Holocene temperature in the Iberian Peninsula reconstructed studying insect subfossils

Remains of chironomid subfossils, a type of insects similar to mosquitoes, were used in a study by researchers from the University of Barcelona, the Pyrenean Ecology Institute (IPE-CSIC), and the University of Bern, to reconstruct the temperature of the Iberian Peninsula in the Holocene, the geological period that goes from 11,000 years ago until now. The results of the study prove some of the climate patterns of the Holocene brought by other methodologies: a rise of temperatures in the beginning and the end of the period, higher temperatures during the Holocene Climate Optimum and a decline of temperatures after the beginning of the Late Holocene.

Holocene temperature in the Iberian Peninsula reconstructed studying insect subfossils
Extraction of the sequence in Basa de la Mora lake by the IPE-CSIC research group
of Quaternary Paleoenvironments [Credit: Anchel Belmonte]

The study, published in the journal The Holocene, is the first reconstruction of the temperature of the peninsula during this period using this indicator. According to the researchers, this is a promising tool to understand the evolution of climate over history and the main natural and anthropic climate changes that shaped ecosystems before instrumental records.

Paleoclimate indicators in larval phase

Chironomidae are from the nematocera family (diptera order), similar to mosquitoes. These insects are abundant worldwide and change gender and amount depending on the temperature in which they live, so they are a good indicator of this climate variable. The research study was conducted in Basa de la Mora lake (Huesca), where researchers took the necessary sediments to carry the study out.

“Regarding the records of Chironomidae, the aim of any paleoenvironmental reconstruction study is to get the larval cephalic capsules, since this is the larval phase of the insects that is developed in the sediments and that from which subfossil remains are obtained”, says Miguel Cañedo-Argüelles, postdoctoral researcher from the Department of Evolutionary Biology, Ecology and Environmental of the UB. Subfossils are biological remains whose fossilization process is not complete due the way these were buried in the sediment and still have organic matter which can be analysed.

These were taken by the IPE-CSIC Research Group of Quaternary Paleoenvironments to get a sequence covering the whole Holocene period. The approximation of temperatures is obtained by comparing the composition of insects taken from the sediment sample over the sequence of the study, with a calibration basis made of many samples of Chironomidae that are taken in the present which are associated with temperature changes.

“In our case, we did not have that comparing element which is common in the study area (Pyrenees), so the sequence we got in Basa de la Mora lake was compared to the results of a study, the most developed and used one in Europe, conducted in 274 lakes in Switzerland and Norway”, says Pol Tarrats.

Regional differences regarding other reconstructions

The results of the study show a temperature rise in the beginning of the Holocene, reaching the highest values in the Holocene Climate Optimum (about 7,800 years ago). There are also high temperatures until about 6,000 years ago, when a decline of temperature started and led to the lowest values in the first stage of the late Holocene (about 4,200 and 2,000 years ago).

Last, researchers detected a rise of temperatures over the two last millenniums, but they state they have to be careful with these data. “We cannot guarantee the observed rise in the reconstruction results from a temperature rise only, we cannot rule out other variables that can influence at other levels, such as the gradual increase of the anthropic activity in the area, which can change the community of Chironomidae to species that adapt to higher temperatures, but there are also human influence indicators”, says Narcís Prat.

Although these conclusions can coincide with other paleoclimate reconstructions, results also highlight some divergences at a regional level. “These differences can occur due the fact that some indicators point out to different seasonal signs. Therefore, Chironomidae are indicators of temperature in summer, while others such as chrysophites or alkenones are related to winter/spring temperatures”, notes the researcher.

A tool to evaluate climate trends

Climate reconstruction of the past in general and temperatures in particular is a relevant tool when evaluating current climate trends within the context of climate change. For researchers, the methodology they use in this study is “an interesting tool to contrast, confirm and disprove patterns on evolution of temperature in the Holocene, as well as adding other indicators to reconstruct temperatures to advance in this study field”.

In this sense, the aim of the research team is to develop a comparing basis to link the present Chironomidae communities in different geographical areas of the Iberian Peninsula with temperature.

“This would allow us, on the one hand, confirm the influence of temperature when explaining the distribution of different species, and on the other, to use specific transfer functions for each area, which would provide a higher precision and strength to the next studies on reconstructing temperatures out of Iberian Peninsula Chironomidae”, concludes Miguel Cañedo-Argüelles.

Participants in the study are the researcher Pol Tarrats, member of the research group Freshwater Ecology, Hydrology and Management (FEHM) of the UB and first author of the article, and the researchers Miguel Cañedo-Argüelles, Narcís Prat and Maria Rieradevall, from the same group; Blas Valero-Garcés and Penélope González-Sampériz, from the Pyrenean Institute of Ecology (IPE-CSIC), and Oliver Heiri, from the University of Bern (Switzerland).

Source: University of Barcelona [November 09, 2018]



The secret behind coral reef diversity? Time, lots of time

Strap on a diving mask and fins and slip under the crystal-clear water near a coral reef in Indonesia, Papua-New Guinea or the Philippines, and you’ll immediately see why divers and snorkelers from across the world flock to the area. Known as the Coral Triangle, the region is famous for its unmatched diversity of reef fish and other marine creatures.

