Book Review: The Texas Tortoise: A Natural History
by Francis L. Rose and Frank W. Judd
University of Oklahoma Press: Norman, 2014. Volume 13 in the Animal Natural History Series
Hardcover. xviii + 188 pp., including 34 color plates, 34 figures, and 3 maps.
List: $35.96, Amazon: $35.96, Ebook version currently unavailable
Review by Tom Lott
This slender volume efficiently summarizes the current understanding of the natural history of the Texas Tortoise (Gopherus berlandieri ), which is the smallest and most sexually dimorphic of the five1 surviving species of North American tortoises. Much of that information has been discovered by the authors themselves during their extensive joint and individual field studies conducted on the south Texas coastal plains populations within the past forty-plus years. A great deal of the natural history of this species, however, remains unknown and the authors are careful to point out specific areas where more study is needed and where they have extrapolated data from other species to partially fill-in some of the gaps.
The introduction includes details of the life and travels of Jean Louis Berlandier, a Frenchman dispatched to Mexico (including what became Texas) in 1826, principally as a botanist to collect plants. The type specimen of the tortoise named in his honor by Harvard's Louis Agassiz was obtained by Lieutenant Darius Couch in 1853 from Berlandier's widow in Matamoros, after his untimely death by drowning in 1851.
The authors subsequently provide a general description of the Texas Tortoise and delve into its relationship to the other North American species of Gopherus, none of which are currently sympatric, but some of which likely were during the Pliocene and Pleistocene Epochs. Also, during those periods, there were at least six additional species known from fossils sharing the continent with the currently extant five. Some of the extinct forms were quite large in comparison to the survivors.
Rose and Judd next re-examine the various systematic proposals that have been proffered for the present members of the genus. The best current evidence suggests that the Texas Tortoise and the Desert Tortoise (sensu lato) are very closely related, and the authors of the recent Desert Tortoise split (Murphy et al. 2011) are taken to task for failing to include the Texas Tortoise in their genetic analysis. Given Rose and Judd's rather critical account of North American tortoise systematics, I was hoping for a more detailed response to the splitting of G. morafkai from G. agassizii (Murphy et al., op. cit.) regarding whether these taxa should have been treated as full species or as subspecies, since this is the only instance of purported parapatric speciation within the genus. This is especially so since virtually all the available literature refers to both "species" collectively as "Desert Tortoises".
The second chapter provides an extensive analysis of the various physiographic factors defining the geographical range of the Texas Tortoise, which neatly coincides with the Tamaulipan Biotic Province (Dice 1943, Blair 1950); in fact, G. berlandieri might well be considered an index species for that province. There is a well-informed discussion of the climatic, edaphic, vegetational, and other influences serving to delineate and/or limit the distribution of this species in south Texas and northeastern Mexico, including the effects of the persistently high relative humidity enjoyed (or endured) throughout much of its range.
In the chapter entitled "Animal Associates and Relationships," Rose and Judd examine the dietary preferences of the Texas Tortoise, which is essentially a herbivore although it may occasionally ingest animal matter opportunistically. Interesting is the tortoises' marked tendency to consume grasses even though they do not possess the gut microbes required to digest the high-energy cellulose portion of the plants; presumably, the grasses provide roughage necessary for the efficient movement of food through the digestive tract.
Predators are briefly discussed, with the usual suspects (raccoons, coyotes, foxes, etc.) exacting the heaviest tolls, with the possible, and ominous exception of the population explosion of feral hogs, which, although its effects on tortoises are as yet unstudied, almost certainly have had serious consequences. As with most species, however, predation pressure on tortoises appears to lessen as the juveniles gain some size—apparently at a carapace length of about 100 mm (3.9 in.). This chapter also discusses a host of diseases and maladies that the tortoises may suffer from due to the effects of various microbes, fungi, and parasites.
Most interesting for this reviewer, however, was the authors' detailing of the mutualistic relationship that exists amongst what they refer to as the "cactus-tortoise-wood rat-rattlesnake community," which should be immediately familiar to any naturalist who has spent time afoot in the brushlands of south Texas (rather than relying on road sightings). They have even determined that the passage of prickly pear cactus (Opuntia engelmanii) seeds through the gut of a tortoise rendered them ten times more likely to successfully germinate.
In the chapter on "Morphology and Anatomy," as the authors themselves admit, they may have expounded a bit much on this topic, but after slogging through the 18 pages, the reader will emerge a bit worn but much wiser regarding tortoise anatomy. Nevertheless, this diversion does seem a bit out of place in a natural history treatise.
