Eurycea lucifuga Rafinesque, 1822
© 2010 Todd Pierson (1 of 53)
Eurycea lucifuga Rafinesque, 1822
J. Eric Juterbock1
1. Historical versus Current Distribution. Cave salamanders (Eurycea lucifuga) range from the southern half of Indiana and extreme southwestern Ohio in the North, to the northern third of Alabama plus extreme northeastern Mississippi and northwestern Georgia in the South. They extend from northern Virginia in the East, to northeastern Oklahoma and extreme southeastern Kansas in the West. However, they are not always uniformly distributed within this range, due to their general (but not absolute) reliance on limestone caves and springs (see "Adult Habitat" below). Hutchison (1966) and Petranka (1998) contain additional information.
2. Historical versus Current Abundance. It is impossible to determine accurately the general abundance of cave salamanders from available data. Although numerous accounts give some indication of the number of individuals collected, and some even indicate the number of individuals seen, only three accounts give any indication of population size/density. Hutchison (1958), after a mark-release-recapture study, presented what he suggested were "rough estimate(s)" that he thought "to be rather close" to actual population sizes in four Virginia caves: 36, 60, 62, and 63. He gave no estimate of density, nor indication of cave size; there has been no subsequent study of these populations. Williams (1980), who collected and preserved the specimens he observed in a 1968 Illinois study, concluded that the investigator has an effect on the size of the visible population and compared his results with those of Hutchison. Whether or not such an effect exists, it seems likely that the removal of at least 68 adults from one cave, as he apparently did during his study, would have at least as great an effect upon the population as would disturbance through visitation.
Juterbock (1998) studied threee ravine sites in Ohio and, after 3 yr of recapturing marked individuals, concluded that estimates of 30–35, 20–25, and 5–10 adults, respectively, were reasonable at the sites, as well as 30–35, 5–10, and 25–30 post-larval immatures, respectively. Densities in the inhabited portion of each of these three habitats varied by a factor of 5. It is interesting that given the localized nature of their occurrence (and not knowing their population or metapopulation genetics), the sizes of all these localized groups are well within an order of magnitude. That said, none of these studies was long term, and none has been repeated. A further caution is evidenced by a removal study of salamanders in an Appalachian streamside community by Petranka and Murray (2001). They estimated that between 8 and 32 consecutive nights of sampling were required to remove 70% of the population for the six studied species. Thus, studies utilizing occasional sighting or capture-release-recapture techniques would probably underestimate population size, possibly substantially so.
To the degree that cave salamanders are dependent upon, or associated with, caves and similar limestone features, there is some reason for concern about their populations. Although the biggest threat to cave faunas may be their extremely localized occurrence, there are three recognized sources of vulnerability for cave organisms (Culver et al., 2000): (1) actions that directly degrade subsurface habitat; (2) actions that degrade surface terrestrial habitat and lead to degradation of subsurface habitat; and (3) actions that degrade surface aquatic habitat and lead to degradation of subsurface habitat. Minton (1998) contains one descriptive account of decline in cave salamander numbers, based upon his observations of Indiana sites from 1948–'93. At a spring on a steep slope of exposed siltstone in Floyd County, cave salamanders, once "regularly found," ceased to be observed as the habitat was degraded over the years.
3. Life History Features. For information beyond that in the following sections, Petranka (1998) is a good recent starting point. Hutchison's (1956, 1958, 1966) reports contain much original material and review previous work.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding migrations of the type typical of pond-breeding frogs and salamanders are unknown. Neither are such migrations suspected, given the life history of cave salamanders. However, that is not to say that such seasonal movements as occur (see "Seasonal Migrations" below) may not also be related to reproduction.
ii. Breeding habitat. There are few records for this species of naturally occurring egg clutches. The sparse evidence is summarized by Petranka (1998) and would indicate sites deep within surface or cave springs or cave streams. Minton (1972, 2001) reported finding large larvae in an Indiana cave approximately 1 km from the entrance.
i. Egg deposition sites. Myers (1958, p. 126) reported that eggs found in early January in a Missouri cave were "attached singly to the bottoms and sides of submerged rocks." The site in the stream was approximately 245 m from the entrance to the cave and about 1 m from where the stream flowed from the cave wall. Green et al. (1967) found eggs in three West Virginia caves attached to the sides of rimstone pools on the floor or sides of the caves, as well as unattached in the silt of the pools.
