We've all heard the story: white-striped and tan-striped White-throated Sparrows usually pair up for nesting. It's the classic - literally textbook - example of negative assortative mating.
While explaining this to my students last week, I was struck with a thought about this I'd never considered: each sparrow has absolutely no idea which form he or she happens to be. Can anyone share insight on the specific mechanisms at work in reinforcing the "attraction for other when otherness cannot be known"?
Look in a car's rear-view mirror? Look down?? Pull out a tan/white feather to inspect??? Remember Mommy / Daddy sparrow???? Different DNA?
I'm not familiar with this particular example, but it might be related to incest-avoidance mechanisms (another form of negative assortative mating) in humans and other primates where familiarity with an individual (co-residence, co-association with the mother) is the cue for high genetic relatedness- this then upregulates altruism and downregulates sexual attraction. In the sparrow example the birds could be avoiding mates that look like their parents or siblings?
See Rowe, K.M.C., and Weatherhead, P.J. (2011). Assortative mating in relation to plumage traits shared by male and female American Robins. The Condor, (113): 4. 881-889.
Could there be some other trait that is DNA-associated with colour of stripes that we are unaware of, by which the robin can sense his own category and thereby "select otherness"? Short or UV-fluorescent toenails!?
Certainly , there are already good explanations in the above answers. But, I want to highlight that, for example birds, have a very good colour vision, they may rotate their heads till 270 ° and they spend much time in preening and putting in order their plumage. Thus, they may develop at least a gross image of their own without the need of a mirror. Often, the choice is just a question of black and white, or grey and red individuals.
I appreciate the insights shared in the thread. The crux of my question rested on the premise that, unlike other assortative mating examples, there really isn't anything in the plumage that an individual could detect to determine its own morph. The plumage differences are on the crown and not visible to the individual.
David Sibley's explanation of this system mentioned some other subtle plumage differences from other places on the body, but based on photographs of the two morphs together, I'm skeptical that those differences are reliably discernible.
Sibley does provide, however, two avenues for a plausible mechanism. First, the white-striped morph averages 2–3% larger than the tan-striped. Thus, simply comparing one's size to others could provide a cue on which selection could act, e.g., large individuals favoring small individuals and vice versa. The second difference is in apparent temperament, with white-striped individuals demonstrably more aggressive in agonistic encounters, more likely to sing, etc.
Those two attributes could readily be discerned by an individual to determine a difference between self and other.
http://www.sibleyguides.com/bird-info/white-throated-sparrow/
- Badges
- Science topic
- Similar topics
- Filing