Two well-publicised papers, published in 2018 and 2019, based on analysis of mitochondrial and nuclear genes, propagate the view that there is more than one species of giant salamander in China, that these species are ‘cryptic’ in that they do not differ in appearance, and that some are in imminent danger of extinction through ignorance of their existence. The authors certainly established that there are a number of distinct genetic lineages of giant salamander in China, enough to convince adherents to the phylogenetic species concept that they constitute different species. However, whether they are ‘good’ biological species is a matter that can be debated endlessly.
Giant salamanders in China in the wild are endangered because of over-collecting for the human food trade and from loss of habitat. Those working on the origins, evolution and conservation of these animals face major difficulties. The escape or release of wild-caught and farmed animals transported alive in large numbers throughout China in recent decades means that the geographical origin of newly-collected specimens cannot be guaranteed. By using specimens in museums collected before the vast increase in trade, the authors of the 2019 paper have overcome this problem but at a cost; the number of available specimens was small—just 17 individuals—since the DNA of many early specimens had been degraded by preservation in formalin.
The lineages are associated with the mountain ranges formed during the great geological upheavals that formed the Tibetan plateau starting about 3.3 million years ago. The authors of the 2019 paper realised that two of the lineages could be attributed to species that had been named in the past.
One lineage was be attributed to the classical domain of the Chinese giant salamander—in the northern Yangtze/Sichuan region—and conforms with Andrias davidianus. A second lineage from the Pearl River tributaries in the Nanling Mountains of south-eastern China appears to be that described by Edward George Boulenger in 1924 as a separate species, Andrias sligoi, that was later lumped into A. davidianus. A third lineage from the Huangshan mountains of north-eastern China has never been described as a separate form previously and could be a new, as yet un-named, species.
Boulenger noted morphological differences between what he named Megalobatrachus (now Andrias) sligoi and M. maximus. He would, wouldn’t he, since that is how new species were described then. But just as at the present with molecular genetic data, different people in the trade regarded some differences as too small to justify separation into a new species; others regarded the tiniest difference sufficient.
At that time Boulenger took his father's (George Albert Boulenger) view that any observable differences between Chinese and Japanese giant salamanders were too small to consider them as two species and continued to lump them into one, M. maximus. While he could find no consistent difference between the Chinese and Japanese forms, others claimed they could and the species maximus was split again into the Chinese, davidianus, and the Japanese, japonicus.
Ignoring the arrangement of tubercles on the head (which appear to differ somewhat in the Chinese and Japanese species) Boulenger also differentiated sligoi by its longer, flatter, and smoother head, and by the shorter distance between the eye and lip.
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| How Boulenger distinguished his new species, M. sligoi |
Boulenger’s new species did not survive as such. Later authors argued it was no different or insufficiently different from davidianus and into the latter it was lumped. Liu in his Amphibians of Western China, published in 1950, condemned Boulenger’s erection of sligoi as a separate species:
Neither the length of the head (which is difficult to define, and which was not defined by Boulenger) nor the relative distance of the eye from the labial border are valid characters.
But Liu did not say why the characters are not valid!
We therefore seem to have agreement between morphology (whether declared ‘valid characters’ or not) and molecular genetics published 95 years later. However, I too have doubts about Boulenger's comparison (see later article). But Boulenger may have been right all along, and the name given recently, South China Giant Salamander, Andrias sligoi, an appropriate one. However, that is only if you agree that species should be defined in that way and not by the biological species concept.
Before accepting the increased number of proposed giant salamander species, perhaps it is worth considering whether the results of the recent artificial mixing up of lineages in both China and Japan (A. davidianus has been released into Japan) have not already invalidated that proposal.
‘Good’ biological species do not or only rarely interbreed in the wild. The classic difficulty with deciding whether species whose ranges do not overlap (i.e. they are allopatric) are ‘good; biological species, is that they do not meet in the wild, and the question of if, say, a geographical barrier were to be removed, would they interbreed naturally, cannot be answered. However, if lineages interbreed freely after translocation, then the case for their being biological species is severely dented if not holed beneath the waterline. Indeed, in the 2018 paper, the authors, do show that hybridisation between lineages has occurred in farms. Similarly, hybridisation between Chinese and Japanese forms has occurred in Japan where the former has been introduced.
On the evidence of hybridisation, then, the case for a number of ‘good’ species of giant salamander, according to the biological species concept, is weak.
The authors of the two papers (many of the authors are common to both) are concerned, rightly, with the conservation of giant salamanders and with the measures that should be taken to ensure their survival in the wild. However, the type of evidence used—that different lineages equal different species—is clearly not acceptable to adherents of the biological species concept. Indeed, if it that premise were correct, two of my daughters-in-law would be of a different species to me and my grandchildren interspecific hybrids. Thus, Jerry Coyne, a world authority on speciation from the University of Chicago, in his blog, Why Evolution is True, wrote:
…virtually every paper I’ve seen on the process of speciation—that is, on the ways that new species come into being—deals not with the accumulation of genetic distance per se, but on the development of reproductive barriers that eventually prevent populations from exchanging genes.
Greg Mayer of the University of Wisconsin, making the same general point from a different case on Coyne’s website:
…At the time, this bothered me, as I saw it as an application of the old morphological species concept, extended to genetic data: if you can tell them apart, they are different species. This is also what Jerry argued against… an arbitrary amount of morphological or genetic difference, or inferred time of separation based on the amount of genetic difference, is not a sound basis for a species concept.
Here, sadly, there may be incompatibility between the politics of conservation and science. Conservationists find it easier to provoke politicians into action with measures to protect species rather than populations and habitats—thus the more species, the better the argument and the greater geographical spread of habitat protection. However, Jerry Coyne has argued cogently:
…the ‘splitting’ of species [in this case discussing the Giraffe, ‘split’ into different ‘species’ by virtue of differences in genetic lineage] is a conservationist motivation, not an attempt to partition out nature in biologically and evolutionary meaningful ways’.
The research on the giant salamanders reminds us of some fundamental biological questions, like the perpetual problem of how we define a species, as well as some urgent practical conservation concerns. Indeed the research highlights the urgent need to protect, manage and re-introduce populations of giant salamanders in the wild.
However we regard Boulenger’s Megalobatrachus (now Andrias) sligoi, the discovery of his type specimen is an interesting story that I will cover in a further article…and can we determine where those giant salamanders used for class dissection in Hong Kong in the 1960s came from?
Boulenger EG.. 1924. On a new giant salamander, living in the Society’s gardens. Proceedings of the Zoological Society of London, 1924, 173–174
Turvey ST, Marr MM, Barnes I, Brace S, Tapley B, Murphy RW, Zhao E, Cunnigham AA. 2019. Historical museum collections clarify the evolutionary history of cryptic species radiation in the world’s largest amphibians. Ecology and Evolution 2019;00:1–15. https://doi.org/10.1002/ece3.5257
Yan F, Lü,J, Zhang B, Yuan Z, Zhao H, Huang S, Wei G, Mi X, Zou D, Xu W, Chen S, Wang J, Xie F, Wu M, Xiao H, Liang Z, Jin J, Wu S, Xue C, Tapley B, Turvey ST, Papenfuss TJ, Cunningham AA, Murphy RW, Zhang Y, Che J. 2018. The Chinese giant salamander exemplifies the hidden extinction of cryptic species. Current Biology, 28, R590–R592. https://doi. org/10.1016/j.cub.2018.04.004
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