Tag Archives: featured

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.

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.”

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:

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.

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.

Guppies father fry after they die

By John Upton

You have to be quite the stud to sire a clutch of ankle-biters long after you’ve croaked it.

Yet that’s just what male members of many species of animals can do. And with apologies to any ghostly egos of dead dads of the animal world, the reality is that these feats are not to their credit.

Females of some species of crabs, salamanders, turtles, lizards, bats and fish can store sperm inside their bodies, which they use to fertilize their eggs many months or even a year or more after they have mated. That means that males can father offspring long after they are dead.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

One such species is the Trinidadian guppy. Female guppies live much longer lives than do male guppies, but the longevity of the sperm when stored inside special ovarian receptacles can make up for the difference.

Researchers introduced a population of lab-reared guppies into a pond beneath a waterfall in Trinidad’s Lower LaLaja. They fastidiously monitored each of the fish as the population grew, studying the Poecilia soap opera dramas of who was mating with who.

The scientists discovered that many guppy fry were fathered by fish that had died generations prior to their births. Within eight months of research, around one quarter of the guppies being born (described as “new recruits” in the following graph) were being fathered by dead males.

Lo ́pez-Sepulcre A, Gordon SP, Paterson IG, Bentzen P, Reznick DN. 2013 Beyond lifetime reproductive success: the posthumous reproductive dynamics of male Trinidadian guppies. Proc R Soc B 280: 20131116.
Lo ́pez-Sepulcre A, Gordon SP, Paterson IG, Bentzen P, Reznick DN. 2013 Beyond lifetime reproductive success: the posthumous reproductive dynamics
of male Trinidadian guppies. Proc R Soc B 280: 20131116.

“Clearly, posthumous reproduction has important fitness consequences for males, as it allows them to expand their reproductive lifespan to equal that of females,” the scientists wrote in a paper, published this month in the journal Proceedings of the Royal Society B. “[L]ong-term sperm storage by females can also buffer the loss of genetic variation in organisms where females outlive males, enabling males represented in stored sperm to reproduce, even after death.”