Generic and Hybrid Populations in Zoos

[JVM]

There are many interesting posts about this topic throughout the board but there has never been a single, all-encompassing topic, often leading to surprise from new members. I wanted to discuss animal populations kept in zoos that are managed at a non-subspecies level or are members of hybridized populations. Very few zoochatters support these populations but as a history-oriented person I still find it an interesting subject to discuss and learn more about.

I am referring to, for example, the currently situation for giraffe in the United States -- in 2004, it was discovered that the Baringo/Rothchild giraffe populations in the United States was interbred significantly with Reticulated giraffe compared to the native population, and lacking enough animals of pure genetic heritage for a sustainable population, most zoos manage a generic giraffe population instead. The AZA is trying to breed masai giraffe instead to build up a subspecies population that can one day replace these generic animals, but they are not breeding at a fast enough rate to replace the current giraffe immediately.

The AZA also tried to form a captive breeding program for pure Asiatic lion a few decades ago, importing animals from Indian zoos to kickstart this effort. Though the survival plan at first seemed quite successful and multiple births were celebrated, it was later discovered in the nineties that some of the founder animals included African-Asiatic hybrids and so the ssp bloodline was impure, and the AZA decided to manage African lions instead.

From other threads I have read, generic leopard have been almost fully phased out in favor of the Amur leopard ssp, generic tiger in accredited zoos I believe have dwindled mostly to rescue animals, there was talk at some point of generic ostrich being phased out in favor of the North African subspecies but from what I have seen this is no longer believed to be the case, and chimpanzees in most zoos have not been tested to be subspecific. Many zoos still hold hybrid orangutan but they are no longer breeding and Bornean and Sumatran are both managed programs. Asian elephants are being managed at a species level not subspecies. I would be curious about any other populations being managed this way currently or who suffered it in the recent past.

This is a case I do not know as well, but some older sources I'd read cast Cuban crocodile as a more significant captive breeding program but in recent years it has come to attention that there is hybridization in the wild between Cuban and American crocodiles which is becoming a threat to the species, and which may be reflected in some captive species. Any information on this case would be interesting if anyone has information to add.

I welcome zoochatters who have more information or can be more helpful on this as I am no expert, and of course my examples are all AZA but I am curious if international zoos have experienced the same issues and found their own solutions.

 

[Zoofan15]

I welcome zoochatters who have more information or can be more helpful on this as I am no expert, and of course my examples are all AZA but I am curious if international zoos have experienced the same issues and found their own solutions.

I’d be happy to offer an Australasian (ZAA) perspective:

While we have numerous coordinated breeding programmes, it’s not unusual to see variations between collections:

We have a thriving Sumatran tiger breeding programme comprising 43 tigers across 18 holders. Three zoos that held Siberian tigers in the 1990’s phased out and joined this breeding programme, given its recognised as the most suitable subspecies for our climate. Interesting, a handful of these holders additionally hold generic tigers, which were previously referred to as Bengal tigers. They play the same role as ambassadors and two of the zoos that hold them in particular are the biggest contributions to wild conservation, so I have no objection per say.

Asian elephant is managed at the species level. The majority are Indian elephants, but we also have a Sri Lankan elephant cow at Taronga Western Plains Zoo and a herd of four female Sumatran elephants at Australia Zoo. They’ve stated an intention to import a Sumatran elephant bull and thus maintain a purebred herd, but otherwise the other zoos in the region disregard maintaining purebred lines. Again, I have no objection to both stances. If a zoo has the resources to maintain a purebred herd, that’s fine with me, but I don’t see it as a priority.

Our Plains zebra population comprises mostly generic Plains zebra. Historically, several zoos held the purebred Grant’s subspecies, but this population has dwindled to 1.1 elderly zebra held at two different New Zealand facilities. A few years ago, two Australian facilities undertook a group import of purebred Grant’s zebra and have attempted to establish a purebred population in the region. It frustrates me other zoos haven’t been more supportive of this initiative given the ease equines can be imported (many other species can’t). There’s really no excuses for not supporting a breeding programme for purebred Grant’s zebra in my opinion when they’re so readily available.

