All posts by Julienne Ng

About Julienne Ng

I study the evolution of color signals. My PhD at the University of Rochester focused on the evolution of dewlap diversity in Anolis distichus. I am currently a postdoc at the University of Colorado Boulder studying the evolution of flower color.

Signals and Speciation: Do Dewlap Color Differences Predict Genetic Differences?

Dewlap and genetic differences between co-occurring Anolis distichus and A. brevirostris

Dewlap and genetic differences between Anolis distichus and A. brevirostris at sites where they co-occur on Hispaniola.

Here at Anole Annals, we’re all familiar with the replicated evolution of different anole ecomorph types in the Greater Antilles. However, divergence into these different ecomorph classes is not enough to explain how the group became so speciose on these islands. Additional factors must therefore have promoted speciation throughout the history of the group.

One potential factor is the flashy anole dewlap. Dewlap diversification across anoles has led to the remarkable array of dewlap color, pattern and size we see today. If dewlap differences did indeed drive speciation in anoles, or are involved with the maintenance of species boundaries, we might expect that as differences in dewlap color and pattern increases between species, genetic differentiation will also increase through fewer hybridization events.

In our study that just came out in the Journal of Herpetology, Rich Glor, Anthony Geneva, Sabina Noll and I set out to test this using two widespread species from the Anolis distichus species complex, A. distichus and A. brevirostris. These two species co-occur in many locations on Hispaniola and, while they often differ in dewlap color where they do co-occur (yellow with an orange patch vs. all pale yellow), in other areas, they co-occur with similarly pale dewlaps. Using mitochondrial DNA, microsatellite and AFLP data, we investigated patterns of genetic differentiation at four sites: two where the species differ in dewlap color, one where the species share the same dewlap color, and another where pale dewlapped A. brevirostris co-occurs with two A. distichus subspecies (one with a similarly pale dewlap and the other with an orange dewlap).

In general, we found that A. distichus and A. brevirostris looked like “good species,” with strong genetic differentiation and little evidence of hybridization, even at a site where they share the same dewlap color. This suggests that dewlap color differences are not associated with genetic differentiation in a manner one might expect if dewlaps were involved in the speciation process or in maintaining species boundaries. However, at the site where A. brevirostris co-occurs with two A. distichus subspecies with both similar and dissimilar dewlap colors, we found some evidence of hybridization and the species were not as highly genetically differentiated. This discrepancy suggests that site-specific factors could be influencing the dewlap’s role in speciation or maintaining species boundaries. For example, as Leo Fleishman’s and Manuel Leal’s work has shown (e.g. 1, 23), the dewlap’s effectiveness as a signal is dependent on the light environment. Further understanding about the environmental differences among our study sites, how species utilize the available light microhabitats within each site, and how the dewlap looks to anoles at each site could provide more insight into our findings.

On the other hand, perhaps we need to be looking beyond the dewlap and focusing instead on whole signaling displays. Anole behavioral displays can also be strikingly different among species (e.g. 1) and may instead be the key to understanding species diversification in Greater Antillean anoles.

The Genetic Consequences of Adaptive Dewlap Divergence

Figure 1 from Ng et al. 2016 showing the transect sampling spanning Anolis distichus populations differing in dewlap color (T1-4) as well as control transects (C1-4). Pie charts show dewlap color variation (top row), mitochondrial clade membership (middle row) and nuclear genetic cluster assignments (bottom row).

Figure 1 from Ng et al. 2016 showing the transect sampling spanning Anolis distichus populations differing in dewlap color (T1-4) as well as control transects (C1-4). Pie charts show dewlap color variation (top row), mitochondrial clade membership (middle row) and nuclear genetic cluster assignments (bottom row).

