Read Ebook: Natural History of the Ornate Box Turtle Terrapene ornata ornata Agassiz by Legler John M

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Prominent landmarks were rare or wanting in most places on the pasture. Locations of captures were determined by triangulation with a Brunton compass, using trees along fences as known points of reference. Rough maps were made in the field and used later, along with compass readings and measurements, to make a more precise record of movements and captures on a large map of the study area. Mapped points of capture in grassy areas were accurate within ten to twenty feet; points of capture in areas where landmarks were nearby were nearly exact. Areas were measured with a planimeter; distances traveled by individuals were measured with a cartometer.

Turtles were measured in the field to the nearest millimeter with large wooden calipers and a clear plastic ruler. Measurements in the laboratory, especially in studies of growth, were made, to the nearest tenth of a millimeter with dial calipers. Measurements made on each specimen examined in the field were: length of carapace, width of carapace, length of plastron , width of plastron , and height. All measurements were made in a straight line. A spring scale of 500 gram capacity, used in the field, gave weights accurately within three grams. A triple-beam balance was used in the laboratory. Unless otherwise noted, measurements are expressed in millimeters and weights are expressed in grams.

Body temperatures were taken by means of a quick-reading Schultheis thermometer inserted into the distal portion of the large intestine with the bulb directed ventrally to avoid puncturing the bladder. Body temperature of turtles were altered little or not at all in the few seconds the turtles were held and no attempt was made to insulate them from the warmth of my hands. Data recorded with body temperature were: air temperature ; ground temperature ; behavior of turtle; weather conditions; nature of vegetation or other cover; and, time of day. Unless otherwise noted, temperatures are expressed in degrees Centigrade.

A maximum-minimum thermometer was installed near the buildings at the Damm Farm. Notes on general weather conditions were made on each visit to the study area. Additional climatological data were obtained from the U. S. Weather Stations in Topeka and Lawrence, from records at the Reservation, and from official bulletins of the U. S. Weather Bureau.

Stomachs and gonads were removed and preserved by standard techniques soon after specimens were killed. The dates given to gonads were, in all instances, the dates when the specimens were killed. Eggs were prepared for incubation in the manner described by Legler . Females laying or containing eggs used in studies of incubation were preserved for further studies and comparison with young hatched from the eggs. Histological preparations were fixed in ten per cent formalin or Bouin's fluid, embedded in paraffin, and stained with hematoxalin and eosin.

Terminology

Names used for the epidermal and bony parts of the shell follow the classification proposed by Carr . The terms "scute," "lamina," and "scale" are used here more or less interchangeably for the epidermal parts as are the terms "plate," "bone," and "element" for the bony parts of the shell.

HABITAT AND LIMITING FACTORS

Ornate box turtles are relatively inconspicuous in natural surroundings and collectors seldom seek out and obtain specimens under completely natural conditions as may be done with certain other reptiles and amphibians by turning rocks, tearing apart logs, or setting traps. Most series of specimens are obtained by hunting after rains on roads or other natural breaks in vegetational cover. Detailed information on habitat preferences is lacking.

The prairies of Nebraska, Kansas, Oklahoma, and northern Texas seem to provide the most nearly optimum habitat for the species; in these regions box turtles are active on a large majority of the days from April to October in years having average or better than average precipitation and population density seems to be greater than in the more arid parts of the range.

HABITAT IN KANSAS

At the Damm Farm the greatest number of box turtles was collected on the pasture, especially in three areas designated in Plate 1 as the "northwest corner," "southern ravine," and "house pond" areas. These three areas had several features in common. All contained ravines and rocky slopes that provided many places of concealment . All contained water for most of the year; and, all were frequented daily by cattle that left an abundant supply of dung in which box turtles foraged. In addition, each of the three areas contained at least one mulberry tree, under which fruit was abundant in the months of June and July.