Common chimpanzee are managed at the species level. A purebred Western chimpanzee arrived here from Europe by accident and since no investigation outside of ZooChat has taken place as to the subspecies status of our region’s founders, there’s a slim chance we may have additional purebreds. Given Common chimpanzee are commonly managed at the species level in other countries and the immense effort involved to create a purebred population alongside the legions of hybrids we have (some of which are infants that could live another 60 years), I fully support a hybrid breeding programme.

 

[birdsandbats]

There are lots of hybrid Bornean x Sumatran Orangutans in North American zoos, orangs are managed at species level so these hybrids are not allowed to breed. However, it was recently discovered that some of the supposedly pure Sumatran are actually hybrids with Tapanuli. The extent of this hybridization is unknown.

 

[15399]

I think there are three "levels" of hybridized animals in US Zoos, of which I'll describe here:

"Level 1": a successful purebred program is present. An example of this is with Tigers, as there are good numbers of three Tiger subspecies yet also many generic Tigers. I have an issue with any respectable zoo opting for hybrid animals in these instances, as the purebred animals are an option of higher conservation value.

"Level 2": Purebred animals are present in small numbers or a struggling program. This is the case with giraffes. Demand for giraffes is greater than the number of purebred masai giraffe available, hence there being a need for generic giraffes in the interim while the masai giraffe population grows. Hopefully in these cases the goal remains replacing the generic individuals with the purebred subspecies.

"Level 3": Purebred animals are not present in a region. If the entire population of a species is generic, I see no problem with Zoos focusing on a generic population. This can still lead to education value, and there may still be some Conservation value depending on the specific demographics of a population. These populations can also often arise unexpectedly if subspecies are split or lumped when a population was already established, leading to a population that was genetically pure to a now-defunct subspecies, or when new scientific evidence shows what were thought to be purebred animals are in fact generic- something I do know has happened with some individual animals.

 

[iloveyourzoos]

Honest question here: When a regional zoo organization (AZA, EAZA, ZAA) decides that it is only able to officially manage on a generic or hybrid level, do individual zoos and/or individual studbook keepers still consider/ track/ submanage within that? Or is it an all or nothing situation?

I imagine that there might be different levels of hybridization within the population (an animal whose lines has been repeatedly hybridized versus one that only has 1/16 non-pure breeding, for example). Or that there might be a mix of a few pure type 1, a few pure type 2, and many many hybrids of varying degrees, but not enough to officially manage as three populations. In such a case, might a zoo or studbook keeper still try to match up the "closest" types within the population, even if they don't have enough to "officially" manage them as separate populations?

 

[Sheather]

I am broadly opposed to purebred species management, as it comes at the expensive of the other genetic diversity of a species. Sub-specific hybrid populations will have greater diversity to rely on in for survival and further evolution in future releases, especially among immunity, and likely best represent the most adaptable common ancestor of different wild sub-populations before diversification. Exceptions might be valid for subspecies which now live in extremely different eco-regions: amur and generic leopard, which is mainly an African/Asian descendant composite without genes from cold climate animals. This is not true for giraffes or African lions. Asiatic lions have more behavioral differences, through social structure, between them and African lions than the different African populations do, though whether this is genetic or environmental is undetermined, so I am not ultimately opposed to maintain Asiatic lions in addition.

Tigers also live in very widely ranging climates, but I follow the mainland tiger taxonomy which places Amur and Bengal as the same population which formerly would have introgressed and bred together before habitat fragmentation. I don't consider them distinct enough to warrant the disregard of the generic tiger in conservation. It is the closest to the wild Bengal tiger's phenotype today, and this 'subspecies' or local population is still under threat in the wild.

