Re: Rearing to Rear (Was "3 reasons to visit the Field Museum")

[Dann Pigdon <dannj@alphalink.com.au>]

T. Michael Keesey writes: 

> On 6/24/07, Dann Pigdon <dannj@alphalink.com.au> wrote:
> > Male humpbacks are really a sight to behold in the mating season. Often a
> > female will reject their advances and roll onto her back at the surface,
> > with her vent in the air. A really large male can still mate with her
> > though, by getting alongside and rolling onto his own back, then sending 
> > his
> > weirdly mobile penis off to explore by itself.
>
> Interesting, since that would provide strong selective pressure for
> greater size. 
>
> (Or were you not referring to body size?...)

Well - the larger the male, the 'larger' the male, so to speak. Amongst 
cetaceans in general, mating is not always a mutual agreement. An insistent 
male has to be larger than the object of his unwanted desire to get close 
enough to begin with (especially if the female still has a calf with her).
The appendage in question then has to curve up and over the bulk of her 
body, and still have enough length left to do the job (should it 
successfully find 'ground zero'). 

So in whales where forced mating is common, there will be selective pressure 
for males to evolve larger body size to not only fend off rival males, but 
to physically overpower the females. If more than one male is harassing an 
up-turned female (and they *will* gang up at times), then the 'larger' male 
is more likely to be able to reach, despite the female's attempt to put 
things out of reach by rolling onto her back at the surface. 

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Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com
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