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PubMed1981

Functional ontogeny of human lymphoid cells as a factor in maternal-fetal tolerance.

The development of immunocompetence during gestation depends upon the sequential differentiation of antigen-specific lymphoid cells in the context of epithelial inducing microenvironments. These early intrauterine events, which appear to be antigen-independent, include clonal diversification of idiotypes and isotypes as well as commitment to B or T cell lineages. The steps in cellular maturation can be traced through the use of lymphocyte differentiation markers. Cooperation among lymphoid subsets, as well as from nonlymphoid cells and possibly other cofactors, is necessary for the effective function of this array of lymphocytes. The rate of expansion of functional immunity may be limited as much by the ontogeny of these collaborating influences as by the intrinsic immaturity of the B and T cells themselves.

Animals↗

PubMed2001

Molecular evolution of Sry and Sox gene.

The mammalian Sry on the short arm of the Y chromosome encodes a nuclear factor-like protein harboring a DNA-binding domain known as the HMG box. The Sox genes encode similar factor like proteins, but the sequence similarity of the HMG box to that of Sry is variable as being at least 60%. The functional relationship of Sox to Sry genes with special reference to sex determination is unclear except for a few items such as human autosomal Sox9. Thus, it is significant to know more about the evolutionary in addition to the functional relationship between Sry and Sox genes for deepening and broadening our understanding concerning primary sex determination. Therefore, to clarify the ancestry and molecular evolution of the mammalian sex determining gene Sry with its evolutionary relationships to the Sox gene, a molecular phylogenetic tree for the HMG box superfamily was constructed and analyzed, and the following conclusions were reached: (1) The nuclear non histone HMG proteins are supposedly the oldest, appearing at least more than one billion years ago, before the divergence of animals and plants. They diverged into two subgroups: one contains HMG14 and HMG17, and the other one contains HMG1 and HMG2 with various other genes. Subsequent divergences include the nucleolar UBF, nuclear SSRP as well as fungal mating protein Mc, MAT and Ste11. (2) The Sox and Sry genes diverged following the diversification of lymphoid transcription factors TCF and LEF. The Sry gene might have definitely evolved from the Sox gene cluster a few hundred million years ago. Additionally, the marsupial Sry, e.g. from Wallabie's and Dunnart's, is distinguished by being distant from eutherian Sry, but being closely related to the Sox gene cluster. (3) Molecular evolutionary rates estimated in mammalian Sry as the divergent rate per 100 million years are much higher than in Sox genes or other genes from the HMG box superfamily. This rapid evolution of Sry might agree with the fact that the Srys are present not on the pseudoautosomal region but on the distal region with no recombination of the Y chromosomal short arm.

Amino Acid Sequence↗

PubMed1989

Diversification and extinction patterns among Neogene perimediterranean mammals.

The best mammalian fossil record during the Neogene of Western Europe is that of the rodents, the most successful and diversified mammal order. The study of origination and extinction during the Neogene (24-3 Ma BP) in one of the best-documented areas, Spain and southern France, gives an insight into the dynamics of these communities and indicates the possible nature of the driving forces. Three main periods of time show a high rate of origination: the late Burdigalian (17.5 Ma BP), the early Vallesian (11.5-11 Ma BP) and the early Pliocene (4.2-3.8 Ma BP). Two of these high origination-rate periods are immediately followed by important extinction events during which all cohorts are deeply affected (11.5-11 Ma BP and 4.2-3.8 Ma BP). The most important extinction event seems to occur during the early Vallesian (11.5-11 Ma BP), which probably includes the middle/late Miocene boundary. At the Miocene/Pliocene boundary, and during the early Pliocene, the faunal turnover seems to become faster, inducing a strong decrease of the mean species duration. Whereas the main immigration event, which occurs at 17.5 Ma BP, can be related to other faunal migrations in terms of the closure of the Tethys, as it occurs also in eastern Africa and in southwest Asia, the middle/late Miocene boundary event may have been related to a period of ice growth in the Southern Hemisphere. The extinction event that affects the planktonic foraminifera at 12 Ma BP cannot be chronologically correlated to this southwestern European land-mammal extinction event, because the calibration of the marine fossil record during that time-span has to be precise. Some limited terrestrial faunal exchanges that occur during the Messinian between southwestern Europe and northwestern Africa do not deeply affect the general faunal dynamics. Both allochthonous cohorts of immigrants become rapidly extinct. Several endemic rodent faunas, indicating insular conditions, have been reported from the southern edge of the western European continent from the middle Miocene up to the Pliocene. All show low taxonomic diversity, strong endemism and short survival. Some of them, like those of the Gargano Islands during the late Miocene, underwent peculiar morphological changes and also speciation. The large number of rodent genera coevolving in the Gargano Islands is indicative of the large surface areas of these islands. The general geographic pattern of southwestern Europe during the Neogene may therefore correspond to a large continental province including Spain and southern France with some kind of fast-modifying archipelago on its southern rim.

