evolution – Ecology Field Notes

Inspired by Gilbert White (naturalist, ornithologist and author of The Natural History and Antiquities of Selborne) the Selborne Society was formed in 1885 as Britain’s first national conservation organisation. Members of the Society went on to establish pre-eminiment organisations such as the National Trust and Royal Society for the Protection of Birds. Today, the Society manages Perivale Wood, an 11.6 hectare Local Nature Reserve in Ealing south-west London, where they organise an open day, and a wide range of indoor meetings and field excursions.

Perivale Wood Gates — Perivale Wood Local Nature Reserve. © John Kane.

dsc_0001-1 — Bluebell wood at Perivale Wood. © Juliet Langton.

I was invited to talk to the Society and members of the public about the biology and ecology of ants. This blog post is a very abbreviated form of that talk with a tiny selection of the slides used to give a bit of an overview. To be honest, I was always a bit uncomfortable with the title of the talk. I knew it would be impossible to cover everything to do with ants, so I focused on some of the areas of ant biology that most interest me.

But what’s so special about ants anyway? Well, ants are everywhere. With over 16,000 extant species found in every terrestrial habitat (apart from the polar regions) they constitute a large proportion of all living biomass. Enormously successful as scavengers, herbivores, granivores, predators and mutualists, ants perform important ecological functions as ecosystem engineers and keystone species. Some species are also highly successful at invading new territories where they can become crop pests or outcompete native species for resources. Their eusocial lifestyles also make them ideal model systems for the study of social evolution.

Part of my fascination with ants comes from the tremendous morphological diversity within and between species. Not only can there be differences between castes within species, but species can range in size from the minuscule Carebara atomus (~1 mm) to the comparatively enormous Dinoponera gigantea (~4 cm). I also have a bit of a soft spot for the myrmecophiles (other invertebrates that live in association with ants) and especially the myrmecomorphs (invertebrates that mimic the appearance and/or behaviours of ants). To share some of the beautifully complex variety of forms in ants and the ant-wannabes I asked the audience to play a game that I call “Ant Bingo!”.

Screen Shot 2018-02-22 at 15.27.30 — Which of these creatures are ants? (Answers at the end of the blog post).

Everyone got into the spirit of it and after discussing some of the characteristic features of ants managed to identify all six ants displayed amongst the other fantastic creatures.

Belonging to the order Hymenoptera, the family Formicidae (what we commonly call ants) emerged in the late Cretaceous (~140 MYA) when they diverged from the Apoidea – spheciform wasps and bees. There are now more than 16,000 species of ants in over 470 genera that we know of – it is thought that there may actually be at least as many species still to be discovered. According to some estimates, there are more than 10 quadrillion individual ants alive at any time.

This variety in form is echoed in the highly complex and variable social structures and life histories that have evolved in different ant species. The numerous ways in which they gather food and create shelters to protect themselves from the elements and potential predators are both fascinating and ingenious. In order to feed the colony, there are ants that harvest honeydew from aphids, some that cultivate elaborate fungus gardens, and others that send out raiding swarms that capture anything too slow to get out of their way. For nest-building, there are ants that use larval silk to weave leaves together in the treetops, those that excavate elaborate underground tunnels, and those that have co-evolved with plants to live within specialized swellings and chambers called domatia which are produced by the plants for the exclusive use of their ant protectors. These examples only briefly touch on a few of the magnificent examples of diverse life strategies found within the ants.

Screen Shot 2018-02-22 at 16.47.50 — A still from an animation explaining different colony-founding strategies used by ants.

There are many different social structures evident between (and sometimes even within) ant species. There are some with single queen colonies and some with multiple queens – in some cases hundreds of reproductive queens can live in the same nest. Queen number can also vary within a species so that there may be colonies with one or many queen(s). The colonies of some ant species can even persist without any queens; in these instances, worker ants can (rather peculiarly) become fully reproductive if the queen dies. These egg-laying workers are called gamergates. At the other extreme, there are the social parasites, where some species don’t produce a worker caste at all – their eggs will only produce the next generations of queens and males. These parasitic queens are known as inquilines, they take over the nests of closely related species who provide a ready workforce so there is no need to expend energy on creating more workers. And then there are what some people call the “slave-making” ants – these ants will raid other nests and carry the brood away to their own nest. The “slave” ants will then work in their new colony, defend it from attack and can even participate in future raids. This process of kidnapping and imprinting is more accurately referred to as dulosis.

I should also emphasise the fact that these social structures may vary over time depending on what life-stage the colony is at. For example, the number of reproductive queens within a colony may vary depending on whether the colony is experiencing a rapid growth phase such as the establishment of a new colony. At this early period, it can be highly beneficial to have many queens all laying eggs at the same time to quickly produce workers to protect the nest, forage for food and care for the brood. But after a time (once the colony is a bit more established) the need for multiple queens is diminished and what was a co-operative breeding chamber becomes an arena for a battle to the death until only one queen remains.

Ants are, in my view, remarkable animals. They have adapted to fill every conceivable terrestrial niche through evolving incredible morphological adaptations, variable social structures, and a dizzying array of life histories. There are also fantastic opportunities for research with many more species to be discovered and behaviours to describe.

