Within recent years, the Palaearctic tortoise fauna has undergone a radical change. If you're interested in the recognition and discovery of new species, in controversy and argument about the status of species, in neat evolutionary stuff such as resource polymorphism and resource-mediated dwarfism, and, least of all, in tortoises, then you should find this a fascinating area. I shall point out to start with that I'm referring specifically to the testudinid tortoises of the genus Testudo, an Old World taxon most closely related to the Asian tortoises (Indotestudo) and the Pancake tortoise Malacochersus tornieri and united with them in the recently-named clade Testudona (Parham et al. 2006a) [T. marginata shown here, from wikipedia].
Mostly inhabiting wooded hillsides, clearings and groves, and scrubland, little known is that some Palaearctic tortoise species are superb diggers, well able to excavate tunnels several metres long. Thanks to the pet trade, I suppose most people imagine that the staple diet for tortoises consists of tomatoes, cucumber slices and lettuce leaves. In fact wild tortoises have a surprisingly diverse diet; snails have proved quite important to some species, and they will also eat faeces and gnaw at bones and carrion. They may not drink, they indulge in vigorous combat during the breeding season, and they make loud vocalisations when they copulate.
Within recent decades just five Testudo species have been recognised (e.g., Ernst & Barbour 1989), and this conservative count will be referred to from hereon as the 'conventional' taxonomy. But, as usual, things aren't so simple anymore. A huge number of new species and newly elevated former subspecies have recently been proposed, meaning that there are now as many as 27 proposed species within the genus Testudo. As is also usual (harking back to comments I made at Tet Zoo ver 1 about the lack of good literature on the extant herpetofauna), this major taxonomic reshuffling has gone unreported in the popular and semi-technical literature, and has been avoided by field guides, so the only way to chase up any of this stuff is to track down the primary literature.
The splitting up of Testudo
The five 'conventionally' recognised Testudo tortoises are; the Spur-thighed tortoise T. graeca Linnaeus, 1758, a species that sports a large conical tubercle on the posterior surface of its thigh; Hermann's tortoise T. hermanni Gmelin, 1789, equipped with a large horny scale at the tail-tip; the Central Asian tortoise T. horsfieldi Gray, 1844 (or T. horsfieldii), a broad-shelled tortoise with just four claws on each forefoot [captive individual shown here]; the Egyptian tortoise T. kleinmanni Lortet, 1883; and the Marginated tortoise T. marginata Schoepff, 1792: a particularly large species with a strongly flared posterior margin to the carapace [see photo below].
However, two of these have now been removed from Testudo. The four-clawed Central Asian tortoise (or Horsfield's tortoise) is now regarded by many experts as being distinct enough for its own 'genus', Agrionemys Khozatsky & Mlynarski, 1966 (the idea that this taxon represented a distinct genus was resurrected in 1957 and initially the name Testudinella Gray, 1870 was used. This turned out to be unavailable due to preoccupation). It has also been proposed that Hermann's tortoise is distinct enough from Testudo to warrant generic separation, and fossils allied to this species - like 'Testudo' turgaica from Kazakhstan and 'Testudo' promarginata from Germany and France - show that its lineage has been distinct since the middle (and possibly Early) Miocene. Accordingly, Lapparent de Broin et al. (2006a) coined Eurotestudo for Hermann's tortoise and the rest of its lineage (see also Lapparent de Broin et al. 2006b, c). However, Fritz & Bininda-Emonds (2007) failed to find support for this and (based on a five-gene data set, as opposed to mtDNA alone) found Hermann's tortoise to form a clade with the Central Asian tortoise. Anyway, Eurotestudo turns out to be a junior synonym of both Chersine Merrem, 1820 and Medaestia Wussow, 1916, contrary to what Lapparent de Broin et al. (2006a) stated. If any name is used for the Hermann's + Central Asian clade, it should be Chersine.
