Raining cats and dogs: Global precipitation patterns a driver for animal diversity

Since the HMS Beagle arrived in the Galapagos with Charles Darwin to meet a fateful family of finches, ecologists have struggled to understand a particularly perplexing question: Why is there a ridiculous abundance of species some places on earth and a scarcity in others? What factors, exactly, drive animal diversity?

With access to a mammoth set of global-scale climate data and a novel strategy, a team from the Department of Watershed Sciences in Quinney College of Natural Resources and the Ecology Center identified several factors to help answer this fundamental ecological question. They discovered that what an animal eats (and how that interacts with climate) shapes Earth's diversity.

The work was recently published in the high-impact journal Ecology Letters.

"Historically studies looking at the distribution of species across Earth's latitudinal gradient have overlooked the role of trophic ecology -- how what animals eat impacts where they are found," said Trisha Atwood, author on the study from the Department of Watershed Sciences and the Ecology Center. "This new work shows that predators, omnivores and herbivores are not randomly scattered across the globe. There are patterns to where we find these groups of animals."

Certain locations have an unexpected abundance of meat-eating predators -- parts of Africa, Europe and Greenland. Herbivores are common in cooler areas, and omnivores tend to be more dominant in warm places. Two key factors emerged as crucial in shaping these patterns: precipitation and plant growth.

Precipitation patterns across time play a big role in determining where different groups of mammals thrive, Atwood said. Geographical areas where precipitation varies by season, without being too extreme, had the highest levels of mammal diversity.

"Keep in mind that we aren't talking about the total amount of rain," said Jaron Adkins, lead author on the research. "If you imagine ecosystems around the world on a scale of precipitation and season, certain places in Utah and the Amazon rainforest fall on one end with low variability -- they have steady levels of precipitation throughout the year. Other regions, like southern California, have really high variability, getting about 75 percent of the annual precipitation between December and March."

But the sweet spot for predators and herbivores fell in a middle zone between the two extremes, he said. Places like Madagascar, where precipitation patterns had an equal split between a wet season and a dry one (six months each), had the ideal ecological cocktail for promoting conditions for these two groups. Omnivore diversity tends to thrive in places with very stable climates.

The second important factor connected with mammal diversity the work uncovered was a measure of the amount of plant growth in an area, measured as "gross primary productivity."

"It makes intuitive sense for plant-eating animals to benefit from plant growth," Adkins said.

But this measure actually impacted carnivores most, according to the research. The strong relationship between predators and plant growth highlights the importance of an abundance of plants on an entire food chain's structural integrity.

"It was surprising that this factor was more important for predators than omnivores and herbivores," Atwood said. "Why this is remains a mystery."

Although evolutionary processes are ultimately responsible for spurring differences in species, climate conditions can impact related factors -- rates of evolutionary change, extinction and animal dispersal -- influencing species and trait-based richness, according to the research.

Animal diversity is rapidly declining in many ecosystems around the world through habitat loss and climate change. This has negative consequences for ecosystems. Forecasting how climate change will disrupt animal systems going forward is extremely important, Atwood said, and this research is a first step in better managing future conditions for animals around the world.

"Animal diversity can act as an alarm system for the stability of ecosystems," Atwood said. "Identifying the ecological mechanisms that help drive richness patterns provides insight for better managing and predicting how diversity could change under future climates."

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Fossil secret may shed light on the diversity of Earth's first animals

A large group of iconic fossils widely believed to shed light on the origins of many of Earth's animals and the communities they lived in may be hiding a secret.

Scientists, led by two from the University of Portsmouth, UK, are the first to model how exceptionally well preserved fossils that record the largest and most intense burst of evolution ever seen could have been moved by mudflows.

The finding, published in Communications Earth & Environment, offers a cautionary note on how palaeontologists build a picture from the remains of the creatures they study.

Until now, it has been widely accepted the fossils buried in mudflows in the Burgess Shale in Canada that show the result of the Cambrian explosion 505 million years ago had all lived together but that's now in doubt.

The Cambrian explosion was responsible for kick-starting the huge diversity of animal life now seen on the planet.

Now, Dr Nic Minter and Dr Orla Bath Enright have found that some of the animals which became fossils could have remained well preserved even after being carried large distances, throwing doubt on the idea the creatures all lived together.

Dr Minter said: "This finding might surprise scientists or lead to them striking a more cautionary tone in how they interpret early marine ecosystems from half a billion years ago.

"It has been assumed that because the Burgess Shale fossils are so well preserved, they couldn't have been transported over large distances. However, this new research shows that the general type of flow responsible for the deposits in which they were buried does not cause further damage to deceased animals. This means the fossils found in individual layers of sediment, and assumed to represent animal communities, could actually have been living far apart in distance."

Drs Minter and Bath Enright, of the University of Portsmouth's School of the Environment, Geography and Geosciences, studied the Burgess Shale area of British Columbia, both on location in the field and with laboratory experiments.

