Speciation-07-web

Speciation-07-web - Speciation 1...

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LECTURE 3 (continued) – Evolutionary Processes: Sexual selection can arise in response to either: 1. Female Choice, in which females choose males using some sort of cue that makes the males look like a good choice. 2. Male Competition, in which the males compete for territory or access to females. Female Choice: Females appear to make their choices based on visual cues that indicate that the male is a good mate. In birds, this is often bright feathers or colors. Typically, bright colors not only good the male noticed, but they may be subtle (and unconscious) indicators of good health. Some interesting examples: - Peacocks . Males have elaborate coloring, because it is thought that females choose the more elaborate male for mating. But, the elaborate feathers and colors may also be an indicator of a male’s health, because only a really healthy male can carry around a really elaborate trail of tail feathers. Furthermore, a recent breeding experiment compared the health of peacock offspring fathered by different males. Surprisingly, the most healthy, fastest growing offspring were fathered by the peacocks with the biggest feathers. So, females that choose flashy males more have more healthy offspring! - Artificial cues: In a very famous example, our own Professor Nancy Burley showed that zebra finch females prefer red leg rings over males with green leg rings. - Nuptial gifts: < Figure 24.8> Sometimes the males provide resources that are used by the female or used to provide for the young. If the male gives better gifts, he is more likely to mate successfully. Again, it is thought that this is a way that females can gauge the “healthiness” of a potential mate. Male-male Competition: Often males compete for the chance to reproduce. Examples include: - antlers on male deer, that are used in battle for territory - elephant seals. These huge seals fight for territory. The winner gets to mate with the females on the beach. Notice that the difference in reproductive success among males is massive. Clearly, male to male competition can be very important! - male lions will fight to gain control of a pride of females. When a new lion takes control, it will kill the young lions that are not genetically related to him. In this way, he ensures that his offspring are more successful. If you are not squeamish, see a movie on http://www.lionresearch.org/behavior_guide/infant.html Also, the females don’t like this because if their children are killed they waste a rare breeding opportunity, so they will fight back! 1
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Speciation-07-web - Speciation 1...

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