Invaded Invasives: Do urban lizards have more parasites and how might this influence their ecology?

Anole invasion

One of my favorite things about Florida, besides the warm weather, is that it’s home to several anole lizards that have invaded from nearby. Some lizards invaders come from Cuba, like the brown anole (Anolis sagrei). Others, like the crested anole (Anolis cristatellus) come from Puerto Rico (like me!). This makes Florida a fascinating place to study what happens when animals invade. These lizards also live in both urban and forest habitats allowing researchers to study how invasion and living in cities can change their ecology and evolution. The brown anole invaded Florida in the late 1800’s and in the last 50 years has been spreading north through the rest of the state (Kolbe et al., 2004). The crested anole was first spotted in south Miami in the mid 70’s and in the last 40 years has been spreading outside of the metropolitan area (Kolbe et al 2012). A new study led by fellow Life in the City contributor Christopher Thawley, asks if urban populations of these lizard invaders differ in their parasites and whether infection can influence their thermoregulation (the temperatures they choose to keep their bodies at).

Brown anole. Photo from flick.com
Crested anole. Photo by Kevin Aviles-Rodriguez

Fig. 1: Brown anole (left; Anolis sagrei) and crested anole (right; Anolis cristatellus)

Parasites more than meets the eye

Figure 2: Drawing of round worms by Da Costa (1963)

The science fiction movie Alien was probably where I first learned that creatures lived inside others. This horrifying introduction is probably why my skin still crawls when a lizard poops a parasite into my hand. Round worms (nematodes) are the most common parasite I’ve encountered in my research with anole lizards. But I was surprise to find that in Thawley’s study it was in fact the most abundant parasite the researchers identified.

Specifically, Thawley et al. found  intestinal round worms, which reproduce in the gut, with females retaining eggs until juveniles hatch and are excreted in fecal matter (Da Costa, 1963; Fig. 2). The second most common parasite was the tongue worm, which despite its name, commonly settles in respiratory tracks of animals. Researchers found tongue worms in the lungs of both species of anole lizards.

Are city lizards more frequently carrying parasites?

The study found that city lizards weren’t more frequently infected with parasites. However, there were differences between species. Brown anoles were more frequently infected with parasites than crested anoles. In addition, when comparing parasite intensity (total number of parasites) brown anoles from the city had twice as many parasites than forest anoles (Fig. 2). Crested anoles were less likely to be infected and had fewer parasites.

Figure 3: Number of parasites of the two lizard species in natural (green) and urban (blue) habitats. Urban brown anoles had twice as many parasites (Thawley et al., 2019)

Breaking the fever

One way in which animals can fight infection from parasites is by increasing their body temperatures (Rakus et al., 2017). Researchers set out to test this hypothesis by creating thermal gradients (a range of temperatures over which animals can freely move to change their body temperatures). They expected to find that lizards infected with parasites or with a high number of parasites would choose to bask at warmer areas of the gradient. However, they found that parasite number did not influence the preferred temperature of the lizards. They also found no differences in the preferred temperature of city and forest lizards. They did find that brown anoles preferred temperatures about 3 degrees Celsius warmer than crested anoles.

 Invaded invasives

This new study was interesting because they show that the likelihood of carrying parasites is not affected by urban habitats. In addition, it’s fascinating that urban brown anoles are infected with twice as many parasites. I would have thought, given their preference for warmer basking areas, that they would be better suited to get rid of infections. Perhaps it is because parasites may be experiencing a higher thermal stress that the intensity of parasites is higher. What parasites have you spotted in your favorite urban dweller?

 

Read the full paper:
Thawley CJ, Moniz HA, Merritt AJ, et al (2019) Urbanization affects body size and parasitism but not thermal preferences in Anolis lizards. J Urban Ecol 5:1–9. doi: 10.1093/jue/juy031

To read more about this topic I suggest you check out:

  1. Da Costa, SCG (1963) Rondonia rondoni travassos, 1920 (Nematoda, Atractidae). Mem. Inst. Oswaldo Cruz 61(1):75-88. http://dx.doi.org/10.1590/S0074-02761963000100005
  2. Kolbe JJ, Glor RE, Schettino LR, et al (2004) Genetic variation increases during biological invasion by a Cuban lizard. Nature 431:177–181. doi: 10.1038/nature02807
  3. Kolbe JJ, VanMiddlesworth PS, Losin N, et al (2012) Climatic niche shift predicts thermal trait response in one but not both introductions of the puerto rican lizard anolis cristatellus to miami, florida, USA. Ecol Evol 2:1503–1516. doi: 10.1002/ece3.263
  4. Rakus, K., Ronsmans, M. and Vanderplasschen, A., 2017. Behavioral fever in ectothermic vertebrates. Developmental & Comparative Immunology, 66, pp.84-91. https://doi.org/10.1016/j.dci.2016.06.027

 

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