New Paper: Sex specific signals help explain aggregations of dung beetles

Last summer, a keen student (Jack Ford) got in touch wanting to learn more about what being a scientist/entomologist is all about.  Jack helped with one of my research projects by helping process soil samples.  Between handfuls of worms and cold, wet earth – we discussed designing and running a small experiment together. We managed to pull it all together, discovered an interesting result, and wrote it up. Excitingly, we have recently had the results published as a short communication in Ecological Entomology (links at the bottom of the post).

The basis of the experiment was simple, when looking for dung beetles in cattle dung, you’ll quickly find individuals are  aggregated amongst dung pats. Some pats have plenty, some have a few, and some have none. There have been considerable efforts made to understand what factors influence the ‘clumping’ of these beetles within pats. A big part of this involves how attractive the dung pat is to colonising insects: what makes ‘Dung Pat X’ so much more attractive than ‘Dung Pat Y’?

beetle

The answer to that question is complex.  A number of factors influence the attractiveness of dung. For instance: whether the animal produced the dung during day or night, the size of the dung pat, the species of the animal, the exposure of the dung, the weather during the beetle’s dispersal flight, etc.

One hypothesis is that dung beetles themselves enhance the attractiveness of a dung pat. We thought this could very well be the case with the species Aphodius fossor – as it never seems to be alone. This species always hanging out with a friend (usually a mate), but often you’ll find a number of pairs within the same dung pat.  It’s a burly beast (as far as the dwelling Aphodiinae go) – measuring a little over a centimetre in length, and having a very convex (almost jelly bean-like size/shape). We figured the commonness, large size, and behaviour of this species would make it a good contender for our experiments.

We suspected the aggregation of these beetles could be due to a few reasons. First of all, when dung beetles colonise a dung pat – they tunnel through it. This aerates the dung environment, encouraging different bacterial communities thus altering the composition of gases fluxing from the dung pat. Beetles might be using this cue to search out new dung pats (possibly an area with friends already enjoying a dung-feast themselves).

An other interesting question involves the pairing of this species. Individuals are almost always with a mate; How does this happen? The world is a big place, even more so for a small insect. One strategy that insects use to find mates are pheromones – chemical signals produced and received by the same species. There are many different types of pheromones that serve a variety of purposes. One such type, attraction/aggregation pheromones are fairly well documented in related scarabaeidae.

We set out  test whether beetles colonising a dung pat made it more or less attractive to additional colonising beetles, and whether differences were sex specific by creating a simple choice experiment. We collected dung from a single (adorable welsh black) cow at Dr Beynon’s Bug Farm, homogenising, then splitting the dung into nine small pats. We then assigned each dung pat to one of three conditions: add four female beetles, add four male beetles, add no beetles. We then gave them a little time in their new home. From herein, these dung pats are considered the ‘experimental pats’.

In the meantime, we constructed arenas using large buckets. We filled them with sand, and drilled holes in the side to fit small lengths of tubing. These tubes led into the smaller containers that would eventually connect to the experimental pats.

F12
Depiction of our experimental set-up

After giving the beetles some time to enjoy their new homes in the treatment pats, we began our experiment. We introduced ninety individuals of each sex into the larger arena in groups of ten. The beetles ambled (slowly) around the arena. Most often, beetles walked cautiously into the tubes – pausing at the tube end with rapid antennae movement – eventually heading back into the main arena, or dropping into the smaller buckets. We promptly removed the beetle when it dropped in, and recorded which bucket it landed in.

When we tallied up the results, and analysed the data – we found something quite interesting. Male beetles had no preference for any type of dung. Females on the other hand preferred dung colonised by males, and consistently avoided dung colonised by other females.

We think that females might avoid dung pats colonised by other females to reduce likelihood of encountering density-dependent mortality (too many mouths, and not enough food/space). This is something that we see relatively often from other insects, and is often achieved through production of ‘host marking’ or ‘anti-aggregation’ pheromones.

