In the five-lined skink each adult female normally produces _Life History and Ecology of the Five-Lined Skink, Eumeces fasciatus

of eggs annually. The size of the clutch produced is subject to

individual variation, and is influenced by the age, size and condition

of the female. Geographic variation in clutch size might also be

expected. Data were obtained from breeding females killed and dissected,

from counts of eggs found in natural nests in the field, and from

clutches of eggs laid by females kept in captivity. For the total of 115

recorded clutches represented by the combined data from all these

sources, the average number of eggs per clutch was 9.5.

In many females dissected for the purpose of obtaining egg counts,

ovulation had not yet occurred. The ovarian eggs present in each of

these females included two main size groups, the larger ones in process

of maturing and evidently destined for deposition in the current season,

and minute, immature ones. A few of intermediate size were always

present, however, resulting in uncertainty as to the size of the clutch

being produced, especially when development had not proceeded far. Even

when the larger eggs formed a fairly distinct size group, some usually

were well below maximum size. Relatively high counts of clutches were

obtained from these examinations of enlarged ovarian eggs. Evidently

development frequently is arrested, and resorption may occur before

ovulation. As a result the numbers of ovarian eggs developing are a poor

indication of actual clutch size. A series of gravid females were

obtained and examined after ovulation; the numbers of eggs in their

oviducts probably indicates accurately the sizes of their clutches.

Gravid females taken from their nest burrows and kept in the laboratory

in containers with loose damp soil soon excavated new burrows and

deposited clutches. Many natural nests were found in the field, and the

egg counts obtained from them provided further data concerning clutch

size. Although most of these clutches probably had their full

complements of eggs, others certainly had sustained losses to predators,

or to the females themselves, which may eat some of the eggs. Therefore

the average number found is erroneously low. Some of the natural nests

found may have contained two or more clutches or parts of them, and the

higher counts obtained from natural nests therefore are also

questionable.

For different sets of data on clutch size, numbers were as follows:

Table 6. Size of Clutch.

=================+===========+============+===========+=========+=========

-----------------+-----------+------------+-----------+---------+---------

Early ovarian | 25 | 11.4 +- .46 | 2.28 | 20 | 5

| | | | |

in captivity | 56 | 9.16 +- .21 | 1.85 | 15 | 4

| | | | |

In natural nests | 34 | 8.82 +- .32 | 1.85 | 16 | 4

-----------------+-----------+------------+-----------+---------+---------

On the average, larger females produce more eggs per clutch than do

smaller females. Of 49 females for which measurements were recorded, and

which had uterine or large ovarian eggs, 31 were 70 mm. or more in

snout-vent length. These 31, mostly or entirely old adults, averaged 9.9

eggs per clutch, whereas 18 others that were 69 mm. or less in

snout-vent length, and that must have been mainly or entirely newly

matured adults in their first breeding season, averaged only 7.8 eggs

per clutch.

Smith (1946:350) states that in the northern part of the range of this

skink there is some indication of decrease in size of clutches. This is

not well shown by published records. For the southern states, most of

the published records of clutch size are by authors who did not clearly

distinguish between the three kinds of five-lined skinks, and there is

some doubt as to which species is involved in each record. For 56

clutches reported upon from north of approximately latitude 37 deg., I

obtain a slightly higher figure than for 11 clutches from south of this

line. Geographic trends are, of course, obscured by individual

variation, and perhaps by abnormal clutches produced by individuals kept

in captivity.

In Table 7, the figures marked with asterisks pertain to clutches that

might have belonged to skinks of the species _E. laticeps_ or _E.

inexpectatus_ since they were recorded in regions where _laticeps_ and

in some cases, _inexpectatus_ also, occurs along with _fasciatus_. If

these questionable clutches are excluded the remaining 55, definitely of

_fasciatus_, average 8.48 eggs per clutch, whereas the 12 questionable

clutches average 8.42. Both figures are close to the average of 8.82 +-

.32 eggs for the 34 natural nests recorded in the present study. For the

total of 1661 eggs of 182 clutches, from the combined sample of all

available records for clutches found in the present study or reported

upon in the literature, the average egg number is 9.13.

