Bark Anole
Appearance: Anolis distichus, the bark anole, is a medium sized anole with a body color that varies from gray, to brown, to green – depending on the population. Body coloration is similar in both sexes but females can be distinguished from males by their lack of a dewlap, smaller adult size, and a relatively flatter head than males. Male dewlap color in this species is widely variable with populations ranging from pale white or yellow, to populations with variably sized red or orange spot in the center, to populations with entirely red or orange dewlaps. Bark anoles co-occur with a variety of species, most of which can be easily distinguished as different ecomorphs with larger heads or bodies such as Crown Giant and Trunk Ground anoles, or more slender frames such as of Trunk Crown, Grass Bush and Twig anoles. In Haiti and the Dominican Republic, the range of bark anoles overlaps with those of other closely-related trunk anole species – Anolis brevirostris, Anolis caudalis, Anolis marron, and Anolis websteri. These species all have a black spot on their neck, which is lacking in Anolis distichus.
Ecology and Habitat: Anolis distichus are trunk anoles, an ecomorph with a compact body plan – short snout and tail, with a relatively wide midsection. Trunk anoles like Anolis distichus primarily occupy the vertical surfaces of trees, usually below the canopy. They are found in a wide variety of natural habitats including xeric scrub to mesic humid forests as well as human-created habitats like buildings, parks, fruit tree groves, and residential areas. Unlike other ecomorphs that flee up trees or run to the ground when approached, bark anoles often shimmy to the opposite side of the trunk, a behavior commonly referred to as “squirrelling”. Bark anoles will eat nearly any prey that can fit in their mouth but their primary diet includes small arthropods like crickets, beetles, and even bees! Bark anoles are especially fond of ants.
Geographic Range and Biogeography: Bark anoles are native to Hispaniola (Haiti and the Dominican Republic) and the central Bahamas. Although they were once considered native to Florida, genetic data suggests these populations are the result of multiple introductions from Hispaniola and the Bahamas some of which occurred at least 50 years ago. They are thought to be introduced to Abaco Island in the northern Bahamas, but fossil evidence of this species on Abaco puts the status of this population into question. Phylogenetic evidence finds that bark anoles arose on the northern paleo-island of Hispaniola, dispersed over-water to colonize the the Bahamas, and spread to areas of to the southern Hispaniolan paleo-island after the two paleo-islands fused to form present day Hispaniola.
The immense variation in body and dewlap color in bark anoles has led to the description of 18 subspecies of Anolis distichus. Research currently underway seeks to understand if these subspecies are in the process of speciation or have perhaps already achieved species status.
Research Highlights:
Bark anoles have long been the intensive research effort with particular interest in using bark anoles to understand 1) the evolution of signals and 2) the process of speciation.
Most anole species possess and make extensive use of their colorful dewlaps for signaling to each other as well as other species. A series of studies led by Julienne Ng has shown that dewlap color is a heritable genetic trait and is associated with signaling environment that animal occupies. Exciting research, currently underway by Winter Beckles, seeks to understand if bark anole populations shift their dewlap color in response to changes in their light environment caused by hurricanes.
Julienne Ng has also found that some subspecies with different dewlaps interbreed freely over a wide geographic area. In contrast, other subspecies pairs are confined to a narrow hybrid zone suggesting that, for these subspecies pairs, hybridization may have negative fitness consequences and those populations may be in the process of speciation. Research I performed as part of my dissertation also found that transitions in dewlap color are associated with diversification events suggesting dewlap divergence may play in role in driving or maintaining speciation events. We also found evidence found that there are more distinct lineages that previously recognized within the Anolis distichus group and one subspecies in particular – Anolis distichus dominicensis is actually three separate lineages. Work I performed with undergraduate researcher (now Yale PhD student) Daniel MacGuigan used multispecies coalescent methods to assess if Anolis distichus represents a single species or multiple species. We found support for at least seven distinct species in the group, but at present we have not updated the taxonomy because the boundaries between these species remain unclear, particularly for the separate lineages of A. distichus dominicensis.
Species account author: Anthony J. Geneva
For more information:
- John David Curlis - March 1, 2022
- Joe Macedonia - January 31, 2022
- Lindsey Swierk - January 27, 2022