The research behind my recent publication in ethology has been featured on Smithsonianscience.org, a website that disseminate some of the interesting research occuring within the umbrella of the Smithsonian Institution.

Read the article here

I have a paper in the May issue of Ethology entitled 'Ontogenetic changes in web design in two orb-web spiders'. Note that there is a mistake in the affiliation (due to a misunderstanding the address was changed by the journal during production). Although it says University of Oxford, the work was actually done while I was a postdoc at the Smithsonian Tropical Research Institute.

Hesselberg, T. (2010). Ontogenetic changes in web design in two orb-web spiders. Ethology 116: 535-545.

The paper can be accessed here if you have an institutional licence. If not you are welcome to contact me for a copy.

Abstract
The first orb web built by newly hatched spiders resembles the adult web in its overall form and structure. However, many details show ontogenetic changes. One possible explanation for these changes is that the tiny early-instar spiders with their minute brains will make more mistakes and build less ‘perfect’ orb webs than older and larger juveniles and adults. To test this hypothesis, known as the size limitation hypothesis, I analysed orb webs from three developmental stages, spiderlings, juveniles and adult females, in two neotropical orb-web spiders, the araneid Eustala illicita and the nephilid Nephila clavipes. Neither species showed clear signs of being behaviourally limited or more prone to committing errors as spiderlings than were older juveniles or adults. These findings therefore do not support the size limitation hypothesis in either species. Finally, I looked for evidence of the ‘biogenetic law’, which predicts that juveniles should build less derived orb webs than the adults. Evidence for this was found in E. illicita, but not in N. clavipes.

Resumen
La primera telaraña orbicular construida por arañas recién salidas del huevo se parece a la tela de una araña adulta en su forma general y estructura. Sin embargo, muchos detalles muestran cambios genéticos. Una posible explicación para estos cambios es que las diminutas arañas con sus pequeños cerebros tendrían mayores errores y construirían telarañas orbiculares menos “perfectas” que arañas jóvenes y adultas, más viejas y largas. Para probar esta hipótesis, conocida como la hipótesis de limitación de tamaño, analice telarañas orbiculares de tres etapas de desarrollo, bebe, jóvenes y hembras adultas; en dos arañas orbiculares neo-tropicales, la araneid Eustala illicita y la nephilid Nephila clavipes. Ninguna especie mostro signos claros de conducta limitada o mas prono a cometer errores cuando bebe que cuando son jóvenes mayores o adultos. Estos resultados por lo tanto no apoyan la hipótesis de limitación de tamaño en cualquier especie. Por último, busque evidencia de la “la ley de biogenética”, que predice que las jóvenes deberían construir menos derivadas telarañas orbiculares que los adultos. Evidencia de lo anterior fue encontrada en E. illicita, pero no en N. clavipes.

The Pars Foundation has published its second volume in its Atlas of Creative Thinking, which attempts to show the creative processes occurring in the minds of artist and scientists.

The new volume centers on the topic of elasticity and includes stunning photographs, entries on elastomers in teeth correction, a jumping pig, resilin and poems.

Finally, I have a short entry in the volume on the elasticity in spider orb webs.

In the April issue of Journalf o Arachnology, I have, together with the Costa Rican student Emilia Triana, a paper entitled 'The web of the acacia orb-spider Eustala illicita (Araneae: Araneidae) with notes on its natural history'. The work in the paper was conducted during my postdoc at STRI in Panama from 2008 to 2009.

Hesselberg, T. and Triana, E. (2010). The web of the acacia orb-spider Eustala illicita (Araneae: Araneidae) with notes on its natural history. Journal of Arachnology, 38:21-26.

The paper can be accessed here if you have an institutional licence. If not you are welcome to contact me for a copy.

Abstract
A great number of spiders build orb-webs and although the overall structure is the result of fixed behavioral patterns, much small-scale inter- and intraspecific variation is nonetheless evident. Thus in order to fully understand the orb-web and web-building behavior in these spiders, we need to study substantial samples of many different species of orb-weavers. However, to date only a few species have been rigorously studied both in the field and in the laboratory. Here, we investigate the ecology, behavior and orb-web of the neotropical spider Eustala illicita (O. Pickard-Cambridge 1889) and suggest it as suitable for further studies based on 1) the ease at which it can be located in abundant numbers in the field, 2) its willingness to build webs in the laboratory, 3) the plasticity of its behavior, and 4) its interesting ecology in the form of interactions with the swollen-thorn acacias and their ant mutualists. Here, we introduce its natural history and then provide a detailed description of orb-webs built in the field and in the laboratory, which we compare to other orb-spiders.

