The wasp Dinocampus coccinellae is a body-snatcher, or perhaps a “bodyguard-snatcher”. She’s on the hunt for a spotted ladybird. When she finds one, she stings it and lays an egg inside its body. Her grub hatches and starts eating the ladybird alive. Around three weeks later, it bursts out of its host.
But the ladybird doesn’t die. The grub hasn’t consumed all of its internal organs, and it leaves the ladybird partially paralysed but very much alive. Once out, it spins a silken cocoon between the ladybird’s legs and over the next week, it slowly transforms into an adult. Meanwhile, the ladybird stands guard over its own parasite. Its warning colours of red and black should deter would-be predators, and it twitches erratically if threats draw near. Its tour of duty only ends when the adult wasp eventually emerges from the cocoon and flies away.
It’s not a very fair fight. In one corner is a tiny ant. In the other is a large wasp, two hundred times heavier and capable of flying. If the two of them compete for the same piece of food, there ought to be no contest. But sometimes the wasp doesn’t even give the ant the honour of stepping into the ring. It picks up the smaller insect in its jaws, flies it to a distant site and drops it from a height, dazed but unharmed.
Julien Grangier and Philip Lester observed these ignominious defeats by pitting native New Zealand ants (Prolasius advenus) against the common wasp (Vespula vulgaris). The insects competed over open cans of tuna while the scientists filmed them.
Their videos revealed that ants would sometimes aggressively defend their food by rushing, biting and spraying them with acid. But typically, they were docile and tolerated the competing wasp. Generally, the wasp was similarly passive but on occasion, it picked up the offending ant and dropped it several centimetres away. In human terms, this would be like being catapulted half the length of a football field.
The wasps never tried to eat the ants, and they never left with one in their jaws. They just wanted them out of the picture. Indeed, the more ants on the food, the further away the wasps dropped them. This may seem like an odd strategy but at least half of the dropped ants never returned to the food. Perhaps they were physically disoriented from their impromptu flight, or perhaps they had lost the chemical trail. Either way, the wasps could feed with fewer chances of taking a faceful of acid.
Reference: Grangier and Lester. 2011. A novel interference behaviour: invasive wasps remove ants from resources and drop them from a height. Biology Letters http://dx.doi.org/10.1098/rsbl.2011.0165
The wing of a fruit fly, viewed against a white background, looks very ordinary. It is transparent, with no obvious colours except for some small brownish spots. But looks can be deceptive. If you put the wing in front of a black background, it suddenly explodes in a kaleidoscope of colour. Oranges, blues, greens, violets – virtually the entire rainbow dances across the wing, except for red.
A French scientist called Claude Charles Goureau first noticed these vivid hues back in 1843. Since then, they have languished in obscurity, “apparently unnoticed by contemporary biologists”. Whenever new species of wasps or flies are described, their discoverers almost never mention the coloured patterns of the wings. The visible pigments have even been described as “evolution in black and white”. It’s like walking through an art gallery with a blindfold.
Now, Ekaterina Shevtsova from Lund University has taken off the blind. By photographing several species against dark backgrounds, she has revealed a world of hidden colour, rivalling that of more obviously beautiful insects. “The claim that fly and wasp wing patterns are no match for the incredible diversity of colourful butterfly wing patterns is obsolete,” she says.
It’s not every day that you hear about spy missions that involve a lack of sex, but clearly parasitic wasps don’t pay much attention to Hollywood clichés.
These insects merge the thriller, science-fiction and horror genres, They lay their eggs inside other animals, turning them into slaves and living larders that are destined to be eaten inside-out by the developing grubs. To find their victims, they perform feats of espionage worthy of any secret agent, tapping into their mark’s communication lines, tailing them back to their homes and infiltrating their families.
Two species of parasitoid wasp – Trichogramma brassicae and Trichogramma evanescens – are particularly skilled at chemical espionage. They’ve learned to home in on sexual chemicals used by male cabbage white butterflies. After sex, a male coats the female with anti-aphrodisiac that turns off other suitors and protects the male’s sexual investment. These chemicals are signals from one male to another that say, “Buzz off, she’s taken.”
But the wasps can sense these chemicals. They feed on the nectar of the same plants that the cabbage white visit and when they do, the wasps jump her. They are tiny, smaller even than the butterfly’s eye (see the image below), and they hitch a ride to the site where she’ll lay her eggs. There, they lay their own eggs inside those of the butterfly. Amazingly, the wasps use the same trick for different species of cabbage white butterflies, which secrete very different anti-aphrodisiacs. They can even sense when the anti-aphrodisiacs are wafting among the general scent of a freshly mated female. It’s all part of a sophisticated “espionage-and-ride” strategy.