The attraction of females to dung pats colonised by males suggests that there could also be signals produced by males, that draw the females in. Male produced pheromones have been identified in a few species of related scarabaeidae. We observed beetles burying part-way into the dung after being added to the dung pats. In the dung beetle, Typhaeus typhoeus (Geotrupidae), males have been observed digging a short tunnel under dung – and defecating with their abdomens in the air (this is thought to represent pheromone release).

What’s sort of curious about this experiment, is that with the two mechanisms we identified – (female-female avoidance) and (female-male attraction), it’s unclear how this would lead to the aggregated distributions we see in nature. Partly, we think this could be due to one signal (attraction) being stronger than the other (avoidance). But there is so much about these beetles we just don’t know, that could be the key to understanding their distributions amongst habitat patches? For instance:

  1. Who moves first? Do males and females arrive/leave at the same time?
  2. Are the signals that we’ve identified from the beetles themselves, or as a result their interaction with the physical/microbial environment of the dung pat?
  3. Do signals depend on beetle density?
  4. As these beetles primarily disperse through flight, how representative of attractiveness are ‘walking’ experiments like this one?
  5. How do the presence of other invertebrate groups act to affect subsequent invertebrate colonisation?

So many questions, so much to discover, and so little time to do it all. I’ve found the deeper I venture into ecology, the more apparent these opportunities and limits become. On that note, I should probably get working on my plans for the final field season of my PhD, time is ticking.

Thanks for reading, and here are links to the paper:

Early View at Ecological Entomology: Manning and Ford (2016)
Pre-Review Draft: Manning_Ford_2016_Draft

 

 

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Bug of the Week: Aphodius erraticus

The bug of the week is Aphodius erraticus. This is a species I have used in experiments during my PhD, and is particularly endearing. Its elytra is a charming golden-bronze, with dark inner striae which almost gives the impression of an extra-long scutellum. This is one of the most common European species, and it can also be found in North America. It was inadvertently introduced across the pond in soil ballast, or perhaps from livestock dung on less than pristine ships.

BOTW

Dung beetles vs Greenhouse Gases: Round Two

DB_Climate_change.pngProducing beef and milk comes with significant environmental costs. Cattle manure may harbour pathogens which have potential to contaminate waterways. Heavy trampling associated with intensive grazing can damage the structural integrity of the soil, making it difficult for plants to grow. Perhaps the largest impact cattle have on the environment is a little more abstract – the gaseous products of cows’ digestive systems.

Cattle are real wind-bags, belching out reams of greenhouse gases (predominately methane). These gases trap heat within the atmosphere, and contribute to global warming. As humans develop larger global appetites for beef and dairy products, the environmental costs of production will also increase. Luckily, have insects to help keep things in check.

When it comes to livestock production, dung beetles are a taxon that often come to the rescue. By burying dung deep into the soil, dung beetles can help reduce E.coli contamination on plants. The same tunnelling and burial action of beetles can also help repair damaged soil structure, improving hydrological properties, and reducing surface compaction. Dung beetles can even help regulate greenhouse gases from the livestock sector. While most greenhouse gases directly emitted from cattle come in the form of enteric fermentation (gaseous byproducts of digestive bacteria expelled via flatulence and burps), a study from 2013 demonstrated that dung itself acts as a source. However when dung beetles tunnel through, and feed on the dung – the team found reduced levels of methane emissions. Could dung beetles be part of the solution to greenhouse gas emissions from cattle? Possibly.

A recent study published in Scientific Reports set out to quantify the benefits dung beetles provide in reducing greenhouse gas emissions within the livestock sector at three scales: dung pat, pasture, and nationwide.

The team found that dung beetles played a significant role in reducing greenhouse gases when considered at the smallest scale: a dung pat. By capturing the gases fluxing from dung pats with or without beetles – the team found that dung beetles could reduce warming potential 7% relative to beetle free controls. When considering the impact of cattle at a pasture level, the effect was even larger – an impressive 12%. While this at first may seem counter-intuitive, the added bonus of dung beetles at a larger scale is due to cattle turning pasture from a sink to a source of greenhouse gases.

