Anole Annals

A new study out in Biology Letters by myself, Devi Stuart-Fox, Terry Ord and Indraneil Das found that two populations of the same species of gliding lizard – Draco cornutus – have diverged in gliding membrane colouration to match the colours of falling leaves in their respective habitats. An Anole Annals post by Ambika Kamath earlier this year looked at the study briefly after we’d spoken at the Animal Behaviour Conference in Princeton, but I thought I’d elaborate a little on working with Draco and how we devised the falling leaf camouflage hypothesis.

Figure 1. Draco cornutus at Bako National Park (photo credit– Devi Stuart-Fox)

Draco are small arboreal agamids, found throughout South-East Asia. They have extendable gliding membranes that they use for gliding between trees in their habitats. They also have dewlaps – like the Anoles – used in broadcast display to communicate with conspecifics. My work generally focuses on the diversity in dewlap colouration among species and how differences in habitat influence signal efficacy and may lead to speciation. This involves measuring the colours of lizards as well as taking behavioural footage of individuals of different species to look at how the patterns of display differ.

httpv://youtu.be/I_oeY9cIWOg

Footage by Terry Ord

Most Draco are very difficult to spot as they are well camouflaged and perch at least 3 metres high in their trees. Given this, searching for movement or displays are the best ways to locate an individual. Walking through the forest, we would often see in our periphery what we would initially dismiss as a falling leaf, only to later discover it was a gliding lizard. Indeed we quickly learnt to focus on ‘falling leaves’ when on the lookout for Draco and this was quite a fruitful approach. Indraneil Das was the first to suggest the gliding membranes were coloured to look like falling leaves – but it was a couple of years until we started to think about how we might test the idea. It became difficult to ignore how similar the fallen leaves on the ground at various study sites so closely resembled the colours and patterns of the gliding membranes of Draco species living in those immediate areas.

Then we made to trip to Niah Caves National Park in northern Borneo and came across a second population of D. cornutus.

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The big question–were they making s’mores?

The first anole paper of 2015 is a doozy. Everyone loves to roast marshmallows around a campfire. Turns out that “everyone” includes crested anoles, A. cristatellus! Read all about it in the paper by Norman Greenhawk in the new journal Life: the Excitement of Biology.

The uninformed often view parasites with disdain, disgust, and/or condemnation. These views however ignore the various ecological roles that parasites play. My colleagues and I are some of the lucky few who look at these organisms through ecological lenses and marvel at what we find.

An Anolis sagrei male from Chiayi County, southwestern Taiwan.

As part of the ongoing research on the exotic invasive brown anole (Anolis sagrei) populations in Taiwan, we collected and examined some specimens for parasites. In addition to the brown anoles, we also examined specimens of Eutropis longicaudata, Eutropis multifasciata, Japalura polygonata xanthostoma, Japalura swinhonis, Plestiodon elegans, and Sphenomorphus indicus, that were collected opportunistically from Taiwan.

We recently reported on the parasites we recorded in 52 of the 91 lizards examined, and the infected individuals harbored one to three species of parasites. We identified the parasites as Cyrtosomum penneri, Kiricephalus pattoni, Mesocoelium sociale, Meteterakis govindi, Oochoristica chinensis, Oswaldocruzia japalurae, Parapharyngodon maplestonei, Pseudabbreviata yambarensis, Pseudoacanthocephalus bufonis, or Strongyluris calotis. We also recorded an unidentifiable acanthocephalan infective juvenile (cystacanth) and an unidentifiable larva of a cestode (sparganum).

Based on the relatively few parasite species recorded from A. sagrei in Taiwan, compared to the large number of parasites reported from A. sagrei throughout its native and introduced range, it is clear that these lizards have been liberated from many of their parasites.

The nematode, Cyrtosomum penneri, which was introduced into Taiwan along with A. sagrei, was a common parasite in the A. sagrei we examined. None were recorded in any of the other lizard species examined. This is most likely because these nematodes are transmitted from one host to another during copulation and appears to have a fair degree of host specificity, so the spread of C. penneri to native lizard species in Taiwan is suggested to be very unlikely. An interesting conclusion that can be drawn from the presence of C. penneri in specimens from both the southwestern and eastern populations of A. sagrei in Taiwan is that sexually mature lizards were introduced into these localities and that they most likely have a common founder population.

