A diet to match their looks: Poop ingestion enhances nursing behaviour in the naked mole rat

6257900180_011c442162_o

As one of only two mammal species to exhibit eusociality, the naked mole-rats have received lots of attention from the scientific community and are well known for their inability to feel pain, extremely long lives, resistance to cancer and, of course, their sheer ugliness. In fact, the naked mole-rats are so bizarre that they were placed in their very own Family (the Heterocephalidae) due to their divergence from their nearest living relative taking place over 31 million years ago! However, what you may not know is that naked mole-rats exhibit a dietary practice which somehow makes them even less appealing: coprophagy – the act of eating poop. Gross.

Everything you’ll ever need to know about the naked mole-rat. (Video by thebrainscoop / Emily Graslie)

Restricted to their complex tunnel systems in desert environments of Eastern Africa, naked mole-rats are severely limited when it comes to what’s on the menu, with root tubers and plant bulbs making up the majority of their diet. These food sources are notoriously difficult to digest and thus require two full passages through the digestive system for nutrients to be fully absorbed. However, this may not be the only advantage to coprophagy in the naked mole-rat…

Colony structure of the naked mole-rat consists of one reproductively dominant queen and the few males with which she mates. The rest of the colony is made up of infertile, subordinate female workers which carry out tasks such as tunnel digging, colony defence, maintenance of chamber cleanliness and rearing the pups produced by the queen.

Picture_6

Pregnant naked mole-rat queen (centre) surrounded by her subordinate workers.

A recent study by a group of Japanese researchers found that workers belonging to a colony whose queen had just given birth were most responsive to the recordings of crying rat pups when compared to other groups of workers. Furthermore, high levels of an oestrogen compound important for parenting, oestradiol, was found in worker urine and faecal matter, but only when the queen was pregnant. However, as a result of their infertility, the worker force is incapable of producing such hormones and should subsequently be useless when it comes to rearing their queen’s pups. However, this is not the case at all. So, what’s happening here?

As it so happens, naked mole-rat workers have specialised bathroom chambers which they share with their queen, meaning they may in fact be acquiring the hormones required for parental care by feasting on royal excrement. To test this hypothesis, the researchers fed groups of workers with either the faeces of an already pregnant queen or the faeces of a non-pregnant queen treated to express high levels of oestradiol and once again assessed worker responsiveness to pup crying. In both cases, the workers exhibited high levels of responsiveness upon hearing the cries of a distressed pup.

Such results suggest that coprophagy is not only important for adequate digestion of food sources but also plays a major physiological role in providing workers with the necessary hormones for effective parenting of the queen’s pups, leading to more successful colony life.

Read more: Non-breeder’s alloparenting behaviors are enhanced by coprophagy in eusocial rodents, the naked mole-rats

Advertisements
Tagged , ,

ESCAPING THE ANTLION’S DEN

The trap-jaw ants (Odontomachus) are a genus of carnivorous ants famous for their large mandibles which are capable of snapping shut at speeds of up to 60 metres/second and generating forces in excess of 300 times their own body weight. Whilst such mandibles are obviously helpful when it comes to killing prey, they are also important for nest defence, with various trap-jaw ant species having been observed ‘catapulting’ intruders away from their nests, and provide a novel mechanism for escaping from predation, with the ant adopting a characteristic posture before snapping its jaws shut against a surface, propelling it backwards in what is known as a ‘jaw jump’.

Demonstrating jaw jumping in Odontomachus (Video by The Patek Lab):

One such predator that trap-jaw ants may need to escape from is the larval stage of the lacewing (dragonfly like insects belonging to the family Myrmeleontidae), known as the ‘antlion’. Antlions employ an ambush hunting strategy, in which they use their large abdomens to dig circular pits in soft, sandy soil before burying themselves in the bottom with their large jaws protruding (akin to the sarlacc for you Star Wars nerds out there). It is here where the antlion patiently waits until an unfortunate insect (usually an ant, hence the name) stumbles into its pit and is dragged beneath the soil and consumed by this voracious predator. Incredibly, if it looks like its potential meal is going to get away, the antlion is able to fling sand at its prey, further destabilising the walls of the pit and causing the prey to slide back towards the bottom.

antlion

The larval and adult stage of the antlion. The holometabolous life-cycles of various insects always surprise me. I think it’s amazing how something so evil looking can transform into something so normal looking over the space of just one month (Larvae photo credit: Joseph Berger; Adult photo credit: Entomart). 