The secret behind coral reef diversity? Time, lots of time
Until now, researchers had a hard time explaining why the Coral Triangle in the Central-Indo Pacific
 is the world’s leading spot of marine biodiversity [Credit: GreensMPs/Flickr]

Fish of all shapes and colors dart in and out of crevices created by the dazzling shapes of corals, colorful sponges and other reef-building organisms. With a little luck, a diver might catch a glimpse of a shark patrolling the reef or a turtle soaring across the landscape of colors.

While underwater enthusiasts have long known and cherished the biodiversity in the Central-Indo Pacific Ocean, scientists have struggled for more than half a century to explain what exactly makes the region the world’s No. 1 hot spot of marine biodiversity and sets it apart from other marine regions around the world.

Several hypotheses have been put forth to explain the Central-Indo Pacific region’s extraordinary diversity. Some researchers suggested species emerge at a faster rate there compared to other parts of the world’s oceans, while others attributed it to the region’s central location between several species-rich swaths of ocean in the broader Indo-West Pacific. Still others pointed to the region’s low extinction rates.

Now, a study led by University of Arizona doctoral student Elizabeth Miller has revealed that Indo-Pacific coral reefs have accumulated their unrivaled richness of fish species not because of some unknown, elusive quality, but simply because they had the time.

“People used to think that new species evolve more quickly in tropical marine areas, so you get the high diversity we see today very quickly,” Miller said. “Instead, we found that diversity in the Central-Indo Pacific has slowly built over a long time.”

The study, published in the journal Proceedings of the Royal Society of London, is the first to show a direct link between time and species richness, according to Miller.

Until now, Miller explained, it was widely believed that tropical coral reefs, similar to tropical rain forests, are hot spots of biodiversity because of an intrinsic propensity to diversify into more species than other regions. Her research showed that wasn’t the case.

The secret behind coral reef diversity? Time, lots of time
A clownfish seeks shelter in its sea anemone home in the Great Barrier Reef, which is part of this study
 [Credit: Deborah Shelton]

The team discovered that speciation rates are actually higher in cold marine areas such as the Arctic and Antarctic. However, while changes in biodiversity in the Central-Indo Pacific region could be compared to a slow but long-burning flame, in colder ocean regions, they are more like fireworks.

“There, species evolve relatively quickly, but each glaciation period clears out much of what was there before,” Miller said. “Once the glaciers recede, they leave empty niches waiting to be repopulated by new species.”

Frequent environmental upheaval results in overall biodiversity being lower in colder ocean regions.

In the Coral Triangle, on the other hand, new species have evolved less rapidly, but because conditions have been much more stable over long periods of geological time, they were more likely to stick around once they appeared and slowly accumulate to the biological diversity we see today.

“This suggests that a region may need long-term stability to accumulate high species diversity,” Miller said. “According to our study, the magic number appears to be 30 million years.”

In the Central-Indo Pacific, plate tectonics created a wide platform of shallow ocean, while its central location made it a target for colonization. It was the right place at the right time for the fishes that colonized the region.

“Things haven’t changed much there in the past 30 to 35 million years,” Miller said. “In contrast, other marine regions, such as the Caribbean, underwent periods of instability and isolation, and therefore fewer colonizations and higher rates extinction of the lineages that were there previously – all those factors add up to less evolutionary time.”

For the study, Miller and her team used distribution data of almost all spiny ray-finned fishes – 17,453 species in total, representing about 72 percent of all marine fishes and about 33 percent of all freshwater fishes. They used several different statistical methods to reconstruct the causes of underlying species richness patterns among global marine regions.

To disentangle how marine fish diversity unfolded over time, the team then used a published evolutionary tree of this fish group and performed biogeographic reconstructions.

“Biogeographic reconstructions help us understand where ancestors were living at various places back in time, based on where species live today and how they are related,” Miller said. “It’s easy if you only compare two species that live in the same place, but if you have thousands of species and go back further and further in time, more ancestors come into play and things become more difficult.”

Evolutionary biologists rely on sophisticated computer algorithms to manage and interpret the extremely large data sets. The method used by Miller and her team created many hypothetical scenarios of where species evolved. The researchers then used these scenarios to test how different models explain today’s biodiversity.

“It’s like drawing family histories, each slightly different,” Miller said. “You start out with analyses and repeat them hundreds of times, each time based on some possible history to try and encompass uncertainty to see how they play out. In our study, it turned out the uncertainty is low, which is reassuring. It means it’s a really robust result.”

The general idea that patterns of diversity can be explained by how long a group has been present rather than how quickly they proliferate is relevant to lots of different systems, according to the researchers. For example, biologists have observed that the timing of colonization explains the high diversity of certain animal groups in terrestrial ecosystems, such as treefrogs in the Amazon rainforests, salamanders in the Appalachian Mountains and lizards in the desert Southwest.

“The general takeaway is that these patterns of high diversity may take tens of millions of years to arise, but can be wiped out in a few years by human impacts,” said John Wiens, senior author of the paper and a professor in the UA Department of Ecology and Evolutionary Biology. “Unfortunately, the high diversity of reef fish in the Coral Triangle may soon disappear because of the impacts of human-induced climate change on coral reefs. The diversity that gets lost in the next few years may take tens of millions of years to get back.”

