Illustrated by Perry Shirley.

When Hybrids Go Wild

By John Upton

Q: How do you make a hybrid trout go wild?

A: You wait.

From a survival-of-the-fittest perspective, a domesticated animal is a poor facsimile of its wild relative. That’s why a salmon or a trout reared in a hatchery is less likely to survive in the ocean and return safely to its home river come spawning time.

When domesticated creatures are mixed with a population of wild ones, such as through fish-stocking programs, their domesticated genes, many of which are ill-suited to the idiosyncrasies of the new environment, can be passed on to the next wild-dwelling generation. The genetic contamination lingers so long in the newly hybridized population that wildlife management policies generally consider it to be permanent.

The good news for a hybrid-wearied world is that recent research suggests that a wild trout population’s newly-hybridized traits could be shed quickly — even if some of the hybrid DNA sticks around.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

Ontario and Concordia University researchers reared brook trout from two hybridized populations and from one wild population in Ontario’s Algonquin Park. They also obtained trout from a nearby hatchery. The four populations were mixed equally in holding tanks, then released into three small, hitherto trout-free lakes in the North Shore region of Lake Huron.

The researchers sampled from the three lakes five months later, testing how well each of the strains had survived the rigors of the new environment. By then, most of the fish had died, which is normal after brook trout are planted

in Ontario waters. Mortality in one of the lakes was 96 percent. In the other two lakes: 80 percent. The scientists found that members of the hybrid and wild populations had similar chances of survival — and that they all fared better than their hatchery cousins.

One of the hybrid populations studied had last been contaminated with hatchery fish some five generations earlier. The other had been hybridized for 11 generations.  The results, the scientists wrote in a paper published recently in Evolutionary Applications, “suggest that within five to eleven generations, selection can remove introduced foreign genes from wild populations.”

The findings are a reminder of the fast pace at which evolution is capable of working.

“Allowing natural selection to act for relatively few generations can produce hybridized populations that closely resemble nearby non-hybridized populations — both physically and ecologically,” said Concordia University’s Andrew Harbicht, one of the researchers behind the study.

“Certain genetic vestiges will persist into the future over the long term. But, generally, the hybrids will behave ecologically similarly to their wild predecessors after a fairly short time period,” Harbicht said.

antiarchs

Natural History of Sex

By John Upton

If you could exchange the orgasmic gift of mammal-style intercourse for the messy ritual of dribbling fluids together, would you?

If you were the lineage of the world’s fish, then the latest evidence suggests that the answer to that unlikely conundrum would be, ‘Yes,’ to the great surprise of scientists documenting backbone-baring animals’ earliest known instances of internal fertilization.

We’re not talking about pudgy, panting penetration following happy hour pitchers. We’re talking rock-hard prehistoric fish, dermal claspers and paired dermal plates — locked, hundreds of millions of years ago, in ocean-floor embraces.

Bow guppy bow wow.

antiarchs
Illustrated by Perry Shirley.

A new scientific study peers into the most intimate moments in the lives of fish of several closely related ancient fish genii — MicrobrachiusPterichthyodes and Bothriolepis. Each was an antiarch, which was a heavily-armored order of fish known as placoderms. Placoderms were early gnathostomes, an infraphylum also called boned vertebrates, which includes all the fish alive today.  Gnathostomes started the branch on our evolutionary family tree that blossomed into lizards, birds and apes.

These long-dead fish were caught in the act of possessing the organs needed for sexual penetration. In a question over which came first, be it fish intercourse or external spawning, the answer would seem to be the former.

(The word antiarch means “opposite anus,” by the by, because a scientist once mistook a fossil’s mouth for its ass. And, while we’re at it, one of the species studied was M. dicki. Because somebody couldn’t help themselves.)

We’ve included a sketch of this primal love making below. Just make sure there are no underaged fish fossils in the room.

Mating Microbrachius
Adapted from a figure in Nature showing Microbrachius mating.

