Hybridization in Puerto Rican Anoles

Our paper on hybridization between Anolis krugi and Anolis pulchellus is now available in the Journal of Evolutionary Biology. As is the case with many papers, this study requires an in-house description to fully appreciate its content. Furthermore, it is important to keep in mind that Javier and I have a very long working relationship (i.e., two decades and counting) and that we both enjoy working with each other under the assumption that "you can either agree with me or you can be wrong," which provides fertile ground for intense discussions and the development of new ideas. 

Javier taking a break after a long day of collecting

After our preliminary results suggested hybridization between A. krugi and A. pulchellus, I blamed Javier for not knowing how to tell apart the two species. My criticism was very short-lived, when he quickly reminded me, “you agreed with every one of my species IDs." The initial results were followed up by a more extensive collection across a wider geographic region. This was then followed by more genetic work, most of which has been spear-headed by Tereza. The genetic dataset, particularly the mtDNA data, confirmed the first set of results, indicating the presence of hybrid individuals across a wide range in western Puerto Rico (see map below). My first question was “can the hybrids represent a third species?” Javier's response: "Give me a break; that makes no sense. The hybrids are nested within groups of ‘pure’ individuals of A. pulchellus, and occur in multiple locations. There is no way that they can be a different species exhibiting such a pattern.” This sentiment was echoed by Tereza. I have to confess that “two against one” is not fair game. It has been great to work with Tereza on this project, as she has provided valuable insights to the development of the current hypotheses presented in the paper.

In the end, this has turned out to be an interesting story. The data clearly show extensive hybridization at some point in the past. NOTE: it might be possible that some events are relatively recent; we are working on that now. If hybridization is ongoing, we can ask a diverse set of questions, so we have our finger crossed. A potentially exciting possibility from our study is the idea of hybrid advantage, which may have resulted in what appears to be a complete replacement of pure A. pulchellus by hybrid individuals across a wide range. Javier's and Tereza's current working hypothesis is that the mtDNA of A. krugi provides some sort of physiological advantage to hybrids A. pulchellus allowing them to outcompete pure A. pulchellus. My working hypothesis, if there is a hybrid advantage, such and advantage is not physiologically. Instead it is behavioral, possibly link to levels of aggression of hybrids males. Please stay tuned, as we are beginning to tackle these questions.

Agressive display male A. pulchellus

Las Aciones Pesan Más Que Las Palabras (Actions Speak Louder Than Words)

As it has become part of the tradition of the Chipojo Lab, we had the honor of hosting another group of 7th and 8th graders . The main purpose of their visit was to interact with a Latino scientist, with the hope that they would realize that science is fun, can take place outside the laboratory setting, and is not limited to a small sub-section of the population. These are the types of opportunities that keep me going and that are central to my academic mission. The students were great, and we had a lot of fun using lizards as an example to tackle topics such as climate change, rapid evolution, and cognition.

Tierra de Gigantes (The Land of the Giants)

Our knowledge of the natural history of giant anoles, such as Anolis cuvieri, is relatively poor. Yesterday I had the opportunity to observe two events that are relatively rarely witnessed in this species. These included a male courting a female and a male-male agonistic interaction. Furthermore, the events occurred sequentially. First, a male began to display to a female and then chased her in an attempt to initiate copulation. As illustrated by the photo below, the copulation attempt progressed to the stage at which the male bites the nuchal region of the female while trying to orient his body properly.

A. cuvieri copulation attempt

Unfortunately for the first male, another male interrupted the copulation. Thus began a long period of aggressive displays between the males. This agonistic event included each male presenting laterally, dewlapping, head-bobbing, and opening its mouths with protruded tongue. Interestingly, neither male was willing to cede the "higher ground", resulting in both individuals constantly moving up their respective perches. Which lasted until both males reached the canopy of their respective perches, a point at which one of the males began to exhibit what appears to be submissive behaviors. These types of observations are clear reminders that "boots on the ground" are needed if we want to understand the complexity and diversity of social behaviors.

Males A. curvieri following the "higher ground" tactic 

     

   

Alsophis portoricensis foraging

Alsophis portoricensis is a rear-fanged colubrid and the largest of the two racers endemic to the island Puerto Rico. Anoles are a staple of their diet, as was the case for the male A. krugi in this photo. However, a close look at the picture shows that anoles are not a completely easy meal, and it is relatively common to find anoles biting the snake. In some instances with sufficient power to cause damage to the snakes, including loosing head scales. Also note, how the snake is trying to inject the venom (which is of the hemorrhagic type) by positioning the lizard at the rear portion of her jaw where the fangs are located.

Alsophis portoricensis feeding on A. krugi

         

Anolis occultus unveiled

Anolis occultus, a member of the twig ecomorph group, is one of the most secretive species of lizard found in Puerto Rico. However, today I was lucky enough to observe a male A. occultus drinking water from the surface of a leaf. It was an amazing few minutes; after a very light rain, the individual began to search for water droplets on the surface of leaves. This was done by slowly walking while searching for the droplets. Once a water droplet was found, the individual would approach it and very deliberately protrude his tongue to lick the droplet as shown by the picture below. 

Anolis occultus drinking water

As an "Experimental Natural Historian" these are the moments that remind me, why it is critical to be in the field as much as possible. It only took a few tiny rain droplets to elicit the behavior, immediately raising the question of how a lizard can sense such a few rain droplets.

Predation Green Iguana

Populations of the introduced green iguana (Iguana iguana) are becoming extremely dense in many areas of Puerto Rico, including the xeric region of Guanica the southwest region of the island. This trend is likely due in part to the fact that there are no large-bodied native lizards on the island and/or the diversity of potential predators is relatively low (i.e., limited to birds). However, as shown in the picture below, the birds of prey are beginning to exploit this "new" and extremely abundant resource. This juvenile iguana ended its days as the meal of a hawk, possibly a red-tailed hawk. The photo was taken at Guanica Dry Forest.   

Red-Tailied Hawk with a green iguana for feeding (his/her) nestlings

What are they eating? (via MANUEL LEAL)

Although we have visited our field sites in the Bahamas and Jamaica, the Chipojo Blog has been relatively quiet. I am currently in Puerto Rico and took the following picture yesterday, while working up in the canopy tower at El Verde. This is relatively common foraging behavior exhibited by A. stratulus. However, I have no idea what they are eating. Through my observations, I am convinced that they are not randomly "cleaning" everything off the leaves (i.e., once the individual is done, that area of the leaf appears cleaner than areas surrounding it). Instead, an individual will slowly walk over the leaf until it finds what he/she seems to be searching for before beginning to exhibit the behavior. Also, the lizards are not drinking water. There is no water on the surface of the leaves, and water-drinking is a very different behavior.