Author Spotlight: Comparison of Two Alternative Adhesive Pad Configurations in Geckos

4 11 2016

Left in the dust: differential effectiveness of the two alternative adhesive pad configurations in geckos (Reptilia: Gekkota)

Anthony P. Russell and Michel-Jean Delaugerre

The ability of geckos to scale smooth surfaces fascinates both scientists and the public at large – holidays taken in warm climates are often enlivened by geckos roaming in the evenings on the walls of hotel rooms, apartments and restaurants. The toe pads of these adept climbers are composed of plate-like scales, which bear microscopic hair-like outgrowths creating reversible molecular bonds with the surfaces on which they move. The form of these toe pads has long been used by scientists to distinguish between different types of geckos; the names of the genera often reflect this (for example, Hemidactylus [half-toe], Lepidodactylus [scaly-toe], Phyllodactylus [leaf-toe]).

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Toe pad configuration of the Moorish gecko (Tarentola mauritanica). Photo by A. Leoncini

One of us (A.P.R.) has been studying gecko evolution and the form and the function of their adhesive apparatus for over 40 years, and has always been aware of two basic “designs” of this system – either a series of broad, overlapping sheets, like the blades of a Venetian blind, along almost the whole of the underside of the toe, or as one or two pairs of squarish, leaf-like plates at the very tips of the toes. The reason for the existence of these two different patterns has, however, defied explanation, although it has been proposed that the leaf-like pattern appears to be particularly associated with rocky surfaces (although the alternative pattern is also encountered among species occupying this type of habitat). What was needed to bring us closer to an answer was a more in-depth ecological study in an environment that would reveal whether there were potential functional differences between these two patterns.

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Toe pad configuration of the European leaf-toed gecko (Euleptes europaea). Photo by A. Leoncini

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The ‘dusty’ surface of the prasinite rock. Photo by Michel-Jean Delaugerre

The other one of us (M-J. D.) noted that on Giraglia, a very small, uninhabited island off the north Corsican coast, an otherwise very aggressive invasive gecko species, the Moorish gecko (Tarentola mauritanica), had colonized it in about 1950, when a concrete building was erected to house the power-plant for the newly-automated lighthouse. The Moorish gecko, which has the familiar pattern of gecko adhesive pads, with the plates extending along much of the length of each toe, likely arrived with the construction materials and established itself on the new building. In the subsequent 65 years, however, the species has failed to make inroads on the rest of the island. Already present, and native to the island, was the European leaf-toed gecko (Euleptes europaea), which elsewhere has not been able to withstand invasion by the Moorish gecko. The leaf-toed gecko has not colonized the newly-erected concrete building, but is widespread on the rocky outcrops of the island, and on the two previously-existing buildings (the 19th century lighthouse and a 16th century lookout tower), both of which are constructed from rock excavated on the island. That rock is prasinite, a metamorphic schist that is crumbly and coated with “dust” derived from the microscopic particles that weather from its surface.

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The Giraglia island. Photo by Michel-Jean Delaugerre

If the Moorish gecko is placed onto the prasinite rock, it has great difficulty moving and clinging, because its large toe pads become fouled with the released dust. By contrast, on such dusty surfaces the toe pads of the leaf-toed gecko do not become fouled because they can be curled away from the surface, leaving the claws to provide grip. The Moorish gecko, because of the highly specialized movements of its toes that bring about attachment and detachment of its large adhesive pads, cannot use its claws independently of the pads and thus cannot negotiate, and is therefore unable to colonise, the dusty prasinite surface.

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Moorish gecko (Tarentola mauritanica). Photo by Michel-Jean Delaugerre

The fortuitous combination of circumstances on Giraglia (two species of gecko with different adhesive pad structure and a dusty rocky surface) has provided a window into the functional differences between the two adhesive pad configurations. Our work has provided the foundation for more detailed observations of how geckos with these two toe pad types might subdivide surfaces on which they move in different parts of the world.





