Natural World (1983) s24e03 Episode Script

In Africa there lives an extraordinary tree She is the queen of the riverbank A monarch whose story stretches back millions of years In tribal cultures, have curious ways have fueled myth and legend They set her apart from other trees She is a sycomore fig Queen of Africa's trees She appears never to flower Yet mysteriously she fruits several times a year She seems to have no regard for season and drops her leaves when she pleases Strangest of all is the relationship upon which she completely depends The two partners couldn't be more different One can withstand a river in flood the other can drown in a dew drop One lives for centuries, the other only hours They differ in size a billion times over At about 1mm long the fig wasp is so small that it could fly through the eye of a needle but no fig tree could exist without it Sycomore figs are found throughout tropical Africa In Southern Kenya they thrive along river banks This is the story of one of those trees Our African queen is a mature sycomore fig She started life as a seed a hundred years ago She provides for many animals To some, she is a hunting ground To others, she is home She feeds a greater variety than any tree in Africa that only a few even notice Every few months, the queen produces up to a ton of fruit To reproduce, she must transfer pollen to make seeds and then disperse them inside figs The last crop fell only days ago, but up above she is starting again Over the next two weeks, the tiny buds swell to become young figs Hidden inside each are the queen's tiny flowers At this stage a fig is not a fruit but a secret garden whose delicate perfume attracts a flock of fig wasps Their arrival will trigger a sequence of events that will resonate out through the bush The wasps are all females, laden with pollen and eggs They must enter the fig via the garden gate to pollinate the flowers and lay their eggs inside A one-way passage leads to the secret garden which is lined with hundreds of microscopic white flowers Some of these flowers will become seeds, others will be a nursery for fig wasps The tree will surround each wasp egg with a capsule, called a gall which will nourish and protect it The wasps will soon die, but inside each hanging garden their offspring will live on The queen is now their surrogate mother and will care for them until they hatch in 2 months' time The fig wasps aren't the only ones to lay eggs in the tree for a pair of grey hornbills is nesting This female's confinement will be temporary She seals herself into the hollow trunk leaving only a slit through which her mate can feed her The swelling figs place a big demand on the queen To feed her wasps and grow seeds, she needs to make sugar with her leaves Animals that eat leaves are a major threat If the queen loses too many, she might have to abort her figs The only thing more damaging is a direct attack on the nursery To protect her leaves and young figs the queen pumps them up with a milky latex which is foul-tasting and sticky Small offenders get stuck down and it's unpleasant enough to ensure that others don't stay too long to feed Sycomore figs have been under attack for millions of years In that time, some insects have evolved strategies to overcome the defenses A fig long horn beetle bites through the veins to disrupt the flow of latex It starts with the main vein and works outwards Downstream of the damage, the flow is cut off and the beetle can feed The fig katydid cuts the flow of latex by cutting off the leaf The pink mantis is a predator but it's still very young and a katydid this size is more monster than meal The mantis can't fly so to get off the leaf it has to get pass the green giant Beneath the tree, the fermenting juice in the last crop of figs attracts vinegar flies An ideal size, the mantis still wants to snatch a bite to eat The male hornbill is working hard for he now has 3 extra mouths to feed For hornbills, nesting is always a risk To try and plan her family for when most food is available the female had to lay before the rains This year they're late, and every day that they are delayed will make finding food a little harder and the chicks a little weaker To try and protect the wasp nursery from parasites after the females enter, the queen close the gate and flooded the garden with an antiseptic liquid He doesn't work against nematode worms which used a female wasp as a Trojan horse and stowed away in her body to get into the fig Inside they burst out and are now breeding to be ready to infect the next generation of fig wasps Outside the nursery is under attack from parasitic wasps They can't get in by the gate so they drill through the long ovipositor, an egg-laying device that works like a hypodermic Forced deep inside, it will deposit an egg on a developing fig wasp The grub that hatches will kill the wasp and take over its gall The driller seems to have evolved the perfect strategy but over time, even parasites can be exploited A smaller banded wasp has an ovipositor just as long but more flexible The little wasps fight for access and when the driller pulls out the winner goes straight for its hole It will use the same shaft to lay its egg on the driller's for these smaller wasps are parasites of parasites In the queen's battle to protect her fig wasps her allies are ants They will kill any parasites they capture Anything they can't subdue, they bite and sting to drive away The ants appear to be protecting the figs and in a sense they are for all are attacted All that is, except one These tiny bug eggs should be the ideal snack for an ant but instead, the ants look after them As they hatch, the ants gather up the babies They're nymphs of a bug called hilda which are herded up to graze as if they were sheep Almost every fig now becomes a paddock The ants are so attentive because a nymph has hollow piercing mouthparts that enable it to tap into the fig's sap The sweet liquid is under pressure so it passes rapidly through the nymph When it comes out, it still contains plenty of sugar So in return for being nursemaids and bodyguards the ants receive the supply of sweet honeydew