Animal parents: from self sacrifice to murder

In the animal kingdom, reproduction is a vast and interesting topic with many different methods having evolved.  Take for example the frog mums who let tadpoles develop in their tummy and then have to regurgitate them.  Or any one of the marsupials who give birth to jellybean sized young who then have to struggle across mum to find her pouch where lies safety and food.  I’ve written before about kangaroos and how females are essentially a baby making conveyor belt with young at various stages ‘on the go’.

Birth might sound difficult for the kangaroo but I’m betting the hyena is looking on wistfully… Female hyenas experience horrific births.  Their birth canal is a funny shape, it’s longer than most similar sized mammals and the umbilical cord is short.  This means there is a higher risk of asphyxiation, but it gets worse.  The baby’s head is too big to pass through the clitoris (hyenas have an unusual genital makeup and urination, fertilisation and birthing are all carried out through the clitoris) so when a mother gives birth, the clitoris tears.  Not just painful, this can be deadly, with estimates of over 10% of females dying the first time they give birth and more than half of cubs being stillborn.  Things don’t get much better for those cubs that survive either… they tend to arrive in litters of two and the one that is born first tends to kill the second within minutes of birth.

Not necessarily a difficult birth, but the frilled shark has to suffer pregnancy for over three years…  The babies grow a frustrating ½ inch per month and don’t emerge into the water until they reach 1 ½ to 2 feet long…

On land, the longest pregnancy falls to elephants who have to endure almost two years of pregnancy before a baby pops out but thankfully, once little ellie has arrived, the whole herd play a role in raising it.  Similarly, sea lions have collective arrangements with a nursery so they can drop off the pups and then head out to feed.  This rota system works well for sea lions but this communal approach isn’t the case for all animals.  In many species, mum and dad don’t actually engage in parenting and in others, the burden falls on just one parent.  And in some cases, this burden can literally kill mum.

Self sacrificing parents include octopus mums who guard their eggs for several months, starving during this time as they can’t leave them.  Once they hatch, the mother dies.  As sad as this is, it pales in comparison to the desert spider.  When the female desert spider lays an egg sac, her insides start to liquefy.  Once her babies hatch, she regurgitates her innards for her young to eat and nine days later, only a husk remains.

When desert spider lays an egg sac, her tissues start to degrade until the spiderlings hatch. Once this happens, she regurgitates her own liquefied insides for the babies to eat.  9 days later they finish up her innards and then head off into the world, leaving her husk behind…

For orangutans the substantial workload falls to mum who has to spend 8 years raising her babies, longer than any other animal single parent.

Whilst pregnancy and childrearing might be tough for mum, not all dads are hands off.  Indeed, in some cases, its only the male who’s involved in child rearing – the male rhea receives eggs from various females to incubate and rear and the same is true for the cassowary.

Indeed, this system – where the males look after the young from several females, and females spread their brood between several males – is common, especially among fish.
– Olivia Judson

Childcare arrangements vary throughout the natural world with some parents having no involvement, some species specialising in single parenthood and others working together to raise their children.  The type of gestation affects the possible roles for parents.  In mammals for example, where the fetus develops in the womb, there isn’t a lot that the males can do.  For birds however, dad can sit on the eggs and provide food for the chicks just as well as mum can.

Looking at a couple of egg examples, we can see there are different levels of involvement and different roles the parents can play.  The spraying characid is a fish that lays its eggs out of water – the female leaps out of water and lays eggs, then the male leaps out and fertilises them, an act which is repeated until about 300 eggs have been laid.  For the next three days, dad has to stay with them and splash the eggs with his tail to keep them from drying out.

For some leeches, parenting is the basic guarding eggs from predators but for African leeches, a kangaroo style approach has been adopted and they carry their young in a pouch, and for another type of leech, the young are glued to their parents tummy.

But moving onto mammals, we find the Dayak fruit bat where both mum and dad produce milk, taking shared responsibility for nursing their young.  Djungarian hamster males are also devoted to their babies.  They “forage for seeds which they stuff into their pouches in their cheeks; on arriving back at the burrow, they unload their cargo by pushing on the pouches with their forepaws so that seeds stream forth” (Judson).  In addition to finding the food, the males help in the birth process, acting as a midwife and helping the pups out.  They also open their airways and lick them clean, even going so far as to eat the placenta.  Male marmosets also carry out a similar role and will go on to play an active role in childrearing.

Hornbills are another devoted parent.  The female climbs into a nest in a tree and seals up the entrance so that there is only space for her beak.  She is then reliant on her partner to bring her food whilst she incubates the chicks.  Once they are born, the father must bring food for the whole family until it is time for them to emerge.  Overall, the female spends as much as 137 days cooped up in the nest.

But there’s always two sides to a story…  And on the flip side to these dedicated parents, we find infanticide.

