scholarly journals Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity

2015 ◽  
Vol 112 (51) ◽  
pp. 15568-15573 ◽  
Author(s):  
Robert P. Lyons ◽  
Christopher A. Scholz ◽  
Andrew S. Cohen ◽  
John W. King ◽  
Erik T. Brown ◽  
...  
Keyword(s):  
Lake Level ◽  
Large Scale ◽  
Late Quaternary ◽  
Cichlid Fish ◽  
Biological Evolution ◽  
Distinct Species ◽  
Lake Malawi ◽  
Freshwater Ecosystems ◽  
Water Levels ◽  
Species Flock

The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9–15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world’s largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species.

scholarly journals Ancestral Hybridization Facilitated Species Diversification in the Lake Malawi Cichlid Fish Adaptive Radiation

2019 ◽  
Vol 37 (4) ◽  
pp. 1100-1113 ◽  
Author(s):  
Hannes Svardal ◽  
Fu Xiang Quah ◽  
Milan Malinsky ◽  
Benjamin P Ngatunga ◽  
Eric A Miska ◽  
...  
Keyword(s):  
Adaptive Radiation ◽  
Large Scale ◽  
Lake Victoria ◽  
Cichlid Fish ◽  
Lake Malawi ◽  
Raw Material ◽  
Founder Population ◽  
East African ◽  
Cichlid Species ◽  
Show Evidence

Abstract The adaptive radiation of cichlid fishes in East African Lake Malawi encompasses over 500 species that are believed to have evolved within the last 800,000 years from a common founder population. It has been proposed that hybridization between ancestral lineages can provide the genetic raw material to fuel such exceptionally high diversification rates, and evidence for this has recently been presented for the Lake Victoria region cichlid superflock. Here, we report that Lake Malawi cichlid genomes also show evidence of hybridization between two lineages that split 3–4 Ma, today represented by Lake Victoria cichlids and the riverine Astatotilapia sp. “ruaha blue.” The two ancestries in Malawi cichlid genomes are present in large blocks of several kilobases, but there is little variation in this pattern between Malawi cichlid species, suggesting that the large-scale mosaic structure of the genomes was largely established prior to the radiation. Nevertheless, tens of thousands of polymorphic variants apparently derived from the hybridization are interspersed in the genomes. These loci show a striking excess of differentiation across ecological subgroups in the Lake Malawi cichlid assemblage, and parental alleles sort differentially into benthic and pelagic Malawi cichlid lineages, consistent with strong differential selection on these loci during species divergence. Furthermore, these loci are enriched for genes involved in immune response and vision, including opsin genes previously identified as important for speciation. Our results reinforce the role of ancestral hybridization in explosive diversification by demonstrating its significance in one of the largest recent vertebrate adaptive radiations.

scholarly journals Ancestral hybridisation facilitated species diversification in the Lake Malawi cichlid fish adaptive radiation

2019 ◽  
Author(s):  
Hannes Svardal ◽  
Fu Xiang Quah ◽  
Milan Malinsky ◽  
Benjamin P Ngatunga ◽  
Eric A Miska ◽  
...  
Keyword(s):  
Adaptive Radiation ◽  
Large Scale ◽  
Lake Victoria ◽  
Cichlid Fish ◽  
Lake Malawi ◽  
Raw Material ◽  
Founder Population ◽  
Cichlid Species ◽  
Show Evidence ◽  
Adaptive Radiations

AbstractThe adaptive radiation of cichlid fishes in East Afrian Lake Malawi encompasses over 500 species that are believed to have evolved within the last 800 thousand years from a common founder population. It has been proposed that hybridisation between ancestral lineages can provide the genetic raw material to fuel such exceptionally high diversification rates, and evidence for this has recently been presented for the Lake Victoria Region cichlid superflock. Here we report that Lake Malawi cichlid genomes also show evidence of hybridisation between two lineages that split 3-4 million years ago, today represented by Lake Victoria cichlids and the riverine Astatotilapia sp. ‘ruaha blue’. The two ancestries in Malawi cichlid genomes are present in large blocks of several kilobases, but there is little variation in this pattern between Malawi cichlid species, suggesting that the large-scale mosaic structure of the genomes was largely established prior to the radiation. Nevertheless, tens of thousands of polymorphic variants apparently derived from the hybridisation are interspersed in the genomes. These loci show a striking excess of differentiation across ecological subgroups in the Lake Malawi cichlid assemblage, and parental alleles sort differentially into benthic and pelagic Malawi cichlid lineages, consistent with strong differential selection on these loci during species divergence. Furthermore, these loci are enriched for genes involved in immune response and vision, including opsin genes previously identified as important for speciation. Our results reinforce the role of ancestral hybridisation in explosive diversification by demonstrating its significance in one of the largest recent vertebrate adaptive radiations.

