Malawi cichlids – how aggressive males create diversity

Blogging on Peer-Reviewed ResearchCertain groups of animals show a remarkable capacity for quickly evolving into new species to seize control of unexploited niches in the environment. And among these ecological opportunists, there are few better examples than the cichlids, a group of freshwater fishes that are one of the most varied group of back-boned animals on the planet.

Malawi cichlidsIn the words of Edward O. Wilson, the entire lineage seems “poised to expand.” The Great Lakes of Africa – Tanganyika, Malawi and Victoria – swarm with a multitude of different species; Lake Malawi alone houses over 500 that live nowhere else in the world.

All of these forms arose from a common ancestor in a remarkably short span of time. Now, a new study suggests that this explosive burst of diversity has been partly fuelled by rivalry between hostile males.

Michael Pauers of the Medical College of Wisconsin found that male cichlids have no time for other males that look like them and will bite, butt and threaten those who bear the same colour scheme. In doing so, they encourage diversity in the lake since mutant males with different tints are less likely to be set upon by territorial defenders.

Continue reading

Blind cavefish not so blind, Beetlemania and other tidbits…

Stories about cavefish are like buses – you get a seeming infinity of nothing and then loads turn up at once. Just 10 posts ago, I wrote about a study which found that you can restore sight to blind cavefish by cross-breeding individuals from different caves.

The different populations lost their eyes through changes to different sets of genes and in the hybrids, each faulty version was paired with a working one. As a result, the hybrids had fully formed and functional eyes despite having lived in darkness for a million years.

Now, a new study shows that the larvae of blind cavefish can detect light (or more accurately, shadows) too, even without working eyes. They can detect shadows and seek shelter in them, just like the sighted surface-dwelling versions of the same species. The key to the behaviour is their pineal gland, a small organ that regulates the body clock and, in some species, is sensitive to light.

I wrote up the research for Nature News; mosey on over for the full story and some possible explanations for why the fish’s pineal has retained the ability to detect light, even though its eyes have been lost.

Some other things to mention:

Cross-breeding restores sight to blind cavefish

Blogging on Peer-Reviewed ResearchIn the caves of Mexico lives a fish which proves that a million years of evolution can be undone with a bit of clever breeding.

Blind cavefishThe blind cavefish (Astyanax mexicanus) is a sightless version of a popular aquarium species, the Mexican tetra. They live in 29 deep caves scattered throughout Mexico, which their sighted ancestors colonised in the middle of the Pleistocene era. In this environment of perpetual darkness, the eyes of these forerunners were of little use and as generations passed, they disappeared entirely. They now navigate through the pitch-blackness by using their lateral lines to sense changes in water pressure.

But there is a deceptively simple way of restoring both the eyes and sight that evolution has taken, and Richard Borowsky from New York University’s Cave Biology Research Group has found it. You merely cross-bred fish from different caves.

Continue reading

Solving the San Francisco plankton mystery

Blogging on Peer-Reviewed ResearchLook into the oceans past the sharks, seals and fish and you will find the tiny phytoplankton. These small organisms form the basis of life in the seas but if their populations get to big, they can also choke the life from it by forming large and suffocating algal blooms.

Solving the San Francisco plankton mysteryThe waters of San Francisco Bay have never had big problems with these blooms and if anything, scientists worried that the waters didn’t have enough phytoplankton. All that changed in 1999, when the phytoplankton population started growing. It has doubled in size since.

Now, scientists from the United States Geological Survey (USGS) have found that the blooms are the result of a long chain of ecological changes in the area. The plankton are just players in a large ensemble drama involves clams, mussels, fish, crabs and a cold snap.

Continue reading

Fake cleaner fish dons multiple disguises

Guess which is which? (The top one is the real deal)

Blogging on Peer-Reviewed Research

Nature is rife with charlatans. Hundreds of animals have evolved to look like other species in order to fool predators into thinking they’re more of a threat, or to sneak up on unsuspecting prey. In the Indo-Pacific lives a fish that does both and has the rare ability to switch between different disguises – the bluestriped fangblenny.

Common though it is, mimicry is usually restrictive and most fakers are stuck with one disguise. Until a few years ago, the only known animal that could switch between different acts was the amazing mimic octopus, which contorts its flexible body to look like seasnakes, lionfish, flounders and other poisonous underwater denizens.

Cleaner and faker

In 2005, Isabelle Cote and Karen Cheney from the University of Queensland discovered that a small reef fish called the bluestriped fangblenny (Plagiotremus rhinorhynchos) is also a dynamic mimic.

Its model is the bluestreak cleaner wrasse Labroides dimidiatus, an industrious species that provides a cleaning service for other reef visitors by picking off parasites and mucus from hard-to-reach places. The fangblenny’s intentions are less welcome. Its resemblance to the helpful wrasse allows it to get close enough to mount quick attacks on larger fish, biting off scales and skin (see image below for why it got it’s name).

Continue reading

Trout with salmon parents could help to revive endangered fish species

Japanese researchers have developed a way of using one species of fish as a surrogate parent for an endangered one by transplanting the sexual equivalent of stem cells. If enough of these cells can be preserved, an extinct species could be resurrected.

Getting excited when fish produce sperm would usually get you strange looks. But for Tomoyuki Okutsu and colleagues at the Tokyo University of Marine Science and Technology, it’s all part of a day’s work. They are trying to use one species of fish as surrogate parents for another, a technique that could help to preserve species that are headed for extinction.

Baby trout can be born from salmon parents using transplanted sex cells.Okutsu works on salmonids, a group of fish that includes salmon and trout. Many members of this tasty clan have suffered greatly from over-fishing in the last few decades, and their populations are dwindling their way to extinction.

If stocks fall below a critical level, they may need a jump-start. One strategy is to freeze some eggs to be fertilised artificially, in the way that many human eggs are in fertility clinics. But it’s much harder for fish eggs – they are large and have lots of fat, which makes them difficult to freeze effectively.

Okutsu’s group have hit on a more effective solution. They use transplanted sexual stem cells to turn another species of fish into surrogate parents for the endangered ones.

Continue reading

Moray eels attack ‘Alien-style’ with second pair of jaws

A skeletal model of a moray eel bite, showing the pharyngeal jaws at work.In the Alien movies, the eponymous monster killed shipmates and marines with a fearsome set of double jaws. That may have been science fiction but science fact isn’t too far off. In our planet’s tropical oceans, moray eels use a ballistic set of second jaws to catch their prey.

These ‘pharyngeal jaws’ are housed in the eel’s throat. When the main jaws close on an unlucky fish, the second set launches forward into the mouth, snags the prey with terrifying, backward-pointing teeth and drags it back into the throat. In fractions of a second, the prey is bitten twice and swallowed. (Have a look at this Quicktime video of the pharyngeal jaws in action)

Continue reading