Author Spotlight: Sexual dimorphism in the horned isopod

12 05 2016

Sexual dimorphism and physiological correlates of horn length in a South African isopod crustacean

D.S. Glazier, S. Clusella-Trullas and J.S. Terblanche

 

Figure 1

Dr. Susana Clusella-Trullas on the left and Dr. John Terblanche in the middle along the rocky shore where specimens of the horned isopod (Deto echinata) were collected. Photo by Douglas Glazier

During October 2012 to March 2013 I spent a wonderful sabbatical leave at Stellenbosch University in South Africa.  There I was hosted by two superb physiological ecologists, Drs. John Terblanche and Susana Clusella-Trullas, who also happen to be husband and wife.  My major objective was to compare the rates of metabolism and water loss of several species of amphipod and isopod crustaceans with differing degrees of adaptation to land life. During one of my field trips to Pringle Bay (Western Cape Province) along the southern coast of South Africa, John and Susana acquainted me with the unusual horned isopod (Deto echinata) that lives abundantly amongst piles of wave-washed rocks along the shore (see Fig. 1).   I was immediately fascinated by the extremely long dorsal spines of the males of this species (Fig. 2), which I had never seen before in any other isopod species that I had collected in many places around the world.

Figure 2

A male horned isopod. Photo by Douglas Glazier

Most isopod species that dwell along rocky shores are notoriously difficult to capture – their association with sea shores and their quick escape responses to intruders has led to them to be called “sea roaches”.  However, I soon learned a useful technique for capturing dozens of these animals in a matter of seconds!  All I had to do was to reach my hand into one of the wet rock crevices (Fig. 3) and legions of these creepy crawlers would quickly scurry up my arm and beyond, reminding me of the scary scarab beetle attack scene in the 1999 movie “The Mummy”.   All I had to do next was to shake or brush my arm over a collection bucket and my collection was complete!

Figure 3

Example of a rocky crevice where I collected numerous individuals of the horned isopod. Photo by Douglas Glazier

Back at John Terblanche’s laboratory I soon realized that the dorsal spines of D. echinata are not only longer in males than females, but they increase disproportionately in length as a male grows in size.  In fact, the scaling slope of male horn length in relation to body length is one of the steepest ever observed for a morphological trait.  My guess was that this extreme “positive allometry” of a sexually dimorphic trait was likely due to sexual selection.  My working hypothesis was that male horn length is a sign of “health”, “strength” or genetic fitness that could influence female mate choice.  An important aspect of fitness is the successful ability to acquire, conserve and store resources.  With the help of John and Susana, I tested this hypothesis by measuring the body condition (body mass per length), activity levels, and rates of energy use and water loss of male D. echinata with different horn lengths (Figs. 4, 5).

Figure 4a

Figure 4b

Examples of male Deto echinata with relatively short and long dorsal spines. Photo by Douglas Glazier

Figure 5

Dr. Terblanche’s laboratory at Stellenbosch University where the rates of metabolism and water loss were measured in individual males of the horned isopod. Photo by Douglas Glazier

As expected, males with relatively long horns had significantly better body condition and faster rates of resting metabolism than males with shorter horns.  However, activity level and rate of water loss were not related to horn length.  It thus seems possible that male horn length is a reliable signal of “good genes” to potential female mates or rival males, thus favoring its evolutionary increase via sexual selection.   Direct observations of female mate choice and male-male competition for mates are needed to further test this hypothesis.

Douglas Glazier





ISOMORPHOLOGY: An Introduction to Principles and Practice

20 04 2016

By Gemma Anderson

What is Isomorphology?

Isomorphology is a comparative method of enquiry into the shared forms of animal, mineral and vegetable morphologies.  The concept of Isomorphology has developed out of observational and intellectual enquiry. After years of drawing from scientific collections, such as those at the Natural History Museum (NHM) and Kew Gardens, I have identified a number of forms and symmetries that can be found in animal, mineral and vegetable species.

