RED-SPOTTED NEWT
Notophthalmus viridescens
 
INTRODUCTION

The red-spotted newt has one of the most complicated life histories of any pond-breeding amphibian in Rhode Island because it has four, not three, life stages (egg, aquatic larva, terrestrial eft, and aquatic adult). Newts eggs are laid in the spring. In the fall, larvae undergo metamorphosis and transform into a juvenile terrestrial form referred to as an 'eft '. The terrestrial eft stage lasts for 2-7 years, then newts undergo a second metamorphoses -from eft to adult- before returning to ponds to breed. Life history strategies of this species are highly variable. In some areas, the eft stage is reproductively active, while in other areas the eft stage is absent and neotenic newts never leave breeding ponds.

Aquatic larvae and adults are typically found in ponds with relatively long hydroperiods (Paton and Egan 2001).

 
IDENTIFICATION

ADULTS

  • Aquatic adults generally have an olive-greenish dorsum and a yellow venter with fine black dots.
  • They have a flatten tail adapted for swimming.
  • Adults have lungs and lack gills.

Adult newt

EFTS

  • In Rhode Island, efts generally have a brown to brownish-orange dorsum and orange venter. At higher elevation sites, and upland areas, efts are often brilliant orange, this morph is rare in Rhode Island.
  • Efts have rough skin.

Eft

Sexual Dimorphism

  • Aquatic males- during the breeding season and late fall- can be distinguished from females by the presence of black pads (excrescences) on the digits of their hind feet and a high tail fin.
  • The vent of the male becomes more enlarged than that of the female (Bishop 1941).

male newt with excrescences
 
SIZE

AGE / SEX SVL (SNOUT VENT LENGTH) (cm)
SAMPLE SIZE

AVERAGE

RANGE

Std. Deviation

ADULT FEMALE

3.6

2.5- 4.3

0.4

18

ADULT MALE

3.7

2.5- 4.5

3.7

29

JUVENILE

2.7

1.9- 3.9 0.5

134

METAMORPH

2.1

1.2- 3.3 0.3

384


AGE / SEX
TL (TOTAL LENGTH) (cm)
SAMPLE SIZE

AVERAGE

RANGE

Std. Deviation

ADULT FEMALE

7.3

5.5- 9.4

1.1

18

ADULT MALE

7.3

4.8- 9.4

1.0

29

JUVENILE

5.2

2.9- 8.0

1.1

134

METAMORPH

4.1

2.6- 6.2

0.6

384



AGE/ SEX
MASS (g)
SAMPLE SIZE

AVERAGE

RANGE

Std. Deviation

ADULT FEMALE

1.28

0.5- 2.0

0.5

18

ADULT MALE

1.31

0.6- 2.2

0.4

29

JUVENILE

0.6

0.1-1.6

0.4

134

METAMORPH

0.3

0.1- 0.8

0.1

384







 
RELATIVE ABUNDANCE
Rhode Island
Newts are relatively abundant in rural areas of Rhode Island. Paton et al. (2000) captured 134 adults immigrating to a 0.16 ha seasonally-flooded pond in southern Rhode Island at Trustom National Wildlife Refuge. There is some evidence that they may have been extirpated from urban areas in the Providence area (Paton and Egan 2001).
Regional
Newts are common to abundant in the region (Klemens 1993; DeGraaf and Yamasaki 2001). Burne (2000) detected newts in only 8% of 78 ponds sampled near Concord, Massachusetts. The majority of the ponds in his study were characterized by longer hydroperiods and only 9 of these ponds were permanent ponds.
 
DISTRIBUTION
Rhode Island
Widespread in the state, although their populations are somewhat localized (Klemens 1993). Paton and Egan (2001) detected them at 17.6 % of 119 randomly-selected ponds west of Narragansett Bay, Rhode Island; 30 of the ponds in their study were permanent ponds.
Regional
They are found throughout New England (DeGraaf and Yamasaki 2001) and are one of the more common species. Klemens (1993) found that they were quite localized along the coast, but more widespread in upland areas.
General
Red-spotted newts are the second most widely distributed salamanders in North America (Petranka 1998a). They range from southern Florida west to Texas and north to southern Canada.
 
