Specimen collection: An essential tool Rocha, L. A.; Aleixo, A.; Allen, G. ...
Science (American Association for the Advancement of Science),
05/2014, Letnik:
344, Številka:
6186
Journal Article
Understanding how genetic variation is generated and maintained in natural populations, and how this process unfolds in a changing environment, remains a central issue in biological research. In this ...work, we analysed patterns of genetic diversity from several populations of three cichlid species from Lake Tanganyika in parallel, using the mitochondrial DNA control region. We sampled populations inhabiting the littoral rocky habitats in both very deep and very shallow areas of the lake. We hypothesized that the former would constitute relatively older, more stable and genetically more diverse populations, because they should have been less severely affected by the well‐documented episodes of dramatic water‐level fluctuations. In agreement with our predictions, populations of all three species sampled in very shallow shorelines showed traces of stronger population growth than populations of the same species inhabiting deep shorelines. However, contrary to our working hypothesis, we found a significant trend towards increased genetic diversity in the younger, demographically less stable populations inhabiting shallow areas, in comparison with the older and more stable populations inhabiting the deep shorelines. We interpret this finding as the result of the establishment of metapopulation dynamics in the former shorelines, by the frequent perturbation and reshuffling of individuals between populations due to the lake‐level fluctuations. The repeated succession of periods of allopatric separation and secondary contact is likely to have further increased the rapid pace of speciation in lacustrine cichlids.
We used nuclear and mitochondrial DNA (mtDNA) sequences from specimens collected throughout Lake Tanganyika to clarify the evolutionary relationship between Lamprologus callipterus and Neolamprologus ...fasciatus. The nuclear data support the reciprocal monophyly of these two shell-breeding lamprologine cichlids. However, mtDNA sequences show that (i) L. callipterus includes two divergent and geographically disjunct (North-South) mtDNA lineages; and that (ii) N. fasciatus individuals cluster in a lineage sister group to the northern lineage of L. callipterus. The two mtDNA lineages of L. callipterus diverged c. 684 kya to 1.2 Ma, coinciding with a major water level low stand in Lake Tanganyika, which divided the lake into isolated sub-lakes. This suggests that the two mtDNA lineages originated as the result of the separation of L. callipterus populations in different sub-basins. The incongruent phylogenetic position of N. fasciatus can best be explained by an ancient unidirectional introgression from L. callipterus into N. fasciatus. Remarkably, our data indicate that this event resulted in the complete mtDNA replacement in N. fasciatus. Our data suggest that hybridization occurred soon after the divergence of the two L. callipterus mtDNA lineages, probably still during the water level low stand, and that subsequently the invading mtDNA lineage spread throughout the lake.
In this study, morphological differences were found that corroborate earlier results that showed the existence of six species within the previously monospecific African pike genus Hepsetus. ...Additional genetic data (coI, mtDNA and rag1, nDNA) confirm the morphology‐based species delineations. Deep genetic divergences imply a relatively old age for diversification within the genus. An identification key for the six species is provided in the present study.
African mole‐rats are subterranean Hystricomorph rodents, distributed widely throughout sub‐Saharan Africa, and displaying a range of social and reproductive strategies from solitary dwelling to the ...‘insect‐like’ sociality of the naked mole‐rat, Heterocephalus glaber. Both molecular systematic studies of Rodentia and the fossil record of bathyergids indicate an ancient origin for the family. This study uses an extensive molecular phylogeny and mitochondrial cytochrome b and 12s rRNA molecular clocks to examine in detail the divergence times, and patterns of speciation of the five extant genera in the context of rift valley formation in Africa. Based on a value of 40–48 million years ago (Myr) for the basal divergence of the family (Heterocephalus), we estimate divergence times of 32–40 Myr for Heliophobius, 20–26 Myr for Georychus/Bathyergus and 12–17 Myr for Cryptomys, the most speciose genus. While early divergences may have been independent of rifting, patterns of distribution of later lineages may have been influenced directly by physical barriers imposed by the formation of the Kenya and Western Rift, and indirectly by accompanying climatic and vegetative changes. Rates of chromosomal evolution and speciation appear to vary markedly within the family. In particular, the genus Cryptomys appears to have undergone an extensive radiation and shows the widest geographical distribution. Of the two distinct clades within this genus, one exhibits considerable karyotypic variation while the other does not, despite comparatively high levels of sequence divergence between some taxa. These different patterns of speciation observed both within the family and within the genus Cryptomys may have been a result of environmental changes associated with rifting.
Gudgeons (
Gobio gobio) from historically Cd and Zn contaminated sites in Flanders (Belgium) were found to be resistant to elevated Cd levels. In previous work, this increased resistance was largely ...explained by increased metallothionein (MT) expression. Recently, environmental cleanup efforts resulted in a significant decrease in Cd concentrations in the surface water. In this study, we evaluated the use of hepatic metal and metallothionein (MT) concentrations as biomarkers of metal exposure before and after the cleanup. Hepatic MT mRNA levels were determined after the environmental metal levels decreased in order to assess the applicability of MT gene expression as an environmental biomarker in natural fish populations. Our data show that both metallothionein protein and gene expression have the potential to be sensitive biomarkers for metal exposure. Significant correlations were found (a) among accumulated metal concentrations and both MT protein and mRNA levels, and (b) between MT protein and mRNA levels. However, our data illustrated that while MT protein and gene expression give a quantitative picture of metal load at a single time point, quantitative information in natural populations cannot always be obtained when different time points (including different years) are compared, since MT gene and protein expression are affected by many other factors in addition to the metal load. Furthermore, the result of the environmental cleanup was reflected in a decrease of hepatic Cd concentrations. Zn remained the most important factor determining MT concentrations. Finally, two differently sized MT mRNAs were amplified to test the hypothesis that 3′-UTR length can offer a protective advantage in conditions of environmental stress. Our data provided no evidence to support this hypothesis. In contrast, the ratio of the long mRNA variant relative to total MT mRNA was surprisingly constant, and independent of exposure history.
