Part 3

On the other hand, Neill (1948a:157) states that in Georgia, inexpectatus is often observed basking on tree trunks, and though adults often forage on the ground, they dash for the nearest tree when disturbed, usually climbing to a considerable height before halting. The juveniles, however, are said to climb only rarely; they hide beneath objects on the ground when they are pursued. Neill stated that E. inexpectatus occurs in dry pine forests where laticeps and fasciatus are lacking, as well as in moist or even swampy woods. E. inexpectatus often forages on the sides of old buildings.

Hoffman (1953:172), in discussing means of differentiating between inexpectatus and fasciatus in Virginia, states that there are ample differences in color and behavior as well as in scalation. He describes the color difference (blue color of tail of juveniles extending anteriorly beyond pelvis; light stripes reddish-orange on head, sublateral line present, in inexpectatus) but he does not describe the differences in behavior. He states that inexpectatus is the most abundant lizard in southeastern Virginia. Carr (1940:76) also states that inexpectatus is less arboreal than laticeps and is often found under logs and boards in dry sand.

E. inexpectatus thus seems to be adapted to a somewhat drier, more open, habitat than that typical of fasciatus, but it is not clear whether either species is more arboreal in habits. It is to be hoped that the present inconclusive summary will draw attention to the problem and will lead to more critical comparisons of the habitats and behavior of the two species by herpetologists in the southeastern states. The differences, both ecological and morphological, that distinguish inexpectatus from fasciatus are of a degree usually found between subspecies of the same species. The extensive geographic overlap between them is indeed remarkable in view of the slight degree of differentiation, morphologically and ecologically. They are, however, complementary in part in their ranges, while laticeps shares all parts of its range with either one or the other, or both of them (see Figures 4 and 5).

Under present conditions, with these three species so similar in habits and so extensively overlapping in geographic range, it is difficult to visualize a barrier such as would have been required for allopatric speciation of the type, usual in vertebrates, to have occurred. One might be tempted to postulate sympatric speciation, with the parent form, presumably fasciatus, giving rise to the other two by abrupt mutations. However, the demonstrable antiquity of the five-lined skinks would allow ample time for divergence, allopatric speciation, and subsequent disappearance of the barrier and intermingling of populations. The displacement of floras and faunas that occurred in the Pleistocene, with the successive advances and retreats of the continental ice sheets might have had some part in bringing about the present overlapping distribution, after the disappearance of the original barrier. Such a barrier might have been an eastward extension of the central grasslands to the Atlantic Coast at a time when the climate of the continent was warmer and drier.

Habitat and Limiting Factors

TEMPERATURE AND MOISTURE RELATIONS

For approximately half the year, at the latitude of northeastern Kansas, five-lined skinks are dormant. In early fall, even before the advent of cold weather, they are hard to find apparently having begun their retirement into the sheltered situations where they spend the winter, even though they may not be fully dormant at that time.

Remarkably little is known of the hibernation habits of this species or of reptiles in general for that matter. The limit of tolerance to low temperatures, the type of insulating medium, the moisture relationships, the specific stimuli which cause the animal to retire to its hibernation site or to emerge from it have not been determined. On only a few occasions have natural hibernating sites or the dormant skinks in them been observed by zoologists. Linsdale (1927:78) recorded one found in a sawdust pile late in the winter of 1924 in Doniphan County, Kansas. Hamilton (1948:211) found skinks of this species hibernating in Grant Parish, Louisiana, in hollow logs 18-20 inches in diameter, five in one log and three in another, on January 23, 1943. Frost in the damp wood almost reached the lizards, which were in a torpid condition. These observations were made when the temperature was 36 deg.F. after the weather had begun to moderate following an unprecedented four-day cold wave when temperatures dropped to within a few degrees of 0 deg.F. In both logs the skinks were accompanied by hibernating anoles (Anolis carolinensis). Neill (1948b:109) in Richmond County, Georgia, found E. fasciatus hibernating in old stumps, fallen timber, piles of debris, or beneath rocks and ground litter. Beneath scraps of rotting wood he often found dead, frost-rimmed specimens which apparently had frozen to death. Hibernating skinks of this species were found singly or in pairs. Some were not fully dormant when found but could only gape and twist when uncovered.