Is there anything cuter than fish that lock arms like that at a time like that? In real life, the width of that embracing scene would have been an adorable inch and a half.

We’re not sure if those are expressions of ecstasy — or the shocked looks that are to be expected when scientific method walks through the doors of ancient history during the most intimate of hypothesized moments. But we did confirm with Flinders University paleontology professor John Long that those big holes are where the eyes and nostrils would be. Because we didn’t want to get anything ass-backwards.

By now you might be wondering such things as, What does this have to do with me? If I took the right medicine, could I lead a life like that? And, How can I not think about this next time I’m bonking my boyfriend, or rolling in the hay at that haystack that my wife and I both like; won’t somebody please come and scoop the vision of adorable ancient randiness from my braincase? Aarrrggghhhhh.

We don’t know the answers to all your implied imaginary questions. What we do know comes from a study published Sunday in Nature by a large team of scientists led by Long.

The scientists analyzed fossils of the three genii that we mentioned earlier, and found in the males what they believe to be evidence of dermal claspers. They also found what they take to be the paired dermal plates of their female counterparts. Place those together and you’ve got yourself some internal fertilization, Velcro style.

The researchers write that the claspers found in these fossils resemble those of ptyctodonts, an order of placoderms that came after the unfortunately-named antiarchs. Those similarities, they wrote, suggest that “all placoderm claspers are homologous,” and that “internal fertilization characterized all placoderms.”

And they say that implies that spawning, which is so popular with the gnathostomes of today, must be an evolutionary adaptation that began with internal fertilization, even though such a transformation had been regarded as implausible.

“The complex physiology of fish that internally fertilize precludes a reversion back to spawning in water,” Long told us. “Yet our analysis shows it was the most likely explanation.”

Illustrated by Perry Shirley

Conservation biology, meet the digital age

By John Upton

Strap a two-kilogram tracking device to a 40-gram wood thrush and watch where it flies. Absolutely nowhere. If researchers had tried to track the migratory patterns of Washington D.C.’s official bird in 1994 using Lotek Engineering’s then-state-of-the-art GPS_1000 animal tracker, that’s what would have happened.

Fast forward past 20 of the birds’ international migrations.

Newer iterations of the same company’s GPS tracking devices, each weighing 2 grams, were attached this summer to the backs of 125 wood thrushes. The birds are migrating to Central America, obliviously recording location data that scientists aim to retrieve and put to use in understanding why their populations are declining.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

Technological marvels of the modern age, including miniaturized microchips and batteries, improved GPS devices, and Big Data are arming conservation biologists with powerful new tracking tools. The progress could barely have come at a more felicitous time, with modern life’s hazardous side effects thrusting countless wildlife populations into little-understood nosedives.

“We don’t know where most animals go,” said Peter Marra, head of the Smithsonian Migratory Bird Center, which is involved with the wood thrush tracking study. “There are an infinite number of questions that we can ask once we can start tracking these animals throughout the year.”

To propel animal-tracking innovation, the Smithsonian Conservation Biology Institute and Smithsonian National Zoological Park are teaming up with Airbus, Intel, United Airlines, and other corporate behemoths under an initiative they’re calling Partners in the Sky. It aims to shrink tracking devices to less than 1 gram; to track tagged animals using satellites and by fitting commercial planes with receivers; and to harness burgeoning computer power to understand and predict the migrations of elephants, whales, salamanders, and other animals.

“Our ultimate goal is to track any animal, anywhere in the world, throughout its life,” Marra said.

Slug End of Road 2 bis

Where did all the bugs go?

By John Upton

Ever noticed that your car’s windshield is smattered with fewer bugs after long country drives than used to be the case? That’s good news for gas-station squeegee duties — but it’s foul news for the planet.

The world’s bug populations are crashing faster than a swarm of mosquitoes into a backwater bug zapper. And that has reverberating yet little-understood consequences for the species and ecosystems that rely on insects for food, pollination, pest control, nutrient cycling, and decomposition.

