sexta-feira, 30 de novembro de 2018

Novas pistas podem explicar por que esse temível leão marsupial desapareceu da Austrália

Artist’s impression of *Thylacoleo carnifex.*

Novas pesquisas sugerem que a mudança climática - e não a atividade humana - fez com que Thylacoleo carnifex, um leão marsupial australiano, fosse extinto.

Por milhões de anos, Thylacoleo carnifex governou as florestas da Austrália, mas essas espécies predatórias desapareceram em torno de 35.000 a 45.000 anos atrás. Os seres humanos apareceram pela primeira vez na Austrália há cerca de 60 mil anos, levando os cientistas a se perguntarem se os humanos eram de alguma forma responsáveis - e não uma sugestão escandalosa, considerando nosso histórico dúbio em tais assuntos.

Nova pesquisa conduzida pela paleontóloga Larisa DeSantis, da Universidade Vanderbilt, com a ajuda de colegas da Universidade de New South Wales e da Universidade de Queensland, sugere que esses leões marsupiais perderam seu habitat devido à mudança climática (o tipo natural - não o induzido pelo homem). versão que estamos presenciando hoje), levando à sua eventual extinção. Humanos, de acordo com esta pesquisa, não tinham nada a ver com isso. De uma vez.

Thylacoleo é o maior mamífero australiano carnívoro conhecido, reinando como um dos predadores mais temíveis da Austrália por 2 milhões de anos. Essas criaturas eram um pouco maiores que os leopardos modernos, mas menores que os leões africanos de hoje. Suas mandíbulas deram um tremendo golpe, produzindo algumas das forças de mordida mais fortes já documentadas em um mamífero.

DeSantis and her colleagues were able to show that Thylacoleo was an exclusive forest dweller, and not accustomed to open habitats, a conclusion reached by applying two different methods.

“Stable isotopes told us that Thylacoleo ate prey that resides in forests,” DeSantis explained to Gizmodo, while a 3D dental analysis of wear-and-tear on this creature’s teeth pointed to the same conclusion. “We determined,” she said, “that Thylacoleo was highly specialized on prey from forested environments and this would’ve made it more vulnerable to extinction with the long-term pattern of aridification that begin around 350,000 years ago.” These findings were presented by DeSantis and her colleagues at a recent meeting of the Society of Vertebrate Paleontology, and a formal science paper is forthcoming.

"Esta pesquisa ajuda a demonstrar que até mesmo os predadores mais ferozes podem sucumbir à mudança climática."

Além das análises químicas e dentárias, uma revisão das características físicas deste animal sugere que ele era um caçador de emboscadas, capaz de se lançar em presas desprevenidas a distâncias próximas. O Thylacoleo, dizem os pesquisadores, não foi construído para perseguir rapidamente presas através de vastas paisagens abertas.

Como DeSantis apontou, a Austrália começou a secar há cerca de 350 mil anos, um processo que transformou florestas exuberantes em savanas abertas. Thylacoleo, sendo altamente adaptado às florestas, simplesmente não poderia se ajustar à perda de seu habitat, tornando-se menos eficaz na caça ao longo do tempo. "Esta pesquisa", disse ela, "ajuda a demonstrar que até mesmo os predadores mais ferozes podem sucumbir à mudança climática".

Study co-author Gilbert Price from the University of Queensland echoed these sentiments in a press release: “When you’re big and bitey, you can eat pretty much anything you want. But our findings show that even the top predators are no match for extreme climate change.”

“Marsupial lions were far more specialised than African lions. They even had a proportionately larger brain than African lions as well as large, uniquely formidable, large can-opener-like thumb claws,” Michael Archer, a paleontologist from the University of New South Wales, said in a statement. “What’s increasingly clear now is that it evidently survived the arrival of humans 60,000 years ago, but apparently not the profound impacts of a rapidly drying climate that undermined the survival of a range of megafaunal mammals in Australia.”

In terms of the study’s shortcomings, the authors admit that they only sampled specimens from New South Wales in Queensland. “Thus,” DeSantis told Gizmodo, “while we don’t have data from Western Australia, all 35 of our samples from eastern Australia suggest that Thylacoleo was a specialist on forest-dwelling prey.”

Curiosamente, este agora extinto leão marsupial era contemporâneo do tilacino, mais conhecido como o tigre da Tasmânia. Este animal, que foi extinto durante o século 20, foi mais capaz de se adaptar aos novos e abertos habitats da Austrália, o que provavelmente explica por que sobreviveu ao período de aridificação da Austrália, enquanto o Thylacoleo não conseguiu. O Thylacoleo carnifex tinha algumas características físicas impressionantes, mas suas adaptações altamente especializadas acabaram se revelando sua ruína.

Extinct 'Siberian Unicorns' Walked the Earth Alongside Modern Humans

Artist’s impression of the “Siberian unicorn,” actually a species of rhino.

