Alpine salamanders are often small in size, and dark brown or black.[8] Members of the subspecies are not wholly black or brown monochrome, but rather have mosaic or spotted patterns.[8] Members of the subspecies Salamandra atra aurorae have bright splotches on its dorsal side and head. The color is often bright yellow, but can range to shades of white or even gray.[8] Distribution of the pigment is dependent on the distribution of certain cells, so may be smooth and even or patchy.[8]
Female S. atra tend to be larger than the males, and can grow up to 151 millimeters, or around 5.9 inches.[8] Males will grow to around 144 millimeters, or 5.6 inches: both measurements include the tail.[8] Males have swollen, visible cloacae, and are more slender than females.[8][14] The salamanders have parotid glands posterior and lateral to their eyes, giving them an elongated head shape.[8] They tend to have between 11 and 13 costal grooves along the sides of their bodies, and a double row of dorsal glands runs down their backs on either side of their spines, down to the tips of their tails.[8]
Most alpine salamanders that are either completely black (melanistic) or predominantly black have the dark pigment as a baseline, but the evolution behind this dark coloring has a winding history.[4] Scientists have studied the hypothesis of if the salamanders start completely black, or if they evolved like that over time.[5] DNA-evidence traced through maternal lineages suggest the latter: that salamanders evolved their black coloration over time.[5]
Biological pigmentation is determined by presentation of specific color-producing cells, called chromatophores, which absorb and/or reflect light in a particular way to then appear as a color.[7][15] In S. atra, there are different cells present or activated, which yield different colors: melanophores contribute to the dark coloration by producing the dark pigment melanin,[7] while xanthophores produce a yellow pigment,[4] and iridophores are simply light-reflecting.[4] The fully-black phenotype seen in S. a. atra results from the salamanders' melanophores in the dermis and epidermis, producing melanin alone.[5][7] Xanthophore-iridophore complexes are responsible for production of yellow spotting, which appears bright. [5] In species without yellow patches, it appears that they do not ever develop these cells.[5] In S. a. aurorae or other salamanders with different coloration on different parts of their body, two distinct skin types are present: one that only contains melanophores (black), and one that has melanophores, xanthophores, and iridophores in combination.[7]
The yellow coloring on some alpine salamanders is thought to be an aposematic strategy to fend off predation.[11] The pure black coloring is also hypothesized to be a form of thermoregulation,[11] though it may also be considered a warning to some predators.[11]
Genetic analysis suggests that the Corsican fire salamander (Salamandra corsica) is the closest related species, and the black-yellow coloration is an ancestral feature of alpine salamanders. Proposed colonization from south (Prealps) to Alps was carried out by the fully melanistic (derived feature) S. a. atra after the last retreat of the ice sheets.[18]
As terrestrial salamanders, these organisms live on land.[8][19] S. atra tend to live underneath stones or logs, or in rocky crevices in their mountainous habitat.[8] They also are diurnal, and most active in the day with periods of inactivity, rest, or sleep at night.[16] They will engage in nocturnal activity on a weather-dependent basis.[20] Ideal weather for alpine salamanders is rainy or post-rain, at temperatures between 3 and 18C (around 37-64 F).[16]
They thrive in forest environments that have silver fir and beech trees.[21][22] Coniferous forests that have high proportions of Norway spruce and European larch trees also provide adequate habitats, even though the salamanders live on the ground floor.[21] Because alpine salamanders are completely terrestrial, they have on-land territories that they tend to return to throughout the day and for refuge. They often return to the same sites for much of their lives.[21] Any time that they leave their sites, they expose themselves to predation and also to the chance of losing their site.[21] Alpine salamanders are ectothermic, so losing a refuge or shelter could leave them exposed to the elements and be extremely costly, if not fatal,[21] due their lack of an internal thermoregulation mechanism.
