Escape tactics by a neotropical montane lizard: a comparison of flight responses against natural and nonnatural predators

Tonically active GABAergic neurons in the dorsal periaqueductal gray control instinctive escape in mice

Escape behavior is a set of locomotor actions that move an animal away from threat. While these actions can be stereotyped, it is advantageous for survival that they are flexible.1,2,3 For example, escape probability depends on predation risk and competing motivations,4,5,6,7,8,9,10,11 and flight to safety requires continuous adjustments of trajectory and must terminate at the appropriate place and time.12,13,14,15,16 This degree of flexibility suggests that modulatory components, like inhibitory networks, act on the neural circuits controlling instinctive escape.17,18,19,20,21,22 In mice, the decision to escape from imminent threats is implemented by a feedforward circuit in the midbrain, where excitatory vesicular glutamate transporter 2-positive (VGluT2+) neurons in the dorsal periaqueductal gray (dPAG) compute escape initiation and escape vigor.23,24,25 Here we tested the hypothesis that local GABAergic neurons within the dPAG control escape behavior by setting the excitability of the dPAG escape network. Using in vitro patch-clamp and in vivo neural activity recordings, we found that vesicular GABA transporter-positive (VGAT+) dPAG neurons fire action potentials tonically in the absence of synaptic inputs and are a major source of inhibition to VGluT2+ dPAG neurons. Activity in VGAT+ dPAG cells transiently decreases at escape onset and increases during escape, peaking at escape termination. Optogenetically increasing or decreasing VGAT+ dPAG activity changes the probability of escape when the stimulation is delivered at threat onset and the duration of escape when delivered after escape initiation. We conclude that the activity of tonically firing VGAT+ dPAG neurons sets a threshold for escape initiation and controls the execution of the flight action.

Comparing the antipredator behaviour of two sympatric, but not syntopic, Liolaemus lizards

The microhabitat preferences of prey animals can modulate how they perceive predation risk, and therefore, their antipredator behaviour. We tested under standardized conditions how microhabitat preferences of two Liolaemus lizards affected their responses when confronted with two types of ambush predators (raptor vs. snake), under two levels of predation risk (low vs. high). These lizard species are sympatric, but not syntopic; L. chiliensis basks on bushes, a complex microhabitat that may provide protection against visual predators, while L. nitidus prefers open microhabitats, basking on the top of large bare rocks, highly exposed to visual predators. If microhabitat complexity modulates the antipredator response, L. chiliensis may perceive lower predation risk, exhibiting lower intensity of antipredator responses than L. nitidus. Both species reduced their activity after being exposed to both predators, but lizards differed in the assessment of predation risk; L. nitidus reduced its activity independently of the predation risk experienced, while L. chiliensis only reduced its activity in the high-risk condition. The microhabitat preferences shaped during the evolution of these species seem to modulate their perception of predation risk, which may cause interspecific differences in the associated costs of their antipredator responses.

Escape distance and escape latency following simulated rapid bird attacks in an Andean lizard, Phymaturus williamsi

Predatory birds represent the greatest risk for many lizard species. However, little is known about the functional relationship between the escape distance and escape latency of lizards during a rapid bird attack. We hypothesised that escape latency and distance in the Andean lizard species Phymaturus williamsi would increase proportionally, but vary according to the means of escape. Over a three-year period we observed seven types of antipredatory behaviour in 98% P. williamsi lizards on simulated predatory bird attacks. Escape distance and latency were positively correlated. 65% of lizards emerged from their refuge within 2 min of an attack. All of these behaviours were positively correlated with escape latency and distance, although we found the former to be more precise. This study contributes to a better understanding of the general antipredatory behaviour in this species of Andean lizard, and will assist in future decisions concerning its conservation.