Bee hives, with their regularly arranged honeycombs and permanently busy workers may seem like the picture of order. But look closer, and hives are often abuzz with secret codes, eavesdropping spies and deadly alliances.
African honeybees are victimised by the parasitic small hive beetle. The beetles move through beehives eating combs, stealing honey and generally making a mess. But at worst, they are a minor pest, for the bees have a way of dealing with them.
They imprison the intruders in the bowels of the hive and carefully remove any eggs they find. In turn, the beetle sometimes fools the bees by acting like one of their own grubs, and gets a free meal instead of imprisonment. In Africa, both species have found themselves in an evolutionary stalemate.
But in 1998, American beekeepers spotted the beetle in hives of their local European-descended honeybees. These insects are gentler versions of their aggressive African relatives, and in them, the beetles found more vulnerable victims.
Miners used to take canaries into unfamiliar shafts to act as early warning systems for the presence of poisons. Today, climate scientists have their own canaries – amphibians. Amphibians – the frogs, toads and salamanders – are particularly susceptible to environmental changes because of their fondness for water, and their porous absorbent skins. They are usually the first to feel the impact of environmental changes.
And feel it they have. They are one of the most threatened groups of animals and one in three species currently faces extinction. The beautiful golden toad (right) was one of the first casualties and disappeared for good in 1989. Even though they are less glamorous than tigers, pandas or polar bears, amphibians are a top priority for conservationists.
The usual factors – introduced predators and vanishing habitats – are partially to blame, but many populations have plummeted in parts of the world untouched by pesky humans. More recently, a large number of these deaths have been pinned on a fatal fungal disease called chytridiomycosis. Hapless individuals become infected when they swim in water used by diseased peers, and fungal spores attach to their skins. The disease had decimated amphibians across the Americans.
But it’s not the only killer – climate change can join their list of enemies. In Costa Rica, warmer and wetter days have led to a loss of rainforest leaf litter that has sent amphibian and reptile populations crashing. The extent of the damage may be even worse than we think. We have very little long-term data on the population sizes of many amphibian species, particularly in the tropics, where the greatest diversity exists. One of the few sites to buck the trend of ignorance is La Selva Biological Station in Costa Rica, which has been monitoring amphibian populations since the 1950s.
As Charles Darwin learned several centuries ago, islands are havens for evolution. Newcomers to these isolated worlds find themselves unshackled from the predators that dogged them on the mainland. They celebrate their freedom by diversifying into a great variety of species. But predators still have ways of tracking them down, and following the footsteps of sailors is one of them. By killing adults and eating eggs, introduced predators such as rats, cats and stoats are responsible for nine in ten of the bird extinctions since 1600.
Now, conservation agencies are getting serious about introduced predators. As an example, they have spent increasingly large budgets in recent years on the eradication of rats from troubled islands. Smaller stowaways like mice typically escape the conservationists’ wrath, and between 2001 and 2005, twenty-five times less money was spent on dealing with them. After all, mice are smaller and less opportunistic than rats and pose very little threat to seabirds.
Or at least that was what scientists used to think. In 2005, Ross Wanless, Peter Ryan and colleagues from the University of Cape Town found that on Gough Island in the south Atlantic, mice had developed sinister appetites. They were eating the chicks of local seabirds alive (see image below).
Over the past decade, some coastal waters have started turning red with alarming frequency. The cause is not some Biblical plague, but dense concentrations of microscopic algae called dinoflagellates. Red tides can often contain more than a million of these cells in a mere millilitre of water. Many are harmless and essential parts of the ocean environment, but others produce toxins that can kill local wildlife and risk the health of humans who eat their poisoned flesh.
These “harmful algal blooms” are more common in warm waters that mix poorly and are unusually rich in nutrients. Their increasing frequency has been blamed on numerous causes, from natural causes, to agricultural run-offs to increasing sea temperatures caused by climate change. But, as is becoming increasingly apparent in ecology, you’re not getting a complete picture of a habitat if you don’t know find out what the local parasites are up to.
Aurelie Chambouvet from the Station Biologique found that the algae responsible for red tides are themselves the victims of other parasitic species of dinoflagellates called Amoebophrya. The parasites act as an natural alga-stat that keeps the local algae populations under a tight leash. The red tides are what happens when that leash breaks.
Chambouvet’s team discovered the abundance of these parasites by taking water samples from an estuary of the Penze River in northern France over three consecutive years,. They used multi-coloured glowing antibodies designed to recognise and stick to molecules unique to both the host species and their parasites. The fluorescent glows revealed a life cycle that, like those of most parasites, is full of brutality and exploitation.
The decades that make up a typical human lifespan can seem like vast stretches of time to us. But to the forces of evolution, they are mere temporary blips. Common wisdom has it that evolution occurs over geological timescales – thousands and millions of years. As such, evolutionary biology takes a lot of criticism for being a ‘descriptive science’, being less open than other fields to that fundamental aspect of science – experimentation. Though there are exceptions, those who study evolution must mostly be content to observe snapshots of life, either present or entombed in rock, and make inferences from there.
But this isn’t always so. Occasionally, evolution happens at astonishingly fast rates, as epitomised by the case of the peppered moths. Today, canny scientists are on the look-out for situations where the evolutionary pressures that weigh upon a species change speedily and which are more amenable to testing. Jonathan Losos and colleagues at Washington University, St Louis, have found one such example in a small Caribbean lizard.
The brown anole lives in the Bahamas and spends much of its time foraging on the ground. Islands provide great opportunities for evolutionary biologists because invading species can drastically change or reverse the evolutionary pressures on the locals. The Bahamas are no exception to this – occasionally, the islands that the brown anole calls home are invaded a larger predatory species, the curly-tailed lizard.
Humans have explored the entire face of the planet, but we haven’t done so alone. Animals and plants came along for the ride, some as passengers and other as stowaways. Today, these hitchhikers pose one of the greatest threats to the planet’s biodiversity, by ousting and outcompeting local species.
Islands are particularly vulnerable to invaders. Cut off from the mainland, island-dwellers often evolve in the absence of predators and competitors, and are prone to developing traits that make them easy pickings for invaders, like docile natures or flightlessness.
Two years ago, I wrote about the ability of invasive predators to change entire island landscapes. In the Aleutian archipelago that runs between Alaska and Russia, Arctic foxes have turned some islands from grassland to tundra by killing the seabirds whose droppings provided the islands’ only fertiliser.
Now, we return to the ill-fated Aleutians to discuss another study that shows how the actions of immigrant predators can even domino into the surrounding waters. This time, the stars are not foxes, but that other ubiquitous opportunist – the brown rat.