Hermann's tortoise has conventionally been thought to consist of two taxa: T. h. hermanni in the western part of its range, and T. h. boettgeri in the Balkans. T. h. boettgeri is far less heavily marked than T. h. hermanni, and on the basis of this difference and others, it has been raised to full species status (as T. boettgeri) by some authors. Furthermore, T. boettgeri has itself been argued to include another overlooked taxon: T. hercegovinesis of the central Dalmatian region (Croatia). If Lapparent de Broin et al. (2006a, b, c) are right in separating Hermann's tortoise from Testudo and regarding it as part of a distinct genus (and they may not be), then it follows that T. boettgeri, and presumably T. hercegovinesis, are members of that same genus [image below, from wikipedia, shows the amazing flaring carapace edge of T. marginata, at left, with a Sardinian tortoise T. marginata sarda at right. The taxonomic status of the Sardinian tortoises is uncertain; they may be recent introductions].
Incidentally, another two extant taxa have recently been argued to warrant separate species status, but this time relative to the Central Asian tortoise A. horsfieldi: A. kazachstanica Chkhikvadze, 1988 and A. rustomovi Chkhikvadze et al., 1990.
The north African tortoise explosion
Under the 'conventional taxonomy', all north African tortoises are regarded as belonging to the same species, Testudo graeca. However, Highfield (1990) argued that these tortoises exhibit a significant amount of morphological diversity: the many north African populations thought to belong to T. graeca could, according to Highfield, be shown to differ markedly from the tortoises properly associated with this name (the type specimen came from 'Santa Cruz in West Barbary'; a location close to Oran, Algeria). They should, therefore, really be recognised as additional distinct species (or so it has been argued).
One tortoise from Algeria was argued by Highfield (1990) to be radically different from the others, and in fact so different that it required the creation of a new genus: Furculachelys nabeulensis, the Tunisian spur-thighed tortoise. The holotype is a partially decomposed, damaged specimen but live animals from the same region were argued to belong to the same taxon. What makes this small tortoise particularly unusual is that its suprapygal (the bone located dorsal to the pygal: the pygal is the midline bone that forms the posterior carapacial border just above the tail) is forked, hence the generic name (it means 'forked tortoise'). Living Tunisian spur-thighed tortoises are reported to be yellowish with black blotches on some of their scutes and, as indicated by the common name, large spikes are usually present on the hindlimbs [image below shows Tunisian spur-thigh, from wikipedia].
One of the most remarkable claims made about Palaearctic tortoise taxonomy is that Timothy the tortoise, kept by the English naturalist Gilbert White, represented a distinct species of which 'he' was the first known representative (Timothy was actually female). White obtained Timothy following the death of his aunt in 1780, and prior to this the tortoise had been purchased by White's uncle from a sailor in 1740. White thought that Timothy might have come from the USA (his aunt also kept box turtles), and identified 'him' as a specimen of T. graeca. Timothy's shell was preserved following her death in 1794, and seems to correspond in its size and coloration with that of some Algerian tortoises described in 1945. Highfield & Martin (1989a) wrote how Timothy and these other individuals represented a distinct species: with a carapace about 25 cm long, they were big compared to T. graeca, and they were distincely patterned too, with a ray-like pattern radiating from their yellowish-greenish vertebral and costal scutes. Bennett, the editor of the 1836 edition of White's book The Natural History and Antiquities of Selborne (1789), added a footnote in which he also argued that Timothy was distinct from T. graeca. As a result he proposed that it was a new species, T. whitei.
Van der Kuyl et al. (2005) were able to test the proposed affinities of individuals referred to T. whitei. Alas, they found that these tortoises fell within T. graeca, and specifically within T. g. graeca. They found T. graeca to consist of two complexes: a T. g. graeca clade, and a T. g. ibera clade. T. g. ibera , sometimes called the Eurasian tortoise (it occurs in Turkey, Greece, Macedonia, Bulgaria and Romania), has been suggested to be worthy of species status on several occasions. Indeed, this was supported by van der Kuyl et al. (2005) who inferred that T. ibera and T. graeca had diverged during the Early or Middle Pleistocene.
New tortoises of Europe and the Middle East
Bour (1995) named T. weissingeri for a population of dull-coloured, dwarf tortoises from the Peloponnese. These animals had conventionally been regarded as a population of Marginated tortoise T. marginata. Several authors later proposed that the supposedly distinct characters of T. weissingeri result from adaptation to a nutrient-poor, arid environment, and subsequent genetic work failed to find any indication that the Pelopennese dwarfs represented a distinct population relative to T. marginata (Fritz et al. 2005).