We sure love dewlaps here on Anole Annals! These flashy signals are incredibly diverse in size, color and pattern, and always make for a gorgeous image (e.g. 1, 2). Yet, we still have much to learn about why there is such a diversity of dewlaps and, furthermore, what are the consequences of such diversity? Previous work by Leal and Fleishman (2002, 2004) suggests that some of this dewlap diversity is due to adaptation for more efficient communication in different habitats. In a recent paper, we sought to identify whether the consequence of such adaptive trait divergence was speciation, or whether locally adapted dewlaps are maintained despite gene flow.

Anolis distichus shows remarkable geographic variation in dewlap color that predictably varies with habitat in a manner consistent with adaptation (Ng et al. 2013). This variation in color across Hispaniola gave us a great opportunity to conduct replicated analyses to identify whether adaptive differences in dewlap color consistently leads to the same genetic outcome.

We sampled populations in the Dominican Republic along five transects that transitioned from populations with orange dewlaps to those with cream or yellow dewlaps. For a comparison, we also sampled four ‘control’ transects where all populations shared a similar dewlap color. If dewlap differences are associated with speciation, we expected to see genetic differentiation between populations at either ends of the transect as this would suggest some level of reproductive isolation. Otherwise, transects showing no evidence of genetic structure would suggest that individuals are freely mating regardless of dewlap color.

Looking at the genetic structure of both nuclear and mitochondrial DNA along each transect, we found that geographic variation in dewlap color is associated with both speciation and gene flow. Three transects showed distinct genetic structure consistent with speciation, with one in particular only showing evidence of hybrids at one site which was a mere 0.89-1.55km away from other sampled sites. On the other hand, the other two transects did not look much different to the control transects, suggesting ongoing gene flow regardless of phenotypic differences.

Considering all transects together, I think there are two main take-aways from our results. First, finding evidence of gene flow across a sharp geographic shift in dewlap color must mean that strong selection is maintaining geographic variation in dewlap color; perhaps due to adaptation to different habitat types. Second, it appears that dewlap divergence does not necessarily lead to speciation. More work, however, is needed along these lines to understand whether the dewlaps we are characterizing as different are actually different from an anole’s perspective or in particular light environments (e.g. 1).

Divergence and Speciation in the Lesser Antilles

Fig. 1 from Muñoz et al.: Anolis marmoratus subspecies on Basse Terre (left) and Grande Terre (right)

Fig. 1 from Muñoz et al. (2013) Anolis marmoratus subspecies on Basse Terre (left) and Grande Terre (right)

Unlike the extensive within-island speciation that anoles have undergone in the Greater Antilles, we have no evidence that the same has occurred in the Lesser Antilles. Rather, Lesser Antillean islands that contain two species are thought to be the result of dispersal events rather than in situ cladogenesis. Despite such low species diversity, however, phenotypic diversity on many of these islands certainly is not lacking. Some Lesser Antillean anoles exhibit spectacular geographic variation in head, body and dewlap colouration and pattern, as well as body size and scalation, that appears to be adaptive to different environments. So, while this variation has not led to complete speciation in any Lesser Antillean anole, is there some evidence that these phenotypically divergent populations are at some stage of the speciation process? Also, how does phenotypic divergence occur on these smaller islands when there seems to be little opportunity for geographical isolation?

AA contributor, Martha Muñoz and colleagues tackle these very questions in a recent paper in Molecular Ecology. Muñoz et al. focus on the stunning phenotypic diversity of the Anolis marmoratus complex on Guadeloupe, which has been categorised into 12 subspecies. On Grande Terre, in particular, two subspecies can be found: A. m. speciosus inhabits mesic habitats in the southwest and A. m. inornatus inhabits the xeric lowlands of the north and east. Males share a yellow-orange coloured dewlap but differ in head, body and eye ring colouration, while females and juveniles of the two subspecies are similarly drab in colour. Continue reading Divergence and Speciation in the Lesser Antilles

Female Dewlaps

Fig. 1 from Harrison and Poe illustrating dewlap differences between males (top) and females (bottom).

