Anole Annals

The last week has seen a spirited discussion of the pros and cons of splitting recognized genera into multiple, smaller genera. We’ve had 34 comments already. Check it out! And if you’re an advocate of splitting genera, that viewpoint has been getting the short end of the stick and could use more support.

As a tangent, the topic of subspecies has come up, and David Hillis has strongly argued for reviving its use. Here’s what he has to say:

First, I don’t think either species or subspecies are “clades.” Species are lineages (the branches on the tree of life). Sexual recombination among individuals results in tokogenetic relationships within species. Clades, on the other hand, are monophyletic groups of lineages on the tree of life. Rather than being defined by tokogenetic relationships, they are defined by phylogenetic relationships.

Traditionally, subspecies are geographical races of species. In other words, they are geographically distinct populations that nonetheless meet and interbreed at contact zones. Sometimes, these contact zones are very broad, as with broad-banded versus southern copperheads. If the contact zones are very narrow, and there is strong evidence that the contact zone is a genetic sink (there is no gene flow across the zone, because of strong selection against hybrids), then I agree that the two entities can be considered separate lineages, and hence species. But in many recent cases, as with the copperhead example, there is abundant evidence that the contact zone is NOT a sink, and that there is NO selection against hybrids. In this case, I disagree strongly with the authors who proposed to split these subspecies into distinct species. That is inconsistent with any lineage species concept…there is a huge area where these two forms intergrade, with no evidence of any loss of fitness. Thus, the two forms are geographical, intergrading races, or subspecies.

I think we will soon see a backlash against the splitting off of geographic races as species as well. Frank Burbrink (who was an author on the copperhead example I mentioned above) and I plan to write a pro/con article about this together, each arguing our respective points of view. Hopefully, this will re-kindle the conversation about subspecies.

Subspecies are unpopular right now because they were long abused in several ways. Inappropriate uses include (1) to describe non-geographic “varieties”; (2) to arbitrarily break up clines; and (3) to describe distinct, isolated lineages that clearly are species. But used in proper context to designate a geographically distinct race, they are certainly reasonable and often useful. They are rarely used in some groups, for several reasons: Groups like freshwater fishes have discrete ranges, so taxa don’t interbreed over broad areas. And many groups are too poorly studied to understand geographic variation. But in well-studied terrestrial groups (like herps), subspecies are perfectly reasonable and useful taxa to designate intergrading geographic races.

Over the last several years, ever since Nicholson et al. proposed dividing Anolis into eight genera, the topic of taxonomic splitting has periodically been discussed in these pages (for example, this post, its comments, and links to other posts).

The general question of when to split taxa recently has been revisited in several comments in AA. A week ago, David Hillis wrote:

“Anolis is a valid name for a monophyletic group on the Tree of Life. It is “special” as a genus only in that the genus name is used as part of a binomial for particular species. It doesn’t make sense to change the scope and application of generic names unless the names are actually misleading about phylogeny (e.g., if Anolis were polyphyletic, then that problem should be fixed). But splitting a valid, monophyletic genus into a bunch of smaller genera, and thereby needlessly changing the names of many species, without fixing any phylogenetic problems with the existing taxon names, is not science. It is just playing around with names. If someone wants to name the groups within genera, then do so…but there is no reason to change the meaning of a existing name (or the names of the all the affected species) in doing so. That is the kind of silliness that gives taxonomists such a deservedly bad reputation among biologists.”

Elswhere, David posted a flowchart on his recommended decision-making process about whether and how to divide recognized genera:

Ivan Prates, in line with comments he made in a recent paper on A. punctatus, then remarked:

“This seems more like a sociological matter.

During the ‘taxonomic revolution’ of the amphibians, about 10 years ago, the (perhaps?) most influential (or faster?) group was the splitter one, and their taxonomic scheme prevailed. Currently, nobody is upset about which species were once named as Bufo, Hyla or Rana. A few do care about Dendrobates – like Anolis, a sexy group with a body of dedicated investigators.

It seems that a single genus makes sense for the community that investigates dactyloid lizards more closely. On the other hand, those who deal with overwhelming levels of herpetological diversity in the tropics (waaaay beyond lizards) see benefit in more partitioned schemes, which correlate more closely to morphology and geography.

So, when we discuss names, it may be healthy not to forget about our diversity as investigators as well. About science, splitting Anolis is not science, but well, not splitting Anolis isn’t science either.”

Over the last decade the term “model species” has taken on new meaning. Species that were once the building blocks for distinct disciplines have taken on new importance in comparative evolutionary studies that integrate perspectives across biological disciplines. Nowhere is this better illustrated than with Anolis lizards. For decades anoles were a workhorse of ecologists and evolutionary biologists, but have, more recently, been embraced by developmental biologists, genomicists, physiologists, and neurobiologists among others. This disciplinary expansion is perhaps most evident with the rapid increase of penis/hemipenis research that has been published using anoles within the year.