Pesando até 7.700 libras, o Elasmotherium sibiricum - um rinoceronte cabeludo extinto, popularmente conhecido como “unicórnio siberiano” - teria desaparecido há 200 mil anos. Uma análise fóssil atualizada sugere que essa espécie formidável ainda existia há cerca de 39 mil anos, e que as condições da Era do Gelo, e não os caçadores humanos, contribuíram para o seu desaparecimento.

Os paleontólogos conhecem cerca de 250 espécies de rinocerontes, das quais apenas cinco ainda existem hoje. Entre os mais espetaculares desses rinocerontes estava o Elasmotherium sibiricum - o unicórnio siberiano. Para os neandertais e os humanos modernos que viveram ao lado e possivelmente caçaram essa enorme criatura na Europa Oriental e Ásia Central, deve ter sido uma visão impressionante e profundamente intimidadora. Evidências fósseis sugerem que o Elasmotherium pesava mais de 3,5 toneladas, estava coberto por uma espessa camada de pelos e ostentava um chifre de porções bíblicas, possivelmente com até 1 metro de comprimento.

Por mais impressionante que tenha sido, os unicórnios siberianos acabaram morrendo. A datação anterior de fósseis sugeriu uma data de expiração em algum ponto entre 200.000 e 100.000 anos atrás, muito antes da extinção da megafauna do Quaternário em larga escala, que ocorreu há 40.000 anos. Nova pesquisa publicada esta semana na Nature Ecology & Evolution está oferecendo uma estimativa mais confiável, datando o fim do Elasmotherium em algum ponto entre 39.000 e 35.000 anos atrás. A extinção dos unicórnios siberianos, portanto, pode agora ser conectada à extinção da megafauna quaternária tardia, um evento que testemunhou o fim do mamute lanoso, do alce irlandês e do gato com dentes de sabre.

Writing in their new study, led by Adrian Lister from the Natural History Museum in London, the researchers said “no absolute dating, genetic analysis or quantitative ecological assessment of this species [had] been undertaken,” which explains why the prior extinction estimate was so far off. The new study overcomes these shortcomings, and includes the use of updated fossil dating techniques.

For the study, an international team of researchers from the UK, Netherlands, and Russia took a closer look at 23 Elasmotherium specimens, including a pristine skull kept at the Natural History Museum. An improved radiocarbon dating technique resulted in the revised extinction dates; many of the samples were slathered in preservation materials, requiring careful preparation for the carbon dating.

“Some of the samples we studied were very contaminated which made the radiocarbon dating very challenging,” Thibaut Devièse, a researcher at Oxford’s School of Archaeology and a co-author of the study, said in a statement. “For this reason we used a novel method of extracting a single amino acid from the bone’s collagen in order to ensure highly accurate results.”

In addition, the researchers succeeded, for the first time ever, in extracting DNA from the Elasmotherium fossils. The ensuing genetic analysis showed that Siberian unicorns split from modern rhinos around 43 million years ago, “settling a debate based on fossil evidence and confirming that the two lineages had diverged by the Eocene,” the researchers wrote in the study. These Ice Age rhinos are the last species of a “highly distinctive and ancient lineage,” according to the research.

Siberian unicorns lived alongside anatomically modern humans and Neanderthals. That ancient hominids may have preyed upon these oversized rhinos is not as outrageous a proposition as it may seem. Early humans, likely a form of Homo erectus, were hunting rhinos in the Philippines around 700,000 years ago. But while rhinos were on the hominid menu, this new research suggests climate change, and not hunters, was responsible for Elasmotherium’s demise.

Esses rinocerontes, como sabemos agora da nova pesquisa, viveram durante a Idade do Gelo pouco antes do Último Máximo Glacial - o estágio no qual as camadas de gelo cobriam sua maior área, cerca de 26.500 anos atrás. A Terra estava propensa a dramáticas mudanças climáticas durante este período, produzindo secas, desertificação, uma queda no nível do mar e a constante invasão das geleiras. Essas rupturas climáticas resultaram fatais para muitas espécies, dentre elas o Elasmotherium.

Para o unicórnio siberiano, isso significou uma perda de habitat e, consequentemente, o desaparecimento de uma fonte crítica de alimento, como o novo estudo supõe. Em experimentos, Lister e seus colegas analisaram as razões isotópicas estáveis dos rinocerontes fossilizados. Os pesquisadores procuraram ligar várias plantas com os níveis de isótopos de carbono e nitrogênio em seus dentes. Os unicórnios siberianos, como revelaram essas análises, viviam em um ambiente de estepe seco, onde mastigavam gramíneas duras e secas. Os rinocerontes, com seu estilo de vida de pastoreio altamente especializado e com números populacionais naturalmente baixos, não conseguiram se adaptar com rapidez suficiente às condições de rápida mudança, sugere o estudo.

A changing climate, and not humans, were thus responsible for the demise of E. sibiricum. Interestingly, it’s a conclusion that jibes well with similar, but unrelated, research, in which scientists claim that humans weren’t responsible for many megafaunal extinctions of the Ice Age. Sadly, the same cannot be said for the ongoing sixth mass extinction, which is most certainly our fault.

Researchers excavated stone cores like this one that early human ancestors used to strike off sharp-edged cutting flakes.

