Fire salamander

The fire salamander (Salamandra salamandra) is a common species of salamander found in Europe.

It is black with yellow spots or stripes to a varying degree; some specimens can be nearly completely black while on others the yellow is dominant. Shades of red and orange may sometimes appear, either replacing or mixing with the yellow according to subspecies. This bright coloration is highly conspicuous and acts to deter predators by honest signalling of its toxicity (aposematism). Fire salamanders can have a very long lifespan; one specimen lived for more than 50 years in Museum Koenig, a German natural history museum.

Despite its wide distribution and abundance, it is classified as Vulnerable on the IUCN Red List due to its susceptibility to infection by the introduced fungus Batrachochytrium salamandrivorans, which has caused severe declines in fire salamanders in parts of its range.

Taxonomy
Several subspecies of the fire salamander are recognized. Most notable are the subspecies fastuosa and bernadezi, which are the only viviparous subspecies – the others are ovoviviparous.
 * S. s. alfredschmidti
 * S. s. almanzoris
 * S. s. bejarae
 * S. s. bernardezi
 * S. s. beschkovi
 * S. s. crespoi
 * S. s. fastuosa (or bonalli) – yellow-striped fire salamander
 * S. s. gallaica – Galician fire salamander
 * S. s. gigliolii
 * S. s. morenica
 * S. s. salamandra – spotted fire salamander, nominate subspecies
 * S. s. terrestris – barred fire salamander
 * S. s. werneri

Some former subspecies have been lately recognized as species for genetic reasons.
 * S. algira Bedriaga, 1883 – African fire salamander
 * S. corsica Savi, 1838 – Corsican fire salamander
 * S. infraimmaculata Martens, 1885 – Near Eastern fire salamander (arouss al ayn)
 * S. longirostris Joger & Steinfartz, 1994 – south Iberian fire salamander

Distribution
Fire salamanders are found in most of southern and central Europe. They are most commonly found at altitudes between 250 m and 1000 m, only rarely below (in Northern Germany sporadically down to 25 m). However, in the Balkans or Spain they are commonly found in higher altitudes as well.

The scientific article titled "Water, Stream Morphology and Landscape: Complex Habitat Determinants for the Fire Salamander Salamandra salamandra" explored the factors influencing the distribution of the fire salamander, a semiaquatic amphibian species, in northern Italy. The study aimed to understand the relationship between environmental features and species distribution, essential for effective habitat conservation.

Researchers evaluated three main factors: stream morphology, biotic features of water, and the composition of the surrounding landscape near wetlands. They collected data from 132 localities over four years and used an information-theoretic approach to build species distribution models. Variance partitioning was then employed to assess the relative importance of environmental variables.

The findings revealed that the distribution of fire salamander larvae was associated with specific environmental conditions. They were found in heterogeneous and shallow streams with scarce periphyton (a type of algae) and rich macrobenthos (aquatic invertebrates), characteristic of oligotrophic water. Additionally, the presence of woodlands in the surrounding landscape played a crucial role in the species' distribution.

The study emphasized the interconnectedness of multiple factors in determining Salamandra salamandra distribution. Stream morphology was the most influential variable, but the combined effects of water features and landscape composition also played significant roles. The article underscores the importance of considering both aquatic and upland habitats in conservation efforts for these and other semiaquatic amphibians.

Genetic differentiation by population
A 2021 research project investigated the role of physical and ecological isolation in shaping genetic differentiation patterns among populations and subspecies of the fire salamander in central Iberia. Researchers utilized microsatellite genetic data and environmental dissimilarity measures to assess the impact of both types of isolation on genetic connectivity.

The analysis revealed significant genetic diversity variation across the study area, with lower diversity in eastern populations near the range limit and higher diversity in western and central populations. The study identified strong genetic structure, as populations from the Iberian Central System (ICS) and the Montes de Toledo Range (MTR) formed distinct genetic groups. Physical isolation, represented by landscape resistance, played a substantial role in genetic differentiation between populations across all spatial extents. Different types of landscape resistance, such as climate-based and landcover-based, provided the best model fits in different regions. The researchers proposed a scenario where gene flow between two subspecies, S. s. bejarae and S. s. almanzoris, was restricted by ecological isolation associated with sharp transitions in precipitation seasonality. However, gene flow between populations with intermediate levels of precipitation seasonality was less restricted. The results provided evidence for ongoing environmental adaptation, leading to the maintenance of distinct ecotypes and evolutionary units.

Habitat, behavior and diet
Fire salamanders live in the forests of central Europe and are more common in hilly areas. They prefer deciduous forests since they like to hide in fallen leaves and around mossy tree trunks. They need small brooks or ponds with clean water in their habitat for the development of the larvae. Whether on land or in water, fire salamanders are inconspicuous. They spend much of their time hidden under wood or other objects. They are active in the evening and the night, but on rainy days they are active in the daytime as well.