The site is an area rich in fossils entombed in the deposits of mudflows and is one of the world's most important fossil sites, with more than 65,000 specimens already collected and, so far, more than 120 species counted.

The Burgess Shale area has been fundamental to scientists in understanding the origins of animal groups and the communities they lived among and has been closely studied multiple times.

The researchers, together with collaborators from the Universities of Southampton and Saskatchewan in Canada, used fieldwork to identify how the mudflows would have behaved, and then used flume tank laboratory tests to mimic the mudflows and are confident that the bodies of certain creatures could have been moved over tens of kilometres without damage, creating the illusion of animal communities which never existed.

The Burgess Shale was discovered in the early 1900s and led to the idea of the 'Cambrian explosion' of life, with the appearance of animals representing almost all the modern phyla, and inspiring copious research and discoveries.

Dr Bath Enright said: "Many would argue that it is fundamental, even ground zero for scientists in understanding the diversity of life."

It's not known precisely what caused the mudflows which buried and moved the animals which became fossilised, but the area was subject to multiple flows, causing well preserved fossils to be found at many different levels in the shale.

"We don't know over what kind of overall time frame these many flows happened, but we know each one produced an 'event bed' that we see today stacked up on top of one another. These flows could pick up animals from multiple places as they moved across the seafloor and then dropped them all together in one place," said Dr Bath Enright.

"When we see multiple species accumulated together it can give the illusion we are seeing a single community. But we argue that an individual 'event bed' could be the product of several communities of animals being picked up from multiple places by a mudflow and then deposited together to give what looks like a much more complicated single community of animals.

"Palaeontologists need to appreciate the nature of the sediments that fossils are preserved within and what the implications of that are. We could be overestimating the complexity of early marine animal communities and therefore the patterns and drivers of evolution that have led to our present day diversity and complexity."

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Seeing evolution happening before your eyes

 Animal diversity and evolution are driven by changes in how our genetic code is expressed. Specific DNA sequences called enhancers control where, when and how strongly genes are expressed during development to create the respective organism. Studying enhancers and how they result in different patterns of gene expression therefore helps us to understand more about how evolution takes place. In addition to driving the evolution of species, enhancers are also relevant to disease: mutations in enhancers are associated with over 80% of all human diseases.

"What we see in terms of biodiversity in nature is caused, to a large degree, by changes in enhancers," explains Justin Crocker, group leader at EMBL Heidelberg. "Understanding -- and subsequently trying to predict -- evolution in the time of climate change, where many animals are under the pressure to adapt quickly to fast changing environments, is an important task."

Despite broad relevance to evolution and disease, researchers still struggle to understand how enhancers are coded in our genomes and how easy it is to reprogram them, for example to prevent or treat diseases. In an attempt to learn more about enhancers, the Crocker group from EMBL Heidelberg performed an extensive study, published in Nature, on a specific enhancer in the model organism Drosophila melanogaster, a species of fruit fly. The group discovered that this enhancer -- which controls the patterns where hair grows on flies -- contains a lot more information than expected.

"Whenever we changed a single letter of the enhancer DNA sequence, we created a significant change to the pattern of gene expression it drove," explains Timothy Fuqua, PhD student at EMBL and first author of the paper. "We also found that almost all mutations to the enhancer alter the gene expression pattern in multiple ways. For example, one mutation controls not only where the expression pattern is within the fly, but also when, and how much of the gene was expressed."

These results were surprising and contradict what had previously been known about enhancers. Researchers thought that these complex gene expression patterns were created by different proteins attaching to the enhancer. A first clue that this might not be true came when Crocker and his team discovered that artificially-produced enhancers did not work as designed. Their most recent results provide support for this idea. "The results showed that developmental enhancers encode a much higher level of information than previously appreciated," Crocker says. "When we received the data, I was honestly shocked! I couldn't believe it and we repeated everything, as we assumed that there has been a mistake."

Importantly, the density of information encoded within the enhancer also constrains how animals can evolve. The study also showed that each possible mutation has a certain possibility for happening. This gives scientists insights into where evolution could lead. "We can use this information to predict patterns in wild fruit flies. Something which has been incredibly difficult to do so far," Fuqua says. "Our results should encourage the community to reassess our assumption about how these regions contribute to human health."

While studying enhancers is a well-established field in molecular biology, this study is unique in the sheer number of mutations having been studied. The group created more than 700 unique, randomly generated mutations within a single enhancer. "Nobody ever has studied so many enhancer variants at this level of depth before. It was as if evolution was happening before our very eyes!" highlights Fuqua. To perform so many experiments, the team built -- assisted by the Janelia Research Campus and the Advanced Light Microscopy Facility at EMBL -- a robot to handle the fly embryos used in the study, and an automated microscope pipeline to take images of each mutated line.

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