What's up, pussy cat? (Publications)
One of the great things about being a University student in the 21st Century is remote access from home to any number of Journals via the University's licence. Normally subscriptions to magazines like Nature and Science cost between USD160 and USD200 a year, for your basic print edition, so it's just great to be able to log in from home, download any number of PDFs and read them at your own leisure.
It's unfortunate that both of these magazines, indeed, many scientific publications, are not made freely available over the internet. I understand the commercial reasons, of course, but there's just something about science that I think means it should be available to everyone, everywhere. As a regular kete were column, I'll talk about some of the absolutely marvellous articles that are printed in at least those two magazines, as well as others that take my fancy from time to time. If any of our readers are interested in having a look at the articles, just leave a comment, or send us an email, and I'll happily forward you the PDF.
Nature this week has a great piece on the Afar region in Ethiopia, which has been one of the key areas for early human (hominid) fossils. The famous "Lucy" was discovered in the Afar region, and this is reflected in the scientific name for her species Australopithecus afarensis, literally "Southern ape-man of the Afar".
Teams have been working in the Afar, which is part of the Great Rift Valley, for many decades now. The area represents a section of the continental crust where the Nubian (to the west) and Somalian (to the east) sections of the African tectonic plate are gradually pulling apart, leading to massive subsidence and geological depressions. The exposure of many strata provides an exceptional opportunity for the 'freeing' of many fossils through a number of sediments, especially during seasonal rains, causing the whole of the rift valley, right through as far south as Mozambique, to be the key to reconstructing early hominids and their ecology. Most of the oldest hominid fossils are found in the Great Rift Valley, including the earliest representative of our own species, Homo sapiens, in the Afar.
The best article of the week, though, is in Science, and it's about the evolution of modern cats. And by modern cats, they dont just mean your moggy, but all modern cats, belonging to the Felidae family.
The cat family are the most successful family belonging to the Carnivora family, occupying every continent in the world except Antarctica. In terms of the study of evolution, though, everyone seems to have this thing for dogs. This isn't entirely surprising, or even unjustified; the single subspecies of wolf Canis lupis familiaris, that we commonly refer to as the domestic dog, represents a massive amount of diversity within a single taxonomic group, produced solely by the process of artificial selection.
But the dog is just one species, and when you look at the whole Canidae family, it really is nothing compared to the cats.
Despite being so well known, the Felidae have remained somewhat of a mystery in terms of their origins, as well as the internal relationships between members of the family: who is more closely related to who? How did they get where they are?
Researchers from the Laboratory of Genomic Diversity at the National Cancer Institute in Maryland did a whole raft of genetic analysis using X chromosomes, Y chromosomes, Autosomes (non-sex chromosomes) and Mitochondrial DNA from 37 living species of cats, including some (marbled cat, serval, pallas cat, and rusty spotted cat) for whom no certain place had been found in the cat family tree. The results are quite remarkeable.
[Click to enlarge]
The figure shows the resultant phylogenetic tree for all 37 species of cats. There are some very interesting points to take away from it:
Firstly, after initial divergence from the last common felid ancestor of the Panthera lineage, which would eventually give rise to todays 'Great' or 'Roaring' Cats, some 10.8 million years ago, the Felidae underwent an extremely rapid radiation; within 4 million years, all eight modern cat lineages had successfully emerged and become established.
Secondly, all four of the previous enigmatic cat species are now, quite confidently, placed within the right group: the marbled cat with the Bay Cat lineage, which diverged from other cats very soon (just over a million years) after the Panthera group; the serval with the Caracal lineage of Africa; the pallas and rusty spotted cat with the Leopard Cat lineage.
Thirdly, the closest living relative of the Felidae is shown to be the Linsang, which were originally thought to resemble cats due to convergent evolution. However, it may actually be that some of the resemblances are in fact due to common descent
Fourthly, some very odd close relationships are found between some lineages which, on the face of it, should look to be much more distantly related. For example, for many years, it was thought that the Puma lineage and the Lynx lineage were sister taxa, that is, that the two lineages were more closely related to each other than either were to any of the six other cat lineages. Well, it now looks like this may not be true: the Puma looks to be more closely related to the lineage that led to our beloved moggy than it is to the Lynx.
Have a look more closely at the Puma lineage, and you may be surprised: the Cheetah is found in this group! This means that the Cheetah, found in the Serengeti plains of eastern Africa is more closely related to the Puma of the North American Rockies than it is to the other African cats, the Leopard and the Lion. Similarly, the Puma is more closely related to the Cheetah than it is to the Jaguar of South America.
This also means that the Cheetah is more closely related to your family cat than it is to any other big cat. Evolution sure does work in wonderful ways.
So this genetic discovery leads to a bit of problem: how did these species get to where they are now, given where they came from and who they are related to? How did the Cheetah and Puma get to where they are, given that they're not as closely related to other species within the same geographical area?
The researchers did some biogeographical modelling of possible migrations throughout the world, correlated with changes in sea-levels during periods of global warming and cooling, shown in Figure 2 below.
[Click to enlarge]
Quite fortuitously, it would seem, the putative migrations match, chronologically, the hypothesised time periods when the 8 lineages split from each other. It's quite complex and would take a lot of time to explain, but I'm sure you'll work it out from the graphic.
I love this kind of work. It's great to see genetic research being used with biogeographical modelling to show past movements of organisms as they arise in evolutionary time. Even more exciting is the implications the results have on our understanding of evolutionary processes themselves - how such a diverse range of animals as the cats can be related to each other in ways that seem both improbable, in the case of the pumas and the cats, and geographically impossible, in the case of pumas and cheetahs.
