Studing Gonium pectorale to Explaint he Origin of Complex Life

Throughout the history of life on Earth, multicellular life evolved from single cells numerous times, but explaining how this happened is one of the major evolutionary puzzles of our time. However, scientists have now completed a study of the complete DNA of one of the most important model organisms, Gonium pectorale, a simple green algae that comprises only 16 cells.

This microscopic organism is helping to fill the evolutionary gap in our understanding. The two year research project was a global collaboration between Kansas State University, Universities of Arizona and Tokyo, and Wits University. It is documented in the prestigious journal Nature Communications.

Pierre Durand, a researcher in the department of Molecular Medicine and Haematology and the Evolutionary Studies Institute at Wits University is one of the project collaborators.

"The evolution from unicellular to multicellular life was a big deal. It changed the way the planet would be forever. From worms to insects, the dinosaurs, grasses, flowering plants, hadedas and humans, you just have to look around and see the extraordinary forms of multicellular existence," says Durand.

"It has been difficult to explain how this occurred because it was not an easy thing to have happened. So questions like 'why did single cells live together in groups at the very beginning of multicellularity when it puts them at a fitness disadvantage?' challenged us for a long time," says Durand. We still don't know most of the answers but this project has certainly filled one of the gaps in our current understanding.

There are many model systems for studying multicellularity but nothing quite like the volvocine green algae, the group to which G. pectorale belongs.

"The evolutionary transition to multicellularity has occurred numerous times in all domains of life, yet the evolutionary history of this transition is not well understood. However, the volvocine green algae include a diverse variety of unicellular, colonial, and multicellular species," says Durand.

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A new Burgess Shale-type Lagertatte From the Ediacaran NeoProterozoic Mongolia

A new Burgess Shale-type deposit from the Ediacaran of western Mongolia

Authors:

Dornbos et al

Abstract:

Preservation of soft-bodied organisms is exceedingly rare in the fossil record. One way that such fossils are preserved is as carbonaceous compressions in fined-grained marine sedimentary rocks. These deposits of exceptional preservation are known as Burgess Shale-type (BST) deposits. During the Cambrian Period, BST deposits are more common and provide a crucial view of early animal evolution. The earliest definitive fossil evidence for macroscopic animal-grade organisms is found in the preceding Ediacaran Period. BST deposits from the Ediacaran are rarer and lack conclusive evidence for animals. Here we report the discovery of a new Ediacaran BST deposit with exceptional preservation of non-mineralizing macro-organisms in thinly bedded black shale from Zavkhan Province, western Mongolia. This fossil assemblage, here named the Zuun-Arts biota, currently consists of two new species of probable macroscopic multicellular benthic algae. One species, Chinggiskhaania bifurcata n. gen., n. sp., dominates the biota. The other species, Zuunartsphyton delicatum n. gen., n. sp., is known from three specimens. SEM-EDS analysis shows that the fossils are composed of aluminosilicate clay minerals and some carbon, a composition comparable to fossils from the Cambrian Burgess Shale biota. This discovery opens a new window through which to view late Precambrian life.

pop sci link.

Did the Chicxulub Impact Trigger a Massive, Global Algae Bloom?

NOx production and rainout from Chicxulub impact ejecta reentry

Authors:

Parkos et al

Abstract:

The Chicxulub impact 66.0 Ma ago initiated the second biggest extinction in the Phanerozoic Eon. The cause of the concurrent oceanic nitrogen isotopic anomaly, however, remains elusive. The Chicxulub impactor struck the Yucatán peninsula, ejecting 2 × 1015 kg of molten and vaporized rock that reentered globally as approximately 1023 microscopic spherules. Here we report that modern techniques indicate that this ejecta generates 1.5 × 1014 moles of NOx, which is enough to cause the observed nitrogen enrichment of the basal layer. Additionally, reentry-based NO production would explain the anomalously heavy isotopic composition of the observed nitrogen. We include N, O, N2, O2, and NO species in simulations of nonequilibrium chemically reacting flow around a reentering spherule. We then determine the net production of NO from all the spherules and use turbulence models to determine how quickly this yield diffuses through the atmosphere. Upon reaching the stratosphere and troposphere, cloud moisture absorbs the NOx and forms nitric acid. We model this process and determine the acidity of the resulting precipitation, which peaks about 1 year after the impact. The precipitation ultimately reaches the upper ocean, where we assume that the well-mixed surface layer is 100 m deep. We then model the naturally occurring carbonate/bicarbonate buffer and determine the net pH. We find that insufficient NOx reaches the ocean to directly cause the observed end-Cretaceous oceanic extinction via acidification and buffer removal. However, the resulting nitrates are sufficient to explain the concurrent nitrogen isotopic anomaly and facilitate an end-Cretaceous algae bloom.

Plants may Have Evolved From TERRESTRIAL Algae 100s of Millions of Years Earlier Than Previously Thought

Plant biologists agree that it all began with green algae. At some point in our planet's history, the common ancestor of trees, ferns, and flowers developed an alternating life cycle--presumably allowing their offspring to float inland and conquer Earth. But on December 16 in Trends in Plant Science, Danish scientists argue that some green algae had been hanging out on land hundreds of millions of years before this adaptation and that land plants actually evolved from terrestrial, not aquatic, algae.

Botanists have suspected this possibility since 1980, but supporters have lacked proof. Now, Carlsberg Laboratory's Jesper Harholt and University of Copenhagen's Øjvind Moestrup and Peter Ulvskov present genetic and morphological evidence that corroborates the theory. Notably, traits that land plants use to survive on land today are well conserved in some species of green algae.

The collaboration began while Harholt and Ulvskov were studying the evolution of the plant cell wall, long considered to be a key adaptation for a terrestrial lifestyle, as it provides body support for plants growing under the influence of gravity.

"We realized that algae have a cell wall that's similarly complex to terrestrial plant cell walls, which seemed peculiar because ancient algae were supposedly growing in water," says Harholt, Science Manager at the Carlsberg Laboratory. "We then started looking for other traits that would support the idea that algae were actually on land before they turned into land plants."

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Did Suspension Feeding Animals in the Ediacaran Cause an Ecological Revolution in Autotrophs?

Proterozoic photosynthesis – a critical review

Author:

Butterfield

Abstract:

Chlorophyll-based photosynthesis has fuelled the biosphere since at least the early Archean, but it was the ecological takeover of oxygenic cyanobacteria in the early Palaeoproterozoic, and of photosynthetic eukaryotes in the late Neoproterozoic, that gave rise to a recognizably modern ocean–atmosphere system. The fossil record offers a unique view of photosynthesis in deep time, but is deeply compromised by differential preservation and non-diagnostic morphologies. The pervasively polyphyletic expression of modern cyanobacterial phenotypes means that few Proterozoic fossils are likely to be members of extant clades; rather than billion-year stasis, their similarity to modern counterparts is better interpreted as a combination of serial convergence and extinction, facilitated by high levels of horizontal gene transfer. There are few grounds for identifying cyanobacterial akinetes or crown-group Nostocales in the Proterozoic record. Such recognition undermines the results of various ancestral state reconstruction analyses, as well as molecular clock estimates calibrated against demonstrably problematic Proterozoic fossils. Eukaryotic organisms are likely to have acquired their (stem-group nostocalean) photoendosymbionts/plastids by at least the Palaeoproterozoic, but remained ecologically marginalized by incumbent cyanobacteria until the late Neoproterozoic appearance of suspension-feeding animals.