Isomorphology is a new term which I have coined. It is derived from ‘Isomorphism’; a mathematical and biological concept. Etymology, from Greek:

Isos– ‘Same/Equal’

Morphe– ‘Form’

Logos– ‘Study’

As a holistic approach to classification, Isomorphology runs parallel to scientific practice while belonging to the domain of artistic creation.  It is complementary to science: it addresses what is left out of scientific classification of animal, vegetable and mineral morphologies as distinct and unrelated. Drawing reveals the shared forms of conventionally unrelated species and the drawing process is intrinsic to the epistemological value of Isomorphology.

fig.28d.iso72(Fig 1)

Isomorphology publication. (c) Anderson

Is Isomorphology Scientific?

Isomorphology relies on science while at the same time building an altered perspective which liberates form from the confines of scientific identification. Isomorphology offers an alternative and visual approach to classification and acts as a reminder that there are many possible ways to find order in the world.  While connected to and derived from the observable, Isomorphology is a symbolic system and a mode of abstraction.  It can be understood as a visual language, which is coextensive with other modes of classification.

Isomorphology in practice

In its practical approach, Isomorphology incorporates both artistic and scientific methods and theories. I found myself reflecting upon the experience of drawing specimens at the Natural History Museum in my Journal, realizing that my process paralleled the process of scientific taxonomy.

fig.19.g.Gemma Anderson-72(Fig 2)

Isomorphology study at the Slacker lab, Darwin Centre, Natural History Museum. (c) Anderson

As noted in my Journal:

The work begins as an abstract idea of form (like the idea of a ‘type’) which leads to the reality of certain specimens which have been classified as this type. The reality of the individual specimen’s variation on the ‘type’ or ‘form’ is what the taxonomist has to deal with, and what I have to deal with through the observational drawing process. This is a difficult process which prompts reflection on ‘ideas’ and ‘ideals’ and the reality of achieving these through practice. Somehow, working through the difficulties of the observable reality allows for an expanding and evolving conception of what the work is, and this is how the conceptual process often evolves- inside the practice.

Drawing from life is always an experiment because no matter how well formed the image or idea in your mind’s eye may be- the individuality of the species is always unimaginable and therein lies the challenge. The rewarding aspect of observational drawing is that the observer can never entirely predict how the work will develop, as it is impossible to imagine the individual nature of specimens. The individual variations are what brings the challenge and surprise to the work, and to the classification process (and this is true in scientific taxonomy). What occurs is a playful improvisation, motivated by an idea, and realized through dealing with the real.

fig.19b-72(Fig 3)

Study of specimens with spiral morphology at the Slacker Lab, Darwin Center, Natural History Museum. (c) Anderson

The drawing process:

  1. Observation

Drawing and handling each specimen enables close observation that reveals unexpected comparisons of form. Observational drawing involves hand-eye coordination, analysis, delineation, abstraction, improvisation, collage and concentration.  My perception of the object is in a process of transition from experience to judgment, insight to application.

  1. Trained Judgement

Concentrated observation creates new perceptual knowledge. The morphology is observed in detail, activating the process of comparison; each form observed joins a bank of knowledge in the observer’s mind and each new drawing experience triggers a different formal memory stored in this bank. Each drawing adds value to each drawing previously made, and vice versa.

  1. Pattern recognition

A necessary process of abstraction occurs within the observational drawing process. All knowledge of the object and its conventional context and name are forgotten; what is left is an involvement in the form of the specimen. The concentration shifts from drawing the whole thing to drawing a series of parts. This process, which concentrates on form, trains the artist to abstract, to draw and to play with the form, eventually without observing the object – entering a new realm of understanding.

fig.20.a.grant-72(Fig 4)

Isomorphology workshop at the Grant Museum. (c) Anderson

Isomorphology as an approach to classification

Isomorphology works as a parallel system to scientific classification. It uses a dynamic artistic practice to emphasize connections rather than divisions, between animal, mineral and vegetable species. In the same way that Isomorphology enlivens the space around scientific taxonomy, each drawing enlivens and re-examines a specimen from the museum collections.

The model of Isomorphology I am proposing shares with the scientific model an important emphasis on morphology and observation, but asks different questions about the relationships between species.  It relies on the discovery of shared forms in nature and on the invention of a practice to classify these forms. In developing the skill of abstract thinking it is possible to unlearn the conventions of classification that are inherited and to observe afresh, to form an individual understanding and to discover relations between objects which were previously unperceived.

