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Anolis morazani. Photo by Josiah Townsend from iNaturalist.

The Anolis crassulus subgroup contains ten morphologically-conserved highland anole species found throughout Nuclear Central America. Its members have long been a source of headache for region’s systematists. To quote Meyer & Wilson (1971): “…specimens of the crassulus group from Guatemala and Mexico have a bewildering array of admixtures of the distinctive characters observed in Honduras… The inter-relationships of the populations… [of the crassulus group] are exceedingly complex, and… we are unable to suggest a satisfactory arrangement.” This was followed up 21 years later by McCranie, Wilson, & Williams (1992): “Clearly, a thorough analysis of crassulus-like specimens from throughout their range… is sorely needed”, and repeated by McCranie & Köhler (2015) 13 years after that.

Despite the need for a thorough investigation into this group, our understanding of the relationships and validity of these taxa has not improved much. This is partly because this subgroup has been poorly represented without broad sampling in larger-scale molecular phylogenies. Two samples in particular, an A. crassulus (from Chiapas, Mexico) and an A. sminthus (from Olancho, Honduras), have been continuously utilized, without additional samples from these species. Most recently, Nicholson et al. (2017; six species) and Poe et al. (2017; three) expanded the molecular sampling for this group, using single exemplars as part of broader analyses.

In a study published last month in BMC Evolutionary Biology, Josiah Townsend and I examined the evolutionary relationships of the majority of this subgroup, in order to provide a starting point for resolving some of the confusion surrounding these taxa.

Fig. 4 from Hofmann & Townsend, 2017: Species tree of the Anolis crassulus subgroup. Black nodes indicate PP > 0.95; PP < 50 not shown. Inset photo: Anolis heteropholidotus (2) by JHT.

The results of our multilocus phylogenetic investigation gave us some interesting new insights into the subgroup. We found support for the monophyly of the A. crassulus subgroup relative to other Anolis (as opposed to its paraphyly, as recovered in Poe et al. 2017), and the validity of all of its species (excepting the two we could not sample). Additionally, we recovered considerable overlooked diversity within this subgroup. Anolis crassulus itself represents at least four lineages corresponding to distribution: the Chortis Highlands of Honduras, the Salvadoran Cordillera, Guatemala, and Chiapas, Mexico. Surprisingly, the sample from Chiapas previously used in many phylogenies was recovered as an undescribed lineage sister to A. anisolepis, not conspecific with any of the four A. crassulus lineages, including another Chiapan lineage. We also recovered the widely-used “A. sminthus” sample (which was previously hypothesized by McCranie and Kohler (2015) as representing an undescribed lineage more closely related to A. crassulus) as an undescribed lineage sister to A. morazani, and found additional mitochondrial lineages within A. heteropholidotus and A. rubribarbaris. Diversification within the group was estimated to have started in the early Miocene in the Chortis Highlands (supporting the results of Nicholson et al. 2017), with the Honduran population of A. crassulus diverging from the other three lineages approximately 13 MYA.

Fig. 5 from Hofmann & Townsend, 2017: Chronogram showing results from divergence dating and ancestral area reconstruction analyses. PP shown when < 1.

Given the relatively deep divergence times within this group when compared with the apparent lack ecological and morphological diversification, we hypothesized that this subgroup represents a non-adaptive radiation, though extensive study is necessary to determine if these traits are as conserved as they appear. A taxonomic revision of the Chortis Highland population of Anolis crassulus is being finalized, but a great deal of work remains in order to improve our understanding of these highland anoles.

One more update from the SICB conference in San Francisco last week!

Across vertebrates, the ratio of lengths of the second and fourth digits of the hand are influenced by testosterone and estrogen. This could be of particular importance in species such as anoles, in which the fourth digits of the hindlimbs are extremely long and critically important in locomotion, but previous studies of the 2D:4D ratio in anoles have produced varying results. In the final poster session at SICB, undergraduate Griffin McNamara, working with Bonnie Kircher in Marty Cohn’s lab at the University of Florida, presented preliminary results from a study of cleared and stained brown anole (Anolis sagrei) hind feet. Griffin has big plans for continuing this work, so watch for future publications with these findings!

A, wattsi is one of five introduced species on the islands. A new report in Living World: the Journal of the Trinidad and Tobago Field Naturalists’ Club, indicates that it’s on the move.