Evidence of a Giant Virus Battle in an Algae's Genome

Provirophages in the Bigelowiella genome bear testimony to past encounters with giant viruses

Authors:

Blanc et al

Abstract:

Virophages are recently discovered double-stranded DNA virus satellites that prey on giant viruses (nucleocytoplasmic large DNA viruses; NCLDVs), which are themselves parasites of unicellular eukaryotes. This coupled parasitism can result in the indirect control of eukaryotic cell mortality by virophages. However, the details of such tripartite relationships remain largely unexplored. We have discovered ∼300 predicted genes of putative virophage origin in the nuclear genome of the unicellular alga Bigelowiella natans. Physical clustering of these genes indicates that virophage genomes are integrated into the B. natans genome. Virophage inserts show high levels of similarity and synteny between each other, indicating that they are closely related. Virophage genes are transcribed not only in the sequenced B. natans strain but also in other Bigelowiella isolates, suggesting that transcriptionally active virophage inserts are widespread in Bigelowiella populations. Evidence that B. natans is also a host to NCLDV members is provided by the identification of NCLDV inserts in its genome. These putative large DNA viruses may be infected by B. natans virophages. We also identify four repeated elements sharing structural and genetic similarities with transpovirons—a class of mobile elements first discovered in giant viruses—that were probably independently inserted in the B. natans genome. We argue that endogenized provirophages may be beneficial to both the virophage and B. natans by (i) increasing the chances for the virophage to coinfect the host cell with an NCLDV prey and (ii) defending the host cell against fatal NCLDV infections.

The Terrestrial Biota Prior to the Evolution of Plants

The terrestrial biota prior to the origin of land plants (embryophytes): a review of the evidence

Authors:

Wellman et al

Abstract:

It is often assumed that life originated and diversified in the oceans prior to colonizing the land. However, environmental constraints in chemical evolution models point towards critical steps leading to the origin of life as having occurred in subaerial settings. The earliest fossil record does not include finds from terrestrial deposits, so much of our understanding about the presence of a terrestrial microbial cover prior to the Proterozoic is based on inference and geochemical proxies that indicate biospheric carbon cycling during the Archaean. Our assessment is that by 2.7 Ga, microbial ecosystems in terrestrial settings were driven by oxygen-generating, photosynthetic cyanobacteria. Studies of modern organisms indicate that both the origin and primary diversification of the eukaryotes could have occurred in terrestrial settings, shortly after 2.0 Ga, but there is no direct fossil evidence of terrestrial eukaryotes until about 1.1 Ga. At this time, it appears that the diversity of life in non-marine habitats exceeded that found in marine settings where sulphidic seas may have impaired eukaryotic physiology and retarded evolution. Geochemical proxies indicate the establishment of an extensive soil-forming microbial cover by 850 Ma, and it is possible that a rise in atmospheric oxygen at this time was due to the evolutionary expansion of green algae into terrestrial habitats. Direct fossil evidence of the earliest terrestrial biotas in the Phanerozoic consists of problematical palynomorphs from the Cambro-Ordovician of Laurentia. These indicate that the evolution of the first land plants (embryophytes) during the Middle Ordovician took place within a landscape that included aeroterrestrial algae which were actively adapting to selection in subaerial settings.

Marine Algae Fossils Found From Cryogenian NeoProterozoic Mongolia

FOSSILS OF PUTATIVE MARINE ALGAE FROM THE CRYOGENIAN GLACIAL INTERLUDE OF MONGOLIA

Authors:

Cohen et al

Abstract:

Neoproterozoic carbonate successions provide a new taphonomic window into the diversification of eukaryotes. We report recently discovered macroscopic organic warty sheets (MOWS) in macerates of limestone from the ca. 662–635 Ma Taishir Formation (Tsagaan Olom Group, Mongolia). Sheets are applanate. One surface contains raised ridges and conspicuous, ∼ 100-µm-tall warty protuberances with depressed tops that enclose internal cavities containing cellular structures. The Taishir MOWS may be the remains of unusual bacterial, protistan, or fungal biofilms, or a previously undocumented, extinct taxon. However, multiple lines of evidence including the morphology of warty protuberances and the presence of cellular architecture within protuberances support the interpretation of MOWS as marine algae, perhaps a member of the Rhodophyta. Regardless of their specific taxonomic affiliation, MOWS increase the diversity of biota reported from the Cryogenian glacial interlude and indicate the presence of macroscopic and morphologically complex multicellular organisms in the Cryogenian.

