All posts by David Delaney

About David Delaney

David is a Ph.D. student in Fred Janzen's lab at Iowa State University. He is interested in predator/prey relationships and microevolutionary processes.

Effects of Age- and Sex-specific Density on Behaviour and Survival of the Brown Anole

A perching brown anole.

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).

Fig 1

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.


Adult Male Density Influences Juvenile Microhabitat Use in Brown Anoles

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.

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.

Continue reading Adult Male Density Influences Juvenile Microhabitat Use in Brown Anoles

SICB 2017: Impacts of Urbanization on Morphology, Thermal Preference, and Parasitism

Chris Thawley at a crossroads.

Chris Thawley at a crossroads.

Urban environments are widespread and expanding across much of the earth, and this urbanization likely affects the flora and fauna in its path. Anoles are no exception and are frequently observed perching on anthropogenic structures. Thus, Chris Thawley, a post-doc in Jason Kolbe’s lab at the University of Rhode Island, and colleagues wondered how the abiotic and biotic changes in urban areas influence anole traits.

Thawley compared populations in urban and natural habitats of two species that we’re quite familiar with on Anole Annals – the Brown Anole (Anolis sagrei) and the Puerto Rican Crested Anole (Anolis cristatellus). Thawley found that A. sagrei prefers warmer temperatures than A. cristatellus, but that urban anoles do not differ in thermal preference than natural anoles for either species. Alternatively, urban male A. cristatellus and both sexes of urban A. sagrei were larger than their natural counterparts. As for parasites, A. sagrei had a higher parasite prevalence than A. cristatellus, but urban anoles did not differ from natural anoles in either species in parasite prevalence. However, for the A. sagrei that were parasitized, urban A. sagrei had higher parasite loads than natural A. sagrei.

These findings show that urbanization can influence anole morphology and parasite ecology. Thawley has just begun this work, and I look forward to seeing his future research on anole adaptation to urban environments!

SICB 2017: A Field Based Approach to Study Behavioral Flexibility


Levi Storks explains his project in New Orleans.

Most animal learning studies have been conducted in the lab with the assumption that those findings are representative of behavior in the field. However, assessing behavior in the field increases ecological relevance. In addition, birds and mammals have received much of the attention in cognitive studies. Yet we on Anole Annals know that these lizards can be quite clever.

Levi Storks, a Ph.D. student in Manuel Leal’s lab at Mizzou, set out to address these issues by designing a method for testing behavioral flexibility in brown anoles (Anolis sagrei). Wild lizards in the Bahamas were allowed to feed unrestricted on a maggot placed in the middle of a testing apparatus in order to acclimate lizards to the structure. Storks then used a clear plastic tube to block the direct route to food, requiring lizards to move to either end to gain access. Lizards that successfully completed this task were then tested to see if they could associate unique patterns on the ends of the tube with single openings.

Storks found that a subset of lizards could successfully complete the first detour task, and lizards made fewer errors over the course of solving the detour task. These findings suggest brown anoles can learn and exhibit behavioral flexibility. Stay tuned for more of Levi’s work as he’ll be applying these methods to assess differences in behavioral flexibility between populations that vary in ecology!   


Does Perch Availability Affect Reproduction in Brown Anoles?

Anolis sagrei - male and female

Effect of perch treatment on (A) latency to reproduce and (B) yolk corticosterone.

Effect of perch treatment on (A) latency to reproduce and (B) yolk corticosterone.

Competition for perches has been an important factor in the diversification of anoles. Yet, we know little about the influence of perch availability on reproduction. To address this, Dan Warner, Matt Lovern, and I housed male / female pairs of brown anoles (Anolis sagrei) in treatments with either high- or low-availability of perches (Fig. 1).

We found that females reduced how often they used perches when perches were limited. More interestingly, though, when perches were limited, females tended to take longer to begin laying eggs (for the first time in a season; p = 0.063, Fig. 2A) and allocated more corticosterone to egg yolk (p = 0.069, Fig. 2B), although these findings were not statistically significant.

Effect of perch treatment on (A) latency to reproduce and (B) yolk corticosterone.

Figure 2. Effect of perch treatment on (A) latency to reproduce and (B) yolk corticosterone.

In many habitats in which brown anoles occur, organic perches are abundant and not likely to be limited. However, in urban areas or on some islands anoles have colonized, perches can be limited. Our study suggests that such habitats may have consequences for reproduction.

Citation for the full paper:

Delaney, DM, MB Lovern, and DA Warner. 2016. Does reduced perch availability affect reproduction in the brown anole? An experimental test in the laboratory. Journal of Herpetology 50:227-232.

Age- and Sex-Specific Variation in Habitat Use by Brown Anoles

Little guys like it narrow. Photo from Daffodil’s Photo Blog.

The influence of habitat use on ecological and evolutionary patterns in Anolis lizards is well documented. Despite extensive work on interspecific variation, how habitat use varies within a species is relatively understudied.

As part of my master’s work in Dan Warner’s lab, we caught and recorded the perch height, width, and substrate (i.e., ground vs. vegetation) of 717 brown anoles (A. sagrei) on a small island in the Halifax River, near Ormond Beach, Florida. The island consisted of two main habitat types (open-canopy and forest) with an intermediate between the two.

Continue reading Age- and Sex-Specific Variation in Habitat Use by Brown Anoles

SICB 2016: Variation in Sperm Morphology of Native and Introduced Populations of Three Anolis Species


From left to right, Ariel Kahrl, Christian Cox, and Bob Cox.

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.

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.

SICB 2016: Tradeoffs between Endurance and Speed in Lizards

Slide from Michele Johnson's SICB talk.

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.

SICB 2016: Phenotypic Correlations Suggest Thermal Adaptation Is Constrained in Lizards and Ladybugs

A male brown anole basking on a tree.

A male brown anole basking on a tree.

Theory predicts that as environmental temperatures change, animals that function better at the new temperatures will be favored by natural selection. Thus, we might expect that climate warming will select for animals with higher thermal optimums (Topt). In addition, thermal performance curves are also characterized by the breadth of temperatures that animals can function. Theory predicts that increases in environmental temperature variation will select for animals with larger thermal breadths (Tbr). Previous work has shown that brown anoles transplanted to a warmer environment experienced strong directional selection favoring individuals with higher Topt and Tbr (Logan et al. 2014). However, it is unclear if selection acts on these two traits independently or if they might be genetically constrained.

Mike Logan, an NSF postdoctoral fellow at Stellenbosch University, gave a talk on a study that he and coauthors (John Curlis, Ingrid Minnaar, Joel McGlothlin, Susana Clusella-Trullas, and Bob Cox) conducted to test this question. They brought brown anoles into the lab and found a significant negative correlation between Topt and Tbr, suggesting that increases in one trait lead to reduction in the other. To test the generality of their findings, they brought ladybugs into the lab and conducted similar trials. Interestingly, they found the same results for ladybugs. This study suggests that these thermal adaptations are evolutionarily constrained in two very distant relatives.

Logan, M. L., Cox, R. M., & Calsbeek, R. 2014. Natural selection on thermal performance in a novel thermal environment. Proceedings of the National Academy of Sciences 111(39):14165-14169.