Photo by Claus Meyer at http://www.nationalgeographicstock.com/
For many years, the South American lizard genus Polychrus has been considered the closest extant outgroup to Anolis. In light of this phylogenetic position, the authors of a new report on the life history of Polychrus acutirostris note that “a comprehensive understanding of Polychrus might help clarify possible ecological factors related to the radiation of anoline lizards as well as to infer the existence of niche conservatism or dietary shifts related to the origin of this large lizard radiation” (Garda et al. 2012).
Members of Polychrus are superficially similar to Anolis, and are mostly medium sized arboreal and diurnal lizards. However, Polychrus also differs from Anolis in both conspicuous (e.g., lack of toepads) and somewhat less conspicuous ways (e.g., its tendency to produce single clutches of multiple eggs, versus multiple one egg clutches in Anolis). In their report, Garda et al. (2012) compare populations of Polychrus acutirostris found in two different Brazilian habitats to test whether size of eggs and clutch size, reproductive seasonality, diet, and size of reproductive adults varies among populations in the manner predicted by life history theory. Although recent work makes Polychrus‘s position as the outgroup to Anolis less certain than it once was (Schulte et al. 2003, Townsend et al. 2011, and this previous AA post), we still have much to learn from the type of comparative studies that Garda et al. have implemented.
Garda et al. (2012) make comparisons among populations of Polychrus acutirostris occupying two regions in central Brazil that make up part of a large swath of open, savannah like habitat south of the Amazonian rainforest: Caatinga and Cerrado. Polychrus acutirostris occurs across these open habitats, whereas the other species of Polychrus are primarily rainforest dwellers. Caatinga and Cerrado habitat differ in several important ways. Garda et al. suggest that the most important difference is the fact that Caatinga receives considerably less rainfall than Cerrado (300-800 mm versus 1,100-1,600 mm per year). Moreover, Cerrado has a predictable rainy season from October through March while precipitation in Caatinga occurs primarily in February and March. As a result of these habitat differences, Garda et al. (2012) use basic life history theory to predict that Caatinga populations will scatter their reproductive efforts throughout the year, produce smaller clutches of larger eggs, have less seasonal dietary shifts, and have smaller body sizes and lower sizes at first reproduction.
Garda et al. obtain new data from Caatinga populations of P. acutirostris by examining hundreds of museum specimens and compare these data to previously published data for Cerrado populations. Garda et al. (2012), recover a somewhat different pattern than they predicted. First, both populations appear to produce a single clutch per year; there was no evidence that populations from the Caatinga are distributing their efforts throughout the year; instead, P. acutirostris reproduction in the Caatinga remains highly seasonal and occurs between August and February, with a peak in November. Cerrado populations exhibit a similar pattern, but tend to reproduce about a month earlier than Caatinga populations. Caatinga populations also tend to produce large numbers of small eggs rather than small numbers of large eggs, suggesting that the “competitive environment for offspring is either unpredictable or that mortality is high but random.” Garda et al. ultimately suggest a continuum of reproductive strategies within P. acutirosris and across Polychrus more generally, where Caatinga populations of P. acutirostris produce the largest number and smallest eggs, Cerrado populations of P. acutirostris produce relatively fewer eggs that are smaller than Caatinga populations and rainforest species produce the smallest numbers of the largest eggs, suggesting that “the competitive environment for offpring is predictably intense and mortality is non-random” in the rainforest.
More of this type of work is needed in Anolis, where information on geographic and seasonal variation in reproduction is often lacking, even among relatively well-studied species.
Adrian A. Garda, Gabriel C. Costa, Frederico G. R. França, Lilian G. Giugliano, Giselle S. Leite, Daniel O. Mesquita, Cristiano Nogueira, Leonora Tavares-Bastos, Mariana M. Vasconcellos, Gustavo H. C. Vieira, Laurie J. Vitt, Fernanda P. Werneck, Helga C. (2012). Reproduction, Body Size, and Diet of Polychrus acutirostris (Squamata: Polychrotidae) in Two Contrasting Environments in Brazil Journal of Herpetology DOI: 10.1670/10-288
- JMIH 2014: Early Records of Fossil Anolis from the Oligocene and Miocene of Florida, USA - August 13, 2014
- JMIH 2014: Relative Contribution of Genetic and Ecological Factors to Morphological Differentiation in Island Populations of Anolis sagrei - August 7, 2014
- JMIH 2014: The Ultrastructure of Spermatid Development within the Anole, Anolis sagrei - August 5, 2014
George Gorman
Back in the 1960’s and 70’s we examined the karyotypes of dozens of species of Anolis, and a couple of species of Polychrus. This sort of research is not presently fashionable, understandably, because of the development of modern techniques of DNA/genetic anaslysis. But perhaps some useful phylogentic hints can emerge.
Polychrus was so weird and so off the curve in karyotype that we could not find any hints of relationship to any Anolis (or any other iguanid, as the family was then defined). Conversely, in reproductive biology, the anoles seem to be the anomaly among “iguanids”, with single egg clutches, each oviduct alternating the production of an egg, while Polychrus appears to be a more “typical” lizard.
Perhaps the origin and evolution of Polychrus has little to do with the origin and evolution of the anoline radiation.
Rich Glor
I think we are about to see a resurgence of interest in that old karyotypic data!
The recent molecular results certainly support your assertion that there may be little reason to expect similarities between Anolis and Polychrus. This work suggests that Polychrus is actually quite distant phylogenetically from Anolis.