Allegheny Mountain dusky salamander COSEWIC assessment and status report: chapter 8
Biology
Desmognathus ochrophaeus is nocturnal. Salamanders remain hidden beneath cover objects during the day. When moisture levels are suitable, they emerge shortly after sunset and may be found foraging in the vicinity of their daytime retreats with peak surface activity shortly after dark (Bishop 1941; Holomuzki 1980).
Desmognathus ochrophaeus is a generalist feeder and eats a diverse array of terrestrial invertebrates. For the most part it seems to be largely insectivorous, taking ants, crane flies, dipteran larvae, lepidopteran larvae, homopterans, hymenoptera, spiders, mites, phalangids, millipedes, and apparently some vegetation (Bishop 1941; Petranka 1998). In Ohio, it feeds mostly on earthworms (Keen 1979), fly larvae, adult beetles, collembolans, and mites (Orr 1989). Occasionally it will prey upon Desmognathus larvae and eggs (Huheey and Brandon 1973; Forester 1983).
This species uses a sit-and-wait (ambush) mode of predation in a home range averaging 1.06 m2 in seepage banks (Orr 1989). Feeding kinematics are similar to other plethodontids, where gape formation involves raising of the upper jaw while the lower one remains fixed. After the sticky tongue pad makes contact with the prey, the salamander's head surges forward and the pad is rapidly retracted as the mouth snaps shut with considerable force (Larsen and Beneski 1988).
During the winter months, feeding is reduced and D. ochrophaeus retreats to seepage areas and underground retreats where ground water temperatures remain relatively constant throughout the winter. At this time, fat bodies have developed to their maximum. The species usually becomes active again in March, at which time yolking of the eggs is complete (Orr 1989). Hibernation typically begins in November in southern parts of the range. In Quebec, the hibernation period is presumably longer, starting earlier in autumn and ending later in spring. However, salamanders are known to leave their winter retreats any time that temperatures are favourable (Petranka 1998).
Mating and egg-laying take place both in the fall and spring in New York State, and presumably in neighbouring Canadian populations (Bishop 1941). Males search for and find females using vision and smell (Uzendoski and Verrell 1993; Evans and Forester 1996). When a male finds a female, he places his snout on her back. This is followed by a fairly elaborate courtship involving a stereotypical tail-straddle walk characteristic of all Desmognathus species (Houck et al. 1985; Mead and Verrell 2002). Eventually a spermatophore is deposited followed by forward movement of the courting pair to position the vent of the female over the spermatophore. The female picks up the sperm cap using her cloacal lip and the cap is withdrawn into the female's cloaca usually over a period of 2-3 hours (Organ 1961). Physical stimulation by the presence of the sperm cap in the female's cloaca inhibits the female's sexual responsiveness to other males (Verrell 1991). In most salamander species, the females can store viable sperm in the epitheca for months, and in some cases, years (Houck and Schwenk 1984).
Male mating capacity is limited in this species, contrary to the traditional assumption for most organisms that males are able to produce large quantities of sperm. This limitation puts constraints on a male’s number of inseminations (Verrell 1988). When given a choice, males select larger females which tend to have more eggs than smaller females, thus giving the male the opportunity to fertilize more eggs per insemination (Verrell 1989). Aggressive behaviour of males towards other males during the courtship season is common and seems to be an important method by which sex recognition occurs in all species of Desmognathus (Organ 1961).
Females are thought to seek nest sites far in advance of laying their eggs and return to the same nest site year after year (Bider and Matte 1996). In comparison to other members of the complex, D. ochrophaeus appears to have a stronger tendency to nest underground (Keen and Orr 1980). Oviposition typically occurs in mud crevices and depressions beneath logs and stumps that are embedded in mud or hillside seeps and springs. Clutch size is positively correlated with snout-vent length and varies from 11 to 14 eggs in New York (Bishop 1941), and 8 to 24 in Pennsylvania (Hall 1977), and in some case up to 40 eggs per female (Verrell 1989). Typically, the eggs are deposited in a cluster, the outermost envelope of the individual eggs being drawn out and attached to a common stalk so that the mass looks like a small bunch of grapes. The mass is attached to the lower surface of the object that serves as cover for the nest. Mature ova measure 2.5-3.0 mm in diameter and well-developed embryos are about 4 mm in diameter (Bishop 1941; Logier 1952; Keen and Orr 1980).