Of the many tortoise taxa conventionally regarded as part of T. graeca, Highfield & Martin (1989b) regarded T. zarudnyi (Nikolski, 1896) of the Iranian central plateau* as a distinct species. A rare, arid-land tortoise with an elongate carapace and flared, serrated marginal scutes, its diagnostic features include eyes which are unusually elongate and almond-shaped rather than rounded, dorsoventrally flattened forelimbs, and with one of the five hand claws noticeably smaller than the others. Almond-shaped eyes are also present in T. ibera and this species and T. zarudnyi are similar in several respects, the 'conventional' opinion being that they grade into one another. Highfield & Martin (1989b) thought that T. zarudnyi and T. ibera were close relatives, and that they are both close to the Marginated tortoise T. marginata.
* Although there is one record from Ashgabad, Turkmenistan.
In a taxonomic revision of the variation present within Middle Eastern tortoises, Perälä (2002) split Middle Eastern populations previously lumped together as T. graeca into eight separate species, and also named a new species from Turkey (T. perses).
Of the five 'conventionally recognised' Testudo species, the most poorly known is the Egyptian tortoise T. kleinmanni Lortet, 1883 [shown here, from wikipedia]. It is small, with females reaching just 13 cm in carapace length. In 1963 a specimen was collected from the Negev Desert in Israel (this was supposed to be the first record of this species from the country, but the occurrence of supposed T. kleinmanni individuals from the region had actually been written about during the 1880s). Perälä (2001) argued that the Negev animal was only superficially similar to T. kleinmanni, and could in fact be readily distinguished from it: with its particularly wide mid-body region, narrow vertebral scutes, and other distinctive features it was deserving of recognition as a new species, and was named T. werneri (after herpetologist Y. L. Werner).
And I think we should stop there, though of course there are multiple other resurrected or 'newly promoted' species that I could discuss as well. Does this amazing proliferation of new species names really reflect actual, genuine discovery? Does it mean that the 'conventional' taxonomy is woefully inadequate and way too conservative? Or does it show that some workers are taking a particularly relaxed view as to what a 'species' is? Are they being misled by intraspecific variation? While this taxonomic inflation is generally in keeping with current trends (see Laissez-faire lumping under fire again on ver 1), many of the newly proposed - or newly resurrected - species have proved controversial. One of the main problems seems to be that all of the 'new' species have been differentiated on morphological grounds (often on shell characters, but also on body size, scale size and distribution, and overall body colour), and there is a widespread suspicion among testudine workers that these are relatively 'plastic' features, prone to substantial variation and easily modified according to an individual's life history. Indeed exactly the same problem has afflicted research on the giant island endemic tortoises of the Indian Ocean (for more on this, see the ver 1 article here).
With so many 'new' species now awaiting detailed evaluation (and with many of the claims being very recent), it is taking a while for the right sort of work to be done. However, to date, the results indicate that 'premature taxonomic inflation' (Parham et al. 2006b) has occurred. Genetic studies suggest that the 'conventional' taxonomy is better supported, and that strikingly little genetic variation exists between some of the putative new species (Fritz et al. 2005, 2006, van der Kuyl et al. 2005, Parham et al. 2006a, b). Given the high conservation priorities of Palaearctic tortoises, it can be argued that unfamiliar species names can obscure important evolutionary lineages [the image below, showing Galapagos giant tortoises, is irrelevant but I thought it looked pretty weird].
As Fritz et al. (2005) noted, most of the newly described or revived Testudo species have been published in 'grey literature'. Indeed, many of the relevant papers have appeared in privately published books and booklets that aren't widely available, or in obscure, hard-to-get journals. Examples of the latter include Emys, Dumerilia, Herpetozoa, Chelonii and Manouria. I know that describing these journals as 'obscure' and 'hard-to-get' is unjust given that they are required and regular reading for specialist testudine researchers, but for the rest of us... well, how many academic libraries do you know of that stock back-issues of Manouria?
