Redlander Peter Coonradt compiles science tidbits. Check in weekly for new briefs.
Fossil leaves reveal ancient CO2 levels
Deciphering the record of past climate is crucial for predicting the progression and effects of the presently warming climate.
The best measure of past sea surface temperatures is found in carbonate rocks made from the shells of tiny sea creatures that once lived near the surface of the ocean.
As temperatures drop, the animals accumulate more of a heavier oxygen isotope in their shells. A picture of past atmospheric CO2 levels has been harder to grasp.
At a recent meeting of the American Geophysical Union, plant physiologist Peter Franks of the University of Sydney in Australia presented data from fossil leaves that were growing at a temperate latitude 64 million years ago, about 1.5 million years after an asteroid impact wiped out the dinosaurs and ejected a monstrous amount of debris into the atmosphere. This data supplements other applications of Franks’ method to other times between 100 and 400 million years ago.
Correlating these CO2 levels with known temperatures at the same times suggests that Earth may be even more sensitive to injections of CO2 than current models predict.
“Temperatures are going to climb further for less carbon and we better be mindful of that,” Franks said, quoted in the journal Science.
Stunning exhibit displays Cuba’s rich culture and biodiversity
Cuba is home to more than 190 species of butterfly, at least 35 of which have not been found elsewhere. It’s home to the world’s smallest bird, the bee hummingbird (Mellisuga helenae) and key coral reef species such as the hawkbill turtle (Eretmochelys imbricata) and spotted eagle ray (Aetobatus narinari).
The island nation’s population of 11 million has a diverse Afro-Caribbean ancestry that’s the product of conquest, colonialism and revolution. The complex interplay between the country’s cultural and natural riches is on display through Aug. 13 in a beautifully curated exhibit at New York’s American Museum of Natural History. Diplomatic, political and economic relations started getting on a normal footing only within the past year, but collaboration in that natural sciences has been going on for a long time. With its relatively small population and lack of intensive development, and protection of pristine marine ecosystems, Cuba is widely recognized as a model of natural preservation and cultural pride.
Mouse gut microbes play havoc with lab experiments
One of the hottest fields in biology is our rapidly expanding knowledge of the microbiome, the community of bacteria, fungi and protozoa that inhabit every part of us and play crucial roles in immunity, digesting food and many other essential functions.
Now researchers are realizing that variations in the gut microbiomes of their lab animals are introducing confounding variables in their experiments.
Physiologist Laura McCabe and her team at Michigan State University found that mice treated with a certain drug lost bone density compared with controls. To repeat the experiment McCabe ordered a seemingly identical batch of mice of the same strain from the same vendor and kept them under the same conditions, as required for a reliable study. Same type of cage, same bedding, same food, same room. This time mice treated with the drug gained bone density instead of losing it. Then she tried a third run and saw no effect at all. Wha….?
Then McCabe had a hunch. Knowing that signals from the gut can affect how bone forms and gets reabsorbed, she took fecal samples from control mice in each of the three experiments and analyzed their gut microbes. Each group had a different microbial make-up to begin with. This strongly suggested that the varying microflora produced different reactions to the drug.
There are many reasons experiments can’t be replicated, either by the original researchers or by outside groups. Sometimes there was a flaw in the original experiment, but often it’s because the replicator is performing a slightly different experiment without realizing it. Growing awareness of the crucial role of the microbiome is adding a whole new dimension to the problem of experimental uniformity and consistency.
There’s no easy fix. The mix of microbial species living in a mouse or other lab animal is always changing and never identical between one mouse and another, and taking a microbial inventory is tricky and time consuming.
The problem has gained the attention of animal caretakers at research labs, who were already diligent in making sure research subjects are kept in uniform conditions. Time of day, temperature, bedding material and even the shelf level of the cage can affect how mice react to an experiment. Mice can even have differing stress responses to male and female investigators. Trying to maintain similar microbiomes across experimental groups adds a whole new challenge in the vivarium.