 

radial_form(Fig 5)

Anderson, Gemma 2015. Radial Symmetry. Copper etching. (c) Anderson

 

Forms of Isomorphology can be realised in everyday observations: in a garden it is possible to observe the forms and symmetries in the plant life; bilateral leaves, branches, bilateral leaves on branches, and to ponder the possible combinations of the forms and symmetries. All of the Isomorphology forms and symmetries can be found in endless configurations in nature.

Training the eye to perceive abstractly and the mind to think creatively whilst simultaneously maintaining a strong connection to the individual specimen is a complex practice. I believe this understanding can be shared with others as a playful educational model, which challenges convention. Isomorphology encourages both learning and ‘unlearning’ – we are de-constructing inherited taxonomies in order to create new knowledge and new approaches.

The Isomorphology project demands close observation of each specimen and I would like to thank the Natural History Museum and Kew Gardens for allowing access to their collections.

 

Further information:

http://www.gemma-anderson.co.uk

http://www.cmadc.uk

http://www.isomorphology.com

 

References

HAECKEL, Ernst. 2005. Art Forms from the Ocean : The Radiolarian Atlas of 1862. Munich: Prestel.

HOOKE, Robert. 1987. Micrographia: Or, some Physiological Descriptions of Minute Bodies made by Magnifying Glasses, with Observations and Inquiries Thereupon. Lincolnwood: Science Heritage.

THOMPSON, D’Arcy Wentworth. 1942. On Growth and Form. (2nd edn). Cambridge University Press.

 





Author Spotlight – Brett Seymoure and Timothy Thurman

30 03 2016

A Bird’s Eye View of Two Mimetic Tropical Butterflies: Coloration Matches Predator’s Sensitivity

IMG_7381

Heliconius sara, photo by Collin Whitsett

In many cases, experiments are designed in offices and during collaborative meetings, with specific questions and aims in mind. Sometimes, however, you are out in the rain forest diligently collecting data for your PI when your own curiosity gets the best of you. For Tim and I, this was exactly the case in May of 2014 when we were sent by our advisor at the Smithsonian Tropical Research Institute, Owen McMillan, to Ecuador to collect Heliconius butterflies. We were on the Eastern slope of the Andes attempting to catch Heliconius sara, a blue, yellow, and black butterfly that flies slowly and majestically, flashing its colors to warn predators of its toxicity. We caught a few H. sara, and then, when taking what had appeared to be an H. sara out of my net, I noticed that the body of the butterfly was quite different, with six legs, not the usual four on H. sara (which, as brush-footed butterflies, have two legs that have been modified into sensory appendages). These six-legged H. sara lookalikes were imposters, perhaps mimics of the unpalatable Heliconius model. This happened a few more times throughout the day, and we realized that if we were duped by these swallowtail imposters, perhaps birds were as well. We didn’t collect as many H. sara as we were hoping, but we decided to turn our unfortunate day of collecting into a curiosity-driven project, which serendipitously resulted in a manuscript in Journal of Zoology. Tim and I have not overlooked that other studies in Journal of Zoology have also been engendered by letting one’s curiosity taking the wheel during serendipitous walks in the forest (see post by Adrian Barnett). Perhaps, as a molecular biologist once told me, zoologists can’t seem to stay focused, or perhaps, we are opportunistic curiosity-driven investigators. Or perhaps both?

Brett Seymoure

Brett Seymoure

Our research project was not a bed of roses though. Once we had decided that we were going to compare the visual signals of the Heliconius sara with Mimoides pausanias, we needed to collect more individuals of both species to enable a strong understanding of the intraspecies variation. Of course, as we set out to catch a few more individuals of the swallowtail mimic, M. pausanias, they weren’t as common as they had been the previous day. It figures that when you aren’t looking for a rare mimic they seem to fly into your net, but when you go looking for them, they are nowhere to be found. We were able to catch one more during the last couple of days of the trip, and luckily for our study, the variation within species was much greater than the variation between species, an indicator of the mimetic association between these two species. One other difficulty that arose during our study was that Mimoides pausanias was a ghost of a species. Very few publications even make mention of the species and in most of those publications they use a different species name. In fact, for the first month of our study we were calling the species by an outdated name. Fortunately, with the help of excellent tropical entomologists, we were able to track down some information on the natural history of Mimoides pausanias.

