New study could reset how scientists view sex determination in painted turtle populations

AUGUST 6, 2019

by Fred Love, Iowa State University

A new study from Iowa State University scientists could flip the established framework for how scientists believe geography influences sex determination in painted turtles on its shell.

The study, published Tuesday in the academic journal Functional Ecology, analyzed decades of data concerning painted turtles, a species widely distributed across North America that undergoes temperature-dependent sex determination. That means the temperatures experienced by an incubating painted turtle egg influence whether an embryo develops the physical characteristics biologists describe as male or female. Warmer temperatures tend to produce females, and cooler temperatures tend to produce males.

The study's findings defied theoretical expectations for how painted turtle populations respond to environmental variation, which could lead scientists to rethink how they look at the topic, said Anna Carter, a postdoctoral research associate in ecology, evolution and organismal biology and lead author.

Continued

How a Painted Turtle Finds Its Way – via Herp Digest

Unlike many species, this common reptile migrates from memory

By Timothy Roth, Aaron R. Krochmal from Blogs Scientific American January 30, 2019

Animal migration is one of the most charismatic, awe-inspiring phenomena of the natural world. Faced with unfavorable, often seasonal, changes in climate or habitat quality, animals, from birds to butterflies and wildebeests to sea turtles, migrate vast distances—often thousands of miles—in search of more favorable conditions. They return the following year, in many cases to the exact location where their journey began.

We know that some species use the Earth’s magnetic field to navigate with GPS-like precision and others gaze skyward and guide their migration by the stars. We are just now learning that for some animals, the key to a successful migration is all in their heads—complex thought and memory are also necessary for a successful migration.

For nearly a decade, we have studied the roles of cognition, learning and memory in the migration of a fairly atypical species—the painted turtle, common to neighborhood ponds and roadside ditches. Yep, that turtle—the one you see in virtually every small body of water in the Eastern U.S., as well as occasionally crawling through your backyard or crossing the road by the grocery.  

They’re not as charismatic as sea turtles, and they sure don’t travel as far (several kilometers for a painted turtle versus several thousand kilometers for a sea turtle), but what they lack in outward charisma they make up in tenacity. When these turtles take to land each summer, migrating to new habitats when their home ponds dry up, they face seemingly insurmountable odds: scorching heat, dehydration, and the crushing tug of gravity (you can’t just float around anymore). And that’s not to mention the new predatory threats from both land and air, and the ever-present threat of vehicles when crossing a road. For a painted turtle, there’s a lot going on during migration.

Painted turtles at our research site, which is on conservation land within a patchwork of old growth woodlands and agricultural fields, follow long, intricate routes with amazing precision—specific to within a few meters—to far-off, permanent water sources year after year, returning home again when the seasons next change. Is this behavior instinctual or learned?

To see just where this incredible migratory behavior came from, we introduced into our site animals without any experience migrating there and monitored their ability to respond to seasonal changes in their habitats. Would they be able to migrate successfully?

For some, yes. Naive juveniles under four years old learned to navigate the complex paths just as precisely as experienced local turtles and were able to locate far-off water sources. Naive adults could not. These results suggest a narrow age window, or critical learning period, in which animals must learn to navigate. This phenomenon is not unlike the process of language learning in humans.

But how can they do this? How can a turtle possibly think its way through migration?

They do it the same way that we do: they form and remember memories of space and place using the neurotransmitter acetylcholine, just like humans. 

Acetylcholine has long been known to play a role in spatial memory in mammals. To test whether the turtle brain also works this way, we gave freely migrating turtles (both experienced adults and naive juveniles) mind-altering drugs that temporarily block acetylcholine in their brains.

While the drugs were active and the turtles were without access to spatial memory, the adults with previous experience in the system wandered aimlessly and were unable to follow their traditional migration routes. As soon as the drugs wore off, they got right back on track and were able to successfully migrate to their winter home. 

And what about naive juvenile turtles? They were unaffected by the drug; they followed the paths perfectly whether on the drug or not. Why? They had no memory to disrupt! This demonstrates that adults use spatial memory to navigate during migration, and that they form these memories as juveniles prior to the age of four. This type of higher-order cognitive processing during migration has been previously attributed only to birds and mammals.

For some, yes. Naive juveniles under four years old learned to navigate the complex paths just as precisely as experienced local turtles and were able to locate far-off water sources. Naive adults could not. These results suggest a narrow age window, or critical learning period, in which animals must learn to navigate. This phenomenon is not unlike the process of language learning in humans.

They do it the same way that we do: they form and remember memories of space and place using the neurotransmitter acetylcholine, just like humans. 

Acetylcholine has long been known to play a role in spatial memory in mammals. To test whether the turtle brain also works this way, we gave freely migrating turtles (both experienced adults and naive juveniles) mind-altering drugs that temporarily block acetylcholine in their brains.

While the drugs were active and the turtles were without access to spatial memory, the adults with previous experience in the system wandered aimlessly and were unable to follow their traditional migration routes. As soon as the drugs wore off, they got right back on track and were able to successfully migrate to their winter home.