The wounds made by the nymphs and parasites are heal for the latex that drives to form a natural rubber The bee doesn't eat it but collects it to take back to seal holes in its own nest It's been two weeks since the hornbill chicks hatched and still it hasn't rained Now the female must break out to help feed her family as soon as she leaves, the eldest chick instinctively starts to plaster up the hole again using droppings and debris from the nest It will be a while before it is ready to leave The rains arouse some that had been sleeping for months They will bring the expected flush of insects but they have come too late for the youngest chick When their mother left the largest chick dominated the food supply The chicks differed in size because the eggs were laid a few days apart and hatched at different times There is a distinct pecking order, so in lean times the chick with the best chance of survival gets to feed first and takes most of the food Even now when both parents providing the smallest dare not feed until the larger is full Despite clear skies, beneath the tree it still seems to be raining These are fig cicadas they emerge after rain and tap straight into the sap Like hilda they vent what they can't absorb But to avoid getting their wings sticky they don't drip but squirt From the trees' point of view this is a major assault In the fight against cicadas, the queen needs all the help she can get For the ants have changed their allegiance Each time a cicada pulls out it leaves a drop of sweet sap which bribes the security The ants are too busy drinking to protect the tree The sap is the only thing the ants will defend But if news of it gets back to the hive then the bees will be back in force At the peak of the invasion the trunk runs with sap and branches and leaves are sticky with sweet drizzle Monkeys are opportunitists Cicadas are only around for a few days each year so they get their fix of sugar while they can To begin with there's no competition but it didn't f long for the news to spread Fortunately for the queen the cicadas disappear as quickly as they came For the past 2 months she has been making sugar to grow seeds and wasps Inside the figs the protective fluid has drained away The exposed galls are no bigger than pinheads The female wasps inside cannot hatch yet, they must wait for a mate Male fig wasps have powerful jaws and a single intension On hatching they cut through to the captive females not to let them out but to let themselves in A male has no wings, and only tiny antennae and eyes but in one area, he's very well-endowed His cleft chin helps guide him in He impregnates a female before she hatches With an organ that is so long and flexible that some males can mate without leaving their galls Inside the trunk, there has been a dramatic change in behavior as if adolescence had set in overnight At dawn, the eldest chick started breaking down the door It's time for it to leave In the confined space the chick hasn't even been able to stretch its wings so if it's to fly, it will lead instinct to kick in before it hits the ground It is an adolescent triumph of instinct over experience but it will be a few days yet before the last chick attempts it The queen can produce up to 100,000 figs Inside each, the female fig wasps have enlarged the holes the males make and are now starting to emerge They look very different to their mates as they have large eyes antennae and wings all will be essential for their mission The parasites hatch too for they will rely on the fig wasps to help them escape from the fig The nematode worms are trying to snag a female wasp They'll burrow into her body and slowly eat her alive but they can't kill her too quickly as she is the only way they reach another fig The male wasps' next job is to cut flowers The white anthers contain pollen and must be chopped down for the females Their mission is to carry the queen's pollen to other trees This is why she raised them Pollination of a queen is exclusively by appointment The fig wasp female scrapes out pollen and carefully packs it into special pockets on her breast It is extraordinary behavior Meanwhile, the males have started to tunnel It will take them some hours but before they die they must release the females from the fig These bees are scouts sent ahead of a swarm to search for a nest site but it is already occupied The baby hornbill is in danger if a single scout gets back then the swarm will descend on the tree It can't let any get away In thousands of figs all over the tree the tiny tunnelers are about to break out In the space of one hour in the late afternoon millions of fig wasps will emerge This is the final act of the males' brief lives For them a glimpse of evening sunshine won't signal freedom but death After 2 months developing inside the fig their lives have been whittled down to an intense few hours Now they give their lives to set the females free The winged courier will never feed They can't survive more than a few hours in the sun and the worms inside are already weakening them Theirs will be a race against time They don't hang about for good reason The ants don't distinguish between parasite and pollinator but it's the price the queen pays for security The ants kept many parasites from laying, so ultimately more fig wasps survived The activity attracts other players In its bid to reach the wasps a tiny day gecko doesn't notice a giant stick insect it plays an important supporting role Fig wasps can't sting and they're so nourishing that in order to catch them the gecko risks going out on a limb Sometimes that is not enough As a last resort, to distract a predator a gecko can jettison its tail It's a remarkable ploy and if the gecko stays out of trouble then its tail will grow back All over the tree, the queen's tiny couriers are being intercepted A spider cannot eat them all at once so it wraps them in silk trapped as a living larder For each wasp that's captured hundreds will fly free It will be the flight of their lives This evening the tiny wasps will set out in search of a fig tree and another secret garden Some will find trees nearby but others will be picked