Our study did also confirm that the digenean, Mesocoelium sociale, and the pentastome, Kiricephalus pattoni are acquired parasite of A. sagrei in Taiwan. Unfortunately, although their infections can be expected to be detrimental to the A. sagrei host, their infection frequencies are relatively low in the A. sagrei populations in Taiwan, and thus have no observed significant impact on the population sizes.

Another interesting finding of our study was that even though the nematodes, Pseudabbreviata yambarensis and Strongyluris calotis, are very common in Japalura swinhonis, a species that is very often sympatric with A. sagrei in Taiwan and which also has a very similar diet as A. sagrei, they have not been found in any of the A. sagrei examined to date. This could be a result of an absence of transmission routes that could be specific to J. swinhonis and thus protect introduced species from the native parasites, or the host-specific limitations of the parasites prevent them from adapting to a new hosts, i.e., A. sagrei.

I would like to encourage everyone involved with research to include parasitological studies in their herpetological works to expand our understanding of host-parasite ecology.

Photo by Julia Klaczko

This is an article wrtten by Stephanie Pappas and posted on livescience. It reports on a paper just published in the Journal of Zoology by Julia Klaczko, Travis Ingram, and me:

A lizard’s penis evolves six times faster than any of its other parts, a new study finds.

The study is the first to directly measure the evolution rate of the penis of any species, though researchers have long suspected that the male genitalia evolve faster than other body parts, said study researcher Julia Klaczko, a biologist at the University of Campinas in Brazil.

“What we see is, sometimes, very close species have very different hemipenes or genitalia,” Klaczko told Live Science. Hemipenes are the pair of organs that make up the version of a penis found in snakes and lizards. But dramatic genital differences are seen among closely related animals with penises, as well. [The 7 Weirdest Animal Penises]

Quick-changing penises

Because penises are often so different even in species that otherwise look almost identical, researchers frequently use genitals to discriminate between different species. Klaczko and her team chose to measure the genitals of 25 species of Anolis, a group of lizards that live in the Caribbean. Anolis lizards are a well-studied group, and researchers have lots of information about the relationships between the species, as well as their habitats and body shapes, Klaczko said.

The lizards’ hemipenes are tubular structures with a groove through which semen can flow. The researchers measured the length and width of the hemipenes in several specimens of each species. For comparison, they also measured the length of the lizards’ limbs, which evolve in response to the vegetation in the animals’ habitats, and the size of their dewlaps, which are the flaps of tissue near the throat that the lizards use for communication.

Next, using mathematical modeling, the researchers estimated the rates of evolution necessary to arrive at the differences in genitals, limbs and dewlaps. The result? Male genitalia change six times faster than either legs or throat flaps, making them more diverse in shape and size from one another than the other body parts.

Picky females or sexual warfare?

Klaczko and her colleagues aren’t sure what drives the rapid alterations in hemipenes. One possibility is that females pick mates with pleasing penises, whether that means their genitals are more stimulating or abetter “fit” in the female genitalia.

Another, less cooperative, possibility is that male and female lizards are locked in an evolutionary arm’s race in which both are trying to control reproduction. If this is the case, then males may be evolving genitals that give them an advantage in fertilization, while females evolve their genitals in an attempt to take that advantage back.

One known example of such a sexual arms race is the duck. Some duck species have corkscrew vaginas that spiral in the opposite direction of the males’ corkscrew penises, so the females can better resist unwanted mating attempts.

So far, the researchers haven’t studied female Anolis genitals, in part because vaginas are just harder to dissect and measure than hemipenes, Klaczko said. The next step, she said, is to try to understand the drivers in the variation in hemipenes’ shape and whether it has to do with differences in habitat, relationships between species, or some other factor.

The researchers reported their findings Jan. 5 in the Journal of Zoology.

Another news article on this research was just published on the Discovery News website.