Source: University of Arizona [November 09, 2018]



Re-inventing the hook: Orangutans spontaneously bend straight wires into hooks to fish for food

The bending of a hook into wire to fish for the handle of a basket is surprisingly challenging for young children under eight years of age. Now cognitive biologists and comparative psychologists from the University of Vienna, the University of St Andrews and the University of Veterinary Medicine Vienna around Isabelle Laumer and Alice Auersperg studied hook tool making for the first time in a non-human primate species – the orangutan. To the researchers’ surprise the apes spontaneously manufactured hook tools out of straight wire within the very first trial and in a second task unbent curved wire to make a straight tool.

Re-inventing the hook: Orangutans spontaneously bend straight wires into hooks to fish for food
Wild male orangutan [Credit: © Graham L. Banes]

Human children are already proficient tool-users and tool-makers from an early age on. Nevertheless, when confronted with a task, which required them to innovate a hooked tool out of a straight piece of wire in order to retrieve a basket from the bottom of a vertical tube, the job proved more challenging for children than one might think: Three to five-year-old children rarely succeed and even at the age of seven less than half of them were able to solve the task. Only at the age of eight the majority of children was able to innovate a hook-tool. Interestingly children of all tested age classes succeeded when given demonstrations on how to bend a hook and use it. Thus, although young children apparently understand what kind of tool is required and are skilled enough to make a functional tool, there seems to be a cognitive obstacle in innovating one.
Cognitive biologists and comparative psychologists from the University of Vienna, the University of St Andrews and the University of Veterinary Medicine in Vienna around Isabelle Laumer now tested for the first time a primate species in the hook-bending task. “We confronted the orangutans with a vertical tube containing a reward basket with a handle and a straight piece of wire. In a second task with a horizontal tube containing a reward at its centre and a piece of wire that was bent at 90°”, explains Isabelle Laumer who conducted the study at the Zoo Leipzig in Germany. “Retrieving the reward from the vertical tube thus required the orangutans to bent a hook into the wire to fish the basket out of the tube. The horizontal tube in turn required the apes to unbent the bent piece of wire in order to make it long enough to push the food out of the tube.”

Re-inventing the hook: Orangutans spontaneously bend straight wires into hooks to fish for food
Male orangutan using a stick tool [Credit: © Alice Auersperg]

Several orangutans mastered the hook bending task and the unbending task. Two orangutans even solved both tasks within the first minutes of the very first trial. “The orangutans mostly bent the hooks directly with their teeth and mouth while keeping the rest of the tool straight. Thereafter they immediately inserted it in correct orientation, hooked the handle and pulled the basket up”, she further explains.
Orangutans share 97% of their DNA with us and are among the most intelligent primates. They have human-like long-term memory, routinely use a variety of sophisticated tools in the wild and construct elaborate sleeping nests each night from foliage and branches. Today orangutans can only be found in the rainforests of Sumatra and Borneo. Like all four great ape species, orangutans are listed as critically endangered (IUCN, Red List). “Habitat loss due to extensive palm-oil production, illegal wildlife trade and poaching are the major threats. Palm oil is the most widely used vegetable oil in the world. As long as there is a demand for palm oil and consumers keep buying products that contain palm oil, the palm industry thrives. According to a 2007 survey by the United Nations Environment Program (UNEP) orangutans will be extinct in the wild within two decades if current deforestation trends continue”, says Isabelle Laumer.

Re-inventing the hook: Orangutans spontaneously bend straight wires into hooks to fish for food
Orangutans in the wild [Credit: © Graham L. Banes]

“The hook-bending task has become a benchmark paradim to test tool innovation abilities in comparative psychology”, says Alice Auersperg from the University of Veterinary Medicine in Vienna. “Considering the speed of their hook innovation, it seems that they actively invented a solution to this problem rather than applying routined behaviours.”

“Finding this capacity in one of our closest relatives is astonishing. In human evolution hook tools appear relatively late. Fish hooks and harpoon-like, curved objects date back only approximately 16.000- 60.000 years. Although New Caledonian crows use hooks with regularity, there are a few observations of wild apes, such as chimpanzees and orangutans, that use previously detached branches to catch and retrieve out-of-reach branches for locomotion in the canopy. This branch-hauling tools might represents one of the earliest and simplest raking tools used and made by great apes and our ancestors”, says Josep Call of the University of St Andrews.

So why struggle younger children with this task? “Follow-up studies showed that childrens difficulty with independently finding the solution cannot be explained by fixedness on unmodified tools, impulsivity nor by not being able to change the strategy. The hook bending task represents a complex problem, for which several unrewarded steps must be performed while keeping the final goal in mind”, explains Isabelle Laumer. “Interestingly, complex problem solving has been associated to certain areas of the medial prefrontal cortex, which mature later in the child development. This explanation, besides children´s strong reliance on social learning might explain their success at a later age.”

The study is published in Scientific Reports.

Source: University of Vienna [November 09, 2018]