Dwarf Siren

An elongate, permanently-gilled, aquatic salamander. Like sirens (which are also in the Family Sirenidae), dwarf sirens lack hind limbs. Other features of sirens and dwarf sirens are lack of eyelids and presence of a horny beak on the upper and lower jaws (Martof 1974). Pseudobranchus have a single gill slit (Martof 1972 1974). There are only three toes on the front limbs and the bushy, external gills sometimes hide the relatively reduced front limbs. Adults reach 10-22 cm total length, and females are slightly larger than males (Martof 1972; Petranka 1998). The tail is about 40% of the total length (Martof 1972). Juveniles differ from the adults in the presence of a dorsal fin which extends from the base of the head to the tail tip (Martof 1972; Petranka 1998).Adult P. striatus have a brownish to black dorsal ground color with parallel yellow or tan stripes running along the back and sides from head to tail tip. There is geographic color variation and two or three subspecies are recognized. Pseudobranchus s. striatus, the broad-striped dwarf siren, has a dark brown to blackish middorsal stripe with a narrow yellow line running down the middle and broader yellow lateral stripes. The venter has a lighter ground color than the back and is heavily mottled with yelow. This subspecies is also considered somewhat stocky in build. Pseudobranchus s. spheniscus, the slender dwarf siren, is smaller and more slim-bodied. This subspecies has a narrow, wedge-shaped head and two (rarely three) narrow tan or yellow lateral stripes. Pseudobranchus s. lustricolus, the Gulf Hammock dwarf siren, is not recognized by all authors; the distribution and affinities of this form merit futher investigation (Moler and Kezer 1993; Petranka 1998). A stocky subspecies, individuals have a dark, broad middorsal stripe containing three narrow yellow stripes. There are two light lateral stripes as well, the upper orangish brown and the lower silvery white. Descriptions from Petranka (1998).Prior to 1993, a single species of dwarf siren was recognized (e.g. Conant and Collins 1991). Moler and Kezer (1993) studied the chromosomes of Pseudobranchus striatus and split that taxon into two separate species with different chromosome complements: P. striatus (n = 24) and P. axanthus (n = 32). The two species are found in sympatry in northern and mid-peninsular Florida, although they seem to prefer different micro-habitats. Pseudobranchus axanthus occur in open ponds and marshes, and P. striatus in cypress swamps. In addition, P. axanthus are commonly found in floating water hyacinth and P. striatus are never found in water hyacinth, preferring a similar floating plant called frog's bit (Limnobium spongia) (Moler and Kezer 1993).

This species is distributed through Atlantic Coast Plain regions of southern South Carolina, Georgia, and northern to mid-peninsular Florida, excluding the westernmost portion of the Florida panhandle (Martof 1972; Petranka 1998). The preferred habitats are cypress ponds in acid pine flatwoods and other permanent and semipermanent bodies of water (Moler and Kezer 1993; Petranka 1998).

Most of what is known about the biology of dwarf sirens comes from studies on P. axanthus. These two species are closely related and are likely to be similar in most features (Petranka 1998). This account reports what is known for P. axanthus, but clearly more research should focus on the life history and biology of P. striatus. Courtship and mating have not been observed (Petranka 1998). Fertilization is presumed to be external (Martof 1972 1974; Sever et al. 1996). Eggs are deposited singly, and the oviposition period lasts from early November through March (Petranka 1998).Often locally abundant. Diet consists of aquatic invertebrates, including earthworms, amphipods, chironomids, and ostracods. When semi-permanent pools dry, dwarf sirens aestivate in burrows10-30 cm underground. Individuals are likely to be preyed upon by birds, turtles, alligators, and aquatic snakes. When disturbed, dwarf sirens sometimes emit a high-pitched yelp. See Petranka (1998) and references therein.

There is no evidence that populations of this species are declining. However, the habitat of dwarf sirens is threatened, and therefore populations are at risk, by development and agriculture which lead to thedestruction of wetlands (Petranka 1998). The Gulf Hammock dwarf siren has been reliably reported from only three localities in lowland areas in the Gulf Hammock region of Florida. It has apparently not been collected since the original description (based on 11 individuals) in 1951. The restricted range and specialized, aquatic habitat suggest that this form deserves conservation attention, however more data are needed to determine the status of these populations and the relationship of this form to other dwarf sirens (Moler 1992a; 1992b).

Dwarf sirens are sometimes seen in the pet trade.

The northern dwarf siren (Pseudobranchus striatus) is a perennibranch salamander lacking hind legs. Found in the Southeastern United States, it one of two currently recognized species of dwarf sirens. Three subspecies are currently recognized; P. s. striatus, the broad-striped dwarf siren, P. s. lustricolus, the Gulf Hammock dwarf siren, and P. s. spheniscus, the slender dwarf siren.