M. Sahnouni

Strongest evidence of early humans butchering animals discovered in North Africa

By Ann GibbonsNov. 29, 2018 , 2:45 PM

Em um alto planalto gramado na Argélia, a apenas 100 quilômetros do Mar Mediterrâneo, os primeiros ancestrais humanos mataram cavalos extintos, antílopes e outros animais com ferramentas de pedra primitivas de 2 milhões a 2,4 milhões de anos atrás. As datas, relatadas hoje, afastam a idade das ferramentas mais antigas no norte da África em até meio milhão de anos e fornecem uma nova visão sobre como esses proto-humanos se espalham pelo continente.

For decades, east Africa has been considered the birthplace of our genus Homo, and the epicenter of early toolmaking for almost 1 million years. The oldest known Homo fossils date back 2.8 million years in Ethiopia. Nearby, just 200,000 years later, scientists have found simple tools, such as thumb-size stone flakes, and fist-size cores from which such flakes were struck, in the nearby Rift Valley of Ethiopia. Claims of even older tools and animal bones with cutmarks stretch back 3.4 million years in east Africa, but those claims are controversial.

Regardless, the long-standing view has been that once hominins, or members of the human family, invented stone tools in east Africa, they didn’t travel far with them until 1.8 million years ago (or, more controversially, 2 million years ago, in China) when tools turn up in Algeria, Georgia, and China.

The new study upends this view. After 25 years of excavations at the Ain Hanech complex—a dry ravine in Algeria—an international team reports the discovery of about 250 primitive tools and 296 bones of animals from a site called Ain Boucherit. About two dozen animal bones have cut marks that show they were skinned, defleshed, or pounded for marrow. Made of limestone and flint, the sharp-edged flakes and round cores—some the size of tennis balls—resemble those found in east Africa. Both represent the earliest known toolkit, the so-called Oldowan technology, named for the site where they were found 80 years ago at Olduvai in Tanzania.

Archaeologist Mohamed Sahnouni excavates the oldest known stone tools in northern Africa at Ain Boucherit.

M. Sahnouni

Ain Hanech lacks volcanic minerals, which provide the gold standard for dating sites in eastern Africa. Instead, the researchers used three other dating methods, notably paleomagnetic dating, which detects known reversals in Earth’s magnetic field that are recorded in rock. The tools and cut-marked bones date as far back as 2.4 million years ago, the researchers report today in Science. They also used the identity of large, extinct animals, such as mastodons and ancient horses, to confirm the dates.

Os ossos com marcas de corte representam "a evidência substantiva mais antiga para o açougue" em qualquer lugar, diz o paleoantropólogo Thomas Plummer, do Queens College da Universidade de Nova York, que não esteve envolvido no estudo. Embora outros locais dessa idade na África Oriental tenham ferramentas de pedra, a evidência para o efetivo açougue de animais não é tão forte, diz ele.

At Ain Hanech, the dates provide “convincing evidence for stone tools and cut-marked bones at about 2 million years or more,” says geochronologist Warren Sharp of the Berkeley Geochronology Center in California. But he finds the 2.4 million date “less compelling,” because of potential issues with the dating methods.

Whether the tools are 2 million or 2.4 million years old, they suggest toolmakers had spread farther and wider across Africa earlier than previously known. “There must have been a corridor through the Sahara with movement between east Africa and North Africa,” says paleoanthropologist Rick Potts of the Smithsonian Institution’s National Museum of Natural History in Washington, D.C. Alternatively, the new dates suggest hominins in at least two different parts of Africa, separated by 5000 kilometers, were sophisticated enough to independently invent rudimentary stone tools and habitually make them, Potts says.

Either way, the study suggests that by 2 million years ago or so, making stone tools and butchering meat with them was routine for human ancestors in distant corners of the African continent. And this technological revolution may have given them the tools they needed to travel farther and wider across Africa and beyond.

Posted in:

Archaeology

doi:10.1126/science.aaw2245

Blazing quasars reveal the universe hit ‘peak star birth’ 3 billion to 4 billion years after the big bang

By Sid PerkinsNov. 29, 2018 , 2:00 PM

When were most of the universe’s stars born? Scientists have long known that the answer is “long ago.” But a new study that scrutinizes the radiation from blazing quasars suggests a far more precise answer: some 3 billion to 4 billion years after the big bang.

Blazing quasars, or “blazars,” are galaxies whose intense brightness is fueled in large part by gas, dust, and stars being sucked into the supermassive black holes that lie at their centers. Unlike most distant stars and galaxies, blazars pump out gamma rays that can be picked up by sensors on space-based observatories orbiting Earth. As material spirals inward along the plane of the galaxy’s disk, powerful beams of radiation (above) emerge along the galaxy’s rotational axis. When one of those spotlightlike beams is pointed toward Earth, the blazars appear particularly bright.