Demonstrating the ambush hunting strategy of antlion larvae (Video by National Geographic):

A study published this week in PLoS ONE made use of this predator-prey system to decipher how the trap-jaw ant, Odontomachus brunneus, utilises jaw jumping to escape from predation. Multiple antlions were collected from the field, allowed to dig their ambush pits in sand-filled containers and starved for a period of 48 hours. Following this starvation period, an individual ant was introduced into each antlion container and the outcome of the predator-prey interaction was observed. Ants were either caught by the antlion, escaped by running up the side of the pit, or escaped by jaw jumping out of the pit. Following this, the mandibles of ants were glued together (thus ensuring they were unable to jump) and these restrained ants were introduced into the antlion containers. The escape rates of these restrained ants were then compared to their unrestrained conspecifics, allowing the researchers to assess the importance of jaw jumping in predation avoidance.

glued mandibles

During this experiment, some unfortunate Odontomachus brunneus workers had their mandibles glued together and thus were unable to avoid predation via jaw jumping (Image from Larabee & Suarez, 2015).

In approximately one third of all trials, O. brunneus was caught by its antlion predator. However, in the remaining two-thirds of the trials, O. brunneus was able to make it out of the encounter alive, with 15 % of such escapes as a result of jaw jumping and the remaining escapees managing to run out of the pit before the antlion was aware of their presence. Such jaw jumping behaviour was only observed after O. brunneus was aware of the antlion, suggesting that jaw jumps were a last-ditch escape attempt. However, this tactic wasn’t always successful, with only 26.5 % of jaw snaps resulting in successful jumps, understandable considering the instability of the pit walls which is further increased by the antlion flinging sand at its potential prey.

Regardless of such failed attempts, jaw jumping still makes a significant difference in the survival rates of O. brunneus, with ants whose mandibles were experimentally glued together significantly more likely to be caught by the antlions. In fact, those ants with unrestrained jaws were almost five times more likely to survive encounters with antlions than those who were unable to use their jaws to jump. Therefore, whilst the primary function of the trap-jaw ant’s powerful mandibles is to hunt prey, they have also been co-opted over evolutionary time for predator avoidance. Such predator-prey co-evolution has most likely taken place as a result of small colony sizes in the trap-jaw ants when compared to other social insect colonies. As a result, workers are no longer considered ‘disposable’ and there is considerable selection for workers to remain alive since this would be highly advantageous for colony productivity.

Here’s a fantastic video which perfectly sums up the entirety of this experiment (Video by Adrian Smith, Fredrick Larabee & Andrew Suarez):

Read more: Larabee, F. J. & Suarez, A. V. (2015) Mandible-powered escape jumps in trap-jaw ants increase survival rates during predator-prey encounters. PloS ONE. 10.1371/journal.pone.0124871.

Tagged , , ,

SUICIDAL STINGLESS BEES

Social insect workers, which typically have no means of direct reproduction, have a variety of methods to protect their nests from potential threats. In the most extreme cases, this often involves the self-sacrifice of defenders. The most widely known example of this can be found in honey bee (Apis mellifera) workers, whose barbed stings remain embedded in the skin of a potential threat to their nest, increasing the efficiency of venom delivery and also sending out alarm pheromones to other workers. This process, known as ‘sting autotomy’ ultimately causes the worker’s death but is advantageous since it increases the chances of deterring a predator from the nest. Nest defence is of utmost importance to workers since the nest contains their mother (the queen), their siblings, food stores, and nesting material. Therefore, if the inclusive fitness benefits are great enough, suicidal nest defence can be selected for.

honey bee sting

Demonstrating sting autotomy in a honey bee worker (Image credit: Kathy Keatley Garvey).

