Siren intermedia

Geographic Range

The lesser siren is found in freshwaters of the eastern United States and Mexico, In the U.S. it is reported from 18 states. It is found on the North American coastal plain from Virginia to Central Florida, around to eastern Texas, and then across the border along the Gulf coast of Mexico south to Veracruz. It ranges in to the interior in the Mississippi River drainage, and around southern Lake Michigan. Siren intermedia has patchy population distributions and has likely been extirpated from its northernmost ranges.

There are currently three subspecies of lesser siren recognized, although it is now being considered two by some. The eastern lesser siren ( Siren intermedia intermedia ) is found from central Alabama to southeast Virginia, within the coastal plain. The western lesser siren ( Siren intermedia nettingi ) is found from Alabama to Texas and up the Mississippi River valley as far north as Michigan. The third subspecies is the Rio Grande siren ( Siren intermedia texana ). This subspecies is found in the lower Rio Grande valley and adjoining portions of Mexico. However, recent studies have suggested that this subspecies is not different from S. i. nettingi and they are included as S. i. nettingi by some sources.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Lesser sirens prefer to inhabit calm, slow-moving backwaters and wetland swamps that are shallow and warm. They are tolerant of turbid water and prefer abundant vegetation and organic debris. They can be found in a wide range of temporary and permanent habitats, including farm ponds, ditches, canals, sluggish streams, floodplain pools, and seasonal ponds. These habitats do not need to be permanent as the lesser siren can aestivate in burrows in the mud if their habitat dries up.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• riparian riparian

Physical Description

Lesser sirens are permanently aquatic, paedomorphic (retains larval features as an adult), perennibranchiate (retains gills throughout life) salamanders. They have an elongated body and are sometimes mistaken for eels. Lesser sirens have reduced forelimbs and lack not only hindlimbs, but a pelvic girdle as well. Lesser sirens have 31-38 costal grooves and grow to 18-69 cm total length.

Lesser sirens range in color from grey to brown to nearly black, with a lighter belly. Individuals with lighter coloration often have dark specks scattered on the dorsal.

Hatchling lesser sirens have bold longitudinal stripes with yellow or red bands on the head. They also have a broad dark band on each side of the body with a lighter band running through the middle. These markings disappear as the larvae grow into adults.

The lateral line system of lesser sirens is unique for salamanders in that it is retained throughout their entire life. Most salamanders only have a lateral line system when they are juveniles. The neuromasts themselves are also different in that they are arranged in pit fields instead of into pit lines. When aestivating these neuromasts are either covered by a mucus cocoon secreted by the siren or they are protected by skin cells that grow to cover them.

Male lesser sirens are larger than females by about 14% and also have enlarged masseter muscle, which causes the head to appear larger than those of females. This likely serves as an advantage in territorial or mating contests.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Development

One study found that lesser siren young tend to hatch synchronously and averaged 11.5 mm in length at time of hatching. They were also found to be more developed than hatchlings from a study done in Arkansas. Hatchlings appear to grow 2-3 times faster than older sirens. Coloration is present at the time of hatching, including dark stripes down either side of the back. The forelimbs are fully formed and most digits have claws by day 55. Reduction of the dorsal fin begins about 2 months after hatching and is finished by the age of 9 months.

• Development - Life Cycle
• neotenic/paedomorphic
• metamorphosis metamorphosis

Reproduction

Only one study has been successful at breeding Siren intermedia in captive conditions (Reinhard, Voitel, and Kupfer, 2013). Male Siren intermedia were observed building and aggressively defending nest sites. Courtship consisted of a pair moving in circles within the nest and coiling around each other. The male was observed rubbing its head against the flank and cloaca of the female. The female deposited her eggs by turning onto her back and positioning her cloaca near the top of the nesting cavity. The male performed the same actions but remained for longer than the female, then jerked abruptly, and turned back over. The circling movements were then resumed. This behavior was repeated multiple times, with the male behaving more aggressively later in courtship, while the female attempted to leave the nest site.