up by the wind and can travel over 100km In the aftermath of the break out the queen is littered with casualties Many didn't make it or gave their lives so that others did One scout got away and although the parents tried they couldn't entice the chick from the nest it simply wasn't ready The queen's leaves have done their job For the last 2 months they've been making sugar but the wasps have flown and her seeds are ready to be dispersed When the wasps left the figs ripened rapidly to become soft and orange and full of sugar It's as if each is shouting: eat me! Over 100 different kinds of birds eat figs all will fly off with a cargo of seeds Some eat little else A green pigeon is a fig specialist that flies miles from its nest in order to feed The birds have waited for the banquet and they wouldn't be frightened off Back at its nest the green pigeon feeds its chicks on a milk of liquid figs In this way, the bounty of the tree is spread far and wide Some can smell the food from miles away Others live close by and while the queen is fruited visit every day Though there's so much on offer that the monkeys can be choosy They discard figs that are full of parasites With tiger beetles below, the wasps will be lucky to get airborne Some figs remain full of parasites Inside them all are dying for parasites need pollinator males to release them If the parasites have been too successful, they can hatch but never leave In this way, the parasite numbers are kept in check Across Africa, more animals eat figs than any other fruit Fig tress are so important because they fruit outside the normal fruiting season If they produced figs only once a year, the short-lived fig wasps would die out To maintain the population of pollinators each tree needs to fruit at random several times a year and this benefits every one In the heat, fig juice ferments into alcohol and the smell attracts a thirsty clientele The butterflies are normally shy and elusive but drinking alcohol through a straw has a predictable effect The inebriated insects are lucky as they don't taste very good and most can still manage to fly The queen's generosity extends beyond the tree for those she provides for, in turn, support others Wherever fish gather a crocodile is never far behind The croc sets its trap in fast water where the fish can't see its jaws It won't see the fish but it will react at the slightest stretch As figs are the bait the croc makes a lot of false strikes But as in any fishing, patience is essential Figs are sometimes eaten by people, but occasionally the tree has something sweeter to offer Traditionally fig wood is used to conjure fire for it's soft and smolder as well The wood in which the bees found sanctuary is now being used to against them Dry elephant dung is the tinder To gather honey the Maasai exploit the bees' instinctively response to smoke It's evolved to protect the colony in the event of forest fire When the bees smell smoke instead of defending the nest they gorge on honey and then flee In a fire it will be more important that they escaped so they could re-establish the colony elsewhere Normally even a single sting triggers an attack but with the smoke there is no reaction The fig's flowers had nothing to do with this honey The queen's exclusive relationship with her wasps means that her flowers never saw the sun and never had a visit from a bee Living by water helps spread the seeds as figs float downstream and sprout along the strand-line A tiny echo of the avenue they came from It can be a one-way ticket unless the seeds can get help Migrating catfish carry some backup stream A lucky few will be planted and fertilized Strangely, no siblings grow beneath the queen Despite the amount of fruit that falls Nothing geminates here not because of shade but because tiny seed-bugs steal all the seeds They are specialists that eat only fig seeds To perpetuate the royal line the queen needs help to get her seeds further afield It doesn't arrive until after dark Fruit bats are the most important seed dispersers They're less agile than birds so the queen makes access easier by dropping her leaves and hanging her figs clear of the branches Each bat needs to eat half its weight in fig pulp each night They eat little else and a diet of fig juice can result in an urge that requires immediate action Importantly for seed dispersal a bat rarely eats in the fig tree but carries the fig a short distance away It doesn't eat everything but sucks out the juice and discards the seeds So beneath its perch sprout tiny fig gardens During the night the female fig wasps have been traveling across Africa A few have found receptive figs by homing in on the scent from the secret garden To enter, the female must squeeze through the gate A wedge-shaped head will help pry it open but it's so tidy that her wings and antennae will be ripped from her and in the final push, she literally busts a gut She must lay her eggs before the nematodes she's carrying burst out and kill her Her final challenge is to negotiate a spiral valve that leads to the flowers It might take an hour and will need all her strength She will be alone in the garden for the gate is closing others arrived too late Inside she is in trouble the nematodes are breaking out She cannot last much longer but must still lay her eggs and complete her mission The tiny wasp's final act is to repay her debt to the queen to unpack the precious pollen and fertilize the flowers It is her gift and the culmination of millions of years of co-evolution between wasp and tree In perpetuating the relationship she makes the ultimate sacrifice The queen's figs have provided for animals from ants to elephants In traveling, they will disperse her seeds No seeds will germinate and somewhere in Africa where a bat perched or an elephant came to drink there will grow a fig tree In a few years it will sprout its first fig and the scent from that secret garden will touch a tiny wasp which will turn upwind in search of the source Once again, the two will come together and continue the extraordinary relationship that has provided for so many over millions of years Transcription by Andrew & Hattie