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PubMed2003

The evolution of population stability as a by-product of life-history evolution.

Proposed mechanisms for the evolution of population stability include group selection through longterm persistence, individual selection acting directly on stability determining the demographic parameters, and the evolution of stability as a by-product of life-history evolution. None of these hypotheses currently has clear empirical support. Using two sets of Drosophila melanogaster populations, we provide experimental evidence of stability evolving as a correlated response to selection on traits not directly related to demography. Four populations (FEJs) were selected for faster development and early reproduction for 125 generations, and the other four (JBs) were ancestral controls. All FEJ and JB populations have been maintained on discrete generations at moderate density, thus eliminating differential selection on stability determining demographic parameters. We derived eight small populations from each FEJ and JB population, and subjected four small populations each to either stabilizing or destabilizing food regimes. Census data on these 64 small populations over 20 generations clearly showed that the FEJ populations have significantly less temporal fluctuations in their numbers in both food regimes compared to their controls. This greater stability of the FEJ populations is probably a by-product of the evolution of reduced fecundity and pre-adult survivorship, as a correlated response to selection for rapid development.

Animals↗
PubMed2003

Time scale of eutherian evolution estimated without assuming a constant rate of molecular evolution.

Controversies over the molecular clock hypothesis were reviewed. Since it is evident that the molecular clock does not hold in an exact sense, accounting for evolution of the rate of molecular evolution is a prerequisite when estimating divergence times with molecular sequences. Recently proposed statistical methods that account for this rate variation are overviewed and one of these procedures is applied to the mitochondrial protein sequences and to the nuclear gene sequences from many mammalian species in order to estimate the time scale of eutherian evolution. This Bayesian method not only takes account of the variation of molecular evolutionary rate among lineages and among genes, but it also incorporates fossil evidence via constraints on node times. With denser taxonomic sampling and a more realistic model of molecular evolution, this Bayesian approach is expected to increase the accuracy of divergence time estimates.

Animals↗
PubMed1994

Embryonic growth and the evolution of the mammalian Y chromosome. II. Suppression of selfish Y-linked growth factors may explain escape from X-inactivation and rapid evolution of Sry.

The mammalian Y chromosome may be an attractor for selfish growth factors. A suppressor of the selfish growth effects would be expected to spread were it to have an appropriate parent-specific expression rule. A suppressor could act by boosting the resource demands of competing female embryos. This possibility may explain incidences of the escape from X-inactivation and provides a rationale for why these genes typically have Y-linked homologues. Alternatively, a suppressor could act to decrease the resource demands of males with the selfish Y. This possibility is supported by the finding that the size of male, but not female, human infants is negatively correlated to the number of X chromosomes. A protracted arms race between a selfish gene and its suppressor may ensue. Both the variation in copy number of Zfy and the unusually fast sequence evolution of Sry may be explained by such an arms race. As required by the model, human Sry is known to have an X-linked suppressor. Preliminary evidence suggests that, as predicted, rapid sequence evolution of Sry may be correlated with female promiscuity. The case for fast sequence evolution as the product of maternal/foetal conflict is strengthened by consideration of the rapid evolution of placental lactogens in both ruminants and rodents.

Animals↗
PubMed2005

The evolution of generalization? Parasitoid flies and the perils of inferring host range evolution from phylogenies.

It is widely assumed that high resource specificity predisposes lineages toward greater likelihood of extinction and lower likelihood of diversification than more generalized lineages. This suggests that host range evolution in parasitic organisms should proceed from generalist to specialist, and specialist lineages should be found at the 'tips' of phylogenies. To test these hypotheses, parsimony and maximum likelihood methods were used to reconstruct the evolution of host range on a phylogeny of parasitoid flies in the family Tachinidae. In contrast to predictions, most reconstructions indicated that generalists were repeatedly derived from specialist lineages and tended to occupy terminal branches of the phylogeny. These results are critically examined with respect to hypotheses concerning the evolution of specialization, the inherent difficulties in inferring host ranges, our knowledge of tachinid-host associations, and the methodological problems associated with ancestral character state reconstruction. Both parsimony and likelihood reconstructions are shown to provide misleading results and it is argued that independent evidence, in addition to phylogenetic trees, is needed to inform models of the evolution of host range and the evolutionary consequences of specialization.

Adaptation, Biological↗
PubMedDate not supplied

[Evolution of adolescent fertility and its association with evolution of income in the Spanish provinces during the period 1975-1985].