In the new study, researchers looked at the radiation beamed toward Earth by more than 700 blazars scattered across the sky. Analyzing the blazars’ gamma ray emissions, they found that some were blocked more effectively than others. That’s significant because when photons from the gamma rays travel through space, they can interact with the low-energy photons from stars to create subatomic particles like electrons and protons. So the more gamma ray emissions blocked, the thicker the fog of photons in that part of intergalactic space—and the more stars required to make them.

Matching the “foggy” regions up to the distance of the blazars—between 200 million and 11.6 billion light-years from Earth—the researchers were able to determine rates of star formation for those regions, accounting for more than 90% of the history of the universe, they report today in Science. Peak rates of star birth, which were about 10 times higher than today’s rates, occurred between 9.7 billion and 10.7 billion years ago.

*Correction, 29 November, 3:50 p.m.: This story has been updated to correct the date range in the headline and first paragraph.

Posted in:

Space

doi:10.1126/science.aaw2247

The moon's far side has a thick, old crust and is pockmarked by many deep craters.

NASA/GODDARD/ARIZONA STATE UNIVERSITY

China sets out for the far side of the moon

By Dennis NormileNov. 29, 2018 , 12:00 PM

SHANGHAI, CHINA—China's ambitious program of lunar exploration is about to attempt a spacefaring first: On 8 December it will launch a probe intended to land on the far side of the moon. Besides boasting rights, the Chang'e-4 lander and rover are expected to produce a host of new insights into the moon's composition and history. "Chang'e-4 is an historical mission," says Bernard Foing, director of the European Space Agency's (ESA's) International Lunar Exploration Working Group in Noordwijk, the Netherlands.

Remote observations have shown that the far side of the moon, invisible from Earth, has a much thicker, older crust and is pockmarked by more and deeper craters than the near side, where large dark plains called maria, formed by ancient lava flows, have erased much of the cratering. The big difference "is still a mystery," Foing says, and Chang'e's trip "can give clues."

China started its lunar program 3 decades after the United States and the Soviet Union ended theirs. Chinese geologists eager to study the moon convinced the government to establish the Lunar Exploration Program under the China National Space Administration (CNSA) in 2004. The agency launched Chang'e-1 and Chang'e-2, named after a Chinese moon goddess, in 2007 and 2010, respectively; both produced "a lot of good science," including high-resolution lunar images and new altimetry measurements, says planetary scientist James Head of Brown University.

In 2013, Chang'e-3 became the first craft to land on the moon since the Soviet Union's Luna 24 sample return mission in 1976. The lander and the small rover it carried gathered data on the moon's topography, mineralogy, and elemental abundance. In a first, the rover was equipped with a ground-penetrating radar that profiled buried lava flows and regolith, the broken up rock and dust that makes up the lunar soil.

Chang'e-4 was designed as an identical backup to Chang'e-3, but when that mission proved successful, China's planners became more ambitious. Going to the far side promised "unique and original science" as well as a chance to "develop China's deep space observational capabilities," says Li Chunlai, deputy director-general of the Chinese Academy of Sciences's National Astronomical Observatories of China (NAOC) in Beijing, which advises CNSA on the program's science objectives.

Chang'e-4 will explore a 12-kilometer-deep lunar crater likely formed by a giant asteroid impact.

CNSA

Because the moon will block direct radio contact with the lander and rover, Chang'e-4 will rely on a communications relay satellite, launched in May. Called Queqiao, it's traveling in a loop 65,000 kilometers beyond the moon at Earth-moon Lagrange Point 2, a gravitational balance point. Chang'e-4 itself will land in the Von Kármán crater within the South Pole–Aitken basin. Likely formed by a giant asteroid impact, the basin is roughly 2500 kilometers across and 12 kilometers deep. "It's the moon's largest, deepest, and oldest impact structure," says planetary geoscientist Xiao Long of the China University of Geosciences in Wuhan.

The impact may have brought material from the moon's upper mantle to the surface, a scenario that data from a visible and near-infrared imaging spectrometer might be able to verify. The imaging spectrometer will also explore the geochemical composition of far-side soil, which is likely to differ from the near side because of the same processes that produced the difference in crust thickness.

The rover's ground-penetrating radar—similar to that on Chang'e-3—will provide another look down to about 100 meters beneath the surface, probing the depth of the regolith and looking for subsurface structures. Combining the radar data with surface images from cameras on the lander and rover might advance scientists' understanding of the cratering process.

Going to the far side also opens "a totally new window for radio astronomy," says Ping Jinsong, a NAOC radio astronomer. On Earth, and even in near-Earth space, natural and humanmade interference hampers low-frequency radio observations. The moon blocks this noise. So the mission carries a trio of low-frequency receivers: one on the lander, one—a collaboration with the Netherlands—on Queqiao, and a third on a microsatellite released from Queqiao into a lunar orbit. (Contact with a second microsatellite carrying a fourth receiver has been lost.) The receivers will listen for solar radio bursts, signals from aurorae on other planets, and the faint signals from the primordial clouds of hydrogen gas that coalesced into the universe's first stars.

