If you think the stars of Pixar’s Finding Nemo had it rough, spare a thought for the plight of real clownfish. These popular fish may struggle to survive in oceans that are becoming enriched with carbon dioxide. High levels of CO2 dissolved in the water can muddle a clownfish’s sense of smell, preventing it from detecting both shelter and threats.
Philip Munday from James Cook University has shown that at levels of carbon dioxide within what’s predicted for the end of the century, a clownfish’s ability to sense predators is completely shot. Some larvae become literally attracted to the smell of danger and start showing risky behaviour. It’s not surprise that they die 5-9 times more frequently at the mouths of predators.
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.
Fizzy drinks like Perrier and Coca-Cola are targeted at a huge range of social groups, but if fruit flies had any capital to spend, they’d be at the top of the list. Unlike posh diners or hyperactive kids, flies have taste sensors that are specially tuned to the flavour of carbonated water.
Humans can pick up five basic tastes – sweet, salty, sour, bitter and umami (savoury). But other animals, with very different diets, can probably expand on this set. And what better place to start looking for these unusual senses than the fruit fly Drosophila, a firm favourite of geneticists worldwide, and an animal with very different taste in food to our own.
Drosophila‘s tongue contains structures that are the equivalent of our own taste buds. They are loaded with taste-sensitive neurons and the activity of specific genes gives these neurons the ability to recognise different tastes.
Other researchers have already isolated the genes that allow Drosophila to tell sweet from bitter. But when Walter Fischler found a group of taste cells that didn’t have either of these genes and connected to a different part of the fly’s brain, he knew he was on to something new.
Rising temperatures and high carbon dioxide emissions are the means through which humans are inadvertently causing the decline of several species. But one animal actively uses both heat and carbon dioxide as murderous weapons – the unassuming honeybee.
With their stings and numbers, bees already seem to be well-defended but they are completely outgunned by giant hornets (right). These two-inch long monsters are three times longer than several times heavier than tiny honeybees and raiding parties can decimate entire hives. European bees mount little in the way of an effective defence, but Japanese bees aren’t so helpless. When their hives are invaded, they launch a mass counterattack.
Swarms of workers dogpile the hornet, pinning it down while vibrating their wing muscles. At the centre of this “heatball”, the frenetic buzzing heats up the hornet to a roasting 45 degrees Celsius.
Scientists have long thought that this manoeuvre bakes the hornet alive, for the bees that surround it are more resistant to high temperatures. But Michio Sugahara and Fumio Sakamoto from Kyoto Gakuen University have found that this isn’t the whole story.
In the movie Finding Nemo, the eponymous clownfish grows up in the security of his home reef and must find his way back after being fry-napped by an overenthusiastic diver. In reality, the larvae of clownfish spend their early lives adrift in the open ocean and only after weeks, or possibly months, do they return to the reefs where they were born.
Their journey is guided by several cues that help them navigate home. The sound of a reef may be one of these but it’s clear that the most important sense for a returning fish is smell. Young fish have very well developed smell organs and respond appropriately to the molecules given off by other fish, and by the sea anemones that they live in. They have a keen nose for things that smell fishy, and there is even some evidence that they can use smell to distinguish the water of their birth reef from that of any other.
But this uncanny homing ability isn’t foolproof. Philip Munday from James Cook University in Australia found that increasing the amount of carbon dioxide in the water muddles the senses of baby clownfish, sending them towards smells they would normally avoid. For an animal that relies so heavily on smell to find a suitable place to live, that could be catastrophic.
Sadly, the conditions in Munday’s experiment have a very good chance of coming to pass. As humans pump ever more carbon dioxide into the atmosphere, at least a third dissolves into the oceans, making them increasingly acidic. Over the past 200 years, the pH of the oceans has fallen 100 times faster than any time in the last 650,000 years. Marine life will suffer as a result – corals will find it harder to build their mighty reefs in water depleted of the ions they need. Shellfish that build limestone skeletons will also face trouble. Now, it seems that the popular clownfish joins the list of species at risk.
We’ve all seen the images of receding glaciers and stranded polar bears that accompany talks of climate change. But rising carbon dioxide levels also have subtler and less familiar effects, and may prove to be a boon for many animal groups. Plant-eating insects, for example, have much to gain in a high -CO2 future as rising concentrations of the gas can compromise the defences of the plants they feed on.
Plants and herbivorous insects are engaged in a silent war that we are rarely privy too, where chemicals act as both weapons and messengers. Munching mandibles trigger the production of signalling molecules like jasmonic acid that announce the presence of invaders to other plants of the plant, neighbouring individuals, or even parasitic wasps, which attack the pests and turn them into living larders for wasp eggs.
The battle isn’t over even after parts of the plant are eaten. Beetles, for example, rely on enzymes called cysteine proteinases to digest the plant proteins they swallow, and free up valuable amino acids for the insects’ own growth. But when plants detect jasmonic acid signals, they produce chemicals called “cysteine proteinase inhibitors” (CystPIs) that block the insects’ digestive enzymes and prevent them from fully digesting their meals.
But these defences may buckle as carbon dioxide levels rise. Jorge Zavala and colleagues at the University of Illinois found that increasing levels of CO2 reduce the ability of soybeans to use jasmonate signals. That shrinks their stockpiles of defensive CystPIs and makes them more vulnerable to hungry pests including two voracious species of beetle – the western corn rootworm (Diabrotica virgifera) and the Japanese beetle (Popillia japonica). Given that soybeans are an increasingly important food crop, it’s in our interest to stop insects from eating them so that we can instead.