[Illustration: FIG. 10. Correlation between size of female and

number of eggs in clutch; females in their first breeding season,

mostly less than 72 mm. in snout-vent length, produce smaller

clutches, on the average, than do larger and older females, but

there is extensive overlap.]

To sum up the available information on clutch size, the number of eggs

is most typically 9, 10, or 11 and is more in large old females, than in

small, newly matured females. In natural nests, even in those that are

successful, there is often some loss of eggs, which are eaten by

predators, or by the female herself, with the result that the egg

counts made by various observers average somewhat lower than the numbers

actually produced. The loss during incubation cannot be measured readily

since it is almost certainly sharply increased by the disturbance

entailed in observing nests. Exposing nests, even momentarily, for

observation, may result in compacting of the surrounding soil,

desiccation, temporary or permanent desertion by the female, and

exposure to predation. Some indication of the incidence of loss during

incubation might be obtained by counting and measuring the eggs in newly

found nests and correlating numbers with size (indicating the length of

time incubated).

Table 7.--Numbers of Eggs Per Clutch, Time of Occurrence, Laying

Dates and Hatching Dates, as Reported in the Literature by Various

Authors.

==========+==============+===============+=========+=============+==========+=============

----------+--------------+---------------+---------+-------------+----------+-------------

Allard | 7* | .... | Yes | .... | .... | Northern

| | | | | |

Bishop | 8* | .... | Yes | .... | .... | Breathitt

| | | | | | Co.,

| | | | | |

Blanchard | 9* | .... | .... | .... | .... | Tennessee

| | | | | |

Burt | 6; 11 | May, and | Yes | June 12, | .... | Douglas

| | June 18, 1926 | | 1926 | | Co.,

| | | | | |

Burt | 9*, 9*, | June 25 to | Yes | .... | .... | Arkansas

| 9*, 10* | July 13, 1926 | | | |

| | | | | |

Burt | 8* | June 6, 1933 | Yes | .... | .... | North

| | | | | |

Burt | 8* | June 28, 1934 | Yes | .... | .... | Scott,

| | | | | |

Burt | 6* | July 7, 1933 | Yes | .... | .... | Emma,

| | | | | |

Burt | 6* | July 8, 1933 | Yes | .... | .... | Elk River,

| | | | | |

| | | | | |

| 11, 13 | .... | .... | .... | July 27 | Ohio

| | | | | |

Dunn | 12* | .... | .... | .... | Aug. 9 |

| | | | | |

Roecker | 6, 7 | .... | Yes | .... | week of | Ontario

| | | | | |

Fitch | 9 | July 22, 1947 | Yes | .... | .... | Vernon

| | | | | |

McCauley | 3; 20 in 3 | | | | |

| combined | .... | Yes | and 6 | 30 | Maryland

| | | | | |

Mason | 6, 7, 8, 8 | .... | No | 31; June 6, | 5, 6, 7, | Co.,

| | | | 6, 13, 20 | 9, 17 | Kansas

| | | | | |

Ruthven | 6, 6, 8, 9, | | | | |

| 11, 13, 14 | .... | Yes | .... | .... | Michigan

| | | | | |

Smith | 9 | .... | Yes | .... | .... | Ohio

----------+--------------+---------------+---------+-------------+----------+-------------

BROODING

Lizards and snakes of several different families, are known to brood

their clutches of eggs, although the great majority of oviparous forms

do not do so. The brooding habit is perhaps best known in _Eumeces

fasciatus_, and has been described by many authors. By far the most

thorough account is that of Noble and Mason (1933) who observed and

experimented upon seven females that laid clutches of eggs in captivity.

These females, kept in separate terraria, excavated nest burrows for

reception of their clutches, and remained with them throughout the time

of incubation. There were three characteristic brooding postures; curved

in a semicircle around the clutch, in an S-shaped figure extending among

them, or lying straight, either over or among the eggs. The brooding

females, taken quietly from their nests without disturbing them, were

found to have temperatures averaging .4 deg.C. higher than the nests.

