In a unique analysis that provides a glimpse into the origin stories of new animal traits, a pair of research studies led by University of California San Diego and Harvard University scientists has traced the evolutionary adaptations of octopus and squid sensing capabilities. The studies, featured on the cover of the April 13 issue of Nature, reveal evolutionary links to human brain receptors.

Researchers with Ryan Hibbs’ newly established laboratory in the School of Biological Sciences at UC San Diego (formerly based at the University of Texas Southwestern Medical Center) and Nicholas Bellono’s lab at Harvard analyzed octopuses and squids, animals known as cephalopods, through a comprehensive lens that spanned atomic-level protein structure to the entire functional organism. They focused on sensory receptors as a key site for evolutionary innovation at the crossroads of ecology, neural processing and behavior.

By looking at the way octopuses and squids sense their marine environments, the researchers discovered new sensory receptor families and determined how they drive distinct behaviors in the environment. With cryo-electron microscopy technology, which uses cryogenic temperatures to capture biological processes and structures in unique ways, they showed that adaptations can help propel new behaviors.

“Cephalopods are well known for their intricate sensory organs, elaborate nervous systems and sophisticated behaviors that are comparable to complex vertebrates, but with radically different organization,” said Hibbs, a professor in the Department of Neurobiology. Hibbs brings expertise on the structure of a family of proteins in humans that mediate communication between brain neurons and other areas such as between neurons and muscle cells. “Cephalopods provide striking examples of convergent and divergent evolution that can be leveraged to understand the molecular basis of novelty across levels of biological organization.”

In one Nature study, the research teams described for the first time the structure of an octopus chemotactile (meaning chemical and touch) receptor, which octopus arms use for taste-by-touch exploration. These chemotactile receptors are similar to human brain and muscle neurotransmitter receptors, but are adapted through evolution to help evaluate possible food sources in the marine environment.

“In octopus, we found that these chemotactile receptors physically contact surfaces to determine whether the animal should eat a potential food source or reject it,” said Hibbs. “Through its structure, we found that these receptors are activated by greasy molecules, including steroids similar to cholesterol. With evolutionary, biophysical and behavioral analyses, we showed how strikingly novel structural adaptations facilitate the receptor’s transition from an ancestral role in neurotransmission to a new function in contact-dependent chemosensation of greasy environmental chemicals.”

The second Nature study focused on squid and their wholly different ambush strategy for capturing food. The researchers combined genetics, physiology and behavioral experiments to discover a new class of ancient chemotactile receptors and determined one structure within the class. They also conducted an evolutionary analysis to link adaptations in squid receptors to more elaborate expansions in octopus. They were then able to place chemotactile and ancestral neurotransmitter receptors on an evolutionary timeline and described how evolutionary adaptations drove the development of new behaviors.

“We discovered a new family of cell surface receptors that offer a rare lens into the evolution of sensation because they represent the most recent and only functionally tractable transition from neurotransmitter to environmental receptors across the entire animal kingdom,” said Hibbs. “Our structures of these unique cephalopod receptors lay a foundation for the mechanistic understanding of major functional transitions in deep evolutionary time and the origin of biological novelty.”

Hibbs says the pair of new studies offers an excellent example of how curiosity in interesting creatures can lead to insights important for all of biology, namely how proteins — life’s building blocks — adapt to mediate new functions and behaviors.

“These studies are a great example of what being a scientist is all about — wonder, exploration and understanding how things work,” he said.

Video: https://youtu.be/WC4h_XIioAw

However, unlike their neighbors, the Xiongnu never developed a writing system, and consequently historical records about the Xiongnu have been almost entirely written and passed down by their rivals and enemies. Such accounts, largely recorded by Han Dynasty chroniclers, provide little useful information on the origins of the Xiongnu, their political rise, or their social organization. Although recent archaeogenetics studies have now traced the origins of the Xiongnu as a political entity to a sudden migration and mixing of disparate nomadic groups in northern Mongolia ca. 200 BCE, such findings have raised more questions than answers.

To better understand the inner workings of the seemingly enigmatic Xiongnu empire, an international team of researchers at the Max Planck Institutes for Evolutionary Anthropology (MPI-EVA) and Geoanthropology (MPI-GEO), Seoul National University, the University of Michigan, and Harvard University conducted an in-depth genetic investigation of two imperial elite Xiongnu cemeteries along the western frontier of the empire: an aristocratic elite cemetery at Takhiltyn Khotgor and a local elite cemetery at Shombuuzyn Belchir.

“We knew that the Xiongnu had a high degree of genetic diversity, but due to a lack of community-scale genomic data it remained unclear whether this diversity emerged from a heterogeneous patchwork of locally homogenous communities or whether local communities were themselves genetically diverse,” explains Juhyeon Lee, first author of the study and PhD student at Seoul National University. “We wanted to know how such genetic diversity was structured at different social and political scales, as well as in relation to power, wealth, and gender.”