A Science paper dealing with the planet’s sixth great extinction, underway since 1500, warns that invertebrate species are faring even worse than vertebrates. Two-thirds of monitored bug populations have declined by an average of 45 percent. Their habitat is being destroyed, and they are being drenched with agricultural insecticides.

The July 25 paper was penned by an international team of researchers led by Stanford University’s Rodolfo Dirzo following an exhaustive literature review. The following chart from the paper shows the  percentage of species of insects in the orders ColeopteraHymenopteraLepidoptera, and Odonata that have declined by as much as 40 percent (shown in dark red) during just the past four decades.

bugs-declines-bThe next chart also includes data on Orthoptera, which includes grasshoppers and crickets.

bugs-declines-aVertebrate populations, meanwhile, have fallen by an average of a quarter, the researchers found. The largest of these species are faring the worst.

vertebrate-declines“In the past 500 years, humans have triggered a wave of extinction, threat, and local population declines that may be comparable in both rate and magnitude with the five previous mass extinctions of Earth’s history,” the researchers wrote in the paper. “This recent pulse of animal loss, hereafter referred to as the Anthropocene defaunation, is not only a conspicuous consequence of human impacts on the planet but also a primary driver of global environmental change in its own right.”

The problem of creepy-crawly declines could be worse than anybody realizes. Unlike charismatic mammals, very few invertebrate species, including lowly centipedes, slugs, spiders, and worms, come under the trained eyes of scientists or conservationists. Fewer than 1 percent of the 1.4 million described species of invertebrates have been assessed for threats by the International Union for Conservation of Nature, which maintains the Red List of Threatened Species. Of those few species that have been assessed, 40 percent were found to be threatened.

Lepidoptera, which includes butterflies, moths, and of course their caterpillar larval stages, are the best studied and monitored order of insects, and evidence suggests that their abundance has fallen by 35 percent worldwide. Lepidopteran species richness is nearly 8 times greater in undisturbed sites than in developed areas, and abundance appears to be 60 percent higher on average in near-pristine environments than elsewhere.

As bad as that might be, it appears that these plant-munchers, which metamorphose into nectar-sucking plant pollinators, are faring far better than lesser-studied orders of insects.

bugs-decline-c

Snails and their shell-less terrestrial gastropod mollusk cousins, the slugs, by sticky contrast, are among the least-well studied. These species may seem like mere pests to many gardeners, but they help break down organic material and they provide food for larger animals. Grasping how slug and snail populations are coping with the defaunation of the Anthropocene relies right now on little more than educated guesswork.

“We mentioned slugs as a point of reference regarding the fact that many groups of invertebrates have been very poorly studied in rigorous, quantitative ways and over long, consistent periods,” Dirzo told us.

Illustrated by Perry Shirley

“Given the fact that at least some species of terrestrial mollusks seem to do well in disturbed areas, I suspect several of them might not be so severely impacted and might be thriving,” Dirzo said. Then again, he added, “given their strong dependence on moist, relatively mild-to-cool habitats, climate disruption might have a strong, negative impact on them.”

Illustrated by Perry Shirley.

Wolverine wipeout

By John Upton

A warming world means a melting cryosphere, which is bad news for species that have evolved to thrive on ice and in snow. Polar bears made depressing history in 2008 when they became the first species to be listed under the U.S. Endangered Species Act solely because of threats from climate change. These sea ice-dwelling carnivores had appeared poised, until Tuesday, to be joined in their global warming-induced regulatory infamy by snow-burrowing wolverines.

Wolverines resemble small bears with bushy tails. They are also known as mountain devils, gluttons, caracajou, and skunk bears. They are the largest member of Mustelidae — a carniverous family of mammals that includes otters, badgers, weasels, and ferrets.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

While polar bears are a highly visible species, wolverines are enchantingly difficult to spot. This is despite their inhabitation of a broad swath of the Arctic that includes northern portions of Europe, Asia, and North America.  In North America, most the populations inhabit Canada and Alaska, although several hundred individuals are estimated to live in the contiguous U.S., mostly in the northern Rocky Mountains. These populations have recently been growing, yet fears over the future of snow in the Lower 48 had federal officials considering adding wolverines to the list of threatened species. On Tuesday, the U.S. Fish & Wildlife Service ruled against the proposed wolverine listing.