Timothy Thurman

Timothy Thurman

Lastly, as Tim and I look back on this research, we realize how fortunate we were to have everything work out as it did. We had no idea that the most interesting finding would be that the two butterfly species are most mimetic in the eyes of their avian predators, flycatchers and jacamars. Depending on the species, birds either can see ultra-violet light (most songbirds and parrots), or as most birds, including flycatchers and jacamars, they cannot. It turns out that the two mimetic butterflies are closely matched in all wavelengths except for ultra-violet – rendering them close mimics in the eyes of their avian predators, but most likely not to each other as to cause themselves any confusion, as butterflies are able to see in the ultra-violet. As always, this study engendered more questions than answers and we hope to take another trip to Ecuador to discover more!

 





Editor Spotlight – Gabriele Uhl

16 02 2016

Gabriele UhlI am delighted to be taking on the role of Senior Editor for invertebrates for the Journal of Zoology. My group has been working for many years mainly in the field of reproductive biology and sexual selection, and our focus has been on spiders. Apart from spider topics, however, we also have been involved in projects exploring aspects of genital morphology and mating strategies in beetles, odonates, heel walkers, grasshoppers and flies, just to name a few animal groups. As to methods, we have been using behavioural analysis, paternity assessment, population genetics, molecular phylogenetics, morphometrics, histology, MicroCT as well as ultrastructural analysis with SEM and TEM. Consequently, this wide approach as to taxa and methods will lay the foundations for being an editor of the Journal of Zoology, which is in itself a journal that spans all aspects of zoology, including interdisciplinary topics. Together with expert reviewers I will scrutinize the submitted original research for its scientific significance. I will strongly advertise that not only novel results will be considered for publication – submission of negative results and replication studies should also be encouraged so long as sample sizes and data analysis are convincing.

Becoming an editor for the Journal of Zoology gives me privileged insight into a wide range of fascinating research and to learn about new approaches and ideas which I am looking forward to very much.

 

Gabriele Uhl

Universität Greifswald

Allgemeine und Systematische Zoologie

http://www.mnf.uni-greifswald.de/institute/fr-biologie/institute-und-forschung/zool-institut-museum/allgemeine-und-systematische-zoologie.html





New Journal of Zoology Podcast

12 01 2016

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

JZO Winter 2016 podcast logoIn this episode, Anthony Russell talks to us about the mystery of the ‘dead bird’ posture in dinosaur fossils and how studying the anatomy of extant birds such as domestic chickens can elucidate it, we will learn from Tiana Kohlsdorf about the ecological significance of animals’ locomotor performance, such running speed and grip, and how it varies between different substrates and habitats, and we are told by Stéphanie Périquet how increased abundance of lions alters the diet and foraging strategies of spotted hyaenas, as demonstrated by their study in the Hwange National Park in Zimbabwe.

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





Author Spotlight: Investigating the ‘dead bird’ posture of non-avialan dinosaurs

11 12 2015

Opisthotonic head displacement in the domestic chicken and its bearing on the ‘dead bird’ posture of non-avialan dinosaurs

A. P. Russell & A. D. Bentley

The research undertaken in this study, published in Journal of Zoology, seeks to examine the intervertebral movement that occurs in dead chickens when the head is drawn back into the “dead bird” (opisthotonic) posture seen in many dinosaur fossils. This posture is highly evocative because it suggests that the animals suffered death throes, thus potentially having implications for how the dinosaur died.

ADAM BENTLEY

Adam Bentley

Our work was initiated by my co-author, Adam Bentley, who, at the time, was an undergraduate student seeking a suitable final year research project. He was fascinated by a recent publication that attempted to evaluate all of the theories that had been advanced to explain this phenomenon in dinosaurs, and to arrive at the most plausible of these. That publication favoured the clinical condition of opisthotonus, resulting from neuromuscular trauma at the time of death. In discussing with Adam the various publications that had considered the opisthotonic posture (and its causes) in dinosaurs, we realized that nobody had systematically documented the vertebral movements associated with this. Given that birds are living dinosaurs, and that chickens are readily available in grocery stores (Asian ones being particularly good sources of chickens with the head and neck still attached), we set out to design a project that would yield statistically robust data and provide us with solid anatomical information.