The diet of the fire salamander consists of various insects, spiders, millipedes, centipedes, earthworms and slugs, but they also occasionally eat newts and young frogs. In captivity, they eat crickets, mealworms, waxworms and silkworm larvae. Small prey will be caught within the range of the vomerine teeth or by the posterior half of the tongue, to which the prey adheres. It weighs about 40 grams. Compared to other salamanders in the region like Luschan's salamander, the fire salamander has been shown to be larger and appears to have a more solid pectoral girdle. Additionally, it has a longer pectoral girdle than Luschan’s salamander. The fire salamander is one of Europe's largest salamanders and can grow to be 15 – long.

Diet and habitat interaction
A study in 2013 aimed to investigate the foraging behavior of fire salamander larvae from different environments, specifically caves and streams, and to understand the roles of local adaptation and phenotypic plasticity in shaping their behavior. The researchers conducted a behavioral experiment using newborn larvae from 11 caves and nine streams in northwest Italy. In the experiment, the larvae were individually maintained in laboratory conditions and subjected to different test conditions, including light/darkness, prey presence/absence, and food deprivation/normal feeding. Video tracking was used to quantify the larvae's movements and foraging strategies.

The results revealed significant differences in foraging behavior between cave and stream larvae. The cave larvae exhibited a more active foraging strategy, especially in darkness and in the absence of prey, suggesting local adaptations to the challenging cave environment with limited food resources. Stream larvae, on the other hand, preferred using peripheral sectors of the test arena, indicating a preference for sit-and-wait behavior, which is advantageous in the presence of detectable and active prey.

The study demonstrated that fire salamander larvae are highly plastic in their foraging behavior. They adjusted their activity levels and movement patterns in response to changes in light conditions, prey availability, and food deprivation. The plastic responses observed were beneficial for increasing encounter rates with prey and optimizing energy utilization in resource-scarce environments. The study revealed an interplay between phenotypic plasticity and local adaptation in shaping the foraging behavior of fire salamander larvae. While plasticity appears to be dominant in the early stages of colonization and adaptation to new environments, local adaptations may also contribute to behavioral differences between cave and stream populations.

Reproduction
Males and females look very similar, except during the breeding season, when the most conspicuous difference is a swollen gland around the male's vent. This gland produces the spermatophore, which carries a sperm packet at its tip. The courtship happens on land. After the male becomes aware of a potential mate, he confronts her and blocks her path. The male rubs her with his chin to express his interest in mating, then crawls beneath her and grasps her front limbs with his own in amplexus. He deposits a spermatophore on the ground, then attempts to lower the female's cloaca into contact with it. If successful, the female draws the sperm packet in and her eggs are fertilized internally. The eggs develop internally and the female deposits the larvae into a body of water just as they hatch. In some subspecies, the larvae continue to develop within the female until she gives birth to fully formed metamorphs. Breeding has not been observed in neotenic fire salamanders.

In captivity, females may retain sperm long-term and use the stored sperm later to produce another clutch. This behavior has not been observed in the wild, likely due to the ability to obtain fresh sperm and the degradation of stored sperm.

Experimental and cave reproduction
A European study investigated the breeding and developmental patterns of the fire salamander in both natural and artificial caves across various regions in Italy. The researchers conducted extensive surveys from 2008 to 2017, exploring a total of 292 sites, comprising 219 natural caves and 73 artificial caves. Among these sites, 52 were found to host underground breeding sites of fire salamanders, with 15 occurring in natural caves and 37 in artificial sites.

The experiment explored environmental features in determining larval distribution inside caves. Fire salamander larvae were observed to choose caves with specific characteristics, such as stable water presence, ease of access, and the presence of rich macrobenthos communities. Larval development in underground springs and natural caves was found to be slower compared to epigean environments, possibly influenced by factors such as temperature and food availability. Furthermore, the lack of light in caves influenced the predation behavior of larvae, with cave populations showing higher adaptability in capturing prey. Cave environments presented unique challenges for fire salamanders, including food scarcity and the occurrence of cannibalism, particularly in resource-poor habitats. However, the study revealed that fire salamanders exhibited strong phenotypic plasticity, which allowed them to adapt and survive in these extreme underground conditions.

The research emphasizes the importance of local adaptations and phenotypic plasticity in the successful colonization of caves by fire salamanders. It also highlights the need for further genetic studies to understand the differentiation between cave and stream populations and the mechanisms driving successful cave exploitation. Despite challenges posed by large urodele genomes, future genome scan and transcriptomic approaches may provide valuable insights into the genetic processes involved in cave adaptation.

Toxicity
The fire salamander's primary alkaloid toxin, samandarin, causes strong muscle convulsions and hypertension combined with hyperventilation in all vertebrates. Through an analysis of the European fire salamander’s skin secretions, scientists have determined that another alkaloid, such as samandarone, is also released by the salamander. These steroids can be swabbed from the salamander’s parotid glands. Samandarine was often the dominant alkaloid present but the ratio varied between salamanders. This ratio, however, was not shown to be sex dependent. Larvae do not produce these alkaloids. Upon maturity, ovaries, livers, and testes appear to produce these defensive steroids. The poison glands of the fire salamander are concentrated in certain areas of the body, especially around the head and the dorsal skin surface. The coloured portions of the animal's skin usually coincide with these glands. Compounds in the skin secretions may be effective against bacterial and fungal infections of the epidermis; some are potentially dangerous to human life.