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
Imagine that one day, you make a pact with your brother or sister, vowing to never have children of your own and instead spend your life raising theirs. You’ll agree to do the grocery shopping, cook for them, clean their rooms and bathe them, until you die.
That seems like a crazy plan, but it’s one that some of the most successful animals in the world – the social insects – have adopted. It’s called ‘eusociality‘ and it’s a puzzle for evolutionary biologists. Why should an animal forgo the chance to reproduce in order to help rear its siblings and their young?
The strategy makes sense if you share enough genes with your close relatives. In helping them, you indirectly ensure the transmission of your own genetic material. But even if this explains the existence of eusociality, it doesn’t explain how such an extreme form of co-operation evolved.
Now, Amy Toth and colleages at the University of Illinois have found a clue in the genes of the paper wasp, Polistes metricus, which suggests that their altruistic actions evolved from motherly behaviour.
Scientists have suggested this theory before as a possible origin for eusociality. It doesn’t take a great leap of imagination to picture how a group of wasp sisters living together and communally looking after their young could become a society in which only a few individuals reproduce and the others share the care. But until now, that theory had never been tested at a genetic level.
Truly eusocial insects like honeybees have physically distinct castes with strongly segregated jobs. The queen’s sole purpose is to lay eggs and she never takes on the menial foraging and brood care of the smaller workers.
Paper wasps are only halfway down the road to eusociality, which makes them an ideal choice for studying its evolution. They have different castes, but they all look much the same and their castes are far less strictly segregated. The roles that individuals perform depends on the age of the colony and fall into four different groups.
Foundresses, females that establish new colonies and care for young as well as laying eggs. After creating the first generation, these females become queens and focus solely on laying more eggs. Their daughters, the workers, take up the task of caring for their new siblings to the exclusion of their own reproduction. Later on in the colony’s life, the queen gives birth to gynes, that neither care for young or lay eggs – their job is to mate with males and become foundresses themselves in the following spring.
Toth decided to look at the patterns of gene activity in these four groups. She reasoned that if the workers’ altruistic actions had originated in maternal care, they would share similar genetic profile to the foundresses, the only other group that also cares for young.
Complex behaviours like caring for young and foraging were hardly going to be the province of a single gene. Toth needed a way to analyse a myriad of genes across the entire wasp genome – a genome that has not yet been fully sequenced.
To overcome this problem, the team took a streamlined approach. They specifically looked at genes that were strongly activated in the brains of 87 wasps from all four groups. Using a powerful sequencing technique from the 454 Life Sciences company, they identified almost 400,000 stretches of relevant DNA across their genomes.
Toth matched these hits to the genome of the closely related honeybee (Apis mellifera), which was fully sequenced last year. They focused on 32 genes, whose honeybee counterparts are involved in worker behaviour. Even though bees and paper wasps started down different evolutionary roads some 100 million years ago, the proteins encoded by these genes have remained very similar.
As predicted, Toth found that the activation pattern of these 32 genes was closest in workers and foundresses, and were distinct from those of queens and gynes, which don’t practice maternal care. Regardless of whether the wasps focused on their siblings or their young, their caring behaviour was governed by similar sets of genes, supporting the idea that eusociality evolved from maternal care.
Today, the vast majority of solitary wasps provide food for their helpless young, often in grisly or murderous ways. During the course of evolution, the twin behaviours of egg-laying and maternal care started to separate.
In the intermediary paper wasps, the behaviours are separated in time – the foundresses practice both at first and then focus on just one when they turn into queens. As this happens, their brain undergo dramatic changes and different sets of genes are switched on.
The final stage down this evolutionary path is the one seen in true eusocial wasps, where egg-laying and maternal care are separated in space, in the bodies of queens and workers.
The study also shows that many evolutionary problems can be addressed without the complete sequence of an animal’s genome. For every full genome we have, we can use next-generation sequencing technology to compare it to the partially sequenced genes of closely-related species, just as the bee and wasp proved here.