Wolverines breed more slowly than most mammals, making them especially vulnerable to breeding disruptions. Once a female reaches the age of three, she normally becomes pregnant every year — but most pregnancies are strategically aborted. That’s because it can take two years or more for the wolverine to forage enough carrion, fruits, and berries, and to hunt enough small animals and insects, to build up the energy reserves needed to raise a litter.

Once she is ready to rear a litter, the female adopts a very specific denning strategy — one that will make it difficult for the species to survive in the parts of its territories where snow becomes history. The wolverines dig their dens in deep snow, forming living spaces around logs and rocks that include tunnels, runways, and bedsites. There has never been a record of a wolverine denning in anything other than excavated snow. And whenever such a cave starts to melt, the wolverine mother abandons it.

“We have determined that habitat loss due to increasing temperatures and reduced late spring snowpack due to climate change is likely to have a significant negative population-level impact on wolverine populations in the contiguous United States,” U.S. Fish & Wildlife Service officials wrote in the proposal to list those populations as threatened.

“In the future, wolverine habitat is likely to be reduced to the point that the wolverine in the contiguous United States is in danger of extinction.”

At least one senior FWS official had been pushing the agency to reject the proposal, arguing that it relies too much on “speculation” about the future effects of climate change. The agency announced on Tuesday that scientists know “too little about the ecology of the wolverine” to list it as threatened or endangered at this time. The ruling “does not close door on this issue,” one official said.

It was this focus on uncertainties that was already making scientists who served on a panel that advised the government on the proposal hot under the collar.

“Myself and the other climate scientists on the panel are disappointed that they’re focusing on the uncertainty, and appear to be ignoring the aspects of science that are much more certain,” said Tim Link, a hydrology professor at the University of Idaho.

Wolverines and polar bears certainly aren’t the only species that will feel the heat as global temperatures rise. Dozens of species of coral might be added to the endangered species list because of the combined effects of disease, warming ocean temperatures, and ocean acidification. Like global warming, ocean acidification is caused by carbon dioxide pollution, which is produced by fossil fuel burning and by deforestation.

“From the history of the Endangered Species Act, if you look at the 1,500-plus species that have been listed, the overwhelming majority have not been listed because of climate change,” said Mike Senator, an attorney with the Defenders of Wildlife, which had been pressuring the government to list wolverines under the Act.

“It’s been the loss of habitat and other threats — but that’s not entirely surprising, given that climate change has been recognized as a relatively recent issue. We certainly expect that we’ll see more species listed, at least in part, because of climate change.”

Illustrated by Perry Shirley

Ocean reserves help with acidification

By John Upton

Our power plants and cars have pumped so much carbon dioxide into the atmosphere that the oceans are becoming more acidic. Something like a quarter of our carbon dioxide pollution dissolves into the seas, where it reacts with water:

CO2 (aq) + H2\leftrightarrow H2CO3 \leftrightarrow HCO3 + H+ \leftrightarrow CO32− + 2 H+

Those leftover hydrogen ions at the right of the equation add up. The hydrogen ion concentration at the surface of the world’s oceans has increased by 26 percent since pre-industrial times, leading to a pH decline of 0.1. That might not sound like much, but it has been enough to kill off billions of farmed shellfish and punch holes in the shells of wild sea snails.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

Shellfish and corals are especially vulnerable to ocean acidification because they rely on calcium carbonate to make their shells and skeletons. Ocean acidification increases concentrations of bicarbonate ions while decreasing concentrations of carbonate ions — and these animals need calcium carbonate to produce their protective body parts.

Fish, meanwhile, are thought to be suffering neurological effects of acidifying oceans, while vast mats of algae are expected to flourish.

