6 posts • Page 1 of 1
I know some reasons two speices wouldn't mate
- different mating seasons
- different environments
- different mating rituals this is a big one for birds because of their songs, colors, and dances all go into choosing a mate
then there are reasons that their gametes wouldn't accept each other if they are different species etc...
I have no clue and Darwin's finches, though
Man in civilization surveys the creature through the glass of his knowledge and sees thereby a feather magnified and the whole image in distortion. - Henry Benson
As February Beetle said, mating rituals for birds play a large part in courtship but it could just be sexual isolation, i.e. mutual attraction between the sexes of different species is absent. They just don't fancy each other!
While different subpopulations were shifting into different island niches, they probably did interbreed, but the offspring would have been a mix of different adaptations for different niches, probably not advantageous mixes. The finches that prefered the potential mates in their developing niches were more likely to produce offspring well-adapted to that niche, and the mating preference was itself a selected advantage.
I think it's easier to visualize with the iguanas. The original population would have been mainland iguanas, and now there are separate marine (diving algae-eaters) and upland (dry-environment scrub-plant-eaters) populations. In the founding population (possible already "weeded through" by a long trip on floating vegetation), some were probably more adept at tearing algae off rocks in the surf, with its watery perils, some were probably better at handling the tough land plants, with the perils of dry heat and lots of sunlight. The shore -preferring subpopulation would have been better-off over the long run breeding with other shore-iguanas than the off-shore iguanas, even though they would have been able to for many many generations. Mixing different shore traits (swimming ability, resistance to the cold salty water, pinching/tearing mouths, rock-climbing) would produce better-adapted offspring than mixing them with good inland traits (burrowing ability, resistance to heat, tougher mouths, etc.). You can see how mating preference that would, eventually, reproductively isolate the groups would also be selected for.
6 posts • Page 1 of 1
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