A 2002 study focused on investigating the variability of toxic alkaloids in the skin secretion of the European fire salamander. The chemical defense mechanisms of the salamander provides valuable insights into the chemical composition of skin secretions in amphibians. The two major alkaloids of focus were, samandarine and samandarone. Using gas chromatography/mass spectrometry, the researchers analyzed individual specimens from two populations of fire salamanders and observed a high degree of intraspecific variability in the ratio of samandarine to samandarone in the skin secretion. Some individuals had a higher concentration of samandarone, while others exhibited equal levels of both alkaloids.

Internal organs contained either no or only small amounts of the alkaloids, and the ratio of alkaloids in the organs differed from that in the skin. Particularly noteworthy was the finding that the larvae found in the oviducts of gravid females were entirely free of alkaloids, and their skin lacked the typical granular glands that are present in adult salamanders. Samandarone may be a product of a separate biosynthetic pathway due to its exclusive presence in skin secretions and organ extracts.

Introduced species
An Israeli research team conducted a comprehensive study investigating the impact of mosquitofish (Gambusia affinis) on endangered Near Eastern fire salamander (S. infraimmaculata) larvae in Israel. The research was conducted through a combination of field surveys and a mesocosm experiment to understand the potential threat posed by mosquitofish to the native amphibian population.

Researchers observed natural breeding pools of fire salamanders, both with and without mosquitofish. The presence of mosquitofish was found to have a detrimental effect on the salamander larvae, leading to reduced densities, smaller sizes, and lower tail:body ratios in the pools with mosquitofish. These observations indicated that mosquitofish predation was causing severe physical damage to the salamander larvae.

To further investigate, a mesocosm experiment was conducted. The researchers manipulated the presence of mosquitofish and structural complexity in the artificial breeding pools. The results supported the field observations, showing that mosquitofish had a significant negative impact on salamander survival, size, and body condition. The fish-inflicted damage included partial tail fins, gill injuries, and limb damage, leading to a reduced likelihood of successful metamorphosis for the salamander larvae in mosquitofish-present mesocosms.

Importantly, the study revealed that increased structural complexity (artificial vegetation) did not provide a refuge for the salamander larvae against mosquitofish predation, contrary to expectations. It was also noted that the use of mosquitofish for mosquito control in permanent ponds could lead to negative consequences for native amphibian populations, as the presence of mosquitofish posed a significant threat to the survival of the fire salamander larvae.

The experiment suggests that mosquitofish pose a serious threat to the endangered fire salamander population in Israel. It also highlights conserving the native amphibian species by reconsidering the use of mosquitofish for mosquito control in habitats where these vulnerable species breed. Efforts to remove mosquitofish from Salamandra-breeding sites are recommended to safeguard the long-term persistence of the fire salamander population and protect against potential ecological disruptions caused by invasive fish species.

Batrachochytrium salamandrivorans
In parts of its range, the fire salamander has become highly endangered by the spread of the introduced chytrid fungus Batrachochytrium salamandrivorans, which has had catastrophic effects on its population. This collapse was first identified from the Netherlands in 2013. The fire salamander in the Netherlands is teetering on the brink of extinction, confined to three small populations in the southern part of the country. Prior to these declines, they were already listed as "Endangered" on the national Red List, and their range had reduced by 57% since 1950, mainly due to changes in water availability and habitat degradation. The remaining populations were limited to specific areas of deciduous forests on hillsides, and their surface activity is restricted to humid periods with night temperatures above 5°C.The species had been considered stable until 2008 when dead individuals were observed, and since 2010, there has been a staggering 96% population decline, with the largest population dropping from 241 individuals to only four in 2011. In 2013, the cause of the decline was officially identified as a new chytrid fungus, Batrachochytrium salamandrivorans (Bsal), likely introduced to Europe from east Asia via captive amphibians.

Since its identification in the Netherlands, Bsal has continued to spread across western Europe, and has infected more populations of S. s. terrestris in Belgium and western Germany, with an isolated but contained occurrence in Spain affecting a population of S. s. hispanica. Dramatic declines have been noted in all affected populations, and some may eventually be entirely extirpated, although at most known sites, fire salamanders persist at low numbers even after disease outbreak, and in one case appear to have recovered. Some localities in the Eifel Mountains where fire salamanders were previously known from appear to now be devoid of fire salamanders, suggesting landscape-scale declines that occurred prior to the disease's identification by science. In 2023, the fire salamander was officially moved from 'Least Concern' to 'Vulnerable' on the IUCN Red List, relating to the past and predicted future declines in the species.