Animals↗

PubMed2005

60 million years of co-divergence in the fig-wasp symbiosis.

Figs (Ficus; ca 750 species) and fig wasps (Agaoninae) are obligate mutualists: all figs are pollinated by agaonines that feed exclusively on figs. This extraordinary symbiosis is the most extreme example of specialization in a plant-pollinator interaction and has fuelled much speculation about co-divergence. The hypothesis that pollinator specialization led to the parallel diversification of fig and pollinator lineages (co-divergence) has so far not been tested due to the lack of robust and comprehensive phylogenetic hypotheses for both partners. We produced and combined the most comprehensive molecular phylogenetic trees to date with fossil data to generate independent age estimates for fig and pollinator lineages, using both non-parametric rate smoothing and penalized likelihood dating methods. Molecular dating of ten pairs of interacting lineages provides an unparalleled example of plant-insect co-divergence over a geological time frame spanning at least 60 million years.

Animals↗

PubMedDate not supplied

Emerging and reemerging helminthiases and the public health of China.

Despite great strides in their control throughout the People's Republic of China, helminth infections remain an important public health problem. The Institute of Parasitic Diseases of the Chinese Academy of Preventive Medicine, under the guidance of the Chinese Ministry of Health, completed a nationwide survey of more than 1 million people that showed the high prevalence and intensity of intestinal nematode infections; prevalence can sometimes exceed 50% in the Yangtze River valley provinces. Schistosoma japonicum is also a major cause of illness in this region. Attempts to control Chinese helminthic diseases with conventional anthelminthic drugs have been partially thwarted by high posttreatment rates of reinfection. Recently, several new human trematode pathogens have been identified. Novel approaches to chemoprophylaxis and vaccination may alleviate the public health problem caused by Chinese helminths. However, recombinant helminth vaccine development will depend on first cataloguing the extensive genetic diversity of Chinese helminths and candidate vaccine antigens. Evidence from biogeography, genetics, and systematics suggests that the genetic diversification of Chinese helminths and their vectors is an ongoing evolutionary process that began 12 million years ago near the convergence of major Asian river systems. Construction of the Three Gorges Super Dam on the Yangtze River may promote the emergence and reemergence of new helminths and their snail vectors

Animals↗

PubMed2002

Surgical treatment of gallstones: changes in a defined population during a 20-year period.