In many species where fatherhood is clear, males will kill offspring that is not there.  Infanticide gets pesky children out of the way so that dad doesn’t have to spend resources, time and energy on raising them.  They also do this because without children around, the females get in season and thus he can get her pregnant and have children of his own.  Squirrels, wolves and primates are some of the creatures that engage in this behaviour and about 34% of gorilla infant deaths and 64% of languar infant deaths are down to infanticide (Bondar).

In species which are particularly prone to infanticide, females have evolved a number of countermeasures such as keeping babies in burrows or pouches so that males can’t get to them but there are times when even mum can’t keep their baby alive.

“In rodents, an increased incidence of infanticide is observed for males during periods of food deprivation, and for females during periods of lactation (which confers high energetic demands).”
– Carin Bondar

In coot and moorhen families, who have a large number of chicks at once, parents tend to feed the closest mouth, but if one chick becomes particularly demanding, the parents will try and discourage it by picking it up and shaking it, sometimes killing it.

In some animals, a male having a mistress can lead to the death of the children, the ultimate in wicked stepmothers!  The mistress will often murder the wife’s children and if the opportunity arises, vice versa.

“In both the house sparrow and the great reed warbler, for example, a male with two mates will help only the female whose clutch hatches first, so to ensure herself of male assistance, a savvy mistress will smash all the wife’s eggs.”
– Olivia Judson

Murder isn’t only a risk that comes from your parents; the sand shark practices intrauterine cannibalism, the biggest fetus gobbles up its embryonic siblings whilst in the womb. Whilst an extreme example, siblingcide is not uncommon in the animal kingdom.  In many invertebrates, cannibalism is the way to get rid of your pesky brothers and sisters and thus not only do you get a good meal, you also guarantee increased access to resources going forward.  Whilst not so extreme, eagles and hyenas also kill their siblings, although they wait until after birth.

Of course there are many other interesting births and parenting techniques in the animal kingdom and I could never do any more than scrape the surface here but if these exmaples have whet your appetite, try checking out some of the links below and look into seahorses, that well known fully involved dad!

Suggested reading:

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Seahorse

Seahorses are amazing!  They are really fascinating, distinctive creatures.

They are very strange but are really a fish.  You can turn them 90 degrees and match up their body parts to that of a fish and it’s much easier to see.  They have gills, fins and a swim bladder, like fish.  They have a bent, flexible neck and a prehensile tail instead of a tail fin.  Their scales have morphed into bony plates and they swim vertically instead of horizontally.

Whilst they are a diverse species, they all have the same basic body plan.  Where they differ is in colour, size – they range in size from 1.5cm to 35cm – and habitat – they are found all around the world, generally in warmer, shallower waters.  That said, they have been found in the Thames Estuary!  They are masters of camouflage and blend into their surroundings so well that you could easily overlook them.

Seahorses eat crustaceans mostly, but occasionally baby seahorses… They are eaten by fish, octopuses, crabs and birds.  Another major threat is the traditional medicine industry where they are used to improve general health and wellbeing.

Apparently the seahorse is the celtic zodiac animal for those born between 19th February and 27th March, which includes me!

But the reason I love the seahorse is that they defy convention.  They use their tail to hold on to stationary objects so that they don’t float away.  This is really important as they are actually really poor swimmers… You could say that they are poorly matched to their environment but they’ve just found an alternative way to survive and thrive.  A reminder to us to think outside the box.

And when it comes to alternative lifestyles, the seahorse is leading the way.  Male seahorses have a very involved role in child rearing and the female has very little to do with it.

Things kick off with a courtship display and a sensual synchronised swimming experience where the two seahorses let go of whatever they are holding onto and drift towards the surface together.  This is thought to bond them and during this process the male shows off his big, empty pouch.  Once they are ready, the female then squirts her eggs into his pouch and then swims away, leaving the male to do the rest.  He then fertilises the eggs with his sperm and then incubates them for 9 to 45 days depending on the species.  As the babies grow, he gets bigger and more sedentary until finally they are ready to be released.  I saw a video of this and the little male seahorse looked like he was in pain.  The babies, fully formed just very small, are expelled from him through a series of muscular contractions.  There can be over 2000 babies which are born independent.

Just before birth, the female reappears to claim her male and almost as soon as the babies have been born, the ritual starts all over again.  A male can have several clutches in one breeding season and is very much on a treadmill of childbirth.

Whilst there are rumours which suggest that seahorses are monogamous, this is not true.  However, unlike some non-monogamous species, all the babies in the pouch belong to the same mother and about half of seahorses mate with the same partner the next season.  This is likely because then they don’t have to move around too much to try and find a new mate which would increase their chance of being eaten.

These fascinating animals defy convention and encourage us to do the same.  Often we do things because that’s the way they are done, blind to the idea there might be another way.