FROM LARGE TO SMALL
Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.
Well, this week I actually counted the items in each bulging file folder and discovered that the animals win hands down. Next biggest is what ails us humans, but we’re doing animal stories this week for sure and we’re starting with the biggest and moving on to some of the smallest.
LOVE SONGS OF THE BOWHEAD
Not so very long ago, the bowhead whale was written off as extinct in the waters around Disko Bay in northwestern Greenland, but the situation has changed and adult bowhead whales, which can be 50 feet long and weigh 100 tons, have returned to the bay. This is because global warming has opened the Northwest Passage, making it ice free in the summer. The bowhead whales from the northern Pacific are returning to Greenland and mating with the small local population for the first time in 125,000 years.
If this weren’t big enough news, Outi Tervo, a PhD student doing research at a field station on Disko Island has discovered some very interesting news about the lead-up to that mating.
Her research team placed hydrophones in Disko Bay and discovered that bowhead whales have developed very sophisticated songs to attract a mate. It turns out that bowhead whales sometimes sing with ‘more than one voice’. They produce two different songs or sounds and mix them together, and bowheads seem to be the only baleen whales that do this. Bowheads also change their songs from year to year and never repeat songs from previous years.
The bowhead whale is in the same weight class as fin whales and blue whales but they produce much more complicated songs, at higher frequencies, between 100 and 2000 hertz – cycles per second. And interestingly enough, the bowhead whale is the only species of ’singing’ whale where the gender of the singers can’t be detected from the song.
So, we have populations mixing that haven’t seen each other in 125,000 years. I suspect that REALLY gives them something to sing about! But that’s not our only whale song story. Read on!
SINGING THE BLUES
While the love song of the bowhead is being sung to new ears, the frequency of the songs sung by blue whales has been steadily creeping downward for the past few decades according to researchers at Scripps Institution of Oceanography at UC San Diego. They feel this lowering of pitch may be good news for the population of the endangered marine mammal.
The scientists studied blue whale song data from around the world and discovered a downward curve in the pitch, or frequency, of the songs. T he decline was tracked in blue whales across the globe, from off the Southern California coast to the Indian and Southern Oceans.
"The basic style of singing is the same, the tones are there, but the animal is shifting the frequency down over time. The more recent it is, the lower the frequency the animal is singing in, and we have found that in every song we have data for," said John Hildebrand, a professor of oceanography in the Marine Physical Laboratory at Scripps.
The researchers examined a list of possible causes for the frequency drop-from climate change to a rise in human-produced ocean noise-and believe it may be explained by the increase of blue whale numbers following bans on commercial whaling activities.
While the function of blue whale songs is not known and scientists have much more to learn, they do know that all singers have been determined to be males and that the high-intensity, or loud, and low-frequency songs propagate long distances across the ocean. Blue whales are widely dispersed during the breeding season and it is likely that songs function to advertise which species is singing and the location of the singing whale.
In the heyday of commercial whaling, as blue whale numbers plummeted, it may have been advantageous for males to sing higher frequency songs, the researchers believe, in order to maximize their transmission distance and their ability to locate potential mates (females) or competitors (other males). They think that when whale densities rise, the females are closer it’s easier for the song to reach her and easier for the whale!
When whales sing, they must use most of the air in their lungs. It’s harder to use the higher pitches and they use more air, just like the sustained notes produced by an opera singer. Blue whales sing to attract females, but if they have to use too much of their energy to sing, it’s harder to do things like eat.
The scientists say the same downward pitch phenomenon may be true in other whales such as fin and humpbacks, but the blue whale song, with a comparatively easier song to analyze, is a good springboard to study other species. The researchers say such knowledge about whale songs could be important in monitoring whale populations and recovery efforts.
Blue whale. (Credit: NOAA Fisheries)
Now we turn our attention from the largest of animals to some of the smallest. Consider the ant . . . . .
HOW DOES YOUR GARDEN GROW?
Well, Guam is drying out and that usually means that within a couple of weeks, I’ll be under siege. The ants have already started coming in the bathroom windows in search of water and then the kitchen will be next. Although they are only annoying for the most part, the fire ants get nuked with insecticide until they glow. Ants perform many valuable services; I just wish they wouldn’t choose my house in which to do them!