OBJECTIVE: To study developments in routine gallstone surgery in a defined population over a 20-year period with regard to incidence of operations, implementation of new methods, postoperative complications, and postoperative duration of hospital stay. DESIGN: Retrospective study of medical records. SETTING: County hospital, Sweden. SUBJECTS: All patients who were residents of Jönköping during one of the three-year periods 1976-1978, 1986-1988, or 1996-1998 and had their first surgical treatment, either cholecystectomy/choledochotomy or therapeutic endoscopy for gallstone disease. RESULTS: The overall annual incidence of operations for gallstones decreased from 2.01 to 1.13/1000 inhabitants between the first and second period (p < 0.001). This is explained by a significant reduction in the number of elective operations while the number of urgent operations increased between the first and second periods from 0.39 to 0.53/1000 (p < 0.05) and continued to increase and reached 0.75/1000 during the third period (p < 0.001). New methods were introduced for the treatment of gallstones that gradually made this type of operation more varied and complex in routine practice. The postoperative hospital stay decreased from 7.0 days during the 1970s to 3.9 days during the 1990s. Postoperative morbidity was unchanged. CONCLUSIONS: The decreasing rate of gallstone surgery noted between the 1970s and 1980s did not continue through the 1990s. Urgent surgery for gallstone disease has gradually become more common and now predominates over elective surgery in routine practice. The introduction of less traumatic surgical techniques contributed to the significant decrease in hospital stay after gallstone surgery. However, morbidity has not decreased and the diversification of surgical techniques used for treatment of gallstones requires continuous evaluation in routine practice.

Adult↗

PubMed2000

The nicking step in V(D)J recombination is independent of synapsis: implications for the immune repertoire.

In all of the transposition reactions that have been characterized thus far, synapsis of two transposon ends is required before any catalytic steps (strand nicking or strand transfer) occur. In V(D)J recombination, there have been inconclusive data concerning the role of synapsis in nicking. Synapsis between two 12-substrates or between two 23-substrates has not been ruled out in any studies thus far. Here we provide the first direct tests of this issue. We find that immobilization of signals does not affect their nicking, even though hairpinning is affected in a manner reflecting its known synaptic requirement. We also find that nicking is kinetically a unireactant enzyme-catalyzed reaction. Time courses are no different between nicking seen for a 12-substrate alone and a reaction involving both a 12- and a 23-substrate. Hence, synapsis is neither a requirement nor an effector of the rate of nicking. These results establish V(D)J recombination as the first example of a DNA transposition-type reaction in which catalytic steps begin prior to synapsis, and the results have direct implications for the order of the steps in V(D)J recombination, for the contribution of V(D)J recombination nicks to genomic instability, and for the diversification of the immune repertoire.

Animals↗

PubMedDate not supplied

[An input of heterochronies to the formation of interspecific differences in wood mice, Sylvaemus (Rodentia)].

Difference in adult size and body shape among the closely related species is the result of diversification in morphogenetic processes. We examined age variation in various external and craniometric characters of four Sylvaemus species from Ukrane fauna, S. uralensis, S. arianus, S. sylvaticus, and S. tauricus, using cross-sectional techniques. The intensive growth period occurred to be different in various species. Rapid growth of S. tauricus continues during all life span, while in other species growth rate becomes slower at different stages. This peculiarity of S. tauricus may be the result of prolonged and more intensive production of somatotropin by adenohypophysis. Side effects of adenohypophysis activation are resulted from changes in S. tauricus skull shape and more intensive pigmentation in comparison with three other species. Prolongation of growth could be developmental mechanism for size increasing in evolution of S. tauricus. The independence of body size and pigmentation is principally the same at interspecific and intraspecific level.

Animals↗

PubMed1987

Development of mammography and breast services in a community hospital.

The growth and development of mammography and related breast services in one community hospital are chronicled and described. With mammography providing the initial stimulus, substantial growth, diversification, and sophistication in diagnosis and treatment of breast disease have developed. The achievement of a cooperative and mutually supportive relationship among radiologists, pathologists, and surgeons committed to the goal of early detection of potentially curable breast cancer has succeeded in identifying increasing numbers of such lesions. The more frequent employment of breast-sparing surgical procedures and the encouraging survival rates in patients detected and treated for these early lesions represents an important contribution to the care of these women. Improvement in the detection of early breast cancer can be achieved by community radiologists, whether in private hospitals or office-based practices.

