Chemosensory predator detection in lacertid lizards

For many animals, the ability to detect and recognise predators is crucial for their survival. Accordingly, species have evolved multiple sensory systems warning them of imminent dangers. One of these, the sense of smell, is probably the oldest and most widespread system, but likely also the least understood. This thesis explores the effects of predator type (mammal or snake), origin (native, invasive or allopatric) and insularity (mainland or island prey populations) on chemosensory abilities of lacertid lizards. Additionally, in order to lay bare the mechanics behind chemosensory predator detection in these lizards, I look into the chemical nature of predator-derived cues. Instigated by the alarming spread of the invasive mongoose (Herpestes auropunctatus, a notorious predator of reptiles) in the Balkan, I set out to test whether lacertids were able to interpret its odour. Surprisingly, individuals of the Asian grass lizard (Takydromus sexlineatus), a lacertid from the native range of the mongoose, exhibited no signs of stress when experimentally confronted with mongoose chemicals; chemicals of a sympatric snake predator elicited the behaviours typical for lacertids in dangerous situations. More puzzling, Dalmatian wall lizards (Podarcis melisellensis) from mainland Croatia did mount the typical anti-predatory response when brought into contact with mongoose scent. However, conspecific wall lizards living on islands failed to recognise mongoose chemicals, or ignored them. In fact, island lizards showed signs of chemosensory deprivation in general: they did not respond to a sympatric snake predator, and brain areas involved in the processing of chemical signals tended to be smaller than in mainland specimens. I hypothesise that insular conditions (limited resource availability and predator relaxation) select against chemosensory investment. In the second part of the thesis, I used a well-known study system (recognition of adder, Vipera berus, chemicals by common lizards, Zootoca vivipara) to test the usefulness of two techniques for the identification of kairomones. I found that neutral lipids, extracted with n-hexane from adder skin, provoked the typical fear-response in lizards. Gas Chromatography – Mass Spectrometry revealed a complex cocktail of 165 different molecules, several of which are likely candidate-kairomones. In a subsequent study, I tested a recently developed technique (Proton-Transfer Reaction Time-of-Flight Mass Spectrometry) that allows real-time capture and extremely accurate mass annotation of volatile molecules. Common lizards can detect the presence of adders based on such volatile molecules only. These results emphasise the complexity of the information prey animals can obtain from their predators’ scent. ​ ​

Jaar van publicatie:2020

Trefwoorden:Doctoral thesis

Toegankelijkheid:Open