This one study supports the assumption that Siren intermedia have complex mating behaviors, external fertilization, and parental care. However, one inconsistency is that females have been found associated with nests in other studies (Godley, 1983).

• Mating System
• monogamous monogamous

Lesser siren mating seasons seem to vary due to location, with southern populations likely breeding earlier than northern populations. Some report mating season to occur in spring, others report it to be during winter, with a range from November to May.

Eggs of Siren intermedia are laid in debris-covered cavities in the water. Only one study has been successful at breeding Siren intermedia in captive conditions (Reinhard, Voitel, and Kupfer, 2013). All other observations come from collections of nests in natural settings.

Biting has been reported in Siren intermedia , and seems to occur most often on females during the breeding season. However, it has been shown that although males seem to be more aggressive and bites occur with increased frequency during the mating season, they also occur at lower frequencies throughout the year and on both sexes as well. This suggests that biting is not restricted to courtship alone.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

In the one study that managed to successfully breed lesser sirens, the male remained with the nest and the female left after oviposition (Reinhard, Voitel, and Kupfer, 2013). The male responded aggressively to any disturbance and did not feed during the time spent guarding the nest. The male was also observed moving and aerating the egg mass, as well as cleaning the nest. Development of the larvae took around 35 days and the male continued to guard the larvae for up to 1 week after hatching. The male also willingly returned to the nest after disturbance, even with the option of several other hides to choose from. The female did not stay with the nest and was aggressively chased from it after mating occured. However, other studies have found females associated with nests (Godley, 1983).

• Parental Investment
• male parental care male parental care
• pre-hatching/birth
  • protecting
    • male
• pre-independence
  • protecting
    • male

Lifespan/Longevity

The lifespan of Siren intermedia is currently unknown.

Behavior

Lesser sirens are nocturnal benthic foragers, searching for food around plants and along the bottom. They are solitary animals and only aggregate when cover availability is limited.

Lesser sirens are capable of aestivation, allowing them to survive drought periods. The lesser siren can aestivate for a period of several weeks up to more than one year. The lesser siren burrows into the mud and secretes a mucous cocoon to help slow water loss. They also reduce their metabolic rate during aestivation. Lesser sirens also increase the osmotic concentration of their bodily fluids and use metabolic water formation to stay hydrated. The gills become reduced and sirens depend on fat stores to survive the dry period.

Smaller sirens have higher metabolic rates and less stored fat compared to larger individuals and therefore do not survive drying as long as larger individuals. This susceptibility of smaller individuals to not survive starvation may be a limiting factor on the westward range of lesser sirens.

Lesser sirens become active within one day of the return of water, however they do not reach their pre-aestivation metabolic rates until they begin feeding. The lesser siren can regain weight lost after 16 weeks of aestivation within 8-11 weeks.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• aestivation
• solitary solitary

Home Range

Lesser sirens in general seem to have small home ranges, with males and larger individuals having larger home ranges than females and smaller individuals. The average home range size found in one study was 95 square meters. There was also considerable overlap occurring between individual home ranges.

Communication and Perception

Lesser sirens produce sounds to communicate with other sirens, which consists of clicks and yelps. Clicks are produced by lesser sirens while they are in their burrow and shortly before leaving it. This appears to be a method of claiming territory as individuals will click more often when close to each other and a resident will click more often when an intruder is added to its aquarium. Yelping sounds appear to be associated with distress as lesser sirens have been observed yelping when being butted and bitten by other sirens.

• Communication Channels
• acoustic acoustic

• Perception Channels
• acoustic acoustic
• chemical chemical

Food Habits

Lesser sirens appear to use chemical cues to find food, owing to their reduced eyes and their preference for habitats with heavy vegetation and murky water. The diet of Siren intermedia is primarily carnivorous. They feed on a variety of small aquatic organisms as well as amphibian larvae (including that of their own species), and adult salamanders. Siren intermedia are known to also prey upon the eggs of their own species.