BACKGROUND: Fertility rates in women under 21, during the period 1975-1985 in Spain, have analyzed, as well as their association with the evolution of the socioeconomic indicators in order to study the distribution and associated factors to adolescent maternity in our environment. METHODS: The fertility rates have been elaborated from the Official Demographic Statistics. The socioeconomic indicators have been obtained from the Statistics Year Book of the National Institute of Statistics and from other complementary sources. The method of weighted linear regression has been used to analyze the association between the indicators and the rates at the provincial level. RESULTS: The fertility rates have decreased a 16% in mothers from 15 to 19 years old in Spain, between 1975 and 1985. The highest accumulated rates belong to the Communities of Canarias (42.8 births by 1000 women of 15 to 19, Galicia (38.1) Murcia (33.7) and Andalucía (30.3). In the regression analysis, the income evolution shows an association with the fertility evolution in the group from 15 to 19 years old, and this association remains when we take into account unemployment, index of provincial development and birth rate, which allows to explain a 49% of the variance. Fertility of adolescent under 15 is only associated with the income evolution, with a determination coefficient of 0.29. CONCLUSIONS: Results indicate that early maternity has decreased in Spain, although there are geographical differences, which cam, in some measure, be related with social-economic factors.

Adolescent↗
PubMed2002

Predicting evolutionary potential: in vitro evolution accurately reproduces natural evolution of the tem beta-lactamase.

To evaluate the validity of our in vitro evolution method as a model for natural evolutionary processes, the TEM-1 beta-lactamase gene was evolved in vitro and was selected for increased resistance to cefotaxime, cefuroxime, ceftazadime, and aztreonam, i.e., the "extended-spectrum" phenotype. The amino acid substitutions recovered in 10 independent in vitro evolvants were compared with the amino acid substitutions in the naturally occurring extended-spectrum TEM alleles. Of the nine substitutions that have arisen multiple times in naturally occurring extended-spectrum TEM alleles, seven were recovered multiple times in vitro. We take this result as evidence that our in vitro evolution technique accurately mimics natural evolution and can therefore be used to predict the results of natural evolutionary processes. Additionally, our results predict that a phenotype not yet observed among TEM beta-lactamases in nature-resistance to cefepime-is likely to arise in nature.

Anti-Bacterial Agents↗
PubMed2005

In vitro evolution and characterization of a ligase ribozyme adapted to acidic conditions: effect of further rounds of evolution.

A ligase ribozyme that accelerates the ligation reaction with an oligonucleotide under low pH conditions was identified by in vitro adaptation in a previous study. We examined the effects of further rounds of evolution to isolate a more active ribozyme. The ribozyme, which was obtained after four rounds of evolution, was randomly mutated, and the resultant RNA library was subjected to in vitro selection at low pH. One ribozyme isolated from the pool was found to react 8,000 times faster than the original b1 ribozyme at pH 4. The reaction rate of the isolated ribozyme was enhanced at various pH values, and its pH dependence was less than that of the original ribozyme or the ribozyme selected with four rounds of evolution. The reaction rate of the isolated ribozyme was reduced in the presence of 3' primer, the sequence of which is complementary to the 3' primer-binding site of the ligase ribozyme. This inhibition induced by the primer oligonucleotide binding to the ribozyme 3' region implies that the 3' region plays a role in the ligation reaction of the ribozyme.

Amino Acid Sequence↗
PubMed1993

Punctuated equilibria or gradual evolution: fluctuating asymmetry and variation in the rate of evolution.

The debate on long-term rates of evolution is polarized around two models: the punctuated equilibrium hypothesis (long periods of very little evolution interrupted by periods of relatively rapid evolutionary change) and the gradual view (the rate of evolution is gradual, albeit with variable rate). Here we suggest that the pace of evolutionary change can be independently determined by estimating the degree of trait asymmetry. Fluctuating asymmetry occurs as a result of random deviations in the development of bilaterally symmetric traits. The degree of fluctuating asymmetry closely reflects the ability of individuals to cope with stress. Traits subject to strong directional selection become less developmentally canalized and more susceptible to the influence of stress. Strong stabilizing selection has the opposite effect. Characters of individuals from periods of rapid evolutionary change should hence be characterized by high variability, high fluctuating asymmetry and fluctuating asymmetry should increase with trait size in the direction of selection. In contrast, characters of individuals from periods of little evolutionary change should demonstrate low variability, low asymmetry and a flat or U-shaped relationship between size and asymmetry.

Animals↗
PubMed1977

Method for the determination of protein evolution rates by amino acid composition. Evolution rate of actins.

