Wednesday, 31 May 2017

Whales reached huge size only recently

Jonathan Amos Science correspondent
24 May 2017

Blue whales are the biggest animals that have ever existed on Earth but they only recently* got that way. 

This is the extraordinary finding from a new study that examined the fossil record of baleens - the group of filter feeders to which the blues belong. 

These animals were relatively small for most of their evolutionary existence and only became the behemoths we know today in the past three million years. 

That is when the climate likely turned the oceans into a "food heaven". 

Favoured prey - such as krill, small crustaceans - suddenly became super-concentrated in places, allowing the baleens with their specialised feeding mechanism to pig-out and evolve colossal forms. 

"The blue whales, the fins and bowheads, and the right whales - they are among the most massive vertebrates to have ever lived," explained Nick Pyenson from the Smithsonian's National Museum of Natural History in Washington DC, US. 

"Some of the dinosaurs were longer, but these big whales even outweighed the largest dinosaurs. And isn't that surprising? People kind of think of gigantism as being a fact of the geologic past. But here we are, living in the time of giants on Planet Earth," he told BBC News. 

Traumatic beetle sex causes rapid evolutionary arms race

24 May 2017

By Chris Simms

Ever wondered what constitutes extreme sex? Cowpea seed beetles certainly know – their sexual act is brutal, and it also seems to encourage a rapid evolutionary arms race between spiked penises and shielding tissue in females.

Extreme genital co-evolution happens in many types of animal, including ducks, fish and fruit flies. For example, female ducks of some species have evolved long and complex internal genitalia, complete with blind alleys, to thwart the unwanted advances of males intent on fowl play. And to counteract this, male ducks have evolved longer and more elaborate penises.

Now Liam Dougherty of the University of Western Australia and his colleagues have discovered how female cowpea seed beetles (Callosobruchus maculatus) are fighting back against the males’ vicious spiked penises (see picture, below).

Once beetles become sexually mature after emerging from the beans in which they live as larvae, they have only one thing on their to-do list – procreation. They don’t eat, or drink, they just look for partners.

“There’s not much courtship,” says Dougherty. “The smaller male jumps on the female and there’s a bit of a struggle. He sort of leans back when he’s fully in. Then there’s a period when the female starts kicking the male. Then they break apart after a few minutes.”
Sexual healing

To peek into what’s happening beneath the shells, Dougherty and his colleagues looked at female sex-related damage in 13 independently bred populations of the beetles. At first, they saw no link between scarring and the thickness of female reproductive tracts. But when male spike length was taken into account, it revealed that scarring was greatest when linings were thin and penis spikes were long.

Bioelectric tweak makes flatworms grow a head instead of a tail

23 May 2017

By Jessica Hamzelou

Cut off the head of a planarian flatworm, and a new one will grow in its place. The worm is one of many creatures that have some kind of memory for lost limbs, enabling them to regenerate what was there before.

Now it seems that this memory can be altered by meddling with the electrical activity of the animals’ cells. Shifting the bioelectric current at the site of the cut changes the type of appendage regenerated – allowing a head to be regrown in place of a tail, for instance.

Michael Levin at Tufts University in Medford, Massachusetts, and his colleagues have shown that after changing the electrical current of the cells once, the animals will continue to randomly regrow a head or a tail. The findings suggest that an animal’s body plan is not just down to its genes and environment – electricity plays a key role, too. “It’s pretty profound,” says Levin.

His team has long been trying to understand how electric currents in the body’s cells affect health and the ability to regenerate damaged tissues – what Levin calls the “bioelectric code”.

On the charge
Charged ions are constantly moving in and out of cells, giving cells a natural electrical charge. The patterns of electrical activity are thought to have an important role in controlling how embryos develop limbs. Levin wants to find out whether they might work in adult animals – and potentially humans – too.

Drugs, including commonly used anaesthetics, can destabilise the electrical charge of cells. In a recent experiment, Levin’s team took this approach to see if altering the electrical charge in worms that had had their heads and their tails cut off might encourage them to grow two heads or tails instead of one head and one tail.

The team found that about 70 per cent of the worms regrew a second tail or head instead of the “correct” body part. The rest appeared to be unaffected.

To probe further, Levin’s student Fallon Durant re-cut the worms that had regenerated the normal body part without giving them any other treatment. She saw the same trend – 70 per cent regrew the wrong part, while 30 per cent looked the same as they had originally. The team repeated the experiment, and saw the same outcome over and over again.

After destabilising a worm’s electrical current once, it is as if each end of the worm makes its own decision – with a preference for the wrong part  –  as to whether it will develop a head or a tail whenever it is cut, says Levin. By altering the bioelectric code, the animal’s body plan can be permanently rewritten, he says.

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