Of hibernating E. laticeps, Neill wrote, "Many examples are covered with a waxy exudation, which I believe to be a secretion of the lizard itself, rather than of the surrounding medium. This exudation has been noted in other species also." Scott and Sheldahl (1937:192) described a hibernating aggregation of Eumeces septentrionalis found in Palo Alto County, Iowa, on February 15, 1937, as follows: "The skinks were found beneath a ledge of yellow clay about four and one-half feet below the surface. The lizards, 52 in number, were assembled in a compact group about the size and shape of a football. A soft, web-like material surrounded the mass and adhered to the bodies of the animals. Upon being uncovered some of them exhibited signs of life; others were dead." Breckenridge (1943:595) reported that a gravel digging crew found hibernating E. septentrionalis in late October and in January at depths of two feet (one), and three feet (groups of three and eight). Tihen (1937:405) recorded that two five-lined skinks found on January 13, 1948, were hibernating eight feet underground at Ranson, Ness County, Kansas. This locality is far to the west of the main range of fasciatus. Conant (1951:30) mentions the finding in Ohio of a young blue-tailed skink under a log where it seemed to be hibernating, on January 22. The spot where it was resting was soggy, and surrounding areas were covered with several inches of water.

In the course of the present study, no five-lined skinks were found hibernating under natural conditions, but on numerous occasions in early spring, two or three or four skinks were found together under massive flat rocks in semi-torpid condition, beside deep holes or crevices which presumably led to their hibernation sites in better insulated cavities. In the winter none could be found in such situations under large rocks, nor in the superficial types of hibernation sites described by Neill and Hamilton in the southern states. In the more severe winter climate of Kansas better protected hibernation sites are required. In the rock ledge situations where skinks were studied, excavation for the purpose of finding hibernating individuals was not practical.

On several occasions when skinks were put in the freezing compartment of a refrigerator and frozen solid, at temperatures several degrees below freezing, they failed to revive when warmed. However, they can survive temperatures a little below freezing. On April 1, 1953, one was placed in the freezing compartment with a thermometer inserted rectally. After 2-1/2 hours when the compartment was opened, this thermometer showed a temperature of -2.5 deg.C, after a delay of several seconds in obtaining a reading because of condensed moisture on the thermometer obscuring the mercury column. Another thermometer that rested beside the skink in the compartment showed 27 deg.F. The skink was limp and immobile. It was placed on a table top at normal room temperature, and it warmed rapidly. When it had reached 1.5 deg.C, it contracted its muscles in response to a light pinch. At 9.5 deg.C it raised its head and had its eyes partly open. Twenty minutes after its removal from the freezing compartment, it was still lying in the same position, its temperature having reached 13.5 deg.C. When handled it seemed dazed for several seconds as if just awaking. Then it crawled away briskly.

On March 28, 1953, a skink was placed in the freezing compartment for about 10 minutes, and upon removal its temperature was recorded as -0.5 deg.C. It was not frozen, but was limp and unresponsive to such stimuli as pinching or pricking. At 1.5 deg.C feeble movements of the legs were noticed. The eyes were still closed. At 3.4 deg.C the legs moved as if in walking. At 6.0 deg.C the skink raised its head and took several steps forward. At 7.5 deg.C it protruded its tongue and dragged itself about for several steps. At 9.0 deg.C movements of the sides indicated an inspiration approximately every three seconds. At 12.2 deg.C it opened its eyes.

On March 25, 1953, a skink that I had caught the day before and left overnight in an unheated room, was found to have burrowed into loose earth in its container. When exposed, its temperature was 1.8 deg.C and it was unable to crawl normally, but took only one step at a time, and progressed with slow lateral squirming motions. Placed on the ground outside the building, in the shade where there was still a little frost, it moved forward persistently for several inches trying to burrow into the surface litter. After a few minutes, its eyes were shut and it seemed incapable of further locomotion. Its temperature was 1.4 deg.C. When placed on its back it was able to turn over slowly after several seconds. A few minutes later its temperature was 0 deg.C, and it was totally helpless, although still capable of feeble movement. When stimulated by touch, it flexed its body a little, or moved each limb slowly in an arc as if walking, the movement taking several seconds. Placed on its back or side it was unable to right itself.

Less than three hours later I saw a skink that was active in the field. Slight movement at the edge of a rock that was exposed to sunshine attracted my attention and turning the rock I found the skink underneath, lively enough to scramble for shelter but slow and stiff compared to those that are fully active. Its temperature was 13.5 deg.C and air temperature was 7.5 deg.C. In damp soil beneath the rock where the lizard was found, temperature was only 5.7 deg.C. It seemed that the skink had been sufficiently warmed by contact with the undersurface of the rock to move into the open, and was just emerging when I approached. After capturing the skink, I set it on a rock in the sunshine, and in five minutes its temperature had risen to 26 deg.C.

