Fuel Exhaust Disrupts Scent Signals for Honeybees

Originally published on National Geographic Daily News, 3 October 2013.

A honeybee foraging. Source: Tracey Newman/University of Southampton.
A honeybee foraging. Source: Tracey Newman/University of Southampton.

To a bee, no two flowers smell quite the same. When honeybees forage for flowers, they search for, learn, and memorize distinctive floral scents and return to the hive to tell other bees what they’ve found through their famous waggle dance.

It is an important ritual that is being disrupted by one of the most pervasive forms of air pollution—diesel exhaust—according to a new study published Thursday in Scientific Reports. The research pinpoints the mechanism by which the fuel-combustion pollutants degrade certain chemicals in floral odors. The absence of those chemicals affects honeybees’ ability to recognize the scent.

Engine exhaust is hardly the only threat facing the honeybee. It is well recognized that exposure to multiple pesticides can impair bees’ olfactory skills, while ground-level ozone, or smog, and ultraviolet (UV) radiation can also degrade floral odor compounds that bees pick up on. Authorities around the globe are grappling with how to address the little-understood cyclical diseases that are causing colonies to dwindle.

The new study offers insight into the specific hazard for pollinators from the fumes from cars, trucks, trains, ships, and heavy machinery. Significantly, the study indicates that honeybees haven’t been helped by the “cleaner” diesel now used in Europe and the United States due to regulations that over the past decade removed sulfur from the fuel. The researchers used ultra-low-sulfur diesel fuel in their experiment…

Read more here.

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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.

Sea slugs with disposable penises…or is it “penes”?

For a species of sea slugs (or nudibranchs) that calls the Pacific Ocean home, penises are apparently disposable. In fact, disposable penises are a natural part of sex for them. That’s according to a paper published recently in the journal Biology Letters.

Scientists first discovered this bright pinkish orange slug — called Chormodoris reticulata for the latin speakers out there — in the 1800s. Many sea slugs are simultaneous hermaphrodites, so have both both male and female parts, so to speak. Also, in terms of the female bits, they typically have two pouches to store sperm — one of which can destroy sperm. So, they can mate with two males and pick with sperm stash to dump. In the human world, we might call this the purest form of rejection, but in animal behavior terms, it’s called “female choice”.

Lots of sea slug species mate in weird ways, so it makes them an interesting group for animal behavior scientists to study. In this case, a team of Japanese researchers went scuba diving to collect Chormodoris specimen during their mating season — in 2005, 2006, 2009, and 2010. Back in the lab, they stuck the slugs in tanks to watch what happened. They either paired two slugs that had been isolated for 24 plus hours, or stuck an isolated slug in a tank with one that had recently mated. In addition, to the observation, they took photos and tissue samples of the slugs’ reproductive layout.

So, based on their study here’s how this particularly brand of kinky sea slug sex works: the slug has a really long penis that’s curled up inside it’s body, with a little bit hanging out. When two slugs are ready to get it on, the little bit hanging out elongates and develops prickly spines on the end. After either seconds or minutes of sex, the end of the penis falls off. It takes at least 24 hours for a new “penis” to uncurl from the spiral section inside the body, but then they’re ready to go at it again. A slug can do this up to three times, and this particular species is the only organism in the world that can chuck it’s penis and mate again 24 hours later. (Other slug species drop their penises after mating season is over, but they have a much longer time to replenish).

Weird sex happens all the time in the animal world, so what makes this particular instance a big deal. Sexual selection rarely happens with hermaphrodites — they have the best of both worlds, so they’re all kind of on an equal playing field. But, because it takes 24 hours for the slug to bounce back, replenished slugs have the advantage.

Smithsonian does a nice job of summing it all up, here.

Chestnuts galore: Happy 30th, TACF!

This year marks the 30th anniversary of the American Chestnut Foundation — a group of chestnut enthusiasts and academics who’ve been stalwartly trying to revive the species since it’s decline in early 20th century. It might surprise young’uns like me to hear that chestnuts once comprised a quarter of eastern forests, which if you think about it is a whole lotta trees. That all changed when a fungus commonly called chestnut blight hopped aboard nursery exports from Asia, and spread across the entire chestnut range within 40 years.

At the end of last summer, I visited TACF’s research farm in Meadowview, a wide part of the road in southwestern Virginia. It was part of a feature article that I wrote for Nature on how TACF and other chestnut restoration efforts are starting to see results. The main goal at Meadowview is to breed an American tree with the right selection of genes from Chinese chestnut to provide resistance to the blight. (Unlike their American counterparts, Chinese chestnuts can survive the blight.) It took them a little under 25 years to do this, but they’ve started to export their chestnut breeding pipeline to local TACF chapters across the US.  I took some pictures while I was there:

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The other side of the Chestnut revival story begins with researchers at SUNY in upstate New York, who have developed genetically modified American chestnuts — American chestnut trees with candidate resistance genes from other chestnut species or other plants. Last March, a test plot of gm chestnuts was planted at the New York Botanical Garden — right across the street from where the blight was first discovered at the Bronx Zoo. In August, I went up to NYC to visit a friend, and of course, I dragged her on a side trip to NYBG to see their baby chestnuts.

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It might seem bleak from an outsider’s perspective, but perhaps one day chestnuts — maybe even genetically modified chestnuts — will comprise eastern forests once again. For more background, here’s my piece. And, if you’re super curious people have written books about this saga (American Chestnut: The Life, Death, and Rebirth of a Perfect Tree does a great job portraying the colorful cast of characters involved, and then apparently Barbara Kingsolver based a character on TACF’s chief scientist in her novel Prodigal Summer.)

Image Credits: HMT.

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.