Summary from the authors: Species-level predation network uncovers high prey specificity in a Neotropical army ant community

Mass raiding army ants fascinated biologists ever since naturalists such as Bates and Darwin wrote about their behavior. Despite this profound human interest and the ecological importance of army ants as top arthropod predators in tropical forests, basic aspects of their biology still remain unknown. With up to 20 sympatric army ant species, certain tropical regions show high local army ant diversity and abundance. We asked how so many top arthropod predators can co-exist? We tackled this question by conducting a large-scale dietary survey of 11 army ant species in one Costa Rican location, i.e. La Selva Biological Station. We identified prey items morphologically, if possible, and via DNA barcoding in difficult cases (e.g., prey larvae). We were thus able construct a high-resolution species-level predation network. Army ant prey nearly exclusively consisted of other ants with 129 ant species being detected among prey. This is roughly 1/4th of all known ant species in this particular area. Most importantly, ecological network analyses revealed a high degree of dietary specialization in army ants, which was accompanied by differentiated prey niches between species. In summary, our results help to explain the coexistence of many army ant species in certain tropical regions. – Philipp Hönle, Technische Universität Darmstadt

Army ant (Nomamyrmex esenbeckii, left) fighting against a leafcutter ant (Acromyrmex, right) while raiding their nest. Photo courtesy of Philipp Hönle.

Hoenle, Philipp O., Nico Blüthgen, Adrian Brückner, Daniel JC Kronauer, Brigitte Fiala, David A. Donoso, M. Alex Smith, Bryan Ospina Jara, and Christoph von Beeren. “Species‐level predation network uncovers high prey specificity in a Neotropical army ant community.” Molecular Ecology. 2019. 28:9 2423-2440.

Interview with the author: Phototactic tails- Evolution and molecular basis of a novel sensory trait in sea snakes

In this blog post, we learn about how coming across an an old paper describing a strange behavior in sea snakes led Jenna Crowe-Riddell to a topic of their PhD research. In this integrative study, Crowe-Riddell and colleagues use a combination of behavioral experiments and transcriptomics to identify a set of candidate genes related to the curious behavior of tail withdrawal in response to light observed in some species of sea snakes. Read on for more details behind the study in our interview with Jenna, with a link to the paper at the end.

Photo from Jenna Crowe-Riddell

What led to your interest in this topic / what was the motivation for this study? 
I was about to embark on my first field trip to catch sea snakes in Broome, Western Australia, as part of my honours research project. I was digging around the old literature and came across a brief and curious paper on how olive sea snakes react to light on their tail paddles. Olive sea snakes (Aipysurus laevis) are a common species in Broome so I asked my supervisor whether we could repeat the experiment. We were both surprised to see a baby olive sea snake repeatedly withdrew its paddle-tail away from our flashlight. I had so many questions about this strange behaviour that I was compelled to continue studying it for my PhD!

What difficulties did you run into along the way? 
There were a lot of challenging aspects to this project because we were studying a novel sensory system in a non-model organism with no genome sequence data available, which meant that analysing RNA-sequencing data was especially difficult. However, one of the most difficult (and enjoyable!) aspects of the research was bringing together a diverse team of people-bioinformaticians, physiologists, vision biologists, wildlife workers, statisticians, etc. to investigate the genetic pathways, ecological mechanisms and behaviour of tail phototaxis. Weaving together these different approaches to tell the evolutionary story of tail phototaxis made writing the manuscript a tricky but rewarding part of the project.

What is the biggest or most surprising finding from this study? 
In snakes, tail phototaxis has only been described in Aipysurus laevis, leading us to predict that this trait evolved in all sea snakes as a response to the ecological shift to the sea. However, our behavioural results show that only three out of eight species tested respond to light on their tails, inferring that tail phototaxis probably evolved in the ancestor of a clade of six Aipysurus sea snakes. That’s only 10% of the approximately 60 species of sea snakes!

Moving forward, what are the next steps for this research?
Expanding the sample size both within and among species to confirm the evolutionary origin of tail phototaxis. Employing a range of anatomical techniques (perhaps in situ hybridisation) to locate the photoreceptive structures within the tail skin. Discover the physiological pathways –e.g. how is light transduced or perceived by the snakes? What intensity and part of the spectrum are snakes most sensitive to? I would also like to gather more data on how these species behave in the wild to better understand ecological factors that contribute to the evolution of dermal photoreception. Finally, we can use our discoveries in sea snakes to make predictions on how this trait convergently evolved in other vertebrates like hagfish, lamprey and aquatic salamanders.

What would your message be for students about to start their first research projects in this topic? 
Be patient. Things never work out the way you think they will but that’s okay because being on the edge of the unknown means that 99.99% of your ideas will probably be wrong! That’s how new knowledge is discovered: by testing out ideas and having them be knocked back, one by one. As my colleague used to say to me “you are cracking stone!” Furthermore, always ask for help. The perception of science as the endeavour of a lone genius is a myth, science is only achieved in teams.

What have you learned about science over the course of this project? 
See above!

Describe the significance of this research for the general scientific community in one sentence.
Our research exemplifies the power of an integrative approach to understanding the evolution of complex sensory traits.

Citation
Crowe-Riddell, J. M., Simões, B. F., Partridge, J. C., Hunt, D. M., Delean, S., Schwerdt, J. G., … Sanders, K. L. (2019). Phototactic tails: Evolution and molecular basis of a novel sensory trait in sea snakes. Molecular Ecology, 28(8), 2013–2028. https://onlinelibrary.wiley.com/doi/10.1111/mec.15022