The stingless bees (Meliponinae) can be found worldwide in the tropics, with colony sizes ranging from 100 – 100,000 workers. Contrary to their name, the stingless bees do in fact possess stingers. However, they are are highly reduced and cannot be used for nest defence. Therefore, stingless bees have become reliant on alternative strategies for nest defence, such as biting, chemical warfare and alarm pheromones.

Inspired by prominent apidologist Francis Ratnieks’ past experiences with the bites of stingless bees, a recently published study in Behavioral Ecology & Sociobiology highlighted just how far some Brazilian species were willing to go in order to defend their nest. Overall, 12 species of Brazilian stingless bees were investigated. To test nest defence behaviour, flags were waved near nest entrances to provoke workers into attack. Attack latency (i.e. the time interval between the start of flag waving and subsequent worker attack), attack duration and number of workers attacking were all measured to produce an aggression score for each species. Following this, the authors tested whether workers were prepared to lose their lives in the defence of their colony by pulling on their wings with forceps. Attacking workers could either relinquish their grip on the flag and survive or continue biting and lose their wings. Finally, all six authors allowed a worker from each species to bite their forearm and measured the pain on a scale of 0 to 5, where 0 = could not be induced to bite and 5 = bite produced a sharp, unpleasant pain.

trigona hyalinata

The stingless bee Trigona hyalinata in full bite mode (Image credit: Francis Ratnieks).

Of those that attacked the flag (nine of the twelve species), the three Trigona species exhibited far higher aggression rates than any other stingless bees, with one particularly devoted T. fuscipennis worker attacking for almost an hour! These same Trigona species also exhibited the most painful bite, with all three of them getting a full five marks on the pain scale. Looking at the pictures of their mandibles, which possessed five sharp ‘teeth’, it’s easy to understand why. Next, consider that there can be up to 100,000 workers in a single colony and you find a worker force that is highly capable of deterring any potential threats away from their nest.

mandibles

The mandibles and pain scores (out of 5) for three particularly aggressive species of Brazilian stingless bee (Trigona hyalinata, Trigona fuscipennis and Trigona spinipes; Image from Shackleton et al., 2015).

The Trigona species were also highly likely to sacrifice themselves for the sake of the colony. T. hyalinata was particularly suicidal when it came to nest defence, with a remarkable 83% of workers suffering from mortal damage rather than relinquishing their grip on the flag. In addition, T. fuscipennis and T. sninipes workers also exhibited fairly high levels of suicidal nest defence behaviour (both at around a 40% frequency). However, suicidal nest defence was not just restricted to the Trigona genus, since it occurred at a rate of 7 – 23% across Tetragona clavipes, Scaptotrigona depilis and Partamona helleri, suggesting that suicidal biting is an example of convergent evolution across the stingless bees and may be more common than once thought.

Read more: Shackleton, K., Toufailia, H. A., Balfour, N. J., Nascimento, F. S., Alves, D. A. & Ratnieks, F. L. W. (2015) Appetite for self-destruction:suicidal biting as a nest defense strategy in Trigona stingless bees. Behav. Ecol. Sociobiol. 69 (2), 273-281.

Tagged , ,

INTRODUCTION

Hello and welcome to “You, me & eusociality”

I’m Ryan, a final year Biological Sciences student at the University of East Anglia in Norwich, UK. Having recently finished my dissertation (and deciding that I wasn’t busy enough with Master’s applications and revision for my upcoming exams), I’ve started this blog to share my fascination with all things relating to eusociality (an advanced state of social organisation in which some individuals forego reproduction in order to focus on rearing the offspring of others).

itsame

Here’s me on a recent trip to Cornwall (I don’t know what I’m doing with my hands)

I will try my very best to post something at least once a week. However, as I am coming into a very busy and important period in my undergraduate degree, I can’t make too many promises at the moment!

For those who are interested, you can keep up with me on Twitter: @RBrock94 or Instagram: ryanbrock94. I also actively encourage any readers to comment with questions/ideas for future posts.

Thank you for reading!

Tagged , , , , ,