Hey Birds! A cautionary tale of tiny kiwis

Wikimedia/G. D. Rowley, PD-1923
Wikimedia/G. D. Rowley, PD-1923
A sketch of the little spotted kiwi from Rowley, G.D., Ornithological Miscellany, 1875–78. The bird once roamed New Zealand’s isles, but saw population losses in the 1800s due to hunting and the introduction of new predators. Source: Wikimedia Commons/G. D. Rowley, PD-1923.

Most people who visit New Zealand never see a kiwi in the wild. You might catch a glimpse of one in a dimly lit indoor cage, but in the wild the country’s national bird is a rare sight. Just to clarify, I’m talking about the awkward looking bird, not the odd looking fruit. New Zealand has five species of kiwi birds, native inhabitants of the “land of the long white cloud”. Thanks to introduced predators and hunting, four are on the REDD list. On the other hand, the little spotted kiwi (Apteryx owenii) has been a conservation success story. That is, until now.

Even though the little spotted kiwi is extremely rare very rare, it’s the only kiwi bird without “endangered” status. Its success story is an interesting one. Around a century ago, things were looking decidedly not good for the little spotted kiwi. It had disappeared from New Zealand’s north island altogether, and in 1912, conservationists took five remaining birds from the Jackson Bay on the South Island and moved them to a small island 5 kilometers off the North Island’s coast called Kapiti. Whether or not a native population already inhabited the island is still up for debate today, but the birds were spotted there in 1929, well after relocation.

By the 1980s, the original south island population was gone, but the birds on Kapiti were actually doing pretty well. Meanwhile, another population on D’Urville island wasn’t doing so great. Conservationists did the same thing again: moving the last remaining male and female birds on D’Urville to nearby Long Island, along with three birds from Kapiti. Around the same time, individuals from Kapiti and founded populations on some of New Zealand’s other coastal isles.

Island chart of LSK population movements through conservation efforts. Source: HMT/Ramstad et al.
Island chart of LSK population movements through conservation efforts. Source: HMT/Ramstad et al.

Taking the last individuals from a species in danger of becoming extinct  and focusing all of the energy on protecting them — either in a small area of their native range in the wild or in captivity — is a go-to worst-case scenario tactic in conservation. It worked for cheetahs, the mexican wolf, and another of New Zealand’s avian residents, the Takahe. So, the Kapiti island population flourished, exceeding 1600 individuals today. Based on numbers alone, spotted kiwis are doing great.

But, recent study published in Proceedings of the Royal Society B gives conservationists pause. Results suggests that these populations have inbred themselves into a genetic bottleneck — when a population drops, its genetic variation gets slashed. Basically, they lack genetic variety. A new disease could swoop in and easily wipe them out; the same goes for other challenges like sudden changes in climate (something that’s not out of the realm of possibility in the next million years).

“Yes, we have eight populations, and yes, they are all growing in size in terms of number of birds,” Kristina Ramstad, a co-author and a biologist at Victoria University in Wellington, NZ, told Science. “But they are all incredibly low in genetic diversity. … If the right disease comes along, it could wipe all of them out.” Science‘s Traci Watson outlines another species — the bengali tiger — that suffers a similar problem: a companion study in Proceedings of the Royal Society B found that the tigers retain only 7% of their ancestors’ genetic variation.

A map of the four populations of little spotted kiwis sampled in this study. There are four others, making eight existing populations in total. Source: HMT.
A map of the four populations of little spotted kiwis sampled in this study. There are four others, making eight existing populations in total. Source: HMT.

As for the kiwi study, Ramstad and her colleagues compared genetic data at 15 spots in the species’s genome from populations on Kapiti to those on Red Mercury, Tiritiri Matangi, and Long Island. All four populations were almost genetically identical and had telltale signs of genetic bottlenecks in recent years. Mysteriously, Kapiti birds are losing some measure of genetic diversity each year. The other groups are too. In fact, little spotted kiwis have the lowest diversity of all kiwi species. On Long Island, a single mating pair from Kapiti founded the population that persists today, and that the birds from D’Urville haven’t contributed at all to the overall genetic diversity of the species. For whatever reason, they never mated and disappeared.

“We don’t know why [the D’Urville birds didn’t breed],” Ramstad told Scientific American. “We don’t know how long little spotted kiwi live and we don’t know what’s their oldest age of reproduction. It’s still a bit of a guess, they keep outliving the scientists following them. So the birds [from D’Urville Island], could have been too old, or one of them could have been infertile. It could simply be a case that they didn’t fancy each other.”

