Archive for April, 2010
From Discovery News:
Why did the rattlesnake cross the road? It didn’t, says new research, and that may be a problem.
New DNA analyses of rattlesnakes in New York State finds that even minor roadways deter snakes from crossing the road to breed. Populations are becoming isolated from each other by roadways, which may threaten their future.
“We worry for the health of these populations because connectivity is so key to responding to environmental pressures and avoiding inbreeding,” said Rulon Clark of San Diego State University, who led the study published in Conservation Biology. The reduced genetic diversity that results from inbreeding makes populations less resistant to diseases or other disturbances.
Groups of up to dozens of rattlesnakes hibernate together in common dens, which serve as a home base. Come spring, they leave to hunt, and males strike out for neighboring dens to mate with females before returning to their home dens for winter.
The males’ visits to nearby dens provide the genetic mixing necessary to keep a population from becoming inbred.
Clark and colleagues wanted to test whether roads were affecting the males’ mating journeys. They collected blood samples from timber rattlesnakes in 19 different dens in different regions of New York State, including dens separated from each other by roads and others with uninterrupted forest between them.
The researchers analyzed selected gene sequences that mutate quickly from generation to generation to determine how related different snakes are to each other and whether certain dens are mixing with others.
The team found that dens without roads between them acted as a single, connected population, while populations separated by roads showed signs of significantly reduced mixing.
“These roads have been in place for maybe nine or 10 timber rattlesnake generations,” Clark said. “That’s not a long time, but even in that relatively short time frame, we found some very strong patterns. It’s somewhat disturbing to see how quickly the populations lose genetic diversity when they become isolated by these roads.”
Other studies have found that species including bobcats, coyotes and bighorn sheep also change their behavior to avoid roads, with consequences for gene flow. But rattlesnakes may be particularly susceptible, because they avoid roads, and when they do try to cross, the consequences are often fatal, Clark said.
“When they do venture across, they move extremely slowly,” he said. “If they’re disturbed by noise or vibration, their natural response is to freeze and rely on their natural camouflage to hope they won’t be detected. With cars, that’s exactly the wrong response.”
It may be possible to help male rattlesnakes complete their conjugal journeys by building underpasses with surrounding fences that help shepherd the snakes under the roads, the researchers note. Appropriately timed road closures during the migratory season could also help.
Kenneth Dodd of the University of Florida in Gainesville agreed that roads are a threat to wildlife, especially snakes, and that methods to help animals cross roads safely should be implemented.
At the same time, Dodd thinks other forces are at work in explaining the genetic differences among rattlesnakes in this area. Dodd was part of research that analyzed some of the same dens as the new study but found less dramatic effects.
“It’s more complicated,” he said. Small population sizes and localized differences in habitat and topography may also be contributing to the separation of populations, not just roads, he explained.
“We believe that the roadway contributes to genetic structuring of the population, but it is not the sole driving force.”
Yes. I know it didn’t say a word about West Virgina, but not only is the timber rattlesnake our only endemic rattler, it is our state reptile.
In retrospect, I don’t know if that was the best choice. It is hard to get people to appreciate a place that celebrates a venomous reptile.
Then this article really steps in it:
The timber rattlesnake was selected for the state reptile designation by a group of Hampshire County Middle School students. Their teacher tells me he would have picked the box turtle. However, the rattler isn’t a bad choice. Aside from the obligatory snake-handling church jokes it might generate, the timber rattler is a lot like a true West Virginian.
The timber rattler is generally not aggressive, but when you mess with one–be ready for a fight. The rattler lives its life in rugged confines and is an apt mountain survivor. The rattler is often reviled and misunderstood, but always commands respect.
Yes, and they are apparently quite inbred because they won’t leave the hollers where they were born. Do we really want to have that animal representing our state?
I was hoping they had a good reason to make them the state reptile. Maybe it would make people appreciate them more and not want to shoot them or chop them up with hoes and shovels (a very good way to get bitten).