Evidently normal room temperatures were maintained in the laboratory

where the terraria were kept. The females occasionally left their nests,

especially in late afternoon, to wander about the terraria, and to bask

in sunlight. While basking, their temperatures averaged 2.7 deg.C. higher

than the nest temperatures. The authors suggested that an important

function of the brooding female was to transfer warmth from absorbed

sunlight to the eggs. They state: "In nature the importance of the

mother's body heat in the incubation of the eggs probably varies greatly

with the type of nesting site selected." They suggest that in clutches

deposited in logs or stumps beneath a thin layer of bark exposed to

direct sunlight the need for warming by the female would be less.

My own observations do not support the idea that brooding by the female

serves to hasten the development of the eggs. Both in the laboratory and

in natural nests, clutches deserted by disturbed females hatched and the

hatching was not unduly delayed. In the field, females were never

observed to bask in the sun beside their nest burrows, and seemingly

left them infrequently even to feed. When a female was caught in her

nest burrow, her temperature nearly always approximated that of the

surrounding earth with which she was in contact. The temperature in each

nest depends primarily upon its situation. When the immediate vicinity

of the nest receives direct sunlight, the eggs are warmed without the

aid of the female, but when there is no sunlight the temperature is much

lower. In order to maintain an appreciably higher nest temperature the

female would have to make frequent trips to spots perhaps several feet

or several yards away to find sunlight. Upon returning to the nest, her

body heat would be quickly dissipated into the eggs and the surrounding

damp soil. She would need to shuttle back and forth almost continually

between the nest and a spot exposed to sunshine. Cloudy weather often

preventing the warming of the eggs by absorption of solar heat prevails

during much of the incubation season, in the region of the present

study, and probably to an even greater extent throughout the range as a

whole.

Noble and Mason state (_op. cit._:9) that while in some non-brooding

kinds of lizards the eggs are actually damaged by turning, the female

_fasciatus_ frequently turns her eggs and moves the whole clutch about

in the nest cavity. On returning to their nests the experimental females

each invariably touched one or more eggs with their tongues as an

olfactory test. Eggs of other kinds of lizards not of the genus

_Eumeces_, and shellacked eggs of _fasciatus_, or paraffin models of

them, ordinarily were discarded immediately after a single touch of the

tongue. Eggs of other individuals of the species, and even the eggs of

_Eumeces laticeps_ were accepted as part of the brood. Any of the

experimental females would quickly retrieve one of her eggs moved a

short distance outside the nest cavity. Even if the whole clutch of eggs

were scattered about, the female would, over a period of hours, gather

the eggs and return them to the nest cavity. This movement of the eggs

is accomplished by rolling or pushing them in a loop of the body or

tail, or, less frequently, by grasping an egg in the jaws, lifting it,

and gently placing it in a new position. Even if the females were

blindfolded, they were still able to retrieve scattered eggs, but one in

which the tongue tip was experimentally removed showed no further

interest in its eggs, presumably having lost the capacity to recognize

them by olfactory test.

In the present study clutches unattended by females were observed to

sustain heavy losses, both in the laboratory and in the field, and no

doubt the attending female performs important functions other than that

of warming the eggs. In the damp or wet nest cavity, the eggs tend to

adhere to each other and to the earth walls and floor, and become sealed

to such surfaces as a result of partial drying, reducing the amount of

surface exposed to the air and probably hindering respiration. An

eggshell sealed in prolonged contact with the soil tends to rot with the

result that it is easily ruptured, and even if it is not broken there is

the likelihood of fungi or microorganisms gaining entry and killing the

embryo. In many of the eggs that were handled to obtain measurements

and weight, rupturing of shells occurred. The shells are tough and

elastic to the extent that even when eggs being handled were

accidentally dropped on the floor on several occasions, no damage to

them resulted. However, slight friction on the shell was sometimes

sufficient to puncture one. Particles of sharp rock from the nest cavity

may adhere to the shell, and result in rupturing, perhaps at weak spots

where prolonged contact with the soil has caused deterioration. The

female tends to keep her eggs in a compact cluster, shifting their

position frequently so that no part of an eggshell adheres to its

surroundings long enough for rotting to occur, and most of the surface

of each egg is exposed to the air.

