Advertisements
Feeds:
Posts
Comments

Archive for the ‘wildlife’ Category

guatemala black howler

Hybridization between species is aspect of evolution that is only just now becoming recognized as a force in evolution. It is sort of taking a biological app from one species and adapting it another, and most studies on this phenomenon look at the app adaptation aspect of hybridization.

However, hybridization is more often than not less advantageous from a natural selection standpoint. Although these “new apps” and heterosis might be good for hybrids, many hybrids are sterile. Or if they aren’t sterile, one sex will either be absent or sterile.

Species generally have mechanisms that prevent hybridization. Many of these are behavioral.   For example, related bird species often won’t exchange genes because the female are simply not attracted to the males’ songs.  But there are molecular responses against hybridization as well.

One of the most contentious hypotheses about hybridization between species is that of reinforcement. What this hypothesis contend is that when two species begin to hybridize readily, there will be a strong selection for greater genetic distance between the two hybridizing species. With greater genetic variation, it will be less likely that the two species will be able to produce viable offspring, and over time, there will be fewer hybrids in the population.

This hypothesis has not been tested much. However, a study of two species of howler monkey in the Mexican state of Tabasco revealed that, yes, reinforcement is a thing.

Mantled and Guatemalan black howler monkeys diverged from a common ancestor about 3 million years ago. The two species have only a narrow contact zone, which is thought to have formed only 10,000 years ago in this tiny part of Mexico.

The researchers examined loci of the genomes of specimens of both species, including those in the hybrid zone. They found that the genetic difference between the two species was greater at the hybrid zone than from monkeys that lived in other regions. This discovery supports the hypothesis of reinforcement.  The greater genetic difference between the two species at the hybrid zone means that this greater genetic difference likely has evolved as a way of keeping the two species from producing lots of hybrids, which might not be as fit or  as good at reproducing in the wild as pure ones.

This discovery of reinforcement means that we have another tool in sorting out whether two species make sense. If we discover that there is greater genetic difference at a hybrid zone between the two species, then we know that they really are quite taxonomically distinct.  If we find the opposite, it means that hybrids aren’t deleterious in the population, and hybridization is either advantageous or neutral for the populations.

Yes, I would like to see this hypothesis tested on the various hybridizing canid populations in the gray wolf species complex. My guess is that it doesn’t exist in these animals, because hybridization isn’t that deleterious. And the genetic divergence isn’t that great to start out with.

But this study gives us a good idea of how hybridization operates in populations, and how some populations evolve to restrict gene flow.

Advertisements

Read Full Post »

cheetah

India’s supreme court is now seeing an interesting case in which taxonomy and endangered species politics converge to have real world consequences. The question is whether African cheetahs can replace Asiatic cheetahs on India’s plains.

Yes, for there were once cheetahs in India. Their traditional quarry was the blackbuck antelope, and many nobles in India kept cheetahs or “hunting leopards,” as the British colonizers called them, for coursing blackbuck.

Cheetahs were not just found in India.  They ranged throughout the Middle East up into the Caucasus and Central Asia. In the wild, this lineage of cheetah is found only in Iran, where they exist in only relict numbers.  In Iran, the situation is made even more complicated with an international human rights scandal in which several cheetah researchers were imprisoned.  Cheetahs have since been extirpated from all of Asia, except for that tiny Iranian population.

So India, a nation with growing wealth and a growing conservation ethic, cannot turn to Iran to reintroduce its former cheetahs.  With Iran out of the question, some experts have suggested that African cheetahs be used as stand-ins.

And this is where things get interesting. African cheetahs are not exactly like the ones in India. There is a bit of a debate about when the two lineages of cheetah split, with one set of papers and researchers suggesting a very recent split (5,000 years ago) and another suggesting a more ancient one (44,000-47,000 years ago).

40,000 years suggests way too much evolutionary distance between the two cheetah populations for African cheetahs to be equivalent of the Asiatic ones.