 

[Zoofan15]

Honest question here: When a regional zoo organization (AZA, EAZA, ZAA) decides that it is only able to officially manage on a generic or hybrid level, do individual zoos and/or individual studbook keepers still consider/ track/ submanage within that? Or is it an all or nothing situation?

Within the ZAA, there’s variation. Asian elephants are managed at the species level, but Australia Zoo (who has four Sumatran elephant cows) has stated an intention to import a Sumatran bull to sustain a purebred herd.

We also manage Plains zebra at the generic level, but two zoos hold herds of purebred Grant’s zebra - one of which has supplied colts to other zoos in the region holding generics.

 

[JVM]

@Zoofan15 Thank you for so much valuable insight! Very interesting to know about the effort to kickstart purebred Grant's zebra and Sumatran elephant!

@birdsandbats I had been wondering how Tapanuli orangutan fit into this, I'm curious to see what other information comes about.

@Neil chace : on what level would you place common chimpanzee? I mean, level 3 seems implied as there is no known subspecies program but there has been talk that genetic testing may reveal pure individuals in the future in the US, and I am hearing they may be level 2 in EAZA.

@Sheather I am slightly confused, so confirm if I am understanding correctly - you support generic giraffes and mainland tigers, but not generic lions (African-Asian) or generic leopards, as you feel they are more distinct splits?

 

[Zoofan15]

@Zoofan15 Thank you for so much valuable insight! Very interesting to know about the effort to kickstart purebred Grant's zebra and Sumatran elephant!

You’re welcome. Personally I hope the Grant’s zebra population will flourish, but it will only do so long term with multiple holders and fresh imports every 2-3 decades given the founder base isn’t huge. I strongly believe that given the ease with which equines can be imported into New Zealand and Australia, there’s no excuse for breeding generics.

The Australasian region held what was widely believed to be a Rothschild’s giraffe population for a few decades, alongside a generic giraffe population. Some zoos held “pure” herds, while another acquired a “purebred” bull to breed with their generic cows. One zoo imported a legit Rothschild’s cow from Europe and was for a time, the proudest of them all. A ban on giraffe imports has since seen the Rothschild’s breeding programme abandoned and indeed all but the aforementioned cow are now regarded as Reticulated/Rothschild’s hybrids.

 

[15399]

@Neil chace : on what level would you place common chimpanzee? I mean, level 3 seems implied as there is no known subspecies program but there has been talk that genetic testing may reveal pure individuals in the future in the US, and I am hearing they may be level 2 in EAZA.

If there are no known subspecific individuals, then yes, it would be in my "Level 3".

 

[Jurek7]

Pure subspecies are rather strange mix, because some programs take care and others not. The examples of the latter in Europe are: snow leopards, African elephants, gibbons, gelada, Galapagos tortoise.

Practically, perhaps most important is to check these few species where there is still a good proportion of wild founders and first generation bred in zoos, and try separating, or at least understanding, subspecies. For example African elephants were imported either from South or East Africa. Also Bornean orangutans are three forms in different parts of Borneo. Galapagos tortoises – those few zoos which still have them, mix different subspecies. Also chimpanzees, gibbons and siamangs.

The additional problems is that subspecies are often a mess. For many species, the information is decades old, based on visual appearance and poor descriptions, and nobody checked it using modern methods and genetics. Siamang is an example: siamangs in mainland Asia and Sumatra are sometimes treated as different subspecies. But, to my knowledge, nobody checked about zoo population.

There are animals which subspecies were never investigated to my knowledge, although their native range is large or broken by geographic barriers, so are likely to have subspecies. Examples are spectacled bear and Solomon Islands / prehensile-tailed skink.

 

[elefante]

On the subject of purebred subspecies, have there been attempts anywhere to breed purebred bison? In North America the only purebred wild herds are in Yellowstone National Park, Wind Cave National Park, Elk Island National Park, and the Henry Mountains herd in Utah. All other public herds have been polluted with cattle genes. I can't imagine any zoo herds are pure.