This paper investigates the usefulness of two mitochondrial genes (16S rRNA and cytochrome
b) to solve taxonomical difficulties within the genus
Hylomyscus and to infer its evolutionary history. Both ...genes proved to be suitable molecular markers for diagnosis of
Hylomyscus species. Nevertheless the resolving powers of these two genes differ, and with both markers (either analyzed singly or in combination), some nodes remain unresolved. This is probably related to the fact that the species emerged during a rapid diversification event that occurred 2–6
Myr ago (4–5
Myr ago for most divergence events). Our molecular data support the recognition of an “
aeta” group, while the “
alleni” and “
parvus” groups are not fully supported. Based on tree topology and genetic divergence, two taxa generally recognized as subspecies should be elevated at the species level (
H. simus and
H. cf kaimosae).
H. stella populations exhibit ancient haplotype segregation that may represent currently unrecognized allopatric species. The existence of cryptic species within
H. parvus is questioned. Finally, three potentially new species may occur in West Central Africa. The Congo and Oubangui Rivers, as well as the Volta and Niger Rivers and/or the Dahomey gap could have formed effective barriers to
Hylomyscus species dispersal, favoring their speciation in allopatry. The pronounced shifts in African climate during the late Pliocene and Miocene, which resulted in major changes in the distribution and composition of the vegetation, could have promoted speciation within the genus (refuge theory). Future reports should focus on the geographic distribution of
Hylomyscus species in order to get a better understanding of the evolutionary history of the genus.
Alongside the eusocial naked mole‐rat, Heterocephalus glaber, Heliophobius argenteocinereus represents the second oldest lineage within the African mole‐rat family Bathyergidae, and phylogenetically ...intermediate between the East African Het. glaber and the South African genera Bathyergus and Georychus. Across its geographic range, Hel.. argenteocinereus is widely distributed on both sides of the East African Rift System (EARS), and is a key taxon for understanding the phylogeographic patterns of divergence of the family as a whole. Phylogenetic analysis of 62 mitochondrial cyt b sequences, representing 48 distinct haplotypes from 26 geographic locations across the range of Heliophobius, consistently and robustly resolved six genetically divergent clades that we recognize as distinct evolutionary species. Early species descriptions of Heliophobius were synonymized into a monotypic taxonomy that recognized only Hel. argentocinereus. These synonyms constitute available names for these rediscovered cryptic lineages, for which combined morphological and genetic evidence for topotypical populations endorses the recognition of six to eight distinct taxa. Bayesian estimates of divergence times using the fossil Proheliophobius as a calibration for the molecular clock suggest that the adaptive radiation of the genus began in the early Miocene, and that cladogenesis, represented in the extant species, reflects a strident signature of tectonic activity that forged the principal graben in the EARS.
Wnt/Wingless signaling in Drosophila Swarup, Sharan; Verheyen, Esther M
Cold Spring Harbor perspectives in biology,
06/2012, Letnik:
4, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The Wingless (Wg) pathway represents one of the best-characterized intercellular signaling networks. Studies performed in Drosophila over the last 30 years have contributed to our understanding of ...the role of Wg signaling in the regulation of tissue growth, polarity, and patterning. These studies have revealed mechanisms conserved in the vertebrate Wnt pathways and illustrate the elegance of using the Drosophila model to understand evolutionarily conserved modes of gene regulation. In this article, we describe the function of Wg signaling in patterning the Drosophila embryonic epidermis and wing imaginal disc. As well, we present an overview of the establishment of the Wg morphogen gradient and discuss the differential modes of Wg-regulated gene expression.
African mole-rats (Bathyergidae, Rodentia) of the (eu)social genus
Fukomys are one of the most speciose mammal genera endemic to Sub-Saharan Africa.
Fukomys distributed in the Zambezian phytochorion ...is characterized by extreme chromosomal variation (2n
=
40–78). We inferred a molecular phylogeny of Zambezian
Fukomys to resolve the interrelationships and the evolutionary history of the known chromosomal races. We sequenced the entire cytochrome b gene (1140
bp) for a total of 66 specimens representing 18 karyotypical races from Zambia. An additional 31 sequences were retrieved from GenBank including data on all other chromosomal races. The haplotypes belonging to a small chromosomal race from Salujinga cluster with the
Fukomys mechowii (Giant mole-rat) haplotypes. Differential degrees of chromosomal variation are observed among the major mole-rat clades, which is most pertinent when comparing the central Zambezian
Fukomys micklemi and the northern Zambezian
Fukomys whytei clades. The karyotypically hyper-diverse (12 known chromosomal races)
Fukomys micklemi clade shows low levels of cytochrome b sequence divergence. Within the
F. whytei clade we find a more conservative pattern of chromosomal diversification (three known chromosomal races) while the levels of sequence divergence are much higher then in the
F. micklemi clade. Our results suggest that chromosomal changes may drive phyletic divergence and, eventually, speciation. The observed cladogenetic events during the Plio-Pleistocene within the
F. mechowii,
F. whytei,
F. damarensis and
F. micklemi clades appear to coincide with climatically mediated speciation bursts in other savannah dwelling mammals, including hominids. Based on the molecular data presented, combined with morphological and chromosomal data, the taxonomic implication seems to be that
Fukomys may contain several (undescribed) cryptic species.
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