The good news is that populations of animals naturally adapt to changes in their environments — and evolutionary changes to help some species cope with ocean acidification are already underway. The bad news is that changes in oceanic pH levels might be happening too quickly for animals to adapt, threatening scores of marine species with extinction.

I asked Ryan Kelly, an assistant professor at the University of Washington’s School of Marine and Environmental Affairs, and a coauthor of a recent BioScience paper about acidification that I wrote about for Pacific Standard, whether we could do anything to help species accelerate the rate with which they evolve needed adaptations.

“‘Accelerating’ species’ evolutionary adaptations to acidification would mean either tweaking the heritability of traits — and it’s unclear whether this is desirable, or how to do it; or increasing the strength of selection — which would mean making the selective impacts of acidification worse than they already are,” Kelly said. “So I’m thinking that, in an evolutionary sense, you don’t want to accelerate adaptation.”

Is there anything that we can do?

“What you do want to do, in order to protect marine ecosystems as we know them, is to preserve the adaptive capacity of the species that make up those ecosystems. That means preserving the genetic diversity that exists within those species, so that when the selective pressures of acidification happen, there will be some variability in those species’ responses. When there’s no genetic diversity, you get no variability in response to selective pressure, and natural selection and evolution doesn’t really work.”

Which means that we need to expand and improve the globe’s network of marine reserves, banning fishing in some places, and giving species the best possible shot of surviving the storm of acidity that’s building around them.

“From a conservation perspective, measures that preserve existing genetic diversity safeguard the adaptive capacity of species and ecosystems. This means working to maintain large population sizes and not fragmenting habitats, which are common conservation measures.”

As U.S. Secretary of State John Kerry led workshops last month dealing with ocean acidification and other ocean health issues, President Barack Obama’s administration proposed sweeping expansions of marine reserves surrounding remote Pacific Ocean atolls. The move would limit fishing for tuna and other species, helping to protect top predators that are critical for ecosystem health, while also protecting smaller species that are killed as bycatch.

“This is an important step in trying to maintain the health of this region and, as a result, the surrounding areas in the Pacific,” said Lance Morgan, president of Marine Conservation Institute. “It will give us more resilience into the future. We’ll have to replicate this and do more work in other areas as well, but it is an important step.”

Meanwhile, the National Oceanic and Atmospheric Administration is planning to expand the boundaries of Gulf of the Farallones National Marine Sanctuary and Cordell Bank National Marine Sanctuary, both of which lie off the West Coast, where strong upwelling leads to especially severe rates of ocean acidification. Meanwhile, Kiribati recently announced that it would close an area the size of California to fishing to help wildlife recover.

Ocean acidification is not a major consideration in the creation of marine reserves, but it’s a growing threat against which the reserves can help populations of wildlife evolve natural defenses.

emu and ostrich

How are emus related to ostriches?

By John Upton

Which came first — the chicken or the egg?

It’s inside an egg that genes combine to code for an individual, so we’re going to go with ‘the egg.’ Next question, please.

Which came first — the ostrich or the emu?

Looking at pictures of these flightless birds, you’d be forgiven for mistaking them for kissing cousins. They’re both swift-footed birds with buns of feathers hitched high — alluring outfits that show off their slender legs and necks.

emu and ostrich
Illustrated by Perry Shirley.

But they’re not as closely related as they might at first seem.

Ostriches and emus are both ratites — members of a group of large flightless birds endemic to the Southern Hemisphere. Ratites were all thought to have descended from a common ancestor; examples of what scientists dub vicariance biogeography, or convergent evolution, in which members of once-conjoined populations become geographically separated, such as through the geological manifestation of a new river, gulf, or mountain, and then pursue their own evolutionary trajectories. In the case of ratites, they were thought to have gone their separate ways following the bust-up of Gondwana, from where their presumed ancestor was thought to have hailed.