Breast Neoplasms↗

PubMed2000

Phylogenetic analysis and trait evolution in Australian lineages of drywood termites (Isoptera, Kalotermitidae).

A phylogenetic analysis of Australian drywood termites (Isoptera, Kalotermitidae) based on partial sequence from the cytochrome oxidase II (COII) and cytochrome b genes is presented. In addition to providing new information on the evolutionary relationships among 25 species from seven genera, we evaluate the relative likelihoods of alternative topological hypotheses, including those derived from morphology-based classifications. We also test the applicability of a molecular clock for estimating the age of the Kalotermitidae and infer the evolution of species-specific variation for habitat type and soldier caste phragmosis by mapping this information onto the independently derived phylogeny. Maximum-likelihood analysis of both nucleotide and protein sequences from a multigene data set jointly support a single topology, which is shown to be the best estimate of the true phylogeny among the alternatives tested. Our results support the monophyly of all genera but question the discrimination between Procryptotermes and Cryptotermes. A basal dichotomy among generic groups suggests two principle lines of divergence within the family. Intergeneric relationships show mixed congruence to previous proposals, resulting in one morphology-based classification being rejected. A molecular clock hypothesis is not supported due to significant among-lineage rate heterogeneity in the COII gene. Patterns revealed through trait mapping suggest that the most recently diverged taxa tend to occupy the driest habitats and that these same taxa reflect a defensive transition away from large mandibulate soldiers toward small phragmotic soldiers. The association between habitat and defensibility supports the hypothesis that these two characters have been tightly linked throughout the social diversification of termites.

Animals↗

PubMed2000

Population dynamics of the symbiotic mushroom Hebeloma cylindrosporum: mycelial persistence and inbreeding.

The pattern of colonization of a forest site by the ectomycorrhizal basidiomycete fungus Hebeloma cylindrosporum Romagnesi was followed from 1993 until 1997. Fruit-bodies of this tetrapolar heterothallic species were mapped, collected and propagated as pure mycelial cultures. Isolates were analysed for their mating-types and molecular markers (rDNA polymorphism and RAPD). Dedikaryotization of the 26 isolates collected in 1993 and the separate analysis of each individual haploid nucleus established that two fully compatible genets, which occupied two nonoverlapping territories, were present. Isolates belonging to the same genet could nevertheless be distinguished from each other based on Southern hybridization using hyperpolymorphic DNA probes. A majority of the 143 isolates collected from 1994 to 1997 belonged to either of the two genets identified in 1993, whose territories extended at a rate of about 0. 45-0.60 m per year. Selfing of the two 1993 genets, rather than outcrossing, was the most likely explanation for the origin of additional genotypes identified between 1995 and 1997. The spatial distribution of fruit-bodies and genets of H. cylindrosporum suggested that only a fraction of the sampled area was favourable to colonization and that genetic diversification through meiospore dispersal may be inhibited by the presence of resident genets, possibly via a somatic incompatibility system.

Agaricus↗

PubMed2002

Natural selection and the diversification of vertebrate immune effectors.

The molecules of the vertebrate immune system provide some of the best documented examples of natural selection acting at the molecular level. The major histocompatibility complex (MHC) molecules are a family of highly polymorphic loci whose products present peptides to T cells. Four distinct lines of evidence support the hypothesis that the natural selection acts to maintain MHC polymorphism: (1) evidence from the unusual allelic frequency distribution seen at MHC loci; (2) evidence from the pattern of nucleotide substitution at MHC loci, which shows an enhanced rate of nonsynonymous (amino acid-altering) substitution in the codons encoding the peptide-binding region of the molecules; (3) the existence of long-lasting polymorphisms at certain MHC loci; and (4) the fact that introns at MHC loci are homogenized by recombination and subsequent genetic drift. Certain other immune system gene families provide evidence that natural selection has acted to create diversity among family members. Examples include molecules of the specific immune system (such as immunoglobulin V region genes) and molecules of the innate immune system (such as defensins).