Dan Warner (left) and Tim Mitchell (right) beside their poster on impacts of population density and time of hatching on survival and early life phenotypes of Anolis sagrei

Tim Mitchell a post-doctoral researcher at University of Minnesota with Emilie Snell-Rood presented his work from his prerious post doc in Dan Warner’s lab where he investigated the impacts of density and timing of hatching on the survival and growth of Anolis sagrei hatchings. Seeking to specifically address these questions:

How does investment in offspring size and number shift seasonally?

Does the timing of hatching influence survival or growth in the field?

And does adult density influence survival or growth of hatchlings in the field?

Adult anoles were brought into the lab on three different dates and breeding was split into three corresponding windows of time: Cohort 1 (February 23^rd – April 27^th), Cohort 2 (June 18^th – July 30^th), and Cohort 3 (September 5^th – October 15^th).  On experimental islands, adult densities were manipulated to create high and low lizard densities. Hatchlings from cohorts 1, 2, and 3 were released onto high and low adult density islands in June, August, and October, respectively, and researchers returned the following spring to recapture the marked lizards.

Breeding in the lab revealed a seasonal shift from producing more smaller offspring early to producing fewer larger offspring later in the season. Adult densities on the islands did not affect hatchling survival, but there was a substantial survival advantage to being an early-hatched lizard. Size and growth of hatchlings were influenced both by timing of hatching and the adult densities. So happy to catch up with my academic family and see the cool research they are doing!

In the face of mate competition, sperm morphology can vary in a way that can enhance an individual’s chances of siring offspring of females. Studies in the past have attributed increased relative testis size as an approximate measure of an individual’s response to sperm competition. However, this does not take into account the internal architecture of the male testes that may contribute to changes in sperm morphology.

This was the focus of a poster presented by Hanna Hall titled “The evolution of sperm and testis morphology in Anolis lizards” in collaboration with Ariel Kahrl and Michelle Johnson. The authors sampled 2-20 individuals of different species of anoles in Puerto Rico and the Dominican Republic. They compared body size, sperm length ( 15 cells per individual), and the composition and size of various layers of the testis, by conducting a phylogenetic least squares regression on the average values obtained for each species.

The authors found that larger body size was associated with a larger testis size, which was in turn correlated with presence of large seminiferous tubules and a larger luminal area, where mature sperm are stored. Contrary to their expectation though, none of these aspects were associated with producing longer sperm. Further the Gonado-Somatic index (GSI), a common metric that serves as an indicator of relative testis size, was not correlated with any aspects of the internal testis architecture.

An interesting finding in this study was that species with a higher proportion of epithelial cells in the testis produced longer sperm. This result was surprising because larger number of epidermal cells may be associated with smaller spermatogonal cells, which would be predicted to form shorter sperm. The authors suggest that the correlation between lumen area and testis size may result because investment in sperm storage is more important, and that species may be producing large number of sperm which may be longer in length. Nevertheless, more data is needed to understand how changes in sperm morphology affect fertilization success and, further, under what circumstances does size and count of epithelial cells vary. The lack of correspondence of these results with that  shown in birds by Lupold et al. 2008 suggests that the mechanisms underlying sperm competition may be taxa or species-specific. We will be eyeing the Johnson Lab for more details on the same in the coming years.

An example of an aggressive display by a lizard. Photo Credits: Neil Losin Photography

Testosterone has long been though to influence male aggression behaviors. But can this same hormone influence aggressive behaviors in females too? Ellee Cook addressed this question in her talk titled “Investigating the potential for testosterone to mediate territorial aggression in female Anolis lizards.”

Ellee focused on studying a population of Anolis gundlachi in the forests of Puerto Rico. Ellee studied the response of focal females to a staged territorial intrusion by another female who was placed on a cage lid, and compared it to a scenario where she directly approached the lizard. She captured the focal females after twenty minutes of the trial and measured their size and took a blood sample to estimate the circulating levels of testosterone. Her prediction was that higher levels of aggression would be correlated with higher levels of testosterone.

Her data showed that females were indeed aggressive towards intruding females and had much higher displays of aggression in comparison to when they were presented only a lid or were directly approached. Surprisingly (or not so surprisingly), testosterone was not a significant predictor of female aggression. In fact, none of the hormonal measures corresponded to female aggression. This finding could have resulted for several reasons: A) the amount of testosterone detected in females was much lower than that found in males, making variation in testosterone  almost impossible to detect; B) High aggression may be caused by spontaneous spikes in testosterone that may be hard to detect; C) Female aggression may be governed by a completely different mechanism.

This study raises an important question about the relevance and drawbacks of existing paradigms which are male-centric and thus cloud our understanding when it comes to female behaviors. Cheers to more feminist paradigms in biology!

