The spread and current range of the cane toad in Australia.

The cane toad (Bufo marinus) was introduced to Australia in what was another failed attempt at biological control.  The Bureau of Sugar Experiment Stations brought over the first cane toads from Hawaii in June of 1935 in an effort to control the cane beetle, which was destroying the sugar cane crops of northern Queensland.  About  100 cane toads were released in August of that year in northern Queensland, but the little buggers multiplied like crazy and today they number over 200 million and have spread as far as New South Wales and the Northern Territory.  One reason they have been able to multiply so successfully is that they are highly toxic, and are toxic at all life stages.  As a result, cane toads have few predators in Australia. Their rapidly spreading invasion has done serious ecological damage — a preliminary risk assessment of cane toads in Kakadu National Park stated that the predation of the cane toad by native wildlife is the greatest risk to biodiversity.

Notice I said few predators.  Although many snakes in Australia are unable to survive the cane toad’s toxins, one native species- the keelback snake (Tropidonophis mairii), is relatively resistant to the deadly toad toxins and remains common in toad-infested areas.  The toad’s toxins have minimal effects on the keelback snake, but the snake still prefers eating native frogs to the invasive cane toad.  Is the keelback’s ability to coexist with toads a result of its ancestral Asian origins, or the result of rapid evolution since the toads’ arrival– and is it’s preference for frogs vs toads an innate or learned behavior?  That’s what a few Australian scientists were hoping to find out.

Image from jcu.edu.au

In order to assess whether or not the keelback’s feeding preference was innate, the scientists looked at two populations of snakes– one in Townsville, where keelbacks and cane toads have lived together for over 60 years, and the other in Darwin, where the snakes and toads have lived together less than four years.  In one experiment, naive snakes were offered a choice of frog or toad for dinner, and the results were recorded.  In the second feeding behavior experiment, the snakes that co-habitated with toads for a long time were tested as to whether or not feeding behavior was learned by being split into two groups- toad-naive and toad-experienced.  The snakes were fed four meals of experimental treatments, followed by a fifth meal to see how prior exposure to toads influenced the snake’s feeding response.  The toad-naive snakes were offered native frogs for their first four meals, and the toad-experienced snakes were offered frogs and cane toads in an alternating sequence.  For the fifth meal, all of the snakes were offered a cane toad.  The final experiment tested toad-naive and toad-experienced snakes for the physiological tolerance to toad toxins by giving the snakes a dose of toad toxin and seeing how it affected the snakes’ performance as they small around a small pool.

The researchers found that being toad-experienced did not affect the keelback’s tolerance to toxins and that prior experience with toads did not significantly affect the tendency of a young keelback snake to consume a toad, showing that  learning plays little or no role in the keelback’s aversion to toads.  The answer as to why keelback snakes are better able to deal with cane toads than the counterparts lies in the species’ biogeographic origin.  In Asia, keelbacks would have encountered Asian toads, something that Australian snakes would not have experienced, since Australia has no native toads.  These previous encounters between snakes and toads during the Pleistoscene and Miocene would have allowed the keelback to evolve their physiological tolerance to toad toxin, which enabled the current-day keelbacks to be better suited to tolerate the toxins of American toads, since the toxins are similar to those of Asian toads.  The snakes’ aversion to cane toads as prey, and their physiological tolerance to the cane toad’s toxins are pre-existing adaptations from the keelback’s ancestral Asian origins, rather than the result of the rapid evolution of adaptations since the toad’s arrival to Australia.

Llewelyn, J., Phillips, B., Brown, G., Schwarzkopf, L., Alford, R., & Shine, R. (2010). Adaptation or preadaptation: why are keelback snakes (Tropidonophis mairii) less vulnerable to invasive cane toads (Bufo marinus) than are other Australian snakes? Evolutionary Ecology DOI: 10.1007/s10682-010-9369-2

This post is a submission in a contest held by NESCent, in which two winners will receive a travel stipend to attend ScienceOnline2011.

