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March 2017

Characterizing the Link Between Climate and Thermal Limits in Beetles

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Kimberly Sheldon

Kimberly Sheldon, an assistant professor at the University of Tennessee, Knoxville (pictured above with a dung beetle near Lake Naivasha, Kenya), studies how temperature change affects insects. (Photo courtesy of Kimberly Sheldon.)

January 31, 2017 by

By Amanda Biederman

Amid concerns over a rapidly changing climate, the abilities of different insects to survive at warmer temperatures has become a major question of interest. Kimberly Sheldon, an assistant professor at the University of Tennessee, Knoxville, is employing a comprehensive approach to this problem.

Sheldon is studying the effects of climate change on temperate and tropical beetles across North and South America. She said it is important for researchers to consider not only increases in mean annual temperature but also increases in temperature variation across different environments.

Sheldon said her experiments were designed to test Daniel Janzen’s 1967 “seasonality hypothesis,” which postulates that an organism’s thermal physiology is driven by adaptation to thermal fluctuation in the environment. Further, the organism’s physiology should drive its capacity for distribution along a thermal gradient.

She said she first became interested in the link between thermal physiology and distributions when reading current perspectives on the topic as a graduate student.

“Around the time I was starting graduate school, I started reading papers by (Janzen’s) colleagues, and they started mentioning the holes and gaps in the work,” Sheldon said. “So then I thought that maybe there were some holes I could fill in.”

In a study published in 2014, Sheldon’s group analyzed four tribes of dung beetles (Canthonini, Dichotomini, Phanaeini) and one genus of carrion beetle (Nicrophorus). The beetles have different morphologies and life history strategies, but they are all distributed across North and South America.

Sheldon’s group collected specimens from the four beetle groups at four geographical sites in the United States, Argentina, Costa Rica, and Ecuador. She hypothesized that beetles from the tropical, thermally stable regions (i.e. Ecuador and Costa Rica) would exhibit a narrower thermal tolerance breadth and distributional range than those from the temperate, thermally variable regions (i.e. United States, Argentina).

To characterize thermal tolerance breadth, Sheldon analyzed beetle behavior during temperature change. The body temperature at which an organism loses its righting ability during either acute cooling or warming is described as its critical thermal minimum (CTmin) or critical thermal maximum (CTmax), respectively. As predicted, Sheldon found that individuals from temperate regions had a broader thermal tolerance than those from tropical regions.

Next, Sheldon examined the link between thermal tolerance and elevational distribution. Her group reported differences in habitat range among species. All four beetle groups are distributed along an elevational gradient, and individuals at higher elevations and latitudes tend to be exposed to cooler temperatures.

Sheldon observed a positive relationship between thermal tolerance breadth and distribution, meaning that beetles from more seasonal, temperate regions exhibited not only a broader thermal tolerance but also a greater capacity to exploit different regions within their environment. This trait may be critical for survival in the future due to the effects of climate change.

In a follow-up study, Sheldon said she plans to investigate differences in phenotypic plasticity among populations. She said she will expose the beetles to different temperatures and determine whether they can adjust their critical thermal limits in order to cope with environmental change. She said she wants to determine whether beetles are capable of shifting their thermal limits and whether there are differences in populations from different latitudes.

Sheldon said it is important for biologists to consider the full ecological picture when studying the effects of climate change on organisms. She said the link between temperature variation and range breadth may be due not only to thermal physiology but also other factors such as competition among groups.

“I think some of the broader ideas are that the organism that can compete really well in its current range may have a hard time competing outside of temperatures that it has experienced,” Sheldon said. “So, some of it could be, for example, temperature-mediated competition that incorporates both elements.”

Read more: “The impact of seasonality in temperature on thermal tolerance and elevational range sizeEcology

Amanda Biederman is a graduate student at Ohio University, where she studies the thermal physiology of Antarctic fishes. She also works as a science writer for the Nanoscale and Quantum Phenomena Institute and writes science news articles for her blog,

The Great Imitator!

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An almost perfect similarity: A wasp (left) and a moth are barely distinguishable from each other.
Credit: Photo Michael Boppré

The masquerade is almost perfect. Certain moths of the subfamily Arctiinae are marked with a yellow and black pattern. But these day-active insects have wasp waists and their antennae resemble those of wasps. Their transparent wings are folded in a wasp-like way. For more than 150 years there has been a plausible explanation for this type of imitation, which is commonly known as mimicry. It says that the moths — just like many hoverflies and other insects — imitate wasps in order to protect themselves from birds and other hostile predators. According to textbook wisdom, these voracious foes have learned from painful experience.