Males do not provide courtship feeding, nest sites, or parental care (Houck et al. 1985). Females, however, apparently remain with their eggs throughout the entire development of the embryos and through hatching. It seems that they do not leave the eggs to forage but may feed on small organisms that enter the nest cavity. The attending females are usually found in the nest coiled around the egg mass, the chin resting upon it or the head thrust into the centre of the mass (Organ 1961). Most females lose weight over the brooding season, using up an estimated 16% of their annual energy budget (Fitzpatrick 1973). The brooding female contributes to the survivorship of her eggs not only by defending them from predators, but also by eating infected eggs. This action halts the spread of fungal infestations in the clutch, increases oxygenation, reduces the yolk layering of the eggs through mechanical stimulation of the eggs, and lowers the rate of egg desiccation by reducing the exposed surface of the egg mass (Tilley 1972; Forester 1979; Forester 1984; Orr 1989). Females can specifically recognize, and will preferentially brood, their own eggs over those of a conspecific (Masters and Forester 1995).
Hatching has been found to occur in March, September, and October in New York (Bishop 1941). Newly hatched larvae average 13-18 mm in total length (Petranka 1998). They have prominent yolk reserves in the belly region, well-developed gills, and a well-developed fin on the dorsal and ventral surfaces of the tail (Organ 1961). The gills are retained for a few days to several weeks, and this is apparently determined largely by the amount of moisture present, and to some extent by temperature. Nevertheless, larvae do not have to enter water to survive. Unlike many other species of salamanders, larval development only requires wet media and may include rock faces near seepages, mossy or muddy areas that are continually moist, or very shallow surface water. During this period, larvae feed on small invertebrates. The larval period can last anywhere from 2-3 weeks upwards to 8 months (Keen and Orr 1980). When larvae transform into juveniles, they are approximately 18 mm in total length. Larvae that experience high temperature and/or high food regimes grow faster and metamorphose earlier than larvae on low-temperature and low-food regimes (Bernardo 1994; Beachy 1995).
Sexual maturity is usually attained at the end of the second year or at the beginning of the third for males when they reach a snout-vent length of at least 30 mm (Bishop 1941; Logier 1952). Females typically reach sexual maturity one year later than males at 3 or 4 years of age, or once they have reached 30-34 mm in snout-vent length (Organ 1961; Petranka 1998). While males reach sexual maturity at a smaller size, they surpass females in body size as they age. This may be because in older individuals the rate of increase in reproductive success with body size is probably greater in males than in females (Bruce 1993). Desroches and Rodrigue (2004) report average longevity at seven years, although the upper limit may reach 15 years (Orr 1989).
Adults, larvae, and eggs of this species may be taken by snakes, crayfish, small mammals and birds, and by other salamanders. The Short-tailed Shrew (Blarina brevicauda) whose burrows are occupied by a large variety of salamanders (Brodie et al. 1979) is a known predator, as are racoons, opossums and skunks. Avian predators include Hermit Thrushes (Catharus guttatus) that uncover salamanders during diurnal foraging (Bishop 1941; Forester 1978; Brodie and Brodie 1980; Hom 1988; Orr 1989; Whiteman and Wissinger 1991). Co-occurring Spring Salamanders, Gyrinophilus porphyriticus, are known to be common predators of D. ochrophaeus (Formanowicz and Brodie 1993; Uzendoski et al. 1993; Hileman and Brodie 1994).
Desmognathus ochrophaeus, like others of its genus, lacks noxious skin secretions that appear to function as an antipredator adaptation in salamanders of many other genera (Brodie 1977). Desmognathus ochrophaeus therefore have a higher potential to suffer from predation than other plethodontid salamanders. However, in some populations it appears to use mimicry of distasteful salamander species to reduce predation (Brodie and Howard 1973).
Predator-induced autotomy (self-amputation) of the tail also seems to be an effective anti-predator strategy. When seized by a predator, the twitching automized tail appears to function in directing the attention of the predator to the tail and away from the salamander. Although tail loss and its regeneration are energetically expensive, and reduce the reproductive output of some plethodontid salamanders, it does not seem to interfere with courtship and insemination success in males (Orr 1989). To make themselves less conspicuous to predators, individuals may also remain immobile when uncovered (Dodd 1990). They also avoid chemical cues from wounded conspecifics, and from predators such as snakes, which may further help them to reduce predation risk (Cupp 1994; Luttershmidt et al. 1994). When disturbed these salamanders often try to flee by running or through violent lateral contortions involving the body and tail (Bishop 1941), and when attacked may bite the predator (Formanowicz and Brodie 1993).
