Part 3

Having heard the call of typical G. carolinensis in Louisiana, I have the impression that it is a little shorter, more sheeplike, and less insectlike than that of G. olivacea. The call of Gastrophryne is of such peculiar quality that it is difficult to describe. Different observers have described it in different terms. Stebbins (1951: 391) has described the call in greatest detail, and also has quoted from the descriptions of it previously published. These descriptions include the following: "high, shrill buzz"; "buzz, harsh and metallic"; "like an electric buzzer"; "like bees at close range but more like sheep at a distance"; "bleating baa"; "shrill, long-drawn quaw quaw"; "whistled wh[=e][=e] followed by a bleat."

Stebbins observed breeding choruses (mazatlanensis) at Pe[~n]a Blanca Springs, Arizona, and stated that sometimes three or four called more or less together, but that they seldom started simultaneously. Occasionally many voices would be heard in unison followed by an interval of silence, but this performance was erratic. At the pond on the Reservation I noted this same tendency many times. After a lull the chorus would begin with a few sporadic croaks, then four or five or even more frogs would be calling simultaneously from an area of a few square yards. Anderson (op. cit.: 34) found that in small groups of calling G. carolinensis there was a distinct tendency to maintain a definite pattern in the sequence of the calls. One "dominant" individual would initiate a series of calls, and others each in turn would take up the chorus.

Pairing takes place soon after the breeding aggregations are formed. On the night of June 4, 1954, a clasping pair was captured and kept in the laboratory in a large jar of water. This pair did not separate, and spawning occurred between noon and 1:30 P. M. on June 5. When the newly laid eggs were discovered at 1:30 P. M. most of them were in a surface film. Some were attached to submerged leaves and a few rested on the bottom. The pair was still joined, but the male was actually clasping only part of the time, and as the frogs moved about in the water, it became evident that they were adhering to each other by the areas of skin contact, which were glued together by their dermal secretion. They were unable to separate immediately, even when they struggled to do so. They were observed for approximately 15 minutes before separation occurred, and during this time they were moving about actively. As they separated, the area of adhesion was discernible on the back of the female. It was U-shaped, following the ridges of the ilia and the sacrum.

On August 2, 1954, after a rain of 3.22 inches, the previously mentioned funnel trap in the ditch had caught 31 ant-eating frogs. Water had collected to a depth of several inches in the depression where the trap was situated. A dozen of the trapped frogs were clasping pairs. These frogs struggled vigorously as they were removed from the traps, handled and marked. As a result most of the clasping males were separated from the females. In handling those of each pair I noticed that they were glued together by dermal secretions, as were those of the pair observed on June 5. The areas of adhesion were of similar shape and location in the different pairs, and included the U-shaped ridge of the female's back and the male's belly, and the inner surfaces of the male's forelegs with the corresponding surfaces of the female's sides where the male clasped.

This adhesion of the members of a pair during mating may be a normal occurrence. The copious secretion of the dermal glands is of especially glutinous quality in Gastrophryne. The adhesion of members of a pair may have survival value. These small frogs are especially shy, and in the breeding ponds they respond to any disturbance with vigorous attempts to escape and hide. Under such circumstances the adhesion may prevent separation. Also, it may serve to prevent displacement of a clasping male by a rival. Anderson (op. cit.) who observed many details of the mating behavior of G. carolinensis, both in the laboratory and under natural conditions, mentioned no such adhesion between members of a pair.

Anderson (op. cit.: 31) discussed the possibility that reproductive isolation might arise in sympatric populations, such as those of G. carolinensis in southern Louisiana, through inherent differences in time of spawning. However, in G. olivacea at least, such isolation would be prevented by individual males returning to breed at different times in the same season. Furthermore, individual differences in choice of breeding time probably result from environmental factors rather than genetic factors in most instances. In G. olivacea in Kansas, time of breeding is controlled by the distribution of heavy rainfall creating favorable conditions. Onset of the breeding season may be hastened or delayed, or an entire year may be missed because of summer drought. If favorable heavy rains are well distributed throughout the summer, frogs of age classes that are not yet sexually mature in the early part of the breeding season, may comprise the bulk of the breeding population in late summer.

DEVELOPMENT OF EGGS AND LARVAE

Eggs laid on June 5 by the pair kept in the laboratory were hatching on June 7, on the average approximately 48 hours from the time of laying. By June 8 all the eggs had hatched and the tadpoles were active. On August 28 and 29 thousands of newly metamorphosed young were in evidence on wet soil at the pond margin; in some the head still was tadpolelike and they had a vestige of the tail stump. These young were remarkably uniform in size, 15 to 16 mm. (the smallest one found was 14-1/2 mm.) and almost all of them had originated from eggs laid after heavy precipitation, totalling 3.22 inches, in the first 36 hours of August. Allowing one day for adults to reach the pond and spawn, and two days more for eggs to hatch, the tadpole stage must have lasted approximately 24 days in this crop of young.