In the section entitled "Size, Growth, and Sexual Dimorphism," the authors return to topics more typically associated with natural history. The Texas Tortoise is unique among its congeners in producing eggs that vary in shape from nearly spherical to elliptical (the more usual shape); this varies with clutch size. There is no relationship between the size of the female and clutch size, as is seen in most species of turtles. Some sources have erroneously asserted that the eggs are flexible and softened when laid, contending that, otherwise, they would not be able to pass through the posterior opening between the carapace and the plastron. But Rose and Judd contradict this with their observations that shelled oviducal eggs in road-killed females, as well as freshly laid ones, were already hard-shelled. The solution to this perceived problem proved to be a slightly hinged posterior plastron, which was sufficiently flexible to allow the passage of hard-shelled eggs. The Texas Tortoise lays eggs between April and mid-September. The eggs may hatch from late August to early November. Hatchlings exhibit no growth from early November until March.
Seven additional chapters deal in detail with the other known aspects of this tortoise's natural history, even including suggestions regarding their captive husbandry, for, despite the authors' frequent repetition that these turtles are "protected" in the state of Texas, they recognize that many continue to be thoughtlessly "adopted." The primary factor justifying their stance against tortoises as pets involves the fact that these are long-lived animals that frequently outlast their benefactors (or the interest thereof), causing them to be neglected or released back into the wild population with the attendant risk of introducing captive-acquired pathogens into the wild inhabitants (as has been well-documented with Desert Tortoises).
If one was active in the field in south Texas prior to the 1970s, he can probably appreciate how abundant the Texas Tortoise actually was, once upon a time. Along with the Texas Horned Lizard and the Ornate Box Turtle, it constituted a trio of iconic, charismatic herps that have since suffered cataclysmic declines in abundance, especially in the northern portions of their south Texas distribution. The coincidence of this decline with the dispersal of the Imported Fire Ant (Solenopsis invicta) is essentially discounted by Rose and Judd with respect to the Texas Tortoise, given that their eggs are hard-shelled, rendering them more-or-less impervious—at least at that stage of vulnerability in many reptiles. They do concede, however, that hatchlings may be susceptible to ants during the drawn-out process of actual hatching. Rather, the authors tend to place the blame for the decline on agricultural practices (especially where the native habitat is completely cleared for monoculture) and road casualties, particularly in those areas of high oil and gas drilling activities, which are unfortunately concentrated in the middle of the tortoise's inland south Texas range.
Although the Texas Tortoise was one of the first reptiles to receive state "protection" in Texas almost fifty years ago, its "threatened" status has done little to stem its decline due to causes other than the pet trade. In the latter category of threats, however, some success has been achieved. Prior to 1967, this tortoise was collected in vast numbers and frequently stored in inhumane conditions prior to and during shipment. This disgrace has disappeared in Texas, but unfortunately G. berlandieri enjoys no protection in neighboring Mexico where, as the authors note, freeze-dried specimens may still be sold as tourist curios playing miniature faux banjos.
In summary, Rose and Judd have achieved a long-overdue triumph in this compendium of the known natural history of the Texas Tortoise, which should become a classic in the genre. Their writing contains an unabashed passion for the welfare of these gentle creatures: "Of the five species of North American land tortoises, Texas tortoises have been the most neglected by biologists and wildlife personnel charged with their welfare. . . . Laws and state regulations enacted to protect tortoises are only as effective as the level at which they are enforced. No gold stars will be given to those saddled with that challenging responsibility in Texas." (Rose and Judd 2014).
Dr. Francis L. Rose, long associated with the biology faculty of Texas Tech University, is currently a professor at Texas State University. Dr. Frank W. Judd has long been a professor at the University of Texas - Pan American.
1A sixth "species" of North American tortoise (Gopherus evgoodei) has recently been proposed (Edwards et al. 2016) by a splitting of the southern populations of G. morafkai in Sonora and Sinaloa.
Blair, W.F. 1950. "The biotic provinces of Texas." Texas J. Sci. 2(1):93-117.
Dice, L.R. 1943. The Biotic Provinces of North America. Ann Arbor: University of Michigan Press.
Edwards, T.; Karl, A. E.; Vaughn, M.; Rosen, P. C.; Torres, C. M.; and R.W. Murphy. 2016. "The desert tortoise trichotomy: Mexico hosts a third, new sister-species of tortoise in the Gopherus morafkai–G. agassizii group." ZooKeys 562: 131–158
Murphy, R. W.; Berry, K. H.; Edwards, T.; Leviton, A. E.; Lathrop, A.; and Riedle, J. D. 2011. "The dazed and confused identity of Agassiz’s land tortoise, Gopherus agassizii (Testudines, Testudinidae) with the description of a new species, and its consequences for conservation." ZooKeys. 113: 39–71
Rose, F. L. and F.W. Judd. 2014. The Texas Tortoise: A Natural History. Norman: University of Oklahoma Press.
[This review originally appeared in the Bulletin of the Southwestern Center for Herpetological Research, Vol. 6(1)]