Just who exactly benefits from copulatory plugs, anyway?  Mating plugs have been documented in a broad range of animal groups, including insects, arachnids, reptiles and rodents and range from a gelatinous substance in bees and nematodes, to a more solid, coagulated protein mixture in primates, or even the whole appendage breaking off in the vagina.  These plugs all act like a cork in a wine bottle, keeping the contents inside- in this case, sperm- and prevent the female from being able to mate with any other suitors.  The one thing that binds all the various compositions of copulatory plugs is the belief that copulatory plugs are exclusively beneficial to the male.

A new study on nematode worms by researchers at the University of Teubingen, Germany is shaking that assumption, indicating that copulatory plugs may be beneficial for the female as well.  The study, published in the journal Frontiers in Zoology, found that in the nematode worm Caenorhabditis remanei, the plug acts as a form of ‘gift’ as opposed to preventing the females from mating again as previously thought.  And what female doesn’t like a gift after sex?

The copulatory plug probably evolved under sperm competition conditions, as a way to limit males’ competition with one another- blocking their competitor’s sperm and ensuring their fertilization of the egg, allowing them to pass on their genetic material.  The plug may not be as effective at this function, as the presence of a mating plug did not hinder how many times the female mated, or how attractive she was to males. However, it did have a positive effect on egg production and number of offspring, with plugged females producing an average of 29 percent more eggs and offspring than their unplugged counterparts in the study.  Nadine Timmermeyer, lead author of the study, said, “We found that plugging has a significant positive effect on egg production, suggesting that plugs may represent a beneficial act of a male towards its female partner rather than a competitive act between males.”

Discussing possible ways that such a seal may benefit both males and females, Timmermeyer said, “A plug may act as a seal, keeping sperm inside the female and preventing the entry of harmful pathogens. It may also contain substances that stimulate the female, or that have nutritious or antimicrobial properties.”  These worms have one thing right- if you’re going to have sex, shouldn’t it be beneficial for both?

Timmermeyer, N., Gerlach, T., Guempel, C., Knoche, J., Pfann, J., Schliessmann, D., & Michiels, N. (2010). The function of copulatory plugs in Caenorhabditis remanei: hints for female benefits Frontiers in Zoology, 7 (1) DOI: 10.1186/1742-9994-7-28

Today Christie and I went to the Museum of Natural History.  We saw an exhibit on bodies and learned 5 interesting facts about the human skeleton that we never knew! Not only did BioRob2006 teach us that, but also taught us what happens when we get old.  Christie really liked Geoff’s human evolution and frameshift mutation explanation, saying that it was a “very interesting hypothesis about human departure from apes.”

In the next hall, there was a copy of The Primate Diaries.  The open page said something about how unicolonial ants pose challenge to “selfish gene” theory. Beside it was a Denim and Tweed wall plaque, illustrating how ants trim trees for more living space. The end of the hall had a big sign by Hoxful Monsters, showing a new tree of life, which suggests that the nervous system evolved only once in animal history.

We walked down to The History Cellar and saw Charles Darwin’s letters, in which Darwin reacts to a bad review of The Origin of Species.  The man standing next to us, who we later learned was Adam Goldstein, said, “Give the old man a break and let’s stop it with ‘Darwinism’.”

We then went to see the new movie at the museum, Three New Species Discovered–in the Stratosphere! GrrlScientist had suggested we go see it before she met up with us, saying “”Wow, THREE new bacterial species in the stratosphere! Where will we find new life next? Perhaps the Moon? Mars?”

Towards the end of our museum visit, GrrlScientist joined us and shared some insight and photos from her own research into the evolution and biogeography of the lories, which are parrots native to the islands of the South Pacific Ocean. Apparently dead birds do tell tales!

After we left the museum, GrrlScientist, Christie and I walked through Central Park, and we looked at all the birds that have returned for spring.  GrrlScientist told me, “human eyes speak volumes to birds, and that the birds will try to hide from our gaze.”  ”Ha!” I told her.  ”That may be cool, but I know something even more interesting.  Did you know birds can dance?”

We continued our walk through the park, and saw The White Sepulchre holding a sign that was only three words long, but by his account, was the best argument against Creationism ever devised.  It said “Serpents can’t talk.”

