Unborn Turtles Actively Regulate their own Temperature – via Herp Digest

Smithsoniam.org 6/12/13 Visit a sunny pond in a meadow, park or zoo and you’ll likely see turtles basking on logs and small lizards hanging out on warm rocks. If you’re in the south, you may even spot an alligator lazing on a bright patch of shore.

Ectotherms (better known as cold-blooded animals) such as these reptiles have to shuttle back and forth between shade and sun in order to manually regulate their body temperature. Insects, fish, amphibians and reptiles all do it. Now, new research suggests that these animals begin their temperature-regulating tasks much earlier than previously thought–while they are embryos encased in their eggs.

Previously, researchers thought of developing embryos as cut off from the outside world. But back in 2011, researchers found that Chinese soft-shelled turtle embryos could move between warmer or cooler patches in their eggs, though they lacked any feet at such an early stage of development. Some of the same Chinese and Australian researchers who published that original finding decided to investigate further to see just how deliberate these movements are.

“Do reptile embryos move away from dangerously high temperatures as well as towards warm temperatures?” the team, writing in the journal Biology Letters, wondered. “And is such embryonic movement due to active thermoregulation, or (more simply) to passive embryonic repositioning caused by local heat-induced changes in viscosity of fluids within the egg?”

In other words, are unborn reptiles purposefully moving from one spot to another within their eggs, much like an adult animal does? The team decided to investigate these questions by experimenting on turtle embryos. They incubated 125 eggs from Chinese three-keeled pond turtles. They randomly assigned each of the eggs to one of five temperature groups: constant temperature, hot on top/cool on the bottom, or at a range of heats directed towards one end of the egg.

When they began the experiment, most embryos sat in the middle of their eggs. A week after exposing them to the different temperature groups, the team again measured the baby turtles’ positioning within the eggs. At the 10-day mark, the researchers again measured the turtles’ positions, and then injected half of the eggs with a poison that euthanized those developing embryos. Finally, after another week, they took one last measurement of the developing turtles and euthanized turtles.

The turtles within the eggs held at constant temperature or those that were in the “warm on the top/cool on the bottom” group tended not to shift around in their eggs, the researchers found. Those belonging to the groups that experienced warm temperatures only on one end of their egg, however, did move around. They gravitated towards warm conditions (84-86°F), but if things heated up too extremely (91°F), they edged towards the cooler side of their egg. Crucially, the embryos that the researchers euthanized stopped moving after receiving the dose of poison. This shows that the embryos themselves, not some passive physical process, are doing the shifting. 

The turtle embryos, the researchers note, behave much like adult reptiles do when thermoregulating their bodies. They warm up and cool down by moving toward or away from heat sources. For species like turtles, temperature during development plays an important part of determining the embryo’s sex. Turtle nests, which are buried in the sand, often experience a range of different temperatures, so embryos could be playing a role in determining their own gender, edging towards the cooler side of the egg if they feel like becoming a male, or the warmer side if they’re more female-inclined, the authors write.

Fiddler crabs keep cool with giant claws

Male fiddler crabs use their giant claws to keep cool as well as attract females, say scientists.

The crabs' oversized limbs are waved to signal strength to potential mates.

US researchers discovered that crabs with an intact major claw also cool faster than those without, showing that the claws help regulate temperature.

Scientists suggest this previously unknown benefit could help offset the energy cost of growing such a large sexual ornament.

There are about 100 species of fiddler crab found in tropical regions around the world.

Males are recognisable by their assymetrical claws, whereas females' claws are equally sized.

To attract the attention of potential mates, males perform elaborate claw-waving displays.

Dr Zachary Darnell and Assistant Professor Pablo Munguia from the University of Texas, US investigated whether the giant claws had a function beyond attracting mates.

Their study focussing on the Gulf coast fiddler crab (Uca Panacea) was recently published in the American Naturalist journal.

In the experiment, researchers shone lamps on crabs with an intact major claw and on crabs that were missing theirs.

They measured the crabs' body temperature every 10 minutes and found that the crabs lacking the large claw took much longer to cool down.

"The major claw likely functions like a heat sink, with heat being transferred from the body to the claw and dissipated into the surrounding air through convective heat transfer," said Dr Darnell.

Although the giant limbs effectively attract the attention of females, they had previously been considered a physical burden.

"The large claw is metabolically costly, it hinders feeding because it is cumbersome for this task, and it reduces endurance capacity when crawling on the sand," Dr Darnell explained.

"Male crabs are both heat-stressed and hungry while on the surface, foraging and performing the claw-waving display."

But Dr Darnell says the team's results are the first evidence to show how the enlarged structure benefits both reproduction and survival.

"With the large claw acting as a heat sink male fiddler crabs can remain on the surface longer, foraging and performing the waving display," he told BBC Nature.

Dr Darnell suggests that the dual function of fiddler crab claws could provide insight for other species.

"A thermoregulatory function of the major claw should change the way scientists think about this structure, and reconsider the costs and benefits associated with the claw and other [sexual] traits."

Ella Davies
Reporter, BBC Nature
http://www.bbc.co.uk/nature/14631028

Wee bit of armour

SOME frogs have bladders that are as big as the rest of their bodies, and they can urinate out radio tracking devices, an ability probably designed to protect their digestive systems, Territory researchers have found.


Charles Darwin University physiological ecologist Chris Tracy knows more about the urinating habits of frogs than most people, although that is not why he began frog watching.

About two years ago Dr Tracy was researching temperature regulation in frogs near Alice Springs when he noticed the 2cm-long electronic tracking devices he and team mates implanted in the 8cm-long frogs were not where they left them.

"I chase frogs around the bush and something interesting happened in this case," Dr Tracy said.

Then the researchers found - through a bit of surgery - the jelly bean sized transmitters were in the frogs' bladders.

"At first we thought it was a little bit odd because we didn't think we put them in the bladders of the frogs," Dr Tracy said. The team found it had happened with three different but closely related native species, so they carried out trials on cane toads using beads and dissected them after a few days to see the progress. Dr Tracy believes tissue comes from the frog's bladder and engulfs a foreign object, pulling it into the bladder as protection against sharp bits from the insects they eat, which could puncture their digestive system. It could also protect against thorns or sharp objects piercing their thin skin when they land from a jump. Because the bladder is so big - to store water - foreign objects are likely to come into contact with it.

"Frogs get around by jumping and they have relatively thin and soft skin and can be kind of clumsy when they land," he said. "If you watch closely when a frog jumps they kind of crash land most of the time. It's certainly the most bizarre thing that I have discovered."



DAVID WOOD  
http://www.ntnews.com.au/article/2010/12/09/199631_ntnews.html