And, if you're wondering, Manouria is a generic name for an Asian tortoise.
Those who keep track of such things may be interested to know that this article has been alluded to since June 2007 at least. Another one to tick off the list.
Refs - -
Bour, R. 1995. Une nouvelle espèce de tortue terrestre dans le Péloponnèse (Grèce). Dumerilia 2, 23-54.
Ernst, C. H. & Barbour, R. W. 1989. Turtles of the World . Smithsonian Institution Press, Washington, D. C. & London.
Fritz, U., Auer, M., Bertolero, A., Cheylan, M., Fattizzo, T., Hundsdörfer, A. K., MartÃn Sampayo, M., Pretus, J. L., Široký, P. & Wink, M. 2006. A rangewide phylogeography of Hermann's tortoise, Testudo hermanni (Reptilia: Testudines: Testudinidae): implications for taxonomy. Zoologica Scripta, 35, 531-543.
- . & Bininda-Emonds, O. R. P. 2007. When genes meet nomenclature: tortoise phylogeny and the shifting generic concepts of Testudo and Geochelone. Zoology 110, 298-307.
- ., Široký, P., Kami, H. & Wink, M. 2005. Environmentally caused dwarfism or a valid species - is Testudo weissingeri Bour, 1996 a distinct evolutionary lineage? New evidence from mitochondrial and nuclear genomic markers. Molecular Phylogenetics and Evolution 37, 389-401.
Highfield, A. C. 1990. Tortoises of north Africa: taxonomy, nomenclature, phylogeny and evolution with notes on field studies in Tunisia. Journal of Chelonian Herpetology 1, 1-56.
- . & Martin, J. 1989a. New light on an old tortoise - Gilbert White's Selborne tortoise re-discovered. Journal of Chelonian Herpetology 1 (1), 13-22.
- . & Martin, J. 1989b. A revision of the testudines of north Africa, Asia and Europe - Genus: Testudo. Journal of Chelonian Herpetology 1 (1), 1-12.
Lapparent de Broin, F, de, Bour, R., Parham, J. F. & Perälä, J. 2006a. Eurotestudo, a new genus for the species Testudo hermanni Gmelin, 1789 (Chelonii, Testudinidae). C. R. Palevol 5, 803-811.
- ., Bour, R., & Perälä, J. 2006b. Morphological definition of Eurotestudo (Testudinidae, Chelonii): first part. Annales de Paléontologie 92, 255-304.
- ., Bour, R., & Perälä, J. 2006c. Morphological definition of Eurotestudo (Testudinidae, Chelonii): second part. Annales de Paléontologie 92, 325-357.
Perälä, J. 2001. A new species of Testudo (Testudines: Testudinidae) from the Middle East, with implications for conservation. Journal of Herpetology 35, 567-582.
- . 2002. Morphological variation among Middle Eastern Testudo graeca L., 1758 (sensu lato) with a focus on taxonomy. Chelonii 3, 78-108.
Parham, J. F., Macey, J. R., Papenfuss, T. J., Feldman, C. R., Türkozan, O., Polymeni, R. & Boore, J. 2006a. The phylogeny of Mediterranean tortoises and their close relatives based on complete mitochondrial genome sequences from museum specimens. Molecular Phylogenetics and Evolution 38, 50-64.
- ., Türkozan, O., Stuart, B. L., Arakelyan. M., Shafei, S., Macey, J. R., Werner, Y. L. & Papenfuss, T. J. 2006b. Genetic evidence for premature taxonomic inflation in Middle Eastern tortoises. Proceedings of the California Academy of Science 57, 955-964.
van der Kuyl, A. C., Ballasina, D. L. P. & Zorgdrager, F. 2005. Mitochondrial haplotype diversity in the tortoise species Testudo graeca from north Africa and the Middle East. BMC Evolutionary Biology 2005, 5:29 doi:10.1186.1471-2148-5-29
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Those tortoises are demonstrating what the zoologist Roger Caras referred to as the triumph of instinct over anatomy (can't remember the exact quote).
By the way, is it known to what extent Palearctic tortoises hybridize in the wild? That could perhaps explain some of the observed morphological diversity.