Another important function of the brooding female seems to be that of

altering the nest burrow and shifting the eggs so that the effects of

unfavorable weather are minimized. The usual response to warm and dry

weather is deepening of the nest burrow. A cavity originally in loose

soil on the underside of a flat rock, having the eggs in contact with

the rock surface, may be displaced downward. The female excavates loose

soil from the floor of the burrow and packs it on the top and sides,

until the eggs are two or even three inches underground, in a cavity

different in position and shape from the original one, although derived

from it by gradual stages. In many instances, however, no such response

to drying was observed. Probably extensive alteration of the nest burrow

no longer is possible after drying of the soil has progressed beyond a

certain stage as these skinks are not strong diggers. In some nests that

were examined frequently, with resulting desertions by the attending

females, the outlines of the cavities became indistinct and the soil

around them became dry and packed. In heavy rains, when nest burrows are

partly flooded, the females move the eggs to avoid their being

submerged. The extent of the female's activity within the nest burrow is

suggested by the glazed condition of the earth walls and floor, and by

the mottled appearance which the eggshells soon acquire as a result of

being slid and dragged about in the nest cavity.

Still another important function of the female is to dampen the nest

burrow to prevent desiccation of the eggs. Even in dry weather, females

taken from nests almost invariably voided water in relatively large

quantities. They drink dew or other available water, and may void the

contents of the bladder to moisten the nest cavity, as on numerous

occasions, when nests were exposed by raising flat rocks covering them,

part of the chamber was seen to be recently watered, and distinctly

moister than the surrounding soil.

Noble and Mason (_op. cit._:16-19) found that brooding females, in the

laboratory, would vigorously defend their eggs against small enemies,

including mice and lizards and the smaller kinds of snakes that were

tested. The female watched alertly as the intruder approached, and

attempted to bite it if it came too near or touched an egg. The females

failed to defend their nests against persons and against a large

blacksnake; when confronted with such a threat, the female would run

from her nest cavity to hide. Cagle (1940:228) stated that the brooding

females found by him stayed in the nests even when the logs in which

they were situated were chopped open with an ax, and that the skinks

would attempt to bite when touched with the finger.

In the present study, females whose nests were exposed never made any

active attempt to defend them. Many darted away and hid as soon as they

were exposed. In other instances, especially when the nest cavity was

only partly exposed, from one side, the female cowered back against the

inner wall, opening her mouth in threat if closely approached. If

further molested she might then attempt to escape. In brooding females a

tendency to sluggishness, and an affinity for the eggs delayed the

usually speedy escape reactions. The temperature of the female was

ordinarily lower than it would have been in the open or on the underside

of a flat rock, and this also tended to slow her reactions. Gravid

females when exposed in nest cavities that still contain no eggs are

similarly sluggish and reluctant to leave differing little or none in

behavior from those that have laid their clutches. Usually the female

was found with her body encircling the eggs, holding them together in a

compact cluster in the center of the nest cavity. The eggs rest in

contact with the loose soil on the floor of the cavity, with each other,

and with the female's body in the case of the outer ones of the cluster.

Normal brooding habits proved to be difficult to follow because the

females were easily disturbed. In many instances those that had

excavated nest burrows, but had not yet laid, deserted the nests after

the disturbance involved in raising the sheltering rock. Females that

had already laid before discovery of their nests were somewhat less

inclined to desert, but many did so.

On numerous occasions, at the time of year when most females are gravid

and are staying in nest burrows, I have discovered well formed nest

burrows empty and seemingly deserted, with no female in evidence

nearby. In some instances the female may have been out foraging or

basking although she was not seen, and in other instances the female may

have been killed by a predator or eliminated by some other accident.

However, it seems that gravid females frequently do desert their

original nest burrows, for one cause or another, and excavate new ones.

Such desertions were noted many times in the females observed on the

study area, where the disturbance from my own activities in raising the

sheltering rocks may have caused shifts, but it was probably not the

sole motivation. One female shifted approximately 120 feet, to excavate

her second nest burrow in a site that was damper and more heavily shaded

than the first site. This was in the notably dry summer of 1952. Most of

the favorite sites under flat rocks in open situations, that were used

in 1950 and 1951, were not occupied in 1952 or 1953, although several

females did use them for original excavations, which were deserted

before laying, as drought conditions developed. In the summers of 1952

and 1953 nests were difficult to find, and those discovered were on the

average deeper and better protected than those found in other years.

