User:Eylul.horozoglu/Lesser siren

Description
In salamanders, sexual size dimorphism is usually female-biased, but in Siren intermedia, it’s the opposite. Males are the larger sex, and they also have significantly larger heads and enlarged masseter muscles than females.

Habitat
Sirens are likely to be found in ponds near other intermittent wetlands. They usually inhabit swamps and ponds, and can survive in dry ponds for up to two years by a process called “aestivating”. Sirens are considered poor overland dispersers because they don’t leave the water, so their geographical distribution is largely determined by pond connectivity and biotic interactions.

Lesser sirens are aquatic salamanders, but their ability to withstand factors like dehydration allows them to have good survival skills in their ephemeral habitats. Sirens are able to osmoregulate and produce a mucoid cocoon during aestivation, which greatly reduces dehydration and electrolyte stress.

Geographic Distribution
Around the world, Siren intermedia are widely distributed across the southeastern United States. Lesser sirens only occur in permanent wetlands, whereas other salamander and frog species can occupy a range of dry and wetlands. Lesser sirens are top predators in permanent wetlands. They can quickly colonize and become dominant consumers in new ponds such as those constructed by beavers. Their ability to aestivate and burrow in soft sediments and live in dense aquatic vegetation in shallow waters facilitates their dominance. In addition, the species’ high productivity, high fecundity, and rapid growth to early sexual maturity allows it reach a high density quickly and easily, and thus establish dominance in the habitat.

Diet
Lesser sirens are filter feeders. They sift through pond bottoms and aquatic vegetation for prey items. They have heavily keratinized beaks and vomerine dental arrays that can inflict substantial wounds. The diet of the lesser siren includes at least 10 different taxa, which includes tadpoles and snails as the majority. They also eat several insects and their larvae, crayfish, mollusks, amphibians, siren eggs, and algae, although the plant material may be an incidental result of their gape-and-suck feeding style.

Life-span
Sirens are most active in the fall and spring seasons, when water temperatures are close to 15°C and there is no danger of drought.

During the summer months, the ponds and other habitats that the lesser siren live in go through periods of drought, which leads to low water levels and possibly dried-up ponds. The lesser siren’s strategy to withstand the rigors of these dry seasons is something called “aestivation”, or summer dormancy, which can last up to 35 weeks, depending on the severity of the drought. During the sixteen-week period from July to October, aquatic lesser sirens increase the osmotic concentration of their body fluids, and slow down bodily functions.

They do this by burrowing themselves into the bottom of its drying pond in tubelike channels about the length and width of their bodies. For the rest of the aestivating process, they then secrete a mucous cocoon. Oxygen consumption and heart rate drop significantly. The gills slowly atrophy and the body shrinks, as fat is metabolized at one-fifth the normal rate. As expected, large individuals store more fat and consume less oxygen per unit weight than small ones, and thus can survive much longer periods of aestivation. Dehydration, inability to store sufficient fat and greater metabolic demand reduce the chance of survival of small sirens during aestivation.

As the drought season comes to an end, lesser sirens become active within a day, and slowly regain the lost weight over the next 8-11 weeks.

Mate Choice
From November to January, males occupy a shelter as a nest site, and actively equip it with java moss from the surrounding nest site, plucking plant material and dragging it back to the nest site. They then defend their territory aggressively against others through biting.

Courting
Courtship includes several repeating behavioral patterns. Once the female approaches the nest site, the male and female start moving within the area, coiling around each other. The male pursues the female’s cloaca closely, sometimes rubbing his head against the flank and the cloacal region of the female. Both the male and the female wave their tail fins by undulating the tail tip.

Oviposition
During oviposition, the female turns on its back, positions the cloaca near the top of the nest cavity and halts for several seconds. Then the male positions his cloaca near the site of oviposition. Eggs are directly coiled into the moss that the male has prepared in the nest. Interlacing of the eggs into the plant material in the nest ensures that the eggs adhere to the nest as a compact mass, and facilitates external fertilization.