I see it as another example of PR-species, forms elevated from race to a species for public relations (often to draw interest to conservation of an animal or a place).
One friend was involved in CD on turtles on the world, and found that various european pond turtle subspecies described were simply wrong (e.g. form was described as larger, but average measurements were practically identical, or sample size was few, or form was described as more spotted, but lots of individuals were unspotted etc.).
BTW, tortoise would become ill from a diet of mostly tomato, cucumber and lettuce. These guys should eat mostly low-calorie weed leaves (as correctly shown on photo). Contact terrarium forums for the current wisdom of what is good for a tortoise.
Hi Jerzy, thanks for comment...
There is no doubt that this happens (though, I would say, often for appropriate reasons actually). However, in this case many of the new taxonomic decisions (but NOT ALL) are made in literature that - it might be argued - is of the 'hobbyist' genre. Frazier (2006), in a review of Justin Gerlach's Giant Tortoises of the Indian Ocean said 'There is a rich, centuries-old tradition of natural history books by gentleman naturalists; and tomes on turtles and tortoises are particularly noteworthy in this genre' (p. 368), concluding with 'As a continuation in the long line of popular literature on chelonians, this book is sure to be well-liked among the large, active community of herpetological enthusiasts, particularly tortoise afficianados. It may not fare so well in the scientific community, where there is, early or late, a requirement for rigorous defense of claims and theoretical constructs, the clear separation of factual information from speculation, and theoretical discussion based on sources that have survived some form of academic review and critique' (p. 372). These comments, I think, apply to much of this so-called 'grey literature'.
Ref - -
Frazier, J. 2006. [Book review] Giant Tortoises of the Indian Ocean. The Genus Dipsochelys Inhabiting the Seychelles Islands and the Extinct Giants of Madagascar and the Mascarenes. Herpetological Review 37, 368-373.
Whether the various promotions of populations and subspecies to specific status be justified or not, I don't see why anyone ought break up monophyletic genera. It causes confusion for no particular gain I can see.
Weren't all chelonians Testudo to Linnaeus?
It's easy to see how a bird species could remain monophyletic from Tashkent to Timbuktu, but to my (admittedly limited) knowledge T. graeca can't fly. Do they get around more than I imagine, or did their genetic heritage simply stabilize geological ages past? Does drift take any local population's genome only in already well-explored, conspecific circles?
I can imagine that with enough time a species might accumulate within its private genome all the variations needed to cope with every eventuality it has encountered, and only afterward expand its range. Then it is found expressing just those characters called upon by local conditions, and seeming distinct to local collectors. Perhaps the same process is seen in amoebae and nematodes, while younger, less experienced lineages are still busy speciating?
Re: "little known is that some Palaearctic tortoise species are superb diggers" Little known, but not particularly surprising to someone of Nearctic origins: one American species is even called the "Gopher Tortoise" (Gopherus)!
--
How closely related are these Palearctic types to Nearctic ones? Are American Box Turtles (Terrapene) closely related to them? My sense is that, at least in American English, "tortoise" means roughly "Primarily terrestrial Chelonian with highly domed carapace": do the animals with this morphotype (including box turtles) form a clade, or is "tortoisehood" a rampantly convergent trait?
I really MUST learn to do my homework before posting questions on the internet!!
So. First stop was the American Museum of Natural History to find Eugene S. Gaffney's WWWebpage (AMNH>Research>Paleontology>Staff) which has a high-level cladogram (and some other neat, illustrated, stuff). It referred me to the ToL Testudines page which gave further detail. And a trip to the Animal Diversity site (University of Michigan) got some lists of genera in families.
So, bit of an answer: American Gopher Tortoises are in the family Testudinidae, along with the Eurasian tortoises like those described in Darren's post and the big island tortoises and...
This family is united in a superfamily(*) Testudinoidea with two other families, Bataguridae and Emyidae. (Relations between Testudinidae and Bataguridae seem to be a bit obscure: some indications that each is paraphyletic with regard to the other.) And American Box Turtles are Emids, along with a lot of lower-carapaced, more aquatic, types. So it appears that there is a monophyletic bunch, the Testudinidae, of tortoises that includes MOST of the types with tortoise morphology, but that Box Turtles evolved their high-domed tortoisiosity convergently.