Finally the team looked at an impressively larger scale: across the whole beef and dairy industries in Finland. They used a technique known as life-cycle analysis. This is an approach that considers the impact of a product over its entire existence (birth-death). There are many inputs associated with conventional livestock operations that contribute to the impact of producing beef and dairy products. In Finland as well as many other northern-situated countries, cattle are unable to spend the entire year on pasture. This means that livestock hangout in barns during the off-season, often consuming grain and silage. Producing this feed comes with it’s own environmental footprint including : fertilisers, transport and soil tillage. Each of these sources adds up, which acts to continually dilute the benefits provided by dung beetles. The team found ultimately, due to a relatively intensive production system, and a short grazing season – benefits provided by dung beetles were a drop in the bucket – representing about 0.08% reduction in greenhouse gas warming potential in the wider context of Finnish beef and dairy industries.

The authors point out that while dung beetles play a relatively small role in reducing greenhouse gas emissions on a national scale, that their story is a small part of a bigger picture. Benefits provided by dung beetles is much greater when systems are characterised by: lower levels of agricultural inputs, longer periods of dung beetle activity, and greater time spent on pasture. These three factors are indicative of production methods practiced throughout much of the world – particularly in tropical environments. Competition for dung in the tropics tends to be stronger as well, where dung is quickly removed and buried. This action might act to further increase the beneficial roles that dung beetles play in reducing greenhouse gas emissions. As dung beetles are sensitive to environmental changes including: the use of veterinary medications, and deforestation – wider environmental disturbances could have the potential to spill over, increasing the footprint of livestock production.

NB: You can (and should) read this paper in its openly-accessible entirety over at Scientific Reports.

Dung beetles help reduce risk of E.coli transmission in lowbush blueberry systems

UntitledHumans and wildlife often have competing interests. In North America, this conflict is epitomised by the white-tailed deer (Odocoileus virginianus). Just take a moment to ask any gardener who lives in an area with a thriving population. Deer have a voracious appetite for tender plants. This is frustratingly paired with their ability to gracefully bound over fences with unparalleled ease. The white tailed deer can drive even the most pedantic of ‘deer-proofing’ gardeners insane.

But deer don’t limit themselves to causing nuisance in domestic gardens. They’re opportunistic generalist browsers, and agricultural fields are generally a perfect location for a nice feed. This can translate to significant yield losses for farmers. Voracious deer browsing can take precedence over many other pest problems, as there is little point in worrying about pests reducing yield quality, when your seedlings become deer fodder.

The damage deer exert on agricultural crops is not just limited to herbivory. The scat of deer can contain fecal pathogens, which can be spread to humans consuming contaminated product. E.coli-O157:H7 is a perfect example, where outbreaks in apple cider and strawberries are thought to have been caused by deer scat contamination.

Enter the dung beetle: Dung beetles are widely known to deliver a slew of ecosystem functions with benefit to sustainable agricultural production. Activity of dung beetles can reduce spread of parasites, improve the hydrological properties of soil, increase pasture herbage growth, and reduce pasture fouling (to name a few). Recently, a team from University of Maine, set out to test whether white tailed deer might act as a source of E.coli O157:H7 contamination in lowbush blueberry production systems and if so, whether a common species of dung beetle might play a role in suppressing the spread of this pathogenic bacterium.

The team conducted a series of experiments, described in detail in an open-access article published in PLoSThe first component was a field survey for different types of animal faeces; turning up scat from deer, black bear, snowshoe hare and wild turkey. The team collected more than 300 samples, and using laboratory methods determined that E.coli O157:H7 was present in lowbush blueberry fields (albeit in low presence 1.9% of samples).