I just hope they make the mountain cur the state dog. One politico wants the beagle (which is from England!) to be the state dog. The mountain cur fits the bill very nicely, and it’s native to the Trans-Allegheny West and the Ohio Valley.
All joking aside, this article shows that there are real consequences to reduced genetic diversity in the wild. These timber rattlesnakes are very much like breeds in a closed registry system, and the biologists are very worried that they could suffer some problems from their depauperate gene pools.
If biologists think about these issues when dealing with the conservation of wild animals, why is it so hard to get dog people thinking about them?
I suppose it is an apple to oranges problem. These snakes represent biodiversity, and they have some role in the ecosystem. Dogs are mostly pets. They have no utility beyond the emotional benefits they give their owners.
But if we are thinking about this long term, dogs and timber rattlesnakes aren’t that different. They are both organisms with genes. They are animals that are still subject to Darwinian pressures, even if we shield dogs from most of them. Dynamic gene pools allow animals to survive changes in the environment. That’s why sexual reproduction evolved. This type of reproduction creates diversity that allows these animals to be more resistant to these changes.
Of course, I’m not predicting some collapse of domestic dogs that result from environmental changes or epidemics. But it is a possibility. And at some point, reduced genetic diversity leads to very low levels of fertility. And then dogs would become like giant pandas or cheetahs. I hope it doesn’t get that bad, but that is where this will all lead if we are not careful.
And then we’ll have to find some other canid to domesticate and turn into a new dog. Black-backed jackals get my first vote, and bray foxes get my second. (Modern wolves are just too hard for the average person to handle, so I don’t think we should consider them. And coyotes are paranoid. Not good candidates at all.)
Of course, I hope it never comes to that.
But if we can worry about genetic diversity in a poisonous snake, I think we at least owe it to our dogs to at least give the diversity and sustainability of their gene pools some consideration.
Now, I would be remiss if I didn’t mention another aspect of West Virginia’s relationship with the timber rattlesnake.
I don’t know if you’ve heard of these churches, but we have congregations in West Virginia that pick up snakes. Because these are Pentecostal churches, there is a lot of movement going on (and speaking in tongues). When you add people holding venomous snakes, it gets a little interesting.
And before you start stereotyping, Obama beat McCain there.
West Virginia is a complex place. It gives some of us complexes.
I’ve been looking into the black-backed jackal this week. At first I was checking into the possibility that they can hybridize with domestic dogs.
I am still skeptical that they can.
However, what I have found about this species is they are quite strange.
There are two populations of this species that are not contiguous. One exists in southern Africa, and the other exists in East Africa. The East African subspecies is larger than the southern African or “Cape” subspecies. It also does not howl and has a more carnivorous diet than the other subspecies. (The only howling jackal in East Africa is the golden jackal).
I have heard people claim that both of these are good enough reasons to consider domestic dogs a separate species from the wolf, but because we’re dealing with two subspecies of a jackal, an animal without all the cultural baggage the dogs and wolves have, it is universally accepted that these both represent Canis mesomelas.
Now, that was weird enough.
It turns out that the East African subspecies has rather amazing variance in its mtDNA sequences. Contiguous populations have been found to have as much as 8 % variance in that part of their genome. That’s a lot, and the questions it has raised have not been answered. We do not know why there is so much variance within this single subspecies.
If I were a molecular geneticist, this is the dog species that would have my attention. After all, the dog genome has been decoded, and we are starting to find answers about the evolutionary relationship between dogs and wolves.
No one has answered these questions, and because it is now accepted that the black-backed jackal and the side-striped jackal are the oldest members of Canis, these animals might have a lot to tell us about the other species in this genus.
Black-backed jackals are much more aggressive with other jackals and with each other than either golden or side-striped jackals, and although they are capable of killing larger prey than themselves because they just that bold.
In essence, a black-backed jackal is a naturally occurring Jack Russell terrier.
They are also probably the first species of the genus Canis with which hominids and later modern humans would have had some familiarity. These are probably the first “dogs” to scavenge off of hunter-gatherer kills.
