Australian placental cats

December 11, 2015 • 8:30 am

by Greg Mayer

Australia is a zoogeographer’s dream world—it’s the most spectacularly distinctive place on Earth, and we know why. Around 250 million years ago, most of the world’s continental plates amalgamated into a single super-continent—Pangaea. During the Mesozoic (the “Age of Reptiles”), Pangaea began breaking up, with many of today’s southern continents (South America, Africa, Antarctica, Australia, and India) pulling away to form the somewhat smaller super-continent of Gondwanaland.

The continental breakup continued, with the various parts of Gondwana separating from one another (hence the traditional rallying cry of irredentist geologists, “Reunite Gondwanaland!”). Africa, India, and, most recently, South America eventually bumped into the northern continental masses, making for interesting geology, and—of the greatest importance for zoogeography—allowing large land animals to move between the major land masses. Such animals are not, in general, susceptible to “occasional means of transport”, as Darwin called them, that allow birds, bats, and smaller animals to traverse greater or lesser expanses of the sea, and thus large land animals require a dryshod path to disperse.

But, unlike those other Gondwanan remnants, Australia has not—yet, anyway—bumped into the northern land masses, and thus has undergone a long and and continuing period of splendiferous isolation, during which time many unique endemic forms have arisen, and radiated into the great variety of ecological niches occupied by different lineages in the rest of the world. Most famous of these are the Australian marsupials, which have undergone a continental-scale adaptive radiation, which Jerry highlighted in chapter 4 of WEIT.

Adaptive radiation and convergence in Australian marsupials (Fig. 20 from WEIT © Kapi Monoyios).
Adaptive radiation and convergence in Australian marsupials (Fig. 20 from WEIT ©  Kapi Monoyios).

This radiation has brought marsupials into most of the ecological niches inhabited by placental mammals in the rest of the world—predators, herbivores, gnawers, burrowers, insectivores, gliders, etc. Two things are evident in the radiation of Australian marsupials. First, that convergence can lead to remarkable similarity when distantly related lineages adapt to similar environments—Jerry highlights this in the figure above; but, second, that sometimes forms inhabiting the same ecological niches can be quite different.

We can see both of these by thinking about which animals are the big, dominant, mammalian carnivores and herbivores. Everywhere on Earth but Australia, these animals are cats, dogs, cattle, and deer (taking cattle in the sense of the family Bovidae, including antelope, goats, etc.). In Australia, the dominant carnivores are the thylacine (or Tasmanian wolf or tiger), native cats (hence, placental cats in the post title, to make clear who I meant), and devils. The skull of the thylacine is remarkably wolf-like, showing a close convergence in shape and dentition to the placental wolf. Native cats have the name, but are less similar to cats; and devils are pretty much sui generis. The dominant big herbivores in Australia are kangaroos: instead of plains full of buffalo and antelope, Australia is full of kangaroos. Although they eat similar types of plants, the modes of locomotion are startlingly distinct, showing that close convergence is not inevitable. (There were some more ungulate-like marsupials in the past, but they are now extinct.)

All this was brought to mind by a new article in BMC Evolutionary Biology by Katrin Koch and colleagues on the placental cats of Australia. For some millennia now, in addition to Darwin’s occasional means of transport, another factor has allowed animals to cross the seas—human transport. And for thousands of years, man has broken Australia’s tens of millions of years of isolation by bringing in a diversity of placental mammals. Most famous is the dingo, the feral descendants of dogs brought from southeast Asia about 4,500 years ago. Since European settlement, the number of mammalian imports—both wild and domestic—has increased dramatically.

A feral cat in Queensland, eating a road killed kangaroo, by Joe Scanlan via the Daily Mail.
When zoogeographic regions collide: a feral cat in Queensland, eating a road killed kangaroo, by Joe Scanlan via the Daily Mail.

In a careful review of historical records (which includes this memorable sentence in his methods section: “Incidentally, I discovered that indexers of books rarely index ‘cat’.”), Ian Abbott (2002) showed that, despite the potential for cats to have been brought to Australia earlier by Aborigines, Malay trepangers (sea cucumber fishermen—it’s great that there’s a word for that!), or shipwrecks, the first cats seem to have been brought in by the earliest European settlers in the late 18th century. The map below shows places where cats were presumed to have been introduced (arrows) and dated records of cat appearance (dots):

Fig. 2 of Abbott (2002).
Fig. 2 of Abbott (2002).

Koch and colleagues looked at microsatellite and mitochondrial DNA—both rapidly evolving parts of the genome, and thus good for studying infraspecific phylogeny—in over 200 feral cats from Western Australia and a number of islands round Australia, including the outlying territories of the Cocos (Keeling) Islands (an island group where cat control is an issue, due to their depredations on wildlife: Algar et al., 2003) and Christmas Island.