The relative numbers of box turtles found in different areas on the Damm Farm were, of course, governed to some extent by my activity in these areas and by the relative ease with which box turtles were seen in different types of vegetational cover. Turtles were more easily seen in the pasture where much of my field work was done on horseback, than in the wooded areas, where excursions were usually made on foot. It was evident, however, after mapping known ranges and studying patterns of movement in marked turtles, that concentrations in the three above-mentioned areas of pasture were an indication of actual preference by turtles for the more favorable habitat in these areas rather than the result of incomplete sampling.

REPRODUCTION

Mating

Mating takes place throughout the season of activity but is most common in spring--soon after emergence from hibernation--and in autumn. Turtles frequently copulated in the laboratory in spring and autumn. Copulation was observed under natural conditions on several occasions but only once at the Damm Farm.

Insemination

Oviducts of several females were flushed by means of a pipette to determine whether they contained sperm. Approximately half of the females captured in May, 1956, had sperm in their oviducts, but females captured in June and July did not. Sperm flushed from the oviducts were in clumps of several hundred and showed no sign of motility a few minutes after the female was anesthetized with chloroform. No sperm were found in the oviducts of immature females but one female of nearly adult size was observed in copulation with a mature male.

Sexual Cycle of Males

Testes were preserved in each month from April to October. The following description of spermatogenesis is based chiefly on material collected in 1955, although testes were preserved also in 1954. Comparison of material obtained in 1954 and 1955 revealed that spermatogenesis began earlier and was more advanced on any given date in 1955 than in 1954.

Testes of mature individuals are pale yellow and slightly oblong. The epididymis is ordinarily dark brown or black and contrasts sharply with the color of the testes. Size of testes was expressed as the average length of both testes. Testes are smallest in April, immediately after emergence from hibernation, and largest in early September . They are nearly spherical when of maximum size; increase in bulk, therefore, is relatively greater than the increase in size shown in Figure 3. They increase in size from April until early June, recede during most of June, and again increase in size in July and August. They remain large from early September until hibernation is begun, becoming only slightly smaller in late September and October.

Increase in size following emergence from hibernation may be due in part to proliferation of the sustentacular cytoplasm. Decrease in size in early June is correlated with the end of the period of most active mating; maximal size is coincident with the peak of the spermatogenic cycle in early September.

Spermatogenesis begins in early May when a few spermatogonia appear in the seminiferous tubules. The histological appearance of testes preserved in April and May is much the same. Nuclei of Sertoli cells, which outnumber the spermatogonia, are evident at the periphery of the tubules and the clear cytoplasm of the cells extends into and nearly fills the lumina. The few darkly stained spermatids that are present in April are cells that probably were produced in the previous summer. Sperm are present in small groups within the sustentacular cytoplasm, but ordinarily are absent in the lumina.

Spermatogenesis is well under way by mid-June; at this time, two or three distinct layers of primary and secondary spermatocytes are present and these cells outnumber the Sertoli cells. The lumina are filled with cellular detritus and are no longer bordered by a clear ring of sustentacular cytoplasm. No sperm are present.

Spermatids appear in late June and a few of them undergo metamorphosis in early July; by mid-July, spermatids and secondary spermatocytes are the dominant cells in the seminiferous tubules, although spermatogonia are still active.

The spermatogenic cycle is completed in the latter half of October when most of the spermatozoa pass into the epididymides. A few spermatozoa and spermatids remain in the seminiferous tubules during hibernation. Although no testicular material was obtained from hibernating turtles, comparisons of sections made in October and April show that the germinal epithelium remains inactive from autumn until spring. Possibly some spermiogenesis takes place in the early phases of hibernation or in the period in late autumn when turtles are intermittently active. It is uncertain whether the reorganization of the sustentacular cytoplasm occurs in autumn, in spring, or in the course of hibernation.

The seminiferous tubules of immature males are small, lack lumina, and contain a few large but inactive spermatogonia . The testes of specimens that were nearly mature contained primary and secondary spermatocytes but lacked lumina; it was thought that such individuals would have matured in the following summer and bred in the following autumn.

Mature sperm were found in epididymides at all times of the year but were most numerous in spring and autumn, the period between spermatogenic cycles . Sperm expelled from the epididymides in autumn matings are seemingly replaced by others from the seminiferous tubules; the epididymides become much smaller when their supply of sperm is nearly exhausted after spring mating.