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(*) I've already heard the sermon about the artificiality, subjectivity, uselessness, etc, of Linnean ranks, o.k.?
Allen Hazen:
According to the most recently published source in Darren's reference list (Fritz & Bininda-Emonds, 2007), Gopherus is the sister taxon to the Asian genus Manouria. These two genera, in turn, form the sister clade to all remaining testudines. So yes, North American gopher tortoises are 'true' tortoises too.
No, box turtles are (apparently secondarily) terrestrial members of the pond turtle family, Emydidae (Stephens & Wiens, 2003). Interestingly, there is also one aquatic box turtle species, the Coahuilan box turtle Terrapene coahuila (Webb et al., 1963).
References:
Stephens, P.R. & Wiens, J.J. 2003. Ecological diversification and phylogeny of emydid turtles. Biological Journal of the Linnean Society 79, 577-610.
Webb, R.G., Minckley, W.L. & Craddock, J.E. 1963: Remarks on the Coahuilan box turtle, Terrapene coahuila (Testudines, Emydidae). The Southwestern Naturalist 8, 89-99.
Ah, I see you applied your self-correcting mechanism while I was composing my reply, Allen.
Allen Hazen: AFAIK, Terrapene belongs to the Emydidae, so is a different family altogether.
There's another emydid that is semi-aquatic, but tends towards terrestriality, the North American wood turtle (Glyptemys insculpta). The Geoemydidae also has a number of species that could be considered more terrestrial than semi-aquatic; these include certain species of Rhinoclemmys, Cuora, Heosemys and Vijayachelys. These do have higher-domed shells than their semi-aquatic counterparts.
According to this site, Gopherus belong to a different subfamily from Testudo, and so would appear to be not very closely related at all.
Let's not forget the Meiolaniidae, and the Late Cretaceous nanshiungchelyid Basilemys, which were also apparently quite tortoise-like in their morphology.
So I suppose "tortoisehood" is indeed a convergent trait; there is a family of "true" tortoises, with members of other families becoming tortoise-like with the adoption of a terrestrial lifestyle.
Bataguridae is a junior synonym of Geoemydidae.
(Unless of course you elevate its two current subfamilies, Batagurinae and Geoemydinae, to family rank, but, interestingly, nobody has done that so far.)
That's not how it works. Neutral alleles disappear over time due to genetic drift at, I suppose, the same rate at which new ones appear; and alleles that affect the morphological phenotype are not terribly likely to be neutral. Frontloading really would require constant miracles; it's not simply wrong because all of its proponents before you have been creationists. :-)
Is there anything that makes you think amoebae and nematodes are anything but busy speciating? (Or which species concept are you using, if any?)
David: OK, but these tortoises are still, apparently, genetically more or less uniform over what seems like an improbably wide range, given their locomotory challenges. If this is not achieved by simple stability, it must be by mixing, right? Do they migrate? Make pilgrimages? Mate preferentially with members of neighboring populations? Post sperm samples?
I don't imagine that all or most amoebae or nematodes are stable, in the nautilus/ginkgo/coelacanth sense, but maybe some are. Their locomotory difficulties seem similar to tortoises', so if any that are stable occupy a similarly wide range, they would be similarly in need of explanation.
Do I use a "species concept"? I try not to, but some creatures with their unseemly similarity to remote ancestors force one (or more) on me.
I don't really understand the "constant miracles" argument. Some creatures maintain more genes than others; I had read that amoebae carry ten times as many as you or I. Having more total genes seems to allow for more phenotypic variation with less pressure to retain genetic innovations. Can you please explain further? I might even learn something.
There are several species of nautilus. The ginkgos have changed appreciably -- all that paleoart that shows modern ginkgo leaves in the Mesozoic is wrong; the farther back in time you go, the more slits the leaves contain and the smaller and more numerous the fruits are. The coelacanths (both species) have undergone a lot of molecular evolution, and more than zero of morphological one, too.
Oops, hit "post" too early.