So, what’s the takeaway message here: should conservations be doing something differently? or is the game just stacked against them? Keeping up connections between surviving populations — so that they mate and pop out genetically diverse kids — seems to be as important as making sure populations in protected areas have the best shot at survival. The sentiment seems to be that things are just a heck of a lot more complicated than originally thought. And, that’s no reason to throw in the towel. New Zealand’s Department of Conservation plans to relocate Kapiti birds (which have the most genetic diversity of the bunch) to smaller islands to boost their DNA. “Don’t keep all of your kiwis on one island” remains the best tactic at the moment.

For more info, check out Science and Scientific American‘s excellent pieces on the study: here and here.


How did humans evolve lactose tolerance?

A cow with an electronic milking machine attached to its udder. Needless to say, dairying was a lot less complicated in ancient times. Source: Wikimedia Commons, CC-1923

This article was originally published on NPR’s The Salt, 28 December 2012.

Got milk? Ancient European farmers who made cheese thousands of years ago certainly had it. But at that time, they lacked a genetic mutation that would have allowed them to digest raw milk’s dominant sugar, lactose, after childhood.

Today, however, 35 percent of the global population — mostly people with European ancestry — can digest lactose in adulthood without a hitch.

So, how did we transition from milk-a-phobics to milkaholics? “The first and most correct answer is, we don’t know,” says Mark Thomas, an evolutionary geneticist at University College London in the U.K.

Most babies can digest milk without getting an upset stomach thanks to an enzyme called lactase. Up until several thousand years ago, that enzyme turned off once a person grew into adulthood — meaning most adults were lactose intolerant (or “lactase nonpersistent,” as scientists call it).

But now that doesn’t happen for most people of Northern and Central European descent and in certain African and Middle Eastern populations. This development of lactose tolerance took only about 20,000 years — the evolutionary equivalent of a hot minute — but it would have required extremely strong selective pressure.

“Something happened when we started drinking milk that reduced mortality,” says Loren Cordain, an exercise physiologist at Colorado State University and an expert on Paleolithic nutrition. That something, though, is a bit of a mystery.

Read more…here.

Moths with ultrasonic “ears”

{{Information |Description=''Galleria mellonella'' dorsal view |Source=http://padil.gov.au/pests-and-diseases/Pest/Main/136311/5845 |Date= |Author=Simon Hinkley & Ken Walker, Museum Victoria |Permission={{cc-by-3.0-au}} |other_versions= }} [[Category:Gall
Dorsal view of a greater wax moth specimen from Australia. Source: Simon Hinkley & Ken Walker/Museum Victoria/Wikimedia Commons
You’ve probably never heard of the greater wax moth. But, according to a paper published in last week’s issue of Biology Letters, they hear just about everything — even sounds that don’t exists…as far as we know. These rather drab-looking insects have the highest hearing frequency range, 30 kilohertz (kHz) to 300 kHz, in the animal kingdom.

Greater wax moths (Galleria mellonella. Believe it or not there’s actually a lesser wax moth out there, too) commonly mooch off bee hives, much to the chagrin of apiarists. Humans spread them around the globe by moving bee hives from one place to another, so while their native range probably encompassed Europe and parts of Asia, they’re invasive pests in Australia and North America. Adult wax moths leave hives for one reason: to mate. At night, the males emit mating calls — at 90 to 95 kHz — to attract females. Their larva — yellowish-green caterpillars called waxworms — inhabit hives around the world and feed off the beeswax, usually from the combs where bee larvae live. Obviously, this doesn’t end well for the bees, and hives can quickly die off once the moths settle in.

Greater wax moths may be a pest, but their mating calls make them a target and a scrumptious food source for bats. While stalking their prey via echolocation, bats also make higher pitched calls to communicate without drawing the attention of an unsuspecting moth. Up until now, the North American gypsy moth (Lymantria dispar, another pest) had the highest hearing frequency limit of any insect: 150 kHz. In contrast, bat echolocation reaches up to 212 kHz. Scientists have always supposed moths’ limits to be much lower, and a group of researchers at University of Strathclyde in Glasgow, Scotland, wondered, “are any moths keeping up in the evolutionary arms-race?”

