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King Island Emu (1 Viewer)

Capreolus

Well-known member
As I mentioned on other threads, I'm writing and illustrating a book on extinct birds. I would like some feedback on the taxonomic status of the King Island Emu and Kangaroo Island Emu, two taxa of dwarf emus that were about half the size of the mainland Emu. Both evolved independently and very recently, after ca. 11 kya, when rising sea levels at the end of the Pleistocene created their island refugia (King I is located off the nw tip of Tasmania, Kangaroo I is located sw of Adelaide, South Australia). Both emus disappeared in the early 1800s.

Heupink et al. (2011) (free-access paper available at http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018728) sequenced the complete mt control and CO1 regions of 22 Emu specimens (18 mainland, 4 King Island), comprising 1,094 bp of the CR and 1,544 bp of CO1. Only 13 (7 CR, 6 CO1) of the 2,638 bp sites were variable. The number of variable sites per specimen ranged from 1 to 8; the 4 King Island specimens had either 5 (n = 1) or 6 (n = 3) variable sites.

Although the King Island Emu specimens exhibited 2 unique haplotypes (differing by 1 substitution), they fall within the range of variation of the mainland Emu in both regions. The maximum distance between any King Island and mainland haplotype is 2 substitutions in the CO1 region (0.13%) and 5 substitutions in the CR region (0.46%).

Heupink et al. therefore concluded that the King Island Emu is a subspecies of the mainland Emu.

Until recently, my opinion has been that the King Island Emu (and by analogy, the Kangaroo Island Emu) was a distinct species, based on the striking difference in size compared to the mainland Emu, as well as its proportionately shorter legs and neotonous domed cranium (the plumage also differed in being nearly black). However, my opinion is waivering, not so much because of Heupink et al. (low genetic diversity alone doesn't necessarily mean closely-related taxa are conspecific), but because of similar examples among mammals, including the diminuitive Florida Key Deer and Bornean Elephant, which are both regarded as subspecies (of the White-tailed Deer and Asian Elephant), indicating that size alone isn't sufficient to determine taxonomic status.

On the other hand, the Pygmy Three-toed Sloth (endemic to Isla Escudo de Veraguas, Panama), has been described as a species distinct from the mainland Brown-throated Three-toed Sloth, on the basis of skull morphology and pelage, although I don't know if genetic sequencing has been done yet. The Florida Keys, Borneo, and Isla Escudo were all formed at the end of the Pleistocene like King and Kangaroo Islands.

Also instructive is the many breeds of dog, which despite their great disparity in size and morphology, all belong to the same species and are all potentially capable of interbreeding (although I would pity the poor lady Chihuahua that catches the eye of a love-truck Great Dane!).

Given my perplexity (and addiction to this site), I'd like to get some feedback from the many learned minds that contribute here. In particular, I'd like to know of any bird species whose subspecies exhibit as great a disparity in size as the examples mentioned here, in which the smallest subspecies is at least 25% smaller than the largest.

Any opinions and feedback would be appreciated.

Thanks,
Rick
 
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I guess my concern would be, is size all that is distinct about these taxa? Body size is, at least for flightless things, one of the first few things that changes as taxa adapt to island environments.

Also would the size act as a barrier to reproduction should the populations come into contact? I used the prior criterion to argue for separate species status of Galapagos Fur Seal from South American Fur Seal, since body size appears to be the most important feature among the group in relation to reproductive isolation.
 
Unfortunately, because both dwarf emus are extinct, determination of their taxonomic status rests primarily on their morphology and genetics. What little is known of their behavior indicates it was similar to that of the mainland Emu. So yes, from what we know, they were primarily distinguished from the mainland Emu by their smaller size. Because emu are flightless, the comparison with large mammals that have also undergone island dwarfing, like the Florida Key Deer and Bornean Elephant, may be apt.

I don't think the retention of the juvenile domed-shaped cranium in adult dwarf emus would be an isolating mechanism, as I think (please correct me if I'm wrong) the shortened muzzles of some dog breeds are also the result of neotony.

In Walker's Mammals of the World (6th ed., 1999), the Galapagos Fur Seal is recognized as a separate species from the South American Fur Seal. Was it once regarded as a subspecies? And are you saying that regarding these two taxa, size would indeed be a reproductive barrier if there was secondary contact?
 
