==============================================================
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 [Male] | August 31, 1951 | 24 |Late June, 1951
| May 23, 1953 | 32 |
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[Illustration: FIG. 5. Ant-eating frogs, a little less than twice
natural size, adult and newly metamorphosed young, showing differences
in size and coloration. The young is darker and has a leaflike middorsal
mark which fades as growth proceeds.]
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.
[Illustration: FIG. 6. Growth in a group of frogs, each marked while
still short of adult size and mostly recaptured after lapse of one or
more hibernation periods. Each line connects records of an individual
frog.]
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.
[Illustration: FIG. 7. Growth in another group of frogs that were marked
as young or small adults and recaptured after intervals of more than a
year. Frogs of this group were, on the average, larger than the
individuals shown in Fig. 6, and they made less rapid growth.]
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.