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PubMed1984

Molecular evolution in Drosophila and the higher Diptera II. A time scale for fly evolution.

In this paper, we examine first the steadiness of the rate of evolutionary change in a larval hemolymph protein, LHP, in numerous Drosophila species. We estimated amino acid sequence divergence from immunological distances measured with the quantitative microcomplement fixation technique. Using tests not depending on knowledge of absolute times of divergence, we estimated the variance of the rate of evolutionary change to be at least 4 times as large as that for a process resembling radioactive decay. Thus, the rate of evolution of this protein is as uniform as that of vertebrate proteins. Our analysis indicates no acceleration of protein evolution in the lineages leading to Hawaiian drosophilines. Second, we give an explicit description of a procedure for calculating the absolute value of the mean rate of evolutionary change in this protein. This procedure is suggested for general use in calculating absolute rates of molecular evolution. The mean rate of evolution of LHP is about 1.2 immunological distance units per million years, which probably corresponds to a unit evolutionary period of 4 million years; LHP thus evolves at a rate comparable to that of mammalian hemoglobins. Finally, we utilize the calibrated rate of LHP evolution to derive a time scale of evolution in the Drosophilidae and higher Diptera.

Animals↗
PubMed2006

Phylogeny of parasitiform mites (Acari) based on rRNA.

Acari (mites and ticks) form one the most diverse lineages of arthropods, but basal relationships in the group are still poorly understood. The current study addresses this issue for one of its two main lineages, the order Parasitiformes. Relationships are examined at the subordinal and infraordinal level using complete 18S and partial 28S nuclear rRNA sequence data. Most currently recognized lineages are recovered with good support, suggesting that nuclear rRNA, and specifically 18S rRNA, is very well suited for analyzing relationships at this level in this lineage. These results were found despite quite variable rates of sequence evolution, with rates "ratcheting up" from relatively low in most non-mite arachnid lineages, to intermediate in Pseudoscorpiones, the mite order Acariformes, and the parasitiform suborders Opilioacarida, Holothyrida, and Ixodida, to high in the parasitiform suborder Mesostigmata. The most species rich mesostigmatid infraorder, Dermanyssina, shows huge distances to the outgroups, but remarkably low within-group divergence in nuclear rRNA. This suggests the possibility of a relatively recent origin of this lineage.

Acari↗
PubMed1992

Statistical properties of bootstrap estimation of phylogenetic variability from nucleotide sequences: II. Four taxa without a molecular clock.

The statistical properties of sample estimation and bootstrap estimation of phylogenetic variability from a sample of nucleotide sequences were studied by considering model trees of three taxa with an outgroup. The cases of constant and varying rates of nucleotide substitution were compared. From sequences obtained by simulation, phylogenetic trees were constructed by using the maximum parsimony (MP) and neighbor-joining (NJ) methods. The effectiveness and consistency of the MP method were studied in terms of proportions of informative sites. The results of simulation showed that bootstrap estimation of the confidence level for an inferred phylogeny can be used even under unequal rates of evolution if the rate differences are not large so that the MP method is not misleading. The condition under which the MP method becomes misleading (inconsistent) is more stringent for slowly evolving sequences than for rapidly evolving ones, and it also depends on the length of the internal branch. If the rate differences are large so that the MP method becomes consistently misleading, then bootstrap estimation will reinforce an erroneous conclusion on topology. Similar conclusions apply to the NJ method with uncorrected distances. The NJ method with corrected distances performs poorly when the sequence length is short but can avoid the inconsistency problem if the sequence length is long and if the distances can be estimated accurately.

Base Sequence↗
PubMed1984

Dissimilar rates in molecular evolution.

In this work we present an evolutionary tree based on the differences in the physico-chemical properties involved in amino acid substitutions, instead of considering, for its construction, only the number of changes between species. Phylogenetic trees were constructed from the differences in bulkiness, refractivity index, hydrophobicity, polarity and optical rotation of 9 vertebrate calcitonins. A correlation of the form y = a xb was found between the number of changes (x) and the differences in any given physico-chemical property (y). This correlation implies that the evolutionary time can not be evaluated directly from the number of changes between species.

Amino Acid Sequence↗
PubMed2003

Evolution of heart rate control after transplantation: conduction versus autonomic innervation.

In cardiac transplantation, the donor organ is not initially innervated and demonstrates decreased heart rate variability (HRV). However, HRV may improve after several months. The mechanism for HRV improvement has not been elucidated; autonomic "reinnervation" of the donor heart has been proposed. The role of atrioatrial conduction from recipient to donor organ has not been evaluated. We prospectively evaluated cardiac transplant patients with a limited electrophysiology study at the time of their surveillance biopsies. Recordings were made of recipient and donor signals, observing conduction properties between recipient and donor atria. Holter recordings were analyzed and HRV was determined using spectral analysis techniques, recording mean RR interval, low-frequency power (LF), high-frequency power (HF), and the LF/HF ratio. These were compared to published norms. From November 1999 to May 2000, 21 patients (6 female) who underwent cardiac transplantation participated at a median age of 101 months (range, 4.1-217 months). Time posttransplant ranged from 26 days to 71 months. Holter data were available for 20 patients and demonstrated dissociated P waves in 13 (65%). The mean heart rate on Holter was 111 beats per minute (bpm) (range, 85-161 bpm). We were able to record distinct recipient atrial signals in 16 of 21 (76%) patients. The average recipient tissue heart rate was 55% that of the donor heart rate. We documented atrioatrial association in only 1 patient. HRV did not reach normal values for most patients and did not increase with time posttransplantation. The LF values were in the normal range for most patients, whereas 3 patients had normal HF values and 2 patients had values just below normal. Recipients of heart transplantation have a predominantly sympathetic influence of HRV. These preliminary data suggest that atrioatrial conduction does not play a role in reestablishing normal heart rate control following pediatric cardiac transplantation.