The team then set out to test whether deer scat, would have the ability to vector E.coli to fruit. This was tested in a field experiment where deer scat spiked with a non-pathogenic strain of E.coli O157:H7 was dropped from 1-m height onto fresh berries. The fruit was harvested several hours later, and using laboratory techniques the team found that quick ‘glancing’ contact between the scat and berries was sufficient to spread E.coli.

There has been previous research conducted demonstrating that dung beetles might play a role in spreading diseases by inadvertently ‘piggybacking’ pathogens  between farms (Xu et al 2003). To test whether dung beetles might play in vectoring E.coli to fruit – the team turned to a common dung beetle known as the ‘scooped scarab’ Onthophagus hectate. The team placed live beetles in a terrarium with blueberry plants, and dung inoculated with the same non-pathenogenic strain of E.coli. Despite large amounts of contact of beetles and the dung –  O. hectate did not play a significant role in spreading E.coli to the blueberries.

Finally the team checked out whether this dung beetle was able to reduce the concentration of E.coli in the soil through their action of burying the dung. Because the fruit of lowbush blueberry hangs close to the ground, often resting on the soil – there is a strong likelihood of transmission from bacteria from the soil, or dung onto the fruit. Here, the team found that the activity of O. hectate significantly reduced the amount of colony forming units found in the soil – supporting the idea that dung beetles could play an active role in suppressing pathogen loads in wild blueberry systems. Dung beetles to the rescue yet again!

This work is another wonderful piece of evidence supporting the philosophy that conserving beneficial insects within landscapes can keep our agricultural ecosystems sustainable. Conserving beneficial insects in lowbush blueberry systems can help control pest populations and support pollination services. Other functions (like suppression of pathogenic bacteria) provided by beneficial invertebrates are often subtle, and can go largely unnoticed and unappreciated.

Next time you find yourself with a bowl of delicious lowbush blueberries – why not take a minute to thank a dung beetle. But for the sake of your health, it wouldn’t hurt to give them a quick run under the tap. Safety first.

References: 

Jones, M.S., Tadepalli, S., Bridges, D.F., Wu, V.C.H., Drummond, F., 2015. Suppression of Escherichia coli O157:H7 by Dung Beetles (Coleoptera: Scarabaeidae) Using the Lowbush Blueberry Agroecosystem as a Model System. PLoS One 10, e0120904. doi:10.1371/journal.pone.0120904

Nichols, E., Spector, S., Louzada, J., Larsen, T., Amezquita, S., Favila, M.E., 2008. Ecological functions and ecosystem services provided by Scarabaeinae dung beetles. Biol. Conserv. 141, 1461–1474. doi:10.1016/j.biocon.2008.04.011

Renkema, J.M., Manning, P., Cutler, G.C., 2013. Predation of lowbush blueberry insect pests by ground beetles (Coleoptera: Carabidae) in the laboratory. J. Pest Sci. (2004). 86, 525–532. doi:10.1007/s10340-013-0480-3

Xu, J., Liu, Q., Jing, H., Pang, B., Yang, J., Zhao, G., Li, H., 2003. Isolation of Escherichia coli O157:H7 from dung beetles Catharsius molossus. Microbiol. Immunol. 47, 45–49. doi:10.1111/j.1348-0421.2003.tb02784.x

Beautiful British Beetles IV: The Minotaur

This is one of my absolutely most favourite beetles. I was shown my first one by my friend Richard, who found it in a very serendipitous moment on a night-time hunt. They’re slow, but faster than you think – a minotaur can slip into its tunnel faster than one would expect. I also came across this beautiful little beetles on Ramsey Island in Pembrokeshire, a gorgeous RSPB reserve known for its fabulous dung beetles (along with seabirds, choughs, pergrines, rare lichens, and a welcoming and knowledgable staff). Looking forward to searching out a couple of my own this weekend in Oxfordshire. minotaur_beetle

A tale of two introductions

toad_beetles

Native to Central and South America, cane toads have a permanent grumpy expression, and the chubby legs of a human toddler. They are large (a typical adult toad can measure up to 15-cm from snout to vent), and can be well over a kilogram in mass. In order to become big and strong, cane toads must consume an impressive number of calories. They achieve this by having a non-discriminatory diet, consuming: insects, other toads, plant matter, small mammals, and even birds.