Sexual Cycle of Females

The following account of o??genesis is based on examination of preserved ovaries from 68 mature specimens. The ages of most specimens were known, inasmuch as the specimens were used in studies of growth as well as gametogenesis. Other data were obtained from adult females that were dissected but not preserved, and from immature females.

Size of ovarian follicles was determined by means of a clear plastic gauge containing notches 5, 10, 15, 20, and 25 millimeters wide. The number of follicles within a given size range could be quickly determined by finding the smallest notch into which the follicles fit. It was necessary to weigh all ovaries after preservation since some of them had not been weighed when fresh. Since all ovarian samples were preserved in the same manner, weights remained relatively the same. Preserved material was lighter than fresh by an average of 13 per cent. Follicles less than one millimeter in diameter were not counted. Corpora lutea and corpora albicantia were studied under a binocular dissecting microscope. No histological studies were made of the female reproductive system.

Ovarian follicles and oviducal eggs were recorded separately for the right and left sides. Each ovary was always kept associated with the oviduct of the same side, but in some instances it was not recorded whether the organs were left or right.

Ovaries ordinarily weighed most in October, March, and April, when most females contained enlarged follicles, and least in August and September when the supply of enlarged follicles was usually exhausted .

Examination of yolks of oviducal eggs revealed that follicles mature when they reach a diameter of 16 to 20 millimeters and a weight of two to two and one-half grams .

The enlarged follicles remaining on the ovaries after ovulation can be grouped according to diameter as: large , medium , and small . Ten females collected in the period from June 2 to 8, after they had ovulated, all had follicles falling in at least one of these size groups, and eight had follicles falling in two or more of the groups. In females having enlarged follicles of more than one of the size groups, there were several follicles in each of two groups and no follicles, or only one follicle, in the remaining group. Enlarged follicles represent future clutches but whether the enlarged follicles will be ovulated in the same season or in a later season is questionable.

Further evidence for multiple clutches was the absence of enlarged ovarian follicles in some females obtained in September. Atretic follicles, ordinarily orange, brown, or purplish, were observed on the ovaries of many of the females examined; in most instances, not more than two follicles of the small or medium size groups were atretic. Atresia was in no instance great enough to account for the complete loss of enlarged follicles.

Further study probably will show that many of the females laying in May and early June lay again before the end of July, and that eggs in the oviducts of females captured in the latter month frequently represent second clutches. Under favorable conditions, eggs laid by the end of July would have a good chance of hatching before the advent of cold weather in autumn; turtles hatching too late to escape from the nest could burrow into its sides and probably escape freezing temperatures.

In all the specimens examined, it was evident that ovulation had occurred or would occur in two successive seasons. Senile or young females might, however, be expected to skip a laying season if only one ovary was functioning.

After ovulation, the collapsed follicle assumes a cuplike shape and becomes a glandular corpus luteum . Corpora lutea are approximately eight millimeters in diameter and are easily discernible at least until the eggs are laid; they are somewhat less distinct after preservation. Corpora lutea undergo rapid involution following oviposition and, after two to three weeks, are little more than small puckerings on the ovarian epithelium. At this stage they are properly referred to as corpora albicantia and are discernible only after careful examination of the ovary under low magnification. Corpora albicantia remain on the ovary until April of the year following ovulation but disappear in May and are never present after the new set of eggs is ovulated. Ovaries of some subadults contained enlarged follicles and, but for their lack of corpora lutea and corpora albicantia, were indistinguishable from those of older, fully mature females.

The corpus luteum of oviparous reptiles seems to be closely associated with the intrauterine life of the eggs and, in viviparous reptiles, it may be an important factor in maintaining optimum gestational environment; however, its functions in all reptiles are poorly understood .

The uterine portion of the oviducts becomes darkened in the breeding season. Darkening of oviducts seemed to coincide with the period when eggs were in the oviducts and it persisted for a variable length of time after the eggs were laid. Oviducts of immature females were ordinarily pale.