Ediacaran Doushantuo Embryo-like Fossils are Only Either Algae or Animals

Cell differentiation and germ–soma separation in Ediacaran animal embryo-like fossils

Authors:

Chen et al

Abstract:

Phosphorites of the Ediacaran Doushantuo Formation (~600 million years old) yield spheroidal microfossils with a palintomic cell cleavage pattern. These fossils have been variously interpreted as sulphur-oxidizing bacteria, unicellular protists, mesomycetozoean-like holozoans, green algae akin to Volvox and blastula embryos of early metazoans or bilaterian animals. However, their complete life cycle is unknown and it is uncertain whether they had a cellularly differentiated ontogenetic stage, making it difficult to test their various phylogenetic interpretations. Here we describe new spheroidal fossils from black phosphorites of the Doushantuo Formation that have been overlooked in previous studies. These fossils represent later developmental stages of previously published blastula-like fossils, and they show evidence for cell differentiation, germ–soma separation, and programmed cell death. Their complex multicellularity is inconsistent with a phylogenetic affinity with bacteria, unicellular protists, or mesomycetozoean-like holozoans. Available evidence also indicates that the Doushantuo fossils are unlikely crown-group animals or volvocine green algae. We conclude that an affinity with cellularly differentiated multicellular eukaryotes, including stem-group animals or algae, is likely but more data are needed to constrain further the exact phylogenetic affinity of the Doushantuo fossils.

Acritarch and Macroalgae Fossils From Calymian MesoProterozoic China

Diagenetic xenotime age constraints on the Sanjiaotang Formation, Luoyu Group, southern margin of the North China Craton: Implications for regional stratigraphic correlation and early evolution of eukaryotes

Authors:

Lan et al

Abstract:

Eukaryote fossil-bearing Ruyang and Luoyu groups are extensively exposed along the southern margin of the North China Craton, but their age has long been a matter of controversy due to the absence of reliable radiometric dates. By dating detrital zircons and diagenetic xenotimes from the Sanjiaotang Formation of the Luoyu Group, this paper confirms that the Ruyang and Luoyu groups were deposited during the period of 1750–1400 Ma. The new age constraints suggest that the Sanjiaotang Formation is coeval with the Xiamaling Formation of the Jixian Group on the northern margin of the North China Craton. Correlation of the Luoyu Group with the Jixian Group is thus indicated. The Ruyang and Luoyu groups contain abundant fossils of eukaryotic organisms such as acritarch and macroalgae. Accordingly, eukaryotic proliferation extends back to the Mesoproterozoic, consistent with results of molecular phylogenetic analysis that a rapid morphological diversification of eukaryotic organisms occurred prior to 1400 Ma.

Algae Radically Reducing Glacier Albedo

The first ecological study of an entire glacier has found that microbes drastically reduce surface reflectivity and have a non-negligible impact on the amount of sunlight that is reflected into space.

The research, led by the University of Leeds and published today [12 June] in the journal FEMS Microbiology Ecology, will help improve climate change models that have previously neglected the role of microbes in darkening the Earth's surface.

Observing how life thrives at extreme cold temperatures also has important implications for the search for life on distant worlds, such as Jupiter's icy moon Europa.

Stefanie Lutz, a PhD student at the School of Earth and Environment at the University of Leeds, and lead author of the study, said: "Our three-week field trip revealed a 'microbial garden' of life forms flourishing in this cold environment, including snow algae, bacteria, fungi and even invertebrates.

"Skiers may have seen snow algae before, but not been able to identify it. They are visible to the naked eye as coloured snow – most often red – and are frequently referred to as 'watermelon snow'."

The study was carried out on the Mittivakkat Glacier in south east Greenland during the summer of 2012, which was the hottest summer and thus the fastest melting season recorded for 150 years.