Alleles↗

PubMed2000

Horizontal transfer and selection in the evolution of P elements.

The roles of selection and horizontal transfer in the evolution of the canonical subfamily of P: elements were studied in the saltans and willistoni species groups of the genus Drosophila (subgenus Sophophora). We estimate that the common ancestor of the canonical P: subfamily dates back 2-3 Myr at the most, despite the much older age (more than 40 Myr) of the P: family as a whole. The evolution of the canonical P: subfamily is characterized by weak selection at nonsynonymous sites. These sites have evolved at three quarters the rate of synonymous sites, in which no selective constraints were detected. Their recent horizontal transfer best explains the high degree of similarity among canonical P: elements from the saltans and willistoni species groups. These results are consistent with a model of P:-element evolution in which selective constraints are imposed at the time of horizontal transfer. Furthermore, it is estimated that the spread and diversification of the canonical subfamily involved a minimum of 11 horizontal transfer events among the 18 species surveyed within the past 3 Myr. The presence of multiple P: subfamilies in the saltans and willistoni species groups is likely to be the result of multiple invasions that have previously swept through these taxa in a succession of horizontal transfer events. These results suggest that horizontal transfer among eukaryotes might be more common than anticipated.

Alcohol Dehydrogenase↗

PubMed2026

Spatiotemporal patterns of Rift Valley fever virus in Africa: a retrospective genomic epidemiology and phylodynamic modelling study.

BACKGROUND: Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic pathogen causing outbreaks in humans and ruminants across Africa and the Arabian Peninsula. Originally restricted to the Great Rift Valley, RVFV has expanded geographically, prompting its classification by WHO as a pathogen of pandemic potential. We investigated the evolutionary and spatial dynamics of RVFV across Africa. METHODS: We used genomic data generated at the International Livestock Research Institute Nairobi genomic laboratory (BioProject PRJNA1106221) and combined with publicly available datasets retrieved from the National Center for Biotechnology (NCBI) GenBank nucleotide database. In retrieving RVFV genome sequences from the NCBI GenBank, we applied the search terms "Rift Valley fever virus segment L AND 6404[SLEN]", "Rift Valley fever virus segment M AND 3885[SLEN]", and "Rift Valley fever virus segment S AND 1520:1690[SLEN]" for L (Large), M (Medium), and S (Small) segments, respectively. For sequences without additional spatiotemporal information, we searched PubMed to extract the associated sequence metadata. We performed molecular clock analysis, phylogenetic inference, phylodynamic modelling (continuous phylogeographic reconstruction), and landscape phylogeography on the three RVFV genome segments (L, M, and S). We aimed to assess evolutionary rates, dispersal patterns, and environmental drivers. Focus was placed on lineage C, the most widely distributed variant. FINDINGS: The global dataset used in this study consisted of large (n=236), medium (n=237), and small (n=247), which were further filtered to exclude potential reassortants and vaccine strains. Genome sequences retrieved from NCBI GenBank database comprised large (n=180), medium (n=184), and small (n=202). The genome sequences from retrospective human and livestock isolates comprised large (n=56), medium (n=53), and small (n=45) collected in Burundi (2018), Kenya (2007, 2018, 2019, 2021, and 2022), and Rwanda (2018 and 2022). Our dataset revealed that RVFV exhibited low overall genetic diversity. Lineage C, however, showed evidence of active evolution, with substitution rates ranging from 3·58 × 10-4 to 9·76 × 10-4 substitutions per site per year. This lineage probably originated in Zimbabwe in the mid-1970s and has since expanded across eastern and southern Africa. Phylogeographic reconstructions revealed rapid spread, with diffusion coefficients exceeding 50 000 km2 per year. INTERPRETATION: Lineage C appears capable of establishing endemic transmission in new regions, with ongoing diversification observed during interepidemic periods. These observations reinforce the value of continuous genomic surveillance, particularly during cryptic transmission phases when adaptive mutations might emerge. Although further evidence is needed, observed trends in climate variability and land-use change point to the potential benefit of targeted surveillance in settings that could be at increased risk, including urban centres and wetlands. FUNDING: This work was supported by the German Federal Ministry for Economic Cooperation and Development, the Rockefeller Foundation, and the Africa Centres for Disease Control and Prevention.

