Genetic diversity and zoo conservation

lintworm said:
Except the slight problem that all available evidence suggests that rafting to Madagascar was anything but commonplace, Madagascar is separated by several hundreds of kilometres of treacherous waters (at least 450 km and often more), distances much bigger than the Caribbean or the Amazon. It was actually so hard to cross that barrier that only 4 mammalian ancestor species (except flying bats and swimming hippopotami) made the cross successfully over a period of about 40 million years. It was so hard to cross that man colonized Madagascar not from nearby east Africa, but from Malaysia as you probably know and that only within the last 2000 years (though they had to deal with a different monsoon pattern, making it even more difficult). So all evidence at hand suggests that rafting across the Mozambique channel was extremely tough and it is thus highly unlikely large populations could cross within a small time period. Do they all descend from one pregnant female, probably not, but it almost can't have been much more given the rarity of successful crossings....
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Rafting was (theoretically) more common in the Palaeogene when the currents were different and vegetation lusher (rafts form in lush environments). The ocean and climate have not been stable through the Tertiary, and back then it wasn't tough to cross the channel.

Tenrecs must've got in from Africa, because crown placentals were absent from the Cretaceous of India and Africa when that piece of Gondwana fragmented. The carnivores must have, probably before the early Miocene when the currents already made it harder, which fits the upper estimation of the euplerid LCA. So yes, multiple raftings took place in the Palaeogene when it was easier.

Mammalian biodiversity on Madagascar controlled by ocean currents
 
For the benefit of anyone who lacks a subscription to Nature, here is the paper linked above as a free download:

https://www.researchgate.net/public...ty_on_Madagascar_controlled_by_ocean_currents

The free link took mere moments to find, by the by :p and contrary to the insinuations above by SealPup does not suggest such raftings to Madagascar were commonplace:

ocean currents could have occasionally transported rafts of animals to Madagascar from Africa during the Eocene.
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...and in fact *does* corroborate the statement by Lintworm that there could have been as few as four rafting events:

. From molecular-clock dating estimates, it is possible to discern four distinct early-Cenozoic to mid-Cenozoic events: the arrival of lemurs between 60 and 50Myr ago, that of tenrecs between 42 and 25Myr ago, that of carnivorans between 26 and 19Myr ago, and that of rodents between 24 and 20 Myr ago
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TeaLovingDave said:
For the benefit of anyone who lacks a subscription to Nature, here is the paper linked above as a free download:

https://www.researchgate.net/public...ty_on_Madagascar_controlled_by_ocean_currents

The free link took mere moments to find, by the by :p and contrary to the insinuations above by SealPup does not suggest such raftings to Madagascar were commonplace:



...and in fact *does* corroborate the statement by Lintworm that there could have been as few as four rafting events:
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Four survived: others will have died out before the present (think Plesiorycteropus, whatever it was) and even the LCAs of the crown groups may have existed on the mainland, for all anyone knows.

And each successful rafting, implies many more that had no consequence. So yes: it was something commonplace, compared to the idea some proto-lemurs of just one species, had rafted just once.
 
SealPup said:
Why do you think monkeys in ISEA stop their distribution where they do? Have you noticed its the crab eating macaques at the extremes, on not just one but several islands? Their lifestyle and sleeping preferences predispose them to accidental rafting all the time.
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There's nothing unusual about Crab-eating Macaque distribution. Everywhere that they occur naturally has elements of typical mainland mammalian fauna or is very close to a larger land-mass. You'd have to be suggesting that all the other mammals on the islands which macaques live upon also had to have rafted to get there.

You're also doing your argument a great disservice by continually trying to state your personal opinions as absolute facts, when those opinions are contrary to or unsupported by the available evidence (e.g. your ideas about the rate of rafting events in the Eocene).
 
Chlidonias said:
There's nothing unusual about Crab-eating Macaque distribution. Everywhere that they occur naturally has elements of typical mainland mammalian fauna or is very close to a larger land-mass. You'd have to be suggesting that all the other mammals on the islands which macaques live upon also had to have rafted to get there.

