Category: New Research Page 27 of 66

Anolis carolinensis dewlapping. Photo by Cowenby available on Wikipedia.

On Sunday, Simon Lailvaux of the University of New Orleans gave one of the first anole talks of the SICB meeting, on his work examining the mechanisms underlying seasonal fluctuations in dewlap size. Simon began the talk by describing observations from field and lab studies (Irschick et al. 2006) that revealed that during the summer breeding season, when male anoles extend the dewlap frequently during behavioral displays, male dewlaps are much larger than during the winter nonbreeding season when the dewlap is used rarely. Simon and his lab then conducted a dietary-restriction study to test the hypothesis that this seasonal plasticity is due to resource availability, but found that diet was not associated with dewlap size (Lailvaux et al. 2012).  So, the search for the mechanism underlying this change in dewlap size was on.

Along with several colleagues from Trinity University – Jack Leifer (a materials engineer) and anolologists Bonnie Kircher and Michele Johnson (full disclosure – that’s yours truly), Simon and colleagues then conducted a laboratory experiment to determine whether reduced dewlap size related to less use in the nonbreeding season. To conduct the experiment, the researchers prevented dewlap extension in one set of male green anoles by tying dental floss loosely around their throats, and compared the dewlap size and skin elasticity of those lizards to an unrestrained control group that could dewlap at will. They found that dewlap size in the restrained group continually decreased over time, as compared to unrestrained lizards that, again, exhibited larger dewlaps in the breeding season. Together, these results suggest that use of the dewlap is directly related to its size. Then, the researchers measured the elasticity of dewlap and non-dewlap (belly) skin, and found that the dewlap is more elastic than belly skin, and that both types of skin samples were more elastic in the summer breeding season than in the winter. Because skin is a dynamic tissue whose mechanical properties are altered by sex steroid hormones, Simon suggested that dewlap size plasticity may be the result of seasonal endocrine fluctuations, combined with behavioral use of the structure.

These results suggest so many next steps.  Look for the upcoming manuscript describing this work in more detail!

References

Irschick, D.J., Ramos, M., Buckley, C., Elstrott, J., Carlisle, E.,Lailvaux, S.P., Bloch, N., Herrel, A. and Vanhooydonck, B. 2006. Are morphology -> performance relationships invariant across different seasons? A test with the green anole lizard (Anolis carolinensis). Oikos 114: 49-59.

Lailvaux, S.P., Gilbert, R.L. and Edwards, J.R. 2012. A performance-based cost to honest signaling in male green anole lizards (Anolis carolinensis). Proceedings of the Royal Society of London B: Biological Sciences 279: 2841-2848

Lauren Davis presenting her work on invasion success in lizards.

As our planet becomes increasingly connected and humans facilitate novel species interactions, we must ask why some introduced species are destructive and others relatively harmless. Lauren Davis, a senior in Dr. Michele Johnson’s lab at Trinity University, conducted a study on behaviors, and their neural correlates, that may influence the invasiveness of non-native lizards. She compared the invasive Anolis sagrei to the native Anolis carolinensis, the invasive House Gecko (Hemidactylus turcicus), and the native Texas Banded Gecko (Coleonux brevis). They hypothesized that highly invasive species display more ‘bold’ behaviors (in this case, the number of enclosure boundaries crossed during an experimental period) and have larger and/or denser neurons in associated brain regions than less invasive species. While there are many documented behavioral trials with boldness in Anolis, geckos have received little attention in this regard. Lauren and her fellow researchers found that A. sagrei is indeed bolder than A. carolinensis, but that the two gecko species do not differ in traits associated with the boldness syndrome (Fig. 1).

Figure 1: Invasive Brown Anoles are bolder than native Green Anoles

The researchers also found that neuron size in brain regions known to influence boldness and aggression were opposite than expected values, so the team plans to analyze neuron density in these regions to help explain the observed behaviors. This is one of the first studies comparing behavior and brain morphology to invasion success, and it paves an exciting path towards our understanding of species interactions in our changing world.

Lauren is graduating in May, and hopes to work in conservation or public health before continuing her education in graduate school.

Anolis sagrei mating. Taken from the Cox lab website.

On the first day of SICB 2015 Robert Cox gave an interesting talk about reproductive investment and sexual selection in lizards. At the center of his talk was the striking notion that males and females are different biologically, yet should still be integrated into cohesive theories of sexual selection. According to Dr. Cox, past theory has generated mutually exclusive ideas about the costs of reproduction for each sex. Whereas theories about females have focused on life history and investment in the egg and offspring, theories about males have focused on mating investment. Cox stressed that this is overly simplified and doesn’t reflect biological reality,  as males and females also share many of the same costs of reproduction as well. Issues like growth, survivorship, energy storage, and parasite load are shared between the sexes. Dr. Cox is now trying to test how sex-specific reproductive mechanisms affect these shared reproductive constraints by surgically removing the gonads of each sex. Preliminary analyses show that parasite load appears to be a shared effect among the sexes regardless of the underlying mechanism (testosterone derived from testes versus estrogen derived from the ovaries). Studies directly comparing the underlying mechanisms of sexual dimorphic anatomy, physiology, and behavior are critical for the further development of sexual selection theory and for improving our understanding of anoles. Studies like Dr. Cox’s are an important step in that direction.

Anolis cristatellus in Miami, Florida. Picture by Jason Kolbe.