Direct observation of herbivory has been recorded for captive members of the siren family ( Siren lacertina and Pseudobranchus axanthus ) and indirect evidence exists for herbivory in lesser sirens. Hill, Mendelson III, and Stabile (2015) suggest that sirens be considered at least facultative herbivores due to these observations as well as other evidence, including that their intestines and gut microbes are comparable to some herbivorous fishes, and that they have been observed ingesting mud, which may suggest detritivory. However, most others suggest that plant matter is consumed incidentally during capture of animal prey.

• Primary Diet
• carnivore carnivore
  • eats eggs
  • insectivore insectivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • vermivore

• Animal Foods
• amphibians
• eggs
• insects
• mollusks

• Plant Foods
• algae

• Other Foods
• detritus detritus

Predation

Known predators are not well reported but almost certainly would consist of snakes, fishes, alligators, and wading birds. Nocturnal activity of lesser sirens is likely an anti-predator defense used to reduce risk of predation.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Lesser sirens are highly productive with great fecundity and rapid growth, reaching sexual maturity in one year. They occupy several ecological positions. They are an early colonizer as well as a dominant species in several successional stages, which makes them unique compared to most other vertebrates. Lesser sirens can also reach very high densities. The only aquatic salamander with higher estimated densities is Eurycea nana (San Marcos Salamander). They also have a larger standing crop size than any other salamander. Their primacy in aquatic habitats is attributes to both their large size and their high numbers. Most vertebrates tend to have one or the other, but not both of these traits. Lesser sirens are able to quickly colonize and become dominant secondary consumers in new ponds. One study found lesser sirens to be keystone predators in ponds in North Carolina by acting as generalist predators on amphibians, reducing the overall densities in ponds; however another study found that the same was not true of similar ponds in South Carolina.

The ability of lesser sirens to aestivate and survive the drying out of ponds enhances their ability to dominate these environments. The ability to be both early colonizers and dominant consumers in later stages is likely only possible for species that are adapted to transitional communities.

• Ecosystem Impact
• keystone species keystone species

Economic Importance for Humans: Positive

Lesser sirens are seen in the pet trade on rare occasions.

• Positive Impacts
• pet trade pet trade

Economic Importance for Humans: Negative

There appear to be no known adverse effects of Siren intermedia on humans.

Conservation Status

The IUCN Red List classifies the Lesser Siren as being of Least Concern due to its wide distribution and the fact that populations are unlikely to be declining at a fast enough rate to warrant a higher threatened status. It is also assumed to have a large population, although more research is needed to determine population trends and potential threats. The Lesser Siren is common in much of its U.S. range, although more verification is needed for some of its Mexican populations as there have been few reports in some areas.

However, local populations can be impacted by loss of wetland habitats and habitat alterations. Flood control measures may reduce potential for dispersal.

The Lesser Siren occurs in a number of protected areas in the United States and is listed under the special protection category in Mexico.

Other Comments

Siren intermedia was first described by LeConte, and later verified by Noble and Marshall.

Additional Links

AmphibiaWeb

Encyclopedia of Life

Contributors

Stephanie Sickler (author), Missouri State University, Brian Greene (editor), Missouri State University.

References

Altig, R. 1967. Food of Siren intermedia nettingi in a Spring-fed Swamp in Southern Illinois. The American Midland Naturalist , 77/1: 239-241.

AmphibiaWeb, 2016. "Siren intermedia" (On-line). AmphibiaWeb. Accessed December 02, 2016 at http://amphibiaweb.org .

Fauth, J. 1999. Identifying Potential Keystone Species from Field Data-an Example from Temporary Ponds. Ecology Letters , 2: 36-43.

