Science Interviews

Interview

Mon, 15th Feb 2016

Animal attraction

Max Gray, University of Cambridge

Listen Now    Download as mp3 from the show Rules of Attraction: The Science of Sex

If you look across the world, at the birds and the bees and the flowers and the Bugs sextrees, almost all of it is geared towards sex. And just as animals have evolved many ways of moving and finding food, there is also a huge amount of variation in the way animals mate. Zoologist Max Gray took Khalil Thirlaway through dating in the animal kingdom... 

Max - Mating is the single most important that any animal is going to do because it’s all about passing on your genes to the next generation, making more of your species which is what life is all about.   So animals need to be very good at it and so there’s a huge amount of pressure - evolutionary pressure - selection if you will towards how mating systems work, and there’s a huge variety in any number of different species that you can think of.

Khalil - So are there any general rules of thumb?

Max - Yes, there are a few.  The main one is that the mating cost is different for males and females - for females, it’s more expensive.  This ultimately comes from the fact that an egg is much bigger than a sperm and when you get into more complicated breeding systems - you know birds laying eggs - an egg costs physically and energetically costs more than creating sperm.  And if you think about mammalian pregnancy, the whole process of pregnancy is far more energetically demanding than creating and ejaculating some sperm.

Khalil - So it sounds like being female is a bit of a short straw in many ways?

Max - It can be in some cases but in other cases it’s definitely better to be female than it is to be male. A favourite example for valentine's day - since St Valentine was the patron saint of beekeeping as well as love - is in honey bees, the queen goes out on her mating flights and mates with a number of males and then, once she's done, she goes back and breeds and forms a colony.  But all the males, after they breed with her as part of the mating process, when they leave, when they disentangle themselves from the queen, their phallus is ripped from them and then they die slowly afterwards.  So it’s definitely better to be a female bee…

Khalil - Ouch…

Max - Another good example is the Australian redback spider where you have again, the male and female start mating, everything is going alright but then the male will do a somersault almost, will flip himself over the female into the female’s mouth - she’ll you know, think this is delicious and start having a nice snack.  Will eat the male’s body but, what’s left behind is that his genitalia is left behind and will continue doing its business on its own - so to speak.  By sacrificing himself in this manner the male is more likely to successfully father some offspring.

Khalil - That is some serious dedication.  It sounds like a bit of a freeforall?

Max - In some senses it is.  I mean, broadly speaking, there a huge number of examples in any different number of cases that you can imagine but, in any species or in a family of species, mating tends to work in roughly the same way, so you can categorise these types of mating systems. A very common one in many species is called polygeny, so this is where one male will have sexual interaction with many females.  The dominant male who is the highest quality male will attract numerous females that he will kind of monopolise in a harem.  So this is what happens with a pride of lions and with many other species as well, but even that’s not that simple because there are some species where this happens, at least on the face of it.  An example of this is cuttlefish - so you have one dominant male cuttlefish that monopolises all his lady cuttlefish but the less dominant males, of whom there are many, will kind of think but they still want to breed, they will still attempt to breed.  And if they come in as males and they get chased off by the dominant male, and that doesn’t work,  So what some of them do is, because they’re a little bit smaller and they’re cuttlefish and they can change their colour, they will pretend to be female - they will adopt the colouration of females and sneak in so they get to be close to all the other females because they look like one and the male won’t notice and then, while he’s looking the other way, they will sneakily mate and get away with it that way.

Khalil - On the subject of mating systems, what about monogamy? You often here, for example, swans mating for life?

Max - You do yes.  It’s quite commonly said that a lot of birds mate for life.  Another example is penguins.  In penguins it’s not actually as simple as that and what seems to be monogamous, broadly speaking is but only on for one season at a time.  You get this thing called” seasonal monogamy” where penguins will mate dedicatedly with one individual until that chick is reared and an adult in it’s own right.  And I think the statistic is only something like 15% of partners then reunite the following year in that specific pair. Swans are another example, as you mentioned, that is often claimed to be monogamous and they do tend to stay together for more than one year at a time - so called life mating.  But even then, it’s not truly monogamous because if you do some genetic testing on all the eggs or the chicks after they hatch, you find there’s still quite a high percentage of those chicks that are fathered by males that are other than the one that their mother was paired with.  And this seems to happen in almost any species that people have done that analysis of, that people claim is monogamous.

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