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PubMed2006

Influence of hydrogeographic history and hybridization on the distribution of genetic variation in the pupfishes Cyprinodon atrorus and C. bifasciatus.

The evolutionary importance of hybridization in animals has been subject of much debate. In this study, we examined the influence of hydrogeographic history and hybridization on the present distribution of nuclear and mitochondrial DNA variation in two pupfish species, Cyprinodon atrorus and Cyprinodon bifasciatus. Results presented here indicate that there has been limited introgression of nuclear genes; however, mtDNA introgression has been substantial, with complete replacement of the C. bifasciatus mitochondrial genome by that of C. atrorus. Subsequent to this replacement, there has been diversification of mitochondrial haplotypes along major geographic regions in the basin. Evidence was also found that mitochondrial replacement follows a predictable, cyclical pattern in this system, with isolation and diversification followed by re-contact and replacement of C. bifasciatus mitochondrial haplotypes by those of C. atrorus. This pattern is best explained by a combination of a numeric bias towards C. atrorus and mating site selection rather than selection for C. atrorus mitochondrial genome. These results demonstrate the important role hybridization can play in evolution.

Animals↗
PubMed2006

Phylogeographic patterns of host-race evolution in Tephritis conura (Diptera: Tephritidae).

Host-race evolution is a prime candidate for sympatric speciation because host shifts must take place in the presence of both hosts. However, the geographic context in which the shift takes place may have strong allopatric or peripatric components if the primary host within a localized area is scarce or even goes extinct. Inference of the relative importance of the geographic mode of speciation may be gained from phylogeographic imprints. Here, we investigate the phylogeography of host races of the tephritid fly Tephritis conura from sympatric, parapatric and allopatric populations of Cirsium heterophyllum and Cirsium oleraceum (Asteraceae) in Europe, for addressing the age and direction, and the geographic context of host-race formation. Haplotype networks of the host races differed significantly in molecular diversity and topology. However, host-race haplotypes were nested within the same network, with a central haplotype H1 being the most common haplotype in both host races. C. heterophyllum flies were genetically more diverse and substructured than flies from C. oleraceum, suggesting that the latter is the derived race. The phylogeographic imprint indicates either that C. heterophyllum flies colonized C. oleraceum during range expansion or that heterophyllum flies went extinct in an area where oleraceum flies persisted (followed by re-immigration). These imprints are in concordance with peripatric diversification, probably in the European Alps and related to the last ice age, where the host-race diversification was largely completed before the postglacial range expansion on C. oleraceum to current areas of sympatry and parapatry with C. heterophyllum.

Animals↗
PubMed2006

Comparative phylogeography of woodland reptiles in California: repeated patterns of cladogenesis and population expansion.

The ultimate goal of comparative phylogeographical analyses is to infer processes of diversification from contemporary geographical patterns of genetic diversity. When such studies are employed across diverse groups in an array of communities, it may be difficult to discover common evolutionary and ecological processes associated with diversification. In order to identify taxa that have responded in a similar fashion to historical events, we conducted comparative phylogeographical analyses on a phylogenetically and ecologically limited set of taxa. Here, we focus on a group of squamate reptiles (snakes and lizards) that share similar ecological requirements and generally occupy the same communities in the western USA. At a gross level, deep genetic division in Contia tenuis, Diadophis punctatus, Elgaria multicarinata, the Charina bottae complex, and Lampropeltis zonata are often concordant in the Transverse Ranges, the Monterey Bay and Sacramento-San Joaquin Delta region, and the southern Sierra Nevada in California. Molecular clock estimates suggest that major phyletic breaks within many of these taxa roughly coincide temporally, and may correspond to important geological events. Furthermore, significant congruence between the phylogeographies of E. multicarinata and L. zonata suggests that the succession of vicariance and dispersal events in these species progressed in concert. Such congruence suggests that E. multicarinata and L. zonata have occupied the same communities through time. However, across our entire multi-taxon data set, the sequence of branching events rarely match between sympatric taxa, indicating the importance of subtle differences in life history features as well as random processes in creating unique genetic patterns. Lastly, coalescent and noncoalescent estimates of population expansion suggest that populations in the more southerly distributed clades of C. tenuis, D. punctatus, E. multicarinata, and L. zonata have been stable, while populations in more northerly clades appear to have recently expanded. This concerted demographic response is consistent with palaeontological data and previous phylogeographical work that suggests that woodland habitat has become more restricted in southern California, but more widespread in the North during Holocene warming. Future phylogeographical work focusing on allied and ecologically associated taxa may add insight into the ecological and evolutionary processes that yield current patterns of genetic diversity.