You're also doing your argument a great disservice by continually trying to state your personal opinions as absolute facts, when those opinions are contrary to or unsupported by the available evidence (e.g. your ideas about the rate of rafting events in the Eocene).
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As far as macaques go,
Macaque evolution and dispersal in insular south‐east Asia

Yes, some primates are predisposed to dispersal by rafting sweepstakes, and those that do, will likely do so repeatedly as suitable conditions prevail.

Everything I said about rafting is a reference to the phenomenon as observed today, or to (relative) ease of crossing accidentally in the Tertiary. Primates could probably not cross at present.

Which is most likely: lemurs share descent from just one family or pregnant female, surviving in an alien environment, or a full founder population stepping off different rafts within a few generations?
 
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SealPup said:
Rafting was (theoretically) more common in the Palaeogene when the currents were different and vegetation lusher (rafts form in lush environments). The ocean and climate have not been stable through the Tertiary, and back then it wasn't tough to cross the channel.
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SealPup said:
Everything I said about rafting is a reference to the phenomenon as observed today, or to (relative) ease of crossing accidentally in the Tertiary. Primates could probably not cross at present.
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The fact you keep flip-flopping between using the incorrect term Tertiary and the correct term Paleogene - sometimes within the same paragraph - doesn't make you look any more correct, for what it is worth. Nor does only ever sharing paywalled abstracts rather than the papers themselves, given that this gives the impression you haven't actually read the research you attempt to use to back up your claims.

Chlidonias said:
The link is only an abstract, so I have no idea what the paper says beyond that.
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Again, with a little time I was able to find a link to a free PDF of the full paper :)

Macaque evolution and dispersal in insular south-east Asia
 
Tertiary is incorrect for the period Palaeocene-Pliocene? ;) The timeframe of rafting events to Madagascar, is hypothesised to have continued beyond the Oligocene, and into the Miocene. This makes sense for rodents, which cross under suboptimal conditions other mammals can't withstand ie. murids are the only land placentals in Sahul, a dispersal record over sea matched only by certain squamates.

But with carnivores it probably pushes the timeline back, because they don't disperse so readily by rafting and those once thought to have, ie. raccoons in the Carribean, usually turned out to be human introductions, and not endemic species. The failure of carnivores to colonise the Caribbean proper before man, is staggering even: despite natural rafts regularly seen departing the mainland, often with fauna such as iguanas, belonging to clades that did colonise the archipelago. How many euplerids must have landed on Madagascar, and how many times, before they became established?

The fact any of these papers is so widely distributed online, is why there is no need to cite everything: if its online there are search engines and sci-hub.
 
SealPup said:
Tertiary is incorrect for the period Palaeocene-Pliocene?
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It is; the first portion of the period in question is now known as the Paleogene (Paleocene, Eocene, and Oligocene) whilst the Pliocene is classified within the Neogene, along with the Miocene. The "Tertiary" is no longer recognised as a valid geological term, in part because it spanned not only these periods but also the Gelasian stage of the Pleistocene.

I suspect you are very well aware of this fact already.


SealPup said:
The fact any of these papers is so widely distributed online, is why there is no need to cite everything: if its online there are search engines and sci-hub.
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In other words, "I'm above such petty matters as showing my sources when engaged in scientific discussion, you will either have to take my word for it or do the legwork yourself"
 
TeaLovingDave said:
It is; the first portion of the period in question is now known as the Paleogene (Paleocene, Eocene, and Oligocene) whilst the Pliocene is classified within the Neogene, along with the Miocene. The "Tertiary" is no longer recognised as a valid geological term, in part because it spanned not only these periods but also the Gelasian stage of the Pleistocene.

I suspect you are very well aware of this fact already.
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Its not "now known" at all, as the terms coexisted for years, and still do. Tertiary = Cenozoic, but - the Quartenary.

In other words, "I'm above such petty matters as showing my sources when engaged in scientific discussion, you will either have to take my word for it or do the legwork yourself"
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But thats not unfair with information tech: material is put our there to be researched, and if no one does what was the point? Obscure journals and very old info are something else, maybe not everyone knows about sci-hub: but if you found both papers so readily so can anyone curious.
 