Banta and McAtee (1906) proposed, on the basis of finding 18 mm TL larvae in early February in Indiana, that oviposition had occurred around the end of December to early January. They also found "small larvae" as late as 20 March. Myers (1958, p. 126) found eggs "in various stages of development, from early cleavage to advanced embryos" in Missouri on 2 January. At the same time, he also found newly hatched larvae, measuring 11 mm TL (approximately 80% of which was SVL). Perhaps Hutchison's (1956) report of a 17 mm (TL or SVL not indicated) larva in Virginia during July could indicate a slow growth rate rather than a later time of oviposition. Myers (1958) "tentatively" interpreted the available data as indicating that the period from oviposition to hatching lasted from as early as October to as late as May. Green et al. (1967) slightly increased that range, reporting eggs in West Virginia caves from 24 September–5 November. The data do not exist to evaluate inter- and intra-population variation for this trait.
ii. Clutch size. Hutchison (1956) counted ovarian eggs in 17 adults collected during July and August in Virginia. They averaged 68.3 (median = 67, range = 49–87). Trauth et al. (1990) counted ovarian eggs in 11 adults collected in Arkansas; these averaged 77.7 (range = 60–120). Clutch size in all likelihood varies with female body size, but insufficient data exist to evaluate such an hypothesis.
i. Length of larval stage. Banta and McAtee (1906) estimated a 12–15 mo larval period as typical for cave salamanders in Indiana. They suggested that some larvae undergo metamorphosis in autumn, when they collected larvae ranging between 31–56.5 mm TL. They concluded that most larvae transformed in March, when they collected an individual metamorphosing. Green et al. (1967) believed that a 30 mm TL larva in one of their West Virginia caves and a 41 mm TL larva reported by Myers (1958) from Tennessee, collected during late February to March, were 1 yr old. Sinclair's (1950) observation of three larvae measuring 22.5 mm, 31.5 mm, and 51.5 mm TL in mid March more clearly demonstrates overlapping generations.
ii. Larval requirements.
a. Food. Rudolph (1978) studied larval food habits of cave salamanders in northeastern Oklahoma and compared them to the larvae of four related salamander species. Of 370 cave salamander food items, 71.6% were ostracods and 12.2% were dipteran larvae; other food items, in order of abundance, included pulmonate snails, ephemeropteran nymphs, isopods, dipteran adults, trichopteran nymphs, adult coleopterans, larval coleopterans, plecopteran nymphs, copepods, and araneae. As expected, most of these food items are aquatic. The food items of larvae of four syntopic species showed some overlap with larval cave salamanders. Most similar in their feeding habits were long-tailed salamander (E. longicauda) larvae, although Rudolph concluded that food competition was probably secondary to competition over space. The other species' food habits probably allow rejection of a hypothesis that cave salamander larvae were only eating things in the proportion in which they occurred in the habitat. Although ostracods were abundant in the diets of all 5 species, they were not the most numerous item for two species. Additionally, certain food items were considerably more abundant in the diets of one or more of the other species than in the diet of cave salamanders (e.g., copepods, amphipods, and isopods for grotto salamanders [Typhlotriton speleaus]; copepods for long-tailed salamanders; and, isopods for Oklahoma salamanders [E. tynerensis]). Still, it is possible that microhabitat segregation may be at least partially responsible for the observed dietary differences.
b. Cover. Banta and McAtee (1906), working in Indiana, indicated that oviposition was in the deepest parts of caves and felt that larvae found at cave mouths and in outside streams were carried there by currents. Sinclair (1950) reported counting hundreds of larvae, at all hours of the day, crawling about the bottom of a surface spring with no cover. He further indicates that he could not find larvae in caves, and that they seemed to prefer cover when they approached metamorphosis. Although the numbers of larvae sound impressive, it is worth noting that, with clutch sizes over 50 (probably averaging 70–75), "hundreds" of larvae, especially if young, might only represent a few clutches. Green et al. (1967) stated that larvae move out of the rimstone pools in which they hatch as those pools overflow in the winter and early spring. Larvae were found in the small, temporary overflow streams and the permanent main stream in the cave; no cover was mentioned. These authors note that larvae were always observed to move downstream, both under their own power and by the action of currents. This alone could explain the appearance of larvae in surface springs and streams, although more needs to be learned about oviposition sites and larval life history. In northeastern Oklahoma (Rudolph, 1978), larvae were found in some surface streams ≤ 45 m from the source spring under unspecified cover. In southwestern Ohio ravines, larvae were rarely seen and presumed to remain underground (unpublished data).