Animals↗
PubMed2006

Distinct population structure in a phenotypically homogeneous rock-dwelling cichlid fish from Lake Tanganyika.

Several lineages of cichlid fishes in the East African Great Lakes display stunning levels of morphological diversification. The rapid evolution of rock-dwelling polygynous mouthbrooders in Lake Malawi, for example, was in part ascribed to their allopatric distribution on disjunct stretches of rocky coast, where even short habitat discontinuities reduce gene flow effectively. However, as seen in other cichlids, ecological barriers do not always prevent gene flow, whereas genetic structure can develop along continuous habitat, and morphological diversification does not necessarily accompany genetic differentiation. The present study investigates the population structure of Variabilichromis moorii, a monogamous substrate-brooding lamprologine of rocky coasts in Lake Tanganyika, which occurs over about 1000 km of shoreline almost without phenotypic variation. Phylogeographic analyses of mitochondrial DNA sequences indicated that dispersal is infrequent and generally occurs between adjacent locations only. Exceptions to this pattern are closely related haplotypes from certain locations on opposite lakeshores, a phenomenon which has been observed in other species and is thought to reflect lake crossing along an underwater ridge in times of low water level. Genetic population differentiation, estimated from mitochondrial DNA and microsatellite data in six adjacent populations, was equally high across localities separated by sandy shores and along uninterrupted stretches of rocky shore. Our results suggest that ecological barriers are not required to induce philopatric behavior in Variabilichromis, and that morphological stasis persists in the face of high levels of neutral genetic differentiation.

Alleles↗
PubMed2006

Co-cladogenesis spanning three phyla: leafhoppers (Insecta: Hemiptera: Cicadellidae) and their dual bacterial symbionts.

Endosymbioses are a major form of biological complexity affecting the ecological and evolutionary diversification of many eukaryotic groups. These associations are exemplified by nutritional symbioses of insects for which phylogenetic studies have demonstrated numerous cases of long-term codiversification between a bacterial and a host lineage. Some insects, including most leafhoppers (Insecta: Hemiptera: Cicadellidae), have more than one bacterial symbiont within specialized host cells, raising questions regarding the patterns of codiversification of these multiple partners and the evolutionary persistence of complex symbiotic systems. Previous studies reported the presence of two dominant symbiont types in a member of the leafhopper subfamily Cicadellinae (sharpshooters). In this study, 16S rRNA sequences were obtained and used to examine the occurrence and evolutionary relationships of the two dominant symbiont types across 29 leafhopper species. Candidatus Sulcia muelleri (Bacteroidetes) was detected in all leafhopper species examined, a finding that is consistent with a previous report of its ancient association with the Auchenorrhyncha (a grouping that includes leafhoppers, treehoppers, cicadas, planthoppers, and spittlebugs). Baumannia cicadellinicola (Proteobacteria), previously known from only five sharpshooter species, was found only in the sharpshooter tribes Cicadellini and Proconiini, as well as in the subfamily Phereurhininae. Mitochondrial and nuclear gene sequences were obtained and used to reconstruct host phylogenies. Analyses of host and symbiont data sets support a congruent evolutionary history between sharpshooters, Sulcia and Baumannia and thus provide the first strong evidence for long-term co-inheritance of multiple symbionts during the diversification of a eukaryotic host. Sulcia shows a fivefold lower rate of 16S rDNA sequence divergence than does Baumannia for the same host pairs. The term 'coprimary' symbiont is proposed for such cases.

Animals↗
PubMed1991

D-D recombination diversifies the CDR 3 region of chicken immunoglobulin heavy chains.

The occurrence of D-D recombination during the embryonic differentiation of chicken B cells was studied. Ig heavy (H) chains were amplified by polymerase chain reaction from day-12 bursal cDNA, and 30 random V-D-J regions were analysed by DNA sequencing. No gene conversion events were observed in any of the V regions, indicating that diversification of the H chains by gene conversion is not yet activated at this stage of embryonic B-cell development. In contrast, the V-D-J joint regions were extremely heterogeneous. Most of the sequenced V-D-J joints were formed by direct joining of the single-germline V mu 1 gene, one of the multiple-germline D elements, and the single J gene. However, three V-D-J regions were clearly longer in size, and their D-region structure indicated recombination between two or three different germline D elements. Thus, the present data suggest that D-D recombination may have a role in diversification of the Ig H-chain repertoire.

Animals↗
PubMed2006

Functionally redundant SHI family genes regulate Arabidopsis gynoecium development in a dose-dependent manner.

