Author: Ambika Kamath Page 1 of 6

Anolis sagrei in Miami, Florida (K.Winchell)

UPDATE: POSITIONS FILLED! SORRY!

We are looking for a field assistant to help us conduct behavioural research on Anolis sagrei on small dredge-spoil islands near Ft. Pierce, FL, from April 22 to May 21. Daily activities include searching for and observing marked lizards as well as collecting habitat data. We will work long hours on most days (beginning 7-8am). Applicants should be prepared for hot and humid work conditions as well as travel on a small boat. Applicants must be comfortable handling lizards and using binoculars and should be adaptable to changing plans. All expenses (airfare, food, lodging) will be covered and a stipend will be provided.

If interested, please contact Ambika Kamath: ambikamath@gmail.com and Nick Herrmann: nicholas.carl.herrmann@gmail.com with a
brief letter describing why you are interested in this position and any relevant research experience along with your CV and the names and contact information of a professional reference whom we may contact by email. We will review applications as they arrive until the position is filled.

Almost anyone who cares about anoles in the US  is aware of the hypothesis that the arrival of brown anoles (Anolis sagrei) into Florida has driven declines in the abundance of native green anoles  (A. carolinensis). Though there is certainly evidence that this hypothesis may be valid to some extent, we’ve previously wondered if the decline is as severe as folks seem to think it is. Have green anoles instead simply shifted to higher perches where we don’t see them as often? An informal mark-recapture effort conducted in Gainesville FL suggests that green anoles may in fact be quite abundant, and  based on the evolutionary history of green and brown anoles across their ranges, we do in fact expect green anoles to shift upwards where they co-occur with brown anoles.

Green anoles, increasingly elusive in Florida

We now have yet another piece of evidence that green anoles may be thriving at the tops of trees , just out of sight. Because of Hurricane Irma, which wreaked havoc across Florida last week, many of those tree canopies have fallen to the ground. And Miami herpetologist Steven Whitfield  reported yesterday seeing “more green anoles in the past two days than I have in the two months before that.” This observation was confirmed by other local biologists as well, in comments on Whitfield’s initial Facebook post that said “Green anoles are all over the place. Seems they were around up in the canopy, but now the canopy is on the ground so they’re easy to see.”

Reposted from my blog.

Over the last few months, there’s been a slow-boiling battle underway between Holly Dunsworth and Jerry Coyne about the evolution of sexual dimorphism in humans, surrounding the question of why male and female humans, on average, differ in size. The battlefield ranged from blogposts to twitter to magazine articles. In a nutshell, Coyne argued that “sexual dimorphism for body size (difference between men and women) in humans is most likely explained by sexual selection” because “males compete for females, and greater size and strength give males an advantage.” His whole argument was motivated by this notion that certain Leftists ignore facts about the biology of sex differences because of their ideological fears, and are therefore being unscientific.

Dunsworth’s response to Coyne’s position was that “it’s not that Jerry Coyne’s facts aren’t necessarily facts, or whatever. It’s that this point of view is too simple and is obviously biased toward some stories, ignoring others. And this particular one he shares…has been the same old story for a long long time.” Dunsworth went on to propose, seemingly off the cuff, alternative hypotheses for sexual dimorphism in body size in humans that were focussed not on men but on women, as examples of the kind of hypothesis that is relatively rarely considered or tested in this field.

Though on the surface this battle may seem to be about specific biological facts (Coyne certainly tries to win by treating it that way), in reality this disagreement is, as Dunsworth argues, about the process by which hypotheses are tested and about how knowledge comes into existence. About which hypotheses are considered for testing in the first place. As a result, the two ended up arguing past each other quite a bit.

As I followed this whole exchange, I shook my head at the timing–I had a paper in preparation that was SO RELEVANT to the centre of this debate! That paper is now available as a preprint, so I can try to outline why I think that Dunsworth is right, and Coyne is being short-sighted. My argument has *nothing* to do with humans, however–I don’t know the human sexual selection literature well enough to weigh in on that. Instead, my argument is by analogy with our knowledge of mating systems in Anolis lizards.

