Tiny molecules drove the evolution of the vertebrates

Blogging on Peer-Reviewed ResearchThe spinal column that runs down your back is an identity badge that signifies your membership among the vertebrates – animals with backbones. Vertebrates have arguably the most complex bodies and genomes of any animal group and certainly, our lineage has come a long way from its last common ancestor.

TigerThe closest evolutionary cousins of the vertebrates are simple aquatic creatures such as the jawless lancelets and the sac-like, immobile sea squirts. How did these simple body plans diversify into the vast array of sophisticated forms wielded by today’s fish, amphibians, reptiles and mammals?

Gene number

Many scientists have suggested that the answer lies in the number of our genes. At three different points, the vertebrate genome (its full suite of genes) experienced a massive jump in size as huge chunks of genes – possibly the entire lot – were duplicated. The first of these coincided with the origins of the group itself and the second happened alongside the rise of the first jawed fish, setting them and their descendants aside from more ancient jawless forms like the lampreys.

So far, there seems to be a tidy connection between gene number and complexity, but the third round of duplication is a bit of a stumbling block. It happened at some point during the evolution of the bony fishes and while this group proceeded to radiate into a multitude of different shapes, their basic body plan stayed essentially the same. No big jump in complexity there.

Indeed, as the full genome sequences of more and more species are revealed, it’s becoming clear that the basic genetic toolkit that controls the development of animal bodies is remarkably consistent across the kingdom. Even the genome of a sea anemone, one of the simplest and most ancient animals on Earth, is strikingly similar to that of vertebrates.

In this light, it’s looking increasingly unlikely that the advent of new genes can account for the large rise in vertebrate complexity. Now, Alysha Heimberg and colleagues from Dartmouth College have proposed a new theory, centred around tiny molecules called microRNAs.

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Earliest bat shows flight developed before echolocation

Blogging on Peer-Reviewed ResearchTheir heads and bodies of bats have amassed an extraordinary array of adaptations that have make them lords of the night sky. Today, the thousand-plus types of bats make up a fifth of living mammal species. Richard Dawkins once described the evolution of bats as “one of the most enthralling stories in all natural history” and as of this week, the story has a clearer beginning.

OnychonycterisThe success of bats hinges on two key abilities: their mastery of flight, a feat matched only by birds and insects; and echolocation, the ability to navigate their way through pitch-blackness by timing the reflections of high-pitched squeaks. For evolutionary scientists, the big question has always been: which came first?

The ‘clawed bat’

Until now, fossil bats haven’t provided any clues for all of them show signs of both echolocation and flight. But a stunning new fossil, discovered by Nancy Simmons from the American Museum of Natural History is an exception and it provides a categorical answer to the long-running debate – the earliest bats could fly but could not echolocate.

The new creature hails from the Green River in Wyoming and is known as Onychonycteris, meaning “clawed bat”. Its fossils date back to about 52.5 million years ago and by comparing it to other prehistoric bats, Simmons found that it is the most ancient member of this lineage so far discovered. It acts as a ‘missing link’ in bat evolution, much like the famous Archaeopteryx hinted that birds may have evolved from dinosaurs.

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New languages evolve in rapid bursts

Blogging on Peer-Reviewed ResearchThe birth of new languages is accompanied by a burst of rapid evolution consisting of large changes in vocabulary that are followed by long periods of relatively slower change.

latin_dictionary.jpgLanguages are often compared to living species because of the way in which they diverge into new tongues over time in an ever-growing linguistic tree. Some critics have claimed that this comparison is a superficial one, a nice metaphor but nothing more.

But the new study by Quentin Atkinson, now at the University of Oxford, suggests that languages evolve at a similar stop-and-start pace, which uncannily echoes a long-standing theory in biology, known as ‘punctuated equilibrium’. The theory’s followers claim that life on Earth also evolved at an uneven pace, full of rapid bursts and slow periods.

Famously championed by the late Stephen Jay Gould, the punctuated equilibrium theory suggests that most species change very little over time and big evolutionary changes are concentrated at rare moments where new species branch off from existing lineages. Together with colleagues from the US and New Zealand, Atkinson found similar patterns in three of the worlds’ largest families of languages.

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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.

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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.

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Evolutionary arms race turns ants into babysitters for Alcon blue butterflies

Blogging on Peer-Reviewed ResearchIn the meadows of Europe, colonies of industrious team-workers are being manipulated by a master slacker. The layabout in question is the Alcon blue butterfly (Maculinea alcon) a large and beautiful summer visitor and its victims are two species of red ants, Myrmica rubra and Myrmica ruginodis.

Myrmica rubra and an Alcon blue butterfly caterpillarThe Alcon blue is a ‘brood parasite’ – the insect world’s equivalent of the cuckoo. David Nash and European colleagues found that its caterpillars are coated in chemicals that smell very similar to those used by the two species it uses as hosts. To ants, these chemicals are badges of identity and so similar are the caterpillars that the ants adopt them and raise them as their own. The more exacting the caterpillar’s chemicals, the higher its chances of being adopted.

The alien larvae are bad news for the colony, for the ants fawn over them at the expense of their own young, which risk starvation. If a small nest takes in even a few caterpillars, it has more than a 50% chance of having no brood of its own. That puts pressure on the ants to fight back and Nash realised that the two species provide a marvellous case study for studying evolutionary arms races (which I’ve blogged about before here).

Theory predicts that if the parasites are common enough, they should be caught in an ongoing battle with their host, evolving to become more sophisticated mimics, while the ants evolve to become more discriminating carers. The two species make a particularly good model for this because their geographical ranges overlap in a fractured mosaic.

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Whales evolved from small aquatic hoofed ancestors

Blogging on Peer-Reviewed ResearchTravel back in time to about 50 million years ago and you might catch a glimpse of a small, unassuming animal walking on slender legs tipped with hooves, by the rivers of southern Asia. It feeds on land but when it picks up signs of danger, it readily takes to the water and wades to safety.

Indohyus

The animal is called Indohyus (literally “India’s pig”) and though it may not look like it, it is the earliest known relative of today’s whales and dolphins. Known mostly through a few fossil teeth, a more complete skeleton was described for the first time last week by Hans Thewissen and colleagues from the Northeastern Ohio Universities. It shows what the missing link between whales and their deer-like ancestors might have looked like and how it probably behaved.Whales look so unlike other mammals that it’s hard to imagine the type of creature that they evolved from. Once they took to the water, their evolutionary journey is fairly clear. A series of incredible fossils have documented their transformation into the masterful swimmers of today’s oceans from early four-legged forms like Pakicetus and Ambulocetus (also discovered by Thewissen). But what did their ancestors look like when they still lived on land?

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