Gene duplication events, and the subsequent functional divergence of duplicates, are believed to be important evolutionary agents, driving morphological diversification. We have studied the structural and functional diversification of members of a plant-specific gene family in Arabidopsis thaliana by analysing mutant phenotypes, expression patterns and phylogeny. The SHI gene family comprises ten members that encode proteins with a RING finger-like zinc finger motif. We show that, despite being highly divergent in sequence, except in two conserved regions, many of the SHI-related genes are partially redundant in function and synergistically promote gynoecium, stamen and leaf development in Arabidopsis. Gynoecia of the loss-of-function sty1-1 mutant display subtle morphological defects, and, although mutations in the related STY2, SHI, SRS3, SRS4, SRS5, SRS7 and LRP1 genes have no apparent effect on gynoecium development, the sty1-1 mutant phenotype is gradually enhanced in double, triple, quadruple and quintuple mutant combinations, suggesting a remarkably extensive functional conservation within the family, which appears to be based on dosage dependency and protection against dominant negative mutations. In multiple mutant lines, all marginal tissues in the apical part of the gynoecium are dramatically reduced or missing, and our data indicate that SHI family members may promote formation of these tissues downstream of the transcriptional co-repressor LEUNIG (LUG).

Arabidopsis↗
PubMed2005

Medicago-Sinorhizobium symbiotic specificity evolution and the geographic expansion of Medicago.

The legume genus Medicago interacts with soil bacteria commonly referred to as rhizobia, in a nitrogen fixing symbiosis. We analysed the diversity of symbiotic association specificity among the two organisms, and its evolution in the plant genus. Nitrogen fixation tests and molecular phylogenetic reconstructions revealed that the genus Medicago includes more symbiotic specificity groups than previously suggested and that plant specificity is highly unstable and has repeatedly switched along the diversification of this genus. A phylogenetic analysis including geographical data shows that bacterial geographical diversity distribution has a strong influence on the geographic distribution of plant species and their ability to colonize new areas. Multiple other modifications of specificity occurred along the diversification of the genus, presumably due to selection for specialization to a single bacterial biovar. Codivergence between plants and bacteria may also have taken place.

Base Sequence↗
PubMed2006

Dynamics of host plant use and species diversity in Polygonia butterflies (Nymphalidae).

The ability of insects to utilize different host plants has been suggested to be a dynamic and transient phase. During or after this phase, species can shift to novel host plants or respecialize on ancestral ones. Expanding the range of host plants might also be a factor leading to higher levels of net speciation rates. In this paper, we have studied the possible importance of host plant range for diversification in the genus Polygonia (Nymphalidae, Nymphalini). We have compared species richness between sistergroups in order to find out if there are any differences in number of species between clades including species that utilize only the ancestral host plants ('urticalean rosids') and their sisterclades with a broader (or in some cases potentially broader) host plant repertoire. Four comparisons could be made, and although these are not all phylogenetically or statistically independent, all showed clades including butterfly species using other or additional host plants than the urticalean rosids to be more species-rich than their sisterclade restricted to the ancestral host plants. These results are consistent with the theory that expansions in host plant range are involved in the process of diversification in butterflies and other phytophagous insects, in line with the general theory that plasticity may drive speciation.

Animals↗
PubMed2006

A time-sequence functional analysis of mating behaviour and genital coupling in Drosophila: role of cryptic female choice and male sex-drive in the evolution of male genitalia.

Male genitalia in Drosophila exemplify strikingly rapid and divergent evolution, whereas female genitalia are relatively invariable. Whereas precopulatory and post-copulatory sexual selection has been invoked to explain this trend, the functional significance of genital structures during copulation remains obscure. We used time-sequence analysis to study the functional significance of external genitalic structures during the course of copulation, between D. melanogaster and D. simulans. This functional analysis has provided new information that reveals the importance of male-driven copulatory mechanics and strategies in the rapid diversification of genitalia. The posterior process, which is a recently evolved sexual character and present only in males of the melanogaster clade, plays a crucial role in mounting as well as in genital coupling. Whereas there is ample evidence for precopulatory and/or post-copulatory female choice, we show here that during copulation there is little or no physical female choice, consequently, males determine copulation duration. We also found subtle differences in copulatory mechanics between very closely related species. We propose that variation in male usage of novel genitalic structures and shifts in copulatory behaviour have played an important role in the diversification of genitalia in species of the Drosophila subgroup.

Animals↗
PubMed2006

Evolution of larval host plant associations and adaptive radiation in pierid butterflies.