For many herpetologists, including those focused on anoles, the hemipenis is ripe with taxonomic characters, easily allowing for the identification of new species. Julia Klaczko and colleagues recently demonstrated that features of the hemipenis are some of the most rapidly evolving characters among anoles, a group already well known for its rapid anatomical evolution. Independent from these taxon-specific interests, developmental biologists became interested in the anole hemipenis because of its unique anatomy compared to other amniotes. Marissa Gredler and members of the Cohn Lab used anoles as one of their reptilian models of external genital development in what is arguably the broadest embryological survey of reptilian phallus development to date. In parallel, Patrick Tschopp and colleagues probed the cellular and molecular regulation of early phallus development among anoles, snakes, chickens and mice, demonstrating that the hemiphalluses (hemipenes and hemiclitores) and hindlimbs of squamates utilize similar molecular networks at the earliest embryonic stages of morphogenesis. Now, just within the last month, two more papers have used anoles in studies of phallus evolution and development, one using cutting-edge molecular techniques to better understand the relationship between limbs and external genitalia and the other addressing the fundamental question of external genital homology using museum specimens that are more than 100 years old.

Before getting into the findings of this new research, lets lay out some of the dirty details of penis evolution. First and foremost, the penises of amniotes are extremely diverse. Squamates have paired lateral phalluses while other clades have a single midline phallus. Each of the amniote lineages uses hydrostatic pressure to achieve an erection, yet accomplish this using different bodily fluids (lymph or blood). In mammals sperm is transferred to the female through a closed urethral tube, but other groups utilize an open channel. Most birds (97%) and the tuatara, have absent or highly reduced phalluses and reproduce with the famed “cloacal kiss.” These large differences in anatomy should not overshadow the spines, bulges, corkscrews, and dramatic differences in size that give species their distinctive features. But with such striking variation, we are forced to wonder how many times the penis evolved. Perhaps the amniote ancestor possessed an intromittent phallus capable to transferring sperm to the female that later diversified in each lineage independently. Or, perhaps the last common amniote ancestor used cloacal apposition to foster internal fertilization and unique phallus morphologies evolved independently at the origin of each lineage. Because adult anatomy provides few clues to phallus homology, Thom Sanger (me), Marissa Gredler, and Marty Cohn looked towards the embryo for help.

Table 1 from Sanger et al. 2015 summarizing phallus variation in amniotes

The tuatara, a species lacking an adult phallus, has presented a problem in attempts to reconstruct the last common ancestor of amniotes because it raises the distinct possibility that reproduction through cloacal apposition was the ancestral condition.

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Anolis cristatellus. Photo by Janson Jones.

If you ever come to Puerto Rico, the first thing you’ll probably notice is the warmth. Yet, for an anole, things are not that simple. Different habitats can have different thermal regimes that potentially influence the lizard’s biology and natural history in different ways. What might be a hot and humid urban park for us can be a heterogeneous thermal landscape for a small lizard.

This is the case for Anolis cristatellus, a lizard common in most parts of Puerto Rico. Back in the early70’s, Ray Huey (1974) studied how habitat influenced this anole’s thermal biology. He found that in open and sunny habitats, this lizard actively thermoregulates and has relatively high and stable body temperatures, but that in shaded forests it is a thermoconformer and has relatively low and variable body temperatures.

Also back in the early ’70s, George Gorman and Paul Licht (1974) found that altitudinal and seasonal variation in temperature had major effects on reproductive cycles of Puerto Rican anoles. So, do reproductive cycles differ between lizards living in thermally distinct — but contiguous — habitats? Ray Huey, George Gorman and I teamed up to find out, and you can find the answer in our recent paper just published in The American Naturalist.

We studied seasonal reproductive cycles of this lizard in two localities in lowland Puerto Rico. Both localities have contiguous but thermally distinctive habitats: open parks and forests, separated by only a few meters. We caught female lizards every month for more than two years and palpated their bellies to establish reproductive condition. At both localities, lizards living in open habitats were more often gravid than were those in the forest. This difference was especially marked during winter months (of course… in a tropical sense). During these cooler months, more than 20% of open lizards were gravid, while essentially none of the forests ones were.

Large-scale geographic variation in reproductive cycles has been described in many taxa, but this is one of the few examples on a micro-geographic scale. Very likely these difference will have significant effects on the population ecology of the species, and these will be reported on soon. But in the meantime, we can say that at least for the reproductive output of Anolis cristatellus, a few meters matter!

Photo by Karen Cusick

From Daffodill’s Photo Blog.