Wright and Wright (1949: 582) stated that the tadpoles metamorphosed after 30 to 50 days, and that the newly metamorphosed frogs are 10 to 12 mm. in length. Length of time required for larval development probably varies a great deal depending on the interaction of several factors such as temperature and food supply.

GROWTH

Little has been recorded concerning the growth rate of Gastrophryne or the time required for it to attain sexual maturity. Wright (1932) found that G. carolinensis in the Okefinokee Swamp region has a mean metamorphosing-size of 10.8 mm. Young thought to be those recently emerged from their first hibernation were those in the size group 15.0 to 20.0 mm., while the frogs in the 20 to 27 mm. size class and those in the 27 to 36 mm. class were interpreted as representing two successively older annual age classes. Anderson (1954: 41) thought he could recognize four successive annual age classes in the same species in southern Louisiana. He found that sexual maturity is attained at a length of 21 to 24 mm. in frogs which he believed to be late in the second year of life.

Allowing for size differences between the two species, Wright's and Anderson's conclusions regarding growth in G. carolinensis, on the basis of size groups, are largely substantiated by my own data on the growth of marked individuals of G. olivacea living under natural conditions in Kansas.

In 1954, an opportunity to investigate the early growth was afforded by unusually favorable circumstances. The population of frogs that emerged from hibernation in the late spring of 1954 included few, if any, that were below adult size; drought had prevented successful breeding in 1952 and 1953. Heavy rains in the first week of June, 1954, and again in the first week of August, resulted in the production of two successive crops of young so widely spaced that they were easily distinguishable. Some young may have been hatched after other minor rains, but certainly these were relatively few. Young from the eggs laid in the first week of August were metamorphosing during the last week of August. Growth in the frogs of this group can be shown by the average size and the size range of the successive samples collected.

TABLE 2. GROWTH IN FROGS METAMORPHOSED IN THE LAST WEEK OF AUGUST, 1954.

=========================================================== |Number in| Mean size |Size range Time of sample | sample | in mm. | in mm. --------------------+---------+----------------+----------- August 27 to 31 | 27 | 15.55 +/- .079 | 15 to 17 --------------------+---------+----------------+----------- September 11 | 114 | 17.2 +/- .033 | 14 to 20 --------------------+---------+----------------+----------- September 15 to 22 | 12 | 18.7 +/- .090 | 16 to 20 --------------------+---------+----------------+----------- September 27 to 30 | 37 | 19.3 +/- .055 | 17 to 21.5 --------------------+---------+----------------+----------- October 1 to 7 | 62 | 20.8 +/- .072 | 17 to 24 --------------------+---------+----------------+----------- October 12 to 17 | 49 | 22.3 +/- .092 | 18 to 24 ===========================================================

By mid-October, six weeks after metamorphosis, these frogs had increased in over-all length by approximately 50 percent. Having grown a little more than 1 mm. per week on the average, they were approximately intermediate in size between small adults and newly metamorphosed young.

The frogs hatched in June were present in relatively small numbers compared with those hatched in August, and were not observed metamorphosing. In late August a sample of 33 judged to belong to the June brood averaged 26.2 (22-28) mm. long. A sample of 39 from the first week of October averaged 28.1 (24.5-32) mm. Frogs of this group thus were approaching small adult size late in their first growing season. Such individuals possibly breed in the summer following their first hibernation, when they are a year old or a little more. Because recaptured frogs were not sacrificed to determine the state of their gonads, the minimum time required to attain sexual maturity was not definitely determined. The available evidence indicates that sexual maturity is most often attained late in the second year of life, at an age of approximately two years. The darkened and distensible throat pouch of the adult male probably is the best available indicator of sexual maturity.

Frogs that metamorphose in late summer have little time to grow before hibernating, and still are small when they emerge in spring. The smallest one found was 19 mm. long (May 19, 1951), and in each year except 1954 many such young were found that were less than 25 mm. in length in May or early June. None of the frogs marked at or near metamorphosing size has been recaptured, but the trend of early growth is well shown by Table 2 and Fig. 3. However, many juveniles that were captured and marked within a few weeks of metamorphosis were recaptured as adults. The selected individuals in Table 3 are considered typical of growth from "half-grown" to small adult size. Growth in many other individuals is shown in Figs. 6 and 7.

TABLE 3. GROWTH IN FROGS MARKED AS YOUNG AND RECAPTURED AS SMALL ADULTS.