Just a decade ago, in his book The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution, famed biologist and writer Richard Dawkins described ratites as a “truly natural” group. “Ostriches, emus, cassowaries, rheas, kiwis, moas and elephant birds really are more closely related to each other than they are to any other birds,” he wrote. “And their shared ancestor was flightless too.”

Dawkins’ statement reflected leading science from the time. But advances in molecular phylogenetics have since revealed the folly of longheld assumptions about ratite evolution. The apparent similarities between different species of ratites are now thought to have been the consequence of convergent evolution — the independent evolution of similar features by different species in far-flung places that inhabit similar ecological niches.

It seems that flightlessness just makes sense in the right environments. Research in recent years has revealed that selection pressures independently pushed the forebears of today’s ratites to shrink their wings, bloat their bodies, flatten their sternums, and evacuate the skies.

Several years ago, University of Florida researchers used BUCKy software to analyze the genomes of various birds, and found that the ratite family tree includes a surprising cousin — tinamous, an order of grouse-resembling birds from Central and South America. These birds spend much of their lives on the ground, but many of the species are perfectly capable of flying. The tanimous were found to be more closely related to emus then they were to ostriches, providing further evidence of the independent evolution of flightlessness in different ratites. The findings were published in the journal Systematic Biology:

(Credit: Systematic Biology)
(Credit: Systematic Biology)

“The independent evidence we obtained provided strong corroboration of the hypothesis that nonostrich paleognaths form a clade,” wrote the three scientists involved with the research in their paper. “This sharply alters our understanding of the evolutionary history of the flightless ratites by providing support for multiple losses of flight. It remains possible there was a single loss of flight early in paleognath history followed by a regain of flight in tinamous, but this is unlikely because the loss of flight appears to be a relatively easy transition for birds whereas the loss followed by the regain of flight has never been documented. The hypothesis that flight has been lost multiple times in the ratites suggests that some of the most distinctive morphological characters in ratites arose through convergent evolution.”

We asked one of the authors of the paper, Edward Braun, an associate professor in the university’s biology department, how this information and similar analyses could help answer our question. Which species is older — the emu or the ostrich?

Braun said that’s a tough question to answer; but he suggested a couple of alternatives, which he then answered.

“One valid question is, ‘When did ostriches start looking like ostriches, and when did emus start looking like emus?'” Braun said. “I suspect that, if the question is asked that way, the answer is, ‘About the same length of time.'”

“On the other hand, another way of asking the question is, ‘When did ostriches separate from other extant birds, relative to emus?’ The answer to that is clear. Ostriches have no close relatives. Ostriches separated from other birds a long time ago; probably in the Paleocene [66 to 56 million years ago], since there are middle Eocene fossils that are probably now extinct parts of the ostrich lineage. Emus are more closely related to rheas, kiwis, and quite close to cassowaries.”

Enjoy this fun video of emus and an ostrich playing with a motorized ball, which helps to reveal differences in the appearances of the species:

bilby

Easter Bilby protects Australia’s outback

By John Upton

Some Australian kids don’t believe in the Easter Bunny.

The clutches of chocolate and colored eggs hidden in the yards and living rooms of environmentally-aware households Down Under are deposited, through orifice unknown, by the Easter Bilby.

Browse the easter sweets selection in just about any Australian store right now and you’ll find foil-wrapped chocolate icons of the adorable outback-dwelling marsupials.

Rabbits are ravenous, fast-breeding, and destructive pests in Australia, where they were introduced by hunters and graziers during the 19th Century. The bare rabbit-resembling bilby, on the other hand, is a native Australian species that’s vulnerable to extinction. Celebrating the Easter Bilby helps Australian kids learn about the ecological importance of native mammals — while avoiding the awkward passions for invasive counterparts that the Easter Bunny can imbue.

bilby
Illustrated by Perry Shirley.

The beauty of the bilby lies in its relationship with Australia’s fragile, old, and nutrient-poor land. It digs through arid and semi-arid soils, bioturbing them, improving water drainage and reducing flooding and erosion. The digging helps spread seeds. It creates microhabitats for bugs and fungi. It turns over soils and helps with nutrient cycling.