They have been stung by wasps and since then have avoided any animal that looks like one. In the scientific journal Ecology and Evolution, a University of Freiburg biologist, Prof. Dr. Michael Boppré and his team have now presented an additional hypothesis that goes beyond this traditional view. Their interpretation is that, above all, the moths’ appearance deceives the very wasps they are mimicking.

As a rule, insects developing imperfect similarity to wasps is enough to keep learning predators at a distance. Yet the Arctiinae that Boppré observed during his biodiversity studies in South and Central America are different. The biologist says, “Especially when they are in flight, even for the trained eye it’s nearly impossible to tell apart the examples from the mimics.” That led Boppré to question why these Arctiinae have evolved this near-perfect imitation and what creatures they are trying to deceive. He says, “The answer — wasps — is stunningly simple.” Wasps hunt other insects as food for their larvae. Yet wasps do not attack each other, even when they are out on hunting flights they do not differentiate the wasps they encounter as originating from their own or other nests. The moths, therefore, are imitating the wasps so that these predators will perceive them as members of the same species and not attack for that reason.

Boppré and his co-authors emphasize that they are expanding upon rather than providing an alternative to the traditional explanation for mimicry. The researcher emphasizes, “The new explanation may seem to be a small detail at the outset, but this concept alone has far-reaching consequences.” The conventional explanation established more than 150 years ago played an immediate role in Charles Darwin’s theory of evolution. It is also based on fundamental assumptions. One of these is that mimicry can only function if the true ‘models’ (in this example the actual wasps), at least at times, are more abundant than their imitators. The assumption says that only then is it probable that predators learn to avoid these species through bad experiences. Species that develop this type of deception must pay for the advantage — the protection that imitation offers — with the cost of being fewer in number. But that’s not the case for these Arctiinae and various other insects. Says Boppré, “The imitation of wasps that innately fail to attack their imitators does not come at this cost.”

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Materials provided by University of Freiburg. Note: Content may be edited for style and length.

Journal Reference:

  1. Michael Boppré, Richard I. Vane-Wright, Wolfgang Wickler. A hypothesis to explain accuracy of wasp resemblances. Ecology and Evolution, 2017; 7 (1): 73 DOI: 10.1002/ece3.2586

Ants craft tiny sponges to dip into honey and carry it home

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Ants use tools to collect honey
Soaking up a liquid lunch
Gábor Lőrinczi

Ants may be smarter than we give them credit for. Tool use is seen as something brainy primates and birds do, but even the humble ant can choose the right tool for the job.

István Maák at the University of Szeged in Hungary and his team offered two species of funnel ants liquids containing water and honey along with a range of tools that might help them carry this food to their nests.

The ants experimented with the tools and chose those that were easiest to handle and could soak up plenty of liquid, such as bits of sponge or paper, despite them not being found in the insects’ natural environment.

This suggests that ants can take into account the properties of both the tool and the liquid they are transporting. It also indicates they can learn to use new tools – even without big brains.

Some ant species are known to use tools, such as mud or sand grains, to collect and transport liquid to their nests. But this is the first time they are shown to select the most suitable ones, says team member Patrizia d’Ettorre from the University of Paris-North, France.

Tool up

To investigate this behaviour, the team offered Aphaenogaster subterranea and A. senilis ants various possible tools, both natural, such as twigs, pine needles and soil grains, and artificial.

The ants experimented with the tools and eventually showed preference for certain tools – even unfamiliar ones. The ants would drop the tool into the liquid, pick it up and then carry it to the workers back in the nest to drink from.

Subterranea workers preferred small soil grains to transfer diluted honey, and sponge for pure honey. Most of them even tore the sponge into smaller bits, presumably for better handling.

Senilis started off using all the tools equally, but then focused on pieces of paper and sponge, which could soak up most of the diluted honey they were offered. This indicates that they can learn as they go along.

Factors such as the weight of the tools could also have influenced the ants’ choice, but the researchers believe the tools’ absorbency and ease of handling mattered the most.

Stuck for space

Aphaenogaster ants possibly developed such tool use because, unlike many other ants, they can’t expand their stomach, says d’Ettorre. “They had to find a way to exploit the valuable resource of liquid food.”

This way, when ants come across a fallen fruit or a dead insect in the wild, their fluids can be transferred to the nest for the rest of the colony.

As ants live in a highly competitive environment, natural selection may favour using such tools to help feed the colony, says Valerie S. Banschbach at Roanoke College, Virginia.

