软壳龟胚胎开始时是雄性，但在适当的温度和蛋白质可以在孵化前变成雌性，according to a sex determination study published in Philosophical Transactions of the Royal Society B.
Spiny softshell turtles are the largest freshwater turtle in North America. They lay their eggs in sunny sandbars or gravel banks near water, which will hatch between 60-80 days later.
A team of researchers, led by Nicole Valenzuela of Iowa State University, found that the creatures (Apalone spinifera) determine their sex based on the amount of protein produced by their chromosomes before they hatch, instead of the amount and type of chromosomes that are present – a phenomenon called sex chromosome dosage compensation.
Not only this, but the whole process depends also on the temperature the egg are incubated in – there could be too many boys if things are too warm.
Valenzuela explains that understanding this type of sex determination can help us learn about why and how animals, including humans, evolved to use proteins and chromosomes to determine sex, which might help in cases where there are sex chromosome abnormalities.
Sex determination is complex and differs between species, and the turtle is no exception. In humans and most mammals, biological sex is determined by the presence of specific chromosomes when an egg is fertilised, but in reptiles like turtles and crocodiles, it is more often determined well after the egg is fertilised, but before it hatches, based on how the egg is incubated.
Read more: Turtle embryos can influence their own sex
Each chromosome is responsible for making proteins that contribute to certain characteristics, so the type of chromosomes determines how much protein is eventually made.
Unlike humans, who have X and Y chromosomes, female softshell turtles have a ZW chromosome, and males have either one or two Z chromosomes. In humans, having only a single sex chromosome like this can have big consequences, such as Klinefelter syndrome and Turner syndrome.
If all the chromosomes are producing the same quantity of proteins, the ZZ males have double the amount of unique Z proteins compared to a ZW female or Z male – except the single Z males weren’t incurring any problems.
To understand what was happening, the team analysed tissue from embryos, hatchlings and adults to see which genes were being expressed.
During early embryo development, they found that expression of genes on the Z chromosomes doubled in female ZW females and Z males to compensate the imbalance of chromosomes, which meant they were producing about as much protein as the ZZ males.
However, during late-stage embryo development, the amount of protein made by the Z chromosome decreased, which allowed the W chromosome to take over and help the embryo become female before it hatches. Once hatched, there is no going back, though.
This meant that the ZW turtles produced the same amount of Z proteins as males in the early stages of embryo development – and so, appeared to be males – but this changed in the later part of embryo development and resulted in females hatching out of the egg.
Fascinatingly, this effect was more pronounced when the eggs were incubated in cooler laboratory conditions – the Z genes actually kept expressing at a higher level when it was warm, and femaleness wouldn’t get the same opportunity to develop, and they could hatch out as male-like instead.
This means that if the climate becomes too warm, more male-like turtles could hatch out, suggest the authors.
A mystery substance is analysed and found to contain, let’s say, five compounds. How is that analysis actually done? How do scientists know what substances they’re working with? There’s no magic box that identifies all chemicals: it takes a lot of time, and complicated machinery. But researchers from Griffith University have figured out one way to speed the process up.
“When we look at complex mixtures of molecules, we can do that by either one of two techniques,” explains Professor Anthony Carroll, from Griffith’s School of Environment and Science and the Griffith Institute for Drug Discovery.
The first technique is called liquid chromatography/mass spectrometry: separating the mixture into discrete substances (liquid chromatography), and then analysing the molecular weight of those substances (mass spectrometry). This tells us which atoms are present, but it doesn’t yield much information on the structure of the molecules.
The second technique is called nuclear magnetic resonance spectroscopy (NMR): it can give information on the structures of molecules, but it doesn’t provide details on mass. It yields data in the form of peaks on a “spectrum”, which chemists can use to learn more about how the atoms are linked – but a mixture with lots of different molecules generates very complicated readings.
“We’ve got these two techniques that give us really useful information, but they’re not tied to each other,” says Carroll.
“We’ve got this mass spectrometry technique which shows all these particular compounds with these particular masses, and we’ve got NMR that gives us a complex forest of peaks associated with all of those compounds, but we’ve got no way of actually knowing what is the molecular weight associated with each of the peaks that we see in the NMR spectrum.”
Carroll and colleagues have figured out how to simplify this, though, by using NMR to determine weight as well as structure.
“What we’ve developed is a technique where we can identify the molecular weights of every component by simply doing an NMR spectrum. And what that then means is that we’ve got not only the masses for the individual molecules, but we’ve got their unique NMR signatures directly tied to a specific mass.”
This is done by looking at the speed of the molecules as they move – or diffuse – through the liquid they’re dissolved in.
“Every molecule is actually moving constantly through a liquid, but depending on the size of the compound, they move at different rates,” explains Carroll.
“The method that we’ve applied in this process is a thing called diffusion NMR or DOSY … we’re not doing any separation in a physical sense, we’re separating all of the molecules using this particular technique in the NMR tube.”
This means that the time taken to do analyses is drastically shorter. Carroll has found it very handy for his research, which looks at finding potential medications from living sources.
“I work on the chemistry of living organisms. We go out and we collect sponges and we collect rainforest plants and we collect microorganisms, and we extract them so that all of the organic molecules that occur within the tissues of those organisms are in one sample.”
Previously, if something in that sample showed promise as a medical treatment, Carroll and colleagues would need to spend one or two weeks in the lab isolating the substance for further analysis.
But with this new technique, “it takes us somewhere between about 10 minutes and maybe an hour to acquire the data.”
The technique doesn’t require any new equipment: it can be done on existing NMR spectrometers, meaning that “this is something that’s transferable”.
A paper describing the technique was published last week in Chemical Science.
Read more:
Infant pterosaurs may have taken to the air as soon as they cracked out of the egg, according to UK scientists. These reptiles dominated the skies during the Triassic, Jurassic and Cretaceous Periods (228 to 66 million years ago), but it’s rare to find fossils of hatchlings or embryos, so researchers previously didn’t know whether babies flew.
Now, a team led by the University of Southampton have found fossils of newly hatched specimens from two pterosaur species. By making wing and body measurements and comparing them with adult fossils, the team found that the infant pterosaurs were already strong enou