 

[birdsandbats]

On the subject of purebred subspecies, have there been attempts anywhere to breed purebred bison? In North America the only purebred wild herds are in Yellowstone National Park, Wind Cave National Park, Elk Island National Park, and the Henry Mountains herd in Utah. All other public herds have been polluted with cattle genes. I can't imagine any zoo herds are pure.

There are a couple of zoos that maintain pure herds - notably Minnesota and Bronx. There's a few other zoos with purebred bison too (like Henry Vilas) but not maintaining populations.

I don't know that I'd call the bison at Wind Cave (or even Yellowstone) wild. The Henry Mountains herd is, though. I don't know anything about the Elk Island herd.

 

[Mickey]

I am broadly opposed to purebred species management, as it comes at the expensive of the other genetic diversity of a species. Sub-specific hybrid populations will have greater diversity to rely on in for survival and further evolution in future releases, especially among immunity, and likely best represent the most adaptable common ancestor of different wild sub-populations before diversification. Exceptions might be valid for subspecies which now live in extremely different eco-regions: amur and generic leopard, which is mainly an African/Asian descendant composite without genes from cold climate animals. This is not true for giraffes or African lions. Asiatic lions have more behavioral differences, through social structure, between them and African lions than the different African populations do, though whether this is genetic or environmental is undetermined, so I am not ultimately opposed to maintain Asiatic lions in addition.

Tigers also live in very widely ranging climates, but I follow the mainland tiger taxonomy which places Amur and Bengal as the same population which formerly would have introgressed and bred together before habitat fragmentation. I don't consider them distinct enough to warrant the disregard of the generic tiger in conservation. It is the closest to the wild Bengal tiger's phenotype today, and this 'subspecies' or local population is still under threat in the wild.

What I understand from this is that you are against subspecies management unless you recognize them as valid?
Correct me if I'm mistaken

 

[elefante]

There are a couple of zoos that maintain pure herds - notably Minnesota and Bronx. There's a few other zoos with purebred bison too (like Henry Vilas) but not maintaining populations.

I don't know that I'd call the bison at Wind Cave (or even Yellowstone) wild. The Henry Mountains herd is, though. I don't know anything about the Elk Island herd.

I'd say the Yellowstone ones are at least.

 

[Hyak_II]

There are a couple of zoos that maintain pure herds - notably Minnesota and Bronx. There's a few other zoos with purebred bison too (like Henry Vilas) but not maintaining populations.

I don't know that I'd call the bison at Wind Cave (or even Yellowstone) wild. The Henry Mountains herd is, though. I don't know anything about the Elk Island herd.

I live about 45 minutes away from elk island, so I’m more than happy to chime in! It is Canadas largest fully enclosed national park.

It is split in two through the middle by a major highway, meaning there are north and south sections of the park. The north section houses pure plains bison, and the south pure wood bison.

The bison are genuinely wild in that they do not receive any assistance in their survival from humans, however given that the parks are entirely enclosed and there isn’t a super heavy predation pressure on them (although there are limited numbers of black bears and cougars in the park, wolves have unfortunately been largely absent in recent years) they do have a set carrying capacity that is regularly exceeded by the bison.

in the past they were generally rounded up and sold to private buyers, but that hasn’t happened in a few years as far as I’m aware. I suppose they’re just filling them now.

Also also, there is a herd of pure animals that is being established in Banff national park, sourced from elk island. Although being intensely monitored, they are also a free living herd.

 

[Wisp O' Mist]

On the subject of purebred subspecies, have there been attempts anywhere to breed purebred bison?

I know that I'm a year late to this specific conversation, but the subject of "purity" among the American Bison is a moot point nowadays.