Adolescent↗
PubMed1991

Evolution of heart rate responsiveness after orthotopic cardiac transplantation.

Although anatomic reinnervation of the donor heart is unlikely after transplantation, individual subjects have been noted to show near physiologic heart rate (HR) responses to exercise. To assess development of this phenomenon, we studied HR changes in response to orthostasis and treadmill exercise in 52 orthotopic cardiac transplant recipients grouped according to time after transplantation. In group 1 (2.0 +/- 0.9 months), no significant increase in HR was seen up to 100 cardiac cycles after standing. A maximal acceleration of 4.0 +/- 3.8 beats was seen within 100 cardiac cycles after standing in group 2 (15.8 +/- 5.6 months). Patients in group 3 (42.4 +/- 12.4 months) showed significant cardioacceleration by 5 cardiac cycles after standing to a maximum of 10.7 +/- 5.8 beats/min within the first 100 cardiac cycles. During exercise, HR increased more rapidly during the first minute in group 3 compared with group 1 (p less than 0.01). After exercise, HR continued to increase in group 1 but decreased rapidly in the other groups, most notably group 3 (-26.5 +/- 16.5 by 2 minutes, p less than 0.0001 vs groups 1 and 2). These data indicate development of functional reinnervation after orthotopic heart transplantation. The phenomenon of early acceleration of the HR after orthostasis and rapid deceleration after exercise in transplant recipients implies a local cardiac mechanism rather than response to circulating catecholamines.

Adolescent↗
PubMed2006

The genomic rate of adaptive evolution.

The role of positive darwinian selection in evolution at the molecular level has been keenly debated for many years, with little resolution. However, a recent increase in DNA sequence data and the development of new methods of analysis have finally made this question tractable. Here, I review the current state-of-play of the field. Initial estimates in Drosophila suggest that approximately 50% of all amino acid substitutions, and a substantial fraction of substitutions in non-coding DNA, have been fixed as a consequence of adaptive evolution. Estimates in microorganisms are even higher. By contrast, there is little evidence of widespread adaptive evolution in our own species.

Adaptation, Physiological↗
PubMed2004

Mitochondrial DNA phylogeny and rates of larval evolution in Macrophiothrix brittlestars.

Phylogenetic analysis has led to significant insights into the evolution of early life-history stages of marine invertebrates. Although echinoderms have been a major focus, developmental and phylogenetic information are relatively poor for ophiuroids, the most species-rich echinoderm class. We used DNA sequences from two mitochondrial genes to develop a phylogenetic hypothesis for 14 brittlestar species in the genus Macrophiothrix (Family Ophiotrichidae). Species are similar in adult form and ecology, but have diverse egg sizes and modes of larval development. In particular, two species have rare larval forms with characteristics that are intermediate between more common modes of feeding and non-feeding development. We use the phylogeny to address whether intermediate larval forms are rare because the evolution of a simplified morphology is rapid once food is no longer required for development. In support of this hypothesis, branch lengths for intermediate forms were short relative to those for species with highly derived non-feeding forms. The absolute rarity of such forms makes robust tests of the hypothesis difficult.

Animals↗
PubMed1999

Enhanced ornithine decarboxylase activity is associated with attenuated rate of damage evolution and reduction of infarct volume in transient middle cerebral artery occlusion in the rat.

Ornithine decarboxylase (ODC) transgenic and alpha-difluoromethyl ornithine (DFMO)-treated rats were exposed to transient middle cerebral occlusion (MCAO) to examine the role of intraischaemic ODC-activity on the evolution of ischaemia-reperfusion damage. Magnetic resonance imaging (MRI) data show that the damage develops slower in ODC transgenic than in DFMO-treated rats, which is not caused by a difference in perfusion. Furthermore, infarct volumes are smaller in the former animals one day later. These data support the idea of endogenous neuroprotective action of ODC.

Animals↗
PubMed1999

Messages from mortality: the evolution of death rates in the old.

Ageing is an increase in mortality and/or decline in fertility with advancing age. Evolutionary theories predict that ageing will evolve in response to the pattern of externally imposed hazards to survival and fertility; a prediction confirmed in new empirical studies. Recent studies of large cohorts of experimental animals and of humans have revealed that mortality rates do not continue to accelerate at very advanced ages. It has been suggested that evolutionary theories cannot account for these mortality patterns; however, this challenge is more apparent than real. Heterogeneity between individuals can shape mortality trajectories for populations, and recent evolutionary theory can both account for such heterogeneity and accommodate late-age mortality patterns.

Journal Article↗
PubMed2004

Rate of molecular evolution of the seminal protein gene SEMG2 correlates with levels of female promiscuity.

Postcopulatory sperm competition is a key aspect of sexual selection and is believed to drive the rapid evolution of both reproductive physiology and reproduction-related genes. It is well-established that mating behavior determines the intensity of sperm competition, with polyandry (i.e., female promiscuity) leading to fiercer sperm competition than monandry. Studies in mammals, particularly primates, showed that, owing to greater sperm competition, polyandrous taxa generally have physiological traits that make them better adapted for fertilization than monandrous species, including bigger testes, larger seminal vesicles, higher sperm counts, richer mitochondrial loading in sperm and more prominent semen coagulation. Here, we show that the degree of polyandry can also impact the dynamics of molecular evolution. Specifically, we show that the evolution of SEMG2, the gene encoding semenogelin II, a main structural component of semen coagulum, is accelerated in polyandrous primates relative to monandrous primates. Our study showcases the intimate relationship between sexual selection and the molecular evolution of reproductive genes.

Animals↗