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About size you maybe better check yourself eg. Eurasian Eagle Owl or Peregrine or Goshawk. Anyway, Bantu Pygmies and Dinka are more different by size than 25% but are the one and only living subspecies of Homo sapiens.

AFAIK, both island forms of emu are very poorly known from just few specimens. So perhaps their visual differences are also exaggerated.
 
Both dwarf emus are known from skins and skeletons of birds collected on King Island and Kangaroo Island in 1802-1803 by the Baudin expedition. Only two survived the return voyage, a representative of each species, and they lived together in the Jardin des Plantes until 1822, dying within a few months of each other. The skin of one, a King Island Emu, and the skeleton of the other, a Kangaroo Island Emu, are still preserved in Paris. There is also a skeleton in Florence (from one of the dwarf emus that died on the return voyage), a skin in Geneva that probably came from the same bird as the skeleton in Paris, a skin in Torino, and a 2nd skin in Paris, of a juvenile (also from emus that died at sea en route back to France). In addition, numerous bones of both emus have been found on their respective islands, so there is plenty of evidence proving how small they were.

I will check the Eurasian Eagle Owl, Peregrine, and Goshawk to see if they include very small subspecies, as you suggest. Thank you.
 
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I think there are two SACC proposals (both passed) that are relevant to this discussion:

One is the proposal for treating Peruvian Pelican as a separate species from Brown Pelican, based among other things on size differences making the perception of mating between them difficult to grasp: http://www.museum.lsu.edu/~Remsen/SACCprop271.html

The second is the proposal to recognize (among others) Trinidad Motmot as a full species: http://www.museum.lsu.edu/~Remsen/SACCprop412.html. If I remember correctly, there was an argument that a population that arrives on a small island CAN (but does not have to) develop at a faster speed than the mainland ones, and therefore can achieve species status in relatively short time (but please review the evidence yourself).

Niels
 
Thank you, Neils! Yes, both proposals sound like they may shed some light on this discussion. I appreciate you suggesting them.

btw...I initially recommended to David Donsker that both taxa be recognized as species when extinct taxa are added to the IOC World List, but a decision hasn't been made yet.

Rick
 
In the case of the Galapagos Fur Seal (which are the smallest species of fur seal), available genetic data has found them to be not terribly differentiated from the South American Fur Seal, and the similar sized New Zealand Fur Seal. We lumped the latter into the former, but maintained Galapagos Fur Seal for it's small body size. Sympatric species of otariid chiefly differ in body size...Large males have trouble reproducing with females of smaller species (to the point where, in the case of male South American Sea Lions and female fur seals, the female is usually crushed to death). Similarly, smaller males of other species are not likely to be able to get access to females of a larger species, due to exclusion from the large size males.
 
Thanks, Mysticete, for elucidating further. If I understand you correctly, you're saying that the South American Fur Seal, Arctocephalus australis and the New Zealand Fur Seal, A forsteri are conspecific? May I also ask, who is the "we" to whom you refer?

Are you also saying that males of the South American Sea Lion, Otaria flavescens sometimes attempt to mate with female South American Fur Seals, despite the fact that they belong to different genera?
 
I refer to my coauthor, Dr. Annalisa Berta, who actually wrote most of the Otariidae section of a recent taxonomic review we did (I wrote the Intro and the Phocid section, and gave opinions on the other stuff)

Yes...we treat the New Zealand Fur Seal as a subspecies of the Southern Fur Seal, which also includes two other subspecies of South American Fur Seal

Yep...Otaria (South American) hybridizing with South American Fur Seals, although most of the attempts end with the female fur seal being crushed to death (yes...there is photo documentation of this as well). There is also morphological evidence for hybridization between a Otaria and Galapagos Sea Lion, which are also different genera. These two species rarely come into contact, and presumably this was a result of vagrancy, although I can't remember the details

Basically, male fur seals and sea lions will mate with anything (as will Elephant Seals). Permanent Testoterone poisoning. There is even documented cases where fur seals have attempted to mate with Penguins!
 
Fascinating stuff, Mysticete.

So, considering the propensity of male otariids to mate like Tiger Woods and that inter-generic hybridization has occurred, would you say that size is an isolating reproductive mechanism in the Otariidae?

btw...the bird book I'm working on was originally part of a larger work on extinct mammals, birds, and herps. I'm now planning on doing each as a separate volume. Did you include the extinct Caribbean Monk Seal in your taxonomic review of the Phocidae?
 