But even if we accept this later date, it is still not that much of a divergence. Currently, most experts recognize only a single species of red fox, but Old World and North American red foxes diverged 400,000 years ago.

African cheetahs have evolved to hunt on open plains. Various small antelopes comprise the majority of their diet. They are not ecologically that different from cheetahs that lived on the plains of India.

So they aren’t that genetically distinct from each other, and they aren’t ecologically that different either.

It would make sense to bring African cheetahs to India. Of course, the legal system and the interpretation of statutes often goes against sound conservation policy.

But if cheetahs are ever to return to India, the question is now in the hands of India’s supreme court.

I hope they decide that those from Africa can stand in. They are far from exact, but they are far from ersatz.

 

Read Full Post »

black squrrel

As long-time readers of this blog know, the black coloration seen in North America and Italian wolves and in coyotes originated in domestic dogs. Indeed, the black coloration in North American wolves originated from a single introgression of a black domestic dog in the Northwest Territories or the Yukon between 1,598 and 7,248 years ago.  Of course, we now know that there is significant gene flow between dogs and certain populations of gray wolf and that this gene flow has been going on for some time.

I have often wondered about color genetics and gene flow between species. One species that is particularly beguiling for speculation for me was always the origin of melanism in Eastern gray squirrels. Melanistic Eastern gray squirrels are more common in Ontario, Quebec, and Michigan, but there are isolated populations south of these locations.

A new paper just published in BMC Biology revealed that melanism in Eastern gray squirrels most likely had its origins from hybridization with the fox squirrel.

Melanism has evolved twice in fox squirrels. The melanistic ones in the Southeast have a mutation called ASIP A3.  Melanistic Western fox squirrels have a mutation that causes a deletion in the MC1R. This allele is called MC1R∆24.

What is interesting is that melanistic Eastern gray squirrel have the same mutation.

The authors contend that the most likely explanation for this shared mutation is hybridization between fox and Eastern gray squirrels, although ancestral polymorphisms and earlier hybridization between gray squirrels and fox squirrels cannot be ruled out as possible origins either. However, The authors think it originated in fox squirrels because it resembles other fox squirrel MC1R haplotypes.

This finding is pretty interesting because I live where both species are common, and I use to live where there were lots of black gray squirrels.  I had read accounts of fox squirrels mating with gray ones, but the accounts I read said that no offspring resulted from the mating.

I assumed that the two species could not hybridize, and I still have not seen any literature that even suggests hybridization could occur until I read this paper.

More work is going to be needed to see exactly how this mutation originated and if there are other traits that originated in one species that now are found in the other.

And yes, there is that old wives’ tail that says that gray squirrels castrate fox squirrels to reduce the competition. What actually happens is that when squirrels are hunted in the early part of the season, the testicles shrink in size, so that they appear to have been castrated.

But I have never heard of these two species hybridizing. Indeed, it may be that the hybridization that transferred that particular mutation onto Eastern gray squirrels happened far back in the evolutionary history of both species, when they were still chemically interfertile.

However, they might still be able to hybridize. It is just that no one has ever documented a true hybrid between the two species.

But I am certainly open to the possibility.

So it is likely that black gray squirrels resulted from introgression, just as black wolves and coyotes do.

Read Full Post »

narwhal hybrid.png

a: beluga skull b. “narluga hybrid” c. male narwhal skull.

In the 1980s, an Inuit subsistence hunter in Greenland killed three gray whales that looked suspiciously like belugas at first. However, they were oddly gray. The fins resembled a beluga’s, while the tail looked like that of a narwhal.

The hunter kept one of the skulls, eventually donating it to science, where became the property of the Greenland Fisheries Research Institute. A scientist working for that institute, Mads Peter Heide-Jørgensen,hypothesized that this skull came from a hybrid between a narwhal and a beluga.

It was only today that a study was released in the journal Nature that revealed that this whale was indeed a hybrid. The DNA analysis revealed that male beluga mated with a female narwhal to produce the creature.