scholarly journals Different Sources of Allelic Variation Drove Repeated Color Pattern Divergence in Cichlid Fishes

2020 ◽  
Author(s):  
Sabine Urban ◽  
Alexander Nater ◽  
Axel Meyer ◽  
Claudius F Kratochwil
Keyword(s):  
Genetic Variation ◽  
De Novo ◽  
Allelic Variation ◽  
Lake Victoria ◽  
Cichlid Fish ◽  
Lake Malawi ◽  
Color Pattern ◽  
Species Flock ◽  
De Novo Mutations ◽  
Phenotypic Divergence

Abstract The adaptive radiations of East African cichlid fish in the Great Lakes Victoria, Malawi, and Tanganyika are well known for their diversity and repeatedly evolved phenotypes. Convergent evolution of melanic horizontal stripes has been linked to a single locus harboring the gene agouti-related peptide 2 (agrp2). However, where and when the causal variants underlying this trait evolved and how they drove phenotypic divergence remained unknown. To test the alternative hypotheses of standing genetic variation versus de novo mutations (independently originating in each radiation), we searched for shared signals of genomic divergence at the agrp2 locus. Although we discovered similar signatures of differentiation at the locus level, the haplotypes associated with stripe patterns are surprisingly different. In Lake Malawi, the highest associated alleles are located within and close to the 5′ untranslated region of agrp2 and likely evolved through recent de novo mutations. In the younger Lake Victoria radiation, stripes are associated with two intronic regions overlapping with a previously reported cis-regulatory interval. The origin of these segregating haplotypes predates the Lake Victoria radiation because they are also found in more basal riverine and Lake Kivu species. This suggests that both segregating haplotypes were present as standing genetic variation at the onset of the Lake Victoria adaptive radiation with its more than 500 species and drove phenotypic divergence within the species flock. Therefore, both new (Lake Malawi) and ancient (Lake Victoria) allelic variation at the same locus fueled rapid and convergent phenotypic evolution.

scholarly journals Female preference for conspecific males based on olfactory cues in a Lake Malawi cichlid fish

2005 ◽  
Vol 1 (4) ◽  
pp. 411-414 ◽  
Author(s):  
Martin Plenderleith ◽  
Cock van Oosterhout ◽  
Rosanna L Robinson ◽  
George F Turner
Keyword(s):  
Cichlid Fish ◽  
Mate Recognition ◽  
Lake Malawi ◽  
Olfactory Cues ◽  
Species Flock ◽  
East African ◽  
Significant Preference ◽  
African Species ◽  
Cichlid Species

Research on reproductive isolation in African cichlid fishes has largely focused on the role of nuptial colours, but other sensory modes may play an important role in mate choice. Here, we compare the relative importance of visual and olfactory cues in mate recognition by females of a Lake Malawi cichlid species. Female Pseudotropheus emmiltos were given a choice of spawning next to a conspecific male or a male of the closely-related sympatric Pseudotropheus fainzilberi . Significant preference for conspecific males only occurred when olfactory cues were present. This suggests that divergence of olfactory signals may have been an important influence on the explosive radiation of the East African species flock.

Major low levels of Lake Malawi and their implications for speciation rates in cichlid fishes

1990 ◽  
Vol 240 (1299) ◽  
pp. 519-553 ◽  
Keyword(s):  
Lake Level ◽  
Sediment Cores ◽  
Lake Malawi ◽  
Species Flock ◽  
Distribution Data ◽  
Drought Risk ◽  
Lake Levels ◽  
Dry Land ◽  
Cichlid Species ◽  
Founder Populations