"Our timing was serendipitous, as it meant we were able to see changes in microbial processes over an extremely fast melting season and observe a process from start to end across all habitats on a glacier surface. This is the most comprehensive study of microbial communities living on a glacier to date," said Lutz.

The research showed that, compared to pure snow and ice, the reflectivity of the glacier (known as the "albedo") can be reduced by up to 80% in places where coloured microbial populations are extremely dense, leading to the darkening of the glacier surface.

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An Exceptionally Preserved Multicelluar Alga From Ediacaran NeoProterozoic Nevada

A Multicellular Alga With Exceptional Preservation From the Ediacaran of Nevada

Authors:

Rowland et al

Abstract:

Elainabella deepspringensis new genus new species is a one-mm-wide, non-biomineralized, three-dimensionally preserved fossil with segmented branches and apparent cellular structure. A single specimen was recovered from an interval of black shale within the Ediacaran portion of the Esmeralda Member of the Deep Spring Formation at Mt. Dunfee in Esmeralda County, Nevada. We interpret the fossil to be the thallus of a multicellular alga of uncertain division. EDS spectral analysis indicates that the exceptional preservation is not due to phosphatization or pyritization. Rather, it appears to be a case of Burgess Shale-type preservation, involving the kerogenization of non-mineralizing organisms. The fossil-bearing shale is closely associated with stromatolites, and we suggest that E. deepspringensis may have been an epibiont on stromatolites or other firm substrates. This is the first multicellular alga and the first occurrence of Burgess Shale-type preservation reported from the Ediacaran of Laurentia.

Possible Algal Origin and Life Cycle of Ediacaran Doushantuo Microfossils

Possible Algal Origin and Life Cycle of Ediacaran Doushantuo Microfossils with Dextral Spiral Structure

Authors:

Zhang et al

Abstract:

In Ediacaran shallow-water dolomites of the Doushantuo Formation (ca. 570 Ma) of southern China, scarce phosphatized microfossils consisting of clusters of coil-like spheroids called Spiralicellula bulbifera and co-occurring spherical forms with helically arranged holes named Helicoforamina wenganica are interpreted to belong to the same taxon because both have a similar relative abundance and both, uniquely in the assemblage, exhibit a consistent dextral spiral feature—the oldest known fossil examples of fixed asymmetry. Thus, we interpret them as different stages of sexual and asexual life cycles in which the spiral structure was maintained throughout most of the developmental phases. While they can be placed with the acritarchs, we suggest they are a chlorophycean green alga, and like many Ediacaran macrofossils, may represent an extinct clade. This is compatible with the shoal-water marine depositional environment in which they lived, as it would have favored photosynthetic organisms over others kinds of encysting non-metazoan protists. This setting militates against their interpretation as putative embryos which has been put forward for a variety of forms co-occurring in the microfossil assemblage. The multiple affinities of the strikingly diverse biota remain far from resolved, but algal origins warrant further consideration.

Playing God: Scientists Forcibly Evolve Multicellularity in Algae (Meanies!)

Scientists have puzzled for centuries over how and why multicellular organisms evolved the almost universal trait of using single cells, such as eggs and sperm, to reproduce. Now researchers led by University of Minnesota College of Biological Sciences postdoctoral fellow William Ratcliff and associate professor Michael Travisano have set a big piece of that puzzle into place by applying experimental evolution to transform a single-celled algae into a multicellular one that reproduces by dispersing single cells.

"Until now, biologists have assumed that this single-cell bottleneck evolved well after multicellularity, as a mechanism to reduce conflicts of interest among the cells making up the organism," says Ratcliff. "Instead, we found that it arose at the same time as multicellularity. This has big implications for how multicellular complexity might arise in nature, because it shows that this key trait, which opens the door to evolving greater multicellular complexity, can evolve rapidly."