Celebrating the 50th Anniversary of Journal of Zoology

11 10 2016

cover-wallace-1865-proceedingsThe Zoological Society of London, founded by Sir Stamford Raffles in 1826, has published scientific papers in zoology since 1830, first as Proceedings and Transactions of the Zoological Society of London, and in 1966 these publications were merged to form the Journal of Zoology. We are delighted to celebrate the 50th anniversary of our journal by releasing a free Virtual Issue of 12 highly cited and influential papers published in Journal of Zoology over the past 50 years.

jzo-anniversary-issue-oct-2016-coverFurthermore, to celebrate this anniversary our October issue consists of a special selection of new research articles considered particularly interesting to our readers. Many of these articles are also featuring in the anniversary edition of the Journal of Zoology podcast. In this new episode you will hear authors summarizing the principal aims and findings of their studies, ranging from investigating the maximum length of giant squids, 3D-modeling of lion paws and tracks, and sexual dimorphism in an isopod crustacean with horns, to studying anti-predator colour adaptations in a blue-tailed lizard, anthropogenic food resource use in brown bears, tissue regeneration in unisexual salamanders and decomposition of ostrich carcasses, with implications for studying dinosaur fossils.lizard_podcast

We hope you will enjoy these special features and celebrate with us 50 years of Journal of Zoology!





Author Spotlight: The Need for New Categorizations of Dietary Specialism in Animals

13 09 2016

Emilio Pagani-Núñez, Craig A. Barnett, Hao Gu & Eben Goodale

Guangxi University, Nanning, Guangxi Zhuang Autonomous Region, People’s Republic of China

 

Moreover, it is not understood when a species will evolve a particular niche width through the device of being polymorphic with phenotypes which are resource specialists, monomorphic with one generalist phenotype, or some intermediate condition.                                                 J. Rouhgarden (1974) The American Naturalist, 108 (962): 429-442

 

Certain ideas are rapidly and broadly accepted by the scientific community, sometimes even by a whole society.  This is the case of the concepts of ‘generalism’ and ‘specialism’, which have improved our understanding of ecological and evolutionary processes in nature.  However, to some extent, many authors have stressed the need to review and reformulate the existing theory about diet specialization.  This motivated us to write our review article “The need for new categorizations of dietary specialism incorporating spatio-temporal variability of individual diet specialization”, published in the September 2016 issue of the Journal of Zoology.

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Great tit nestling (Parus major), photo by Emilio Pagani-Nunez

At present, there is no consensus among researchers on a definition of diet specialization. We searched papers defining great and blue tits as ‘generalists’ or ‘specialists’ and we observed a great inconsistency among authors in how they classified the two species.  Traditionally, diet specialization was conceptualized as a continuous gradient from totally generalist species to completely specialized species that were behaviourally and physically adapted to eat specific food types. However, the discovery of individual diet specialization (IDS) challenges the traditional gradient of specialization within and among species. IDS means that, within species and populations, different individuals can specialize in the exploitation of different subsets of the available resources.

Species with broad diets and widespread distributions can provide useful examples of how species theoretically considered as generalists can show a surprising level of specialization at both the population and the individual level. Conversely, irrespective of distribution range, species inhabiting variable environments can evolve strikingly variable levels of specialization among individuals from both spatial and temporal perspective. In this paper, we reviewed the literature on specialization in great tits and blue tits.  Both species are considered caterpillar specialists at the centre of their ranges, but this reliance on caterpillars declines at the periphery of their ranges (e.g. the Mediterranean).  Specifically, we found that great tits show a higher level of IDS than blue tits do, developing new dietary specializations when the most common prey is not available.

Another issue that has not been well explored in the literature is the role of foraging innovations in promoting novel dietary specializations. Research in foraging innovations also has a long history of research (e.g. the opening of milk bottle tops by great and blue tits in United Kingdom). There have been few attempts to link foraging innovations to the capacity to evolve contrasting levels of specialization from the species to the individual level. However, the capacity for foraging innovations may explain why certain ‘generalist’ species show such contrasting levels of specialization between populations and individuals.

Here, we introduce a new categorization of specialization that takes into account all these factors.  We define obligate specialists as species composed of individuals that are primarily adapted to exploiting a single resource (e.g. hummingbirds). Facultative specialists are species in which individuals are adapted to exploit a single food type or niche, but occasionally they can exploit alternative food resources (e.g. birds of prey). Facultative generalists are species composed of individuals that are able to develop novel specializations to preferably exploit alternative resources, (e.g. great tits and sea otters).  Finally, obligate generalists are able to exploit a wide variety of resources (or one if it is very abundant), with a limited capacity to incorporate foraging innovations (e.g. many passerine species).

By publishing our new classification, our aim is to provide clearer and more workable definitions of diet specialization within and among populations and species. We also are interested in initiating a debate among ecologists about the necessity of incorporating IDS as well as spatial and temporal variation into studies of foraging ecology.  This general framework is also attractive because it is applicable to a wide variety of taxa and makes comparison among taxa easier.

 





New Journal of Zoology Podcast

10 08 2016

A new episode of the Journal of Zoology podcast is now available and you can listen to it here.