iii. Larval polymorphisms. None known.
iv. Features of metamorphosis. In southwestern Ohio, the smallest metamorphic animals appear in the surface-active population in late summer, at approximately 35–40 mm SVL and probably 18–21 mo old. Metamorphosis in Ohio does not appear to be at all synchronous. Of individuals captured while undergoing metamorphosis, 10 individuals were captured at two sites between May and September, with six of these in August (unpublished data). The smallest two metamorphosing salamanders were 27 mm SVL (captured in July and September); the largest one was 41 mm SVL in May (the second smallest of its age/size class [n = 8, SVL range = 38–50] in a collection containing a 23 mm SVL larva); the median size was 32 mm SVL. Only three larvae were captured at these sites, with SVLs of 15 mm (2 May), 23 mm (24 May), and 24 mm (13 June). I am aware of no other data on the timing of metamorphosis that is this complete (although individuals at these sites could only be found on the surface from April–September).
The smallest metamorphosed specimen reported by Williams (1980) was a 31 mm SVL female, and the largest larva was 33 mm SVL; TLs were 68 mm and 70 mm, respectively. He concluded that metamorphosis usually occurred between 25–35 mm SVL. He reported 26 larval specimens, but indicated that this was too small a sample to determine age classes; no data beyond those of the previous sentence were presented. Green et al. (1967) stated that metamorphosis occurred between 50–56 mm TL. Sinclair (1950) found two recently metamorphosed animals (59 and 60.5 mm TL) in a Tennessee cave on 2 June.
Rudolph (1978) studied northeastern Oklahoma populations found in surface springs, as well as caves, and stated that metamorphic size for cave salamanders in these populations is approximately 25 mm SVL. He indicated that recently hatched larvae appeared in springs during winter and early spring, and their spring and summer growth usually allowed them to metamorphose between July–October of the same year. Metamorphosis at this time was also supported by the observation of recently metamorphosed animals in the nearby terrestrial habitat. However, he adds that during winter one can usually find a few large larvae, because some individuals overwinter and metamorphose during their second spring. This implies that metamorphosis could occur as early as about 6 mo or as late as perhaps 18 mo.
Apparently, the only indication of growth in larval cave salamanders is contained in the two samples Rudolph (1978) collected from the same surface stream in northeastern Oklahoma. In those, there was a median size (SVL) difference of 10.5 mm (8 June 1976 collection: n = 17, median = 14 mm, range 10–22 mm; 1 August 1976 collection: n = 26, median = 24.5, range 19–29 mm).
v. Post-metamorphic migrations. None known.
vi. Neoteny. Unknown, although some larvae will overwinter and metamorphose the following year (Minton, 1972; Rudolph, 1978; see also Petranka, 1998)
D. Juvenile Habitat. There is no evidence that juvenile habitats differ from those of adults. One possible exception involves the timing of habitat use. In southwestern Ohio, I found that adults were much more likely to be active on the surface in late spring as compared to juveniles, whereas juveniles were much more likely to be active on the surface in late summer. For example, at one site over three years, 27 individual adults were captured in May, but only two in August or September; for juveniles, the numbers were 19 and 22, respectively (chi-squared = 16.7, p << 0.001). The surface habitat at these sites generally is drier in late summer.
E. Adult Habitat. Adults are essentially terrestrial and/or associated with caves in limestone regions (e.g., Peters, 1946). Although most records are from, and the species appears to be most abundant in, the twilight regions of caves, where they climb over walls and ledges, they are also found outside of caves, under stones, logs, and other surface matter, as well as deeper in caves. Hutchison (1958) reported one locality where the species is associated with a non-calcareous cave. Banta and McAtee (1906) indicated that cave salamanders were found on the walls of the caves and rarely on the cave floor or in the water. Green et al. (1967) agree with this assessment, but Williams (1980) collected 16% of his adult specimens from the stream; most were under rocks. Petranka (1998) summarizes the variety of relevant reports, as well as cautioning that the species' restriction to cave habitats is over-emphasized. Certainly there are no caves in Hamilton County, Ohio, where terrestrial stage individuals are infrequent to common in at least six county and one city park units. Here the habitat consists of forested limestone ravines, at least some of which appear to have subsurface water flow (Davis et al., 1998; Juterbock, 1998). In these situations, adults seldom are seen free of cover, regardless of whether or not it was during the day or night (personal observations). Metamorphosed individuals of all ages are found in the stream bed, but rarely in the water; they are under rocks (mostly), logs, and debris. They only are present on the surface when there is water present or when the soil is muddy (unpublished data). Smith (1961) reported that spring-fed cypress swamps, located "well away from" rock bluffs, were the Illinois sites where cave salamanders were most abundant. Adults and larvae were commonly found there under leaves and logs. I have also seen numerous individuals of various sizes active on the surface of a roadcut on a hillside above a stream in Kentucky (personal observations).