ANTHONY RUSSELL

Anthony Russell

The key to being able to conduct the project successfully was the presence in my lab of a state-of-the-art digital radiography system that allowed us to pose and image the chicken carcasses in repeatable positions that mimicked the head retraction process. We began by determining the carriage of the head “at rest” (when the chicken is standing), and then established five equally-spaced stages of displacement to the fully retracted position with the top of the head resting on the hip girdle. We were able to document 15 chickens in this way (ten of which constituted our test group), and we recorded the angles of 11 neck joints for all of the stations along the cervical retraction pathway. We then repeated these procedures for protraction of the neck (a movement we dubbed protonic displacement), to determine the relative mobility of the joints when the head was forced forward and downward. The patterns here turned out to be quite different from those seen in neck retraction. Overall, for our sample of 10 chickens we were able to record displacement data for 11 joints in 14 positions, yielding 1540 angles for analysis.

This work was time consuming and challenging, but the outcome was very revealing. We found that certain neck joints are highly flexible whereas others are highly restricted in their movements. Although our research cannot answer questions as to why, in any given instance, a particular dinosaur fossil may have assumed the opisthotonic posture, our findings provide us with information about how to explore the anatomy of the neck vertebrae of dinosaurs (and other fossils) to see if such displacement was physically possible (because it has been reported that it is confined to certain groups of amniote vertebrates). It also raises questions about scale. Chickens are relatively small, and their head and neck relatively easily displaced by modest external forces. At larger sizes (as is typical of dinosaur fossils and even large birds, such as ostriches) the head and neck are bulkier and offer greater resistance to displacement (especially in terrestrial as opposed to aquatic situations). Thus, circumstantial evidence relating to the conditions of preservation and burial of each specimen remains important for determining why that particular animal expresses the opisthotonic posture. The form of the neck facilitates such displacement, but whether perimortem physiological symptoms, or postmortem decay phenomena, were responsible must be determined by examining “the scene of the crime”.

Anthony Russell





Editorial Board Member’s Choice

4 11 2015

By Maria Luisa da Silva

Agonistic sounds and swim bladder morphology in a malapterurid electric catfish

K. S. Boyle, G. Bolen & E. Parmentier, 2015, Journal of Zoology, 296: 249-260.

I was glad to read this article about sound production in fish, because it is a field that must be better studied and this study represents an effort to cover the lack of information. The difficulties to study behaviour in fish start because they live in the water and we are terrestrial, so this team of researchers from University of Liège, Belgium, kept some individuals of Malapterurus beninensis in several aquaria and recorded their agonistic sounds. Many fish species produce sounds and sometimes it is a mystery which structure is responsible for the sound emission. The movement of the protactor muscle linked at “elastic spring apparatus” (ESA) during the production of low frequency drumming sounds in doradid catfish has already been described, and the authors present a detailed sound analysis of broadband clicks trains, unusual emissions among catfish families, with high-quality spectrograms and oscillograms.

The sounds that the authors observed M. beninensis to make were ratchet, click train and mouth sounds. Mouth sounds were single event, of low frequency and coincided with a bite-like motion, whereas ratchet and click sounds were high-frequency and occured in trains. This species also produced bubble sounds, however they did not coincide with behavioural interactions and seemed to be by-products of air released from the orobranchial chamber or the swim bladder. The authors also show impressive images of the swim bladder obtained by computerized tomography and histological and ultrastructure analysis. What is particularly interesting is that this structure has evolved several times among Siluriformes, especially in a group that also uses electrical signals for defence. However, the scope for answering questions like the authors proposed – ‘What is the evolutionary function of the ESA morphology in Malapteruridae?’ – it is limited in laboratory experiments to analyse and to interpret natural behaviour associated with sound production. If it is possible to study this species in a semi-captive, almost natural condition, with some control and maybe with waterproof cameras to identify which individual produce the sound, we might be better able to answer evolutionary questions about sound production in these fish.








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