A new aestivation strategy for land molluscs: hanging upside down like bats

Abstract

Introduction: Many land molluscs survival strategies are still poorly understood or have not been even reported, especially in the Neotropics. Methods: I collected 25 adult Tikoconus (Tikoconus) costarricanus from Reserva Forestal Río Macho, Costa Rica. I kept the specimens for 8 days in terrariums to film their behavior. Objective: To analyse the behavior of T. costarricanus, with emphasis on its strategies to survive drought and probably also predation. Results: This snail has at least three unusual behaviors that probably help them reduce dehydration and may be escape from enemies and avoid diseases: hanging upside down like bats, falling and grooming. During aestivation, they compress the body and hang upside down from leaves, like bats hang from perches. They attach to the underside of leaves with mucus from a caudal gland. Disengagement is done with vigorous shell rotations and foot twisting in contorting sequences, and can be done as reaction to direct sunlight, and probably to avoid predators and parasites. They groom their own shell, shell lappets and foot, an unusual behavior among land snails. This species feeds mainly on epiphyllous mosses, algae and lichens, occasionally adding arthropod eggs and carrion. Egg laying is similar to other euconulids and valloniid snails. Conclusions: Aestivating hanging upside down is a drought avoiding trait described here for the first time and is also a new function for the caudal gland mucus. Leaf detaching is done by a contortion sequence of shell rotations and foot twisting; its complexity and duration varies according to the leaf side where the snail is located.

Selección de microhábitat, y actividad diaria y estacional del caracol Tikoconus costarricanus (Stylommatophora: Euconulidae) en el sotobosque de bosques tropicales húmedos de montaña.

“…Many active T. costarricanus snails seem to avoid leaves´ upper side, even though food is more abundant there and their pigmentation help them camouflage with epiphytes, suggesting that there are difficulties on this side of the leaves (Barrientos, 2019b(Barrientos, , 2020. Besides this, snail frequency on the upper side of leaves changes with season and daytime.…”

“…Hernández-Quinta (2013) suggested that leaf side preference may represent a strategy against adverse climatic conditions, predators, or simply a place for protected rest. In the case of T. costarricanus, probably due to their reduced size and dehydration susceptibility, specimens avoid being on the upper side of leaves due to three reasons: 1) direct sunlight impact that cause water loss and induce throwing themselves to the ground (Barrientos, 2020); 2) low relative humidity, which induce aestivation on the underside of leaves (Barrientos, 2020); and 3) rain and canopy drip, which force them to find a protected place on the underside of leaves. Why are rain and canopy drip so significant?…”

“…Along the morning temperature continues to rise and the number of snails on the upper side of leaves decreases as well as the relative humidity (Abdalah-Hernández et al, 2020). During this period, lack of moisture and, maybe, direct sunlight, forced them to aestivate some hours (Barrientos, 2020). The cycle starts again around sunset when temperature falls.…”

“…1A). Other behaviours that they could be doing while active were: eating, defecating, moving or grooming (Barrientos 2020). I considered specimens "inactive" when optical tentacles were withdrawn in the body.…”

“…I considered specimens "inactive" when optical tentacles were withdrawn in the body. Inactive specimens could be: "resting", when tentacles were withdrawn, cephalopodium was extended and the whole foot sole was in contact with leaf surface; or "aestivating in bat-like hanging position" (for details about this position see Barrientos 2020) (Fig. 1B).…”