As compared with other North American lizards in general, _Eumeces

fasciatus_ is notable for the relatively exposed and superficial

situations chosen as nesting sites. However, it occurs in a climate of

high humidity; in contrast, the great majority of our lizards live in

arid climates where the eggs are in much greater danger of desiccation,

and require better shelter to maintain the humidity at a sufficiently

high level. Accounts in the literature and observations in the present

study indicate that these skinks exercise a wide range of choice of

nesting sites. Ruthven (1911:264) stated that in northern Michigan nests

were usually in decaying logs; occasional nests were found in burrows in

sand, but invariably decaying wood was present in or around at least

part of the nest.

Blanchard (1922) mentions a nest in Tennessee that may have been made by

either this species or _E. laticeps_ "in a hollow in a dead willow tree

about fifteen feet from the ground buried in the loose, damp, rotted

wood." Noble and Mason (_op. cit._:16) quote Blanchard (_in litt._) that

in northern Michigan _fasciatus_ nests in logs that are exposed to

sunlight. Conant (1951:31) stated that several clutches of eggs found in

Ohio were an inch to six inches beneath the upper surface of the log or

stump which sheltered them. Evans and Roecker (1951:70) record finding

two incubating females inside rotten pine logs, in Ontario. Cagle,

studying this species near Elkville, Illinois, in oak-hickory woods,

found 25 natural nests of which three were in loose soil among the

roots of a fallen tree, another was under loose bark of a log, and the

remainder were all in cavities of partly decayed logs. Bishop (1926:119)

recorded finding a female with a clutch of eggs beneath damp boards at

Quicksand, Breathitt County, Kentucky.

In the present study, more than one hundred natural nests were found, of

which just one (containing two clutches of eggs) was in decaying wood

beneath the bark of an old log. All other nests were beneath rocks. On

the University of Kansas Natural History Reservation, where most of the

nests were found, the policy is not to tear apart decaying logs;

therefore the nests probably present in such situations were not

ordinarily found. On several occasions groups of hatchlings were seen on

logs within which they probably had hatched. In the area of the study,

however, decaying logs are scarce. The hardwood forests consist mostly

of young trees that are second growth on cutover areas or pioneer on

areas that were previously grassland. Because of frequent cutting there

are few old mature trees, and logs have not accumulated on the forest

floor. In northeastern Kansas, nesting in logs is comparatively rare. On

wooded slopes and the edges of level hilltops, the flat limestone rocks

that are often abundant provide preferred nesting sites. Even on

collecting trips off the Reservation, where stumps and logs could be

torn apart and searched, flat rocks were found to provide the main

source of nesting sites. These nest rocks varied from less than an inch

in thickness to nine inches or more, and from a few inches in diameter

to three feet or more. Some were resting loosely on the surface of the

soil and others were deeply sunken, on one side. Some were in situations

exposing them to nearly the maximum amount of sunshine whereas others

were in sites nearly always shaded. The varied character of the nesting

sites chosen demonstrated a wide range of tolerance for temperature,

moisture, and other factors, in the gravid and brooding female and in

the developing embryo.

As already mentioned, Noble and Mason (_op. cit._:9-10) noted that

females would accept and brood the eggs of other individuals just as

readily as their own, and several writers have reported gregarious

nesting habits, with two or more females occupying either the same nest

cavity, or separate cavities that were in close proximity. For instance,

Cagle wrote that among the small logs he found to contain nests, four

logs each contained one nest, five each contained two nests, and two

each contained three nests, while three other nests were found within an

eight inch square area in loose soil among tree roots. McCauley

(1939:93) in Maryland found three females brooding clutches of eggs,

which totaled 20, and which were so near together that there was

uncertainty as to which clutch certain eggs belonged in.

Life History and Ecology of the Five-Lined Skink, Eumeces fasciatus · 第 6 / 16 段

In the five-lined skink each adult female normally produces one clutch