What they found was that the cats of mainland Western Australia, and the big island of Tasmania, were all genetically fairly similar (the red areas in the figure), while the smaller islands were more distinct genetically, including an island very close to the mainland (Dirk Hartog Island, DHI–green), as well as the two outlying islands of Cocos (yellow) and Christmas (blue). Curiously, two smaller islands off southeastern Australia grouped with Christmas. Small island populations can diverge due to random genetic effects (founder effect and genetic drift), historic phenomena (founded from different sources), and selective differences (distinct environments on islands). But it’s hard to tease these apart from these data alone.

Fig. 2 Map of Australia, Southeast Asia and Europe with possible invasion routes. Possible invasion routes of cats shown on a map of Australia and Southeast Asia with Europe (EU) in the top left-hand corner. Arrows indicate invasion routes with highest support from the phylogeographic model selection approach (model 10 grey arrows; further details in Additional file 4: Figure S3). STRUCTURE plots showing ancestry (K = 4) inferred from microsatellite data for mainland Australia, Australian islands and Southeast Asia. Each individual cat is represented by a single vertical line in plots for each location. Abbreviations for populations follow Table 1
Fig. 2 of Koch et al. (2015). Map of Australia, Southeast Asia and Europe with possible invasion routes. Possible invasion routes of cats shown on a map of Australia and Southeast Asia with Europe (EU) in the top left-hand corner. Arrows indicate invasion routes with highest support from the phylogeographic model selection approach (model 10 grey arrows; further details in Additional file 4: Figure S3). STRUCTURE plots showing ancestry (K = 4) inferred from microsatellite data for mainland Australia, Australian islands and Southeast Asia. Each individual cat is represented by a single vertical line in plots for each location.

This paper has made a minor splash in the media (see Jerry’s mention here about NY Times coverage), with most places proclaiming that it shows that Australian cats came from Europe as opposed to southeast Asia. Now, the paper does show that of the 63 mitochondrial haplotypes that they found, 25 are also present in Europe (the European data are from a paper by another group). But to distinguish sources of colonization, you need to have samples from all the potential sources, find out if the source populations have any diagnostic or characteristic alleles or mutations, and then see if these are found in the colonized (i.e., Australian) populations. But Koch et al. had only three non-Australian cats—apparently one from Sulawesi, and two from Borneo. (Curiously, they refer to these as “Malaysian”, and also use that term for 17th century Malay trepangers. But Malaysia is a 20th century political construct, and Sulawesi is in Indonesia, not Malaysia, so Malay would be a better term that covers the cultural/linguistic/geographic region.)

The three Malay cats group with Australian mainland cats. But on such a slim basis, we can make no conclusions about the relative importance of the two potential source areas. While concluding their data “indicate a mainly European origin of feral cats in Australia”, the authors do allow that, “However, caution is needed in inferring the involvement of Asian cats in the history of cat colonization in Australia due to the small number of Asian samples.” We can, in fact, be sure that a significant, if not the greatest, part of Australian cat ancestry is European, but that is because of the historical researches of Abbott (2002). The genetic work of Koch et al. lays a basis for further studies of genetic variation in Australian cats and their relation to cats from other regions, but it does not, on its own, really speak to the latter question.

Abbott, I. 2002. Origin and spread of the cat, Felis catus, on mainland Australia, with a discussion of the magnitude of its early impact on native fauna. Wildlife Research 29:51-74. abstract

Algar, D., G. J. Angus, R.I. Brazell, C. Gilbert and D.J. Tonkin. 2003. Feral cats in paradise: focus on Cocos. Atoll Research Bulletin 505. (Actually published in 2004.)   pdf

K. Koch, K., D. Algar, J. B. Searle, M. Pfenninger and K. Schwenk. 2015. A voyage to Terra Australis: human-mediated dispersal of cats. BMC Evolutionary Biology 15 (262), 10 pp. pdf

Solenodons on the BBC

June 17, 2010 • 12:28 am

by Greg Mayer

BBC reporter Rebecca Morelle has been hot on the trail of the nearly extinct Hispaniolan solenodon in the mountains of the Dominican Republic. (There is another living species of solenodon in Cuba.) Here’s what they look like.

Male Solenodon paradoxus. Plate 2, Allen 1910.

The BBC pursued them along with Dominican and British scientists, breathlessly recording their hopes of finding them, their adventures along the way, and their ultimate triumph (there’s also a kid’s version version of the story).  The BBC articles have many videos and pictures, including one of a cat (next to last photo) emerging from a solenodon burrow– the kittehs are eating them!

Solenodons are among my favorite mammals, not just because they are so bizarre in their own right, but for the zoogeographic lessons we can learn from them and other island animals. In WEIT (and earlier writings), Jerry, despite being a geneticist, emphasized the biogeographic evidence for evolution. In doing so, he was following a long tradition, dating back to Darwin and Wallace themselves. P.J. Darlington (from Jerry’s and my alma mater, the MCZ), perhaps the greatest zoogeographer of the last century, said that zoogeography showed Darwin evolution.