Reference: toth, Varala, Newman, Miguez, Hutchison, Willoughby, Simons, Egholm, Hunt, Hudson & Robinson. 2007. Wasp gene expression supports and evolutionary link between maternal behaviour and eusociality. Sceince
Viruses and bacteria often act as parasites, infecting a host, reproducing at its expense and causing disease and death. But not always – sometimes, their infections are positively beneficial and on rare occasions, they can actually defend their hosts from parasitism rather than playing the role themselves.
In the body of one species of aphid, a bacterium and a virus have formed a unlikely partnership to defend their host from a lethal wasp called Aphidius ervi. The wasp turns aphids into living larders for its larvae, laying eggs inside unfortunate animals that are eventually eaten from the inside out. But the pea aphid (Acyrthosiphon pisum) has a defence – some individuals are infected by guardian bacteria (Hamiltonella defensa) that save their host by somehow killing the developing wasp larvae.
H.defensa can be passed down from mother to daughter or even sexually transmitted. Infection rates go up dramatically when aphids are threatened by parasitic wasps. But not all strains are the same; some provide substantially more protection than others and Kerry Oliver from the University of Georgia has found out why.
H.defensa‘s is only defensive when it itself is infected by a virus – a bacteriophage called APSE (or “A.pisum secondary endosymbiont” in full). APSE produces toxins that are suspected to target the tissues of animals, such as those of invading wasp grubs. The phage infects the bacteria, which in turn infect the aphids – it’s this initial step that protects against the wasps.
This is the seventh of eight posts on evolutionary research to celebrate Darwin’s bicentennial. It combines many of my favourite topics – symbiosis, horizontal gene transfer, parasitic wasps and viruses.
Parasitic wasps make a living by snatching the bodies of other insects and using them as living incubators for their grubs. Some species target caterpillars, and subdue them with a biological weapon. They inject the victim with “virus-like particles” called polydnaviruses (PDVs), which weaken its immune system and leave the wasp grub to develop unopposed. Without the infection, the wasp egg would be surrounded by blood cells and killed.
The wasps’ partners in body-snatching are very different to all other viruses. Once they have infected other cells, they never use the opportunity to make more copies of themselves. They actually can’t. To complete their life cycles, viruses need to package their genetic material within a coat made of proteins. In most cases, the instructions for building these coats are encoded within the virus’s genome, but polydnaviruses lack these key instructions entirely. Without them, the virus is stuck within whatever cell it infects.
It’s such a weird set-up that some scientists have questioned whether the polydnaviruses actually count as viruses at all or whether they are “genetic secretions” from the wasps themselves. Where on earth are those missing coat genes?
Annie Bezier form Francois Rabelais University has found the answer and it’s an astonishing one. The viruses’ coat genes haven’t disappeared – they’ve just been relocated to the genomes of their wasp hosts.
In this way, the wasps and the viruses have formed an unbreakable alliance, where neither can survive without the other’s help. Without the virus, the next generation of wasps would be overwhelmed by the defences of their caterpillar larders. Without the wasp, the virus would never be able to reproduce. Some viruses may be able to live happily alongside their host with little ill effect; others may even be beneficial in some way. But this is the first example of a virus co-evolving with its host in a compulsory binding pact.
This is the second of eight posts on evolutionary research to celebrate Darwin’s bicentennial.
When new species arise, they can set off evolutionary chain reactions that cause even more new species to spring forth – fresh buds on the tree of life create conditions that encourage more budding on different branches.
Biologists have long suspected that these “cascades of speciation” exist but have struggled to test them. Enter Andrew Forbes from the University of Notre Dame – his team of has found a stunning new proof of the concept by studying a fruit fly called the apple maggot (Rhagoletis pomonella) and the parasitic wasps that use it as a host.
Contrary to its name, the apple maggot’s natural host is not apples – it’s hawthorn. The fly only developed a taste for apples about 150 years ago, when the fruit was first introduced to North America. This culinary switch has created two races of apple maggot – one that eats hawthorn and another that eats apples. Even though they are often found in the same place, the two races don’t mix and they don’t breed together. They are well on the road to becoming separate, genetically distinct species.
And so are their parasites. A wasp called Diachasma alloeum specialises in attacking apple maggots. It lays its eggs inside the fly larvae, and its grubs eat the victim from the inside out. Forbes found that the wasp has also started to form separate races that don’t crossbreed with one another, even though they have overlapping ranges. By adapting to new host plants, the flies inadvertently set up barriers that separated their respective parasites from one another. Now, the wasp, like its hosts, are also on the way to becoming separate species. It’s a fantastic example of diversity bringing itself about.