Gregarious Slender Salamander
© 2006 William Flaxington (1 of 9)
Batrachoseps gregarius Jockusch, Wake and Yanev, 1998
Robert W. Hansen1
1. Historical versus Current Distribution. Gregarious slender salamanders (Batrachoseps gregarius) are found on the western slopes of the central and southern Sierra Nevada of California, from the southern boundary of Yosemite National Park south to just north of the Kern River (Jockusch et al., 1998; Wake and Jockusch, 2000). Northernmost records are for Feliciana Mountain and Jerseydale Ranger Station (Mariposa County). Southern range limit is Rancheria Road, 3 mi north of the Kern River (Kern County). Especially abundant along riparian corridors of the White River–Arrastre Creek drainages in southern Tulare and northern Kern counties. Elevational range is from < 100 m to about 1,800 m, with southern populations (e.g., Tulare and Kern counties) generally occurring below 900 m. Although mostly confined to foothills and middle-elevation mountainous regions, gregarious slender salamanders extend onto the floor of the Central Valley along riparian corridors (e.g., San Joaquin River north of Fresno, Kings River at Centerville). There is little evidence of modification of the historical range. Some range-margin populations along the eastern edge of the Central Valley may have been affected by housing, agriculture, or other development.
2. Historical versus Current Abundance. In our experience, gregarious slender salamanders may be locally abundant at some sites and difficult to find at others, but long-term trends are not evident.
3. Life History Features.
i. Breeding migrations. Unknown. However, based upon their observations of the local distributions of adult females, Jockusch and Mahoney (1997) suggest that surface movements related to egg laying are more extensive than previously thought.
ii. Breeding habitat. Unknown.
i. Egg deposition sites. The following information is taken from Jockusch and Mahoney (1997), who reported on numerous nest sites discovered at both the northern end of the range (near the Madera–Mariposa County line within mixed coniferous forest, 1,400 m elevation) and from the southern end of the range (in foothill oak woodland, Tulare County, 430 m elevation). Most females deposit eggs in communal nests that are then abandoned, although adult males and subadults may be found under the same cover objects (spent females also have been found with eggs but apparently do not remain under these cover objects for extended periods). Eggs are laid beneath downed logs, bark slabs, rocks, or within damp leaf litter usually associated with surface water—stream or seep margins. Nests at the foothill site were located under deeply imbedded rocks in a grassy pasture, while those from the higher elevation forested area were found under a variety of surface objects.
ii. Clutch size. Egg counts ranged from < 10 eggs (the product of a single female) to > 300 eggs, which were attributed to > 18 females. Clutch size is correlated with female body size and also varies geographically. Females from the northern end of the range produce larger clutches (mean = 15.3 eggs for 50 clutches; record = 29 eggs), while those from the southern part of the range produce fewer eggs (mean = 7.3 eggs for 20 clutches; maximum = 14 eggs; Jockusch, 1997b; Jockusch and Mahoney, 1997).
C. Direct Development. Timing of egg laying varies with elevation and latitude. At the southern end of the range and at lower elevations, egg laying coincides with the start of the rainy season (Jockusch and Mahoney, 1997). Onset of fall rains in this part of the Sierra Nevada is unpredictable and varies from year to year; thus, egg-laying occurs from mid November to early January, depending on local rainfall. At higher elevation sites, egg laying occurs later (late March to late April; Jockusch and Mahoney, 1997; R.W.H., unpublished data).
Developmental times for lab-incubated (at 13 ˚C) eggs ranged from 65 d (for 50 eggs from a southern population) to 73 d (for 222 eggs from northern sites; Jockusch and Mahoney, 1997). Hatchlings were observed 6 March in the foothills of Fresno County in an area where females lay eggs in December–January.
D. Juvenile Habitat. Unknown.
E. Adult Habitat. Gregarious slender salamanders occur principally in the oak woodlands of the Sierra Nevada foothills, dominated by blue oak, interior live oak, and foothill pine, but also range into mixed conifer forests grown to Ponderosa pine, incense cedar, white fir, and black oak. At their northern range limits, gregarious slender salamanders are abundant within a closed canopy conifer forest with sugar pine and giant sequoias. Annual precipitation at higher elevation sites may exceed 110 cm, with snow often present from November–April (Jockusch et al., 1998). Also recorded from low elevation riparian corridors associated with interior live oak (San Joaquin River north of Fresno) or valley oak (Kings River near Centerville). Gregarious slender salamanders from the east side of the Central Valley along Ash Slough (Madera County) occur in annual grassland. They generally are absent from steep slopes.
The southernmost population, just north of the Kern River, occupies arid rolling grassland with scattered rocks; rainfall averages only 27 cm/yr. Salamanders at this site have been found under rocks with desert night lizards (Xantusia vigilis), night snakes (Hypsiglena torquata), side-blotched lizards (Uta stansburiana), western fence lizards (Sceloporus occidentalis), and Gilbert skinks (Eumeces gilberti).
At some higher elevation sites in Fresno and Madera counties, gregarious slender salamanders may occur in settings that are similar ecologically to those of the allopatric relictual slender salamanders (B. relictus), namely under or within woody debris adjacent to seeps or other moist places within coniferous forests. This is in marked contrast to the large majority of gregarious slender salamander collection sites, most of which are in relatively open oak woodlands subject to high summer temperatures.