And these ants may have been happy to try novel materials because which particular tools are available in their natural habitat varies according to the season.

“Many other accomplishments of these small-brained creatures rival those of humans or even surpass them, such as farming fungi species or using ‘dead reckoning’, a sophisticated navigation to find their way back to the nest,” says Banschbach. “The size of brain needed for specific cognitive tasks is not clear.”

“Tool use in insects is largely genetically controlled and evolved from selection of advantageous genetic mutations,” says Gavin R. Hunt at the University of Auckland, New Zealand. This is unlike most tool use in birds or primates, which begins as novel behaviour and can sometimes be enhanced through genetic changes, he says.

Journal reference: Animal Behaviour, DOI: 10.1016/j.anbehav.2016.11.005

Beetles that pose as an ant’s abdomen to hitch a ride!

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How do you hitch a ride on an army ant? Try masquerading as an ant butt. At least, that’s the strategy that seems to work for the newly described beetle species Nymphister kronaueri.

Seen from above, a colony of Eciton mexicanum army ants marching across the forest floor looked perfectly normal to researchers surveying the insects in Costa Rica. But viewed from the side, many of the ants appeared to have a little extra junk in the trunk, sporting what seemed to be two abdomens stacked on top of each other, the scientists reported in a new study.

Closer inspection revealed that the topmost “abdomen” was actually a tiny hitchhiker — a beetle species unknown to science, holding on tight with its mandibles and perfectly camouflaged to resemble the rear end of the ant it clung to. [Cool Close-Up Photos Show Ants of the World]

Unlike most known ant species, army ants don’t build permanent nests. Instead, vast colonies that can number in the tens of thousands travel as a group between temporary nest sites known as “bivouacs,” which are constructed around the queen and larvae from the living bodies of worker ants.

Beetles Pose as an Ant's Butt to Grab a Ride

An ant that appears to have a double abdomen is actually carrying a disguised beetle hitchhiker.

Credit: D. Kronauer

Army ants in the Eciton genus that live in neotropical habitats are typically stationary for three weeks and migratory for two weeks, moving to a new nest site every night during their migratory phase — a process that can take up to 9 hours, the study’s lead author and ecologist Christoph von Beeren, a postdoctoral researcher with the Technical University Darmstadt in Germany, told Live Science in an email.

Army ants hunt insects and other arthropods, such as spiders, mites and millipedes. But many types of arthropod species known as myrmecophiles, or “ant lovers,” have come to depend on ants for survival, living off their garbage scraps or hiding within ant colonies as protection from other predators. To keep up with migrating army ants, some “ant lover” species — including many types of beetles — use the ants themselves as a taxi service, stowing away on workers or larvae, von Beeren said.

Von Beeren and study co-author Daniel Kronauer, who traveled to Costa Rica to investigate army ants and associated species, discovered the beetle as they were puzzling over what appeared to be an army ant with two abdomens that they had captured in a vial. And then suddenly, the hidden rider revealed itself.

“When we shook the vial the beetle detached and expanded its legs and antennae — that is the moment we realized we had discovered something new here,” von Beeren said.

Nymphister kronaueri uses its long mandibles to grip an army ant's "waist."

Nymphister kronaueri uses its long mandibles to grip an army ant’s “waist.”

Credit: von Beeren and Tishechkin DOI 10.1186/s40850-016-0010-x

The stealthy and highly specialized beetle N. kronaueri associates exclusively with one army ant species — E. mexicanum — and attaches only to medium-size worker ants, the researchers discovered. Its long mandibles are used like a pair of pliers, grasping the ant between its petiole — essentially the ant’s “waist” — and a wider knob at the top of the abdomen.

Much like the ants it rides, N. kronaueri is shiny and reddish brown in color, and is about the same size and shape as an ant abdomen, which could explain how it can ride atop them and stay unharmed by the colony. Arthropods that coexist with ants fool their hosts into accepting them with chemical signals or physical mimicry — or both — but not enough is yet known about this new beetle species to tell for sure how it succeeds at tricking ants into accepting it as a passenger, von Beeren told Live Science.

The beetle’s highly effective camouflage could also explain why the species was only recently discovered by scientists. Though army ants have been extensively studied, this conspicuous yet overlooked hitchhiker serves as an important reminder of how much is yet to be learned about ants — and the insects that are along for the ride, the researchers noted.

The findings were published online today (Feb. 9) in the open access journal BMC Zoology.

Original article on Live Science.