Rift Valley fever virus↗

PubMed1999

[Vectors and environmental factors in malaria].

Malaria is a major risk for more than two billion human beings on Earth, and is the cause of 700,000 to 2.5 million deaths per year. The causative factor, Plasmodium (four species), involves an asexual cycle in man and a sexual one in anopheline mosquitoes. The four species of Plasmodium are pathogenic for man but P. falciparum accounts for more than 90% of deaths. Only black Africans are refractory to P. vivax, a characteristic linked to the lack of Duffy antigen. Among the 400 species of anophelines so far recorded, less than 50 are recognized malaria vectors. Every one has its own geographic and ecological characteristics, which locally induce the epidemiological trends and its biodiversity. In a given site transmission depends on competent anopheline species, their infective rate and their biting rate. Inhabitants of endemic areas develop during infancy immunity which protect them during the rest of their lives. This immunity (premunition) between parasite and its host is acquired at an heavy price of infant mortality. It can decrease rapidly when people leave endemic areas. Because inhabitants of endemic areas continue to harbor asymptomatic parasites they become good parasite reservoirs. The diversity of epidemiological situations needs a diversification of malaria control measures. The prognosis of the evolution of malaria depends on control measures, applied or not, and on the evolution of climatic and anthropic environment, which are very hard to predict for the time being.

Animals↗

PubMed2003

Rapid divergence of the ecdysone receptor in Diptera and Lepidoptera suggests coevolution between ECR and USP-RXR.

Ecdysteroid hormones are major regulators in reproduction and development of insects, including larval molts and metamorphosis. The functional ecdysone receptor is a heterodimer of ECR (NR1H1) and USP-RXR (NR2B4), which is the orthologue of vertebrate retinoid X receptors (RXR alpha, beta, gamma). Both proteins belong to the superfamily of nuclear hormone receptors, ligand-dependent transcription factors that share two conserved domains: the DNA-binding domain (DBD) and the ligand-binding domain (LBD). In order to gain further insight into the evolution of metamorphosis and gene regulation by ecdysone in arthropods, we performed a phylogenetic analysis of both partners of the heterodimer ECR/USP-RXR. Overall, 38 USP-RXR and 19 ECR protein sequences, from 33 species, have been used for this analysis. Interestingly, sequence alignments and structural comparisons reveal high divergence rates, for both ECR and USP-RXR, specifically among Diptera and Lepidoptera. The most impressive differences affect the ligand-binding domain of USP-RXR. In addition, ECR sequences show variability in other domains, namely the DNA-binding and the carboxy-terminal F domains. Our data provide the first evidence that ECR and USP-RXR may have coevolved during holometabolous insect diversification, leading to a functional divergence of the ecdysone receptor. These results have general implications on fundamental aspects of insect development, evolution of nuclear receptors, and the design of specific insecticides.

Amino Acid Sequence↗

PubMed2003

Phylogeny of choanozoa, apusozoa, and other protozoa and early eukaryote megaevolution.