JZO_butterfly_podcast_imageIn this episode, Tim Thurman and Brett Seymoure talk to us about their study on two mimetic butterflies and how similar they appear to the eyes of their predators, we will learn from Lucy Lush how biologging technology can improve our ability to record and analyse wild animal behaviour, and we are told by Niklas Björklund how ants can help protect conifer seedlings from pests in forest plantations via non-consumptive interactions with pine weevils.

You may subscribe to iTunes to receive the latest Journal of Zoology podcasts.





Winner of the 2015 Journal of Zoology ‘Paper of the Year’ award

2 08 2016

JoZ Blog

Biochemical correlates of aggressive behavior in the Siamese fighting fish

M. D. Regan, R. S. Dhillon, D. P. L. Toews, B. Speers-Roesch, M. A. Sackville, S. Pinto, J. S. Bystriansky and G. R. Scott

 

Aggressive interactions between individuals of the same species can result in the evolution of exaggerated body traits that improve success in these interactions, and subsequently, access to resources such as food and mates. Although conspicuous morphological adaptations such as antlers are usually what come to mind, metabolic processes that occur hidden within cells are required to sustain aggressive behaviour, so their enhancement may also be important for a successful outcome.

Siamese fighting fish, Betta splendens Siamese fighting fish, Betta splendens; photo by Dave Toews

With this in mind, we designed a study to examine the intersection of aggressive behaviour and metabolic biochemistry using the Siamese fighting fish, a staple of the world’s pet shops. Male Siamese fighting fish are notoriously…

View original post 378 more words





21st Century Lizards: Small, Rare and Trendy – Author Spotlight with Shai Meiri

18 07 2016

 

When I was a kid, what passed for phylogenetic trees in the illustrated books I used to read, were drawings showing not just the relationships (often vaguely drawn) between groups, but also their diversity. In such drawings mammals were invariably shown (correctly!) as having increased hugely in diversity after the KT. Reptiles on the other hand, were shown to be in decline after the Mesozoic, and the lines depicting diversity of lizards and snakes were invariably very thin, much more so than those depicting mammals and birds. As an undergraduate student (late) in the previous millennium I was taught that there are a lot of birds, and many mammals, but that amphibians and reptiles are relatively minor groups, with fewer species than in either endotherm class. Ten years ago, when I started studying lizards (i.e., resumed what I used to do as a kid, chasing lizards around, but nowadays calling it a profession) I knew this wasn’t the case. But had I known just how many lizard species are going to be recognized nowadays, I might have despaired and never started. Simply put – reptile taxonomists are running rampant, discovering, splitting, and describing about 200 new species every year: the number of recognized lizard species has increased by 31% since the turn of the century. As a macroecologist I try desperately to keep up.

Photo 1 Cyrtodactylus durio by Lee Grismer

Cyrtodactylus durio, described in Malaysia in 2010 by Grismer et al. Photo by Lee Grismer

Who are all these new lizards, which the writers of children’s nature books and the professors who taught me zoology never knew? And why were they described only recently? In a study now published in Journal of Zoology I set out to check.

My first thoughts were to blame eroding species concepts (“taxonomic inflation”), certainly a major cause of elevating subspecies to species level, as well as to recognize new species that older generations of taxonomists would have ranked as mere varieties, or ecotypes within polytypic species. Alternatively, new species may be difficult to detect because they inhabit places that previous generations of herpetologists seldom visited, and have restricted ranges. Likewise, they may have individual-level traits making them difficult to detect: perhaps they are small? Or are active at night? Or below ground (or high in the canopy)?

Some of those hypotheses were already examined in other animal taxa. Using my macroecological database of lizard traits, and data on the distribution of all reptiles we are now finishing to assemble (see http://www.gardinitiative.org/index.html), I now explicitly tested them for the 1323 lizard species described in the 21st century until the beginning of my study (just under a year ago, the number is already 1406 as of April 2016).

Photo 2 graph from the paper

The locations where lizards have been described during the 21st century (dots). Warmer colours signify more descriptions in that country.