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Surface activity is strongly correlated with soil moisture and temperature, to some extent. For foothill areas, salamanders are surface active from the onset of fall rains (late October to November) to March–April. At higher elevations (> 1,200 m), activity may occur in all but the coldest months. Body temperatures of salamanders found under surface cover averaged 12.3 ˚C (range = 5.0–19.0 ˚C, n = 280; R.W.H., unpublished data).
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). We have not recorded surface activity at substrate temperatures below 5 ˚C. Presumably, salamanders retreat underground below the frost line.
K. Interspecific Associations/Exclusions. Sympatric with Sequoia slender salamanders (B. kawia) in the South Fork Kaweah River drainage (Jockusch et al., 1998). Their distribution is allopatric to that of relictual slender salamanders, which generally occur at higher elevations and wetter sites, although their ranges converge in several drainages in southern Tulare County and northern Kern County (Brame and Murray, 1968; Jockusch et al., 1998). Just beyond the northern range limits for relictual slender salamanders, gregarious slender salamanders are found at higher elevations and occur in moist coniferous forest settings that are typical of relictual slender salamander sites farther south. The ranges of Kings River slender salamanders (B. regius) and gregarious slender salamanders closely approach, but do not overlap, in the Kings River drainage (Fresno County), where Kings River slender salamanders are restricted to moist, north-facing slopes.
The southernmost locality for gregarious slender salamanders (just north of the Kern River) is < 10 km from populations of Kern Canyon slender salamanders (B. simatus) in lower Kern River Canyon. Salamanders assigned to black-bellied salamanders (B. nigriventris) occur about 37 km south of the southernmost gregarious slender salamander locality, although we suspect that populations belonging to one or both species may occur in the intervening semi-arid foothills of the Tehachapi Mountains.
In the central Sierra Nevada (between Calaveras and Mariposa counties), the ranges of gregarious slender salamanders, California slender salamanders (B. attenuatus), and Hell Hollow slender salamanders (B. diabolicus) converge, but sympatry is recorded only for the latter two species. Fieldwork is needed in that area to better define the distributional relationships among those species.
L. Age/Size at Reproductive Maturity. Nine adult males from the northern end of the range measured 29.9–40.2 mm SVL (mean = 35.9 mm); 10 females ranged from 38.4–46.0 mm SVL (mean = 42.5 mm; Jockusch et al., 1998). An adult female from Fresno County measured 50 mm SVL.
M. Longevity. Unknown.
N. Feeding Behavior. Has not been described, although all Batrachoseps species observed thus far use a projectile tongue to capture small invertebrates.
O. Predators. Predation in the wild is undocumented, although captive night snakes (Hypsiglena torquata) and ring-necked snakes (Diadophis punctatus) have eaten gregarious slender salamanders (R.W.H., unpublished data).
P. Anti-Predator Mechanisms. Defensive behaviors include tail autotomy, coiling, immobility, and flipping followed by immobility. Most adults coil tightly or remain immobile when discovered under surface cover; their dark brown or reddish brown coloration is effectively cryptic.
Q. Diseases. Unknown.
R. Parasites. Unknown.
S. Comments. Until the work of Brame and Murray (1968) and Yanev (1978, 1980), Sierra Nevada populations of attenuate Batrachoseps were included within California slender salamanders (B. attenuatus), a wide-ranging composite species. Yanev restricted the name B. attenuatus in the Sierra Nevada to the northern and central portion of that range, allocating Sierran populations of B. attenuatus from Mariposa County southward to black-bellied slender salamanders (B. nigriventris). Jockusch et al. (1998) demonstrated that Sierra Nevada B. nigriventris were specifically distinct from southern California and coastal populations of that species and described gregarious slender salamanders to accommodate the Sierran portion of the range. Thus, some earlier references (e.g., Stebbins, 1951; Basey, 1969, 1976; Basey and Sinclear, 1980) provide information about B. gregarius under the name B. attenuatus. Additionally, many museum specimens of “B. attenuatus” from the Sierra Nevada are mis-identified and could represent any of a number of species, including B. gregarius, B. diabolicus, B. relictus, or B. kawia. Wake and Jockusch (2000) include B. gregarius in a B. nigriventris complex, consisting of B. nigriventris, B. gregarius, B. simatus, and B. stebbinsi, as well as undescribed taxa from the southern Sierra Nevada.
Substantial variation exists in morphology, allozymes, and mtDNA gene sequences between northern and southern populations of gregarious slender salamanders (Jockusch et al., 1998). Features of reproductive biology (spring versus fall egg-laying and pronounced clutch size differences) also vary, suggesting that B. gregarius as currently recognized may comprise > 1 species. Jockusch et al. (1998) considered this possibility, but tentatively regarded intermediate populations as having undergone recent local gene flow and thus chose to recognize a single species.
4. Conservation. Gregarious slender salamanders are especially abundant along riparian corridors of the White River–Arrastre Creek drainages in southern Tulare and northern Kern counties. There is little evidence of changes in distribution compared with the historical range, and long-term trends in abundance are not evident. Some range-margin populations along the eastern edge of the Central Valley may have been affected by housing, agriculture, or other development.
In general, the distributions of Batrachoseps species in the southern Sierra Nevada are complex and incompletely known. Additional field and laboratory studies are underway to resolve outstanding taxonomic and distributional questions.
1 Robert W. Hansen
2 David B. Wake
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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