The voracious appetite of the cane toad has made it a popular choice as a biological control agent. As toads hop through sugar plantations, they gobble up pest insects reducing the need for applying chemical insecticides. While early biological control programs augmented cane toad populations within their native range, scientists soon began to explore whether cane toads would be successful in new environments. After cane toad introductions to several Caribbean islands in the were successful in the 1930s,  a larger island, much further away began to show interest.

Across the South Pacific, Australia was struggling with a serious pest problem on sugar cane plantations. The cane beetle (Dermolepida albohirtum) – a small black and grey scarab native to Australia – was greatly reducing sugar yields. Having recently launched a successful biological control campaign to suppress the spread of prickly pear cactus, Australia gave the cane toads a shot – releasing thousands of young toads in the late 1930s.

Unfortunately, the toads did very little to control populations of cane beetles. The low levels of cover in sugar cane plantations reduced the foraging activity of cane toads. Additionally, adult beetles live near the top of plants and cane toads are ineffective climbers. Furthermore, the larvae of the cane beetles live deep in the soil feeding on sugar cane roots – far from the mouths of hungry toads. As the environment wasn’t right, and the food wasn’t accessible, the toads turned their bumpy backs on cane beetles. Instead they began consuming almost everything else, having devastating effects on Australian fauna.

The destructive impact that cane toads have had in Australia is not unique. The country has a long history of spectacularly invasive species which have been introduced either purposely or accidentally. Rabbits, camels, red foxes, feral goats, donkeys, and pigs are all thriving, and doing a number on the native flora and fauna. However, Australia is also the site of one of the most successful biological introductions to date: dung beetles.

In the 1960s, entomologist George Bornemissza realised that accumulating cattle dung was quickly blanketing pastures, where an estimated 2,000 km2  of land was lost to dung on an annual basis. While the immediate repercussion of  dung involves the limiting available grazing area, stagnant dung causes a myriad of other problems including: higher fluxes of greenhouse gases, increased rates of parasite transmission and provides ample habitat for pest flies to reproduce. The reason why this was such a problem in Australia was because a key group of insects were missing from the cow pats: dung beetles.

Australian dung beetles evolved to use the fibrous dry pellets of marsupials, and were unable to cope with the wet messy dung of bovines. In the late 1960s after careful planning and deliberation, the Australian government released 23 species of dung beetles from around the world at different points around Australia. These beetles had evolved to deal with dung of similar consistency, and went straight to work. Today, many species have successfully established and are thriving on the huge amounts of dung produced by the 29 million odd cattle in Austalia. While dung beetles free pasture from dung, their activity also improves soil fertility, removes habitat for the larvae of blood-sucking flies, and halts the spread of enteric parasites.

However, recent research from Australia demonstrates that these two introductions are interacting in an alarming way. Cane toads, which were imported to control a scarab beetle pest have instead switched their energy to controlling another type of scarab: dung beetles.  In a study published this week in the journal Ecosystems,  the profound impact our management choices have upon the surrounding ecosystems are clearly illustrated through the example of cane toads and dung beetles.

The study was conducted in the north of the Tarnami desert – which unsurprisingly is a hot and dry area. In order to raise cattle, you need to ensure that animals have access to plenty of water. As natural water sources aren’t terribly common, producers create water points through the use of boreholes and pumps. Water is driven from deep underground into two principal types of water sources : earthen dams where toads can easily access the water, or into large plastic or metal tanks which essentially removes toad access.

