When the weather is too hot, Spiny Lava Lizards spend less time trying to attract a partner, says an article in New Scientist (26 July 2023). In fact, they get less selective – less picky – in the heat. 

Nicola Rossi at the National University of Cordoba in Argentina, and his colleagues, studied the behaviour of the Spiny Lava Lizard (Tropidurus spinulosus), which is a reptile native to South America. 

The researchers tested two groups of Spiny Lava Lizards living in a nature reserve in Argentina. One group lives on a rocky outcrop that receives lots of sunlight with an average temperature of 30 degrees Celsius (86F). The second group lives in a zone with lots of shade trees, where the average temperature is 26.5C (80F). The researchers watched the lizards in the wild for 20 days.

The researchers found that to attract a partner, the Spiny Lava Lizard bobs its head. It also does ‘push-ups around the rocks they guard to signal their ability,’ says Nicola Rossi. ‘It requires a lot of energy’ to do push-ups. 

The lizards in the warm area were less active during the hottest hours, around midday. They tended to move around mostly in the morning and late afternoon.

Next, the researchers brought 42 male lizards and 35 female lizards inside into the laboratory – some were placed in a location where the temperature was normal, and others were placed in a location 2C to 4C warmer than usual, called the hot zone.

The researchers gave each lizard a choice of two partners. The two partners were behind a glass barrier. 

Male lizards did just as many push-ups regardless of temperature, but less head bobs in the hot zone – some male lizards even stopped nodding their head to attract a partner.

Male lizards in the hot zone spent more time in the shade (up to four times more hours than male lizards in the normal zone), which meant that they were not spending much time with females.

Female lizards in the normal zone chose males with more colourful areas on the sides of their bodies – a sign of manliness. However, in the hot zone, females did fewer head bobs and didn’t care how colourful the male was – they just chose any male. Nicola Rossi says that ‘if they are choosing their mates randomly, then they are not choosing the best males.’

The research scientists are concerned about increasing temperatures in the Spiny Lava Lizard’s usual habitat due to climate warming. Daniel Ariano-Sanchez at the University of the Valley of Guatemala, who was not involved in the study, says that the species of lizard ‘will probably not adapt fast enough to cope with the rate of temperature increase that is expected in the future.’ Lizards are ectothermic, so they are vulnerable to dramatic temperature differences that might harm their physical abilities to attract a partner. 

Journal reference:

PLoS ONE DOI: 10.1371/journal.pone.0285656

Photographer: Shutterstock/reptiles4all on the New Scientist webpage

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM