Lighting Up Anoles at Night!

anolis lizard lit up by artificial lighting at night

Photo by James Stroud

How we perceive and interact with the world is strongly shaped by natural light. How much light there is at a given time determines whether we’re sleepy or awake, and whether we’re bracing for winter or excited for long summer days. The annual switch to daylights savings time shows us how even a small shift in our perceived light cycle can disrupt our internal clocks!

The amount of illumination an animal experiences – its photoperiod – is also vitally important in nature, from determining sleep cycles to the seasonal timing of reproduction. However, the increasing urbanization of natural habitats has led to huge shifts in the exposure of wildlife to light due to the use of electric lighting at night in urban areas. This artificial light at night has the potential to seriously affect the life cycle of many organisms through, for example, changes in endocrine function, melatonin production, and reproductive timing. On the other hand, artificial lighting at night may also have positive effects in some cases: organisms that forage or hunt at night, for instance, may have increased perception of prey and greater success in obtaining nutrients.

In a recent paper, Thawley and Kolbe investigate the effect of artificial light at night on one of our favorite species of lizards, Anolis sagrei. Using captured anoles from a wild population in a forested area with low levels of artificial lighting at night, they use laboratory experiments to see the effects of this artificial lighting on the anole’s body condition, glucocorticoid levels, and reproductive cycles.

The authors found that artificial lighting at night actually increased the growth rate of anoles in captivity! Females under ‘artificial light at night’ condition grew 1.8 times faster than their counterparts experiencing the ‘dark at night’ condition, and males grew 1.2 times more! This suggests that artificial lighting at night could have a huge biological consequences for this species. As the authors hypothesized, the female anoles exposed to artificial lighting at night also started laying eggs much earlier than their control counterparts. In particular, smaller females under artificial lighting at night managed to produce similar total egg output to that of larger females, potentially representing a tremendous gain in reproductive fitness for these smaller individuals.

All this would seem to suggest that artificial lighting might be a boon for Anolis sagrei! However, the authors suggest some caution in this interpretation, as their experimental set-up did not include foraging costs or predation – both of which could also interact with the effects of artificial lighting to create downsides for Anolis sagrei in these new lit-up urban environments.

Overall, this paper is an illuminating look at how the artificial lighting at night associated with increased urbanization can impact the lives of Anolis sagrei – I encourage you to check it out!

Citation: Thawley, Christopher J., and Jason J. Kolbe. 2020. Artificial light at night increases growth and reproductive output in Anolis lizards. Proceedings of the Royal Society B 287.1919: 20191682. [https://doi.org/10.1098/rspb.2019.1682]