Firstly, that's not the case: they carry ten times as much junk as you or I (repetitive DNA, retrovirus corpses in all stages of decay, that sort of thing). Secondly, having more genes wouldn't mean maintaining more alleles of the same gene in the population.
Depending on which of the 25-upwards species concepts -- definitions of the term "species" -- you choose, there are between 101 and 249 endemic bird species in Mexico.
Is there any species concept that is "more accepted" or more "popular" than others? I don't know much about it, but it seems like some groups are treated inconsistently (especially bird "species" with massive non-clinal variation over a huge range - some are split finely, others are a single mass.)
Also, does anyone else think fossil hominids are too split? I really don't see how the hominids closer to us than chimpanzees can form 6+ genera. Is there a reason for this I don't understand?
Any group with at least six species can form six genera, because there's no minimum or maximum amount of variation (however defined) required or allowed for a genus.
Now I do think palaeoanthropologists' enthusiasm for giving every new find a new genus is excessive, but it's somewhat consoling to see how many of these genera have eventually been sunk into Homo or Australopithecus.
(Now, it might be an amusing thought exercise to try and make out what taxonomy of the human total group would be if we were to insist on monophyletic genera. The Palaeos.org page on the Hominini has an attempt of sorts.)
David: It's good to know that about amoeba DNA's coding/non-coding ratio. I knew there were more than one each of nautilus and coelacanth species. I don't doubt that the degree of fine-tuning each must have achieved over the eons would (could we fully apprehend it) beggar imagination. Alleles of the same gene? Phenotypes arise by wondrously complicated pathways. I only meant that every genome is a product of a long history, and retains responses to many circumstances an individual may never encounter.
I still don't understand the "constant miracles" remark. Chickens still carry genes for teeth, and for long tails, either of which might someday turn out useful in some environment. Is that miraculous, or just untidy?
However, we haven't got to the central question: how can T. graeca maintain its genetic uniformity over such a wide range, considering its limited mobility? And is it unique, in this regard?
These genes are for the most part broken, and repairing them would require a sizable amount of mutations
By being promiscuous, I suppose, so that the genes travel around even if the animals don't.
Would surprise me.
Nathan, if you're having problems with the idea that T. graeca is (relatively) uniform across its range (south-east Spain, north-west Africa, the Balkans, Turkey, Iran, Syria, Georgia), note firstly that terrestrial animals were able to move between the African and European sides of the Med during the Pleistocene. Some workers have suggested a Europe-Africa land bridge at 1.3 Ma, but more popular seems to be an eastern European route that was available late in the Early Pleistocene. I can't pretend to have kept up to date on this however.
Furthemore, I haven't got time to dig out the reference, but I have a vague recollection of an article in TREE by Kevin de Queiroz in which trans-Mediterranean over-water dispersal in tortoises was used as a case study. The article was called something like 'The renaissance of dispersalism in biogeography', though the title might have been more catchy :)
What I'm hearing is that T.g.'s genome (a) is (presumed?) not especially stable, and (b) circulates not especially fast, but fast enough to exceed drift and local selection. Promiscuity can't transport the genome any faster than the testudinous lotharios and strumpets can walk (or float) between assignations -- unless we're enlisting African swallows. I guess what's surprising to me, then, is how slow "fast enough" seems to be. There must have been work on this.
I would like to take issue with your comments and general hypothesis. First, you state "Van der Kuyl et al. (2005) were able to test the proposed affinities of individuals referred to T. whitei. Alas, they found that these tortoises fell within T. graeca, and specifically within T. g. graeca. "
If you actually read this article carefully (and communicate with the authors) you will note that they mrely assumed that the animals they were comparing fell within these taxa. They relied upon ex-pets and zoo animals of unknown origin, guessed at their identity, and conducted no field collection of samples whatsoever from many of the forms discussed. The whole article is contaminated by this highly defective methodology. If you are unable to accurately establish the status of the animals you are comparing, any conclusions reached are clearly invalid. Garbage in - garbage out is as true in taxonomy as it is in computing.
What is required here is some additional, accurate, baseline DNA data. This can only be collected from populations in situ - not from a mixed bag of ex-pets with guessed identities and unknown origins.
Andy C. Highfield
www.tortoisetrust.org