China's ambitious lunar program will continue with Chang'e-5, a sample return mission, due for launch next year. It will retrieve up to 2 kilograms of soil and rock from the Oceanus Procellarum, a vast lunar mare on the near side untouched by previous landings, and one of the moon's youngest volcanic flows. "It's a great objective and will potentially yield some fantastic science," says Bradley Jolliff, a planetary scientist at Washington University in St. Louis, Missouri, who has urged the United States to launch its own lunar sample return mission.

If China continues its tradition of developing moon missions in pairs, a second sample return mission, Chang'e-6, might follow. Head notes that NASA, ESA, Japan, Russia, and India have all taken a renewed interest in our planet's companion, which holds clues to Earth's own history. "Chang'e-4 and 5 are a major part of this renaissance," Head says, "and in many ways are the current vanguard."

‘Siberian unicorn’ may have walked with early humans

By Frankie SchembriNov. 29, 2018 , 11:10 AM

Nossos parentes mais antigos poderiam ter andado com unicórnios. Mas o Elasmotherium sibiricum, comumente conhecido como unicórnio siberiano, provavelmente parecia mais um rinoceronte robusto e peludo com um chifre de um metro de comprimento do que um puro cavalo branco. Estimações anteriores colocam a extinção de E. sibiricum há 200 mil anos, mas novos espécimes sugerem que ela pode ter sobrevivido até cerca de 39 mil anos atrás, sobrepondo-se brevemente aos primeiros humanos na área, relata o Gizmodo.

Análises de isótopos dos fósseis mostraram que os rinocerontes viviam em uma dieta de gramíneas duras e secas, e provavelmente morreram quando o clima de mudança da idade do gelo acabou com sua principal fonte de alimento, relatam os pesquisadores nesta semana na revista Nature Ecology & Evolution.

A análise de DNA também mostrou que E. sibiricum se separou dos rinocerontes modernos na árvore evolucionária há cerca de 43 milhões de anos.

This special DNA isn’t just from moms anymore

By Mitch LeslieNov. 27, 2018 , 2:05 PM

As mitocôndrias, as organelas que alimentam as células, abrigam seu próprio DNA, e os cientistas há muito achavam que apenas as mães podiam passar esse material genético para seus filhos. Mas um novo estudo sugere que os pais podem não ser os críticos que pensávamos que fossem, os relatórios NOVA da PBS.

Ao sequenciar o DNA mitocondrial de indivíduos com sintomas misteriosos e seus parentes, os cientistas descobriram evidências de herança paterna em 17 pessoas de três famílias diferentes, revelam esta semana na revista Proceedings of National Academy of Sciences.

A transmissão do pai para a prole - que os pesquisadores já viram em ovelhas, moscas e até em camundongos - é provavelmente rara em humanos, mas o novo trabalho sugere que mais de nós pode estar carregando um legado mitocondrial de nossos pais do que imaginávamos.

quinta-feira, 29 de novembro de 2018

Restauração morfológica: o que é?

A aplicação de técnicas de restauração passiva, embora produza uma série de benefícios ao sistema, na maioria dos casos não consegue recuperar determinadas condições ambientais dele, seja pela irreversibilidade do processo degradante, seja por seu longo tempo de recuperação, como no caso de rios de planície com limitada potência de canal.

Nessas situações, a restauração morfológica e funcional é propiciada ou acelerada pela restauração ativa. Contudo, por serem extremamente caros e trabalhosos, os métodos desse tipo de restauração têm aplicação em um número bastante reduzido de casos.

As técnicas, embora variadas, exigem bom conhecimento da dinâmica fluvial, bem como da estrutura e do funcionamento do sistema. As estruturas mais comumente implantadas no canal são:

dissipadores: estruturas transversais ou diagonais relativamente baixas fixadas no fundo cuja função é reduzir e dissipar a energia do canal para evitar a erosão e a incisão dele, bem como diminuir a capacidade do fluxo de transportar sedimento; também são utilizados para aumentar a taxa de oxigênio na água (Fig. 9.10A);
defletores: estruturas semelhantes aos dissipadores e que promovem o direcionamento do fluxo para uma função específica, como induzir a deposição ou a incisão localizada (Fig. 9.10B);
soleiras: estruturas desobstrutivas submersas em qualquer nível de água que podem ou não estar ligadas à margem do canal. Têm a função de diversificar o ambiente do fundo de canal, reduzindo a energia excedente e servindo de ancoragem à vegetação e de abrigo aos peixes (Fig. 9.10C).

*(Imagem retirada do livro Geomorfologia Fluvial, Editora Oficina de Textos. Todos os direitos reservados.)*

Tudo a ver

Geomorfologia fluvial integra a coleção básicos em Geografia, oferecendo uma sólida introdução aos processos fluviais e às morfologias derivadas, ressaltando sua importância no gerenciamento, preservação e recuperação dos rios.

As camadas de uma paisagem

As paisagens apresentam grande variedade ao longo da superfície terrestre, o que ocorre em função de diversos fatores de diferenciação (clima, tectônica, relevo etc.). Elas também variam ao longo do tempo.

