Domestic cats are known killers, and when let loose they can
do real predatory damage. Cats (Felis catus) can wipe out entire populations of native birds and small mammals such as mice, squirrels and rabbits when introduced to island environments. Eradication efforts have historically been implemented to remove these non-native predators from islands. A new study shows that domestic cats can wreak havoc on the mainland as well. Researchers say un-owned cats kill far more birds and mammals than previously thought, making them the greatest human-related cause of these wildlife deaths in the United States.
There’s a certain expression a wet dog wears as it trots up to you, a kind of gleam in the eye that says, “I’m about to shake so vigorously that in a mere 4 seconds, 70 percent of the water in my fur will fly off of my coat and on to you.”
But the wet-dog shake, though it’s an annoyance to us, may be a survival technique to dogs. The water that sticks to a mammal’s fur can lower its body temperature, causing hypothermia, so it behooves wild animals to get rid of all that water as quickly and efficiently as possible.
To find out just how efficient the wet-dog method is, researchers from the Hu lab at Georgia Tech filmed 33 different wet zoo mammals from rats to kangaroos to lions and tigers and bears (oh yes) with high-speed cameras and analyzed the motion of their bodies, skin, and fur. Their research was first published back in 2010, but their latest study, published in the Journal of the Royal Society Interface, improves their mathematical model of the wet-dog shake and reveals how much force the furballs can generate. (The paper is not yet online; we will provide a link when it becomes available.)
Creatures as large as elephants are unusual; it takes a long time to evolve such size.
How long does it take for a mammal as small as a mouse to evolve into something as large as an elephant? A really, really long time, a recent study has found: about 24 million generations, at minimum.
To get that number, researchers looked at the evolution of body mass over the last 70 million years, after the dinosaurs went extinct and surviving animals expanded into the ecological niches they left behind. That estimate is far longer than earlier estimates, which, extrapolating from bursts of super-fast evolution in mice, range from just 200,000 to 2 million generations. Such speedy evolution, in actuality, is probably not sustainable over the long term—hence the lengthy new estimate.
What’s the News: Researchers have now found a well-preserved fossil of the earliest known member of the animal group that encompasses today’s placental mammals, which includes humans. The shrew-like creature, named Juramaia sinensis, or “Jurassic mother from China,” dates back to 160 million years ago, 35 million years earlier than the oldest mammal fossil previously discovered. The Nature study gives some tangible support to genetic evidence suggesting that the two main types of mammals split well before the previous oldest mammal fossils.
What’s the News: Mammals’ increased brain size may have come from long-ago natural selection for a better sense of smell, suggests a new study published today in Science. By reconstructing in 3D the skulls of two animals far back on the mammal family tree, the researchers saw that growth of smell-related brain regions accounted for much of the early increase in brain size as mammals developed.
What’s the News: After tracking baby gray catbirds with miniature radio transmitters, biologists found that cats were by far the #1 bird killer: 47 percent of the birds died at the paws of pet and feral felines (out of 80 percent that were killed by predators in general). This echoes some biologists’ view that cats are a destructive, human-assisted invasive species: “Cats are way up there in terms of threats to birds — they are a formidable force in driving out native species,” said one of the authors of the study.
What’s the Context:
Not So Fast: While cats were the biggest threat to birds in this study, the lead author notes that the biggest culprit for bird deaths over all is still building collisions.
Reference: Balogh, Anne L., Ryder, Thomas B., and Marra, Peter P. 2011. Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats. Journal of Ornithology. DOI 10.1007/s10336-011-0648-7 (pdf)
Image: flickr / emilydickinsonridesabmx
It’s no secret that an alarming number of species around the world, especially vertebrates, are in trouble. But is the notion that the Earth is on the brink of a sixth major extinction event—the first since the dinosaur die-off—true, or alarmist? In Nature this week, a team of scientists sought to answer the question directly by counting as many species (and extinctions) as they could in the fossil record and the recent historical record. The result is gloomy news: There’s still a chance to avert much of the crisis, but if nothing changes, such a mass extinction event really could happen in the span of just a few centuries.
Mass extinctions include events in which 75 percent of the species on Earth disappear within a geologically short time period, usually on the order of a few hundred thousand to a couple million years. It’s happened only five times before in the past 540 million years of multicellular life on Earth. (The last great extinction occurred 65 million years ago, when the dinosaurs were wiped out.) At current rates of extinction, the study found, Earth will enter its sixth mass extinction within the next 300 to 2,000 years. [MSNBC]
That range of time the researchers give is so large because of the great diversity of life—it makes it hard to track exactly how many species are disappearing, and how quickly. (Indeed, DISCOVER has covered how biologists are discovering many new species these days just as those species face extinction). So Anthony Barnosky and his team made conservative estimates based on the available evidence. For instance, they pegged the rate of mammal extinction at 80 species out of a total of 5,000-plus in the last five centuries. That may not sound like much, but when you consider the speed at which things typically happen on a geologic scale, it is a faster rate of species loss than the previous five mass extinctions saw, scientists believe.
“This is fantastic news because before these camera trap images surfaced, only 12 other Javan rhino births were recorded in the past decade,” WWF-Indonesia Ujung Kulon programme chief Adhi Hariyadi said. “The population in Ujung Kulon represents the last real hope for the survival of a species that is on the brink of extinction.” [AFP]
Scientists who track the species had feared that perhaps as few as 40 Javan rhinos remained. This video footage recorded in November and December of last year, as well as other observations, suggests that the population is probably a little larger now, but still only about 50.
Even with 15 percent of their hearts removed, newborn mice possess the extraordinary ability to mend themselves, researchers report today in the journal Science. It’s the first time that mammals outside of the womb have shown the regenerative ability to repair the heart.
Only newborn mice could regenerate part of their hearts, and they lost this ability after about a week after birth. Still, the results were quite impressive: Olson’s team removed 15 percent of the heart one day after birth, and when the researchers checked up three weeks later, the whole heart was repaired in 99 percent of the mice. Until now, scientists had seen fish and amphibians regenerate heart tissue as adults, but only embryonic mammals had been spotted doing the same.
“When a person has a heart attack and heart muscle cells are lost, the heart loses pump function, causing heart failure and eventual death,” said Eric Olson, a molecular biologist at Southwestern Medical Centre in Dallas, Texas. “Now that we know that the mammalian heart indeed possesses the potential to regenerate, at least early in life, we can begin to search for drugs or genes or other things that might reawaken this potential in the adult heart of mice and eventually of humans.” [The Guardian]
First they have to understand what the newborn rodent’s bodies are up to. Initially, Olson and colleagues weren’t sure how the mice were mending themselves—with stem cells, or cells that had already become muscle cells. But the appearance of the cells gave them away, says Dr. Stephen Badylak, who wasn’t involved in the study.
This week in bizarre new forms of mammal reproduction: mice who have genetic material from two fathers but nary a mother, the next step in a progression of scientific efforts to get more creative with sex and reproduction.
“It has been a weird project, but we wanted to see if it could be done” in mice, says Richard Behringer, lead author of the study and a developmental geneticist at M.D. Anderson in Houston. [Wall Street Journal]
Weird, and also complex: The process requires several generations and some creative genetic trickery. To make it happen, Behringer’s team started with a single male mouse. Let’s call him Fred. Scientists took cells from Fred and transformed them into a line of induced pluripotent stem cells, which can grow into any kind of cell in the body. Normally, of course, a male’s sex chromosomes are X and Y. But when the researchers created these stem cells, some of them—about 1 percent—lost the Y chromosome through ordinary mistakes that happen in cell division.
Thus, the scientists had a batch of Fred-derived stem cells that had no Y, and thus were labeled XO cells. The next step was to take ordinary mice blastocysts—early stage embryos that had been conceived in the traditional fashion—and inject the XO cells into them. When this XO-injected embryo was implanted into a normal female mouse, she gave birth to offspring called chimera—what we call animals with two or more genetically distinct populations of cells. In this case the mouse possessed, in addition to the normal cells from its mother and father, some XO cells derived from Fred.