In an article published today in the journal Nature Communications, the researchers described how they produced the multi-celled strain by repeatedly selecting and culturing algae that settled quickly to the bottom of a liquid-filled test tube. After 73 rounds, they discovered that the algae in one of the tubes had gone multicellular.

Observing the new form, Ratcliff and Travisano discovered that it reproduced by actively breaking up, shedding motile single cells that go on to grow into new multicellular clusters. They developed a mathematical model that explained the reproductive benefit of this single-celled strategy over hypothetical alternatives in which the cluster would produce larger propagules. The model predicted that reproduction from single cells would be more successful in the long run. Even though single cells are less likely to survive than larger propagules, this disadvantage is more than made up for by their sheer number.

In collaboration with Matthew Herron and Frank Rosenzweig at the University of Montana, the researchers are now working to find the genetic basis for multicellularity and experimentally evolve even greater multicellular complexity.

link.

NomNomNom! Green Algae Which Consume Cryanobacteria

Ediacaran Embryo Fossils Are Algae or Animal, Not Bacterial

FTIR microspectroscopy of Ediacaran phosphatized microfossils from the Doushantuo Formation, Weng’an, South China

Authors:

1. Motoko Igisu (a, b)
2. Tsuyoshi Komiya (a)
3. Mika Kawashima (c)
4. Satoru Nakashima (c)
5. Yuichiro Ueno (d, e)
6. Jian Han (f)
7. Degan Shu (f)
8. Yong Li (g)
9. Junfeng Guo (g)
10. Shigenori Maruyama (d, e)
11. Ken Takai (b, e, h)

Affiliations:

a. Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153–8902, Japan

b. Precambrian Ecosystem Laboratory, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2–15 Natsushima-cho, Yokosuka 237–0061, Japan

c. Department of Earth and Space Science, Osaka University, 1–1 Machikaneyama-cho, Toyonaka-shi, Osaka 560–0043, Japan

d. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152–8551, Japan

e. Earth-Life Science Institute, Tokyo Institute of Technology

f. Department of Geology and Key Laboratory for Continental Dynamics, Northwest University, Xi'an 710069, China

g. School of Earth Sciences and Resources Management, Chang'an University, Xi'an 710054, China

h. Subsurface Geobiology Advanced Research (SUGAR) project, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2–15 Natsushima-cho, Yokosuka 237–0061, Japan

Abstracts:

Phosphatized microfossils from ca. 580 Ma from the Doushantuo Formation in the Weng’an region of South China were analyzed by Fourier transform infrared (FTIR) microspectroscopy for their chemical characterization. Two morpho-types of phosphatized embryo-like fossils (Megasphaera and Megaclonophycus) were analyzed, together with algal fossils. Transmission IR spectra of the microfossils have absorption bands of around 2960 cm− 1 and 2925 cm− 1, indicating the presence of aliphatic hydrocarbon (anti-symmetric aliphatic CH3 and aliphatic CH2), and have an additional band of around 1595 cm− 1, probably derived from aromatic moieties (aromatic C = C). In addition, IR microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo-like fossils. The embryo-like fossils appear to show three types of CH3/CH2 peak height ratios (R3/2) and aromatic C = C/CH2 peak height ratios (RC=C/2 values): (1) high-R3/2/low-RC=C/2 type (R3/2 = ~ 0.2–1.0 and RC=C/2 ~ 0–2), (2) low-R3/2/medium-RC=C/2 type (R3/2 = ~ 0.2–0.6 and RC=C/2 = ~ 1–4); (3) low-R3/2/high-RC=C/2 type (R3/2 = ~ 0.2–0.6 and RC=C/2 ~ 1–8). All three types are contained in both Megasphaera and Megaclonophycus. Raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration, indicating the organics were embedded in situ prior to thermal maturation. The IR spectroscopic differences might reflect differences in original organic compositions of microorganisms, and/or immediate post-mortem alteration. This suggests that the origins of phosphatized embryo-like fossils are more diverse than was previously recognized on the basis of their morphology. A comparison of R3/2 and RC=C/2 values in the embryo-like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo-like fossils belong to animal embryo, others are algae, but none of them originate from bacteria.