F. Home Range Size. In one southwestern Ohio ravine, over the course of three surface-active seasons, 31 adults were recaptured at least once. Of these, 22 (71%) had maximum ranges along the ravine (at least 50 m of habitat) of ≤ 10 m, and mean distances between captures of ≤ 10 m (unpublished data). Thirteen of the 22 (42% of the total 31) were recaptured after overwintering below the surface at least once (and thus at least seasonally shifting the area in which they were active).
G. Territories. Territoriality has not been reported and seems unlikely. Smith (1961), for example, reported that a single large rock might contain "a number" of individuals.
H. Aestivation/Avoiding Dessication. Aestivation has not been reported and seems unlikely, especially given the cave/spring habitat of this species. However, it is not clear what effects drought may have on the species. Hutchison (1958) found at least one individual in at least one of his four Virginia study caves each month except January.
I. Seasonal Migrations. Hutchison (1958) measured the distance from the mouth of one of his Virginia study caves to the site of each salamander's capture during the year. The salamanders were closest to the mouth in June–July and farthest from the mouth in February–March. He concluded that these data were evidence that migration from the cave did not occur. They do, however, clearly indicate seasonal movements within the cave ecosystem, from a June mean of 4.7 m from the mouth to a March mean of 26.6 m from the mouth. Hutchison (1958) also found that the visible population in all caves that he studied increased from late February to March (in different caves) to a peak in June and then declined dramatically by September. These data mirror the distance data and support a hypothesis of seasonal movements within the habitat. Williams (1980) collected almost 4–5 times as many individuals in May–June as he had in March–April, after which the July and August numbers returned to the level he had seen before the peak. As noted above (see "Historical versus Current Abundance" above), removing 60 or more individuals from the population during the spring should have affected summer counts. Juterbock (unpublished data) found a May–June peak in the surface-active population in southwestern Ohio limestone ravines, with a lesser, secondary peak (comprised primarily of juveniles) in late August to September. Although surface activity is unlikely in the winter in these ravine habitats, the overall pattern is similar to that described for caves and indicates at least seasonal movements from surface (active) to subsurface (inactive?) habitat.
J. Torpor (Hibernation). Considered unlikely by Hutchison (1958), who saw salamanders that were active during the winter while deep in the caves.
K. Interspecific Associations/Exclusions. Hutchison studied cave salamanders and long-tailed salamanders from four caves in Virginia. He found that the two species often shared the twilight zones of caves, with cave salamanders usually more abundant. However, because he found long-tailed salamanders in "comparatively larger numbers" in areas where cave salamanders did not occur (Hutchison, 1958, p. 11), he concluded that interspecific competition between the two species may occur. The similarities of diet (see "Larval requirements" above and "Feeding Behavior" below) may offer a hint as to the mechanism involved.
L. Age/Size at Reproductive Maturity. Hutchison (1958) reported that Virginia males were mature at > 46 mm SVL, and females at > 48 mm SVL. In southern Illinois, Williams (1980) reported that females > 49 mm SVL were mature. Juterbock (1998), sexing recaptured individuals by means of externally visible characteristics, found the smallest mature males in Ohio to be 54 mm SVL and the smallest mature females to be 56 mm SVL. One of the smallest individuals was 53 mm and could not be sexed on 3 May, but was clearly a male when recaptured on 31 May of the same year. Although not nearly as dramatic, many of the smallest mature individuals he recorded were previously observed as unsexable immatures. The differences in size indicated by these three accounts may be real variation or an artifact of using different techniques.
Mostly because of the uncertainty surrounding larval age classes, age at maturity is problematic. The recapture data from southwestern Ohio (unpublished data) leave little doubt that at least 2 yr are required before maturity is attained after the summer of metamorphosis. This would be either the third or fourth summer after the winter of hatching (or approximately 2.5 or 3.5 yr of age), depending upon the length of the larval period. As noted above, it is likely that the duration of the larval period varies, probably both within and between populations. From a conservation perspective, this is one of the more glaring gaps in our knowledge of the species.
