Trend Towards Splitting Species

With my new-found access to this wide cross-section of people knowledgeable about animals, I want to get your opinions on a topic that I have often pondered and debated with my brother. (He's an evolutionary biologist; I'm a computer programmer.) That topic is my belief that scientists tend to split species too often.

I'm new to the forum, so please tell me if this topic is not appropriate or if I should have put it in a different section. "Wildlife" seemed like the closest fit.

With my interest in zoos and birding, I have often contemplating the lumping and splitting of species. It seems to me that the trend lately has been to split, and DNA testing is usually cited as the justification for the split.

However, with my cynical nature, I have to question some of this. Scientists trying to build a reputation for themselves can do so faster by publishing an article that says, "the people before me were wrong; here's how it really is...." If they do a study that merely confirms a previously-held belief, they are less likely to get published or noticed.

Now don't get me wrong - I hold scientists in high regard, and I believe that a higher percentage of scientists are ethical than of the general population. I just think that subconsciously, people are more likely to look for a reason to change than to look for a reason to stay the same.

The two pairs of species I tend to use as examples in these discussions are Tufted Titmouse/Black-crested Titmouse and Sumatran/Bornean Orangutan.

The titmice are visually identical except one has a black crest and the other has a black spot between the eyes. In the narrow band where they overlap (and where I happen to live), they hybridize readily. Their vocalizations are similar enough that I cannot tell them apart, although I am not trained in what I should listen for. But since this is a zoo forum, let's focus on the orangs.

Ten years ago when I first started learning about taxonomy, most sources I found listed orangutans as a single species with two subspecies - Bornean and Sumatran. Nowadays, every current source I've found lists them as separate species.

The idea of some level of separation makes sense given that they live on separate islands and never mix in the wild, so they have evolved separately for a long time. But full species status does not make sense to me. In captivity, they readily breed and have fertile offspring. In the wild, if we took a bunch of Borneans and dropped them into the Sumatran forest, I assume they would mix in and happily make hybrid babies.

They even look alike to me. I've seen diagrams showing how the adult males differ, but not once have I been able to see the differences in live animals. Not too long ago I stood in a zoo that had both side-by-side, and I couldn't see the differences. Perhaps that's because most captive orangutans are likely hybrids and I have had no exposure to pure-breeds.

So I am interested in your opinions on a few things:

1. Specifically with orangutans, do you think separate species are warranted, and are they visibly distinguishable to you?

2. How much weight should genetic testing have in determining speciation vs. other factors such as ability to produce fertile offspring? What other factors should be considered?

3. Do you agree that the trend is to split, or are you noticing a considerable amount of lumping lately that I have missed?

4. Other than the recent developments in DNA testing and my cynical view that people look for change, are there other factors that are driving the splitting trend?

 

I would say here in Europe we do consciously separate both Bornean and Sumatran orangs when considering for breeding programs. Your suggestion of hybridization being a fate of all captive orangs is thus not justified. Ofcourse a portion of the captives are hybrids and these are more or less now prevented from breeding (save for a few "less" ethical zoos).

Having said that the issue of the ease of hybridization of both Sumatran and Bornean has puzzled me also for a good number of years. The rigid notion is that full species status prevents any hybridization more or less. However, looking at the evolutionary process and conditions driving a need to rapidly evolve / adaptability in species in order to survive even that notion gets to become an ... argumentative option open to debate.

 

Seperate animal-species which look alike because science has found out their DNA differsis in my opinion justified because the DNA tells us there is a difference. This can be in behaviour, voice, even smell or other thing not visible to us but prop. noticeable for the species involved !
In captive populations it therefor would be wise to keep them apart because mixing the different DNA-lines can have negative effectes for example forming mutations.
By the way, species-explosions by new DNA-research and difference in voice have happened recently by Bushbaby's, Mouse lemurs and several Frog-species.
For conservation-efforts it's becoming not easier but as said, let's try to keep them seperated if it's possible !

 

Very debatable topic, and very variable for each taxon I think. I very much believe that the Orangs should be separate species, as they actually have different numbers of chromosomes, which is a pretty important difference IMHO. Physical differences visible to basic human observation (as opposed to detailed study) are not a good indicator of taxonomic difference.

Of course, the amount of difference required for speciation depends on the species concept being used. Many scientists have rejected the Biological Species Concept (that species are reproductively-isolated populations), as it is too broad (or even too narrow for some taxa).

Much splitting has occurred recently, but this is (I think) mostly because DNA technology has allowed us to obtain much more information than was previously available, leading to better understanding of populations and species. In some cases it has revealed that two species are actually one, but in most cases the opposite is true.