SealPup said:
Four survived: others will have died out before the present (think Plesiorycteropus, whatever it was) and even the LCAs of the crown groups may have existed on the mainland, for all anyone knows.

And each successful rafting, implies many more that had no consequence. So yes: it was something commonplace, compared to the idea some proto-lemurs of just one species, had rafted just once.
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Plesiorycyeropus has been shown to be a tenrec and I am going to leave it at that for his discussion. Goodnight.
 
lintworm said:
Plesiorycyeropus has been shown to be a tenrec and I am going to leave it at that for his discussion. Goodnight.
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Has not been shown any such thing, unless you know something I don't: the Horowitz postcrania matrix not long ago, even recovered Plesiorycteropus as an aardvark, still. As far as I know, its still just a generalised animal with digging adaptations, as might be the primitive habit for placentals, though not to extremes seen in ie. P. or armadillos. I remember Asher couldn't tell if P. was an afrothere or a laurasiothere, although he did use DNA as well as anatomical markers, so he was not just applying a molecular constraint to an analysis.

P. is the sort of generalised mammal you might have expected in the Eocene, and would prbly have been lumped thoughtlessly as a palaeanodont or something instead of a tubulidentate, if it was. The Palaeocene and Eocene were full of creatures like that, prbly similar to the ancestral placental, their relationships still being worked out. Only the very late age of P. attracts comment and most mammalogists have ignored it as too poorly known, so if its one of those animals people first find out about from textbooks mentioning them only in passing, there is a reason for that...
 
Vision said:
A Molecular Phylogeny of Plesiorycteropus Reassigns the Extinct Mammalian Order ‘Bibymalagasia’

What's funny is that this was actually the very first result on a google search I did... That, when I thought you just said anyone should be able to find anything because "material is put out there to be researched."

See how citing is always important?
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Some kind of lipotyphlan relationship for P. is old hat, so you could have been referring to a few ppl. And tenrecs always were best candidates for geographical reasons.
 
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DDcorvus said:
Did you realise it will not kill you to admit you're wrong.
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About?

The Buckley paper uses just one line of molecular evidence, one that contradicts other lines of molecular evidence at times ie. lack of support for euarchontoglires. So its not definitive by any means, nor do molecular phylogenies always match up with the fossil/morphological record 100% (ie. afrotheria has next to no morphological basis, and there was a brief reappearance of debates about Volantia not long ago). So no, its not proved yet, unless its backed by other lines of evidence.

And the analysis did not include potamogalids, which is important in figuring out how/when Plesiorycteropus got there, given that Plesiorycteropus looks outside of tenrecidae in that topology. If they are more stemward, then that supports one colonisation of Madagascar, but if they are crownward of Plesiorycteropus, that would support two. Why were they unsampled?

Though TBH this is not about different clades of lemurs or tenrecs arriving at different times: its just a possibility. raised by the distance of P. to other(?) tenrecs, and perhaps ayeayes to the other Madagascan lemurs. My point was it is rubbish to assume there was just one raft with a family or pregnant female on board. Multiple rafts would supply a more diverse founding population, either washed downriver in the same storm, or because populations were occasionally recieving new genes from new rafts in the crucial process of establishment. Yes, I stand by my guns that survival risks in a too-unfamiliar environment, plus low numbers and genetic diversity, would otherwise be too likely to destroy any single family of animals arriving on just one raft, or their descendants in few generations. There is not a single reason to assume there was just one founding raft.

For some reason its a myth with an old pedigree that won't die, same as vicariance: despite the fact there are nonrandom elements involved in sweeptakes hypothesis, when it is understood correctly. I have even heard it said Aussie aboriginals are all descended from one canoe hitting Sahul, though people had the ability to direct their watercraft, unlike accidental rafters. These things make good, simple yet romantic narratives, I guess.
 
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I'm curious, just how many genetically distinct individuals need to be present in a population for you to consider them healthy enough? It can be tough to imagine all the lemurs present today descended from only one female or one family group, but can you positively say that several hundred (if not more by your definitions) completely distinct founders made their way to the island within a generation or two?

~Thylo
 
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