As cane toad tadoples need a reliable water source to complete development, and adult cane toads require also require intermittent access to moisture – the team hypothesised that there would be higher densities of cane toads near earthen dams in comparison to tanks. Because these toads are known to prey on all sorts of insects, they hypothesised that higher densities of toads would cause lower densities of dung beetles.  Finally, the team hypothesised that lower densities of dung beetles would mean lower rates of dung removal. By sampling at 13 different watering points (five dams and eight tanks), the team found crystal clear answers to their questions.

Population densities of cane toads were five times higher in areas surrounding earthen dams, than surrounding tanks. Abundance of dung beetles was 12 times higher near tanks in comparison to earthen dams, thought to be caused by high predation rates. Finally, the increased population of dung beetles at tanks meant 13% higher rates of dung removal in comparison to rates at earthen dams.

By making the switch from earthen dams to tanks, cattle ranchers can play a significant role in reducing the spread of a problematic invasive species, while protecting a group of beneficial introduced species. As tanks are less prone to evaporation and seepage, less water is extracted, meaning fuel is saved. This is a more economically and environmentally sustainable option for cattle ranchers. Hopefully with time, more operations will make the switch to slow down the toads, thus supporting dung beetles and the myriad  of ecosystem services they provide.

References
Baillie, C. 2008. Assessment of evaporation losses and evaporation mitigation technologies for on farm water storages across Australia. Cooperative Research Centre for Irrigation Futures, Irrigation Matters Series, (05/08).

Feit, B., Dempster, T., Gibb, H., & Letnic, M. 2015. Invasive Cane Toads’ Predatory Impact on Dung Beetles is Mediated by Reservoir Type at Artificial Water Points. Ecosystems, 1-13.

Lever, C. 2001. The cane toad: the history and ecology of a successful colonist. Westbury Academic & Scientific Publishing.

Nichols, E., Spector, S., Louzada, J., Larsen, T., Amezquita, S., Favila, M. E., & Network, T. S. R. (2008). Ecological functions and ecosystem services provided by Scarabaeinae dung beetles. Biological conservation, 141(6), 1461-1474.

Penttilä, A., Slade, E. M., Simojoki, A., Riutta, T., Minkkinen, K., & Roslin, T. (2013). Quantifying beetle-mediated effects on gas fluxes from dung Pats. PloS one, 8(8), e71454.

Happy Taxonomy Day!

March 19th is Taxonomy Day, a 24-hour period dedicated to the science of defining where biological organisms belong, based on their common characteristics. If the mnemonic “Kings Play Chess On Fine Green Silk” is familiar, you’ve already had a lesson in taxonomy. This represents how we classify organisms from the most broad category (Kingdom), all the way  down to the finest (Species).

For my Taxonomy Day post, I chose to focus on two species I am very familiar with Aphodius fimetarius and Aphodius pedellus. These species of dung beetles superficially look almost identical, and nobody realised that they were completely different species until they were kayotyped. This is a process where the chromosomes of an organism are isolated, stained, and examined under a microscope. When several different representative beetles of this brilliant beetle were examined under the scope, their chromosomes were completely different. There weren’t any examples of individuals where chromosomes looked like a mixture of the two types, meaning there were no instances of hybridisation.

Scientists then realised that the species had different morphological characteristics as well. One species had a more densely punctured pronotum than the other. Even more striking differences were found when the aedeagus (male genitals) of the two different species were compared. As the characteristics of individual beetles vary greatly from one to the next, it can be easy to lump things into species when they look the same. Through collaborations between traditional taxonomy, and new molecular methods – we can learn more about the wonderful diversity that often remains hidden out of sight.

ped_fim

Reference
Miraldo, A., Krell, F.-T., Smalén, M., Angus, R. and Roslin, T. 2014. Making the cryptic visible – resolving the species complex of Aphodius fimetarius (Linnaeus) and Aphodius pedellus (de Geer) (Coleoptera: Aphodiidae) by three complementary methods. Systematic Entomology 39: 531–547.