There are no "pure" bison anymore, and there likely haven't been for nearly a century. DNA testing has only just recently gotten sensitive enough to detect even the most minute of traces of cattle DNA. Maternal, nuclear... doesn't matter, all bison are now considered hybrids.

Yes, even the Yellowstone Park herd.

Genomic evaluation of hybridization in historic and modern North American Bison (Bison bison) | Scientific Reports

 

[PossumRoach]

I’m surprised no one has brought up more primates to the discussion yet since primates are a taxa that tends to be split a lot. Examples include spider monkeys, tufted capuchins, and grey langurs.

 

[15399]

I know that I'm a year late to this specific conversation, but the subject of "purity" among the American Bison is a moot point nowadays.

There are no "pure" bison anymore, and there likely haven't been for nearly a century. DNA testing has only just recently gotten sensitive enough to detect even the most minute of traces of cattle DNA. Maternal, nuclear... doesn't matter, all bison are now considered hybrids.

Yes, even the Yellowstone Park herd.

Genomic evaluation of hybridization in historic and modern North American Bison (Bison bison) | Scientific Reports

I guess this begs the question though of does this really matter? It's well-accepted that many humans have a small percentage of neanderthal DNA. But are people with a small amount of neanderthal DNA any "less human" than those without neanderthal DNA? Personally, I would say it doesn't, especially as in the wild it's rather common to get hybridization zones between different species, some of which may or may not be fertile. Yes, if a bison, say, had 25% cattle genes, that's obviously a significant amount and it'd be a hybrid. But I'm willing to bet if you surveyed wildlife around the world, it'd be extremely common to find individuals with 1-2% of their genome made up of another species' DNA. Speciation just be weird like that sometimes.

I’m surprised no one has brought up more primates to the discussion yet since primates are a taxa that tends to be split a lot. Examples include spider monkeys, tufted capuchins, and grey langurs.

Spider monkeys are a great example. A lot of the Geoffroy's spider monkeys in US zoos have become generics specifically because of recent taxonomic splits. While zoos are hoping to slowly transition to the two purebred spider monkey programs, the generic Geoffroy's program is still breeding to fill in gaps in the meantime. Squirrel monkeys are another example, however I for one am very skeptical of some of the recent splits here.

 

[Wisp O' Mist]

I guess this begs the question though of does this really matter? It's well-accepted that many humans have a small percentage of neanderthal DNA. But are people with a small amount of neanderthal DNA any "less human" than those without neanderthal DNA? Personally, I would say it doesn't, especially as in the wild it's rather common to get hybridization zones between different species, some of which may or may not be fertile. Yes, if a bison, say, had 25% cattle genes, that's obviously a significant amount and it'd be a hybrid. But I'm willing to bet if you surveyed wildlife around the world, it'd be extremely common to find individuals with 1-2% of their genome made up of another species' DNA. Speciation just be weird like that sometimes.

Oh believe me, prior to this new study you absolutely would've gotten people who would've insisted that 0.25% to 2.5% of cattle DNA "mattered".

"But what if those cattle genes affect the cold hardiness of the bison?!? What if they affect their metabolisms?!?" And so on and so forth. I've actually had people say stuff like that to me with a straight face.

Even when I've pointed out that vast majority of humans have other humanoid DNA in them, sometimes as much as or even more than 5%, they've still trotted out the same garbage about how even a tiny bit of cattle blood running through the veins of every living bison is somehow going to kill off the whole species.

Bison people, and most unfortunately, especially conservation-minded bison people, have been chasing the white whale of bison "purity" for over twenty years. To the point that prior to that study, any amount of cattle DNA was considered grounds for culling in bison herds being managed for conservation purposes.

And bison being managed as livestock? Considered completely worthless to bison conservation, to the point that the IUCN Red List didn't even count them as part of the overall bison population!

No, cattle DNA doesn't matter. I've never been convinced that it does and when this study came out, I practically threw myself a party because I was so happy to finally be vindicated.