Climate change reduces male fertility, could help drive extinction

Researchers are honing in on a little-studied but significant consequence of climate change: male infertility. Could this potential cause of extinction and biodiversity loss also threaten the human species?

Men have long understood the dangers of exposing their reproductive glands to excessive heat. More than a decade ago, celebrity chef Gordon Ramsey publicly admitted that all that time near hot stoves ultimately caused him fertility loss and a low sperm count. "My balls were burning," he said, with typical bluntness.  

Nature and Environment | 30.07.2018

From sitting too long with a laptop, to boiling saunas and hot cellphones in tight jean pockets, burning issues around the midriff have become a pressing fertility enemy for modern men.

Recent research is implicating rising heat due to climate change as an extinction threat for certain species — so what about our own?

Read moreNo help for the infertile in Africa

Nature and Environment | 26.07.2018

The world warms, births decline

While day-to-day thermal threats to male reproductivity can be combated with common sense, what happens when there is little escape from a world that is warming due to climate change?

Sweltering — and less fertile?

This past July, Alan Barreca, an environmental economist from the University of California in Los Angeles released a study showing that "temperature shocks" linked to climate change were reducing birth rates, despite increased sexual activity in summer months.

Derived from 80 years of birth and weather data out of the United States, the study confirmed a higher number of babies being born in August and September (nine months after the depths of winter), while fewer babies were conceived in summer due to higher temperatures.

The researchers warned that the higher frequency and severity of heat waves — which is expected as climate change carries on — will hasten this decline in fertility.

"Climate change projections show dramatic increases in hot weather," Barreca told DW. "This increase in hot weather will harm our reproductive health in the future."

Damaging the seed of life

This human dimension to the problem of decreased fertility in a warming world is just one part of a significantly more far-reaching problem.

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A study by researchers at the University of East Anglia,published today in Nature Communications, shows "clear evidence" that heat-wave stress reduces "sperm number and viability" in insects, those most ubiquitous of living creatures.

Climate change is affecting reproduction among insects

"In warm-blooded systems, heat is not a good thing for male fertility," Matthew Gage, a professor of evolutionary ecology at the University of East Anglia and lead researcher on the study, told DW.

However, humans and other warm-blooded animals are able to regulate their internal reproductive systems, meaning that their sperm is somewhat protected under heat stress, Gage explained.

Yet as heat waves become more frequent, few have looked at "cold-blooded organisms [such as insects] that comprise the majority of biodiversity on Earth," he added.

Read more: Beetle mania: The planet's most successful creatures?

After exposing beetles that thrive in tropical environments to heat stress, the research not only confirmed a hunch about fertility loss in the planet's most common species, but also noted "male reproductive damage" and "transgenerational impacts" that could help clarify increasing species extinction rates.

It's the first such study to reveal a link between heat-wave stress and long-lasting genetic or DNA damage — and the potential for heat stress to create permanently sterile males.

Read moreBiodiversity collapse imminent in world's tropics, study says

Megabugs: 10 of the largest insects in the world

Macrodontia cervicornis

This beetle can measure up to 17cm in length, in part thanks to its enormous mandibles - the pair of appendages near its mouth. Also known as the 'sabertooth longhorn beetle' this insect dwells in the rainforests of Colombia, Ecuador, Peru, Bolivia, the Guianas and Brazil.

Megabugs: 10 of the largest insects in the world

Giant weta

There are 11 species of the giant weta in the world, and the largest can be up to 10cm in length - not including their spindly legs or long antennae. They're also known to be rather heavy - with one example recording 70g. The beetles are unique to New Zealand, and all but one species are considered endangered.

Megabugs: 10 of the largest insects in the world

Goliath beetle

Among the largest insects on earth, the Goliath beetle can measure up to 11cm and weigh 100 grams in the larval stage (although adults are around half this weight). There are five species of Goliath beetle. They're found in tropical rainforests in Africa, where they mainly eat tree sap and fruit.

