======================================================
| Number | Number | Ratio of
Locality | of | of | adults to
| adults | juveniles | juveniles
---------------------+--------+-----------+----------
Capitan Mountains | 57 | 15 | 100:26
Sierra Blanca | 30 | 22 | 100:73
Sacramentos, 1958 | 42 | 30 | 100:71
Sacramentos, '56-'57 | 46 | 35 | 100:76
+--------+-----------+----------
All | 175 | 102 | 100:58
---------------------+--------+-----------+----------
For purposes of this study we had only to age the individuals into adult
and subadult classes. The criterion for adult status was breeding
capability. A five-millimeter testis was the smallest size found in
individuals that probably bred, and all of these were 40 mm. or more in
snout-vent length. We arbitrarily considered individuals smaller than 40
mm. to be subadult. This probably does injustice to reality (females
were treated the same way), but it should be noted that any error
introduced in this way was almost certain to have increased the number
of "subadults" in the samples. Thus, the hypothesis above based on
age-ratios is not automatically invalid because of improper aging.
_Timing of the breeding season_
The time in which egg-clusters are deposited is a good rough index to
events in the breeding cycle. We found four egg-clusters, one on July
14, 1957, and three on July 27, 1957; the only other eggs taken to date
were found in late August (Lowe, 1950:94). Thus, courtship could occur
in June, oviposition in July and August, and hatching from August to
September. Actually, it is likely that the season is more restricted in
time for any one year. Lowe's find was made in a year in which the
summer rains were late, beginning in late July (Stebbins, 1951:137),
whereas ours were made in a year having abundant and relatively early
rainfall, beginning in late June. Microclimatic humidity is of extreme
importance to both the salamanders and their food.
We suppose a great deal of breeding activity takes place underground;
the chronology of events in such sites may bear no close relationship to
those occurring at the surface, yet it is likely that a close parallel
would be found. Breeding activities are ordinarily associated in time
with greatest food abundance.
_Clutch-size_
By clutch-size we refer to the number of eggs in laid clusters. We
collected clutches of six, four, four and one; adding one more of three
(Lowe, _op. cit._) gives an average of 3.6 eggs per cluster; the average
is 4.2 eggs if our clutch of one is discarded on the grounds it was
incomplete.
For comparison we have listed (Table 6) clutch-sizes for some other
plethodontids. It should be noted that these numbers refer only to eggs
deposited in clusters, and not to large ovarian eggs. Thus, _Aneides
hardii_ has the lowest range in clutch-size of any North American
plethodontid on record. It has been noted in other species that low
clutch-size is correlated with low productivity, slow population
turnover, and long average life-expectancy (Lack, 1954:103-105; Pitelka
and Johnston, MS). If this is the case with this salamander, several
other features in its environment and habits would tend to reinforce
such population structure: the animals are exceedingly well-concealed
(they were first described only 17 years ago [Taylor, 1941]), apparently
have few natural enemies (one garter snake [_Thamnophis_] was collected
within the habitat of the salamander in three years), apparently have
few and benign parasites, and abundant and readily available food.
Table 6.--Ranges and Mean Values of Clutch-sizes in Salamanders of
the North American Plethodontidae[1]
==========================================
| Range | Mean
---------------------------+-------+------
_Desmognathus_ spp.[2] | 11-40 | 20
_Leurognathus marmorata_ | 28 |
_Plethodon cinereus_ | 3-13 | 9
_Plethodon_ spp. | 8-18 | 13
_Ensatina eschscholtzii_ | 12-14 | 13
_Hemidactylium scutatum_ | 30 |
_Batrachoseps_ spp. | 7-74 |
_Aneides hardii_[3] | 1-6 | 3.6
_Aneides_ spp. | 7-19 | 13
_Stereochilus marginatus_ | | 57
_Pseudotriton ruber_ | 72 |
_Manculus quadridigitatus_ | 3-48 |
---------------------------+-------+------
[1] From Bishop (1947) and Stebbins (1951).
[2] Clusters of one and two occasionally found in _D. ochrophaeus_.
[3] This study, and from Lowe (1950).
_Eggs and "incubation"_
Our information concerning eggs essentially duplicates that already
reported (see Stebbins, 1951). All egg clusters that we found were in
small chambers within decomposing fir logs. In each instance the eggs
were suspended from the roofs of the chambers. The clutch of six eggs
was a compact mass, and the individual suspensory cables of the eggs
were intertwined and fused with one another. The clutches of four eggs,
although they too were compact clusters, had each suspensory pedicel
distinct from the others. The surface of the eggs was lightly moist, but
did not glisten with water, and each egg was completely free of the
others. The outer coat of jelly of the fresh eggs measured about 6.4 by
5.7 mm. as they hung suspended; sizes were uniform and no egg was
notably smaller or larger than the others.
We attempted to keep eggs artificially, but mold destroyed them after 12
days. We had difficulty keeping them wet without inundating them, for
the climate at Las Cruces, New Mexico, where we kept the eggs, is
exceedingly dry in summer. Until death, embryos were active and
responsive to disturbances around them. This was at a time when the limb
buds could not be detected and when the external gills were evident only
under close scrutiny.
Two times we found adult female salamanders in the chambers with the egg
clusters. The other two egg clutches seemingly had no attendant adult,
but our method of going through a log was such that we could easily have
alarmed any attendant animal well before we found the eggs, allowing
time for the adult to move away from the eggs. We presume that
incubation, so-called, in _A. hardii_ is similar to that found in other
plethodontids (see, for example, Gordon, 1952:683). Our findings on the
conditions of the stomachs of these attendant adults have been outlined
above ("Food and Foraging"). Our limited data suggest that only females
are found in chambers with eggs.