HABITAT NON BREEDING

Efts
The completely terrestrial efts are habitat generalists. They are usually found in deciduous and coniferous woodlands, but also use pastures and meadows (Klemens 1993). Healy (1974a, 1975) tracked postlarval efts from breeding ponds to upland habitats, and found they require approximately 1 year to migrate to permanent forest residences. While in the forested habitat, efts live under leaf litter and other debris during dry periods and are active during wet periods when temperatures exceed 12° C (Petranka 1998a). They move about the forest floor in search of food and are frequently observed in groups where food sources are most abundant, for example, around a decaying log or mushroom (Petranka 1998a). During the cold months of winter, they hibernate on land, burrowing under logs and other debris (Degraaf and Yamasaki 2001).

Gibbs (1998a) found that in Connecticut newts avoided edges, thus their movements were affected by forest borders and streambeds. However in Maine, DeMaynadier and Hunter (1998) found newts were less sensitive than other species of amphibians to forest edges and suggested they are less vulnerable to current timber management practices.

Adults
Adult newts remain aquatic all year, unless the pond in which they live dries up (Petranka 1998a). When ponds do dry up, newts may remain in the basin of the pond, in the upland close to the pond, or move to a neighboring pond (Ptingsten and Downs 1989). By the same token, if the pond is shallow and freezes solid in the winter, newts leave the pond for the upland or a deeper pond (Gill 1978a). Morin (1983) found that in South Carolina newts, avoided desiccation by burrowing under leaf litter and other debris. Newts return to their home pond once the pond refills or unfreezes (Ptingsten and Downs 1989). During fieldwork at Trustom Pond, NWR in Rhode Island (Paton et al. 2000), we had aquatic adults entering ponds in the spring and emigrating from ponds in the fall. These individuals were olive-green, but the tail fin was not as high as some aquatic adults; they presumably wintered in adjacent upland areas. Gill (1978a; 1978b) reported similar behavior in his pond in Virginia; he found that adults migrated to the breeding pond in early spring (March-April) and emigrated during the fall (August-September).

Aquatic adults are active throughout the winter. They have been seen swimming under the ice in ponds and streams and have been observed during the winter in groups of 20-40 (Morgan and Grierson 1932). As mentioned above, in some areas larval never undergo metamorphosis to an eft stage. Rather they are neotenic and spend their entire life in ponds (Lazell 1976). To our knowledge, no neotenic populations exist in Rhode Island.

 
HABITAT BREEDING
Adults newts tend to breed in permanent or semi-permanent water bodies, including lakes, large ponds, reservoirs, ditches, swamps, marshes, and slow moving streams or canals (Bishop 1941; Gates and Thompson 1982; Petranka 1998a). In southern New England, they appear to prefer shallow, still water, with an open canopy and dense aquatic vegetation (e.g., emergent or submergent macrophytes) (Klemens 1993; Petranka 19998a). It has been our experience that they are more likely to be found in sites with high densities and diversity of aquatic invertebrates (C. Heinz, pers. obs.).
   
 
HYDROLOGY
 
MOVEMENT CHRONOLOGY

In Rhode Island, adults start moving back to temporary ponds during the first week of March, with most adults at ponds by the end of March, although some immigrate to ponds as late as mid-April (Paton and Crouch In press). According to Ptingsten and Downs (1989), newts in transition from eft to adult typically migrate back to breeding ponds during August and September (a few return in the spring).

Young red-spotted newts (efts) are among the last metamorphs to emerge from ponds in Rhode Island, with the first leaving in mid-September and some leaving as late as mid- to late November.

 

 
REPRODUCTION

In Rhode Island newts breed during late spring. In contrast, adults in many northern populations court in both the spring and fall-though females oviposit only in the spring (Gage 1891; Bishop 1941); whereas, in many southern population, adults breed from late autumn through early spring (Petranka 1998a). Courtship commences with males searching the pond looking for sexually active females. If a female is encountered and responds when the male first approaches, he performs a brief 'hula' dance or a lateral display involving body and tail undulations (Petranka 1998a). The interested female then nudges the males- providing the signal for the intent male to deposit one or more spermatophores. The female picks up the spermatophore in her expanded vent where it remains until she deposits her eggs (Arnold 1977; Humphries 1955; Verrell 1982a, 1990a).

If this initial courtship strategy fails, as it does more than 50 % of the time in laboratory experiments, the male employs a more aggressive approach (Petranka 1998a). The male will use his strong back legs to engage the female in amplexus where they can remain for several hours. During this time the male uses several tactics to entice the female including waving his tail back and forth attempting to waft his scent towards the female's nostrils (Petranka 1998a). After some time, the male releases his hold and deposits one or more spermatophores which hopefully the female will collect (Petranka 1998a). Gill (1978b) reported that in some regions females can breed as many as 20-30 times.