Megabugs: 10 of the largest insects in the world

Queen Alexandra's birdwing

This butterfly is the largest in the world, with females' wingspans reaching just over 25cm. An endangered species, it is restricted to about 100km of coastal rainforest in the Oro Province in eastern Papua New Guinea. The species was named in 1907 in honor of Alexandra of Denmark.

Megabugs: 10 of the largest insects in the world

Tarantula hawk wasp

This is what's known as a 'spider wasp' because - yep, you guessed it - it hunts tarantula spiders. They use their sting - one of the most painful insect stings in the world - to paralyze their prey before hauling it to their nest, where they lay a single egg on the victim, which when it hatches to a larva eats the prey alive. At about 5cm long, it's one of the largest wasps in the animal kingdom.

Megabugs: 10 of the largest insects in the world

Atlas beetle

This is a species of rhinoceros beetle, known for its feisty behavior. Named after Atlas, a Titan condemned to hold up the sky for eternity in Greek mythology, the male beetles can reach up to 13cm in length. They're found in southern Asia, particularly Indonesia.

Megabugs: 10 of the largest insects in the world

Giant water bug

The giant water bug encompasses a large species of carnivorous freshwater insects, which includes the 'Lethocerus' that can grow to more than 12cm in length. Their large foreleg pincers are used to catch underwater prey like small fish and frogs. In some places they're known as 'toe biters' because of their tendency to deliver a painful nip when disturbed by swimmers that get too close. 

Megabugs: 10 of the largest insects in the world

Atlas moth

This insect may have a tiny body, but it's wingspan measures a whopping 25-30cm, and it has a wing surface area of about 400cm squared. It lives in dry rainforests and shrublands throughout South Asia, South East Asia, and East Asia. It doesn't eat - it's only purpose as an adult is to find a mate, which takes around two weeks. Once they breed and the females lay eggs, they die.

Megabugs: 10 of the largest insects in the world

Praying mantis

This exquisite insect is usually between 1.5cm and 16cm long, but can reach lengths of up to 20cm. They are carnivorous and feed mainly on other insects, although females sometimes eat their mate just after, or even during, mating. Formidable predators, the praying mantis can turn its head 180 degrees to observe its surroundings with all five of its eyes.

Megabugs: 10 of the largest insects in the world

Phryganistria chinensis Zhao

Only officially discovered in 2016, the only recorded spotting of this superbly long stick insect measured it at 62.4cm. Found in the Guangxi Zhuang region of China by Zhao Li, of the Insect Museum of West China, it's the longest insect in the world. Li brought it back to the museum where it laid six eggs - after hatching, even the smallest offspring measured 26cm.

Explaining biodiversity loss

"Could this be one of the reasons why populations decline and go extinct under climate change?" Gage asked. "Obviously, if you're not very good at reproducing, that's not going to help your population viability," he pointed out.

A heat wave will ultimately pass and a creature may survive it — but, added Gage, "this can't undo the problem of damaged sperm."

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Eco Africa | 29.10.2018

Why do we need diversity of species?

Upon examining insects that had suffered a heat wave, "their offspring showed shortened lifespan and lower reproductive fitness," said Gage, pointing out that this represents a transgenerational defect.

The significance of this linkage is potentially devastating for biodiversity loss on a warming planet.

Read moreScientists race to name unknown species before biodiversity disappears

That could be taken a step further as all living organisms ultimately depend on each other for survival. For instance, without pollinating insects, the human diet would be far poorer. 

Read more'We cannot survive without insects'

Taking the heat

A 2017 review of studies into rapidly declining sperm counts in men went as far as to warn of human extinction if the trend of a recorded 50 to 60 percent drop in sperm count in males from North America, Europe and Australia from 1973 to 2011 continues.

The study cited "multiple environmental and lifestyle influences" that might explain the declining sperm count. These included prenatal endocrine disruption caused by exposure to chemicals, or maternal smoking — while exposure to pesticides could be a prime culprit in adult life. 

Yet conclusive evidence linking declining fertility to any specific environmental problem is lacking.

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Tomorrow Today | 27.04.2018

Are humans a threatened species?