Nesting

Activities of one gravid female, typical in most respects of the activities of several other gravid females observed at the Damm Farm, illustrate pre-nesting behavior . A trailer was attached to the female on the morning of June 7. She was recovered early on the following afternoon; her movements in the elapsed period had been restricted to a small, deep, ravine 150 feet long and 20 to 30 feet wide. She had traversed each edge of the ravine at least once and had crossed it six or seven times, keeping mostly to areas on the upper parts of south--or west--facing slopes where vegetation was sparse or lacking. In six places she had dug into the ground, probably to test the suitability of the soil for nesting. In three places she dug beneath rocks that jutted out from the bank, and in two places merely scratched away the upper crust of soil. Her most recent attempt at digging consisted of a flask-shaped cavity that, but for the lack of eggs and a covering of earth, was like a completed nest . The cavity was 55 millimeters deep, 80 millimeters wide at the bottom, and 60 millimeters wide at the opening. For several inches about the opening the earth was slightly damp. That piled on the rim of the opening was of the consistency of thick mud, indicating that the female had voided fluid first on the surface of the earth and again inside the cavity to soften the soil. Subsequently during eight days her activities were similar but not so extensive as on the day described above. It was determined by daily palpation that she laid her eggs somewhere in the general area of the ravine on June 15 but the nest could not be found.

No completed nests containing eggs were discovered at the Damm Farm but the locations of several robbed nests and partly completed nests provided some information on preferred sites. The nests found were on bare, well-drained, sloping areas and were protected from erosion by upslope clumps of sod or rocks. The nest cavity illustrated in Plate 21 was at the edge of the sod-line on the upper lip of the west-facing bank of a ravine. One nest had been excavated in a shallow den beneath an overhanging limestone rock. Three nests were on west- or south-facing slopes and one was on the north-facing bank of a ravine. Box turtles presumably select bare areas for nesting because of the greater ease of digging. One female at the Damm Farm was thought to have laid her eggs in a cultivated field and William R. Brecheisen told me he discovered two nests in a wheat field being plowed in July, 1955.

The repeated excavation of trial nest cavities presumably exhausts the supply of liquid in the female's bladder. Frequent imbibing of water is probably necessary if the search for a nesting site is continued for more than a day or two. Standing water was usually available in ponds, ravines, ditches, and other low areas at the Damm Farm in June. Nesting in June, therefore, is advantageous not only because of the greater length of time provided for incubation and hatching but also because of the amount of water available for drinking. Females can probably be more selective in the choice of a nesting site if their explorations are not limited by lack of water.

A nest made by a captive female at the Reservation was of normal proportions except for an accessory cavity that opened from the neck of the nest, immediately below the surface of the ground. This smaller cavity contained a single egg. This peculiar nest may have resulted from the efforts of two different females since several were kept in the same outdoor pen.

Eggs

Shells of the eggs are translucent and pinkish or yellowish when the eggs are in the oviducts. After several days outside the oviducts the shells become chalky-white and nearly opaque. Eggs incubated in the laboratory retained the pinkish color somewhat longer than elsewhere on their under-surfaces, which were in contact with moist cotton, but eventually even this part of the shell became white. Infertile eggs remained translucent and eventually became dark yellow, never becoming white; they could be distinguished from fertile eggs on the basis of color alone. Shells of infertile eggs became brittle and slimy after several weeks.

In 1956, three fertile eggs, from clutches that were at different stages of incubation, were immersed in water for 48 hours. The eggs rested on the bottom of the bowl in the same position in which they had been placed in the incubation dishes; when turned, they returned invariably to the original position. The embryos in two of the eggs were still living ten days after the eggs were removed from the water; the embryo in the remaining egg was dead. Eggs immersed in water increased in size and weight at the same rate as eggs in incubation dishes, indicating that absorption of water probably operates on a threshold principle, the amount absorbed being no more than normal even under wet conditions.

Natural nests usually are in well-drained areas, but water probably stands in some nests for short periods after heavy rains. Provided the nest cavity itself is not damaged, water in the nest is probably more beneficial than harmful to the eggs; however, nests that are inundated during floods probably have little chance of survival.

Embryonic Development

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