I think you are being a little cynical, although in some cases splitting is excessive, and driven more by a need to split (whether for good, e.g. conservation benefits, or bad, e.g. more publications) than actual strong evidence. I think overall that I'm on your brother's side

 

Sorry if I gave the wrong impression. I was suggesting that hybridization is a fact, not a fate. We can control the future, but not the past.

I know that for the past few decades zoos have made an effort to keep the two groups separate. But for centuries prior to that, many institutions and individual collectors allowed they to mix. Also, I assume that most orangs in zoos were captive-bred from parents who were captive-bred. If that is true, then most captive orangs would be hybrid to some extent.

Of course, may assumption may be wrong. Perhaps we've rebooted the breeding program with wild-caught individuals. I'd be happy to learn I am wrong, but I imagine it would be very difficult to get permission to take orangs from the wild these days.

 

I didn't know about the different number of chromosomes; I think that alone would justify the split.

True. And I hadn't looked at it this way before, but history will likely show that the past few decades and the next few are the most volatile period ever for taxon changes. We are experiencing a spike in changes due to DNA research, but that may eventually settle down to a more manageable rate of change.

I am definitely cynical, but also I like the role of Devil's advocate. I think when a group of people agree on everything, no one learns anything. I like to try to see things from different angles and get different opinions. And you are very wise to take my brother's side on this. He actually knows what he's talking about; I'm just running my mouth.

 

Absolutely. I didn't mean to imply that the visual aspect should carry much weight. (Although I now realize that I did mention it for both of my examples.) It's just difficult for me to not notice that part of it.

I understand this position, and in a perfect world, I would agree. But for the sake of discussion, let me toss out an alternative.

Given that many species are threatened or endangered, habitat loss is not going to be reversed on a large scale, and financial resources for conservation will always be limited, does it make sense to try to save every species or subspecies? If we concentrate our resources on saving the genus (even if that is a hybrid of the various species), won't we be much more likely to have success in the long run?

I am not sure what my position is on this, but it's worth considering.

 

I ´ll add one example, a food for thought. It is about flamingos, this time about the feral colony in Germany/Holland.

Flamingos (6 species recognized as of now) are favourite zoo birds and were imported in tens of thousands into Europe, for zoos and private collections. A small part of them escaped and eventually, more then 30 years ago, established a small breeding colony in Zwillbrocker Venn (on the border between D/NL).

This colony consists of 3 species, the Caribbean, Greaters and Chileans, and their hybrids. These 3 species rutinely create mixed pairs and produce hybrid offspring, in all possible combinations of species and were doing so for decades. For some time it was believed that hybrids will soon prevale in the colony and one day will create a new "westeuropean race" consisting of genes from all 3 species.

But the following years of observation showed a different picture. Even if most hybrid chicks successfully fledged, practically all died within the first 3 years of their life. Right now the colony consists of 25-30 Chileans, ca 10 Greaters, 1 Caribbean and only 2-3 hybrids, most of these birds already hatched in Zwillbrocker Venn.

Nobody knows the cause of the high mortality of hybrid flamingos in the wilds of the Western Europe. Chileans and Greaters are both naturally hardy, enough to survive the winter there, their mixed offspring should have this ability too. Even the few pure Caribbeans (tropical in nature), that turned up at the colony in past decades, lived for many years, but their mixed offpring all died before reaching a maturity.

This is in sharp contrast with zoo colonies. Most zoos in the past kept several flamingo species together and produced hybrids without hesitation (some still do, shame on them). And these hybrids showed not a significantly higher mortality in captivity then their purebred cousins in the same colony. Their sheltered life kept them alive where their wild counterparts failed.

In the highly theoretical situation where wild populations of flamingos would die out and zoos would try to save them by crossing the remaining few specimen of several species - how (un-)fit would be these to survive in the wild?

The taxonomy of these 3 flamingo species (Caribbean, Greater, Chilean) made a similar way that happens now with many other species. Till 1970es they were considered to be just 3 subspecies of one single species. And only around 2000, the Caribbean and Greater were split from subspecies to full species level, but many zoos still not respect this split and label the Caribbean as Phoenicopterus ruber ruber and the Greater as Phoenicopterus ruber roseus.

Are Caribbeans and Greaters two "good" species or just one species with two subspecies? I don´t know and their genetical differencies are actually not sooo big. But the poor survival rates of their hybrids in the wild show that it makes ZERO sence to produce any hybrids even in captivity. The same, according to me, applies to all other animal species/subspecies. We are not able to recognize all the important adaptations they developed to survive, so we should stay on the safe side and not mix anything. I would even suggest to keeep and breed animals based on their source population, not only subspecies.

