Ibáñez, Alejandro, Bartłomiej Zając, Izabella Sambak, Michał Woźniakiewicz, Aneta Woźniakiewicz, and Maciej Pabijan. "Chemical signal diversity in male sand lizards (Lacerta agilis) along an urbanization gradient." Scientific Reports 15, no. 1 (2025): 6958.

 

What They Did

The researchers captured male sand lizards (Lacerta agilis) from urban, suburban, and rural areas around Krakow, Poland and compared the chemical composition of their femoral gland secretions, which are involved in attracting mates. They found that urban and suburban lizards tended to produce a more varied mix of compounds than rural lizards. In addition, the compounds dodecanoic acid, tetradecanoic acid, n-pentadecanoic acid, (+)-α-tocopherol, and cholecalciferol were the most important in distinguishing lizards from different areas. Dodecanoic acid, tetradecanoic acid, and n-pentadecanoic acid are all fatty acids, (+)-α-tocopherol is a form of vitamin E, and cholecalciferol is a form of vitamin D. 

The secretions from suburban lizards had the highest amounts of dodecanoic acid, tetradecanoic acid, n-pentadecanoic acid, and cholecalciferol. Secretions from suburban and urban lizards had the most (+)-α-tocopherol. Secretions from urban lizards had more tetradecanoic acid and cholecalciferol than those from rural lizards, but less than those from suburban lizards. 

The researchers suggest that the greater variety of compounds produced by lizards in more human-influenced habitats may be related to the complexity of those environments compared to the rural habitat, which consisted of fairly uniform forest and meadow. They note that fatty acids are also energy sources for the lizards, so secreting them has a cost, which implies some benefit that outweighs that cost in suburban environments. The  (+)-α-tocopherol and cholecalciferol may function as mate-attractants themselves, and the (+)-α-tocopherol may also help preserve the mate-attractant compounds from ultraviolet radiation, which is more abundant in areas without a tree canopy.

Further Exploration

Anoles are one of the most common lizards in my area, and it turns out they differ from most other lizards in that they don’t produce the femoral gland secretions, which might be related to their more visual displays of flashing their dewlaps and doing “push-ups” (see https://www.anoleannals.org/2020/06/05/vasotocin-and-chemical-communication-in-anolis-carolinensis.) 

I was also surprised to see that the sand lizard researchers used the Shannon index to compare the diversity of femoral secretion chemicals among lizards. I’m used to seeing the Shannon index used to compare species diversity among different habitats, vegetation survey plots, and the like. But of course, it’s just math, and you can have the categories be anything you like. [If you’re not familiar, the Shannon index is equal to  -Σp_i * ln(p_i), where p_i is the proportion of each species relative to the total. You add up the proportion times the natural log of the proportion for each species, then change the sign because the natural log of a number less than 1 is negative]. This makes me think it would be fun to calculate the Shannon index of my local library by book categories such as fiction type (fantasy, romance, etc.) or Dewey Decimal range. 

The researchers also used nonmetric multidimensional scaling to visualize the degree of secretion chemical similarity among the lizards; I’m again much more familiar with this method for showing the similarity among survey plots, generally for plant species composition.  I’m curious what other applications it might have, but that’s a rabbit hole for another day!

Image credit: Reinhold Möller 

https://commons.wikimedia.org/wiki/File:Fighting_Sand_lizards_(Lacerta_agilis)_4295304.jpg