From the Mammal Review paper by P. A. Fleming et al.
Mammal Review

The effect of native Australian diggers, such as bilbies, echidnas, and wombats, is “increased plant vigour and resilience, increased biodiversity and consequently improved ecosystem functioning,” scientists wrote in a Mammal Review paper published last year.

But Australian ecosystems have been ravaged during the past two centuries by introduced species, including rabbits, pigs, and camels, and by land clearing. The native diggers are hunted by introduced cats and foxes. Those pressures have helped push half of the nation’s digging mammals toward extinction, the researchers concluded following an exhaustive review of scientific literature. “[T]he loss of digging mammals has contributed to the deterioration of ecosystems,” they wrote.

Rabbits dig as well — but they apparently do not dig deep enough to produce the same benefits as bilbies. Previous research has shown that digging bilbies foster 80 percent more seedlings than do digging rabbits.

“When bilbies, bandicoots, and bettongs dig for food, their diggings are deep, roughly-conical pits which penetrate deep into the soil layers,” Murdoch University wildlife biologist Trish Fleming, one of the coauthors of the Mammal Review paper, told Wonk on the Wildlife.

“Rabbits dig shallower pits, which disturb a large area of the top soil layers. This would expose the soil to drying out, which means it’s less suitable for soil microorganisms or for new seeds.”

Then there’s the wee issue of rabbit plagues. Looking out across an affected Australian farm, the land can appear as if it is moving.

“Rabbits feed on soft shoots of plants, and then will dig up any vegetation within reach, including the roots and bark off trees.  In plague numbers, they wipe out any living plant material.  There are expanses of productive lands which have never recovered from plagues of rabbits,” Fleming said.

So go and get stuffed with caramel, Easter Rabbit. Aussies don’t need your type sniffing about in their gardens.

peacock

Here comes the peacockstepper

By John Upton

What’s hotter than a cutie in decadent clothes?

A cutie in decadent clothes — who can dance like no one is watching.

Sexual selection is a term coined by Charles Darwin to explain why some species have developed elaborately ornamental feathers and antlers — appendages that help woo mates. In humans, it has been argued that sexual selection pressures gave rise to facial hair and ample bosoms.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The elaborate trains of peacocks are among the most classical examples of sexual selection. During breeding time, peahens will visit areas where peacocks vie for their attention with spectacular dances. The peacocks raise their trains in a semicircle and whip them around, sometimes leaning them over the judging peahen. They shake their tail feathers and perform a jig with their feet.

A peahen readied for an eye-tracking experiment. Photo by Jessica Yorzinski.
A peahen readied for an eye-tracking experiment. Photo by Jessica Yorzinski.

A team of researchers set out to try to figure out just what actually interests the peahens during these spectacular courtship displays. They trained captive peahens to wear a patch over one eye and an infrared eye-tracker on the other. Then they watched while peacocks wooed their ridiculously-attired subjects inside black-plastic enclosures that minimized distractions.

After analyzing the footage and data, the scientists realized something surprising. The peahens weren’t looking at the tops of the brightly colored feathers. They were watching the peacocks’ lower regions.

“Based on the scanpath of where the females are looking, you can see that their gaze is focused on the lower train — that is, the lower feathers as well as the legs,” Jessica Yorzinski, an evolutionary biologist who studies animal communication, told Wonk on the Wildlife.

what-peahens-watch

“The peahens may be assessing the width or symmetry of the peacock’s lower train and this could indirectly tell the peahens about the quality of that potential mate,” Yorzinski said. “For example, it’s possible that peacocks with more symmetrical trains produce peachicks that are healthier.”

So what’s the point of having such long and elaborate feathers if peahens are so interested in peacocks’ lower bodies? Yorzinski and fellow researchers explain their theory in a recent paper published in The Journal of Experimental Biology:

Even though we found that the peahens were primarily assessing the lower train, the upper train of the peacock may play an important role in courtship as a long-distance attraction signal in dense vegetation.