Butterflies in the family Pieridae (Lepidoptera: Papilionoidea) feed as larvae on plants belonging primarily to three distantly related angiosperm orders: Fabales (legumes and allied plants), Brassicales (crucifers and related plants containing mustard oil glucosides), and Santalales ('mistletoes'). However, some utilize plants from 13 other families in a further eight orders. We investigated the evolutionary history of host plant use of the Pieridae in the context of a recent phylogenetic hypothesis of the family, using simple character optimization. Although there is a close association between host plant and butterfly higher classification, we find no evidence for cospeciation but a pattern of repeated colonization and specialization. The ancestral host of the family appears to be Fabaceae or Fabales, with multiple independent shifts to other orders, including three to Santalales. The shift to Brassicales, which contain secondary compounds (glucosinolates), promoted diversification and adaptive radiation within the subfamily Pierinae. Subsequent shifts from crucifers to mistletoes (aerial-stem hemiparasites) facilitated further diversification, and more recent shifts from mistletoes to mistletoe host trees led to exploitation of novel host plants outside the conventional three orders. Possible mechanisms underlying these host shifts are briefly discussed. In the Pierinae, a striking association between host plant, larval and adult behaviour, adult phenotype, and mimicry calls for further research into possible relationships between host specialization, plant chemistry and butterfly palatability.

Adaptation, Physiological↗
PubMed1988

The development of cell lineages: a sequential model.

The concept of cell lineage and the empirical characterization of specific lineages provide valuable insight into the problems of developmental biology. Of central interest is the decision-making process that results in the diversification of cell lines. Studies of the haemopoietic system, in which stem cells can be committed to one of at least six pathways of differentiation, have suggested that the restriction of differentiation potentials is a progressive and stochastic process. We have recently proposed an alternative model which hypothesizes that lineage potentials during haemopoiesis are expressed individually and in a predetermined sequence as progenitor cells mature. The model first arises from experimental studies which show that both normal myeloid progenitor cells and a human promyeloid cell line, which are able to differentiate towards either neutrophils or monocytes, express these potentials sequentially in culture. The close linear relationship between other haemopoietic progenitor cells is inferred from collective data from studies of bipotent progenitor cells and of haemopoietic proliferative disorders. If the development of haemopoietic cell lineages shows a tendency to follow a particular program, such a mechanism is likely to operate throughout development. In this paper we consider the evidence in favour of programmed events within progenitor cells implementing diversification, and the implications of predetermined and restricted pathways of embryonic development.

Animals↗
PubMedDate not supplied

Portfolio theory and cost-effectiveness analysis: a further discussion.

OBJECTIVES: Portfolio theory has been suggested as a means to improve the risk-return characteristics of investments in health-care programs through diversification when costs and effects are uncertain. This approach is based on the assumption that the investment proportions are not subject to uncertainty and that the budget can be invested in toto in health-care programs. METHODS: In the present paper we develop an algorithm that accounts for the fact that investment proportions in health-care programs may be uncertain (due to the uncertainty associated with costs) and limited (due to the size of the programs). The initial budget allocation across programs may therefore be revised at the end of the investment period to cover the extra costs of some programs with the leftover budget of other programs in the portfolio. RESULTS: Once the total budget is equivalent to or exceeds the expected costs of the programs in the portfolio, the initial budget allocation policy does not impact the risk-return characteristics of the combined portfolio, i.e., there is no benefit from diversification anymore. CONCLUSION: The applicability of portfolio methods to improve the risk-return characteristics of investments in health care is limited to situations where the available budget is much smaller than the expected costs of the programs to be funded.

Algorithms↗
PubMedDate not supplied

Evidence for distinct roles of the SEPALLATA gene LEAFY HULL STERILE1 in Eleusine indica and Megathyrsus maximus (Poaceae).

LEAFY HULL STERILE1 (LHS1) is an MIKC-type MADS-box gene in the SEPALLATA class. Expression patterns of LHS1 homologs vary among species of grasses, and may be involved in determining palea and lemma morphology, specifying the terminal floret of the spikelet, and sex determination. Here we present LHS1 expression data from Eleusine indica (subfamily Chloridoideae) and Megathyrsus maximus (subfamily Panicoideae) to provide further insights into the hypothesized roles of the gene. E. indica has spikelets with three to eight florets that mature acropetally; E. indica LHS1 (EiLHS1) is expressed in the palea and lemma of all florets. In contrast, M. maximus has spikelets with two florets that mature basipetally; M. maximus LHS1 (MmLHS1) is expressed in the palea and lemma of the distal floret only. These data are consistent with the hypothesis that LHS1 plays a role in determining palea and lemma morphology and specifies the terminal floret of basipetally maturing grass spikelets. However, LHS1 expression does not correlate with floret sex expression; MmLHS1 is restricted to the bisexual distal floret, whereas EiLHS1 is expressed in both sterile and bisexual floret meristems. Phylogenetic analyses reconstruct a complex pattern of LHS1 expression evolution in grasses. LHS1 expression within the gynoecium has apparently been lost twice, once before diversification of a major clade within tribe Paniceae, and once in subfamily Chloridoideae. These data suggest that LHS1 has multiple roles during spikelet development and may have played a role in the diversification of spikelet morphology.

