Author: David Delaney Page 1 of 2

Chris Thawley at a crossroads.

Plants and animals across the globe are dealing with increasingly changing environments resulting from urbanization. One such habitat alteration is artificial light at night (ALAN) that may affect how animals acquire or use energy. Because brown anoles (Anolis sagrei) are common invaders of urban habitats, they make good models to examine the consequences associated with ALAN. Thus, Chris Thawley of Jason Kolbe’s lab at University of Rhode Island altered the level of ALAN on female brown anoles to examine how ALAN might affect morphology, reproduction, and stress.

If this sounds familiar, Chris talked about this work at the 2017 JMIH meeting, which caught Anole Annals press. To recap, Chris found that ALAN increased female growth, advanced the start of egg laying to earlier in the season, and increased the reproductive output of smaller females. However, he hypothesized that such beneficial effects would be countered by negative effects on other traits. Thus, Chris measured levels of the stress hormone corticosterone in the blood of females, hypothesizing that those exposed to ALAN would have higher stress. Although marginally non-significant, females actually tended to have lower corticosterone levels. Chris presented new data for this presentation showing that male corticosterone levels were unaffected by ALAN too, suggesting neither adult male nor female brown anoles have a stress response to artificial light.

Thus, it appears ALAN exposure over this 7-week study was beneficial for brown anole reproduction. However, Chris cautioned that there may be negative consequences on other traits such as immunity or HPA function. ALAN might also induce negative consequences for reproduction later in life, such as a reduced lifespan. I recommend keeping an eye on the Kolbe lab to find out!

Putter, Austin, and a real big tree they visited while travelling to the meeting.

The effect of urbanization on animals was the topic of many presentations at this year’s SICB meeting. One difference in the abiotic environment of urban areas is that they are often hotter than neighboring natural areas. Sarin “Putter” Tiatragul and colleagues (Josh Hall, Nathaniel Palik, and Dan Warner) at Auburn University are interested in whether urban environments might influence the nesting ecology and development of anoles. Thus, they set to the field to search for nest sites of the Puerto Rican Crested Anole (Anolis cristatellus).

Putter predicted females would choose warm, open-canopied nest sites at both urban and forested habitats, but that the availability of such locations would not be equal between sites. As predicted, randomly available areas in urban habitat had less tree cover and were warmer than randomly available locations in the forest. In the forest, females nested in locations that were similar to what was randomly available (no preference) in terms of distance to the nearest tree, canopy cover, and nest temperature. However, urban anoles nested in less open areas and closer to trees than what was randomly available in the urban habitat. This resulted in female-chosen nests sites being cooler than what was randomly available.

These findings suggest female anoles in forested areas are not choosing nest sites, probably because the forested habitat is homogenous and provides little variation to choose amongst. However, females in urban areas search out cooler microhabitats possibly to achieve favorable incubation conditions for their offspring. Putter also suggested these females may be simply nesting close to where they normally occur, which is close to trees. Either way, females are using the habitat differently in urban areas and such variation will likely have consequences for offspring during development.

An adult male brown anole.

Greetings anole biologists and enthusiasts! I write to you from Fred Janzen’s 30-year field site along the Mississippi River in northwest Illinois, where I’m collecting data for my dissertation studies. Unfortunately, there aren’t any anoles here, but the painted and common snapping turtle densities are impressive. Fortunately for this post, however, current field work has been paused as a team of inmates are cleaning up debris from recent flooding of the area. Thus, I’ll give a brief update on the last chapter of my master’s research with Dan Warner and the brown anoles* of northeastern Florida.

A good bit of Anolis work has shown that species partition perch height and width to reduce competition. However, less work has focused on habitat partitioning within species of anoles. Thus, my thesis work examined whether similar partitioning exists between age and sex classes of the brown anole, and attempted to identify the drivers and mechanisms of such age-specific habitat use. First, we found that juveniles on Dan’s study islands perch on lower and thinner perches, and use the ground more frequently, than adults (discussed in another Anole Annals post). We then altered the density of adult males in mesh enclosures in the lab, and found that juveniles perch lower in the presence of adult males and have a greater response as adult male density increases (discussed in another Anole Annals post also).

Juvenile Anolis sagrei survival in response to adult male and female density (F4, 164 = 3.67, P = 0.0069).