 And what about naive juvenile turtles? They were unaffected by the drug; they followed the paths perfectly whether on the drug or not. Why? They had no memory to disrupt! This demonstrates that adults use spatial memory to navigate during migration, and that they form these memories as juveniles prior to the age of four. This type of higher-order cognitive processing during migration has been previously attributed only to birds and mammals.

So, it turns out that if you’re a turtle, migration is more than just showing up and muddling through on instinct; you actually have to pay attention and think. And for the turtles, that’s a good thing.

Challenging environments—those with the most extreme, highly variable conditions—tend to produce animals with advanced cognitive abilities, including flexibility in learning and memory.

As climate change continues to disrupt environments, animals will have to rely on cognition to learn new things, including altering the timing, direction and destination of their migrations.

So even though the odds are stacked against them, maybe, just maybe, turtles can outsmart the impacts of climate change.

Go to 

https://blogs.scientificamerican.com/observations/how-a-painted-turtle-finds-its-way/#googDisableSync

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The views expressed here are not necessarily those of Scientific American

Winnipeg man raises rescued tiny turtles in his basement – via Herp Digest

CBC – Mon, 21 Oct, 2013

Manitoba biologist Doug Collicutt has become the surrogate parent to 10 baby painted turtles.

They hatched from eggs that were accidentally dug up in a parking lot at Grand Beach Provincial Park in July. Now, the little guys — the size of a toonie — are wading it out (literally, just swimming and hanging out in an aquarium) at Collicutt's house until next year when warmer weather returns.

His son, who was working as an interpreter at the park was given the eggs by other park workers who turned them up while doing maintenance work.

The location wasn't a great spot to rebury them, Collicutt noted. So his son kept them and passed them on to Collicutt.

"I've always had a great passion for turtles and had reared eggs and hatchlings before. It was only a couple of years ago when I helped rescue a clutch of snapping turtle eggs from a trail at a condo development along Winnipeg's Red River," he wrote in his .

Collicutt put the painted turtle eggs in a bucket of sand on his freezer. He wasn't sure if they would hatch but recently saw one and then nine more soon after.

He intends to feed them a diet of fish and lettuce.

And for the record, he has no intention to name them after the Teenage Mutant Ninja Turtles. In fact, he's leaving them nameless.

"I'm long past the age where I felt it necessary to name pets, and anyway these baby turtles aren't pets, they're just temporary lodgers in my basement," he stated in the blog.

Painted turtles set to become all-female – via Herp Digest

New Scientist 5/3/2013 

Males don't stand a chance in a warmer world, if they happen to be painted turtles. A temperature rise of around 1 °C is all it would take for the species to become 100 per cent female and earmarked for extinction. 

Painted turtles (Chrysemys picta), found in lakes and streams across North America, are one of many reptile species whose sex is determined by temperature. Eggs in warm nests are likely to hatch as females, while males hatch in cooler nests, although no one is sure why.

In recent years, many researchers have raised concerns that global warming could skew the sex ratios of these reptiles. Rory Telemeco and his colleagues at Iowa State University developed a mathematical model to predict whether the painted turtles might be affected.

For over 25 years, Telemeco's colleague, Fredric Janzen, documented the nesting times and sex ratio of painted turtle hatchlings on a small island in the Mississippi river in Carroll County, Illinois. He found that females can shift their nesting dates by about 10 days to ensure their eggs develop at temperatures that produce an even mix of males and females.

The team used this finding, along with historical records of soil and air temperatures, to create a mathematical model that predicts the sex ratio of eggs laid at different temperatures. In a preliminary test of the model, the group correctly predicted the sexes of 40 out of 46 hatchlings born in the wild.

Sex ratio Telemeco's team then used the same model to predict what might happen to the sex ratio of future hatchlings. Conservative climate models predict that average temperatures in the US Midwest will rise by 4 °C over the next century. The group's model suggests that this temperature hike would result in nests of all-female hatchlings, even if the turtles nest earlier, when temperatures are cooler. In fact, average temperatures only need to rise by 1.1 °C to have this effect, the team found. "It's ultimately extinction," says Telemeco. 

Richard Shine, an evolutionary biologist at the University of Sydney in Australia, who was not involved in the study, says the findings are likely to apply to many species where sex is dependent on temperature. "All crocodilians, a smattering of turtles and lizards, plus some fishes", will be affected, he says. "Just laying your eggs a few weeks earlier won't be enough to cancel the effects of warming," he says.

But Shine is optimistic about the turtles' chances of survival. The animals could adapt by laying their eggs in shadier locations, or evolving the ability to cope with warmer conditions.

Telemeco is less sure. "The problem is that climate change is happening so rapidly that an evolutionary response, especially in long-lived organisms, is not likely," he says.

Clues to the turtles' chances of survival may come from a better understanding of the species' genome, which was sequenced last month. Observing how gene expression changes in response to temperature shifts might provide insight into how the turtles adapted to their current environment and also how they might respond to future changes, says Telemeco. Journal reference: American Naturalist, DOI: 10.1086/670051; Genome Biology, DOI:10.1186/gb-2013-14-3-r28