The good news is that increased understanding of the role of the microbiome is opening new possibilities for treating many diseases. Resident microbes have already been shown to influence susceptibility to HIV and asthma, predisposition to obesity across generations and how the body responds to drugs. For MSU’s McCabe, her conflicting results led to a whole new study of how gut microbes help regulate bone density. She’s already found that mice that lost bone density in her experiment started off with more bacteria associated with inflammation.
As the possibilities expand, researchers just have to be able to ensure microbial consistency across experimental populations. Easier said than done.
Engineers seek to prevent catastrophic flood near Mt. St. Helens
Geologists have determined that 3,350 years ago a catastrophic flood inundated the Cowlitz River Valley in southern Washington under 20 meters of water and mud. The cause of the flood was the rupture of Spirit Lake at the foot of Mt. St. Helens.
The eruption of Mt. St. Helens 36 years ago created a new natural dam of volcanic debris around Spirit Lake, raising the lake bottom 64 meters and plugging the lake’s previous outlet, the north fork of the Toutle River.
With no outlet, rain and snowmelt swelled the lake and created the prospect of a breach that would release a flow five times that of the nearby Columbia River.
The U.S. Army Corps of Engineers rushed in and bored a tunnel from the lake to Coldwater Creek in 1984 to relieve the build-up of water.
Now that tunnel is in danger of collapse.
Frequent earthquakes caused by gurgling magma beneath Mt. St. Helens have pushed the ground upward by nearly a meter and constricted nearly a quarter of the tunnel’s diameter.
The U.S. Forest Service, whose budget is already strapped by escalating costs of fighting forest fires, has already spent $7 million for emergency repairs.
Now USFS is looking for a more permanent solution.
Options include doing a complete rehab of the failing 100-meter segment of the existing tunnel, boring a new more heavily fortified tunnel, or cutting a channel through the debris field to create a new outflow river.
All of these engineering challenges are complicated by the fact that debris from the eruption 36 years ago has increased the sediment load in local rivers 10- to 50- times higher than it was before the eruption, a condition that will persist for decades or centuries.
Women are key players in ISIS recruitment networks
Given the abuse and subjugation of women in ISIS controlled territory, it’s a big surprise that two studies of online ISIS recruiting networks show women to be more active and influential than men.
One paper in the journal Science and another in the online journal Science Advances use techniques from epidemiology and statistical tools from a branch of mathematics known as graph theory to measure how information and resources flow through online terrorist networks.
Physicist Neil Johnson of the University of Miami models human organization and conflict.
His approach was not to look at millions of individual terror-related messages but to focus instead on aggregates, which in turn become connected to other aggregates to form vast networks.
Because sites like Facebook and Twitter aggressively shut down sites and users suspected of terrorist activities, Johnson’s team studied the Russian social network site Vkontakte, which has 360 million users worldwide.
They uncovered 196 pro-IS groups with a total of more than 100,000 members.
The team was startled to find that about 40 percent of those participants declare themselves to be female.
Even more surprising, a measurement of the importance of individuals in a network called their betweenness centrality (BC), showing which members serve as key points of communication between far-flung elements of a network, revealed that women had twice as high a BC score as men.
That’s especially striking considering that in typical corporate settings women’s BC score is less than men.
The second study by Johnson’s group used a mathematical model to track the growth of pro-IS groups over a 6-month period.
It showed that small groups with only a few dozen participants follow a predictable coalescence process of merging with other groups to form larger networks.
This is different from the contagion phenomenon that occurs with disease epidemics, in which a vector is transmitted simply from individual to individual.
Further, Johnson and his team write, “...pro-ISIS aggregates exhibit the ability to collectively adapt in a way that can extend their lifetime and increase their maximal size despite the fact that the aggregate is an ad hoc group of followers who have never met, do not know each other and do not live in the same city or country.”