Afterwards, I met a few friends for drinks.  Andrew Bernadin suggested that I order endorphins on the rocks.  While we were sipping away, he told me about the plasticity of human nature, and that mating strategies are variable and influenced by culture.  While discussing male dominance, he quoted Franz de Waal and said “for males, this is an all-or-nothing game; rank determines who will sow his seed far and wide and who will not sow his seed at all.”  I told him that I recently read in The Primate Diaries that the importance of female choice is overlooked in chimpanzees. When we began talking about monogamy, Anna shared something really interesting–in birds, the more monogamous the species, the bigger the brain! Zen Faulkes said that this may not be the same case with humans, and told us about a recent study he read, the author theorizes that if you’re monogamous, you have a large brain to cheat. Jennifurret, decided to end the debate and reminded us of the diversity of mating strategies in the world.

As we left the bar, I was glad to be out in the warm air that came with May.  After all, I only just read in The Spittoon that researchers tie variation in cancer gene to winter temperatures.

We walked over to the Metamagician and the Hellfire Club, where we listened to Jerry Coyne on science organisations and accommodationism.  Afterwards, Jennifurret talked about the problems with some universities and teaching evolution in colleges.  Maybe we should tell the universities to hire The Southern Fried Scientist, who gets really excited by clear cases of convergent evolution. I bet he could do a better job of teaching evolution!

Oh crap! Is that the time??? Now it’s too late to go catch the Carnival of Evolution!  I guess I’ll have to catch it next month, over at Deep Sea News.

So you think dancing is just for humans?  Well up until recently, many scientists would have agreed with you.

“For a long time, people have thought that the ability to move to a beat was unique to humans,” said Adena Schachner of Harvard University, who led one of two studies published today in Current Biology.

It turns out, dancing is for the birds.  The two studies show that vocal-mimicking animals, particularly parrots, are able to dance–they can bob their heads, tap their feet, and sway to the beat of the music.

Don’t believe me?  The video below shows a cockatoo named Snowball dancing to his favorite song, “Everybody” by the Backstreet Boys.  When the researches changed the tempo of the music, Snowball would adjust the tempo of his dancing so stay synchronized with the music.

The theory was that natural selection for vocal mimicry resulted in a brain mechanism that was also needed for moving to a beat, and that only animals that can mimic sound should be able to keep a beat.

One of the two research teams watched over 1,000 videos of dancing animals on YouTube, and analyzed the videos frame-by-frame.  Potentially fake videos were omitted, in which the animal was following a visual cue or the music was added in during post-production.

“Our analyses showed that these birds’ movements were more lined up with the musical beat than we’d expect by chance,” says Adena Schachner, a researcher in the study, in a press release. “We found strong evidence that they were synchronizing with the beat, something that has not been seen before in other species.”

Only the vocal mimics (14 species of parrot and 1 species of elephant) showed evidence of being able to keep a beat.

The researchers now suspect that the parrots’ dancing skills are related to another ability they share with humans, vocal learning, implying an evolutionary link between the two abilities.  This suggests that keeping a beat to music relies on the neural circuitry for complex vocal learning, which requires a tight link between auditory and motor circuits in the brain.

“Our data suggests that some of the brain mechanisms needed for human dance originally evolved to allow us to imitate sound,” says Schachner.

The human ability to keep time with music may have also evolved as a byproduct of vocal mimicry–the cognitive processes needed for both actions are related.  Both abilities require you to take in auditory input, and monitor your output and sound input at the same time, which allow you to fix your output and line up better with what you hear.

So what I want to know is….where do I sign up for a job like this???

Aniruddh D. Patel, John R. Iversen, Micah R. Bregman, Irena Schulz (2009). Experimental Evidence for Synchronization to a Musical Beat in a Nonhuman Animal Current Biology, 19 (10), 1-4
Adena Schachner, Timothy F. Brady, Irene M. Pepperberg, Marc D. Hauser (2009). Spontaneous Motor Entrainment to Music in Multiple Vocal Mimicking Species Current Biology, 19 (10), 1-6

Imagine you’re sitting down to a family dinner with your siblings, you’re a vegetarian, and your older, bigger, bullying brother just won the fight for the mashed potatoes and ate the last of them, and now the only thing left on the dining table is chicken. Sure you could eat chicken, but it would be difficult for you. Well, that’s sort of how life is for Africa’s large carnivore species, especially for cheetahs and African wild dogs.