Hurlbert (1970b) found that efts returning to the ponds as adults for the first time breed later than older adults.

 
EGG MASS
Females oviposit eggs singly under leaves (both dead and alive), stems of aquatic plants or on other debris where they are often covered by bits of vegetation (Petranka 1998a). Newly deposited eggs are about 1.5 mm (0.06 inches) in diameter, are light to dark brown in color, and are surrounded by three elliptical envelopes (Petranka 1998a). Females deposit 6-10 eggs per day (Ptingsten and Downs 1989) and scattered them widely through out the aquatic habitat. 80-450 eggs are deposited annually (Albert and Albert-Knoop 1999); thus, the process may take several weeks to complete (Petranka 1998a). The eggs, as well as the larvae, the eft, and the adult, are toxic (Ptingsten and Downs 1989).
 
LARVAE
Hatching is temperature dependent and usually takes 3-5 weeks. (Ptingsten and Downs 1989; Petranka 1998a). Larvae are approximately 6 mm in length and are light green in color (Ptingsten and Downs 1989). Newt larvae have a black line extending through their eye; a characteristic which aids in separating them from the larvae of spotted salamanders (Ambystoma maculatum).

Red-spotted newt larva
 
METAMORPHS
As discussed in previous sections, the newt metamorph is referred to as a red eft or simply an eft. We do not have red efts in southern Rhode Island, but efts which have brown dorsums and orangish bellies. The eft is terrestrial and will not return to the pond to breed for 2-7 years. Not all populations of newts produce the eft - a phenomenon that is still a mystery (Albert and Albert-Knoop 1999). Newts that skip the eft stage are referred to as neotenes. These individuals do not leave the pond. They mature to adults in 2 years, growing much faster than their terrestrial counterparts because they are able to feed throughout the year; efts generally forage only during the warmer months.

 
JUVENILES
Estimates of the length of the juvenile stage terrestrial 'eft' are highly variable. Bishop (1941) reported that efts became sexually mature after 2-3 years and re-entered water then. However, Healy (1974) reported that efts in interior sites in Massachusetts remained on land for 3-7 years before immigrating back to aquatic habitats. In either case, once the transformation is complete adults reproduce for the first time the following spring (Ptingsten and Downs 1989).
 
FOOD
Adults
Adults prey on insects (their preferred prey), leeches, ostracods, copepods, snails, finger clams, beetle larva, mosquitoes, worms, mosquitoes, water mites, spiders, tiny mollusks, crustaceans, young amphibians and anuran/caudata eggs (Conant and Collins 1991; Petranka 1998a),
Larvae
Larval mainly feed on invertebrates (Petranka 1998a). They also will ingest molted skin (DeGraaf and Yamasaki 2001). One beneficial characteristic of newts is that they feed on midge and mosquito larvae, thus reducing the numbers of these human pests (Albert and Albert-Knoop 1999).

Efts
Efts consume diet of worms, grubs and small insects. In wet years efts forage more and thus grow faster (Ptingsten and Downs 1989).

 
PREDATION
Adults
Adults and efts have few predators as their skin is toxic. Brightly colored adults tend to be more toxic than brownish efts, which is an example of batesian mimicry (Petranka 1998a). Gill (1978c) reported that adult newts in some area are severely attacked by amphibian blood leeches; he found that the newts will exit the ponds temporality during the summer to rid themselves of the leeches.
Larvae
 
CONSERVATION CONCERNS

According to Petranka (1998a) newts were one of the few species whose population may have increased as a result of European colonization. Newts thrive in heavily vegetated farm ponds, which apparently provides cover from predatory fish. Farm ponds increased dramatically with increased colonization; therefore, presumably newt populations increased as well. However, as southern New England has reforested with the abandonment of extensive agricultural fields, newt habitat has seemingly declined.

In Maine, where large areas of forest are clear-cutted, newts appear to be less sensitive than other amphibian species to forest fragmentation (DeMaynadier and Hunter 1998). However, our ongoing research suggests that they may be extirpated from urban areas in the state (Paton and Egan 2001). Presumably, habitat fragmentation and roads have a negative impact on these species, as the eft stage is so critical to maintaining metapopulations (Gill 1978). These anthropogenic habitat changes may provide significant dispersal barriers that prevent dispersal among breeding ponds and to eventual extirpation from isolated breeding ponds. Klemens (1993) felt that newt populations in eastern Connecticut were threatened by increased suburbanization of the region.

In another study, Robinson (1993) found newts to be less stressed by acid rain than other amphibians, apparently because they can regulate their sodium balance.

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