If species splitting was the cause, then I would not necessarily reveal many changes in the traits of “new” (i.e., described this century) and “old” species (those described between 1758 and 1999). But I did identify some interesting differences: as is usually the case, newly described species have small distribution ranges. They are also more likely than old species to be threatened with extinction and suffer population declines. New lizards are also small bodied, and often nocturnal (geckos are especially dominant). It seems that the greatest increase in species description rates has occurred in Southeast Asia. This century, new species of lizards have been described in 96 countries, mostly Australia (105 species), Argentina (103), Vietnam (66), Brazil (64), Madagascar (60), Malaysia (58), and the Philippines (48). Africa, however, saw relatively few new descriptions – I assume this reflects geopolitical reasons rather than postulate that we have anywhere near complete lists of African lizards. Similarly, relatively few burrowing species have been described this century – and I think this is likely to reflect our ignorance, rather than a comprehensive knowledge of burrowing forms such as amphisbaenians and dibamids. These assumptions are nearly testable (one can certainly refute them…).

Photo 3 Cnemaspis psychedelica by Lee Grismer

The aptly named Cnemaspis psychedelica, described on an island off the shore of Vietnam in 2010 by Grismer et al. Photo by Lee Grismer

When and at what number of species will this stop? How many species of lizards exist and when will we know them all? Unfortunately, given the accelerating rates of species descriptions, these are questions I cannot answer.

But the species that are being discovered are far from boring, dull, or ugly – some are strikingly beautiful. We need to keep on cataloging them, caring about them, and protecting them.

Shai Meiri

Tel Aviv University

 





Author Spotlight: The Astonishing Bites of Crocodilians and How They Do It

15 06 2016

Ontogenetic bite-force modeling of Alligator mississippiensis: implications for dietary transitions in a large-bodied vertebrate and the evolution of crocodylian feeding

P. M. Gignac and G. M. Erickson

Alligators and crocodiles are impressive predators that can generate up to 3,000 and 4,000-pound bite forces, which they use to subdue large prey such as deer and wildebeests. To put that much force into perspective, being captured in the jaws of a large crocodilian is comparable to being pinned beneath a 2016 Ford Mustang, or having Dwayne “The Rock” Johnson stand on you with another dozen Dwayne “The Rock” Johnsons standing on him. You may have heard before that these animals are the living kings of chomp, brandishing the title for the most forceful bites measured in any animal to date. Not only is that true, but today’s species are not even the largest crocodilians to have ever lived—not by far.

So, how is it even possible for an animal to generate this much force?

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Paul Gignac holding the head of a 12-foot American alligator during a bite force test. Photo by Joern Hurum

That is a super question, and it is the central focus of our new study. Our research team has been working with these animals for more than a decade, trying to understand their unique lifestyles and how they make a living. Before this research we measured the bites of every living crocodilian species, and we were astonished to discover how much force is behind them. In our new Journal of Zoology study we dissected a growth series of American alligators to examine how the jaw musculature changes across development. We documented muscle position, arrangement, and—particularly—fascicle orientations, which allowed us to build mathematical models of theoretical bite forces that incorporated muscle morphology, position, physiology, and activation. We tested these models against the bite forces we had measured directly (in vivo) for similarly sized animals, and our calculations turned out not to differ from the in vivo values.

We then went back into the experimentally validated models and looked at how muscle positions, sizes, and force outputs changed from hatchlings through large-bodied adults. We found that all muscles had meaningful contributions to those 3,000 and 4,000-pound bite forces, but one muscle in particular called the “ventral pterygoideus” was the major player. If you have ever seen a crocodilian for yourself, you might have thought that it had oddly thick neck. Well, it turns out, that is not all neck! The ventral pterygoideus muscle is so large that it spill out behind the head and wraps around the jaw, attaching from below and behind. This muscle makes up about half of the overall muscle mass that goes into generating a bite, but it contributes more than 60% of the bite force in most individuals and an astonishing 70% in exceptionally large adults.

This one muscle is so large that it could not fit inside the head, where the other jaw muscles are housed, even if it was the only one. Instead, it seems that over time this muscle was pushed backwards towards the animal’s neck, which allowed it to become massive while also maintaining the fairly low-profile skull that is typical of crocodilians. As a result, these near-shore predators can hide in shallow water to ambush animals that come too close for a drink, while also being capable of sustaining the thousands of pounds of bite force necessary to capture and consume such prey.

We also discovered a few particulars about this large muscle that are important. For instance, it has fascicles arranged in a chevron pattern (like a “V”), similar to those in your calf muscles or deltoids, which is a great way to pack a lot of force into a given volume of space. So not only is the ventral pterygoideus muscle enormous, but it is also particularly good at generating force, even for its large size.

It is this combination of traits that have helped crocodilians become masters of their domain since the age of the dinosaurs. Our next step is to figure out how they got to be this way by plotting out the evolution of the crocodilian jaw system across 240 million years of its evolutionary history from a gracile and svelte morphology to the intimidating and powerful one we commonly think of today.