Humans and wildlife are sharing the same spaces more and more frequently, but there’s still much that we do not know about how animal behavior is altered in urban environments. To address these questions, graduate student Kevin Avilés-Rodriguez (pictured below) and Dr. Jason Kolbe of the University of Rhode Island studied the responses of Anolis cristatellus to simulated predators in urban and natural environments in Puerto Rico. They found that lizards in an urban habitat had shorter flight initiation distances (the distance a simulated predator – in this case, Kevin – could approach before the lizard fled) than in a natural, forested site.  In addition, lizards’ predator-escape behaviors generally corresponded to the sizes of their perches and to their proximity to vegetation, but perch types differed between the urban and natural sites.  Whereas lizards in natural habitats tended to jump into nearby plants to escape, urban lizards tended to avoid capture by squirreling on larger, more isolated perches.  Kevin also reported that lizards perching on cement walls had adjusted their predator responses dramatically, as they generally did not jump or squirrel. In sum, this study suggests that habituation to humans and/or human-shaped habitats have altered the responses of these lizards to potential predators in important ways.

Kevin Aviles, stalking lizards in the field. Photo from Kolbe lab website.

How do lizards move in nature? Note the added emphasis on “in nature.” For many years people have studied the mechanics and patterns of of lizard movement and anoles have played an important role in this research. But today Jerry Husak of the University of St. Thomas in St. Paul reminded us that most of this research has focused on characterizing maximum performance ability, despite the fact that  animals rarely achieve this level of activity in nature. For example, most of the time many lizards are merely scurrying about on the ground and not sprinting at their full ability. Hence, although measuring maximal spring speed in the lab is a common theme, this measurement may not actually reflect what animals do in nature. Dr. Husak also stressed to the audience that animal locomotion is context dependent. Specifically, a lizard’s speed depends on whether it is moving in grass or over rocks, and whether it is foraging or fleeing from a predator. During his enlightening discussion, which included a description of him trying to sprint on a frozen Minnesota sidewalk, Dr. Husak described a series of biotic and abiotic factors that should be incorporated into models of terrestrial lizard movement.  Finally, he concluded by challenging our obsession with maximum sprint speed once again by asking whether running at top speed can lead animals to make to costly mistakes. Based on a set of foraging data, he showed that this may be the case.  Dr. Husak’s talk highlighted the importance of understanding the natural habits of lizard behavior and performance. 

When I was a kid, the first week of January used to be such a bummer for me because it meant that the holidays were over. But now the first week of each year means that the annual meeting of the Society for Integrative and Comparative Biology (SICB) is underway! The meetings run from January 3rd until January 7th, and there are 30 talks/posters this year about anoles! I won’t be attending this year, as I’m currently based out of Australia (AKA land of no anoles), so I’ll be looking forward to the posts on this blog to hear what’s new and exciting in Anolis research. Stay tuned!

Hey, that’s not an anole! American Rubyspot Damselfly (Hetaerina americana). Copyright Steve Collins

My colleagues and I recently published a paper documenting character displacement in Anolis carolinensis following the invasion of A. sagrei into Florida. The former moved up into the trees and evolved larger toepads. We did a lot of work in that paper to show with a high degree of certainty that the interaction between the two species is what led to character displacement in A. carolinensis. However, an open question remains as to exactly what kind of interaction, or interactions, they share. Most likely, the two species are competing for food (i.e. exploitative competition). They may also be interacting indirectly through a shared predator or parasite (i.e., apparent competition), and they are  known to eat each other’s hatchlings (i.e., intraguild predation).

Today, I’d like to explore another possible interaction in depth: perhaps the two species have diverged to lessen aggressive interspecific interactions for space and territory (i.e., interference competition). For more, let’s turn to the anoles of the Odonata world (provocative statement, I know!): rubyspot damselflies (Hetaerina spp).

In a recent issue of the Proceedings of the Royal Society B, Jonathan Drury and Greg Grether investigated the role of aggressive (or agonistic) interactions in driving divergence between two species of rubyspot damselflies.

Previous work [1,2,3] in Grether’s group had shown that male competitor recognition in rubyspot damselflies depends on hindwing coloration, and that cross-species recognition and male wing coloration diverges between species living in the same area. This suggests that aggressive interactions between males of different species have driven divergence in wing color to reduce the frequency of energy-intensive, aggressive interactions between species. This divergence is consistent with a type of character displacement called Agonistic Character Displacement (ACD), which is the divergence between species in some sort of species recognition trait to lessen the negative effects of aggressive encounters.

However, another type of character displacement, Reproductive Character Displacement (RCD) is also consistent with these previous findings. RCD is divergence, usually in some sort of mate recognition trait, between two species. By diverging in such a trait (think anole dewlaps), males and females of different species are less likely to spend precious time courting or mating in wasteful, failed cross-species reproductive efforts.

By this point, you, the astute reader, may have noticed that both ACD and RCD predict changes in signaling traits–the former species recognition traits, and the latter mate recognition traits.

Whenever the same trait functions as a signal for both species and mate recognition, and that does happen often, telling apart the action of these two distinct processes (i.e., selection to reduce wasted aggressive effort versus selection to reduce wasted reproductive effort ) can be very difficult*.

Drury and Grether designed a very nice test for successfully discerning between these two hypotheses.

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Winter is coming to the Northern Hemisphere, which can only mean one thing: SICB is upon us. Every January, the Society for Integrative and Comparative Biology (SICB) hosts its annual meeting. SICB 2015 will take place in West Palm Beach, Florida. Perhaps it’s due to the fact that southern Florida is the global epicenter for Anolis invasions, but talks and posters about anoles will be particularly numerous at this meeting. By searching for presentations containing the keyword “Anolis,”,  got 30 hits! That’s a much better turnout than the last few years, and hopefully a sign that Anolis presence at large annual meetings is on the rise. What’s more, there are two Anolis talks scheduled for the Huey symposium. This symposium is a competition for the best student talk hosted by the Division of Ecology and Evolution, and is named after anolologist and distinguished evolutionary biologist Ray Huey. I won’t be there this year, but I look forward to reading about all the new and interesting research involving anoles on this blog. Best of luck to all the presenters!