The primary diversification of eukaryotes involved protozoa, especially zooflagellates-flagellate protozoa without plastids. Understanding the origins of the higher eukaryotic kingdoms (two purely heterotrophic, Animalia and Fungi, and two primarily photosynthetic, Plantae and Chromista) depends on clarifying evolutionary relationships among the phyla of the ancestral kingdom Protozoa. We therefore sequenced 18S rRNA genes from 10 strains from the protozoan phyla Choanozoa and Apusozoa. Eukaryote diversity is encompassed by three early-radiating, arguably monophyletic groups: Amoebozoa, opisthokonts, and bikonts. Our taxon-rich rRNA phylogeny for eukaryotes allowing for intersite rate variation strongly supports the opisthokont clade (animals, Choanozoa, Fungi). It agrees with the view that Choanozoa are sisters of or ancestral to animals and reveals a novel nonflagellate choanozoan lineage, Ministeriida, sister either to choanoflagellates, traditionally considered animal ancestors, or to animals. Maximum likelihood trees suggest that within animals Placozoa are derived from medusozoan Cnidaria (we therefore place Placozoa as a class within subphylum Medusozoa of the Cnidaria) and hexactinellid sponges evolved from demosponges. The bikont and amoebozoan radiations are both very ill resolved. Bikonts comprise the kingdoms Plantae and Chromista and three major protozoan groups: alveolates, excavates, and Rhizaria. Our analysis weakly suggests that Apusozoa, represented by Ancyromonas and the apusomonads ( Apusomonas and the highly diverse and much more ancient genus Amastigomonas, from which it evolved), are not closely related to other Rhizaria and may be the most divergent bikont lineages. Although Ancyromonas and apusomonads appear deeply divergent in 18S rRNA trees, the trees neither refute nor support the monophyly of Apusozoa. The bikont phylum Cercozoa weakly but consistently appears as sister to Retaria (Foraminifera; Radiolaria), together forming a hitherto largely unrecognized major protozoan assemblage (core Rhizaria) in the eukaryote tree. Both 18S rRNA sequence trees and a rare deletion show that nonciliate haplosporidian and paramyxid parasites of shellfish (together comprising the Ascetosporea) are not two separate phyla, as often thought, but part of the Cercozoa, and may be related to the plant-parasitic plasmodiophorids and phagomyxids, which were originally the only parasites included in the Cercozoa. We discuss rRNA trees in relation to other evidence concerning the basal diversification and root of the eukaryotic tree and argue that bikonts and opisthokonts, at least, are holophyletic. Amoebozoa and bikonts may be sisters-jointly called anterokonts, as they ancestrally had an anterior cilium, not a posterior one like opisthokonts; this contrasting ciliary orientation may reflect a primary divergence in feeding mode of the first eukaryotes. Anterokonts also differ from opisthokonts in sterol biosynthesis (cycloartenol versus lanosterol pathway), major exoskeletal polymers (cellulose versus chitin), and mitochondrial cristae (ancestrally tubular not flat), possibly also primary divergences.

Amino Acid Motifs↗

PubMed1989

Evolution and extinction in the marine realm: some constraints imposed by phytoplankton.

The organic and mineralized remains of planktonic algae provide a rich record of microplankton evolution extending over nearly half of the preserved geological record. In general, Phanerozoic patterns of phytoplankton radiation and extinction parallel those documented for skeletonized marine invertebrates, both augmenting and constraining thought about evolution in the oceans. Rapidly increasing knowledge of Proterozoic plankton is making possible the recognition of additional episodes of diversification and extinction that antedate the Ediacaran radiation of macroscopic animals. In contrast to earlier phytoplankton history, the late Mesozoic and Cainozoic record is documented in sufficient detail to constrain theories of mass extinction in more than a general way. Broad patterns of diversity change in planktonic algae show similarities across the Cretaceous-Tertiary and Eocene-Oligocene boundaries, but detailed comparisons of origination and extinction rates in calcareous nannoplankton, as well as other algae and skeletonized protozoans, suggest that the two episodes were quite distinct. Common causation appears unlikely, casting doubt on monolithic theories of mass extinction, whether periodic or not. Studies of mass extinction highlight a broader class of insights that paleontologists can contribute to evolutionary biology: the evaluation of evolutionary change in the context of evolving Earth-surface environments.

Biological Evolution↗