Island faunas, especially of oceanic islands (i.e. islands never connected to a mainland, such as the Galapagos), exhibit what I like to call the three “D’s”: they are depauperate (having fewer species than equivalent pieces of mainland), they are disharmonious in their taxonomic composition (major groups from the nearest mainlands are missing, while others are curiously diversified), and show evidence of dispersal (the taxa in the fauna are able to travel over water).

The terrestrial mammals of the West Indies are definitely depauperate (there are many fewer species on Jamaica than in an equivalent piece of, say, Honduras). And they are disharmonious: the only major terrestrial mammal groups in the West Indies are insectivores (solenodons, and another, recently extinct, genus Nesophontes, called island-shrews), ground sloths (also recently extinct), monkeys (again, recently extinct), and a couple of groups of rodents (some recently extinct, but a modest number of survivors). They are completely lacking the most diverse groups of the surrounding mainlands: carnivores, both large (cougar, jaguar, bear) and small (raccoon, skunk, coati), hoofed mammals (deer, tapir, peccaries), opossums, and others.

The signs of dispersal are less clear in West Indian mammals. Rodents disperse over water well (by what Darwin called “occasional means of transport”), as, oddly, do sloths (they crossed from South to North America before the Panama land bridge formed); but insectivores and monkeys are not known for water-crossing. If we add in bats, we do see clear evidence of dispersal in the many species shared between islands and mainlands. But overall, some zoogeographers have seen the insectivores and monkeys as perhaps relicts of a former land connection, and the argument over whether the West Indies are oceanic or old continental islands (islands once connected to continents, but so long ago as to obscure the faunal characteristics: Madagascar is a classic example) is an old one in zoogeography. Indeed, the West Indies contain oceanic islands (the Lesser Antilles) and even recent continental islands (Trinidad), so that Cuba or Hispaniola being old continental islands would just complete the range of possible faunal conditions.

Female Solenodon paradoxus. Plate 3, Allen 1910.

Island faunas also show the two “E’s”: endemism (species being found on the islands and nowhere else) and extinction (island species go readily extinct when confronted by man, his habitat changes, and his many introduced species from the mainland). West Indian terrestrial mammals show high endemism (the solenodons and island-shrews are each endemic families, and there are others; no species is shared between islands and mainland), and also, regrettably, extinction: two of the four known solenodon species are extinct, and the living two are in trouble; about 80% of the 80 or so species of West Indian terrestrial mammals have become extinct in the last few thousand years.

Young Solenodon paradoxus. Plate 1, Allen 1910.

Darwin (and Wallace) argued that all five of these “D” and “E” phenomena could be explained by descent with modification, creating a consilience of inductions: if organisms had to cross water barriers by occasional means of transport (floating, swimming, flying, etc.), rather than being created in situ, then some species and groups wouldn’t get there, those that did would diversify under different biotic conditions than those on the mainland, thus filling different places in the economy of nature, and thus not being adapted to the presence of mainland forms.

The plates here are from G. M. Allen’s classic 1910 monograph, published as one of the Memoirs of the Museum of Comparative Zooogy, on the anatomy of the Hispaniolan solenodon. Most have probably never been posted to the web, so I do so here.  Here’s a Hispaniolan solenodon at the Museum of Comparative Zoology, from an unsourced photo I found on the web; it is perhaps one of the specimens studied by Allen a century ago.

Solenodon paradoxus at the MCZ.


Allen, G.M. 1910. Solenodon paradoxus. Memoirs of the Museum of Comparative Zoology 40:1-54.

Allen, G.M. 1942. Extinct and Vanishing Mammals of the Western Hemisphere with the Marine Species of All the Oceans. Special Publication No. 11 American Committee for International Wild Life Preservation.

Coyne, J. A. 2005. The faith that dare not speak its name: the case against intelligent design. The New Republic Aug. 22, pp. 21-33.

Darlington, P.J. 1959. Darwin and zoogeography. Proceedings of the American Philosophical Society 103:307-319.

Darwin, C. 1859. On the Origin of Species. John Murray, London. Chap. 12, “Geographical Distribution”.

Mac Phee, R.D.E., C. Flemming, & D.P. Lunde. 1999. “Last occurrence” of the Antillean insectivoran Nesophontes: new radiometric dates and their interpretation. American Museum Novitates 3261, 20 pp.

Morgan, G.S. & C.A. Woods. 1986. Extinction and zoogeography of West Indian land mammals. Biological Journal of the Linnean Society (London) 28:167-203.

Steadman, D.W., P.S. Martin, R.D.E. MacPhee, A.J.T Jull, H.G.McDonald, C.A. Woods, M. Iturralde-Vinent  & G.W.L. Hodgins. 2005. Asynchronous extinction of late Quaternary sloths on continents and islands. Proceedings of the National Academy of Science USA 102:11763–11768.

Wallace, A.R. 1880. Island Life. Macmillan, London.