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Female Festive Anole (photo: Ambika Kamath)

Sexual dimorphism–differences between the sexes in what they look like–is rampant across animals. But how do these differences arise? Why and how might natural selection or sexual selection act differently on males and females? In a new paper from Duryea et al. (2016) published last month, we begin to see what answers to these questions look like in our very favourite organism, the festive anole, Anolis sagrei.

The data presented in this paper is unprecedented in anoles–by catching every lizard on Kidd Cay for four successive years, the authors assigned parentage to three generations of offspring, and thus assigned reproductive success to three generations of adults. Using these measures of reproductive success for males and females, they ask a straightforward question: is reproductive success correlated with body size, and do these relationships differ between males and females?

The results, however, are not straightforward: patterns of selection differ quite a bit across the three years of sampling, especially in females. But overall, we see directional selection on body size in males (bigger males father more offspring who survive to adulthood than smaller males), possibly explaining why male festive anoles are 30% larger than females.

We don’t yet understand the origins of sexual size dimorphism in anoles–why in particular, does the shape of selection on female body size vary so much? Do large males sire more offspring who survive to adulthood because they mate more often, or because their offspring are somehow better at surviving? Duryea et al. have propelled forward the state of our knowledge with a formidable dataset that raises exciting new questions.

Some weeks ago, a paper I wrote on the display behaviour and morphology of fan-throated lizards was published early online at the Journal of Herpetology. Some unfortunate timing meant that my paper did not incorporate these lizards’ new taxonomy, recently published by V. Deepak and colleagues. In this post, I’m going to summarize my results, and explore them in the context of what we now know about Sitana (Agamidae) systematics.

Male fan-throated lizards (surprise, surprise) have fans under their throats that are displayed in a manner analogous to the Anolis dewlap. The appearance of the throat-fan varies dramatically across this group, from small and mostly white to large and blue, black, and orange. I wanted to answer two broad questions

1. Does display behaviour vary with throat-fan morphology? In other words, if you have different tools with which to communicate, do you communicate differently?
2. Can we examine morphological and environmental variation to deduce anything about how this variation in throat-fan morphology has evolved?

Figure 1 from my paper, showing sampled sites and throat-fan variants.

To address these two questions, I measured the display behaviour, morphology, and environment of eight populations of lizards, from three “throat-fan variants.” I found the following:

1. The main axis of variation in display behaviour differed between the coloured-fan variant and everybody else. Displays were fewer and longer in the coloured-fan variant, and included more head twists. The same axis of display behaviour did not differ between the white-fan and the intermediate-fan variants, though there was variation in the frequency of head-bobs across populations with different-sized throat-fans. These differences in display behaviour make sense in light of morphology. Head twisting was more frequent in the variant with a large blue section on the throat-fan that appears iridescent. Head-bobs, which often co-occur with a fully extended throat-fan, were more frequent in the variant(s) with smaller throat-fans (see Figure 6 in my paper for more).
2. Throat-fan elaboration (both size and colour) was paired with increased male-biased sexual size dimorphism, suggesting sexual selection as a likely selective force driving throat-fan variation.
3. Habitat structure did not co-vary with throat-fan morphology, suggesting that the visual environment is unlikely to play much of a role in the maintenance of this variation in throat-fan morphology. But because these lizards all persist in human-modified landscapes, it is difficult to discern how important the visual environment was for the origin of dewlap diversification in this group.

Figure 2 from Deepak et al. 2016.

Based on geography, I can tell that all three of the coloured-fan variant populations I sampled belong to the newly described Sarada darwinii. The white-fan populations are Sitana laticeps and Sitana spinaecephalus (+ one population I’m not sure about), and the northern and southern intermediate-fan populations are Sitana ponticeriana and Sitana visiri respectively. Recast in terms of these species delimitations, I found that:

1. Display behaviour differs between the genera Sitana and Sarada. It doesn’t vary consistently with species within Sitana, though variation in head-bobbing should be explored further.
2. There are two broad possibilities for throat-fan evolution in the group. One possibility is that throat-fan elaboration and a shift towards male-biased SSD has evolved independently twice, once in Sarada (Clade 1) and once in the South India/Sri Lanka clade (Clade 3 in the phylogeny) in Sitana. The other possibility is the reduction of dewlap size and colour in the west Indian Sitana clade (Clade 2). This question won’t be definitively answerable until we have a phylogeny that includes the remaining north-eastern species of Sitana as well as more species of the sister genus Otocryptis, which also vary in the presence and morphology of the throat-fan.

