Death‐feigning propensity varies within dice snake populations but not with sex or colour morph

Abstract

Once cornered by a predator, prey can try to intimidate the assailant or repel it, with irritating sprays for example. If seized, they may scratch, bite or struggle to cause the predator to release its grip. At the other extreme, they can adopt passive behaviours such as death feigning (DF, i.e. thanatosis). DF is observed widely across the animal kingdom; it usually involves a combination of displays such as immobility, supination, leg‐folding, mouth opening and release of nauseating secretions. When displaying DF, individuals are highly vulnerable and effectively bet on the attitude of the predator; this risky choice is presumably under positive selection. We explored how propensity for DF varies among and within populations of dice snakes (Natrix tessellata). We also considered the influence of sex, body size, reproductive status, colour morph and presence of injuries (N = 2760 snakes; five populations). DF propensity differed among populations, possibly due to variation in local predation pressures. Larger snakes displayed DF more frequently and carried more signs of probable past predation attempts (scars and recent injuries). We found no sex effect on antipredator behaviour. Gravid females used DF less frequently compared with non‐gravid females. Differential expression of DF across populations, body sizes and reproductive status suggests that this complex behaviour was selected to respond to environmental and intrinsic factors. Future studies should explore which elements affect duration, intensity and success of DF in defence against various predators.

Dead snake! A strategy for survival: Thanatosis in some Panamanian snakes with a review of death-feigning in American snakes

“…Bleeding or spraying blood from the mouth can be an anti-predator strategy in itself; thanatosis is sometimes accompanied by the production of small bloody bubbles forming a red foam in the open mouth (Golubović et al 2021).…”

“…The strategy or strategies deployed and their duration may depend on factors such as the type of predator (Moore et al 2020), size of the snake (Gerald 2008), or state of pregnancy (Gregory and Gregory 2006). Likewise, within the same species or population, behaviors can be employed to various degrees and with differing frequencies (Golubović et al 2021).…”

Sex-specific effects of a parasite on stress-induced freezing behavior in a natural beetle-nematode system

“…Across the animal kingdom, different species have evolved a wide variety of anti-predator strategies that fit their lifestyle, body design and behavior. When directly faced with a predator or perceived threat, some animals react by feigning death as an attempt to fool the predator [1][2][3][4]. In some scientific disciplines this is referred to as thanatosis [5,6] or tonic immobility [7,8].…”

Defensive tail displays in dice snakes (Natrix tessellata) are influenced by colour morph and sex

“…The dice snake (Natrix tessellata) is a nonvenomous, oviparous, colubrid snake with a large distribution range (Mebert, 2011) and is recognized as a species that has complex defensive displays (Golubović et al, 2021). For the purpose of this study, we tested adult individuals (snout-to-vent length, SVL; for adult males 48 cm, for adult females 55 cm; Luiselli and Rugiero, 2005) during an ongoing ecological study on Golem Grad Island (40°52 08 N, 20°59 23 E, Prespa Lake, North Macedonia).…”

“…Dice snakes perform a diversity of presumed antipredator responses when captured, from twisting and coiling, to bluffing aggressive displays (flattening the head combined with hissing and faking strikes) and releasing of foul mixture of faeces and cloacal secretions, and finally to tonic immobility, often accompanied by an open mouth and autohemorrhaging (Golubović et al, 2021). Tail waving has been neglected heretofore in this species, but our results indicate that it occurs in at least two phases of the antipredator response of dice snakes: rarely on capture and more commonly in the final stages of post-capture immobility.…”