Panama – Anole Annals

Dan Nicholson at SICB 2020

Evolution has long thought to be a slow process, taking thousands if not millions of years. Recently, there has been a paradigm shift in how scientists think about evolution. We now know that we can observe evolution on a contemporary timescale, observable to the human eye. Dan Nicholson, a Ph.D. Candidate at Queen Mary University of London in Rob Knell’s lab, is working with Mike Logan and others to observe the effects of habitat change on the evolutionary ecology of Anolis apletophallus.

Dan and his team transplanted anoles from the mainland of Panama to several islands around Barro Colorado Island in July of 2017. Before release, they recorded the anoles’ morphological characteristics, including hindlimb and forelimb length, toe pad size, and head depth, and well as characteristics of their perch location, including height and width. Tracking changes in these characteristics can detect natural selection at work. At SICB 2019, Dan reported the results of the first generation of island anoles.

At SICB 2020, Dan included the trends of the second generation of island anoles. The preliminary results indicate the island anoles have continued to use wider perches than the mainland anoles. However, the majority of the island anole morphological traits now align with the mainland anoles. The exception is that hindlimb length of the island anoles decreased, while the mainland anoles hindlimb length has increased.

Some potential causes of these results, Dan speculates, include genetic drift due to the small population size. The islands started with a robust number of anoles, but over the two years of this study, their numbers have rapidly dwindled. Another possibility is the island anoles are aligning with the mainland anoles morphologically due to gene flow. In the future, Dan wants to further analyze the preliminary results from a population angle, looking at changes in groups of traits instead of individual traits.

You can learn more about Dan’s research by following him on twitter.

Anolis apletophallus from Panama, a well-studied species from the Panama mainland.

Over the past 15 to 20 years, the study of evolution has undergone something of a paradigm shift. Whereas scientists used to believe that evolution in most animals was a slow process, only observable over longer timescales, we now know that evolution is fast. Meaningful change can occur in many types of traits, including morphology and physiology, in just a handful of generations of a given organism. With this shift in our understanding, many biologists have begun conducting experiments which attempt to observe evolutionary processes in action, and shed light on how evolutionary mechanisms play out in the real world.

Dan Nicholson, a student in Rob Knell’s lab at Queen Mary University of London, worked with Mike Logan and a team of researchers to do just this in a tropical anole, Anolis apletophallus. Dan and his colleagues caught over 400 individual anoles from the mainland and introduced them to a novel environment: four small, anole-free islands formed when the Panama Canal was created. Two of these islands were similar to mainland habitats, while two had wider types of vegetation. Prior to placement on these islands, Dan measured a suite of characters of these individuals, including perch height, size, leg length, head, and toe morphology, enabling him to observe any changes in the distribution of these traits over time.

After leaving the anoles on their new tropical island homes for a year, Dan returned to recapture the survivors and measure both them and their offspring. By comparing the traits of the surviving lizards and their young with those of the population founders, Dan could observe changes in traits as well as measure natural selection on them. At SICB 2019, Dan reported that he found that anoles on islands with wider vegetation did indeed use these broader perches and that anoles also perched closer to the ground. Correspondingly, he found that toe pad size decreased and that hindlimb lengths were longer on some islands, potentially allowing lizards to better exploit lower, broader perches.

Anoles on all islands also showed a reduction in head depth. The reason is unclear, but Dan is looking into whether differences in competition or the prey community are potentially driving this pattern. Finally, measuring selection was very difficult and analyses proved problematic, though in some cases selection estimates do seem to match with observed changes in morphological characters. Dan and his team are hoping that adding data from another generation of anoles will clarify these effects, so stay tuned!

Keep track of the latest from Dan on Twitter: @DanJNicholson

Natural Selection on Morphology in a Tropical Lizard After a Rapid Shift in Habitat Structure NICHOLSON, DJ*; LOGAN, ML; COX, C; CHUNG, A; DEGON, Z; DUBOIS, M; NEEL, L; CURLIS, JD; MCMILLAN, WO; GARNER, T; KNELL, RJ; Queen Mary University London

Tag: Panama

SICB 2020: Impacts of a Novel Environment on a Tropical Anole Species

SICB 2019: Does a Tropical Anole Evolve When Colonizing a Novel Habitat?