The authors attribute the speed, variety and novelty of these adaptations to evolutionary pressure applied by authorities trying to eliminate them.
And they conclude that while “...the amount of explicit pro-ISIS material online may have declined since summer of 2015, it is possible that there is lower detection due to novel adaptations being employed.”
Plant sex ratios show a response to climate change
Only around 6 percent of angiosperms (flowering plants) are unisexual, i.e. either purely male or purely female. The rest are hermaphrodites, with both male and female sex organs.
Humans and most other animals have a sex ratio close to 50-50.
Geneticists and evolutionary biologists have used mathematical models and game theory, backed up by field studies, to show how this outcome is ordained by evolution.
However the variability of sex ratios in flowering plants seems to be a way they can adapt to environmental stresses such as climate change.
What remains to be seen is whether these adaptations happen fast enough to rescue populations from extinction in our rapidly changing climate.
In one study, William K. Petry of U.C. Irvine and colleagues looked at four decades of data showing the spatial distribution of the unisexual plant Valeriana edulis (valerian) over an 1,800 meter elevation range on a Colorado mountainside.
Increased elevation was associated with increased water availability and female frequency.
Males of the species require less water and were thus better able to survive at lower, more arid elevations.
As the climate became drier over time, male frequency increased further upslope.
This increased the availability of pollen to upslope female plants, resulting in increased seedset.
Hence the overall response to climate change was a migration of the population to a higher, wetter elevation.
Hermaphroditic plant mating systems also respond to changing conditions via reproductive plasticity.
Since self fertilization can have deleterious genetic effects due to inbreeding, most hermaphrodites have sophisticated means to prevent self pollination.
However self pollination can provide a reproductive backup system in case pollen from other plants doesn’t arrive.
About 42 percent of hermaphroditic angiosperms have mixed mating systems in which a plant carries seeds from self pollination as well as from a different individual.
Climate change can disrupt the synchronization of plant pollen production and the abundance of insects which transport pollen from one plant’s flowers to those of another.
This then has the effect of increasing the prevalence of self fertilization and inbreeding.
Octopus and squid populations are booming
It’s well known that ocean ecosystems are under stress from pollution, overfishing and climate change. However populations of cephalopods, the class that includes octopus, squid and cuttlefish, have greatly expanded worldwide since 1953.
The population growth includes near shore species as well as those that inhabit the open ocean.
No one knows why this is happening, but their short life spans and rapid breeding could be making them more adaptable to changing conditions in the ocean.
Making a new breed of dairy cows: hornless, not dehorned
Natural hornlessness is common in cattle raised for beef, but in the United States, 80 percent of dairy cattle have to have their horns removed.
Animal-rights activists have protested that the dehorning process is cruel.
Scientists with the St. Paul Minnesota biotech startup Recombinetics used the genome editing technique known as TALENs to edit variants associated with hornlessness in beef cattle into the genome of some dairy cows, and reported in the journal Nature Biotechnology that that created five, live hornless calves with no off-target effects.
Search for dark matter particle near a dead end
When astrophysicists measured the angular momentum of rotating spiral galaxies they realized the gravitational field produced by the galaxies’ mass is too weak to keep the systems from flying apart.
The galaxies must be held together by additional gravity produced by some form of mass they couldn’t see. They called it dark matter, and it makes up 26.8 percent of the total mass-energy of the universe.
Physicists can only guess what it might be.
The leading candidate is the hypothetical Weakly Interacting Massive Particle, or WIMP.
In the early 1980s, experimental physicists at the CERN accelerator in Geneva discovered the fleeting W and Z boson particles.
The theory of supersymmetry predicts that these bosons should have a stable, uncharged cousin with a mass several hundred times greater than a proton, and that these WIMPs should have been produced in great quantity in the big bang. For 30 years physicists have been looking for traces of the elusive WIMP particle. Now, more than a kilometer beneath the tallest peak in Italy’s Apennine Mountains, scientists are watching a one-ton tank of liquid xenon, the biggest WIMP detector ever, hoping to see traces of the particles passing through from outer space.