Lake Malawi, the third largest lake in Africa, is several million years old. Lake levels have fluctuated to a considerable extent in the late Pleistocene. Although tectonism may have influenced earlier level changes, the more recent changes have been climatically controlled. Major recessions occurred in the period before 25000 years ago and 10740 ± 130 years ago, with further large falls between 1150 and 1250 A. D. and within the period 1500-1850. The 1500-1850 lake recession-refilling cycle is documented by using a variety of techniques. Sediment cores show an erosional hiatus stretching across the southern area of Lake Malawi down to water depths of at least 121 m. Diatoms sharply decline in abundance and diversity across this break, with Melosira nyassensis dominating in the post-erosion period. During the low stage, exposed littoral sands were reworked into aeolian dune-fields along windward shorelines. Oral histories reflect a group memory of this low period, which is supported by 14 C dated archaeological finds in beach ridges surrounding the lake. Dating by 210 Pb methods show that lacustrine sedimentation had resumed by about 1860. At this time, early explorers, such as Livingstone, were reporting evidence of rising lake levels. Hydrological modelling shows that the lake-level changes indicated are possible in the timespan available. Various permutations of rainfall and timescale are discussed, e. g. a drop of 110 m over 250 years would require rainfall at 50% of modern values. The changes in lake level imply longterm changes in climate; these are highly relevant in the field of drought-risk assessment. The species flock of rocky-shore dwelling Lake Malawi cichlids known as ‘Mbuna’ contains about 200 species in Malawi’s waters. Mitochondrial DNA differentiation shows that the flock as a whole is of extremely recent origin. Almost every rocky outcrop and island has a unique Mbuna fauna, with endemic colour forms and species. As many of these islands and outcrops were dry land within the last 200-300 years, the establishment of the faunas has taken place within that time. The evolution of distinct forms in such a brief timespan is discussed in relation to current ideas on allopatric speciation. The present diversity of the Malawi cichlid-species flock, and particularly the Mbuna, may be readily explained by the rapidity with which small founder populations can diverge from the parent population, as demonstrated by the present chronological evidence on changes in lake levels and by the Mbuna distribution data. The repeated recessions and refillings of the lake have provided numerous opportunities for the establishment of different founder populations and consequently different selection pressures, leading to further bouts of speciation.

The Wealden environment: Anglo-Paris Basin

1959 ◽  
Vol 242 (692) ◽  
pp. 283-346 ◽  
Keyword(s):  
Lake Level ◽  
Large Scale ◽  
Water Levels ◽  
Paris Basin ◽  
Delta Front ◽  
Fine Grained ◽  
Base Level ◽  
Mouth Bar ◽  
Underwater Slope

The Wealden cyclothems in the Weald are distinct from other sedimentary cycles so far reported. Their re-interpretation is based on recent sedimentological studies of analogous modern environments. The largely arenaceous lower part of each of the two megacyclothems in the Hastings Beds records the several environments of a growing and subsiding delta pile. Levee, crevasse and backswamp alluvium, pond-and-mere muds, channel sediments, shoreface sands, distributary mouth-bar and pro-delta deposits, etc., seem to be recognizable. The deltas advanced into lakes with fairly steady or falling water levels. Rates of deposition, up to 1 cm per 5 to 6 years, are suggested by certain of the fine-grained shoreface sands. ‘Classical' rather than birdfoot types of delta seem to be represented. The exposed portions were surrounded by extensive shallow water platforms. No major breaks of underwater slope are detectable: large-scale foresets are probably absent. The upper argillaceous parts of the megacyclothems, together with the back-delta (northern) portions of the arenaceous members immediately benath , are now regarded as having been formed during times of rising lake level. The clays and their basal beds are transgressive delta-front and pro-delta lakesediments, while the back-delta sands and silts below seem to have been valley-plug, levee and crevasse alluvium formed earlier behind the retreating coast in direct response to the rising base level. Alluvium also constitutes the more argillaceous parts of certain minor cyclothems of a different type. Extensive horsetail reedswamp grew offshore during times of retreat. The reeds were not able to establish themselves everywhere during periods of deltaic advance, owing to rapid silting, more frequent scour and the greater depth of suitable bottom sediments. Bigger plants as well as scattered horsetails grew on the surfaces of the deltas. Estuaries-of-inundation must have characterized these periods. The first major (Wadhurst) transgression advanced quickly, the reed beds in any one place lasting only a few years. Birdfoot deltas may have formed during its early stages for a short while. Close lithological, faunal, floral and petrological similarities between the cyclothems show that the same changes of environment were repeated several times. Probably the major fluctuations of lake level were in part relative only, being due either to changes in the rate of subsidence or to repeated river diversions causing the periodic abandonment of deltas and their consequent inundation. But, at certain horizons, continuity of deposition between the Wealden of Sussex and that of northern France is indicated by the petrology of the detritus. Hence the long-term fluctuations in lake level were probably also due in part to distant movements of the sea back and forth across the Paris basin. These in turn would have influenced channel ‘fixing’ and abandonment in the English alluvial plain. Short-term fluctuations of lake level were numerous. Some, near the base of the Wealden, may have been tidal in origin. Others took place mostly during times of deltaic advance. Several lines of evidence suggest the existence of well-marked seasons. Fundamental changes occurred during Weald Clay times, when the Wealden environments gradually coalesced and became transformed into a brackish arm of the advancing sea.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