Go to the Anole Annals calendar site on Zazzle.com, use this code:

NYESSENTIALS

Discount until midnite Pacific time on January 11.

Theory predicts that males should invest more in ejaculate production when the likelihood of sperm competition is high, thereby increasing the chance of fertilization. However, ejaculates can be energetically costly, and increased investment into sperm production should only occur if there are fitness benefits associated with that increased investment. Growing experimental evidence suggests that sperm traits respond plastically to social environment. However, it is not known whether fine-scale spatial variation in the local density of male competitors or potential female mates corresponds to individual variation in ejaculate production.

Island population with capture records of males (blue) and female (red) anoles.

Matt Kustra of the Cox lab examined a wild population to test the prediction that, as the risk of sperm competition increases (i.e., higher local density of male competitors), males will increase their total investment in their ejaculates (sperm count). He also tested for correlations between sperm morphology, specifically midpiece size and local density.

To do this, he and the Cox lab collected wild adults from an island population in Florida. They generated a map of each tree on the island using ArcGIS, then marked the location of males and females on this map. Using the kernel density function, they estimated the local density of individual males by taking into account all conspecific adults that were captured within a 5.8 m radius of an individual’s own capture location.

Matt found that length of the sperm midpiece increased with local density, whereas length of the sperm head and sperm count decreased with local density. Contrary to his predictions, he found that total investment in sperm count decreased with local density. This could be because males in high density environments have depleted their sperm stores because they have more opportunities to mate, or it could be because males are investing less per ejaculate if mating frequency is higher.

These findings indicate that fine-scale differences in local density within a wild population can affect sperm count and various sperm phenotypes. In the future, the Cox lab hopes to measure fitness in this populations to understand how sperm phenotypes shape individual reproductive success.

Whereas in the Greater Antilles islands anoles evolved ecomorphs and live in communities with up to 11 species in sympatry, islands in the Lesser Antilles support only one or two species each. However, islands such as Dominica have populations of anoles that experience selective pressures resulting in different ecotypes.

Figure from Thorpe et al. 2004

While Dominica is relatively small, the mountainous topology results in highly variable environmental conditions across the island with cool mountainous regions and warm coastal regions and thermal vents. The single endemic anole species present on the island, Anolis oculatus, exhibits four morphologically distinct ecotypes (Montane, Atlantic, North Caribbean and South Caribbean) and despite levels of gene flow between these ecotypes are high, adaptive differentiation in this system is maintained.

Photo by Aurélien Miralles

Tricia Neptune, a graduate student in the Watson lab, at Midwestern State University, explored whether these ecotypes also show any differences in metabolic rate (by measuring oxygen consumption) and its sensitivity to temperature (Q10) at ecologically-relevant temperatures.

Results show that size differences between ecotypes are reflected in their physiology with the south Caribbean ecotype exhibiting higher oxygen consumption and Q10 compared to the other three ecotypes. Tricia hypothesize that these differences in metabolism and temperature sensitivity are in part responsible for maintaining relaxed geographic segregation among ecotypes.

Tricia plans to incorporate data on sprint speed, bite force as well as investigate thermoregulation strategies in this species. It will also be interesting to see a comparative study between the A. oculatus ecotypes and the introduced Puerto Rican crested anole, A. cristatellus.

Figure from Thorpe et al. 2004

The cover slide of Michael Yuan’s talk at SICB 2018.

Convergent forms of anoles can be found across the Greater Antilles, with similar phenotypic and ecological morphs filling similar microhabitats from island to island.  Anole ecomorphs are in part defined by the extent of arboreality, as most species in the Greater Antilles spend a lot of time in trees.  Crandell et al. 2014 found arboreality to be associated with significant differences in claw characteristics in Costa Rica and Panama.  In Greater Antillean anoles, similar research into claw morphology has yet to investigate if this relationship holds across ecomorphs. Michael Yaun, a PhD student in the Wang lab at UC Berkeley, set out to investigate the patterns of variation of claw morphology in the Greater Antillean anoles.

Anolis barbouri is shown as an outlier in a PCA. The flattened claws of this ground-dwelling anole are illustrated in black to the right.

Michael sampled 566 individuals, which included 55 species of anoles, all 6 ecomorphs, and another 8 species without any ecomorph designations.  His results suggest that perch height and diameter produced differential effects on claw characteristics.  Performance traits like toepad lamellae number and area were not correlated with claw height and length.  Michael’s study uncovered only one anole that conformed to previous research: Anolis barbouri, the only truly terrestrial species in the data set, possessing flattened claws.  Intriguingly, twig anoles have the most divergent claws, an inspiring result for future directions!