On your marks, get set, go! The race of child versus parent

By: Gwendolyn Park

At some point in our childhood, most of us have challenged an adult to a race, believing we will win, and gain the recognition for being the fastest. However, in most outcomes the adult wins as their body structures and muscle strength are greater than that of a child, making us unequally matched. The same idea follows over into the locomotory abilities of many juvenile and adult relationships seen throughout the animal kingdom, especially in lizards. However, most literature describes generalized locomotion abilities, that are based solely on adult centric observations, leaving differences in movement pattern by age an under-investigated area of research.

Pedro Oliveria and his colleagues at the Porto University in Portugal, decided it was just as important to understand how sensitivity to temperature changes, might impact locomotory performance differently across age and sex variations of nocturnal Moorish geckos. Moorish geckos like all lizards, are ectothermic species which means they rely on the environment to regulate body temperature. As such, they have a variety of behavioural responses to changes in temperature of their surroundings. The variety of their reaction to temperature changes, however, are dependent on their individual sensitivity to their own body temperature and is a response of interest when examining the effects of temperature on locomotor performance.

The scientists tested these ideas by setting up a maximum sprint speed tests at three set environmental temperatures (25°C, 27°C, 29°C) by startling the geckos through physical touch. The study individuals were composed of adult (male and female) and 15- and 30-day-old hatchings. For each individual’s test, a high-speed camera was used to record each gecko’s run across the study track, with three separate sprints recorded at each temperature. The videos were than digitally analyzed to determine the fastest speed recorded during each individual gecko run across the study track at each temperature. The researchers found that once again the adults out preformed the hatchlings at each temperature, with adult’s top speed being significantly faster than that of the hatchlings. They suggested that juveniles are likely to rely on a different trait to help them survive in their shared environment that is separate from locomotory speed.

Upon further examination, Oliveria and his team found that between the adult sexes, males demonstrated faster run speeds than that of females across the examined temperatures. Their findings illustrated how each sex spends their resources, with female energy being mainly diverted to reproduction, while males focus their energy on covering large areas to find mates and to defend their territory, helping those that spend more promote their own reproductive fitness. Additionally, independent of between group variation, body temperature sensitivity showed a positive relationship, such that at the highest temperature the sprint speed was the fastest for every group. Moorish geckos were previously observed to prefer a body temperature of 29.8 degrees and as such are expected to have the highest performance output at temperatures close to that value, as this study observed.

Overall, the relationship of locomotion performance abilities was shown to be related to temperature with both sex and age being contributing factors on what the highest output can be. It also shows that individuals can vary in response to environmental stimuli, as what is optimal for one might not also follow with the benefits needs in another. While, adults always seem to win the race, at some point the body conditions equalize and the race becomes far.

Oliveira, P., Gomes, V., Riaño, G., & Rato, C. (2023). Ontogenic differences and sexual dimorphism of the locomotor performance in a nocturnal gecko, Tarentola mauritanica. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, 339, 28– 36.