Anolis carolinensis on Kauai. Photo by Jonathan Losos.

Green anoles (A. carolinensis) have been introduced to a number of Pacific islands, including Hawaii. In a recent paper in Current Herpetology (published by the Herpetological Society of Japan), Goldberg and Kraus examine the reproductive cycle of Hawaiian green anoles and find it very similar to what occurs in their native range.

Here’s the abstract of the paper:

Reproduction was studied in an invasive population of Anolis carolinensis in the Hawaiian Islands, USA. Timing of events in the reproductive cycle was similar between A. carolinensis populations in Hawaii and native populations of the species in the southeastern United States. In Hawaii, males of A. carolinensisundergo a prolonged period of spermiogenesis (sperm formation) starting in November (n=1) and December (n=1) and continuing into August. Gravid A. carolinensis females in Hawaii (n=40) produce one egg in continuous succession from March into August. Reproductive activity in A. carolinensis in Hawaii ceased prior to the colder, wetter, winter months.

Sperm of Anolis sagrei. Picture by Ariel Kahrl.

Caribbean anoles are making their way to Florida in all sorts of ways. Swimming across the sea is not one of them; however, once they arrive, some consistent and interesting patterns begin to emerge for something that swims inside them.

Sperm morphology can vary widely among individuals and between species, and this variation can be due to both intrinsic (genetic) and environmental factors. Large genetic variation in a trait means that the raw materials for evolution are abundant, and populations can diverge over space and time in relatively few generations. Much of this variation, however, could also be the result phenotypic plasticity since the environment that males experience during their lifetime can impact the shape and size of their sperm. Although previous studies have documented how sperm morphology can differ among populations, no studies have determined how introduction into novel habitats might influence this morphology.

Novel environments can influence traits through adaptive evolution, plastic responses to new conditions, or through random changes in gene frequencies (genetic drift and/or founder effects). Random changes in gene frequencies are likely to occur when populations expand into a new range because the founding population tends to be small and thus the gene pool is limited. By studying independent evolutionary trajectories (e.g. multiple species, or independent populations of the same species), we can rule out random changes in gene frequencies if the patterns we find are consistent among groups. As usual, anoles make excellent models for this work.

Ariel Kahrl and Bob Cox examined testis size and sperm morphology (head length, midpiece length, and tail length) for three species of Caribbean anoles (A. cristatellus, A. distichus, and A. sagrei) in their native ranges (Puerto Rico, Dominican Republic, Bahamas, respectively) as well as in Florida where each species is naturalized.

Although the results differed among species for some measures of sperm morphology, they found a few consistent patterns: sperm from introduced anoles had shorter tails and longer midpieces than those collected from native congeners (Figure 1). Furthermore, introduced populations had smaller testes than those from the native range.

Figure 1. Anolis spermatozoa (A). Population means +/- SE calculated from individual mean values (across 15 cells per male) for length of the sperm head, midpiece, and tail in native (black symbols) and introduced (white symbols) populations of three species of Anolis lizards. Significant differences between populations (P < 0.05) were determined using Tukey’s HSD test and are noted with an asterisk.

There are two main reasons that differences in sperm morphology between native and introduced populations are probably not the result of random genetic shifts. First, the size of the midpiece and tail correlate with swimming speed in sperm. The midpiece of the sperm is the housing unit for the mitochondria which powers the cell as it moves, and the length of the tail can directly influence the speed at which the sperm swims (longer tail = greater speed). Because the observed changes in morphology likely impact function, adaptive evolution may be the source of these population differences. Second, the observed differences between the native and introduced populations are fairly consistent among species. Were these changes due to genetic drift or founder effects, it is unlikely that all three species would demonstrate similar changes in morphology. This pattern is more indicative of convergent evolution or phenotypic  plasticity because the south Florida environment may generate similar plastic responses in all three species.

What is left to be determined are the proximate causes of these changes in sperm morphology. The observed changes could be due to the process of introduction per se, or they could be caused by unique features of the south Florida environment. Conveniently, many anole species have been introduced to new areas on multiple, independent occasions.  Adding more species from other introductions (e.g. green anoles in Hawaii; brown anoles in California or Taiwan) would provide further insight.

Kahrl, A.F. and Cox, R.M., 2017. Consistent Differences in Sperm Morphology and Testis Size between Native and Introduced Populations of Three Anolis Lizard Species. Journal of Herpetology, 51(4), pp.532-537. http://www.bioone.org/doi/abs/10.1670/16-184

A press release from Arizona State University:

Microscopic image of a 120-day regenerated lizard tail labeled with green fluorescent proteins that mark collagen. This image reveals the bony vertebrae of the original tail replaced with a cartilage structure that surrounds the spinal cord.

Photo: Joanna Palade

For those who travel with posters to conferences, here is a neat idea… have your poster printed on fabric. This one turned out really nice! Was done using Spoonflower in North Carolina (www.spoonflower.com). The cost is around $22.00 + shipping, but not having to travel with a poster tube is pretty enticing. I have no affiliation with company, just wanted to share. 

A female green anole from Hahajima in the Osagawara Islands.

We’ve had a series of posts about the anoles of the Osagawara Islands, of Japan, the “Galápagos of the Orient” [1, 2]. Now a new paper (pdf here) from Masakado Kawata’s lab has resequenced genomes of multiple individuals and measured morphology to assess how large the founding population was and what sorts of morphological changes have occurred since colonization, as well as identifying some genes potentially under selection.

Here’s the abstract:

Invaded species often can rapidly expand and establish in novel environments through adaptive evolution, resulting in devastating effects on native communities. However, it is unclear if genetic variation at whole-genomic levels is actually reduced in the introduced populations and which genetic changes have occurred responding to adaptation to new environments. In the 1960s, Anolis carolinensis was introduced onto one of the Ogasawara Islands, Japan, and subsequently expanded its range rapidly throughout two of the islands. Morphological comparison showed that lower hindlimb length in the introduced populations tended to be longer than those in its native Florida populations. Using re-sequenced whole genomic data, we estimated that the effective population size at the time of introduction was actually small (less than 50). We also inferred putative genomic regions subject to natural selection after this introduction event using SweeD and a method based on Tajima’s D, π and FST. Five candidate genes that were potentially subject to selection were estimated by both methods.The results suggest that there were standing variations that could potentially contribute to adaptation to nonnative environments despite the founder population being small.

The Seventh Anole Symposium is now only two months away (17-18th March 2018), so we are making a last call for registration for the meeting. If you want to attend please follow the link below to submit your registration by 11:59 EST January 31st to secure your spot. We will send out a payment link to registrants the following week.

Winning Symposium t-shirt design by Eric-Alain Parker

Click HERE to register

Looks like it’s time for an updated compilation of anole covers! This one’s from the December 2017 issue of Mesoamerican Herpetology. Here’s what they have to say:

Javier Sunyer is a Spanish herpetologist who has lived in the Neotropics for the last 20 years. His work includes over 80 scientific papers and notes, dealing mostly with the distribution, natural history, and conservation of the Nicaraguan herpetofauna. Currently, he is a Research Associate at the Universidad Nacional Autónoma de Nicaragua-León (UNAN-León) and an Associate Editor/Section Editor for Mesoamerican Herpetology. Pictured on our cover is an image of Kempton’s Anole (Norops kemptoni), photographed in January 2006 at Alto Chiquero, Parque Nacional Volcán Barú, Provincia de Chiriquí, Panama. Adult males are territorial, and often display their colorful dewlap to intruders.