The function and evolution of anole dewlaps have been the focus of studies for decades. As flashy, showy displays of color, it’s no wonder that dewlaps even captured the attention of Darwin. However, most studies to date have focused solely on male dewlaps leaving female dewlaps much neglected (but see Johnson & Wade, 2010 and Vanhooydonck et al., 2009). While the possession of dewlaps is less common in females than males, and female dewlaps are often rather diminutive compared to the male’s, the mere presence of female dewlaps in a good number of species, combined with striking variation in color, pattern and size across the genus, begs the question of what is driving the evolution and maintenance of such female ornamentation? Continue reading Female Dewlaps

Evolution of a Lizard Room, Part VIII: Egg Incubation

Incubating eggs

Incubating eggs

As Dan Warner mentioned in a recent post, moisture availability is extremely important to the development and survival of anole embryos. Throughout our time breeding anoles in the lab, we have experimented with different methods of incubating eggs, including different substrates (potting soil, a mixture of soil and vermiculite, and just vermiculite), differing proportions of water and vermiculite, and supplementing substrate with water throughout incubation. We have now settled on a recipe that seems to minimize death, mould, and desiccation in our Anolis distichus eggs.

We currently start by mixing a recipe that combines 220g of vermiculite with 380g of water. According to a water potential curve for vermiculite, this mixture has a water potential of -150kPa. We then put 130g of the mix into clear small deli cups which have pre-punched holes on the side for ventilation. The clear cups make it easy to quickly monitor eggs and to spot new hatchlings. We store these cups in our lizard room at a temperature of about 29C.  As eggs get older they are gradually rotated closer to a small fan that is set on a timer to run 10 mins twice daily to increase airflow. We’ve found that the recipe we’re using does not require addition of more water during incubation.

I’ve heard and read about many different ways that people are treating anole eggs and would love if AA readers shared how they take care of their anole eggs!

Anole Research at Animal Behavior Meeting in Summer of 2011

Thom’s recent post on the upcoming SICB meeting reminded me that I was yet to share the anole research I learned about at the Animal Behavior Meeting this past summer in Bloomington, Indiana. There were just a handful of presentations on herp research during the meeting, and I was excited to see that there were others presenting work on anoles:

Sarah Flanagan presented work from her Honors thesis with Catherine Bevier whereby she used mate choice experiments to test whether female Anolis sagrei prefer males with greater physiological capacities and/or higher quality territories. Sarah’s study showed that females preferred males with depleted liver glycogen (glycogen levels were measured in leg muscle and liver samples after mate choice trials). Females, however, did not show a preference for males in a territory filled with plants over males in bare territories. Continue reading Anole Research at Animal Behavior Meeting in Summer of 2011

Evolution of a Lizard Room, Part IV: Crickets

Left: Tubs used to house crickets. Right: The set up inside a cricket tub.

To continue our series on lab anole husbandry, let’s talk food! We feed our room full of hungry anoles Acheta crickets ordered from Fluker Farms. We house crickets in 21-gallon plastic tubs (bought from places like Target or Home Depot) that have been modified for ventilation – we cut holes in the lids and glue wire screen on top. We provide egg layer mash for food, water crystals (usually used for plants) on a small deli cup lid for water, and egg crates to give them places to hide. Continue reading Evolution of a Lizard Room, Part IV: Crickets

Evolution of a Lizard Room Part I: Introduction

Anolis carolinensis hatchling and the egg from which it hatched

Breeding anoles to look at inheritance of dewlap color has been a major component of my research. It has also, however, been a major frustration. Every step of the process, from keeping the anoles happy enough to reproduce, to finding eggs, to successfully raising healthy hatchlings to adults has required much tweaking over the years. It has certainly been a work-in-progress and I am happy to say that with both minor and major changes over the years, our lab has transformed into a baby-making factory! This post is the first of a series discussing aspects of anole care, in the hope of both sharing our ideas with people in the anole community, as well as to start a discussion on other techniques people are using to breed/care for anoles. Continue reading Evolution of a Lizard Room Part I: Introduction