Before knowing about the phylogeny, I predicted that throat-fan elaboration had evolved twice in fan-throated lizards, based on a suite of differences between the coloured-fan variant (now Sarada) and the intermediate-fan variant (now Sitana Clade 3). The main ones are:

1. Different display behaviour.
2. Different allometric relationships between body size and throat-fan size, suggesting different ways in which throat-fans have gotten big.
3. Different spectral reflectances from the blue and orange patches, plus the presence/absence of black on the throat-fan.
4. The ability of Sitana, but not Sarada, to turn “on” and “off” the blue colour on their throat-fans (more about this in a future post!).

These differences now lead me to favour the first of the two possibilities outlined above: repeated, somewhat parallel evolution of throat-fan elaboration, as opposed to the loss of an elaborate throat-fan. Given that the sister genus Otocryptis has also either evolved or lost a throat-fan (throat-fans are present in O. nigristima and O. wiegmanni but not O. beddomi), this group is positively rife with lability in display evolution, offering all sorts of exciting possibilities for future research!

I’m currently reading a 274 page tome called “The Biology and Biodemography of Anolis carolinensis” by Robert E. Gordon. Dating back to 1956, this impressive piece of scholarship is Gordon’s Ph.D. thesis. Gordon collected the bulk of his data in biweekly nocturnal surveys of the demography and spatial ecology of two populations of green anoles. The surveys continued for over a year, and consequently, this document is filled with insights into these lizards’ ecology.

One sentence that caught my attention was this, from page 195:

Anolis activity is primarily diurnal, although movement and feeding were observed at night under conditions of bright moonlight.

We’ve had observations of anoles feeding at artificial lights before, but have any of you night-owl herpers observed something similar under natural light?

A figure from Gordon (1956). Can we please bring back this elegant asymmetric bar graph plotting style?

Dewlap morphology and colouration of Fan-throated lizards. Clade 1: A. Sarada darwini sp. nov., B. Sarada deccanensis comb. nov., C. Sitana superba sp. nov.; Clade 2: D. Sitana spinaecephalus sp. nov., E. Sitana laticeps sp. nov.; Clade 3: F. Sitana ponticeriana, G. Sitana visiri sp. nov., H. Sitana cf. bahiri. Scale bar = 10 mm

V. Deepak and his colleagues from five different institutions in India have published a revision of the systematics of fan-throated lizards in India. This work nicely expands on the project of figuring out the diversity of this clade of magnificent lizards, following the description of two new species from Sri Lanka last year.

I’ll be writing more about this paper and these lizards in weeks to come, but for now, here’s a figure from the paper, and below, the abstract!

Abstract

We revise the taxonomy of the agamid genus Sitana Cuvier, 1829, a widely distributed terrestrial lizard from the Indian subcontinent based on detailed comparative analyses of external morphology, osteology and molecular data. We sampled 81 locations spread over 160,000 km² in Peninsular India including type localities, which represented two known and five previously undescribed species. Based on general similarity in body shape and dewlap all species were hitherto identified as members of the genus Sitana. However, Sitana deccanensis and two other morphotypes, which are endemic to north Karnataka and Maharashtra in Peninsular India, are very distinct from the rest of the known members of the genus Sitana based on their external morphology and osteology. Moreover, members of this distinct morphological group were monophyletic in the molecular tree, and this clade (clade 1) was sister to two well-supported clades (2 and 3) constituting the rest of the Sitana. The interclade genetic divergence in mtDNA between clade 1 and clades 2 and 3 was 21-23%, whereas clade 2 and clade 3 exhibited 14- 16% genetic divergence. Thus, we designate a new genus name “Sarada” gen. nov. for species represented in Clade 1, which also includes the recently resurrected Sitana deccanensis. We describe two new species in Sarada gen. nov. and three new species in Sitana. Similarity in the dewlap of Sitana and Sarada gen. nov. is attributed to similar function (sexual signaling) and similarity in body shape is attributed to a similar terrestrial life style and/or common ancestry.