Meanwhile, physicists are hoping to produce WIMPs in the Large Hadron Collider atom smasher, and astronomers hope to see signs of WIMPS annihilating each other in the center of our galaxy, as supersymmetry predicts.
So far, nothing. Just as disheartening, the world’s largest atom smasher has yet to provide any experimental evidence that the underlying theory of supersymmetry is real..
XENON1T team leader Elena Aprile of Columbia University was quoted in Science magazine saying, “We’re perhaps losing faith that one ton or even ten tons (of xenon) will be enough to see anything.” No other dark matter candidates are suggested by known physics.
Dark matter hunters may not know what to look for next if WIMPs turn out not to exist.
Gruesome Bronze Age archaeological find in northern Europe
In 1996 on the banks of the Tollense River in northern Germany an amateur archaeologist found a single arm bone sticking out of the steep riverbank.
A flint arrowhead was firmly embedded in it.
That led to a test excavation that revealed more bones, a bashed-in skull and a club resembling a baseball bat.
Radiocarbon dating fixed the remains at 3,200 years old. A series of excavations from 2009 to 2015 along a 3-kilometer stretch of the river revealed the remains of a huge battle involving many hundreds of warriors, which in turn gives a startling glimpse of the level of social organization in Europe during the Bronze Age. Northern Europe of that time was long dismissed as a backwater, overshadowed by more sophisticated civilizations in ancient Greece and the Near East.
However the scale of this battle, which probably took place on a single day, gives a much different picture.
In one 450-square meter site alone were the remains of at least 130 warriors and five horses, and that’s at most only 10 percent of the carnage.
Chemical analysis of teeth reveals that many of the fighters came not from the local area but from many regions as far away as southern Europe.
Artifacts including axes, arrowheads and sophisticated jewelry made of bronze were also found. Why the battle took place at this location is still a mystery since there were no large population centers anywhere near.
However researchers excavated a 120-meter long causeway across the valley, parts of which were dated to 500 years before the battle. “To organize a battle like this over tremendous distances and gather all these people in one place is a tremendous achievement,” said Helle Vandkilde, an archaeologist at Aarhus University in Denmark. “It could be the first evidence of a turning point in social organization and warfare in Europe.”
Muslim nation aims for Mars
The United Arab Emirates (UAE) has an ambitious plan to launch a science mission to Mars in July, 2020. The spacecraft Hope will probe the Martian atmosphere and beam back “the first holistic view of the entire dynamics of the lower atmosphere of Mars,” according to lead scientist Sarah Amiri.
What makes the Hope mission uniquely innovative is its planned orbital path around the Red Planet.
Five of the six satellites currently orbiting Mars are in polar orbits, which enable them to view any point on the planet’s surface twice per Martian day.
Hope’s non-polar orbit will allow the spacecraft to monitor the atmosphere at various latitudes in the course of a single day, giving researchers an ongoing view of how the atmosphere evolves over Martian seasons.
Hope’s other objective will be to examine how the Martian atmosphere dissipates into outer space.
This will involve studying the link between processes in the lower atmosphere, which contains most of the planet’s water vapor, and the escape of hydrogen and oxygen from the upper atmosphere.
That loss has left the surface of Mars dry and uninhabitable, a fate we’ve avoided here on Earth for reasons yet to be fully understood. The impetus for UAE space exploration began in the late 1970s when the Emirates’ founder, Sheik Zayed, met with several Apollo astronauts at his palace..
“From that time, His Highness became interested in space,” according to Mohammad Al Ahbabi, director general of the UAE space agency in Abu Dhabi.