But there’s interesting news about another kind of ant that to my knowledge isn’t found here on Guam (although given our propinquity for invaders, it’s probably only a matter of time). It seems there are ants who are farmers.
Leaf-cutter ants, which cultivate fungus for food, have many remarkable qualities and here’s a new one to add to the list: the ant farmers, like their human counterparts, depend on nitrogen-fixing bacteria to make their gardens grow. The research highlights a previously unknown symbiosis between ants and bacteria and provides insight into how leaf-cutter ants have come to dominate the American tropics and subtropics. (Ah, explains why we don’t have them here!)
This partnership between ant and microbe allows leaf-cutter ants to be amazingly successful. Their underground nests, some the size of small houses, can harbor millions of inhabitants. In the Amazon forest they comprise four times more biomass than do all other land animals combined. (And I’m really happy we don’t have them here!)
The new study shows the nitrogen, which is extracted from the air by the bacteria, ends up in the ants themselves and, ultimately, benefits the nitrogen-poor ecosystems where the ants thrive.
The fungus-growing ants are technically herbivores. They make their living by carving up foliage and carrying it back to their nests in endless columns to provide the raw material for the fungus they grow as food. But the plants have less nitrogen than the ants need to survive.
Enter the nitrogen-fixing bacteria, two species of which were isolated in laboratory and field colonies of the ants. But merely finding the bacteria wasn’t enough. It was necessary to prove that the ants were actually utilizing the nutrient to confirm a true mutualism.
One other type of insect, the termite, has been previously shown to utilize nitrogen-fixing bacteria. And other bacteria-ant symbioses have been documented. However, the discovery of the nitrogen-fixing mutualism in ants has significant ecological implications, because ants are dominant in virtually all of the world’s terrestrial ecosystems. The new work suggests that an important source of nitrogen in the American tropics and subtropics is derived through the partnership of ant and bacteria.
So . . . . they’re farmers and they cultivate bacteria. But that’s not the only interesting story about leaf-cutter ants. They may have picked up cozying up with bacteria, but they’ve given up cozying up to something interesting. Read on!
These leafcutter ants are located on a spongy fungus garden, which they grow themselves.
WHERE HAVE ALL THE BOYS GONE?
Scientists have recently discovered that a species of fungus-gardening ant is the only ant species in the world known to have dispensed with males entirely.
Most social insects—the wasps, ants and bees—are relatively used to daily life without males. Their colonies are well run by swarms of sterile sisters lorded over by an egg-laying queen. But, eventually, all social insect species have the ability to produce a crop of males who go forth in the world to fertilize new queens and make new colonies.
But scientists have recently discovered that queens of the ant species Mycocepurus smithii reproduce without fertilization and males appear to be totally absent.
Animals that are completely asexual are relatively rare, which makes this is a very interesting ant. Asexual species don’t mix their genes through recombination, so you’d expect harmful mutations to accumulate over time and for the species to go extinct more quickly than others. They don’t generally persist for very long over evolutionary time.
Previous studies of the ants, which are found in Puerto Rico and Panama, have pointed toward the ants being completely asexual. One study in particular, showed that the ants reproduced in the lab without males, and that no amount of stress induced the production of males.
Scientists believed that specimens of male ants previously collected in Brazil in the 1960s could be males of this species, but the researchers analyzed those males and discovered that they belonged to another closely related (sexually reproducing) species of fungus-farming ant.
After reviewing the literature on previous studies of these ants, the researches have concluded that the species is very likely to be totally asexual across its entire range, from Northern Mexico through Central America to Brazil, including some Caribbean islands.
As for the age of the species, the scientists estimate the ants could have first evolved within the last one to two million years, a very young species given that the fungus-farming ants evolved 50 million years ago.
Mycocepurus smithii ants tending their fungus garden. These are the only known completely asexual ants in the world. (Credit: Photo courtesy of Alex Wild
So, we farm and we have no males. There’s an alternate lifestyle for you!
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