Veja a seguir o exemplo da Fig. 1.2. Podemos ver a paisagem dissecada da borda da bacia sedimentar do Jatobá, que levou milhões de anos para ser esculpida. O arenito que dá estrutura a ela recobria grande parte do Nordeste brasileiro e foi muito erodido após a abertura do Oceano Atlântico.

*Fig 1. Morros-testemunhos do Parque Nacional do Catimbau PE o arranjo. (Imagem retirada do livro Cartografia de Paisagens – 2ª ed., Editora Oficina de Textos. Todos os direitos reservados.)*

Essa área se manteve relativamente preservada da longa erosão por estar, em parte, aprisionada numa estrutura tectônica de afundamento denominada aulacógeno, que se formou durante o processo de separação continental e abertura oceânica.

Além dos testemunhos sedimentares, a paisagem da Fig. 1 ainda se insere no contexto climático quente e semiárido que condiciona a formação de um relevo aplainado com encostas côncavas (com pouco sedimento acumulado), geralmente apresentando escarpas.

Esse ambiente, estruturado sobre um arenito, origina solos arenosos profundos que, combinando-se com o clima, provocam grande estresse hídrico sobre a vegetação, favorecendo espécies xerófilas com diversas estratégias de armazenamento de água.

A beleza cênica do lugar ainda teve influência na criação de uma sociedade teocrática alternativa, organizada por um líder espiritual que ficou conhecido localmente como Meu Rei. Foi ainda essa beleza estética, aliada a seus aspectos florísticos e arqueológicos, que levou o governo brasileiro a criar, como forma de preservar a área, o Parque Nacional do Catimbau (PE).

Independentemente de se tratar de paisagem ou paleopaisagem, o que se pode apreender é que essas unidades geoecológicas e culturais são formadas por três camadas (Fig. 2): uma física, outra biológica e uma terceira de ordem cultural/social.

*Fig 2. Conjunto dos elementos que compõem uma paisagem. (Imagem retirada do livro Cartografia de Paisagens – 2ª ed., Editora Oficina de Textos. Todos os direitos reservados.)*

A camada física pode ser chamada de potencial natural e inclui o conjunto da estrutura e trajetória dos processos tectônicos e climáticos e a influência destes sobre a diversidade das formas de relevo e os regimes de drenagem superficial e subterrânea.
A segunda camada é constituída pela atividade biológica que se desenvolve sobre um potencial natural. Esse potencial vai condicionar ou limitar a história biogeográfica, bem como o arranjo ecológico da fauna e da flora e o produto de sua interação com o substrato na formação dos solos.
Por último, a apropriação cultural inclui a história humana, enquanto história de suas representações sociais, interesses políticos, demandas econômicas e sua intervenção a partir de obras de engenharia e atividades diversas.

Logo, o estudo da paisagem demanda o reconhecimento de seu potencial natural, de sua atividade biológica e também de sua apropriação cultural. Para a cartografia de paisagens, contudo, interessa primariamente a fisionomia das camadas, isto é, seu aspecto visível, e secundariamente seu funcionamento e desenvolvimento.

Tudo a ver

Está disponível em nosso lojão Cartografia de paisagens – 2ª ed. Revista e atualizada, detalha os procedimentos de descrição e representação das paisagens e apresenta as abordagens de mapeamento em diferentes escalas.

Genome of tiny predator with big appetite

Geoffrey Ian McFaddenEmail author

BMC Biology201816:140

https://doi.org/10.1186/s12915-018-0610-8

Published: 28 November 2018

The original article was published in BMC Biology 2018 16:137

Abstract

The capture and enslavement of eukaryotic algae by unicellular predators to acquire photosynthesis was a major driving force in early eukaryotic diversification. A genome presented in BMC Biology provides a glimpse of how such a tiny predator might have preyed on red algae and detained them to create new lineages of photosynthetic organisms.

Commentary

Few biologists will have heard of Goniomonas, though they could find this minute, colorless biflagellate in just about any stream or inlet they cared to look in. But why should they care? Well, Goniomonas is an important piece in the puzzle of how the colorful flags of photosynthesis came to be daubed across numerous different and unrelated branches of the tree of eukaryotes [1].

Goniomonas first came to my attention 25 years ago when friend and cryptomonad aficionado David Hill showed me a little ‘bug’ he had retrieved from the Yarra River in Melbourne. Once I had grasped what I was viewing, I knew we had to get its DNA and try to unravel how Goniomonas is related to the photosynthetic cryptomonads. Cryptomonads, you see, are the ‘smoking gun’ of a remarkable and massively influential evolutionary process known as secondary endosymbiosis.

Plastids—the subcellular structures in plants and algae where photosynthesis occurs—first arose by endosymbiosis of a cyanobacterium. The cyanobacterium was engulfed by a eukaryotic phagotroph, but instead of being digested for food as normally would happen to a phagotroph’s prey, it was detained as a solar cell to perform the metabolic magic of using light energy to smash water, release electrons, and string carbon atoms together to create the fuel of life—glucose. This initial endosymbiosis, referred to as the primary endosymbiosis, spawned the red algae, the glaucophytes, and the green algae and their eventual descendants, the plants. The plastids in these photosynthesizers have two bounding membranes, now clearly understood to derive from the pair of membranes that enclose your typical, Gram-negative cyanobacterium.