The skull was quite strange. Belugas have 40 homodont teeth. Narwhals are toothless, except males. The males have one really long canine tooth that sticks out as a tusk. Sometimes, they have two, but most have only one true tooth. It is spiraled like what is expected form the mythical unicorn. They do have only a few vestigial teeth.

The hybrid had 18 teeth, many of which were pointed out horizontally and spiraled like the vestigial teeth of the narwhal.

Isotopic analysis also revealed that the hybrid had a different diet from either parent species, both of which catch fish or squid in the open water. The beluga hunts fish at depths of up to 500 meters, while the narwhal hunts fish or squid at depths exceeding 800 meters. The isotopic analysis revealed that the narluga was eating mostly benthic prey, which means it was eating mostly shellfish from the sea floor.

So this study raises so many questions. Analysis of the narwhal genome revealed that gene flow between the two species stopped between 1.25 and 1.65 million years ago. The initial split happened around 4 million years ago, and that study thought that an viable hybrids would be unable to reproduce. However, the authors of the study cautioned that a larger sample size of individual narwhal and beluga genomes from across their range might reveal more recent dates on when gene flow stopped (if it did at all).

So it is not entirely clear that this hybrid would have been sterile, but we also have no further evidence of hybrids anywhere else.  It is quite possible that these hybrids could be fertile, and if they are, climate change could cause the eventual genetic extinction of the narwhal.

The morphology and feeding behavior this odd whale might point to the origins of the narwhal. Perhaps the ancestral narwhal was a benthic feeding whale that later lost its teeth to become a whale that hunts squid and fish at great depths with an almost toothless mouth.

Having teeth like the hybrid is a great adaptation for this particular diet, because the forward pointing teeth can poke around and dislodge shellfish more easily.

If these hybrids are fertile, then one could see the eventual development of a hybrid whale species that has its own niche as a benthic feeder in the arctic.

It is an amazing find, and chances are there will be more discovered. Further, as scientists examine genomes from belugas and narwhals from a wide geographic distribution, we might see evidence of some hybridization.

Hybridization could also increase genetic diversity in narwhals, but if these hybrids must eat a fundamentally different diet than narwhals do, it might become difficult for these hybrids to add their genes to narwhal populations. They just cannot hang out for extensive periods of time, before they have to split off and engage in divergent feeding behavior.

So this discovery does generate lots of speculation and raises several important questions that need to be addressed.

Pretty cool.

Read Full Post »

lined seahorse

Seahorse always fascinated me. When I was a kid, we’d go to the souvenir shops at the beach in North Carolina, and of course, there would be many shells and sand dollars to buy. And you could pick up a dried-out seahorse. The racks would be full of dried out seahorses, hundreds and hundreds of them.

I never really thought about seahorses as being potentially threatened by anything. My child brain could not fathom how much trouble they could be facing.  But even those species that live off the coast of the United States and Canada are under threat from pollution and over-development. They are also in demand for Chinese traditional medicine, and with the Chinese economy growing as rapidly as it has for the past few decades, this demand has only increased the pressure for both species.

Two species found in the Western Atlantic are the lined seahorse (Hippocampus erectus) and the longsnout or slender sea horse (H. reidi).  The lined sea horse has a more northerly distribution than the longsnout, but their ranges do overlap from North Carolina to Venezuela. The two species do not readily hybridize in the wild, though they certainly have done so in captivity.

With the lined sea horse being listed as “vulnerable” by the IUCN and the longsnout as “near threatened,” there are real conservation concerns for both species, and they are indeed being bred in captivity now with hopes of giving a boost to the dwindling wild populations.

However, these two species are often housed together in aquarium and zoos, and they have interbred.  A recent paper in the Journal for Zoo and Aquarium Research has identified a simple molecular technique for identifying hybrids in captive populations, but the paper also notes the possible issues with hybrids.