This high dependency on a quality nest site supports the theory that many terrestrial salamanders, including S. atra, engage in territorial behaviors.[21] Capture-recapture methods suggest that the species is very stationary;[23] 12 metres (39 ft) was the maximum observed distance traveled by one individual during the summer season. About 120 individuals per hectare were counted in most suitable areas with over 2000 individuals per hectare also observed, suggesting that this rather cryptic species is quite abundant.[17]
They employ scent-marking techniques for territorial behaviors, and to mark their territories using fecal pellets so they can identify their own shelters.[21] Scent-marking is an intra-species communication, where chemical signals convey specific messages to other S. atra individuals.[21][24] Alpine salamanders can determine if a found fecal pellet has been left by a member of their same sex and/or species.[21] Thus, this technique serves a double purpose to warn other salamanders that that particular location has already been claimed.[21]
One of the greatest dangers to alpine salamanders overall is commercial deforestation in their habitats.[26] Machinery like tractors or other forestry tools can compress the soil, eliminating some of the small insects that S. atra eat or eliminating potential nooks and burrows for them to use as shelters.[26] Many scientists propose changes in the lumber industry as an attempt to heal these habitats.[26] These salamanders may also change their morphology as global temperatures rise.[27] Amphibians and other organisms that do not internally regulate their body temperature may need adaption mechanisms to remain at ideal physiological temperatures in the face of changing climates.[27] Other issues like acid rain or precipitation changes could prompt many animals, including alpine salamanders, to be forced into new habitats.[27] Alpine salamanders play a crucial role in their ecosystems.[28] There are already animal and ecosystem conservation laws in Europe, but many scholars recommend additional ones to protect the flora and fauna.[12]
Due to their toxicity,[10][11] as well as decreased concentration of animals at high altitudes,[29] researchers are unsure of consistent predators for alpine salamanders with limited observation.[8] These salamanders do move slowly, which could increase their risk of being caught.[29] Generally, predators of the broad category of toxic Salamandra species can include birds, rats and snakes, as well as other, larger carnivorous mammals like raccoons, minks, wild boars and foxes.[10]
One notable predator of S. atra is young snakes.[29] In particular, juvenile European adders (Vipera berus) pose a risk because they live at similarly high altitudes to alpine salamanders.[29] S. atra have been suggested to make up just under half of these snakes' diets in some locations.[29] They may hunt for alpine salamanders during early morning hours, when S. atra is most active.[29] There also has been recorded evidence of these snakes swallowing alpine salamanders.[29] V. berus, alongside the grass snake (Natrix natrix), are noted predators of alpine salamanders in the Italian Alps.[8]
Male and female alpine salamanders have relatively similar diets.[30] Some specific organisms they prey on include species such as beetles, snails, millipedes, and spiders,[31] but alpine salamanders display preferences among prey.[30] S. atra typically consume organisms from the Coleoptera and mollusca taxa.[30] These taxa are the most crucial component of their diet. They also tend to eat larger prey since they themselves are larger salamanders.[30] Such preference indicates a dimensional selectivity, in which the energy intake of prey consumption is maximized.[30] Though alpine salamanders have definite dietary preferences, they have a substantial amount of variation in their diet[30] that corresponds to their own optimized physical needs and prey-catching abilities.[citation needed]
The alpine salamander engages in a promiscuous mating pattern,[20] meaning that they engage in multiple partner pairings. Males immigrate and travel farther than females do, potentially to find mates and following a scent emitted by females.[20] Typically, males migrated when they were in the juvenile stage of life.[20] Female S. atra find and defend their shelters, which is a potential reason that they may stay more local than males.[20]
Alpine salamanders live in a sex ratio of 1:1.[33] Mating occurs on land. The male clasps the female at the forelegs, and fertilization is internal. S. atra are categorized as viviparous, meaning that their young are born alive and unlike many other amphibians, do not go through metamorphosis[8][9] They give birth to 2 young, sometimes 3 or 4. New young alpine salamanders may measure as long as 50 millimetres (2 in) at birth, with the mother measuring only 120 millimetres (4.7 in).[citation needed]
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