Intimate Relations, Naturally Trivia Quiz

Answer: Scaring off predators

The breast of the common cuckoo does resemble that of the sparrowhawk however, rather than keeping predators away, the mimicry keeps the host species away when the cuckoo is depositing its egg and getting rid of one of the host's eggs.

The common cuckoo is known to have used more than 100 different host species and may lay more than 50 eggs in a season. Egg mimicry is helped by individual cuckoos specialising in particular hosts. Longer internal incubation of the egg within the cuckoo gives it a head start over the host's eggs.

Answer: Nerve control

The life cycle of the lancet liver fluke (Dicrocoelium dendriticum) begins in its ruminant host. Eggs are excreted in the dung, a food source for the snail. The snail ingests them and becomes infected by a larval stage of the fluke. These eventually migrate to the lungs where they are expelled in slime balls.

An ant, possibly using the slime trail as a moisture source, eats a slime ball infested with juvenile flukes. One of the flukes then heads for the sub-esophageal ganglion, a cluster of nerves, whilst the others go through the next stage of maturity. The fluke takes control of the ant which then heads up to the end of blade of grass, clamps its mandibles into the grass and awaits its fate.

Interestingly, the zombie ant only stays on the blade of grass at night. If it survives the night uneaten, it goes back to being an ordinary ant during the day. However, it will repeat this nocturnal pattern until it is eaten. Why only at night? The heat of the sun would kill the ant (and hence the parasite) if it stayed out on top all day.

Answer: As a source of nutrients

The parasite is the mussel. The bivalve (Epioblasma triquetra) snaps shut its shell over the head of the fish and squirts its larvae into the fish's gills. The fish is then released and acts as a source of nutrients for the mussel's larval glochidia stage. Why the common logperch (Percina caprodes)? Its head is tough enough to survive the clamping process.

Answer: Velvet belly lanternshark

This barnacle is a rare example of an animal in the process of evolving from being a filter-feeder to a parasite. It has lost its shell but still possesses many of the features of barnacles.

The typical barnacle is like a shrimp inside a shell with beating feathery legs to gather food for feeding into its gut via its mouth. The Anelasma squalicola still has its legs, mouth and gut but doesn't use them. Instead its peduncle (normally used to anchor barnacles to rocks) has been modified to absorb nutrients through root-like filaments, by-passing the mouth and gut.

The Anelasma has been found on several species of squaloid shark and typically appears in pairs on a shark, perhaps to ensure having a mate. It also appears to castrate or retard the sexual development of its host shark.

Answer: Tongue

The tongue-eating louse (Cymothoa exigua) does not quite do what its name suggests. The louse starts off as a male attached to the gill arches where it sucks blood. As it matures it changes to being a female and moves forward to clamp onto the fish's tongue.

It cuts into the blood vessels serving the tongue, which then wastes away and falls off. The louse then clamps onto the stump and takes over the role as the fish's tongue. There are eight species of fish known to be parasitised by this louse.

Answer: Reduces the rat's aversion to cat pee

With decreased aversion to cat's urine, rats are more likely to hang around where cats live and so are more likely to be caught. People infected by this parasite are also more accepting of the smell of cat's urine, although getting infected is not a good idea. Toxoplasmosis has been associated with neurological disorders and is a potentially life-threatening condition in people.

You may ask why the protozoan has evolved to do this. The cat is the only known host in which the parasite can sexually reproduce. Making the rat more likely to be caught increases the chances of completing and beginning the parasite's life-cycle.

In another twist, it appears that infected male rats become more attractive to female rats and as a result are more likely to produce young, passing on the parasite to the offspring and so increasing the chances of the parasite successfully completing its lifecycle.

Answer: The host changes colour to red

The nematode enjoys a symbiotic relationship with the Photorhabdus luminescens bacteria, which it carries in its gut. It senses carbon dioxide emissions, amongst other things, to hunt down its prey. Once inside the host, the nematode ejects the bacteria from its stomach, the host's immune system is overcome and the bacteria produces antibiotics to keep the competition at bay. Finally, as the bacteria digests the host, the host gradually changes to a pinkish-red colour. This deters larger predators such as birds and is a form of defensive mimicry.

A faint bioluminescence is also produced by the bacteria. It has been postulated that this caused the "Angel's Glow" seen on some wounded soldiers in the aftermath of the Battle of Shiloh during the American Civil War. Lying around in mud for a couple of days in low temperatures, these wounds are thought to have been infected by this bacteria. The cocktail of antibiotics created by the Photorhabdia bacteria in fact increased the survival rate of these particular soldiers, speeding up healing and resulting in fewer complications.

Answer: Wasp larvae

Once the eggs find their way into a caterpillar, they hatch out and seek out other parasitic larvae within the caterpillar, including their own siblings. If there are no parasitic larvae available, they appear to wait until the caterpillar is parasitised. They do not, however, eat the caterpillar.

There is also a variety which waits for the caterpillar to be eaten by a wasp. The wasp regurgitates the food (and trigonalid eggs) for its own larvae which are then eaten by the newly-hatched trigonalid larvae.

Answer: Mimics a caterpillar with the eye stalk

The lifecycle of this flatworm (Leucochloridium paradoxum) starts in the songbird. The bird poops and the snail ingests the eggs from the faeces. Sporocysts emerge and these form into a long broodsac which occupies one of the tentacles (or eye stalks) of the snail. The left stalk is preferred.

To make the snail mimic a caterpillar (a more natural food for songbirds), the broodsac puts on a pulsing colourful display, which increases in intensity with more daylight. The flatworm also seems to affect the snail's ability to detect light levels, overcoming its natural tendency to avoid daylight and so increasing the likelihood of it being eaten.

Answer: Build a special web to support its cocoon

When the egg hatches, the larva of the wasp (Hymenoepimecis argyraphaga) feeds on spider's blood whilst the spider (Leucauge argyra) goes about its business as normal.

After a couple of weeks, the larva injects a chemical into the spider which induces the spider to build a reinforced web to the larva's specifications and then sit in the middle of it. The larva then kills the spider, sucks out its juices, casts it away and then creates a cocoon for itself in which to pupate and which it hangs off this custom web.