============================================================== Individual | Dates | Length | Probable time and sex | of capture | in mm. |of metamorphosis -----------------+-----------------+---------+---------------- No. 1 [Female] | August 28, 1951 | 21.5 |Mid-July, 1951 | May 5, 1952 | 23 | | July 3, 1952 | 32 | | August 31, 1952 | 33 | -----------------+-----------------+---------+---------------- No. 2 [Female] | June 8, 1950 | 25 |Late July, 1949 | May 24, 1951 | 31 | | July 30, 1951 | 34 | | June 24, 1952 | 35 | -----------------+-----------------+---------+---------------- No. 3 | August 31, 1951 | 24 |Late June, 1951 | May 23, 1953 | 32 | ==============================================================

The trend of growth after attainment of minimum adult size is also well shown by the records of marked individuals recaptured. Many of these were marked while they were still small so that their approximate ages are known. For those recaptured in their second year, after one hibernation, length averaged 30.92 mm. Some of this group were young metamorphosed late the preceding summer and still far short of adult size (as small as 23 mm.) when recaptured. Others were relatively large, up to 33 mm. A group of 22 recaptured frogs known to be in their third year averaged 33.3 mm. (males 31.9, females 35.3, excluding four individuals of undetermined sex). Fifteen other recaptured frogs were known to be in their fourth year at least, and some probably were older, as they were already large adults when first examined. These 15 averaged 36.6 mm. (males 34.7, females 37.9 mm.). Size was similar in a sample of 58 individuals intercepted en route to the breeding pond in heavy rains of June and August, 1954. The 38 males in this sample ranged in size from 30 mm. to 38 mm., averaging 34.5. The 20 females ranged from 34 mm. to 40 mm., averaging 37.65. The large average and maximum size in this sample of a breeding population may be typical after periods of drought years have prevented successful reproduction. Summer drought in 1952 and 1953 prevented breeding in those years, or, at least, it drastically reduced the numbers of young produced. One-year-old and two-year-old frogs may not have been represented at all in the sample of 58. Three-year-old frogs presumably made up a substantial part of the sample, since 1951 was a year of successful breeding.

Differences in size between species and geographic variation in size in Gastrophryne have been given little attention by herpetologists, but if understood, would help to clarify relationships. Hecht and Matalas stated in their revision (1946: 5) that size is of no importance as a taxonomic character, as typical carolinensis, olivacea, and mazatlanensis all averaged approximately the same--26 to 28 mm.--females slightly larger than males. However, they arbitrarily classed as adults all individuals 22.5 mm. in length or larger, having found individuals this small that showed the darkened and distensible throat pouches characteristic of adult males. From the trend of my own measurements of G. olivacea in northeastern Kansas, I conclude that either many immature individuals were included in their samples, or that the populations sampled included some with individuals that were remarkably small as adults.

The population which I studied may be considered typical of G. olivacea. They averaged large, including individuals up to 42 mm. in length, well above the maximum sizes for any reported in the literature. At metamorphosis these olivacea are of approximately 50 percent greater length than G. carolinensis as reported by Wright and Wright (1949: 573) and Anderson (1954: 41). Yet Blair (1950: 152) observed that in eastern Oklahoma, where the ranges of olivacea and carolinensis overlap, the latter is larger. On the basis of field and laboratory observations he tentatively concluded that one of the main barriers to interbreeding was the reluctance of the males of carolinensis to clasp the smaller females of olivacea.

That size differs in different populations, and is still poorly understood, is illustrated by the following discrepant figures from various authors.

TABLE 4. SIZE RANGE OF ADULTS IN VARIOUS POPULATIONS OF GASTROPHRYNE.

===============+=======================+=================+============= Species or | Geographic population | Authority |Size range of subspecies | sampled | |adults in mm. ---------------+-----------------------+-----------------+------------- | | | olivacea |Douglas Co., Kansas |present study | 31 to 42 | | | olivacea |entire range |Wright and Wright| 19 to 38 | | (1949) | | | | carolinensis |entire range |Wright and Wright| 20 to 36 | | (1949) | | | | carolinensis |southern Louisiana |Anderson | 22 to 35 | | (1954) | | | | areolata |southeastern Texas |Wright and Wright| 23 to 29 | | (1949) | | | | mazatlanensis|Arizona and New Mexico |Wright and Wright| 22 to 30 | | (1949) | | | | mazatlanensis|Santa Cruz Co., Arizona|Stebbins | 25.2 to 31.5 | | (1951) | ---------------+-----------------------+-----------------+-------------

COLOR AND PATTERN

The color pattern changes in the course of development, and the shade of color changes in response to environmental conditions. At the time of metamorphosis, young are dark brown with specks of black and with a dark, cuneate, leaflike middorsal mark. The narrow end of this mark arises just behind the head, and the mark extends posteriorly as far as the hind leg insertions. At its widest, the mark covers about half the width of the dorsal surface. The lateral edges of the mark are sharply defined, but at its anterior and posterior ends it blends into the ground color. In most individuals smaller than 20 mm., this dorsal mark is well defined and conspicuous. As growth proceeds, however, it becomes faint. In frogs 19 to 25 mm. long the marks have disappeared. In individuals of this size the brown ground color is markedly paler than in those newly metamorphosed, but is darker than in adults.