But primary endosymbiosis was merely the first chapter in the acquisition of photosynthesis by eukaryotes. Once the cyanobacterium was tamed, it was transplanted horizontally into several disjunct eukaryotic lineages by multiple secondary endosymbioses. These secondary endosymbioses—sometimes involving a red alga and sometimes involving a green alga, but curiously never a glaucophyte—resulted in the eukaryotic alga becoming the detainee in one or another phagotroph to create a metaorganism comprising a relic cyanobacterium inside a eukaryote inside yet another eukaryote. How do we know this with certainty? Cryptomonads. These little algae are a classic Darwinian transition form in this shell game, retaining all the shells of the two sequential engulfment processes, plus a few tell-tale bits and pieces of the swallowed ones.

The crucial piece in cryptomonads is the vestigial nucleus of the engulfed red alga, which we now refer to as the nucleomorph in recognition of Dennis Greenwood’s seminal observation that it had the morphology of a little nucleus sequestered between the shells (membranes) of the metaorganism (references in [2]). Nucleomorph genomes confirm that this little structure is indeed the relic nucleus of the red algal endosymbiont and prove unequivocally that secondary endosymbiosis did happen, and that cryptomonads are one result [3]. Nucleomorphs give credence to all the other putative secondary endosymbioses where the nucleomorph, and even some of the membrane shells, have apparently disappeared with reduction of the endosymbiont through increased integration into the metaorganisms.

Goniomonas genomes and a window into the origins of photosynthesis

But back to Goniomonas. The German phycologist Georg Fresenius recognized Goniomonas as a cryptomonad 160 years ago on the basis of its asymmetric shape, presence of ejectisomes (enigmatic ejectile structures that burst like party streamers from the cell under duress), and the two unequal flagella emerging from a deep, complicated anterior invagination [4] (Fig. 1). Where Goniomonas differs to most cryptomonads—which are either blueish-greenish or reddish-brownish depending on which of the endosymbiont’s phycobilin pigments they retain—is it lacks any color, and apparently any plastid [5]. This raises the question of whether it had a plastid and carelessly lost it, or whether it is a representative of the cryptomonads before they entered into their complex secondary endosymbiotic relationship with a red alga? A first step would be to infer how Goniomonas relates to photosynthetic cryptomonads, and DNA sequences were the obvious approach.

Fig. 1.
Scanning electron micrograph of the tiny predator *Goniomonas avonlea* (colourised). Typical cryptomonad features such as the flat, asymmetric shape, two anterior flagella emerging from a complex invagination, and the light armour plating are visible. Photo credit E. Kim. Bar = 5 μm

To get DNA sequences from organisms one typically needs a goodly amount of them. Goniomonas is a predator, so when Hill and I wanted to grow it up in large numbers, we opted to provide it with loads of bacteria to engulf and digest—this was as simple as me popping a grain of wheat into several flasks of culture media to support bacterial growth, whilst Hill arduously plucked out individual Goniomonas cells with a micropipette and placed them in solitary confinement with only food for company. Hill and I got a clonal culture and a ribosomal RNA sequence from Goniomonas truncata, and could show it was sister to photosynthetic cryptomonads [6].

In their recent article in BMC Biology, Cenci et al. report the entire genome of a related species, Goniomonas avonlea [7], which hails from the setting of Lucy Montgomery’s novel Anne of Green Gables. The G. avonlea genome paints the first complete picture of how cryptomonads might have functioned before they crossed the tracks and made a pact with an alga to become autotrophic. It is a fascinating window into how things probably were with cryptomonads before they switched lifestyles.

As genomes go, the G. avonlea blueprint is still a bit of a roughie, remaining in ~ 32,000 unjoined pieces. That’s because the genome is huge for such a tiny organism, with a final size approaching 100 megabases; the effort to get it fully assembled and polished would be formidable. Gene count, at ~ 18,000 non-redundant proteins, is also impressive, and these genes are, on average, interrupted by about five introns each. But numbers aside, what does the genome tell us about how G. avonlea makes its living, now and in the past? Quite a bit as it happens. A concerted search turned up no convincing evidence for G. avonlea now having, or ever having had, a plastid. Thus, we can be pretty certain this type of cryptomonad is ancestrally heterotrophic. Metabolic pathways typically taken care of by the plastid in plants and algae—namely fatty acid synthesis, isoprenoid precursor synthesis, iron sulfur cluster generation, and heme synthesis—are apparently done in the cytosol of G. avonlea using canonical eukaryotic machinery not related to cyanobacteria. Thus, there are no traces of plastid-type metabolisms lurking in the genome, and Goniomonas appears to be a living representative of the pre-secondary-endosymbiosis cryptomonads.

An ancestral phagotroph?