As compared with its reptilian associates in northeastern Kansas, Eumeces fasciatus is outstanding in its ability to become active and carry on normal activities at relatively low air temperatures. In spring it is usually seen in the open before any other kind of reptile, because it has the capacity to move about sluggishly at temperatures so low that some other reptiles are numbed and completely immobilized, and because it has small size enabling it to make rapid adjustment upward by insolation, or contact with sunshine-warmed surfaces. By virtue of this ability it has been able to extend its range farther northward than most other reptiles, and it has gained the advantage of a longer growing season. This advantage was especially apparent in the spring of 1953. A mid-March warm spell with seven out of eight successive days having maximum temperatures in the sixties culminated on March 20, with a maximum air temperature of 82 deg.F. This warmth was sufficient to activate most of the five-lined skinks, and a few reptiles of other kinds. After the unseasonably high temperature of March 20, there was rapid return to cooler weather with temperatures frequently below normal throughout April. As a result there was little activity of other kinds of reptiles that month, but five-lined skinks were active on most days. On only a few days, those with temperatures in the low forties or those on which the sky remained overcast, did the skinks remain inactive. On most days maximum temperatures were in the fifties and sky was clear. Under these conditions the skinks were able to emerge and bask, rapidly raising their body temperatures far above those of the air and substrate.

By the end of April some kinds of deciduous trees have not yet begun to leaf out, and in most other kinds the leaves are still in an early stage of development. Absence of a leaf canopy during April permits the skinks to utilize the spring sunshine to maintain their body temperatures at almost the same high level that they maintain in the same situations in hot summer weather.

Table 2. Temperatures (in Degrees Centigrade) of Skinks Found Under Flat Rocks Exposed to Sunshine, Contrasted With Air Temperatures; Spring of 1953.

==========+==========+============+===========+ | Age | Skink | Air | Date | and sex |temperature |temperature| ----------+----------+------------+-----------+ March 23 | Ad. | 20.8 | 12.4 | March 23 | young | 24.7 | 12.4 | March 25 | Ad. | 22.8 | 12.5 | March 25 | young | 21.0 | 12.5 | March 25 | young | 25.7 | 14.5 | March 25 | young | 22.5 | 14.5 | March 27 | Ad. | 26.6 | 16.5 | March 27 | young | 22.0 | 16.5 | March 27 | Ad. | 22.5 | 16.5 | March 27 | Ad. | 20.5 | 16.2 | March 27 | Ad. | 26.5 | 19.3 | March 27 | Ad. | 30.7 | 19.3 | April 4 | young | 22.0 | 18.1 | April 5 | Ad. | 26.0 | 13.0 | April 6 | Ad. | 31.5 | 13.5 | April 6 | Ad. | 23.7 | 16.0 | April 6 | Ad. | 22.2 | 16.0 | April 6 | Ad. | 20.0 | 16.0 | April 6 | Ad. | 20.0 | 16.0 | April 6 | Ad. | 26.5 | 20.3 | April 20 | Ad. | 29.7 | 17.2 | April 20 | Ad. | 25.8 | 17.2 | ----------+----------+------------+-----------+

Recent studies by Cowles and Bogert (1944:288-289) and Bogert (1949:198) have brought out the fact that terrestrial poikilotherms, and especially lizards, maintain fairly high and constant body temperatures through behavioral thermoregulation, during their periods of activity. For genera and species of lizards, there are optimum body temperatures, which the individual tends to maintain, fluctuating within a range of only a few degrees while it is active. Forms that are not closely related may differ notably in their optimum temperatures, although within any one genus the range is slight. For example in the iguanid genus, Sceloporus, Bogert found that different species from such distant regions as Arizona and Florida agreed in having body temperatures approximating 35 deg. or 36 deg.C., while different members of the teiid genus Cnemidophorus in the same two regions were found to approximate 41 deg.C. in mean temperatures. In commenting on the distribution of North American lizards as affected by opportunity for behavioral thermoregulation by direct insolation, Bogert (op. cit.:205) wrote: "Such secretive lizards as skinks (principally Eumeces in North America) with low body temperature preferences approximating 30 deg.C. are dominant in Florida and the Gulf Coast, in contrast to the Teiidae and Iguanidae (several genera in the United States), which are far more abundant in the arid regions of the Southwest." Bogert and Cowles (1947:19) record that in a large individual of Eumeces inexpectatus taken near the Archbold Biological Station in Florida, the body temperature was 33.2 deg.C.

