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
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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