From my time studying Zoology I can confirm that unlike my initial assumptions, evolution can often be one of the most complex, intriguing and poorly understood aspects of studying a particular group of animals. Initially, I was of the impression that the evolution of an animal was always presented clearly in black and white, and that it followed a simple pathway upon which all scientists unanimously agreed on, how wrong I was! It was only after spending a great deal on months on the subject, that I realised the sheer amount of inconclusive and debated relationships between animals of all shapes and sizes, big cats included.
In order to fully begin to develop an understanding of a particular group of animals, whether that be a particular species such as Panthera leo (Lion) or just Mammals or even Vertebrates as a whole, I found that understanding at least the basic evolutionary relationships between the animals within that group massively helped me when attempting to make sense of their sometime complex biology. As I touched upon yesterday, I wish for this blog to remain accessible for everyone, and not just people with a scientific background or knowledge, so today’s post will be a brief overview of Panthera evolution, enough as to bring everyone onto more or less the same page.
Of course, with the amount of conflicting studies published, I could write a whole series of posts about the evolution of big cats, (maybe I will in the future) but for today, I want to focus on the results of one particular study that caught my eye a few months ago. I’m having a little difficulty in uploading a copy of the study onto WordPress so if you would like a copy please do email me at email@example.com “Supermatrix and species tree methods resolve phylogenetic relationships within the big cats, Panthera (Carnivora:Felidae)” is a lot more interesting than the title suggests!
Conducted in 2010, this study recognises the fact that no two matching molecular evolutionary trees have been published for Panthera. Evolutionary trees are diagrams used to represent relationships between different organisms of a group. For example, Vertebrates have an evolutionary tree which is well agreed upon within the scientific community, I’ve included a simplified form of the tree below and it should be very familiar to those of you who have studied either Biology/Zoology or Geology/Paleontology.
Trees can be drawn up using either morphological (characters you can observe such as spots or stripes in the case of big cats ) or molecular (genetic data taken from samples of DNA etc) data. To provide conclusive answers to which animals are more closely related, molecular evolutionary trees are the more accepted method to determining evolutionary relationships within the scientific community.
The study by Brian W. Davis, Gang Li and William J. Murphy from Texas A&M University in 2010 produced a new molecular evolutionary tree (phylogeny) based on data collected from the following
- autosomes (any chromosome that is not a sex determining chromosome)
- both sex chromosomes (the chromosome which determines the sex of the organism, i.e male or female)
- mitochondrial genome (genetic information contained in the chromosome of the mitochondrion, composed of mitochondrial DNA).
Their results produced a tree which on first glance may appear somewhat surprising.
As you can see, their study places the Snow Leopard and Tiger as sister species. This means that they share an ancestor not shared between any other members of the group. For example, if we had a random species called Panthera random, then the Snow Leopard and Tiger would share P random as their ancestor, whilst the Jaguar, Lion and Leopard would share a different common ancestor Panthera notrandom for example. P notrandom would not be an ancestor to the Snow Leopard and Tiger, just as P random would not be an ancestor for the Jaguar, Lion or Leopard.
Don’t worry if you find that concept tricky to understand! It took me about three months to get my head around this topic (phylogenetics) and that was just the briefest of overviews. I’ll be sure to write a separate post about this going into greater detail because as I mentioned earlier, although you don’t need to have an expert level knowledge of evolution and phylogenies, it can go some way to helping understand how different species are related and in the case of big cats, historical events and how these may affect their future.
The study shows that the Snow Leopard and Tiger diverged from the rest of the species in Panthera approximately 3.9 million years ago. Then, at about 3.6 million years ago, Jaguars diverged leaving Lions and Leopards to split around 2 million years ago. This tree surprised me for a number of reasons which I’m sure will be revealed in the next few posts, however it also proves why studying evolution on a molecular level (using genomes and DNA) is so important. From initial observations you could be easily forgiven for thinking that Snow Leopards, Jaguars and Leopards are the three most closely related species of big cat because of the patterns on their fur and their ability to climb trees. These are examples of grouping animals together on the basis of their morphological (appearance) and behavioral traits, forms the basis of a branch of science called cladistics.
Evolutionary trees produced by cladistics (often called Cladograms) sometimes look extremely different to those produced by molecular data, such as the one in the study, which in turn can give you a false idea of how different species are related. This is especially important in big cats considering an evolutionary tree built on cladistics alone would look drastically different to ones built on genetic information. Most likely, the Leopard and Snow Leopard would be the most closely related species, with the Jaguar diverging sometime before. I’m conscious not to waffle on too much here as I would like to keep this as simple as possible and I’ll sum up as much I can in two take home messages.
- Contrary to what you would initially believe, genetic data shows that the Snow Leopard and Tiger are the two oldest, and most closely related species of big cat.
- Molecular phylogenetics is the most accurate way of determining the relationships between different species of big cat (and animals in general), however many relationships throughout the animal kingdom are still up for debate!
If you have any more specific questions or would like to know more about either phylogenetics or anything mentioned in the above post please do feel free to email me at firstname.lastname@example.org or reach me on twitter @pantherablog. If you would like me email you a copy of the 2010 study please also do feel free to drop me an email and I’ll reply as soon as possible, it’s well worth a read!