A method has been developed to determine the actin evolution rate. The method is based on amino acid compositon. The actin evolution rate has been established to be extremely low. Only three or less amino acid changes per hundred amino acid residues have accumulated for a 100 million years. One can explain the conservative nature of actin evolution as a sequence of its unique tightly fitted structure rich in biologically active centres at short distances from each other. The peculiar invariability of polar amino acids leads to a conclusion that some given distribution of charges is necessary for the unique functioning of actin molecules.

Actins↗
PubMedDate not supplied

Evolution of oxygen by plants in relation to biosphere evolution.

The process of water decomposition by plants is discussed in connection with biosphere evolution. This process consists of two parts: water oxidation and oxygen evolution. The origin of the water oxidation process took place after the synthesis of chlorine-type pigments, the structure of which corresponds to a more oxidized state than the bacteriochlorophyll type. The ability of plants to evolve oxygen is the result of a long evolution process. The capability of decomposing water in the lung wave length spectral region by algae and higher plants, which can be only seen under anaerobic conditions was discovered. This mechanism was suggested to be a reflection of a relict form of plant apparatus having operated under ancient, strictly anaerobic, conditions.

Biological Evolution↗
PubMed1995

Speculations on the evolution of the genetic code IV. The evolution of the aminoacyl-tRNA synthetases.

An evolutionary scheme is postulated in which a primitive code, involving only guanine and cytosine, would code for glycine(GG.), alanine(GC.), arginine(CG.) and proline(CC.). There evolves from this primitive code families of related amino acids as the code expands. The evolution of the aminoacyl-tRNA synthetases are considered to be indicators for the evolution of the genetic code. The postulated model for the evolution of the genetic code is used to give an evolutionary interpretation to the recent work on the structure and sequences of the aminoacyl-tRNA synthetases.

Amino Acid Sequence↗
PubMed1990

Evolution of collagen IV genes from a 54-base pair exon: a role for introns in gene evolution.

The exon structure of the collagen IV gene provides a striking example for collagen evolution and the role of introns in gene evolution. Collagen IV, a major component of basement membranes, differs from the fibrillar collagens in that it contains numerous interruptions in the triple helical Gly-X-Y repeat domain. We have characterized all 47 exons in the mouse alpha 2(IV) collagen gene and find two 36-, two 45-, and one 54-bp exons as well as one 99- and three 108-bp exons encoding the Gly-X-Y repeat sequence. All these exons sizes are also found in the fibrillar collagen genes. Strikingly, of the 24 interruption sequences present in the alpha 2-chain of mouse collagen IV, 11 are encoded at the exon/intron borders of the gene, part of one interruption sequence is encoded by an exon of its own, and the remaining interruptions are encoded within the body of exons. In such "fusion exons" the Gly-X-Y encoding domain is also derived from 36-, 45-, or 54-bp sequence elements. These data support the idea that collagen IV genes evolved from a primordial 54-bp coding unit. We furthermore interpret these data to suggest that the interruption sequences in collagen IV may have evolved from introns, presumably by inactivation of splice site signals, following which intronic sequences could have been recruited into exons. We speculated that this mechanism could provide a role for introns in gene evolution in general.

Amino Acid Sequence↗
PubMed1996

Evolution of disintegrin cysteine-rich and mammalian matrix-degrading metalloproteinases: gene duplication and divergence of a common ancestor rather than convergent evolution.

The evolution of the Metalloproteinase Disintegrin Cysteine-rich (MDC) gene family and that of the mammalian Matrix-degrading Metalloproteinases (MMPs) are compared. The alignment of snake venom and mammalian MDC and MMP precursor sequences generated a phylogenetic tree that grouped these proteins mainly according to their function. Based on this observation, a common ancestry is suggested for mammalian and snake venom MDCs; it is also possible that gene duplication of the already-assembled domain structure, followed by divergence of the copies, may have significantly contributed to the evolution of the functionally diverse MDC proteins. The data also suggest that the structural resemblance of the zinc-binding motif of venom MDCs and MMPs may best be explained by common ancestry and conservation of the proteolytic motifs during the divergence of the proteins rather than through convergent evolution.

Amino Acid Sequence↗
PubMedDate not supplied

Exobiology, the study of the origin, evolution and distribution of life within the context of cosmic evolution: a review.

