Part 2

The salamanders captured prey by pursuit. A salamander would pursue a fly until it was caught, or until it moved out of the field of action. The salamanders were attracted by movements of flies, and ignored those that were completely quiet; predation was oriented almost wholly on a visual basis. Once they were within 2 to 4 mm. of a fly they would snap out the tongue to secure the fly; they were successful in capturing vestigial-winged flies in about 75 per cent of all tries. The relative success of capture was greater when the animals were fresh from the field and less after they had become fattened. The vigor of their pursuit also decreased noticeably once they became fat. About two days after any new fly colony was placed in the terrarium, a salamander would take up a position just inside the lip of the milk bottle, which was placed on its side. From this vantage point the salamanders took heavy toll of the fly populations, eating both adults and larvae.

Initially the salamanders foraged indiscriminately in daylight or in darkness. Later, as they became fat, they avoided high light intensity and were active only at night or under artificial light of low intensity. The latter pattern of activity is probably typical of the pattern they maintain under natural conditions. Certainly we never saw individuals abroad in daylight at Cloudcroft, yet under favorable environmental conditions they were to be found in sites that required considerable movement over open areas of the ground surface.

For several months two individuals of Eurycea longicauda were kept in with A. hardii. Foraging of these two plethodontids is nearly identical, but the tongue of an adult Eurycea can be extended somewhat more than one-half inch in capturing flies; for A. hardii this distance is usually less than one-quarter inch. The relatively short tongue of A. hardii can be correlated with its life in restricted, subsurface chambers, where prey most frequently is close to salamanders; E. longicauda inhabits significantly more open sites.

Parasites

Thirty of the adult Aneides collected were examined for parasites; most were parasitized by two species of nematodes, Oswaldocruzia sp. and Thelandros sp. The former is found in the anterior part of the small intestine and occasionally in the stomach, and the latter occurs in the rectum. There were no gross intestinal pathological changes in the salamanders resulting from parasitism. In fact, no pathological or structural abnormalities were noted in any of the salamanders examined. We believe the two nematodes are well-tolerated by the salamander.

Table 2.--Occurrence of Parasitic Nematodes in Aneides hardii

=========================+=============+==============+=================== | | | | | Number of | Per cent of | | nematodes | nematodes that | Per cent of | per host | were immature | salamanders +-------+------+-------+----------- | infected | | | | | | range | mean | July | Aug.-Sept. -------------------------+-------------+-------+------+-------+----------- | | | | | Oswaldocruzia sp. | 83 | 2-15 | 3.6 | 100 | 20 | | | | | Thelandros sp. | 90 | 1-17 | 3.3 | 64.6 | 5.7 -------------------------+-------------+-------+------+-------+-----------

The numerical and temporal occurrence of the nematodes is summarized in Table 2. It should be noted that of the 17 worms constituting the maximum infection by Thelandros, only one was an adult worm; the maximum number of adult Thelandros in any one host was five. Similarly, the heaviest Oswaldocruzia infection, 15 worms, consisted of immature individuals; the maximum number of adult worms in any one host was ten.

The monthly variation in the relative occurrence of young stages versus adult in both nematodes (Table 2) suggests that the parasites are eliminated from hosts sometime in the long period, late September to early June, when A. hardii exists subterraneously; the worms thus would be reacquired annually when the salamanders resumed living on the "surface" or near the surface. Table 2 shows that the majority of the worms are immature (100 per cent, in Oswaldocruzia) in samples taken in July. Additionally, all but one individual of those constituting the 20 per cent occurring as immature Oswaldocruzia in the period August to September were actually collected in early August. These were found in one salamander, and this constituted the heaviest infection for the period; crowding effects may have led to retardation of development of the worms.

If it is true that parasites are reacquired each spring--we assume that no temperature factors or immune reactions are delaying development of the worms, and no unusually long external ovic or free-living phase is a necessary part of their life-history--then the host-parasite data can be used as a basis for hypothesizing about the winter life of the salamander. During "surface" life the incidence of parasitism is high (90 per cent and 83 per cent: see Table 2), indicating that salamanders are readily invaded in times of activity. Salamanders examined in September were all parasitized and probably carried nematodes with them into their winter retreats. This part of their habitat should thus be contaminated with infective stages of both parasites. Yet the salamanders seem to become re-infected when the period of summer activity starts (note the high incidence of immature parasites in salamanders taken in July); therefore, the salamanders lose their worms in winter. This suggests that during their subterranean life salamanders are inactive, and avoid ingestion of infective stages of the parasites. A fairly complete hibernation such as we suppose they undergo has been reported by Szymanski (1914) for Salamandra on the basis of kymographic records of movement.

Characteristics of Breeding

Sex-ratio

Tables 3 and 4 show the distribution of sexes for two subsections of our sample. The ratio of males to females in the total sample was nearly 1:1. There were differences in ratios between the three general localities: the two northerly sites had fewer females than males, when compared with the Cloudcroft samples. This is true for the samples of adults, but not for the juveniles, where in each instance the females predominated. We cannot absolutely explain these differences in ratios. Possibly the data on adults reflect different patterns of activity among the sexes so that adult females are simply not present in numbers where we looked for them. They could be located underground, in connection with "incubating" duties; if this is true it would account for the fact that so few egg-clusters have been found in logs.

Table 3.--Sex Ratios in Aneides hardii, Total Sample

=================================================== | Number | Number | Ratio of Locality | of | of | males to | males | females | females ---------------------+--------+---------+---------- Capitan Mountains | 35 | 31 | 100:87 Sierra Blanca | 28 | 21 | 100:75 Sacramentos, 1958 | 23 | 20 | 100:121 Sacramentos, '56-'57 | 34 | 43 | 100:126 +--------+---------+---------- All | 120 | 123 | 1:1 ---------------------+--------+---------+----------

Table 4.--Sex Ratios in Aneides hardii, Adults

=================================================== | Number | Number | Ratio of Locality | of | of | males to | males | females | females ---------------------+--------+---------+---------- Capitan Mountains | 35 | 19 | 100:54 Sierra Blanca | 22 | 7 | 100:32 Sacramentos, 1958 | 15 | 14 | 100:93 Sacramentos, '56-'57 | 22 | 16 | 100:73 ---------------------+--------+---------+----------

Age-ratio

The data in Table 5 show adult salamanders to outnumber young at each collecting locality. This is probably not an accurate reflection of actual age composition in this species. Yet, we obtained the same general result in all three years of the study. We assume, therefore, that young were located where we could not catch many of them; probably they were underground. Sites of hatching and of the activities of early life would thus occur where we think the bulk of eggs are laid.

Table 5.--Age Ratios, Adults-juveniles

====================================================== | 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.