Resumen
Un gran número de arañas construyen telas orbiculares y, a pesar de que la estructura es el resultado de patrones fijos de comportamiento, resulta evidente la variación inter e intraespecífica a pequeñas escalas. Para lograr entender las telas orbiculares y el comportamiento de construcción en estas arañas, es necesario estudiar un número considerable de diferentes especies tejedoras de telas orbiculares. Sin embargo, hasta la fecha pocas han sido rigurosamente estudiadas tanto en el campo como en el laboratorio. En este trabajo investigamos la ecología, el comportamiento y la tela orbicular de la araña neotropical Eustala illicita y la sugerimos como una especie apta para futuros estudios basados en: i) la facilidad para ubicarla en el campo en números abundantes, ii) su voluntad de construir tela en laboratorio, iii) la plasticidad de su comportamiento y iv) su interesante interacción con las acacias y sus hormigas mutualistas. Aquí introducimos su historia natural, y describimos detalladamente sus telas orbiculares construidas en el campo y el laboratorio y las comparamos con otras especies.

I have been elected as a non-stipendiary research fellow at Wolfson College, University of Oxford, from the 1st of January 2010 until the end of my Marie Curie fellowship.

Wolfson College is one of the newer Oxford colleges and exclusively a postgraduate college.

New paper:

Hesselberg, T. and Lehmann, F.-O. (2009) The role of experience in flight behaviour of Drosophila. Journal of Experimental Biology 212, 3377-3386.

The paper is from postdoc in the BioFuture Research Group of Fritz-Olaf Lehmann at the University of Ulm in Germany. I was there from 2006 to 2007, but due to delays with analysing the data and writing-up as well as a tough review process the paper is first out now.

The paper can be accessed here if you have an institutional licence. Other interested are welcome to contact me for a copy.

Abstract
Experience plays a key role in the acquisition of complex motor skills in running and flight of many vertebrates. To evaluate the significance of previous experience for the efficiency of motor behaviour in an insect, we investigated the flight behaviour of the fruit fly Drosophila. We reared flies in chambers in which the animals could freely walk and extend their wings, but could not gain any flight experience. These naive animals were compared with control flies under both open- and closed-loop tethered flight conditions in a flight simulator as well as in a free-flight arena. The data suggest that the overall flight behaviour in Drosophila seems to be predetermined because both groups exhibited similar mean stroke amplitude and stroke frequency, similar open-loop responses to visual stimulation and the immediate ability to track visual objects under closed-loop feedback conditions. In short free flight bouts, peak saccadic turning rate, angular acceleration, peak horizontal speed and flight altitude were also similar in naive and control flies. However, we found significant changes in other key parameters in naive animals such as a reduction in mean horizontal speed (–23%) and subtle changes in mean turning rate (–48%). Naive flies produced 25% less yaw torque-equivalent stroke amplitudes than the controls in response to a visual stripe rotating in open loop around the tethered animal, potentially suggesting a flight-dependent adaptation of the visuo-motor gain in the control group. This change ceased after the animals experienced visual closed-loop feedback. During closed-loop flight conditions, naive flies had 53% larger differences in left and right stroke amplitude when fixating a visual object, thus steering control was less precise. We discuss two alternative hypotheses to explain our results: the `neuronal experience' hypothesis, suggesting that there are some elements of learning and fine-tuning involved during the first flight experiences in Drosophila and the `muscular exercise' hypothesis. Our experiments support the first hypothesis because maximum locomotor capacity seems not to be significantly impaired in the naive group. Although this study primarily confirms the genetic pre-disposition for flight in Drosophila, previous experience may apparently adjust locomotor fine control and aerial performance, although this effect seems to be small compared with vertebrates.

Today, I have started my new two year Marie Curie Intra-European Fellowship in the Silk Group at the Department of Zoology, University of Oxford.

My Smithsonian Postdoctoral Fellowship ended today and I have therefore left the Smithsonian Tropical Research Institute, but will stay a few more weeks in Panama to get more field data and to analyze data. Over the summer more data will be gathered in Denmark and I will finish analyzing the data and start writing it up.

Welcome to www.thomashesselberg.com. This personal web site is primarily intended for people interested in my research, but it also has links to and descriptions of some of my other professional interests.