In The Descent of Man and Selection in Relation to Sex, published in 1871 (which the researchers awesomely cite in their paper), Darwin noted that peahens can appear coy and uninterested in males, despite the elaborate mating displays. Yorzinski and her colleagues helped explain this phenomenon by discovering that peahens spend more than two-thirds of their time scanning the environment for predators and the like, even as a beautiful peacock dances in front of them.

It’s nice to watch a beautiful dancer, but, from a peahen’s perspective, there’s not much point in finding an idyllically cute male if they’re going to be eaten before they get the chance to mate with them.

Illustrated by Perry Shirley.

Why fish need wood

By John Upton

Trees don’t just provide habitat for arboreal and terrestrial creatures — dead trees that have toppled over in shallow waters are critical for aquatic wildlife. Woody habitat in lake littoral zones provides shelter for fish. It also supports the growth of algae and the like, which are eaten by herbivorous fish and other critters.

As the globe warms and as aquifers are sucked dry, lake levels in many parts of the world are falling. And as a lake’s water level drops, semi-submerged trees that ring the lake’s shallows can be left high-and-dry. That can decimate fish populations — harming birds and other species that feed on them.

“Reduced lake levels generally decrease littoral habitat, which is critical to aquatic food webs,” wrote University of Wisconsin researchers in a recent paper published by the Canadian Journal of Fisheries and Aquatic Sciences. “Fishes across all trophic levels are known to rely heavily on littoral food sources, with littoral zones supporting 65% of the consumption by lentic fish communities and 57% of their body carbon.”

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The scientists sampled fish from 2000 until 2005 and again from 2007 to 2009 in Wisconsin’s Little Rock Lake, which is in the Great Lakes region. Declining water levels in the Great Lakes, which is Earth’s largest body of fresh surface water, are a major worry for scientists.

During the monitoring period, drought led to a decline in water levels of a little more than a meter. That left three quarters of the lake’s woody habitat stranded on land. The following graphs from the paper show the close relationship between water levels and woody habitat:

lake-level

The sampling results painted a picture of an ecosystem in steep decline — a decline that the scientists linked to the loss of soggy wood.

Things got so bad during the drought that the scientists’ minnow traps started to come up empty.

“The rapid decline of the perch population was associated with the loss of available CWH [coarse woody habitat],” the paper states. “Perch first failed to appear in a trapping event in 2005, after only a 10% loss of CWH. No perch were detected in 2008 or 2009 after 58% and 72% of the available CWH had been stranded from the littoral zone.”

The loss of the perch was blamed on the declining water levels, with changed temperature and oxygen levels potentially contributing. A loss of food was also stated as a potential factor. As was the loss of spawning habitat and loss of shelter from predators due to the disappearance of woody habitat.

“Previous research has suggested the potential for predator–prey encounter rates to increase with reduced CWH, which would result in intense bass predation on perch. … [T]he severe depletion of the perch population might have been exacerbated by the relatively high densities of bass in Little Rock South, which initially increased with reduced lake level.”

Eventually, though, the largemouth bass were found to grow more slowly as the lake’s water level fell.

The study’s lead author, Jereme Gaeta, tells Wonk on the Wildlife that the findings have implications for a warming planet.

“Future climate projections are uncertain, but we generally expect evaporation to outpace precipitation in many regions such as northern Wisconsin,” Gaeta said. “Our research shows that loss of littoral habitat can change not only the way fishes interact but also change fish community and food web structure.”

To help protect aquatic communities from the loss of littoral woody habitat, the paper recommends manually placing dead trees in lakes — something scientists call tree drops.

“Potential preventative measures when lake levels drop are limited. Our best options are to protect and restore natural shorelines to ensure future inputs of woody structure are possible and, when water levels begin to drop, add trees to deeper waters or steeper shorelines,” Gaeta said.

Little Rock Lake
This photograph from the paper shows wood stranded above Little Rock Lake’s shoreline as water levels declined.

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