Plethodontid salamanders lack lungs and therefore rely on cutaneous and buccal respiration for gas exchange (Desroches and Rodrigue 2004). An important consequence is that the skin must be moist and permeable for gas exchange to occur, and this restricts plethodontids to moist microhabitats. Even in moist terrestrial habitats, plethodontids lose water when outside retreats or burrows (Feder 1983). The rate of dehydration depends on body size, relative air humidity, and ambient temperature, with dehydration being more rapid in small individuals, under conditions of lower relative humidity, and at high temperatures (Spotila 1972).
Water loss may restrict foraging and courtship on all but very wet nights, and surface activity may be abandoned during dry periods. Thus the lives of plethodontids may consist of long periods of inactivity interspersed with brief periods of activity when thermal and hydric conditions permit. Key specializations (low metabolic rate, large energy stores, profound resistance to starvation) may enable them to survive indefinite periods between unpredictable bouts of feeding (Feder 1983; Feder and Londos 1984). Desmognathus ochrophaeus is less active and ingests less prey when the air temperature is low (0º-5ºC), and it remains in subterranean refugia when the minimum daily air temperature is below 0ºC (Keen 1979).
The movements of D. ochrophaeus in Canada are not well known. Desmognathus ochrophaeus has the ability to disperse either across land or along waterways,but is not believed to typically be a long distance disperser. This species is, however, the most terrestrial of the Dusky Salamanders and actively disperses up to 75 m from open water in the summer (Bishop 1941; Organ 1961). In rock faces in North Carolina, individuals averaged 40-45 cm in movements between successive captures and appeared to have a limited range (Huheey and Brandon 1973). In Ohio, mean home range for individuals was less than 1 m2, although a minimum of 25% of individuals returned home after being displaced 30 m (Holomuzki 1982). In North Carolina, in optimal habitat, some females occurred as close as 4 cm to each other. Reproductive effort by a given female tends to occur in the same 5 m segment of stream during successive years; this likely indicated that gravid females home from nearby terrestrial habitats to a "preferred" or "previously known" stream segment during the reproductive season (Forester 1977). The extent to which adults establish and defend territories remains poorly understood.
The Yellow Spotted Salamander (Ambystoma maculatum) and the Blue-Spotted Salamander (Ambystoma laterale) are killed annually in large numbers by vehicles in eastern Canada during their relatively long-distance migrations (R. Alvo and J. Bonin, pers. obs.). For D. ochrophaeus, however, the very small home ranges that have been observed in the U.S. suggest that very few, if any, get killed on roads, and overall movement may be quite limited.
Habitat type and the presence of larger predatory species affect movement and resource use in stream salamander communities. In Quebec, Gyrinophilus porphyriticus could potentially affect the presence of D. ochrophaeus because it is considerably larger and preys upon D. ochrophaeus. Where D. fuscus is present, D. ochrophaeus is known to move away from surface water to drier, less desirable substrates (Krzysik 1979).It has been hypothesized that interspecific competition may have been a driving factor behind the evolution of body size and terrestrialism within the genus Desmognathus (Krzysik 1979).
Desmognathine populations vary in size as a function of the abundance of other salamander species in the habitat, because of competition and predation (Southerland 1986; Roudebush and Taylor 1987). This is suggested by the absence of D. ochrophaeus from the more permanent streams containing D. fuscus in Quebec (Bonin 1993), and by the results of other ecological studies on Desmognathus salamanders (Hairston 1949, 1980).
Desmognathus ochrophaeus differs relative to other Desmognathus species in its greater tolerance to water loss, which enables it to travel long distances from permanent water sources (Houck and Bellis 1972). This may alleviate hunting pressure on prey in stream habitats, and reduce intra/interspecific competition. Other key specializations, including low metabolic rate, large energy stores, and resistance to starvation, allow D. ochrophaeus to survive long periods without feeding (Feder 1983; Feder and Londos 1984).
Larvae of D. ochrophaeus are specially adapted to survive in very intermittent seepages or in areas containing only a small amount of surface moisture. This ability may enable D. ochrophaeus to escape predation and competition by larger stream salamanders that require more permanent water sources for larval development.
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