Zooplankton migrate under influence of moonlight in dark Arctic winter

New research performed by biologists from different universities has shown that zooplankton migrate vertically through the waters of the Arctic Ocean by using moonlight during dark winter nights. By studying acoustic data recorded by moored instruments, the scientists found that the vertical migration patterns of zooplankton in winter are driven by lunar illumination across the entire Arctic, in fjord, shelf, slope and open sea environments. During the Arctic winter, zooplankton shift their known diel vertical migration (DVM) periods from a solar day (24 hours) to a lunar day (24.8 hours) when the moon rises above the horizon. In addition, mass sinking of zooplankton from the surface waters to a depth of approximately 50 meters occurs during periods of full moon (every 29.5 days). The scientists suggest that lunar vertical migration (LVM) may enable zooplankton to avoid visual predators, such as carnivorous zooplankters, fish and birds, which use moonlight to hunt during the polar night. The discovery of LVM in the Arctic indicates that light-mediated patterns of biological migration may occur even without the presence of sunlight and has important implications for the exchange of carbon between the surface waters and deeper waters during the Arctic winter.

Journal reference: Last, K. S., Hobbs, L., Berge, J., Brierley, A. S. & Cottier, F. (2016). Moonlight Drives Ocean-Scale Mass Vertical Migration of Zooplankton during the Arctic Winter. Current Biology, 26, 1-8.

Image: Icebergs in the Arctic near Cape York, Greenland. Credit: Brocken Inaglory, Wikimedia Commons.

Fossil remains of new hominin species Homo naledi discovered in South Africa

Paleontologists have discovered the fossil remains of a new hominin species in a dark cave system in South Africa and published their preliminary results in eLife. The new species has been named Homo naledi, which means “star man” in Sotho, after the Dinaledi Chamber of the Rising Star cave system where it was found. Homo naledi is characterized by a small body and brain size, but it also features several adaptations of the hands and feet that are relatively similar to modern humans. The age of Homo naledi and its position in the phylogenetic tree of hominins is still unresolved, but it is believed to be one of the more primitive ancestors of mankind. So far, an unprecedented 1550 remains of at least 15 individuals of Homo naledi have been unearthed, representing the largest fossil assemblage of a single hominin species ever found in Africa. Given the richness and exceptional preservation state of these fossils, it is speculated that Homo naledi may have been capable of performing primitive burial rites.

Journal references:

Berger, L. R., Hawks, J., de Ruiter, D. J., Churchill, S. E., Schmid, P., Delezene, L. K., … & Zipfel, B. (2015). Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. eLife4, e09560.

Dirks, P. H., Berger, L. R., Roberts, E. M., Kramers, J. D., Hawks, J., Randolph-Quinney, P. S., … & Tucker, S. (2015). Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife4, e09561.

Image: Fossil remains of Homo naledi, the new hominin species discovered in South Africa. Source: Lee Berger, Wikimedia Commons.

Fossil pigments reveal that dinosaurs may have laid colored eggs

Scientists at the University of Bonn have found pigments in fossilized eggs of dinosaurs, which indicates that dinosaurs may have laid colored eggs similar to modern birds. The scientists performed organic geochemical analyses on well preserved, 66 million year old fossil remains of eggshells belonging to the oviraptor Heyuannia huangi and discovered the presence of the pigments protoporphyrin and biliverdin. These pigments are known to be responsible for the blue and green colors in present-day robin and emu eggs, respectively, which suggests that the studied oviraptor eggs may have had blue-green colors as well. It is believed that these oviraptor eggs were laid in partially open ground nests and therefore, their blue-green coloring may have provided a means of camouflage against predators. This study is the first to reconstruct the color of dinosaur eggs and provides a link between the reproductive biology of dinosaurs and the evolutionary traits inherited by modern birds.

Journal reference: Wiemann, J., Yang, T. R., Sander, P. N., Schneider, M., Engeser, M., Kath-Schorr, S., … & Sander, P. M. (2015). The blue-green eggs of dinosaurs: How fossil metabolites provide insights into the evolution of bird reproduction (No. e1323). PeerJ PrePrints.

Image: Reconstruction of Tyrannosaurus rex in Palais de la Découverte, Paris, France. Source: David Monniaux, Wikimedia Commons.

Permian-Triassic mass extinction was caused by ocean acidification

New findings of scientists from several universities published in Science show that the Permian-Triassic mass extinction (~ 252 million years ago), the greatest extinction event of all time, was caused by ocean acidification. The researchers studied boron isotopes from marine sediments in order to reconstruct seawater pH and subsequently combined these data with quantitative modeling techniques to develop a scenario for the mass extinction. Their results show that seawater pH remained relatively stable during the first phase of the extinction, but rapidly shifted to more acidic values during the second phase, which lasted ~ 10 thousand years. This acidification of the oceans had dramatic consequences for life on Earth and is thought to be associated with the release of massive amounts of carbon, related to the volcanism of the Siberian Traps. Up to 96 % of living marine species became extinct during the Permian-Triassic mass extinction and now, it has been shown for the first time that ocean acidification was the responsible mechanism.