From so simple a beginning indeed.
[FIGURES FROM SCIENCE MAGAZINE 6 JAN 2006]
It's unfortunate that both of these magazines, indeed, many scientific publications, are not made freely available over the internet. I understand the commercial reasons, of course, but there's just something about science that I think means it should be available to everyone, everywhere. As a regular kete were column, I'll talk about some of the absolutely marvellous articles that are printed in at least those two magazines, as well as others that take my fancy from time to time. If any of our readers are interested in having a look at the articles, just leave a comment, or send us an email, and I'll happily forward you the PDF.
Nature this week has a great piece on the Afar region in Ethiopia, which has been one of the key areas for early human (hominid) fossils. The famous "Lucy" was discovered in the Afar region, and this is reflected in the scientific name for her species Australopithecus afarensis, literally "Southern ape-man of the Afar".
Teams have been working in the Afar, which is part of the Great Rift Valley, for many decades now. The area represents a section of the continental crust where the Nubian (to the west) and Somalian (to the east) sections of the African tectonic plate are gradually pulling apart, leading to massive subsidence and geological depressions. The exposure of many strata provides an exceptional opportunity for the 'freeing' of many fossils through a number of sediments, especially during seasonal rains, causing the whole of the rift valley, right through as far south as Mozambique, to be the key to reconstructing early hominids and their ecology. Most of the oldest hominid fossils are found in the Great Rift Valley, including the earliest representative of our own species, Homo sapiens, in the Afar.
The best article of the week, though, is in Science, and it's about the evolution of modern cats. And by modern cats, they dont just mean your moggy, but all modern cats, belonging to the Felidae family.
The cat family are the most successful family belonging to the Carnivora family, occupying every continent in the world except Antarctica. In terms of the study of evolution, though, everyone seems to have this thing for dogs. This isn't entirely surprising, or even unjustified; the single subspecies of wolf Canis lupis familiaris, that we commonly refer to as the domestic dog, represents a massive amount of diversity within a single taxonomic group, produced solely by the process of artificial selection.
But the dog is just one species, and when you look at the whole Canidae family, it really is nothing compared to the cats.
Despite being so well known, the Felidae have remained somewhat of a mystery in terms of their origins, as well as the internal relationships between members of the family: who is more closely related to who? How did they get where they are?
Researchers from the Laboratory of Genomic Diversity at the National Cancer Institute in Maryland did a whole raft of genetic analysis using X chromosomes, Y chromosomes, Autosomes (non-sex chromosomes) and Mitochondrial DNA from 37 living species of cats, including some (marbled cat, serval, pallas cat, and rusty spotted cat) for whom no certain place had been found in the cat family tree. The results are quite remarkeable.
[Click to enlarge]
The figure shows the resultant phylogenetic tree for all 37 species of cats. There are some very interesting points to take away from it:
Firstly, after initial divergence from the last common felid ancestor of the Panthera lineage, which would eventually give rise to todays 'Great' or 'Roaring' Cats, some 10.8 million years ago, the Felidae underwent an extremely rapid radiation; within 4 million years, all eight modern cat lineages had successfully emerged and become established.
Secondly, all four of the previous enigmatic cat species are now, quite confidently, placed within the right group: the marbled cat with the Bay Cat lineage, which diverged from other cats very soon (just over a million years) after the Panthera group; the serval with the Caracal lineage of Africa; the pallas and rusty spotted cat with the Leopard Cat lineage.
Thirdly, the closest living relative of the Felidae is shown to be the Linsang, which were originally thought to resemble cats due to convergent evolution. However, it may actually be that some of the resemblances are in fact due to common descent
Fourthly, some very odd close relationships are found between some lineages which, on the face of it, should look to be much more distantly related. For example, for many years, it was thought that the Puma lineage and the Lynx lineage were sister taxa, that is, that the two lineages were more closely related to each other than either were to any of the six other cat lineages. Well, it now looks like this may not be true: the Puma looks to be more closely related to the lineage that led to our beloved moggy than it is to the Lynx.
Have a look more closely at the Puma lineage, and you may be surprised: the Cheetah is found in this group! This means that the Cheetah, found in the Serengeti plains of eastern Africa is more closely related to the Puma of the North American Rockies than it is to the other African cats, the Leopard and the Lion. Similarly, the Puma is more closely related to the Cheetah than it is to the Jaguar of South America.
This also means that the Cheetah is more closely related to your family cat than it is to any other big cat. Evolution sure does work in wonderful ways.
So this genetic discovery leads to a bit of problem: how did these species get to where they are now, given where they came from and who they are related to? How did the Cheetah and Puma get to where they are, given that they're not as closely related to other species within the same geographical area?
The researchers did some biogeographical modelling of possible migrations throughout the world, correlated with changes in sea-levels during periods of global warming and cooling, shown in Figure 2 below.
[Click to enlarge]
Quite fortuitously, it would seem, the putative migrations match, chronologically, the hypothesised time periods when the 8 lineages split from each other. It's quite complex and would take a lot of time to explain, but I'm sure you'll work it out from the graphic.
I love this kind of work. It's great to see genetic research being used with biogeographical modelling to show past movements of organisms as they arise in evolutionary time. Even more exciting is the implications the results have on our understanding of evolutionary processes themselves - how such a diverse range of animals as the cats can be related to each other in ways that seem both improbable, in the case of the pumas and the cats, and geographically impossible, in the case of pumas and cheetahs.
From so simple a beginning indeed.
[FIGURES FROM SCIENCE MAGAZINE 6 JAN 2006]
posted by Anonymous at 11:41 PM
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