In the 1952 season, a small thermometer of the type described by Bogert (op. cit.:197) was frequently carried on collecting trips, and cloacal temperatures were recorded for the lizards collected. For those found in traps the opportunity for behavioral thermoregulation was limited, and temperatures usually approximated those of the air. The circumstances of capture, and the air temperatures were recorded for most of the skinks taken. For those found under rocks or in other shelter, the temperature usually approximated that of the immediate surroundings, and averaged much lower than for those taken in the open, but some found in such shelters had temperatures many degrees higher than their surroundings, and were fully active, having evidently just taken to cover to escape notice as the collector approached. As soon as a lizard was secured it was held in a leather glove or heavy cloth to prevent conduction of heat from the collector's hand, and a reading was taken within a few seconds. Most of the skinks found in the open could not be caught immediately but were secured only after minutes of maneuvering on the part of both collector and lizard. In most instances this maneuvering probably entailed some loss of heat by the lizard, as it interrupted its thermoregulatory behavior to run to a place of concealment, usually in shadow on a tree trunk, or in or beneath ground litter. Excluding all those not found active in the open, the mean temperature, in a sample of 41, was 31.5 deg.C. +- .60. This figure is thought to be slightly too low because of heat loss by many of the skinks in the time required to capture them.

In order to test the range of tolerance and verify the preferred optimum temperature of the five-lined skink, an experimental terrarium was set up providing extremes of temperature at each end. A false floor of 1/8 inch wire screen was provided, with a seven-inch strip of galvanized sheet metal beneath it at each end. Beneath the screen and sheet metal at one end the space was filled with chopped ice, and "dry ice." Observations were made on hot, clear summer days, with the terrarium arranged so that the half of it containing ice, was in shadow, and the other half was in sunshine. The strip of metal, warmed by direct sunlight, became uncomfortably hot to the touch while at the other end the sheet metal and overlying screen were cooled by the ice. A narrow zone across the middle of the terrarium had screen but no underlying sheet metal and was the only part within which the lizard could maintain normal temperature, one end being uncomfortably hot and the other end too cool. A large dead skink left on the metal strip in direct sunlight for five minutes had a cloacal temperature of 45.3 deg.C., and after five minutes on the screen at the cool end, its temperature had dropped to 25.5 deg.C. On several occasions a number of skinks were put in the terrarium and their temperatures taken at brief intervals. Temperatures ranged from 21.6 deg.C. to 37.7 deg.C. but were mostly within a much narrower range, from 28 deg. to 36 deg.C. One skink that seemed to be sick was sluggish in behavior, not responding to the extremes of temperatures as readily as the other individuals and his temperature fluctuated widely and irregularly. Eliminating this individual, 66 temperature readings taken, from five other skinks, gave a mean of 32.6 deg.C. +- .235. While nearly all the temperature readings were within a range of ten degrees, two of the readings were outstandingly low and perhaps should be discarded. If this is done, a mean of 33.8 deg.C. +- .19 is obtained for the remaining 64. There is distinct bimodality in this series however, with a mean of 34.2 deg. for the 49 higher readings, and a mean of 28.8 deg.C. for the 15 lower temperatures. A similar bimodality is evident in the readings obtained from skinks caught in the open under natural conditions. It seems that the lower readings result from lags in the skinks' response when body temperature drops slightly below the optimum. The skink is quick to make adjustment whenever its temperature appreciably exceeds this optimum level, and is in extreme discomfort at only a few degrees higher temperature. At slightly lower temperatures, however, the skink experiences no discomfort, and only slightly decreased efficiency in its various functions, and its thermoregulatory behavior in making readjustment toward the optimum is likely to be leisurely and interrupted unless its temperature drops below 28 deg.C.

Catching the skinks in the experimental terrarium at frequent intervals to take their temperatures involved some disturbance to them, interrupting their thermoregulatory behavior. The experimenter's first attempt to grasp a skink sometimes failed, and it then dashed about the terrarium for several seconds, probably altering its temperature somewhat. Nevertheless most of the lizards' movements were motivated by thermoregulation. This was especially evident when they were left undisturbed, and is illustrated by the following notes on behavior of an adult female and half-grown young of fasciatus and a young E. obsoletus on the afternoon of July 21, 1952.

2:58 All resting over cooled metal.

3:01 Female runs to line of sunshine and shadow, coming to rest with approximately half her body in sunshine, the other half in shadow over the cooled metal.

3:03 Female reverses position so that hindquarters previously in shadow are now in sunshine, and forequarters are in shadow.

3:03-1/2 Young runs to middle coming to rest in sunshine on screen.

3:04 Female moves back to the cool end.

3:05 Young moves to edge of cooled metal but not over it, in a narrow middle strip that has sunshine.