Fauth, J., W. Resetarits, W. Resetarits Jr.. 1999. Biting in the Salamander Siren intermedia intermedia: Courtship Component or Agonsitic Behavior?. Journal of Herpetology , 33/3: 493-496.

Frese, P., A. Mathis, R. Wilkinson. 2003. Population Characteristics, Growth, and Spatial Activity of Siren intermedia in an Intensively Managed Wetland. The Southwestern Naturalist , 48/4: 534-542.

Gehlbach, F., R. Gordon, J. Jordan. 1973. Aestivation of the Salamander, Siren intermedia. The American Midland Naturalist , 89/2: 455-463.

Gehlbach, F., S. Kennedy. 1978. Population Ecology of a Highly Productive Aquatic Salamander (Siren intermedia). The Southwestern Naturalist , 23/3: 423-429.

Godley, J. 1983. Observations on the Courtship, Nests, and Young of Siren intermedia in Southern Florida. The American Midland Naturalist , 110/1: 215-219.

Hampton, P. 2009. Ecology of the Lesser Siren, Siren intermedia, in an Isolated Eastern Texas Pond. Journal of Herpetology , 43-4: 704-709.

Hill, R., J. Mendelson III, J. Stabile. 2015. Direct Observation and Review of Herbivory in Sirenidae (Amphibia: Caudata). Notes of the Southeastern Naturalist , 14/1: N5-N9.

Martin, B., D. Goodding, N. Ford, J. Placyk Jr.. 2013. Sensory Mediation of foraging Behavior in the Western Lesser Siren (Siren intermedia nettingi). Journal of Herpetology , 47/1: 75-77.

McAllister, C., S. Goldberg, S. Trauth, C. Bursey, H. Holshuh, B. Cochran. 1994. Helminths of the Western Lesser Siren, Siren intermedia nettingi (Caudata: Sirenidae), from Arkansas. The Helminthological Society of Washington , 61/2: 234-238.

Noble, G., B. Marshall. 1932. The Validity of Siren intermedia LeConte, with Observations on its Life History. American Museum Novitates , 532: 1-17.

Parra-Olea, G., D. Wake, G. Hammerson. 2008. "Siren intermedia" (On-line). The IUCN Red List of Threatened Species. Accessed July 28, 2016 at http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T59491A11936674.en .

Petranka, J. 1998. Salamanders of the United States and Canada . Washington and London: Smithsonian Institution Press.

Raymond, L. 1991. Seasonal Activity of Siren intermedia in Northwestern Louisiana (Amphibia: Sirenidae). The Southwestern Naturalist , 36/1: 144-147.

Reinhard, S., S. Voitel, A. Kupfer. 2013. External Fertilisation and Parental Care in the Paedomorphic Salamander Siren intermedia Barnes, 1826 (Urodela: Sirenidae). Zoologischer Anzeiger , 253: 1-5.

Reno, H., H. Middleton III. 1973. Lateral Line System of Siren intermedia Le Conte (Amphibia: Sirenidae), During Aquatic Activity and Aestivation. Acta Zoologica , 54: 21-29.

Sever, D., L. Rania, J. Krenz. 1996. Reproduction of the Salamander Siren intermedia Le Conte with Special Reference to Oviducal Anatomy and Mode of Fertilization. Journal of Morphology , 227: 335-348.

Snodgrass, J., J. Ackerman, A. Bryan Jr., J. Burger. 1999. Influence of Hydroperiod, Isolation, and Heterospecifics on the Distribution of Aquatic Salamanders (Siren and Amphiuma) Among Depression Wetlands. Copeia , 1999/1: 107-113.

Sugg, D., A. Karlin, C. Preston, D. Heath. 1988. Morphological Variation in the Salamander, Siren intermedia nettingi. Journal of Herpetology , 22/2: 243-247.

Sullivan, A., P. Frese, A. Mathis. 2000. Does the aquatic salamander, Siren intermedia, respond to chemical cues from prey?. Journal of Herpetology , 34/4: 607-611.