[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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

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.


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