Hutchison (1958) observed an overall male:female sex ratio of 1.51:1 in his four Virginia caves. Three of those caves, with total sample sizes of 38, 54, and 59, had individual ratios of 0.65, 1.6, and 1.1, respectively (so the largest sample was the closest to 1:1). Williams (1980) reported a ratio of 1.125:1 (n = 70) with males dominant. In contrast, Juterbock (unpublished) found that (based upon externally detectable characteristics of marked salamanders) mature females insignificantly outnumbered males 39:26 (chi-squared = 2.6, p = 0.11) in southwestern Ohio. Only at the site with the most adults captured (52%) was the difference significant (11 males, 23 females; chi squared = 4.24, p = 0.04). It is not known whether these differences represent a real result of interspecific variation in life history or an artifact of what are actually rather small samples.
M. Longevity. Not known.
N. Feeding Behavior. Peck (1974) surveyed for food in the guts of 112 cave salamanders (11 were empty) from nine (mostly southeastern) states and found a minimum of 73 prey species. These included annelid worms, snails, crustaceans, millipedes, various arachnids, and 14 orders of insects (14 families of beetles, 12 families of flies, and 4 families of hymenopterans). Spiders, crickets, and at least four families of flies were found in at least 10% of those guts containing food items. Peck and Richardson (1976) studied the diets of an additional 213 cave salamanders from four southeastern states, primarily to elucidate any differences in feeding ecology with respect to location within the cave. They found that the salamanders were best fed within the twilight zone of the cave and least well-fed in the zone of permanent darkness. The major dietary difference discovered was the importance of trichopteran insects, but these were an ephemeral resource at only a few of the studied caves. They identified at least 101 taxa of prey in the study. Hutchison (1958) compared the food items in guts of 13 cave salamanders and 10 long-tailed salamanders. He found seven orders of insects (more fly taxa and individuals), three orders of arachnids (but no spiders), and isopods. The frequency of occurrence of most taxa was slightly greater for cave salamanders than for long-tailed salamanders, but their diets overlapped greatly.
O. Predators. There appear to be no records of specific predators attacking or consuming cave salamanders, but their responses to disturbance (see "Anti-Predator Mechanisms" below) presumably evolved for a reason. Numerous authors have suggested potential predators (e.g., Hutchison, 1958).
P. Anti-Predator Mechanisms. As do most plethodontid salamanders, cave salamanders possess skin glands that secrete noxious substances. Cave salamanders and their relatives raise and undulate the tail over the head, which, because the body is coiled, rests near the vent (Brodie, 1977). Brodie (1977) has witnessed congeneric species use this posture when attacked by short-tailed shrews (Blarina brevicauda) and blue jays (Cyanocitta cristata). In tests with shrews, he noted that 12 of 13 attacks resulted in bites to the tail, with the shrew briefly retreating and wiping its mouth; this should allow the salamander a brief opportunity to escape.
Under this scenario, one would expect that one explanation of broken tails would be failed predation attempts. The percentage of individuals with broken or obviously regenerating tails varies widely in different populations: approximately 4% in Virginia (Hutchison, 1956); 28.3% in Illinois (Williams, 1980); and 59.5% of 74 adults, 16.4% of 61 immatures in Ohio (unpublished data). This difference between tail damage rates of adults and immatures is significant (chi squared = 24.5, p << 0.001) and presumably relates to the accumulation of time spent in the terrestrial environment. It is worth noting that the Ohio populations occur in ravines, not caves, in a generally urban area. Whatever else may be harassing cave salamanders at these sites (and I have observed children turning rocks at these places), there also are urban population levels of raccoons, and all the Ohio sites studied did occasionally exhibit signs of raccoon foraging.
Q. Diseases. No records.
R. Parasites. McAllister et al. (1995d), in a study of another species of Eurycea in Arkansas, noted the first record of the nematode Desmognathinema nantahalaensis in cave salamanders.
4. Conservation. It is impossible to accurately determine from available data the general abundance, and therefore the conservation status, of cave salamanders. Because cave salamanders are dependent upon, or associated with, caves and similar limestone features, there is some reason for concern. Although the biggest threat to cave faunas may be their extremely localized occurrence, actions that directly degrade subsurface habitat or surface terrestrial and/or aquatic habitats negatively affect populations. Cave salamanders are listed as Endangered in Ohio, Mississippi, and Kansas (Levell, 1997), and considered Rare in West Virginia.
1J. Eric Juterbock
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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