Notophthalmus viridescens

Red-spotted Eastern Newt

Eastern Newt 

Notophthalmus viridescens

Notophthalmus viridescens
Notophthalmus viridescens

Subspecies: Red-Spotted Newt N.v. viridescens

Three Life Forms of the Eastern Newt

Red-Spotted Eastern newts have three different life stages.  The Larval Aquatic Stage, the “Red Eft” , and the lunged aquatic adult.

Larval Aquatic Stage

The larval Eastern Newt emerge clusters of eggs attached to underwater vegetation.  At birth, they 8mm in size.  The aquatic larval stage lasts for around 50 days (late summer), after which they lose their gills and metamophosize into the Red Eft.

Red Eft:

Red Efts are the juvenile forms of the Red-spotted Eastern Newt.   The largest changes are the absent gills, and the brilliant orange body color with 10-12 black outlined red spots.  Numerous field guides write that the Red Eft Stage concludes after 1-3 years, but scientific literature describes the Red Eft stage lasting 3-7 years.  Some current studies evaluating the differences between subspecies note that other Subspecies can skip the Red Eft stage and develop directly into aquatic gilled adults.  When metamorphosis is absent, it is termed paedomorphosis.

Adult Eastern Newt:

Adult (6.5-14cm)return to live in aquatic environments where they breed and carry out the rest of their life.   Their  back is olive-green to dark brown, and their belly yellowish.  The adults are also covered in black spots and have a paddle-shaped tail with a distinct keel . Adults never turn back to the Eft Stage.

Breeding:

Eastern Newts breed at the end of winter and into early spring.  Females deposit 200-400 eggs on submerged vegetation.  The young hatch in 3-8 weeks.

Habitat

The larval and adult forms live in aquatic habitats (steams, ponds, lakes, backwaters).  The Red Eft form lives in terrestrial woodlands typical of the Appalachian Mountains.

Behavior

The Eastern Newt is active during the day from March to October.

Range

Nova Scotia west to the Great lakes; Southern boundary in Northwest South Carolina west to Alabama  (Appalachian Mountain).

Food

Adults consume larval stage arthropods (insects, crustaceans), molluscs, salamander and frog eggs.

Other Subspecies:

Broken-striped, Central, Peninsula

Newt Family:

The Newt family lacks the obvious coastal grooves (side groves)typical of salamanders.

Kidney Collecting Ducts May Serve as Secondary Sexual Structures

The Eastern Newt pelvic kidney collecting ducts may act as secondary sexual structures, although their role in reproduction has not been confirmed (Siegel et al. 2012).  Increased collecting duct epithelial cell activity is associated with an increased size/height of the epithelial cells when examined using histological methods.   Researchers evaluating a relationship between these changes and reproductive activity, found that there is a direct correlation between the increased height of the collecting duct epithelium in males during the reproductive activity, and the increased epithelial height of other secondary sexual structures (genial glands, dorsal glands of the cloaca, and tail).   The increased size of the collecting duct epithelium corresponds to increased secretions during reproductive activity.

Eastern Newt Subspecies are a Model for Divergent Evolution without Speciation

Eastern Newts exhibit polyphenism in their metamorphosis to different life stages.  They can change into a terrestrial Eft and then to an aquatic lunged adult.  They can change directly into a lunged aquatic adult, or they can become a gilled aquatic adult without metamorphosis (paedomorphosis).

The Red-Spotted subspecies has a shorter larval stage and changes into the terrestrial eft stage sooner, and more often than the Broken-striped subspecies who may change directly into the adult stage (skipping the eft stage).  These differences in phenotype persist even when individuals are raised in captivity in the same artificial environment (a pond drying over 3 months, or a pond that does not dry out at all) (Takahashi et al. 2011). Thus, the divergence has evolved due to natural selection over many generations due to the polyphenism that preexisted in the species, and the differences persist even when one subspecies is exposed to the environmental pressures of the other subspecies.  These phenotypic differences between the subspecies correspond to the habitat that they live in.  The Red-spotted subspecies has diverged from the Broken-striped subspecies because of the suitable terrestrial habitat in the Red-Spotted subspecies range, and the suitable wetlands in the Broken-striped range.  This divergent evolution has not resulted in speciation (creation of separate species) because there is still gene flow between the subspecies, meaning that they still mate with each other along their overlapping ranges.

The Red-spotted newt is a model of how divergent evolution can still occur due to exposure to different environmental pressures, despite breeding between subspecies (gene flow).  Thus, divergent evolution can begin well before complete reproductive isolation.   However, speciation (evolution to the point where they become separate species that no longer interbreed) would require reproductive isolation.

 

References:

1. Dustin S. Siegel; Christopher M. Murray; Emily R. Wilson; Emily R. Puleo; Keith A. True; Robert D. Aldridge. Sexual Kidneys in the Red-spotted Newt (Notophthalmus viridescens) Journal of Herpetology (0022-1511) 2012-03-01. Vol.46,Iss.1;p.136-144  Source: JSTOR

2. Mizuki K. Takahashi; Yukiko Y. Takahashi; Matthew J. Parris. Rapid Change in Life-Cycle Polyphenism across a Subspecies Boundary of the Eastern Newt, Notophthalmus viridescens
Journal of Herpetology
(0022-1511) 2011-09-01. Vol.45,Iss.3;p.379-384

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