Egg guarding
In S. intermedia, parental care is fulfilled by the males. Paternal care as observed in the lesser siren is very rare for salamanders. After the female completes oviposition and leaves the nest, the

male stays in close proximity to the eggs. The total number of eggs can be around 120–130, with a diameter of about 3 mm. The male constantly moves the egg mass, circles around it, and aerates the eggs through vigorous tail fanning. The tail-fanning behavior of the male towards the eggs can enhance sperm dispersal. Additionally, the male continuously cleans the nest from sand and other materials, to improve hygienic conditions and possibly to prevent infections from pathogens and fungi. It is also likely that males remove dead or infected eggs, in order to prevent further infection of the viable eggs.

The development of the larvae takes around 35 days. Paternal care continues after the larvae hatch and the male aggressively defends the larvae up to one week after hatching.

Mutualisms
Siren intermedia has important effects on community structure. It is an important predator in temporary ponds, where it complements the keystone predator role of eastern newts (Notophthalmus viridescens). S. intermedia reduces the total densities of the anuran larvae, and by doing that, it allows the eastern newts to act as keystone predators over a broad range of prey densities.

Enemies
Adult mole salamanders (Ambystoma talpoideum) and lesser sirens (Siren intermedia), are the top two predators in temporary ponds of the southeastern United States. Siren intermedia competes with and is an intraguild predator of A. talpoideum, limiting its growth and controlling its recruitment.

Vision
Western Lesser Sirens (Siren intermedia nettingi) have poor eyesight. They rely on their other senses to forage, hunt, and survive.

Respiration
All species in the sirenidae family are paedomorphic, eel-shaped salamanders that live in aquatic environments. They respire through their gills, lungs and skin, and survive well in hypoxic environments low in oxygen. Siren intermedia is unique among amphibians in its ability to construct a mucoid cocoon that slows down dehydration during aestivation, and the lesser siren can withstand long periods of food deprivation without ill effects. During aestivation, respiration slows down significantly, and gills atrophy over the next 16 or more weeks.

Acoustic behavior
Acoustic behavior is generally considered insignificant in most salamanders, but some aquatic species, like the lesser siren, produce some underwater sounds. Acoustic behavior serves a functional service in S. intermedia, especially since it is nocturnal and it burrows in sediments, swims and crawls through densely vegetated waters. Its visual and olfactory senses are very limited in this habitat, and thus the possibility of predation and other risks are high in this case. Nevertheless, acoustic behavior in lesser sirens is still infrequent, and becomes even less frequent with undisturbed habitat residency, perhaps because of their familiarity with the environment.

Siren intermedia make and responds to underwater sounds that may have specific communicational significance. Resting sirens are usually silent, but they may produce trains of pulsed sounds or “clicks”. Their tendency to click is greater in groups than in single specimens, which suggests that they are involved in intraspecific communication. These acoustic behaviors occur most often when other sirens are present. They are emitted at different pulse rates by specimens clicking simultaneously, and are associated with head-jerking motions. Head-jerking may offer visual reinforcement of an acoustically defended individual space, or it may be required for sound production. S. intermedia can produce clicks by moving the horny jaw coverings together rapidly, and head-jerking may be associated with such movement when it is particularly forceful. This means of sound production is similar to the upper and lower teeth of humans, clicking with the mouth open.

Another frequently produced sound ("yelp") is associated with cases of distress, or alarm. When S. intermedia butt or bite each other in their habitat, the bitten or injured individuals may swim away quickly, emitting yelps at frequencies of 880 Hz. These yelp sounds could have communicational significance if they prevent further attack or signal to other individuals that one is injured.

Osmoregulation
Animals that inhabit freshwater habitats have high-affinity sodium uptake systems. Therefore, the better an animal is adapted to freshwater, the lower the rate of sodium loss and uptake. Sirens have a high sodium affinity (around 0.2 peq/g per day), and thus are able to resist the harmful effects of low-sodium environments.