Because greater wax moths live all over the world, they hear lots of different bat calls, making them an ideal test subject. Great wax moths hear through tiny tympanal membranes (and by tiny I mean smaller than a millimeter), which vibrate when they pick up sounds, and activate the four nearby receptor cells that transmit a nerve signal to the brain. The set up is simple, but comparable to how a human ear drum works. The research team ordered greater wax moth larvae from a website that specializes in “live” food for exotic animals, and waited for the larvae to cocoon, pupate, and emerge as adults from their lab incubator. Suspending 20 adult moths so they couldn’t fly off, the researchers measured how much their tympanal membranes vibrated and whether they transmitted a signal when they heard sounds from 30 kHz to 300 kHz. At 300 kHz, all the moths “ear drums” vibrated, and 15 of the 20 specimen showed neural activity.

“Such extreme auditory frequency sensitivity is unmatched in the animal kingdom,” the researchers say. By comparison, humans hear between .02 and 20 kHz, and dolphins, another animal that relies on echolocation, can hear up 160 kHz. It’s safe to say greater wax moths are worthy opponents to bats trying to swoop in and eat them for dinner.

No animal known to scientists can make a sound as high as 300 kHz. So, why did these moths evolve such ultrasonic hearing?

In New Scientist’s write-up of the study, Hannah Moir, a member of the research team who specializes in bioaccoustics, posits two possible explanations: 1. Bats are actually making higher frequency sounds than we can record (microphones have trouble detecting sounds over 150 kHz). 2. It’s an accident. They needed to pick up high frequency bat calls, and this is just a side perk of that adaptation. Either way, f bats feel selection pressure to expand their range, these moths are already one step ahead.

Evolutionary mysteries aside, the research actually has some practical implications. Moir’s collaborator James Windmill hopes to use what they learned from the greater wax moth to develop new ultrasonic tech — think itty bitty microphones. I personally see inspiration for a Saturday morning cartoon here. If comics can feature ticks and cockroaches saving the world, a moth with ultrasonic hearing at least seems more plausible. Perhaps as Spiderman’s slightly less exciting cousin?

The Salt’s Top Posts Of 2012

Credit: Stephan Kuhn/Creative Commons
Credit: Stephan Kuhn/Creative Commons

One of my stories made the 2012 top ten list for NPR’s fabulous food blog, The Salt.

The piece actually ran last Friday, so it’s fairly recent. It’s about the debate over how humans evolved lactose tolerance — quite the mystery in the scientific community. Basically, 10,000 years ago most babies could drink milk because they had the gene for lactase, but the gene turned off in adults. Milk and dairying came with ancient agriculture, and several mutations for lactose tolerance became more frequent — people were passing them down to children. But if milk gave them diarrhea, then what made them drink it, and what gave milk drinkers a survival advantage? Turns out the answer is a bit of a can of worms. For more on that, here’s the original story. It ranked #3 on the list, so not too shabby.

And now…*celebratory dancing*!

Floozy beetles prevent harms of inbreeding

Male Flour Beetle: “Woman! Why are you hooking up with Jeff from the hardware store?… And Bob the Doctor?…and Ted the investment banker?”

Female Flour Beetle: “Sorry, Jerry, but you’re sperm’s just not genetically compatible.”

In the September 23rd issue of Science, researchers across the pond at the University of East Anglia found that inbred populations have a natural increase in female promiscuity to thank for preventing the harmful effects in offspring that come with getting it on with one’s cousin.  Females actually take on more mates to screen out sperm from males that aren’t a good fit genetically.

For awhile, scientists have been wrestling with the evolutionary enigma of why some girls are so darn trampy. Although fairly rare in humans (to my knowledge?!), polyandry – where multiple males fertilize a female’s eggs – is commonplace for a wide variety of organisms from chimps to sea urchins. However, in a lot of these situations, things don’t turn out so great for the female. Hence, the enigma.

Using red flour beetles as their model species, the Brits set up inbred and non-inbred mating groups. They found that females who hooked up with just one partner only produced about half as many surviving offspring as those who mated with five males. The Brits double checked for male infertility, but found nothing. So, the only other explanation was that those guys just didn’t have the most “genetically compatible” sperm aka they were too closely related. The scientists then took it a step further and manipulated non-inbred populations to start inbreeding. Sure enough, after about 15 generations, the females started getting frisky and changed their mating patterns. They’re still working on how exactly the females weed out the bad sperm, but…

Moral of the story: Genetic diversity is super important, and a species will go to to great lengths to preserve it.  And, don’t hook up with your cousin, even if you’re a beetle.