Sheik Zayed died in 2004, but his legacy lives on in a space program that’s poised to become a global player in planetary exploration. The Hope mission is being run out of the Mohammad Bin Rashid Space Centre (MBRSC) in Dubai, which already operates two Earth-imaging satellites and a third is slated for launch from Japan this year. These and the Hope project are nurturing a whole new generation of Emirati planetary scientists to analyze data from these missions, embracing science as preparation for the coming post-petroleum economy.
Climate change may have caused collapse of Andean civilization
The pre-Incan Wari state integrated disparate cultures in the highlands and coastal plain of present day Peru until about 1,000 years ago when a sustained drought unleashed centuries of violence and deprivation. This is the finding presented by bioarchaeologist Tiffiny Tung of Vanderbilt University at the World Congress on Mummy Studies.
Tung’s work is based on cutting-edge analysis of skeletons from before, during and after the collapse, documenting injuries and changes in bone chemistry.
Starting around 600 A.D., 800 years before the rise of the Inca, the Wari expanded their domain from the southern Peruvian highlands to conquer nearly all of present day Peru.
Sometimes they used force and took captives, and in other places they expanded peacefully by building canals and expanding the benefits of agriculture.
Their empire remained stable and prosperous until about the year 1000.
Tung studied bones excavated from two sites, one dated between 897 and 1150 and the other dated from 1270 to 1390, several centuries after the collapse.
In the earlier sample group 20 percent of adult skulls showed evidence of non-lethal healed skull fractures.
Skulls from after the collapse showed the same number of non-lethal head injuries but fatal head injuries had risen to 40 percent of adults and 44 percent of children.
“The violence becomes much more deadly,” Tung reported in her presentation. “These violent deaths aren’t from community brawls. This is much more systematic lethal violence, but it’s unclear if it’s from civil war or warfare with those perceived as outsiders.”
Tung’s co-worker Theresa Miller, a chemical engineering student at Vanderbilt, used carbon isotope ratios in the bones to infer changes in Wari diets during and after the collapse.
The mainstay of the Wari diet was maize but they also ate meat from domesticated alpacas and llamas, which left a distinctive ratio of nitrogen isotopes.
Several hundred years later, Miller found, men and children were still eating maize but not meat, but women’s carbon isotopes had changed dramatically.
And the whole population’s nitrogen levels shot up, which can be a sign of starvation.
Core samples from Andean lakes and glaciers show that by this time the drought had been going on for several centuries.
In their heyday the Wari honored their dead with fabric wrappings and funary masks and many were buried with offerings.
They also kept mummified trophy heads of decapitated captives.
However Tung reported that skeletons dated after the collapse of Wari society were found jumbled in a ditch, many with cut marks indicating the flesh had been stripped off.
Tung now hopes to more precisely date the moment when Wari society tipped from social cohesion to indiscriminate violence to see if there is a correlation with a specific social or environmental shift.
There’s little doubt that over a broader time scale the climatic shift had to be a significant factor in the collapse of that ancient civilization.
PCBs still a threat to apex marine predators
In the late 1960s polychlorinated biphenyls (PCBs) were detected in high concentrations in wildlife in Sweden and associated with significant population declines in the affected species.
Marine apex predators are most vulnerable to these toxic compounds because the chemicals are absorbed by all species, and since big fish eat little fish their concentrations increase as they accumulate up the food chain.
And because PCBs persist for so long they get distributed to all oceans of the world.
Marine mammals are especially affected because, unlike fish, whales dolphins and seals pass the chemicals to their offspring via the mother’s milk.
PCB use and manufacture were banned in the U.S. in 1979 and in the U.K. in 1987, and in 2004 the Stockholm Convention committed more than 90 nations to phasing out persistent organic pollutants, including PCBs.
Since PCBs were banned tissue concentrations in many species have declined and populations recovered between 1970 and 2010.
Unfortunately PCBs have stopped declining and their concentrations are still excessively high in orcas and bottlenose dolphins in the northeast Atlantic and several cetacean species in the Mediterranean Sea, and are associated with long term population declines and low or zero rates of reproduction.