This video clip from the BBC2 documentary Natural World: Attenborough and the Empire of the Ants shows wood ants (Formica sp.) defending their nest:

Further online resources about ants:

Answers to Ant Bingo! (those in bold are ants)

Cyphotes sp. Wingless wasp
Salticidae (jumping spider) mimicking Tetraponera mocquerysi
Tricondyla annulicornis tiger beetle
Azteca instabilis alate queen
Dorylus sp. male
Soldier termite Syntermes sp.
Velvet ant Mutillidae sp.
Discothyrea mixta
ant-mimicking staphylinid beetle Ecitomorpha cf. breviceps
Ecitocryptus sp. rove beetle
Eciton mexicanum with Nymphister kronaueri beetle attached
Leptomyrmex unicolor
Cephalotes varians

Cheats and Deceits: How animals and plants exploit and mislead. By Martin Stevens. Published by Oxford University Press (2016).

Last year, on a trip to Devon, I saw my first ever oil beetle (Meloe proscarabaeus). She was beautiful. Her black carapace glistened violet and blue in the sunlight. She was gravid and crawling along the footpath in search of a place to dig a nest burrow to lay her eggs. But what I did not yet appreciate was the extraordinary life cycle of these captivating beetles. The young of a related species, Meloe franciscanus, emerge from the nest and swarm up a nearby plant where they congregate in a mass mimicking the shape of a female solitary bee (Habropoda pallida) and release a chemical compound similar to the bee’s sexual pheromones. This proves all too irresistible to male bees who are drawn to this aggregation and attempt to mate with it, presenting the larvae with the perfect opportunity to grab hold of the bee and clamber onto his back. He then carries these passengers with him until he finds a female to mate with at which point the larvae instantly decamp onto the female. From here they then transfer to her nest where they devour the stored nectar, pollen and the bee’s eggs. The evolution of this complex mimicry is absolutely fascinating and forms part of Martin Stevens‘ interrogation of deception in Cheats and Deceits: How animals and plants exploit and mislead.

This book is an immensely informative and enjoyable exploration of the multiple roles deception plays in nature. Stevens sets out a detailed examination of a wide variety of instances of natural deception from well documented examples such as the evolution of camouflage through industrial melanism in the Peppered Moth (Biston betularia) to current research into the resemblance to falling leaves in the movement and colouration of Draco cornutus, a gliding lizard from Borneo. It is to Stevens’ credit that this book makes for entertaining and effortless reading while clearly citing all the relevant research within context and pointing to areas where knowledge is still lacking.

The language of deception is important. Stevens takes the time to explain some of the more commonly used terms associated with deception such as camouflage (blending in to the environment), mimicry (assuming the appearance – be that visual, chemical, behavioural or acoustic – of another organism) and masquerade (taking the form of an inedible object – as with stick insects). Mimicry and masquerade therefore lead to misidentification while camouflage reduces detectability or impairs recognition. Mimicry also comes in various guises some of which can be described as: aggressive, when predators mimic harmless species to enable prey capture; Batesian, when a palatable species mimics the characters of an unpalatable species, as seen in the chicks of an Amazonian bird Laniocera hypopyrra mimicking toxic caterpillars; and imperfect mimicry, as with hoverflies roughly resembling certain species of wasps and bees (for which there are a number of competing theories).

This, of course, only scratches the surface of a vast area of research that Stevens specialises in as head of the Sensory Ecology and Evolution group at the University of Exeter where he continues to research these themes. His enthusiasm for his topic is highly infectious; you find yourself transported from an explanation of background matching in cuttlefish, to an historical aside concerning the development of military camouflage, and on again to a description of his own field experiments in testing the efficacy of disruptive colouration.

“We must trust to nothing but facts: these are presented to us by nature and cannot deceive. We ought, in every instance, to submit our reasoning to the test of experiment, and never to search for truth but by the natural road of experiment and observation.” ~ 18th-century chemist Antoine Lavoisier

The book does rely heavily on zoological examples, and although Stevens doesn’t entirely neglect plants his observations do tend to mainly focus on carnivorous plants and orchids. But to be fair, Stevens does make the point that more research into botanical forms of deception is required and suggests that this should be undertaken with a view to specifically exploring the roles of chemical signalling and sensory exploitation. One of the examples cited in the book is the orchid Epipactis veratrifolia which attracts female hoverflies to lay eggs on the plant by releasing chemicals that mimic the alarm pheromones of aphids (the food source of hoverfly larvae). This may rather be a means by which the orchid exploits an inbuilt perceptual preference for chemicals associated with hoverfly larval food sources – either way the plant is deceiving the insect in order to ensure protection from aphid infestation.

A form of deception more commonly associated with orchids is that of exploiting male insects to pollinate plants by mimicking the female form through the shape and colouration of the flower. However, Stevens points out that this mimicry is sometimes (as in Cryptostylis orchids) not particularly convincing to human eyes, but is overwhelmingly so to the male wasp which tries to mate with the flower and thus collects the pollinium which will be deposited at the next Cryptostylis flower that he visits. With this example (as with the oil beetle, among others) the author cautions researchers of deception in nature to be aware of anthropocentric biases that may arise through our observations and study, and to (wherever possible) approach our subjects in the manner and with the senses of the deceived species.

I am utterly delighted and inspired by this book and am certain that I will return to it again and again as a point of reference. I have no hesitations in highly recommending it to researchers, field naturalists and those with a passing interest in natural history.

Postscript

At the time of writing, Phil Torres and Aaron Pomerantz have discovered and documented kleptoparasitism of ants in a species of butterfly (Adelotypa annulifera) in the Peruvian Amazon which they believe might mimic ants through their wing patterns. This seems to me an ideal opportunity for further research looking at visual and chemical mimicry given both the wing patterns and larval associations.