The rise of a multiethnic empire

Researchers found that individuals within the two cemeteries exhibited extremely high genetic diversity, to a degree comparable with that found across the Xiongnu Empire as a whole. In fact, high genetic diversity and heterogeneity was present at all levels — across the empire, within individual communities, and even within individual families — confirming the characterization of the Xiongnu Empire as a multiethnic empire. However, much of this diversity was stratified by status. The lowest status individuals (interred as satellite burials of the elites, likely reflecting a servant status) exhibited the highest genetic diversity and heterogeneity, suggesting that these individuals originated from far-flung parts of the Xiongnu Empire or beyond. In contrast, local and aristocratic elites buried in wood-plank coffins within square tombs and stone ring graves exhibited lower overall genetic diversity and harbored higher proportions of eastern Eurasian ancestries, suggesting that elite status and power was concentrated among specific genetic subsets of the broader Xiongnu population. Nevertheless, even elite families appear to have used marriage to cement ties to newly incorporated groups, especially at Shombuuzyn Belchir.

“We now have a better idea of how the Xiongnu expanded their empire by incorporating disparate groups and leveraging marriage and kinship into empire building,” says senior author Dr. Choongwon Jeong, Associate Professor of Biological Sciences at Seoul National University.

Powerful women in Xiongnu society

A second major finding was that high status Xiongnu burials and elite grave goods were disproportionately associated with women, corroborating textual and archaeological evidence that Xiongnu women played especially prominent political roles in the expansion and integration of new territories along the empire’s frontier. At the aristocratic elite cemetery of Takhiltyn Khotgor, researchers found that the elite monumental tombs had been built for women, with each prominent woman flanked by a host of commoner males buried in simple graves. The women were interred in elaborate coffins with the golden sun and moon emblems of Xiongnu imperial power and one tomb even contained a team of six horses and a partial chariot. At the nearby local elite cemetery of Shombuuzyn Belchir, women likewise occupied the wealthiest and most elaborate graves, with grave goods consisting of wooden coffins, golden emblems and gilded objects, glass and faience beads, Chinese mirrors, a bronze cauldron, silk clothing, wooden carts, and more than a dozen livestock, as well as three objects conventionally associated with male horse-mounted warriors: a Chinese lacquer cup, a gilded iron belt clasp, and horse tack. Such objects and their symbolism convey the great political power of the women.

“Women held great power as agents of the Xiongnu imperial state along the frontier, often holding exclusive noble ranks, maintaining Xiongnu traditions, and engaging in both steppe power politics and the so-called Silk Road networks of exchange,” says Dr. Bryan Miller, project archaeologist and Assistant Professor of Central Asian Art & Archaeology at the University of Michigan.

Children in Xiongnu society

Genetic analysis also provided rare insights into the social roles of children in Xiongnu society. “Children received differential mortuary treatment depending upon age and sex, giving clues to the ages at which gender and status were ascribed in Xiongnu society,” says senior author Dr. Christina Warinner, Associate Professor of Anthropology at Harvard University and Group Leader at the Max Planck Institute for Evolutionary Anthropology. Researchers found, for example, that although adolescent Xiongnu boys as young as 11-12 years old were buried with a bow and arrows, in a manner resembling that of adult males, younger boys were not. This suggests that the gendered social roles of hunter and warrior were not ascribed to boys until late childhood or early adolescence.

The legacy of the Xiongnu today

Although the Xiongnu empire ultimately disintegrated in the late 1st century CE, the findings of the study point to the enduring social and cultural legacy of the Xiongnu. “Our results confirm the long-standing nomadic tradition of elite princesses playing critical roles in the political and economic life of the empires, especially in periphery regions — a tradition that began with the Xiongnu and continued more than a thousand years later under the Mongol Empire,” says Dr. Jamsranjav Bayarsaikhan, project archaeologist and Mongolian Archaeology Project: Surveying the Steppes (MAPSS) project coordinator at the Max Planck Institute for Geoanthropology. “While history has at times dismissed nomadic empires as fragile and short, their strong traditions have never been broken.”

In the largest study of its kind, this approach was used to look more closely at the diets of killer whale from the eastern and northern coasts of Canada all the way to northern Norway. It provides the most detailed overview of North Atlantic killer whales diets to date. As climate change leads to a northward redistribution of killer whales, the results have implications not only for the health and survival of these killer whales, but also in terms of potential impacts on sensitive species within Arctic ecosystems.

A new tool to keep track of shifting diets

“In a context of climate change, it becomes increasingly urgent to understand and be able to quantify killer whale diets and how they are changing so that we can foresee the potential impacts on local food webs,” says Anaïs Remili, a PhD candidate in the Department of Natural Resource Sciences at McGill University and the first author on a paper published in Journal of Animal Ecology. “By measuring the composition of the fatty acids of approximately 200 killer whales and of 900 of their prey of different species, we were able estimate the specific proportions of each prey species in the whales’ diets. This means that scientists can potentially keep track of any shifts in these diets in the future.”

