Amplexus

Amplexus :  to wind around.  Or, from the Latin definition: to embrace.  

Amplexus is what happens when a male frog has found a mate and he needs to take up a position in which he can fertilize the female's eggs.  

This fertilization usually happens outside of the female's body, straight after the eggs have been released and before the 'jelly' surrounding the eggs begins to swell.  For the male's sperm to make contact with as many of his mate's eggs as possible, the male needs to position his cloaca as close as possible to hers.  There are two main types and a few variations:

Amplexus explained

Inguinal amplexus:

  • The male frog needs to clasp the female just infront of her back legs.  Then, as the eggs are being laid by the female frog, the male  moves his cloaca as close as possible to the female's to make sure that as many eggs as possible are fertilised.  The cloaca is an opening or chamber that frogs have (and other vertebrates) from which they can expel sperm, eggs, urine and faeces opening from a vent.  This differs from mammals as in mammals there tends to be a separate opening, or orifice, for each function, eg urine, faeces and the reproductive system. 

Axillary amplexus:

  • The male frog clasps the female frog behind her front limbs and this means that the cloaca of both of them are close together without having to perform twists or bends to make this happen.  

There is another form of amplexus which is known as 'glued amplexus'.  This is when the frogs are too large or have such short limbs that it would be impossible for them to carry out either inguinal or axillary amplexus, as they would not be able to move their limbs into the correct position.

So glued amplexus is a method where the male frogs secretes, or oozes out, a sticky substance from his abdominal glands and because it is so sticky, he can then attach himself to the female frog.  The thing is, the stickiness is so incredible and effective, that it is actually very difficult for the frogs to become separate again!  This means that potentially they could be stuck together for quite some time in this position until either the sticky substance breaks down or indeed the female sheds her skin and carries on her way.  

Amplexus
  • Amplexus can last for a few hours at the most and then the frogs will go their own ways, but in some cases it has been known for amplexus to continue for days and even weeks.  Some true toads from the Atelopus genus, which includes stubfoot toads and harlequin toads, are the most likely to perform amplexus in this way.  
  • In amplexus like this, the female frog is able to continue feeding and remains healthy whereas the poor male frog is unable to feed properly and efficiently and ends up becoming thinner and weaker as the days and weeks progress.
  • For frogs to be able to perform amplexus, they use their nuptial pads.  These are present on sexually active frog.  They are what the frogs use to be able to hold on to the female frog.  With frogs being a bit slippery, the nuptial pads are essential for them to be able to stay in the right position on the female without sliding away.  
  • The nuptial pads are rough swellings on the outer edge of a frogs 'thumb' which act to make the grip onto the female more secure.  
  • The nuptial pads are bigger in species that breed in water as they would require a greater grip since being in the water which might be faster flowing than a pond.  
  • Nuptial pads may not be found on all frogs and toads, especially those that breed on land - perhaps this is because the issue of grip is not as important as for those who breed around or in water.
› Amplexus

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