 

I think the scientists and public pay too much attention on the DNA research and species split, and I believe the excess molecular taxonomy research occupy many attentions and funds which otherwise will give to field research, which I think is more meaningful. Meanwhile, it is still hard for me to believe the Borneo orangutan and Sumatra orangutan, east lowland, west lowland and mountain gorilla, yellow-cheeked and buff-cheeked gibbon are different species.

 

Very good points. I was unaware of the difference in the survival rate of hybrids in captivity vs. the wild.

 

Not so. Very few Orangutans bred successfully in zoos before the 1960's- there were indeed individual breedings, some pairs even producing several young like the famous Sumatran pair 'Guas' and 'Guarina' at Philadelphia Zoo but it was by no means a common occurence. Also, those pairs that did breed tended to have originated together either from Borneo or from Sumatra so many offspring were in fact purebred and hybrids, though undoubtedly occurring, would have been in the minority. Hybrids only started to occur more regularly with the increase in the number of Zoos keeping Orangutans when some 'mixed' pairs of Orangs were inadvertently obtained by a number of Zoos, mostly in the 1960-80's era but even then they only represented a small percentage of the captive-bred Orangutan population.

But with the advent of karyotyping/DNA testing, it became possible to test all Zoo Orangs about which there was any doubt of their ancestry. The mistakenly-produced hybrids were reliably identified ,segregated out and(for the most part) not allowed to breed anymore, while all further approved breeding was from then on only with purebred animals.

Whether Bornean and Sumatran Orangs should be defined as full species is an arguable point. Certainly there are many subtle differences in their appearance, and some in their behaviour too. There is some scientific opinion too that not only they are full species but that in Borneo there are two or three different subspecies of that Orangutan. I don't know what criteria they use to discriminate between them though.

 

Thanks for the information. I have no idea where I heard it or read it, but I once "learned" that most captive orangs were hybrids. I'm glad to know I was wrong.

This (and the chromosome argument) means that I need to find a new species for my lump/split debate.

 

I did some reading about this, and while I couldn't find any authoritative sources, I found several sites that said all great apes have 48 chromosomes, while humans have 46. I found some interesting stuff that talked about how two pairs of chimp chromosomes fused together to form one human pair, but that is for a different discussion.

The only article I could find that talked about the genetic differences is one from 1996 that I've come across several times over the years: The mitochondrial DNA molecule of sumatran orangutan and a molecular proposal for two (Bornean and Sumatran) species of orangutan - Springer

The abstract is available at that link, and the relevant part is:

...molecular difference between Sumatran and Bornean orangutan is... greater than that between the two chimpanzees.... Considering their limited morphological distinction the comparison revealed unexpectedly great molecular difference between the two orangutans. The nucleotide difference between the orangutans is about 75% of that between Homo and the common chimpanzee, whereas the amino acid difference exceeds that between Homo and the common chimpanzee
​

There is no mention of the number of chromosomes. If the number was different, I think that would be important enough to include in the abstract.

If you have any relevant links for this topic, I would love to do more reading. However, I don't have access to most scientific journals.

 

There are still a quite a few elderly Hybrids in Zoos, but when they die out, this phenomenom will be a thing of the past.

 

They don't have differing numbers of Chromosones. But 'Chromosone 2' has a slight but distinct difference in appearance between the two species/subspecies. I think that is how the karyotyping recognition works.

 

Yup, that appears to be the case. I must have got muddled and thought, as the two could be differentiated by looking at the chromosomes, that there must be different numbers of them (but there's not). Should have checked my sources before posting!

 

Very interesting example Jana, thanks for sharing it. I suppose that if it had gone the other way, with the hybrids more successful than the pure birds in their new environment (hypothetically totally possible), then totally different (and potentially wrong) conclusions may have been drawn regarding flamingo taxonomy (i.e. that the two taxa are subspecies, not "good" full species).

Definitely food for thought.

 

Personally I still think they should be treated as subspecies- distinct yes, but not to the extent that warrants full species status- however long they have been seperated from each other for, they are still all 'orangutans'.

As someone said, if you dropped a load of Borneans into the Sumatran jungles, or vice versa (perish the thought ),they would surely hybridise without difficulty, just as they do(or rather did) when allowed to in Zoos. And as the (so-called) 'hybrids' are fully fertile, that is even more evidence to me they are the same species.

I see a similar problem with the Gorillas- on a subspecies level they are certainly different, but IMO they do not justify these 'full species' distinctions.

 

It all depends on what your definition of a species is. One major problem is that we only care about subspecies for large charismatic animals, and even then only a select few of those. Whereas, when an animal is raised to the level of a species it automatically gets more attention.

 

Agreed, but I hate it when we have to fudge one thing to fix another thing. IMO we ought to be able to define species in the way that makes the most sense, we should manage survival plans the way that makes sense, and those two don't have to be the same.

But since we live in the real world, we have to play the game....