Segmental muscle twitching behaviour in the flanks of lancehead vipers Bothrops spp in response to human approach

Abstract

Bothrops species are known to have a wide range of defensive behaviours against potential threats. Herein we show a frequently observed, but to date undocumented, behaviour in male and female Bothrops spp of varying sizes in newly arrived specimens from the wild, short-or long-term captives as well as in captive born individuals. The behaviour consists of irregular, synchronous or asynchronous muscular twitches in segments of the body flanks in otherwise motionless snakes. We named this ‘Segmental Muscle Twitching Behaviour’ (SMTB). We observed fifteen Bothrops spp from six species groups for incidence of this behaviour and made videos of snakes during the ‘alertness’ and ‘threatening’ phases of response to human approach. We found the behaviour in only five species, these belong to the monophyletic Bothrops jararacussu and Bothrops atrox species groups, suggesting a single evolutionary origin of this behaviour. Macroscopically, SMTB varied in the number of segments involved and the twitches had uneven intensities. Although recurrent and often replicable in similar situations during human approach, the behaviour was not displayed consistently. In addition, SMTB can be interrupted, stay inactive for quite some time and then restart. Hypotheses to explain this behaviour are suggested