New research on the correlation between increased male infertility and climate change could therefore prove to be especially instructive. Moreover, if this link is contributing to broader biodiversity loss, the consequences will again be devastating for all life.

This is why Gage and his team are starting to trace the link between heat stress and loss of male fertility — and transgeneration DNA defects — in a host of other insects and cold-blooded animals, including fish that spawn in very cold waters.

"It adds up to a pretty hard time for populations that are already suffering stress from all sorts of other things like habitat loss, or chemicals being put into the system," noted Gage of the latest death knell for threatened species across the planet.

If further research proves that a warming world is impairing the seed of life, the revelation could be the ultimate inspiration to double down on fighting climate change.

Read moreTo save species, limit global warming

Beasts that could come back from extinction

No fear of a t-rex sequel

Five films on, Jurassic Park still has us captivated by the idea of humans coming face-to-face with our planet's most terrifying former inhabitants. But the fantasy of resurrecting a dinosaur from DNA in the belly of an amber-trapped mosquito is a long way from reality. Leading de-extinction scientists say making use of genetic material more than a million years old won't be possible.

Beasts that could come back from extinction

And then there were two

Since the last male northern white rhino — a 45-year-old called Sudan — died earlier in 2018, elderly females Najon and Fatu are the last of their kind. But scientists hope that embryos in deep freeze could bring the "functionally extinct" species back from the edge. They were created in-vitro from the sperm of a deceased male northern white and the eggs of the closely related southern white.

Beasts that could come back from extinction

Not so dead after all?

When the dodo — a fatally trusting and tasty bird — disappered from Mauritius in the 17th century, few believed mankind could extinguish the life of an entire species. Only after 19th century naturalist Georges Cuvier proved extinction was possible did the dodo became a symbol of that destructive power. Now, the hunt is on for dodo DNA, in the hope we may also prove our power to resurrect.

Beasts that could come back from extinction

Fragile life

By the time the last Pyrenean ibex Celia died in 2000, scientists had already gathered and frozen her tissue cells. Three years later, a goat gave birth to Celia's clone, created by injecting her DNA into a goat's egg. In fact, dozens of hybrid eggs were implanted. Only seven animals became pregnant, and one carried to full term — and the resurrected ibex survived only a few minutes after birth.

Beasts that could come back from extinction

Passage from the past

This is Martha, the last passenger pigeon, who died in 1914. The plump North American birds were a favorite for the plate, and hunting combined with deforestation wiped them out even as conservationists warned of their senseless demise. Revive & Restore, an organization thta promotes "de-extinction," sees the passenger pigeon as the perfect model project to show resurrection science's potential.

Beasts that could come back from extinction

Numbat mother

European colonists in Australia put a bounty on the head of the thylacine, or Tasmanian tiger, a marsupial apex predator. The last known member of the species died in Hobart Zoo in 1936. Now, scientists have decoded the animal's entire genome from a joey preserved in ethanol, and hope to insert its genes into the DNA of its closest surviving relative, a diminutive marsupial called the numbat.

Beasts that could come back from extinction

Pleistocene Park

The most impressive species with any chance of making a comeback is the woolly mammoth, whose closest living relative is the Asian elephant. Scientists at Harvard University say the ice-age giants could play a role in slowing permafrost melt and, therefore, climate change. But their "Pleistocene Park" concept would need 80,000 animals to have any real impact — pure science fiction, say critics.

Beasts that could come back from extinction

One heck of a cow

The auroch once roamed the length and breadth of Eurasia, but hunting and habitat loss wiped them out close to 400 years ago. Yet their descendents — domesticated cattle — live on, and "back-breeding" programs have tried to resurrect the auroch by selecting for characteristics of the wild ancestor. An early German attempt resulted in Heck cattle, which have been reintroduced to parts of Europe.

Beasts that could come back from extinction

Meet the ancestors

We once shared the planet with other human species, like the Neanderthal, with whom we even interbred. Many of us still carry Neanderthal DNA. But we are also prime suspects in their extermination. What would it be like to confront the relations we once wiped out? Scientists are growing homo sapiens-Neanderthal hybrid brain matter in the lab to examine the differences between them and us.

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