Flowers↗
PubMed1998

Determinant spreading during experimental autoimmune encephalomyelitis: is it potentiating, protecting or participating in the disease?

During many autoimmune conditions, a T-cell response initially focused to a self-antigen evolves towards the recruitment of T cells to multiple antigenic determinants. Here we discuss whether such determinant spreading involves T cells activated in the peripheral lymphoid organs, or alternatively, whether the diversification occurs after infiltration of the initiating T cells into the target organ, for example, into the central nervous system during experimental autoimmune encephalomyelitis, a prototype for multiple sclerosis. The expression of myelin antigens in the thymus and spleen may not only contribute to the induction of tolerance but also to determinant spreading. In this case, the outcome of in vivo diversification may ultimately be determined by the balance between type 1 and type 2 responses to antigenic determinants derived from myelin components. Thus, spreading T cells could modulate disease progression positively or negatively, depending upon the nature of the accompanying cytokine secretion profile.

Animals↗
PubMed2005

Natural history of hepatitis C virus-related liver fibrosis after renal transplantation.

The aim of our study was to assess hepatitis C virus (HCV) evolution and long-term liver histology outcome in anti-HCV(+)/RNA(+) renal transplant (RT) patients. A total of 51 anti-HCV(+)/RNA(+) RT patients underwent liver biopsies (LB) every 3-4 years after transplantation (two LBs, n = 51; three LBs, n = 42; four LBs, n = 9). The hypervariable region (HVR)-1 of the HCV genome from all patients was characterized over time. Overall, the rate of liver fibrosis progression was 0.09 +/- 0.03 Metavir units/year. We identified three groups of patients: those in whom liver fibrosis remained stable (n = 21), those with progressing liver fibrosis (n = 21) and those with a regression in liver fibrosis (n = 10). In the last two groups, the progression and the regression of liver fibrosis were gradual during follow-up. Ferritin levels and hepatosiderosis were significantly higher in fibrosers. Initial fibrosis stage and high diversification of the HVR-1 of HCV genome between transplantation and the first liver biopsy were independent factors associated with liver fibrosis regression. In conclusion, in the current study, more than 10 years after renal transplantation, HCV infection was not harmful upon liver histology in more than 50% of patients. The diversification of the HVR-1 might be used to predict liver fibrosis outcome.

Adult↗
PubMed1991

The implementation of community-based crisis services for people with acute psychiatric illness.

This article describes three recently established community-based crisis services for people with acute psychiatric illness. Data were obtained from local information systems developed in the early phase of service operation. Patterns of service were found to vary among the teams in terms of the frequency of contact with the client, the period of contact with the client and the overall numbers of contacts. Such diversification of services reflects, at least in part, the differences in the service networks within which the new services were Such diversification of services is inevitable and creative, and the evaluation of these services must consider not only the short-term impact of crisis services, but also the impact of the network of care services on longer term outcomes for the client.

Acute Disease↗
PubMed2026

The OsUVR8-OsNAC3-OsERF117 signaling module mediates metabolic acclimation and climate adaptation in rice.

Ultraviolet-B (UV-B; 280 to 315 nanometers) radiation increasingly threatens crop productivity, yet the genetic basis of plant adaptation remains poorly understood. We delineate a UV-B signaling module in rice that links photoreceptor activation to transcriptional reprogramming and metabolic acclimation. The AP2/ERF transcription factor OsERF117 acts as a central regulator, directly activating flavonoid and melatonin biosynthetic genes to drive photoprotective metabolite accumulation and enhance UV-B stress tolerance. Promoter variation in OsERF117 defines 10 haplotypes across 4093 rice accessions, with high-expression haplotypes enriched in high-UV-B regions and correlated with adaptive divergence. OsERF117 is transcriptionally activated by OsNAC3, with a cis-regulatory SNP at an OsNAC3-binding site modulating responsiveness and contributing to subspecies diversification. Genetic and biochemical evidence supports a model in which UV-B-activated OsUVR8 promotes OsNAC3 activity and antagonizes OsCOP1-mediated ubiquitination and degradation in rice. This OsUVR8-OsCOP1-OsNAC3-OsERF117 module reveals how UV-B perception drives regulatory and metabolic diversification, offering targets for breeding UV-B-resilient crops.

Oryza↗