Journal reference: Clarkson, M. O., Kasemann, S. A., Wood, R. A., Lenton, T. M., Daines, S. J., Richoz, S., … & Tipper, E. T. (2015). Ocean acidification and the Permo-Triassic mass extinction. Science348(6231), 229-232.

Image: Eruption of the Tavurvur volcano on February 13, 2009 near Rabaul, New Britain, Papua New Guinea. Source: Taro Taylor, Wikimedia Commons.

Emperor penguins on Antarctica forced into refugia during last glacial maximum

Research of biologists published in Global Change Biology indicates that emperor penguins on Antarctica were forced into refugia by extreme cold during the last glacial maximum (~ 19.5 – 16 thousand years ago). By comparing the DNA of fossil emperor penguins with the DNA of living individuals and colonies, the scientists were able to reconstruct the population dynamics of emperor penguins on Antarctica through time. Their results show three mitochondrial clades within emperor penguins at the time of the last glacial maximum, which suggests that these birds were isolated in three small, separate populations and may have survived in refugia such as the Ross Sea. The population sizes of emperor penguins are related to the balance between sea ice available for breeding and open water available for foraging. Sea ice extent around Antarctica was much greater during the last glacial maximum than at present and therefore, reduced food availability resulted in severe losses among populations of emperor penguins.

Journal reference: Younger, J. L., Clucas, G. V., Kooyman, G., Wienecke, B., Rogers, A. D., Trathan, P. N., … & Miller, K. J. (2015). Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum. Global change biology21(6), 2215-2226.

Image: Emperor penguin colony foraging along the Weddell Sea, Antarctica. Source: Christopher Michel, Wikimedia Commons.

Rise of animals on Earth delayed by insufficient oxygen

Geologists of different universities have found that insufficient levels of atmospheric oxygen during the mid-Proterozoic (~ 1.8 billion to 800 million years ago) delayed the evolutionary rise of animals on Earth. They studied chromium isotope data from shallow marine Proterozoic sediments and compared them to younger Phanerozoic sediments deposited in similar environments. Their findings suggest that chromium oxidation in the Proterozoic was very limited and that oxygen levels were at most 0.1 % of present atmospheric levels. Previous estimates of atmospheric concentrations have varied greatly, but it was generally accepted that oxygen existed at Earth’s surface during the Proterozoic. The late appearance and diversification of metazoans was therefore long thought to be limited by genetic advancements and ecological innovation, but now it appears that their evolution was instead delayed by low levels of oxygen.

Journal reference: Planavsky, N. J., Reinhard, C. T., Wang, X., Thomson, D., McGoldrick, P., Rainbird, R. H., … & Lyons, T. W. (2014). Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals. Science346(6209), 635-638.

Image: Cirrus clouds above Warsaw, Poland. Source: Przemyslaw Idzkiewicz, Wikimedia Commons.

Corals actively supply nutrients to their environment

In a new study published in PNAS, corals have been shown to actively manipulate their environment by stirring up currents to supply nutrients to reef ecosystems. The scientists studied six different species of growing reef corals in a laboratory tank and observed their movements with microscopes and video cameras. They found that through small epidermal appendages called cilia, polyps are able to create vortical currents that greatly enhance their exchange of dissolved oxygen and nutrients such as nitrogen and phosphorus with the surrounding water. Coral reefs were previously assumed to be dependent entirely on ambient flow and turbulence for their nourishment, but these results show that they have the ability to actively affect mass transport. This mechanism may be critical to the survival of corals and is likely part of their evolutionary succes.

Click here to watch the accompanying video for a fascinating look at how corals stir up water currents and control nutrient transport.

Journal reference: Shapiro, O. H., Fernandez, V. I., Garren, M., Guasto, J. S., Debaillon-Vesque, F. P., Kramarsky-Winter, E., … & Stocker, R. (2014). Vortical ciliary flows actively enhance mass transport in reef corals. Proceedings of the National Academy of Sciences111(37), 13391-13396.

Image: Corals in the Red Sea, Egypt. Source: Mahmoud Habeeb, Wikimedia Commons.

Species extinction rates higher than previously thought

According to a new study performed by biologists, the current extinction rates of terrestrial animal and plant species associated with human activities may be up to 10 times higher than previously thought. By using fossil datasets and mathematical models, the scientists were able to estimate new natural background rates of species diversification and extinction. Their results indicate that until now, these background rates are likely to have been overestimated and should be in the order of 0.1 extinction per million species per year, rather than 1 extinction per million species per year. Because current rates of extinction are compared against background levels, these new results have major implications for the apparent impact of mankind on life on Earth: the effects may be even more severe than expected.

Journal reference: De Vos, J. M., Joppa, L. N., Gittleman, J. L., Stephens, P. R., & Pimm, S. L. (2014). Estimating the normal background rate of species extinction. Conservation Biology.

Image: Fossil remains of Archaeopteryx displayed in the Museum für Naturkunde in Berlin, Germany. Source: H. Raab, Wikimedia Commons.