Orca food habits vary — by region and individual

The team found that killer whales have very different diets throughout the North Atlantic. In some areas, killer whales prefer to consume other whales: belugas and narwhals in the Eastern Canadian Arctic and baleen whales and porpoises in Eastern Canada.

Killer whales feed predominantly on fish, especially herring in the Eastern North Atlantic (Norway, Faroe Islands, Iceland), and in the Central North Atlantic (Greenland) they primarily eat seals.

Interestingly, however, the McGill researchers also found that not all the whales in any given location feed on the same prey. For example, in the Eastern Canadian Arctic, half of the whales eat mainly belugas and narwhals, while the other half consume mainly ringed seals. In Greenland, killer whales consumed a mixture of all available prey. Lastly, in Iceland, the Faroe Islands, and Norway, most whales are herring eaters, but a small number of whales in Norway and Iceland also consume a substantial proportion of marine mammals such as porpoises and seals. It is the first time that researchers have been able to detect individual diet preferences with this level of detail.

“Quantifying the diets of killer whales and other top predators is crucial in a context of changing environments, because it can provide insights into how these animals adapt to shifts in their prey populations and habitat conditions,” adds Melissa McKinney, the senior author on the paper, an Assistant Professor in the Department of Natural Resource Sciences at McGill and the Canada Research Chair in Ecological Change and Environmental Stressors. “Our results also point to the need for further research on the ecology of the individuals since we found such large differences among individuals of the same populations.”

“The study is really understanding the genetics of skeleton,” says senior author Nora Renthal of Boston Children’s Hospital and Harvard University. As a pediatric endocrinologist who cares for children with skeletal diseases, she is interested in understanding how bones grow. “Height is a good starting point to understand the relationship between genes, growth plates, and skeletal growth because we can measure the height of every human being.”

To pinpoint height-associated genes, the team screened 600 million mouse cartilage cells to identify genes that, when deleted, can alter cell growth and maturation. These types of cellular changes in the growth plate are known to lead to variations in human height. The search turned up 145 genes mostly linked to skeletal disorders and are crucial for growth plate maturation and bone formation.

The team then compared the discovered genes with data from genome-wide association studies (GWAS) of human height. GWAS allows researchers to survey the entire human genome to identify hotspots where “height genes” are located in our DNA. But these regions can contain multiple genes, making it hard for researchers to track down and study an individual target.

“That’s kind of like looking for your friend’s house, but you only know the zip code,” says Renthal. “It’s difficult.”

The comparison revealed that genes affecting cartilage cells overlap with hotspots from human height GWAS, precisely locating genes in our DNA that likely play a role in determining our stature. Renthal and her team also discovered that many of the GWAS suggested height genes led to early maturation in cartilage cells. These findings suggest that genetic changes affecting cartilage cell maturation may influence height more.

Renthal notes that studies in mouse cells may not fully translate to humans, and GWAS are observational studies that cannot fully illustrate the cause and effects of height. But her study provides a novel method to bridge the two methods and provide new insights into human genetics.

Next, the team plans to use the method to understand hormones’ effect on cartilage cells. They will also look into some of the 145 genes that have no known connection to skeletal growth. The investigation may reveal new genes and pathways that play a role in the bones.

“I see patients with skeletal dysplasia, where there isn’t any treatment because genetics made their bones grow this way,” says Renthal. “It’s my hope that the more we can understand about the biology of the growth plate, the more we would be able to intervene at earlier times in growing skeletons and the life of a kid.”

To discover exoplanets, planets which orbit stars other than the Sun, by imaging astronomers have up until now used “blind surveys”: stars are selected for imaging consider factors such as age and distance but are otherwise unbiased. However, blind surveys find planets very infrequently. Knowing where to look would help increase detection rates.

An international research team led by Subaru Telescope, the University of Tokyo, the University of Texas-San Antonio, and the Astrobiology Center of Japan, searched for hints of unknown planets in the data from the European Space Agency’s Gaia mission and its predecessor, Hipparcos. The team identified a star, HIP 99770 located 133 light-years away in the constellation Cygnus, whose motion suggests that an unseen planet is gravitationally pulling on it. Direct imaging observations with the Subaru Telescope detected the planet, HIP 99770 b.

The newly discovered planet is 14-16 times more massive than Jupiter. Its orbit is just over 3 times further from its star than Jupiter is from the Sun. The planet is 10 times hotter than Jupiter, with signs of water and carbon monoxide in its atmosphere.

A decade from now, astronomers hope to image a potentially-habitable planet with a size and temperature like the Earth using observatories like the Thirty Meter Telescope (TMT). Compared with HIP 99770 b, this Earth twin will be smaller and closer to its star, traits that will make it harder to detect. But with precise motion measurements, researchers will know where to look in this game of planetary hide and seek.