The primary goal of exobiological research is to reach a better understanding of the processes leading to the origin, evolution and distribution of life on Earth or elsewhere in the universe. In this endeavour, scientists from a wide variety of disciplines are involved, such as astronomy, planetary research, organic chemistry, palaeontology and the various subdisciplines of biology including microbial ecology and molecular biology. Space technology plays an important part by offering the opportunity for exploring our solar system, for collecting extraterrestrial samples, and for utilizing the peculiar environment of space as a tool. Exobiological activities include comparison of the overall pattern of chemical evolution of potential precursors of life, in the interstellar medium, and on the planets and small bodies of our solar system; tracing the history of life on Earth back to its roots; deciphering the environments of the planets in our solar system and of their satellites, throughout their history, with regard to their habitability; searching for other planetary systems in our Galaxy and for signals of extraterrestrial civilizations; testing the impact of space environment on survivability of resistant life forms. This evolutionary approach towards understanding the phenomenon of life in the context of cosmic evolution may eventually contribute to a better understanding of the processes regulating the interactions of life with its environment on Earth.

Astronomical Phenomena↗
PubMed2005

Recasting developmental evolution in terms of genetic pathway and network evolution ... and the implications for comparative biology.

The morphological features of complex organisms are the outcomes of developmental processes. Developmental processes, in turn, reflect the genetic networks that underlie them. Differences in morphology must ultimately, therefore, reflect differences in the underlying genetic networks. A mutation that affects a developmental process does so by affecting either a gene whose product acts as an upstream controlling element, an intermediary connecting link, or as a downstream output of the network that governs the trait's development. Although the immense diversity of gene networks in the animal and plant kingdoms would seem to preclude any general "rules" of network evolution, the material discussed here suggests that the patterns of genetic pathway and network evolution actually fall into a number of discrete modes. The potential utility of this conceptual framework in reconstructing instances of developmental evolution and for comparative neurobiology will be discussed.

Animals↗
PubMed2004

Mutual benefit can promote the evolution of preferential interactions and in this way can lead to the evolution of true altruism.

We analyse the evolution of the assortment of encounters through active choice of companions among individuals that interact cooperatively in a situation of mutual benefit. Using a simple mathematical model, we show that mutual benefit can favour the evolution of a preference to interact with individuals that are similar to themselves with respect to an arbitrary tag even when both the preference and the tag depend on two independent and unlinked genes. Two necessary requisites to obtain this result are: (i) a small population or a large subdivided metapulation and (ii) an asymmetry between partners in such a way that one of them (donor) proposes the cooperation and elects the partner, whereas the other (receiver) never rejects the offer. We also show that mutual benefit can be the starting point for the evolution of altruistic behaviours as long as there are preferential interactions. This requires that the tag used in the election of partners is the altruistic or selfish behaviour itself.

Alleles↗
PubMed2003

The evolution of the cortico-cerebellar complex in primates: anatomical connections predict patterns of correlated evolution.

Investigations into the evolution of the primate brain have tended to neglect the role of connectivity in determining which brain structures have changed in size, focusing instead on changes in the size of the whole brain or of individual brain structures, such as the neocortex, in isolation. We show that the primate cerebellum, neocortex, vestibular nuclei and relays between them exhibit correlated volumetric evolution, even after removing the effects of change in other structures. The patterns of correlated evolution among individual nuclei correspond to their known patterns of connectivity. These results support the idea that the brain evolved by mosaic size change in arrays of functionally connected structures. Furthermore, they suggest that the much discussed expansion of the primate neocortex should be re-evaluated in the light of conjoint cerebellar expansion.

Anatomy, Comparative↗
PubMed1997

Molecular evolution of the second ancient human mariner transposon, Hsmar2, illustrates patterns of neutral evolution in the human genome lineage.

A consensus sequence for the second ancient mariner identified in the human genome, Hsmar2, was constructed by majority rule from full-length and partial sequences of 44 of the +/-1000 copies in the genome. This 1300 base pair (bp) consensus has 31 bp imperfect terminal repeats (ITRs) and encodes a 351 amino acid (aa) mariner transposase. The sequence of this transposase has allowed classification of Hsmar2 as a basal lineage of the irritans subfamily of mariners, sharing at most 38% aa identity with other members of the subfamily. The individual copies in the human genome are all highly mutated from the consensus, having suffered numerous small and some large insertions and deletions (indels), including many insertions of S and J subfamily Alu elements. The copies differ, on average, from the consensus by 11.6%, have suffered 11.8 indels per kilobase (kb), and only 3.7% of the 30 hypermutable CpG dinucleotide pairs in the consensus remain intact. This level of divergence indicates that the ancestrally active Hsmar2 element represented by the consensus was present in the human genome lineage about 80 million years (Myr) ago. Each copy has apparently evolved since then largely independently of the others, and with little constraint on its transposase coding capacity. This pattern of molecular evolution fits the current model for mariner transposon evolution. These copies provide multiple independent datasets for evaluating the pattern of neutral evolution in the human genome, for example, they confirm that most indels are very short and that deletions are twice as common as insertions.

Amino Acid Sequence↗