Yet no studies have found that these animals have contributed to the dog genome. There are plenty of dogs in East and Southern Africa that look like black backed jackals, and some traditional societies call such dogs “jackal-dogs.” I have not heard of any verified hybrids between these two species, although they are often speculated.
I don’t think I can believe until I see a study that shows a definite hybrid, because I think what we’re seeing here is that jackals and dogs are developing similar conformation in what is called parallel evolution. Both of these animals live in the same habitat and both share a common ancestor. However, the ancestor for the dogs was the Eurasian wolf, which evolved from different line of the ancient Canis species. When the two species have to live in the same habitat and eat the same food, the Eurasian wolf derived species begins to develop adaptations and phenotypes that are similar to the native East and Southern African species. (This differs from convergent evolution because convergent evolution is when two entirely unrelated species develop similar features and adaptations– like the wolf-like canids and the Thylacine.)
Now, that’s the established view. This is also pretty much what I think is happening here.
However, I was confronted with a study that did make me scratch my head.
In South Africa’s Western Cape Province, bones dating to the later Stone Age that were assumed to be domestic dogs , simply because of their proximity to human settlements. When the DNA was tested, these “dogs” all turned out to be black-backed jackals. That means that humans have had a relationship with Canis mesomelas that could have become like the relationship between humans and the wolves that became dogs.
It is also possible that there were populations of black-backed jackals that were semi-domesticated before the arrival of wolf-derived domestic dogs. When these dogs arrived, they replaced the semi-domesticated black-backed jackals as the most common canids in the camps.
That we have never been able to fully domesticate these jackals is another big question to the Coppinger hypothesis, because it is very likely that these jackals have been relying upon human kills and the excesses of civilization for a very long time. Yet there is no evidence of fully domesticated form of black-backed jackal, which would definitely be genetically distinct from the wolf-derived domestic dogs.
Now, I found all of this out through a discussion on the blog and through e-mail with a reader who has seen golden jackals and dogs live in close proximity in India. This reader is skeptical of the evidence that dogs are derived from C. lupus and thinks that jackals did play some role. I am willing to admit that the golden jackal and Ethiopian wolf may have played some minuscule role, as could the coyote. However, black-backed and side-striped jackals probably did not.
I am open to the possibility that such hybrids exist, but I want proof n terms DNA evidence. I know these “Africanis” dogs look like jackals, but as we have seen time and again, looks alone cannot indicate that sort of relationship.
I want to thank Gurjinder Sahota for alerting me to these studies, and at least opening my mind about the possibility that black-backed jackals could hybridize with domestic dog and that jackals might be an ancestor of the domestic dog. Most of the links in this post actually come from our discussions on this blog and via e-mail.
Although I was aware that East African black-backed jackals had wide variance in their mtDNA sequences, I had no idea that ancient African dog remains have been found to be black-backed jackals.
I think the really big question is why black-backed jackals were never turned into true domestic animals. I think the big reason may have to do with their heightened aggression towards their social partners. I don’t think hunter-gatherers would tolerate that sort of aggression in a pet , which is one reason why I think the original wolf populations were far less aggressive towards their social partners than modern wolves are now. Further, both wolves and men had similar ecological niches, which is the basis of Schleidt and Shalter’s theory about the co-evolution of man and dog.
To me, this questions all lead back to one major conundrum:
Why wolves and not these others?
I still think there is a chance that a semi domesticated “dog” derived from black-backed jackals may have existed in southern Africa.
This is in the city of Braşov.
This wolf bitch raises her litter without a mate or helpers.
Because she is not entirely paranoid about people, she can utilize the excesses of our civilization to raise her offspring.
Do you think this might have say something about the benefits of domestication for the ancient Canis lupus who joined forces with us?
Of course, hunter-gatherer camps really didn’t produce that kind of excess waste, but if a bitch wolf had her pups near a human camp in order to scavenge off of the humans, her puppies could easily be taken as pets.
Pet keeping is nearly universal among people– including hunter-gatherers.