G. avonlea also seems well equipped gene-wise to digest its prey, having a panoply of lysozymes to chew through the cell walls of those bacteria unfortunate enough to end up going down the gullet of the predator and into its food vacuoles. For me though, the jewel-in-the-crown of the G. avonlea genome are glycan hydrolases belonging to the GH50 family, which cleave β-1,4 glycosidic bonds of agarose, a principal component of red algal cell walls. G. avonlea thus seems equipped to be algivorous, capable of digesting the walls of red algal prey cells. In today’s oceans and streams, most red algae are multicellular and too large to be preyed upon by a miniscule flagellate like G. avonlea, but unicellular red algae small enough for a Goniomonas cell to engulf are not uncommon and were perhaps more so in earlier times. Thus, if G. avonlea does indeed engulf and digest red algae, it is not too much of a stretch to imagine a scenario where the prey cell is detained and not digested—exactly the kind of event predicted to have occurred at the outset of a secondary endosymbiosis creating the photosynthetic cryptomonads [2, 3].

Goniomonas is thus a nice fit for the ancestral phagotroph that was routinely capturing and digesting red algae and could have commenced a longer and more sustained relationship with its prey to embark on the acquisition of photosynthesis through a secondary endosymbiosis. But what does Goniomonas tell us about the other, non-cryptomonad eukaryotes that also have reduced red algal endosymbionts for plastids?

Major eukaryote groups including the heterokonts/stramenopiles (algae like brown kelps, diatoms, and golden flagellates), haptophytes (abundant limestone-armoured phytoplankton whose dead ancestors comprise most of the white cliffs of Dover), dinoflagellates (including the symbionts of corals crucial for reef building and the toxic basis of certain red tides), and alveolates (parasites of animals and protists that cause diseases such as malaria and toxoplasmosis and possess relic, non-photosynthetic plastids) all harbour secondary endosymbionts of red algal origin. A long-standing debate about whether all these different types of organisms gained their red algal endosymbiont in one event—perhaps akin to the one discussed here in which a Goniomonas-like phagotroph captured and retained a red alga—or whether each of them descends from a separate capture of a red alga by different ancestors remains wide open, despite 40 years of investigation [8, 9, 10].

The genome of Goniomonas doesn’t yet resolve this debate, but it gives us an extant model with which to explore what the phagotrophic partner in the extraordinary amalgam that led to at least one group of complex algae, the cryptomonads, was like. We might just have extant descendants of the two partners—predator and prey—with which to better understand how a great swathe of eukaryotic diversity originated through secondary endosymbiosis. Maybe we should feed our Goniomonas on red algae rather than bacteria.

Declarations

Acknowledgements

Not applicable.

Funding

GIM is supported by an Australian Research Council Laureate Fellowship.

Availability of data and materials

Not applicable.

Author’s contributions

GIM wrote the manuscript. GIM read and approved the final manuscript.

Competing interests

The author declares that he has no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

References

Archibald JM. One plus one equals one: Symbiosis and the evolution of complex life. Oxford: Oxford University Press; 2014.Google Scholar
McFadden GI. The cryptomonad nucleomorph. Protoplasma. 2017;254:1903–7.View ArticleGoogle Scholar
Douglas S, Zauner S, Fraunholz M, Beaton M, Penny S, Deng L-T, Wu X, Reith M, Cavalier-Smith T, Maier U-G. The highly reduced genome of an enslaved algal nucleus. Nature. 2001;410:1091–6.View ArticleGoogle Scholar
Fresenius G. Beiträge zur Kenntniss mikroskopischer Organismen. Abh Senckenberg Naturforsch Ges. 1858;2:1–34.Google Scholar
Kim E, Archibald JM. Ultrastructure and molecular phylogeny of the cryptomonad Goniomonas avonlea sp. nov. Protist. 2013;164:160–82.View ArticleGoogle Scholar
McFadden GI, Gilson PR, Hill DRA. Goniomonas—rRNA sequences indicate that this phagotrophic flagellate is a close relative of the host component of cryptomonads. Eur J Phycol. 1994;29(1):29–32.View ArticleGoogle Scholar
Cenci U, Sibbald S, Curtis B, Kamikawa R, Eme L, Moog D, Henrissat B, Marechal E, Chabi M, Djemel C, et al. Nuclear genomne sequene of the plastid lacking cryptomonad Goniomonas avonlea: phylogenomic and metabolic insights into the evolution of secondary plastids. BMC Biol. 2018. https://doi.org/10.1186/s12915-018-0593-5.
Cavalier-Smith T. The kingdom Chromista: origin and systematics. In: Round F, Chapman D, editors. Progress in phycological research, vol. 3. Bristol: Biopress; 1986. p. 309–47.Google Scholar
Gould SB, Maier UG, Martin WF. Protein import and the origin of red complex plastids. Curr Biol. 2015;25(12):R515–21.View ArticleGoogle Scholar
Waller RF, Gornik SG, Koreny L, Pain A. Metabolic pathway redundancy within the apicomplexan-dinoflagellate radiation argues against an ancient chromalveolate plastid. Commun Integr Biol. 2016;9(1):e1116653.View ArticleGoogle Scholar