And the problem is not limited to European waters.
Orcas (killer whales) remain the most PCB-contaminated species on earth in all areas of the ocean.
They have long life spans, travel great distances and have a long lactation period, all of which add to their vulnerability.
Coastal bottlenose dolphins, false killer whales, beluga whales in the St. Lawrence River, polar bears in the arctic and some sea eagle species in the Northern Hemisphere may also be at risk.
China’s recent industrialization is thought to have increased concentrations of PCBs and other pollutants and contributed to the probable extinction of the Yangtze River dolphin and the critically endangered Yangtze River finless porpoise,
Indo-Pacific humpback dolphins, plus Ganges River dolphins in India and Indus River dolphins in Pakistan.
PCBs have been shown to be toxic to fish but empirical evidence of PCB toxicity in wild fish is lacking.
However fish apex predators such as large sharks are also long lived and feed on the same fish as large marine mammal predators.
There has been a decline in great white shark sightings in the most PCB-contaminated regions of the northeast Atlantic.
Bull sharks, great hammerheads, shortfin mako and tiger sharks may also be affected.
A paper in Science by Paul D. Jepson of the Zoological Society of London and Robin J. Law of the U.K. Centre for Environment, Fisheries and Agriculture calls for research into pathways of PCB contamination of the oceans.
What portion of PCB contamination is being recycled in the ocean, and how much is still being added to the ocean by, for example, dredging of PCB-laden rivers and estuaries and leakage from old landfills? The authors also point to a need to study nations’ compliance with the Stockholm accord.
A common origin for scales, feathers and hair
Many evolutionary relationships are revealed not through anatomical comparisons of adults of different species but through observations of developmental processes from embryo to adulthood.
Hair, scales and feathers are so different from one another that it has been assumed by many biologists that they evolved independently.
The lack of intermediate forms between scales and hairs in the fossil record and big differences in their protein composition argue against a common ancestry.
However a new study convincingly shows that all are generated by the same program early in embryonic development.
Czech evolutionary biologists Nicolas Di-Poï and Michel C. Milinkovitch examined scale development in crocodiles, lizards and snakes and found that they develop from the same localized regions in the embryo as bird feathers and mammalian hair follicles, and all follow the same molecular developmental pathways.
That means our hair is produced by a genetic program that evolved about 312 million years ago in the ancestor of all four legged land animals.
Venus flytrap evolved defensive tactic into carnivorous lifestyle
Plants can’t run away from predators, so they’ve had to evolve other ways to keep herbivores from eating them.
Some plants, including ancestors of the Venus flytrap, have an alarm system that goes off when trigger hairs are stimulated by a herbivorous insect.
The alarm generates electrical impulses that stimulate glands which produce jasmonic acid, which in turn triggers the synthesis of self defense toxins and hydrolase inhibitors.
Insects use hydrolase to break down plant proteins for digestion, so the plant’s hydrolase inhibitors essentially render the plant indigestible for the insect.
New genetic research by biophysicist Rainer Hedrich and bioinformaticist Jörg Shultz of the Julius Maximillian University of Würzburg in Germany has shown how the Venus flytrap amped up this defensive system to digest insects instead of simply warding them off.
The researchers tracked the activation of Venus flytrap genes as the plants trapped and digested their insect prey.
The jasmonic acid release triggered by the flytrap’s alarm system causes tens of thousands of tiny glands to produce much greater quantities of hydrolases than would be needed to simply repel the insect.
These molecules are made in sufficient quantities to digest the insect trapped by the flytrap.
Then the glands are triggered by another set of genes to help the flytrap absorb nutrients from the digested insect.
The researchers found that these genes are the same ones expressed in the roots of other plants to help them absorb nutrients from the soil.
As so often happens in evolution, old systems are adapted for new uses.
Tropical species are especially vulnerable to climate change
There’s greater seasonal temperature variation in temperate latitudes than in the tropics.
In Minnesota it gets brutally cold in winter and devilishly hot in summer. Near the equator temperatures don’t change much throughout the year.
In 1967 ecologist Daniel Janzen theorized that plant and animal species in the tropics evolved with narrower thermal tolerances than those in temperate zones.
Because of that, he went on to argue, this narrower thermal tolerance places a greater constraint on tropical species’ elevational ranges.
Dispersing or migrating over a mountain pass would be more difficult for tropical species because of their limited tolerance for temperature changes due to elevation.
Janzen made his case before climate change was on everyone’s mind. Now we’re more conscious that seasonal temperature ranges change not only with latitude and elevation but also through time.
It seems likely that tropical species that are “specialists” in a narrow temperature regime will have a harder time migrating to higher elevations or evolving adaptations to increased temperatures.
They would therefore be at greater risk of extinction in a changing climate than plants and animals evolved to tolerate greater temperature variation.
Wei-Ping Chan at the Biodiversity Research Center in Taiwan and his co-authors in Taiwan, the U.S. and Brazil have published a paper in the journal Science which analyzes a database of elevational range size for 16,592 species of rodents, bats, birds, lizards, snakes, salamanders and frogs on 180 mountain gradients over a range of latitudes.
They looked at the relationship between species’ elevational range and seasonal temperature range, diurnal (daily) temperature range and and mean annual rainfall.
The study doesn’t provide a simple predictive model but it does confirm narrower elevational ranges for species at lower latitudes.
A separate Science paper by researchers not involved in the study concludes that the analytical method applied by Chan et al will be useful for understanding how climate variation shapes the geographical distribution of species.
Both sets of authors lament the lack of adequate data from the tropics to “extrapolate macroecological patterns or to model future environmental responses to changes in climate.”
Comb jelly raises questions about the origin of the through-gut
Some things are so basic we seldom stop to wonder how they came about. Like the fact that we take in food via the mouth, digest it as it passes through the gut, and expel the remains through the anus.
That’s how it works for us and nearly all members of the animal kingdom, from fish to earthworms. But not quite all.
Sponges, sea anemones and jellyfish eat and excrete through the same opening. The original potty mouths.
They descended from ancestors that lived before the through-gut appeared 540 million years ago.
The through-gut proved to be such a useful innovation that it got passed on to the great majority of animal species alive today. The through-gut is especially useful for animals that move through their environment, unlike sponges and sea anemones that are anchored in place.
It makes sense that you’d want your mouth, brain and sense organs at your front end. And there are clear advantages in having your waste products jettisoned where they won’t pollute your food.
And it makes it possible to eat while digesting what you ate previously. The through gut is one of a whole package of features of bilateral animals.
They not only have a difference between their front and back ends, but also their upper (dorsal) and lower (ventral) aspects.
What’s above and what’s below pose different challenges. But the left and right sides are the same. All this is basic textbook stuff, but now along comes biologist William Browne of the University of Florida and his videos of primitive gelatinous sea creatures called comb jellies or ctenophores. They evolved long before animals known to have through-guts. In 1880 the German zoologist Carl Chun noticed a pair of tiny pores next to the comb jelly mouth but concluded they weren’t for defecation. But Browne made video recordings of comb jellies consuming tiny crustaceans and zebrafish genetically altered to glow with red fluorescence.
Browne’s videos show the prey circulating through the comb jelly’s network of canals.
Two to three hours later the indigestible parts are jettisoned through the pores.
And extreme closeups of the pores show them encircled by a ring of sphincter like muscles. Which raises the question: did comb jellies evolve their own through-gut independently? Or are they the true ancestor of all us bilateral animals?
Browne is currently testing the latter possibility by seeing if comb jellies activate the same genes when developing their pores that other animals do when growing an anus.