Phylogenetics Show Green Algae Closest to Ancestors of Plants?

t was previously thought that land plants evolved from stonewort-like algae. However, new research published in BioMed Central's open access journal BMC Evolutionary Biology shows that the closest relatives to land plants are actually conjugating green algae such as Spirogyra.

Ancestors of green plants began to colonise the land about 500 million years ago and it is generally accepted that they evolved from streptophyte algae (a group of green, fresh water algae). But this group of algae is very diverse and currently ranges from simple, one cell, flagellates to more complex, branching, algae such as stoneworts (Chara).

It was thought that Charales were the closest relatives to land plants because they share (amongst other characteristics) a similar method of fertilisation, oogamy, with a large egg and small swimming sperm. For flowering plants this sperm is contained within pollen grains. In contrast, another type of streptophytes, the Zygnematales, use conjugation, a method of reproduction where the gametes are of equal size, isogamy, and one or both crawl, amoeba-like, into a fertilization tube where they meet and fuse.

Some phylogenetic analysis had been done previously, on a smaller number of genes, which seemed to support the Charales theory. However, a multinational team, involving researchers in Germany and Canada, analysed genetic divergence in 129 genes from 40 different green plant taxa. This data showed that, despite the differences in reproductive strategy, the closest living relatives to land plants are in fact the Zygnematales.

Dr Becker explained, "It seems that Zygnematales have lost oogamy and their ability to produce sperm and egg cells, and instead, possibly due to selection pressure in the absence of free water, use conjugation for reproduction. Investigation of such a large number of genes has shown that, despite their apparent simplicity, Zygnematales have genetic traces of other complex traits also associated with green land plants. Consequently Zygnematales true place as the closest living relative to land plants has been revealed."

no time.

Last Glacial Maximum's Effect on Kelp Genetics

Kelp genes reveal effects of subantarctic sea ice during the Last Glacial Maximum

1. Ceridwen I. Fraser1,
2. Raisa Nikula,
3. Hamish G. Spencer and
4. Jonathan M. Waters

-Author Affiliations

1.
Allan Wilson Centre for Molecular Ecology and Evolution, Department of Zoology, University of Otago, 340 Great King Street, Dunedin 9016, New Zealand

1.

Edited by Gary R. Carvalho, University of Wales, Bangor, Great Britain, and accepted by the Editorial Board December 23, 2008 (received for review October 23, 2008)

Abstract

The end of the Last Glacial Maximum (LGM) dramatically reshaped temperate ecosystems, with many species moving poleward as temperatures rose and ice receded. Whereas reinvading terrestrial taxa tracked melting glaciers, marine biota recolonized ocean habitats freed by retreating sea ice. The extent of sea ice in the Southern Hemisphere during the LGM has, however, yet to be fully resolved, with most palaeogeographic studies suggesting only minimal or patchy ice cover in subantarctic waters. Here, through population genetic analyses of the widespread Southern Bull Kelp (Durvillaea antarctica), we present evidence for persistent ice scour affecting subantarctic islands during the LGM. Using mitochondrial and chloroplast genetic markers (COI; rbcL) to genetically characterize some 300 kelp samples from 45 Southern Ocean localities, we reveal a remarkable pattern of recent recolonization in the subantarctic. Specifically, in contrast to the marked phylogeographic structure observed across coastal New Zealand and Chile (10- to 100-km scales), subantarctic samples show striking genetic homogeneity over vast distances (10,000-km scales), with a single widespread haplotype observed for each marker. From these results, we suggest that sea ice expanded further and ice scour during the LGM impacted shallow-water subantarctic marine ecosystems more extensively than previously suggested.

First, since it's my drum to beat lately, repeat after me: the world is not in a stable state.

Secondly, this makes for interesting thoughts on the extent of the southern hemisphere's ice during that last LGM.