Quite excited by our findings that adult male density influences juvenile microhabitat choice, we set up two field experiments to assess 1) how adult male and female densities independently affect juvenile microhabitat use and survival, and 2) how juvenile presence affects adult male and female microhabitat use. Interestingly, we found that after just four days of exposure, adult male, but not female, presence reduced juvenile survival (Fig 1). However, we found no evidence that juveniles shifted microhabitat use behaviorally, nor were juveniles selected against in a pattern consistent with the observed age-specific habitat use in the field (e.g., selection favoring low perching juveniles) in response to either adult males or females. One large difference between the lab and field experiments is that the lab experiment used larger juveniles than the field experiment. Perhaps the smaller field juveniles innately perched in safe microhabitats, thus reducing their ability to behaviorally respond to adult threats. In addition, strong past selection favoring low perching hatchlings may have reduced the phenotypic variation needed to detect any selective patterns. The second field experiment revealed that adult microhabitat use is not affected by the presence of juveniles.

This last chapter has recently been published and is freely available through this link until 25 July 2017 (Delaney and Warner. 2017. Animal Behaviour 129:31-41). After that, shoot me an email.

For now, I’ll be studying fitness tradeoffs in maternal investment strategies in turtles. However, once an anologist, always an anologist. So I’ll keep an eye on Anole Annals to get my Anolis fix, until I find my way back south.

Happy noosing!

*Note – I’m certain that “Dan Warner and the Brown Anoles” should be a band name.

Fig 1. Photographs of the housing conditions used in the experiment. (a) One of the experimental enclosures (with an artificial tree) surrounded by blinds on all sides (note, the front blind was pulled back to reveal the tree and cage). (b) Close-up of the available horizontal perches. (c) Juvenile Anolis sagrei with its identification number on the lateral body surface for visual identification.

For many animals, optimal habitats vary across age classes, and individuals shift habitat use as they age. While many studies have documented such age-specific habitat use, most are observational and do not identify the causal factors. In addition, we know that competition between species has been an important driver of habitat use in Anolis lizards. However, less is known about the role of competition on habitat use within species of anoles, especially between age classes.

Dan Warner and I previously found that adults use higher and thicker perches than juveniles at our field site in northeastern Florida (Delaney and Warner 2016). We hypothesized that this variation was a result of adults forcing juveniles to suboptimal habitat. Thus, we altered the density of adult males in mesh enclosures (Fig. 1) in the lab and monitored changes in juvenile microhabitat choice.

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Ariel Kahrl, Christian Cox, and Bob Cox.

Sperm morphology is highly variable across animals and is a great model for studying the evolution of sexually selected traits.

Ariel Kahrl, a Ph.D. student in Bob Cox’s lab at the University of Virginia, gave a talk on a study which she and coauthor Cox did just that. They sampled sperm from native and introduced populations of Anolis sagrei, A. distichus, and A. cristatellus to look at variation in morphology.

Variation in sperm morphology between native and introduced populations of three Anolis species.

Interestingly, they found that introduced and native populations often varied in sperm morphology (i.e., head, midpiece, and tail lengths). Moreover, these effects were consistent between the three species tested!

Kahrl also pointed out that the variation observed in sperm morphology between males of a single species was often as large as that observed between different species. This study suggests that sperm morphology is highly plastic and/or is capable of rapid evolution in response to environmental change. Further work is needed to elucidate what selective pressures are driving the variation observed between introduced and native populations of these three species.

Slide from Michele Johnson’s SICB talk.

Muscles used for short, rapid movements should experience different physiological demands than those used for slow, stalking movements. Fortunately, lizards display a wide range of movement patterns from sit-and-wait foraging to slowly stalking prey. Thus, they are ideal for addressing questions on the evolution of muscle morphology, physiology, and behavior.

Dr. Michele Johnson and colleagues of Trinity University addressed such a question which Johnson presented during a talk at the SICB meeting in Portland. Although most studies of locomotion focus on the hindlimb, Johnson and colleagues wondered if forelimb muscle physiology is associated with lizard locomotor behavior. To address this, they made 30 minute observations on a minimum of 40 males of 6 species and recorded the frequency and type of locomotor behavior and social display. This information allowed them to classify lizards as “short-burst” species that often run, jump, and perform push-ups as a component of their social displays (green anole, Texas spiny lizard, northern curly tail) or “endurance” species that more frequently crawl (little brown skink, Mediterranean house gecko, spotted whiptail).

They found that short-burst species have more tonic fibers (involved in maintaining posture and balance) in the forelimb musculature, and endurance species have more twitch fibers (used during quick movement). In addition, species with more frequent locomotion had more twitch fibers. Relative fiber size increased in species that ran often and decreased with crawling behavior. Their study suggests that the evolution of forelimb fiber type is associated with the frequency of locomotion and that fiber size is associated with the speed of locomotion.