March 1, 2024

Indrella ampulla’s genetic tapestry reveals isolated color forms in Palghat Gap

  • A study found that gene flow between the three color variations of the semi-slug Indrella ampulla is limited and highlights the Palghat Gap as a barrier to it.
  • Although Indrella ampulla has a delicate shell on its back, it doesn’t fit neatly into the snail or slug categories.
  • Endemic to the Western Ghats, the species does not face any immediate threat, but researchers suggest the importance of a broader landscape approach to conservation.

A recent study investigates gene flow between three semi-slug color variations Indrella Ampoule and finds that Palghat Gap, a low mountain pass in the Western Ghats, is a significant barrier, isolating the color red in the south from its yellow and orange counterparts in the north of the Gap. The study also alludes to the influence of paleoclimatic conditions on the genetic diversity of the species.

Endemic to the Western Ghats, Indrella Ampoule It comes in three distinct and vivid color forms – yellow, orange and red. The species belongs to the genus Indrela, which is a monotypic genus, a taxonomic category that houses only one species under its umbrella.

Distinct from a snail or slug, Indrella not only does it carry a delicate shell on its back, but it also has the distinction of being one of the most visually appealing understory dwellers in the biodiversity hotspot of the Western Ghats.

Under duress, this semi-esma, despite possessing a shell, is unable to retreat into it. Instead, when faced with a predatory threat, Indrella foam on the shell. NA Aravind, a researcher at the Ashoka Trust for Research in Ecology and Environment (ATREE) who has extensively studied this species, notes that unlike other snails, Indrella does not produce a thick goo as a defense mechanism. Instead, it secretes white foam to deter its only known predator, the Cochin cane turtle (Vijayachelys silvatica).

A yellow Indrella Ampoule feeds on decomposing waste. Photo by Surya Narayanan.

The period of activity of Indrella Ampoule it is limited to late summer, after the initial monsoon rains (late April to May) and during the southwest monsoon season (June to October), during which the average temperature is around 18 degrees to 25 degrees Celsius . An opportunistic feeder, a 2021 study reports that the species has been observed to feed on a wide variety of flora, including fresh plant matter from angiosperms, mushrooms, and lichens, and to feed on dead plant and animal matter. In one case, the red form was found feeding on human feces in Valparai in the Anamalai forest region.

Polymorphism and restricted gene flow

The researchers of the genetic study, published in November 2023, analyzed 32 individuals of the species and were surprised to find three distinct color morphs in one species, as they had started the study with the hypothesis that the three colors were distinct species.

A juvenile Indrella Ampoule. All semilesma juveniles are brown before changing color. Photo by Surya Narayanan.

Despite being the same species, the red form is restricted to the south of Palghat Gap, while the yellow and orange are found in the north, with no genetic flow between the red and its northern counterparts. Aravind, co-author of the study, says the lack of gene flow is due to the complete isolation of the red forms, through the Palghat Gap, from the yellow and orange individuals. The study affirms the role of the Palghat Gap as a barrier to gene flow of various taxonomic groups such as mammals, birds, reptiles, amphibians, insects and plants and now also molluscs.

Beware of Palghat Gap: isolates the red form

The Western Ghats of India are a 1,600 km long stretch of hills stretching from Gujarat in the west to Kerala in the south. The most prominent geographical break in the region, the Palghat Gap, is located at an altitude of 140 m above mean sea level, with a width varying between 13 and 40 km.

An orange Indrella Ampoule. The orange and yellow colored forms are distributed north of Palghat Gap. Photo by Surya Narayanan.

Aravind points to the likelihood of aridification and drought due to the poor monsoon that separated the northern and southern Palghat Gap, which could have led to the separation and isolation of the red form. “They probably wouldn’t be able to cross the Gap dry zone to facilitate gene flow,” he shares.

Although the species has a restricted distribution, it is found in a wide variety of habitats, such as moist evergreen forests, coffee and cardamom plantations, and even human habitations near natural forests. “You will see them abundantly in the places where they are found, but the distribution ends abruptly; in the case of the yellow and orange forms, in Kudremukh”, says Maitreya Sil, one of the first authors of the study.

A yellow Indrella Ampoule feeds on a plant. Photo by Surya Narayanan.

The yellow and orange morphs are distributed in Kudremukh and below Kudremukh with Agumbe as the northernmost limit. They are widely distributed in places like Valparai, Silent Valley, Kodagu and other places, says Sil. Although yellow and orange share habitats, orange is more widely distributed than yellow, which is largely restricted to Wayanad and adjoining areas.

Although researchers do not see any immediate threat to the species, they do not rule out the likelihood of land use and climate change impacting its population. Since the species is restricted to certain landscapes but is not endangered or threatened, Aravind recommends a broader landscape approach to conserving the species. “The entire landscape has to be protected so that the externalities that affect its survival can be considerably reduced,” he says.


To hear: [Podcast] Impressions: Finding Molluscs with Devapriya Chattopadhyay


Banner image: Red Indrella Ampoule which occurs in the south of the Palghat Gap. A recent study investigates gene flow between three color variations of the demi-slug and finds that Palghat Gap plays the barrier, isolating the red color from its yellow and orange counterparts in the northern Gap. Photo by Surya Narayanan

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