African wild dogs and cheetahs, the smallest and most endangered of Africa’s large predators, have the greatest dietary overlap of all African carnivores, as well as the smallest number of prey species to choose from. Both species predominantly dine on Thomson’s gazelle and impala, two small species of ungulate. The risk of extinction increases when a species has fewer food options. Larger carnivores such as lions, spotted hyenas and leopards have more options in their prey, minimizing competition and giving them a more secure status.

Researchers from Nelson Mandela Metropolitan University (NMMU) in South Africa recently conducted a study on prey preferences and dietary overlap amongst Africa’s large predators. The species in the study were leopards, lions, spotted hyenas, cheetahs and African wild dogs. The conservation status of each species into was taken into account during data analysis, which served as a method to estimate the number of surviving individuals within each of the five carnivore species studied.

The researchers found that almost three-quarters of the actual diet for African wild dogs and cheetahs overlapped, the greatest amount of overlap between any of the other large carnivores. The overlap for the preferred diet of these two species was also over 70 percent.

When the scientists looked at the data in comparison to the conservation status of each species, they found that the smaller the dietary options available to a species, the more endangered that species was. Leopards, who have the broadest range of prey to choose from, are of the least conservation concern.

The evolution of Africa’s large predators is now negatively affecting those who evolved to become more specialized. African wild dogs and cheetahs, which have the fewest number of prey options, are also the most threatened, and also suffer from the greatest amount of dietary overlap.

The current theory is that competition with and predation by lions and spotted hyenas forces African wild dogs to exist at low densities. Long-term data shows that the wild dogs were most abundant in the Serengeti during the 1960s and 1970s, when lions and spotted hyenas were more scarce. Over the next two decades, as lion and hyena populations doubled, the African wild dog population declined up until local extinction. The recent findings in the study at NMMU suggest that food limitation may have been a factor in the extinction of the wild dogs in the Serengeti. The decline of the preferred prey species of the wild dogs placed them under greater pressure, and they ultimately went in extinct in that location.

African wild dogs also suffer from human persecution, habitat loss, disease and competition with lions and spotted hyenas. The larger predators interfere with the wild dog’s kills, in addition to lions actually killing the dogs themselves.

Cheetahs suffer from habitat loss, exploitation human interference, disease, predation as well as other predators stealing their food. Habitat loss is their greatest threat, because it reduces the availability of suitable prey species and thus reduces their success in hunting. Competition with other predators also threatens Cheetahs in the Serengeti, where lions kill cheetah cubs.

Cheetah cub mortality depends on the mother’s vigilance and anti-predator behavior. When the mother has to spend more time hunting because of fewer suitable prey options, she has less time to protect her cubs. The same holds true for African wild dogs. The more effort they have to put in to taking down prey, the fewer guard dogs they can leave behind to guard the pups.

Food limitation, and competition for resources between species can now be added to the list of threats for African wild dogs and chetahs, particularly in conservation areas that are free from habitat alteration and human persecution, but where management strategies have led to unnaturally high population densities of all predators found there, which reduces the availability of food.

Conflict with humans restricts large carnivores predominantly to conservation areas. But in clumping the carnivores together in one area, it increases the likelihood that they will have to compete for resources, such as prey, by creating artificially high population densities, and may eventually lead to further extinctions.

The successful management of conservation areas is crucial to ensuring that further extinctions do not take place.  One way to do this is to vary the prey species in the conservation area, and to make sure that the preferred prey species of the more threatened carnivores are available at all times.

By keeping an eye on things and actively engaging in the management of conservation areas, we can ensure that they only serve to booster endangered populations, rather than cause further damage.

Hayward, M., & Kerley, G. (2008). Prey preferences and dietary overlap amongst Africa’s large predators South African Journal of Wildlife Research, 38 (2), 93-108 DOI: 10.3957/0379-4369-38.2.93

How do people show their devotion to Darwin?  Tattoos of course!  

Photos courtesy of Carl Zimmer’s blog, The Loom.  Check out the entire Science Tattoo Emporium.