFD (Heuristic Filter Design), is applied to
the design of photometric systems for the Gaia space astrometry mission. The
optimized systems show a number of interesting features, not least the
persistence of broad, overlapping filters. These HFD systems perform as least
as well as other proposed systems for Gaia...
Phylogenetic analysis of AhR pathway genes and their evolutionary rate variations were studied on aquatic animals. The gene sequences for the proteins involved in this pathway were obtained from major phylogenetic groups of mollusc, amphibian, fish and aquatic mammal. These genes were distributed under four major steps of toxicology regulation: formation of cytosolic complex, translocation of AhR, heterodimerization of AhR and induction of CYP1A. The NJ, MP and ML algorithm were used on protein coding DNA sequences to deduce the evolutionary relationship for the respective AhR pathway gene among different aquatic animals. The rate of nonsynonymous nucleotide substitutions per nonsynonymous site (d~N~) and synonymous nucleotide substitutions per synonymous site (d~S~) were calculated for different clade of the respective phylogenetic tree for each AhR pathway gene. The phylogenetic analysis suggests that evolutionary pattern of AhR pathway genes in aquatic animals is characterized mainly by gene duplication events. The d~N~ values indicate that AhR pathway genes are well conserved in aquatic animals, except for CYP1A gene. Furthermore, the d~N~ value indicates that AhR pathway genes are less conserved in fish than in any other aquatic animals...
Alignment of DNA and protein sequences is a basic tool in the study of evolutionary, structural and functional relationship among macromolecules. Present sequence alignment methods are somewhat error-prone, often producing systematic bias. Errors in sequence alignments sometimes lead to subsequent misinterpretation of evolutionary, structural and functional information in genes, proteins and genomes. In traditional sequence alignment algorithms, alignments of DNA and protein sequences are conducted separately. It has been long believed that the phylogenetic signal disappears more rapidly from DNA sequences than from encoded proteins. It is therefore generally preferable to align sequences at the amino acid level. Here we present a new method—DNA^+Pro^, which aggregates DNA and protein sequences into combined DNA-protein sequences and align them in a combined fashion. We demonstrate that combining sequences improve the quality of multiple sequence alignment and solve practical evolutionary problems in primate immunodeficiency virus proteins and bacterial restriction enzymes. In addition to increased theoretical information contents, the distance estimations are more biological significant in combined alignment than in protein only or DNA only alignments. By integrating information buried separately in DNA and protein sequences...
I consider the problem of evolutionary branching in adaptive dynamics without applying the limits of separation of timescales between ecological and evolutionary processes. I derive expressions for the waiting time for a branching event to occur and survive in terms of both ecological and evolutionary parameters, and show how demographic stochasticity alone can result in the frequent failure of adaptive branching.