2017 ◽  
Vol 4 ◽  
pp. 55-98
Author(s):  
Kathleen Springer ◽  
Jeffrey Pigati ◽  
Eric Scott
Keyword(s):  
Las Vegas ◽  
Late Quaternary ◽  
Plant Macrofossils ◽  
Distinct Species ◽  
American Southwest ◽  
Local Fauna ◽  
Climatic Oscillations ◽  
Las Vegas Valley ◽  
National Monument ◽  
Desert Wetlands

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

scholarly journals Comparative genomics suggests a taxonomic revision of the Staphylococcus cohnii species complex

2021 ◽  
Author(s):  
Anna Lavecchia ◽  
Matteo Chiara ◽  
Caterina De Virgilio ◽  
Caterina Manzari ◽  
Carlo Pazzani ◽  
...  
Keyword(s):  
Comparative Genomics ◽  
Species Complex ◽  
Large Scale ◽  
Genomic Sequence ◽  
Bacterial Species ◽  
Taxonomic Revision ◽  
Distinct Species ◽  
The Novel ◽  
Staphylococcus Cohnii ◽  
Taxonomic Assignments

Abstract Staphylococcus cohnii (SC), a coagulase-negative bacterium, was first isolated in 1975 from human skin. Early phenotypic analyses led to the delineation of two subspecies (subsp.), Staphylococcus cohnii subsp. cohnii (SCC) and Staphylococcus cohnii subsp. urealyticus (SCU). SCC was considered to be specific to humans whereas SCU apparently demonstrated a wider host range, from lower primates to humans. The type strains ATCC 29974 and ATCC 49330 have been designated for SCC and SCU, respectively. Comparative analysis of 66 complete genome sequences—including a novel SC isolate—revealed unexpected patterns within the SC complex, both in terms of genomic sequence identity and gene content, highlighting the presence of 3 phylogenetically distinct groups. Based on our observations, and on the current guidelines for taxonomic classification for bacterial species, we propose a revision of the SC species complex. We suggest that SCC and SCU should be regarded as two distinct species: SC and SU (Staphylococcus urealyticus), and that two distinct subspecies, SCC and SCB (SC subsp. barensis, represented by the novel strain isolated in Bari) should be recognized within SC. Furthermore, since large scale comparative genomics studies recurrently suggest inconsistencies or conflicts in taxonomic assignments of bacterial species, we believe that the approach proposed here might be considered for more general application.

scholarly journals Common Pool Resource Management: Assessing Water Resources Planning for Hydrologically Connected Surface and Groundwater Systems

Hydrology ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 51
Author(s):  
Francisco Muñoz-Arriola ◽  
Tarik Abdel-Monem ◽  
Alessandro Amaranto
Keyword(s):  
Water Resources ◽  
Collective Action ◽  
Large Scale ◽  
Integrated Management ◽  
Design Principles ◽  
Water Levels ◽  
High Plains ◽  
Common Pool Resource ◽  
Common Pool ◽  
Connected Surface

Common pool resource (CPR) management has the potential to overcome the collective action dilemma, defined as the tendency for individual users to exploit natural resources and contribute to a tragedy of the commons. Design principles associated with effective CPR management help to ensure that arrangements work to the mutual benefit of water users. This study contributes to current research on CPR management by examining the process of implementing integrated management planning through the lens of CPR design principles. Integrated management plans facilitate the management of a complex common pool resource, ground and surface water resources having a hydrological connection. Water governance structures were evaluated through the use of participatory methods and observed records of interannual changes in rainfall, evapotranspiration, and ground water levels across the Northern High Plains. The findings, documented in statutes, field interviews and observed hydrologic variables, point to the potential for addressing large-scale collective action dilemmas, while building on the strengths of local control and participation. The feasibility of a “bottom up” system to foster groundwater resilience was evidenced by reductions in groundwater depths of 2 m in less than a decade.

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