The obvious problem is that conservation plans for restoring species are designed to restore a particular species, not hybrids between the two. Yes, this is the big boondoggle behind conserving species that hybrid with another, but it is one thing to have hybrids readily occurring in the wild. And it is quite another if hybrids largely exist because of aquarium practices.

So the authors urge zoos and aquariums to stop putting these two species together and to work much harder at maintaining “purebred” populations of each species.

However, the authors point out that the hybrids could be useful for conservation in another way. With improved seahorse husbandry techniques, various farms could potentially breed populations of hybrid seahorses and fill the needs of the growing Chinese market.

These two species may have split from their common ancestor over 14 million years ago, but hybrids between fish species can happen between species that have been divergent for many millions of years.

Humanity’s effects upon the ocean have been greatly underestimated.  Much of what has happened to the ocean has been out of our sight for so long that we assumed that all was fine.

But future for many species of seahorse is not secure at all, and if we are to be proactive and work on restoring diminishing stocks of various species, we must work on controlling potential problems that can come from hybridization in captivity.

So for conservation purposes, we must try to keep strains distinct for those that could be released into the wild, but for the Chinese medicine market, breed the mutts.
,

 

Read Full Post »

This video was posted on an outdoor channel in Eastern Washington:

This guy is a good naturalist, and he has excellent trail camera placement.

But what he’s actually seeing are not hybrids. What he is seeing is the wonderful transition from the mule deer type that is common in the interior West to the black-tailed deer type, which is common more toward the Pacific Coast.

Those two deer are now recognized as a single species (Odocoileus hemionus), though the mule deer type is recognized to have some hybridization from the white-tailed because it possesses white-tail-like mitochondrial DNA.

Hybridization does occur between white-tails and mule deer, but the survival rate is quite low among the F1s. Mule deer have a stotting evasion behavior, which is incompatible with the white-tail’s bounding pattern. The offspring inherit both behaviors, and they cannot effectively evade predators.  The stotting behavior is used to communicate to a predator that might be hunting the mule deer on the open range that this deer awfully healthy and that it should try a different target. White-tailed deer are forest deer, and they just bound away from predators.

But apparently, there was an introgression of a white-tailed deer matriline into what became mule deer at the Pleistocene/Holocene boundary.

So this transition from true interior West mule deer to the Pacific blacktails apparently starts in Eastern Washington, and of course, you’re going to see the transition somewhere. These two forms interbreed because they are subspecies, and at some point, you’re going to hit the transtional zone between the two, where it gets hard to tell which is which.

 

Read Full Post »

The 17-year-cicadas (Magicicada) are coming out this year in this part of Ohio, as well as the Northern Panhandle of WV and parts of Western PA.  They emerged last night on our lawn and began their adult form on our silver maples.

(All photos by Jenna Coleman).

magicicada 2019

The discarded exoskeleton of the Magicicada nymph:

magicicade nymph husk

An adult one is bursting through its nymph exoskeleton.

bursting throuhg the exoskeleton

The adult exoskeleton is pasty and takes a few hours to harden into black.

pasty exoskeleton magicicada

hardened into black

Our maples are covered with discarded nymph exoskeletons, drying adults, and adults that are almost ready to start whirring in the trees.

maples coavered

The adult form is so oddly ugly that it is beautiful.

magiicada

magicada 2

magicciada 3

These cicadas have a life-cycle based upon brood. They spend 17 years underground. When that time comes in late May, they climb up out of the ground and begin mating and laying eggs. Their will be whirring loudly from the trees in a couple of days, and by the end of June, you won’t see a single one. This reproductive strategy is meant to overwhelm their many predators with so many easy targets that more than a few will manage to reproduce.

This blog covered another Magicicada outbreak in 2017, but that was a different brood. This one is Brood VII. That one was Brood V. 

So we are ready for the weird noise of these cicadas as they complete their final life stage.

And we will soon be tired of it.

 

 

 

 

Read Full Post »

Older Posts »

%d bloggers like this: