Despite its romantic holiday association, mistletoe has long been villainized in ecology circles for being a parasite—the vine wraps itself around trees and steals nutrients from them to survive. Nobody likes a mooch, but researchers in Australia have found that this parasitic plant is not all bad. In fact, their findings [pdf] published in the Proceedings of the Royal Society of Biological Sciences this July suggest mistletoe may actually be a keystone species in forest ecosystems. The plant is relatively sparse but plays a critical role in maintaining the overall health and diversity of species in its environment.
Flukes that parasitize amphibians
The enemy of my enemy is my friend—especially if I’m a frog and my enemies are competing parasites. A recent study in PNAS found that frogs populations exposed to a more diverse set of flukes actually had lower rates of infection, with fewer frogs in the group afflicted with tiny hitchhikers.
Researchers at the University of Colorado-Boulder bred Pacific chorus frogs in a lab and put their tadpoles in different tanks with anywhere from one to six different types of flukes. On average, 40% of the frogs that came into contact with only a single fluke species developed infections, while 34% of frogs exposed to four flukes and 23% of frogs exposed to six flukes were infected (the numbers for two, three flukes followed a roughly similar trend). Additionally, some of the fluke species make frogs sicker than others, and oddly enough, the frogs exposed to a greater variety of flukes had a lower proportion of infections from these dangerous species.
Fruit fly larvae and wasp
What’s the News: Fruit fly larvae have unusually high alcohol tolerance, which scientists used to think was because they happen to feed on yeast in rotting fruit. Turns out they’re in it for the alcohol, too—as medication. According to a new study*, alcohol protects them from the wasp parasites that lay eggs in fruit fly larvae.
Hookworms are longer-lived than viruses and bacteria;
they could have had a more significant effect on human evolution.
Humans live in all sorts of places—high deserts, tropical lowlands, frigid tundra. Over the millennia, you’d expect each population’s assortment of genes to evolve to reflect the demands and dangers of its home environment: those who live in the deserts would possess genes for extra skin pigments to help keep their tender integument from burning (like African peoples), and those who live in sub-zero climes much of the year would have genes that keep them well-insulated in fat (like the Inuit). But what if factors other than climate, like the food available nearby or the viruses, bacteria, and parasites native to the area, also had an effect on various human populations’ genetic toolkits?
It’s a fascinating question, but, given that we have to reconstruct all this supposed evolution from the current state of modern genomes, finding an answer isn’t easy. A recent paper takes an important first step by looking for correlations between 500,000 different genetic markers and certain environmental characteristics, like humidity, temperature, the local diet, and the prevalence of parasites and other pathogens.
Parasitic wasps have a terrifying but weirdly impressive knack for taking over the bodies and brains of other many-legged creatures, making spiders weave them bespoke silk cocoons, obedient cockroaches incubate their eggs, and paralyzed, partially devoured ladybugs guard their young. But for the European paper wasp, as a new study describes, the tables are turned: It’s the host rather than the parasite—and the things the Xenos vesparum fly larvae inside it lead it to do are at least as odd as any of the above.
What’s the News: Infections that change an organism’s personality are a strange little corner of biology, with toxoplasmosis, which brainwashes mice and rats to have no fear of cats, topping the list. But scientists think that more pedestrian infections could play a role in shaping personality, especially when they happen early in life. Ducklings provide the latest data that this theory may have something to it.
Don’t you forget about bumblebees. While DISCOVER and others have extensively covered the mysterious colony collapse disorder that’s been crashing honeybee populations around the world, bumblebees have not escaped the tide of doom.
Sydney Cameron leads a team that just published a new study of bumblebees in this week’s Proceedings of the National Academy of Sciences, and tallied up some scary numbers.
The relative abundance of four species of bumble bees over the past few decades has dropped by more than 90%—and those disappearing species are also suffering from low genetic diversity, which makes them that much more susceptible to disease or any other environmental pressures. [TIME]
In addition, the geographic ranges of those species shrunk precipitously—between 23 and 87 percent, depending upon the case. That reduction in range could have catastrophic impacts on agriculture:
The wild pink salmon of western Canada are in trouble: In the early 2000s, their numbers in some locations swiftly dropped by 90 percent or more. One explanation put forth for this steep population decline is that sea lice, parasites ubiquitous on farmed salmon, jumped to the wild variety of the fish. But this week in the Proceedings of the National Academy of Sciences, a new study casts doubt on that idea and says the sea lice are not to blame.
When Gary Marty of the University of California, Davis, and his colleagues looked at that aspect for the Broughton Archipelago of western Canada, they found that salmon survival was not lower in years when the juveniles passed by louse-infested farms. This, they say, suggests that something other than sea lice must be reducing survival rates. [New Scientist]
Marty’s team checked up on a decade worth of data dating back to before the 2002 crash, and found a few interesting things. First, they say, the predominance of the lice in wild populations appears to predict the number found in farms a little later, suggesting the parasites travel from wild salmon to farmed ones and not the other way around. Second, they argue, it does appear that a high number of lice in the farmed fish predicts higher than normal exposure for the juveniles of the wild variety, but that increased exposure can’t account for the huge population drop in the wild salmon.
Here’s one that I didn’t touch on in DISCOVER’s creepy gallery of zombie animals controlled by mind-altering parasites: A parasitic fungus called Ophiocordyceps unilateralis that infects a plain old carpenter ant and takes over its brain, leading the ant to bite into the vein that runs down the center of a leaf on the underside. The ant dies shortly thereafter, but the fungus gains the nutrients it needs to grow this crazy stalk out of the ant’s body and release spores to create the next generation of ant-controlling fungi.
This cryptic cycle has been going on for at least 48 million years.
In a study forthcoming in Biology Letters, Harvard’s David Hughes argues that a fossilized leaf found in a fossil-rich part of Germany’s Rhine Rift Valley bears the scars of the ant’s trademark death bite. The ant bites down hard so the fungus will have a stable position when it grows a stalk out of the ant’s head. But even so, Hughes says, he doubted the mark would turn up in the fossil record—that is, until serendipity reared its random head:
Biologists are a step closer to figuring out the bizarre animals known as bdelloid rotifers, thanks to a new study in Science.
This group of near-microscopic aquatic organisms has lived for tens of millions of years without sex, can withstand blasts of gamma radiation, and if their habitat dries up they can survive for years in a dessicated state. Two years ago, DISCOVER covered the findings that determined how these all-female invertebrates manage to diversify their genes without sex: Their genome breaks apart when they dry up, and as they reassemble when water returns, they pull in new DNA from a host of other beings. Now, the new study says, drying up is also the key to how rotifers avoid parasites that would normally take advantage of their asexual ways.