Yes, in my opinion, if you are bsc, size is the most important barrier to reproductive isolation

that said voice and breeding site selection may play a role. I recently read a paper that said Subantarctic and Antarctic Fur seals, when they breed on the same island, prefer different environments (Tussocky mounds vs gravel beaches).

Voice has been argued to also be significant in reproductive isolation between fur seals in Australia, but there hasn't been a whole lot of research in this area. We really are only now starting to get more interest in speciation processes in marine mammals, and some groups, such as killer whales, seem to have some pretty weird stuff going on.

by the way, are you planning on Including the Japanese Sea Lion? This has recently (in our review, but also other authors) been considered a separate species from the California Sea Lion. There have been no confirmed sightings since the 1960's, and while some people hold out hope for survival in Korean waters, I suspect it is extinct.
 
So if size is the most important factor in reproductive isolation in otariids, then it's plausible that it's an isolating mechanism in other large mammals...and perhaps also in large birds, like the emus? The difference in size between the dwarf emus and the mainland Emu was so great I don't know if reproduction would have been mechanically possible. Are there any otariid species where the females are 50% smaller than the males?

It's been a few years since I've worked on the mammals (birds have been occupying all my time), but yes, I was planning on including the Japanese Sea Lion, though as a subspecies; I wasn't aware of the recent change in its taxonomic status. I still have my Red Data Book from 1978, where it's listed as Endangered on a pink page.
 
well...Otariids have strong sexual dimorphism and are not to picky on mates. I simply use them as a good example of how size can be important in maintaining reproductive isolation. Most birds that I am aware of tend to rely on vocals/displays much more than mammals, but of course we don't know what was going on in the extinct emu. I think if the body size difference was drastic, than yes, it could function as a reproductive barrier. I just am not knowledgable on what degree of size difference between the two bird species is necessary to make things...awkward.

I wanna say there was a recent SACC proposal that used body size differences as evidence of reproductive isolation (along the same line of reasoning), but I can't recall which proposal or what group of birds!
 
Also remember that if the length difference is 2x, then likely the weight difference is between 4x and 8x.

I think the SACC proposal is the Peruvian Pelican one that I mentioned in a previous post.

Niels
 
According to Marchant and Higgins (1990), the average length of the tarsus of the mainland Emu is 41.93 cm (39.5 - 45 cm; n = 89). According to Parker (1984), the average length of the tarsus of the King Island Emu is 23.21 cm (20.5 - 27.8 cm; n = 50),

So the tarsus of the King Island Emu is, on average, only 55% as long as the tarsus of the mainland Emu. Conversely, the tarsus of the mainland Emu is 181% longer than that of the King Island Emu.

I've read both proposals, Neils, and am working my way through Stiles's paper on Momotus. Was Trinidad attached to the mainland during the Pleistocene? If so, wouldn't that mean that bahamensis evolved after Trinidad became isolated at the end of the Pleistocene?
 
Murphy in "A Birdwatchers guide to Trinidad and Tobago" says: Trinidad became an island about 10,000 years ago at the end of the Wisconsinan glaciation of the Pleistocene Epoch.

He did not include a reference for where he had that from. But his argument about rising sea levels as ice caps melted corresponds to what I have read elsewhere.

In Stiles, a relevant quote would be:
The splitting off of bahamensis occurred relatively recently; at the geographic terminus of the Andes, it is however possible that the Trinidad-Tobago population had begun to differentiate well before rising sea levels severed the land connection to Venezuela’s Paria Peninsula. In any case, this population has diverged phenotypically to a much more marked degree than has argenticinctus, doubtless reflecting its small size and total isolation during at least the last 10-15,000 years, which could have facilitated fixation of unique alleles via selection or genetic drift.

Niels
 
Sorry NJ...I must have remembered your comment on the Pelican, but then had already forgotten it was mentioned already in this thread!
 
I was hoping that bahamensis would show that speciation can occur very rapidly on a continental-shelf island attached to the mainland in the Pleistocene and isolated for only the last 10 ky or so. Interestingly, the map in Stiles (p. 5 / 33) shows that there isn't a contiguous representative of the momota complex on the mainland opposite Trindiad. The nearest representative, momota (sensu stricto), occurs south of the Orinoco.
 
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