On page 159, Coyne mentions the fairy wren as a specie that seems to be monogamous in mating, but in fact only are monogamous with 'social mates' and literally MATE with other males of the population.
Find another example of a specie that has a separate, monogamous-like 'social mate' but mates with others that is not the 'social mate.' Describe the differences between the males and the females of the specie. What sort of selective advantage do you think there is in having a different mating mate and social mate? How could this have developed?
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Long-term observation has also shown that gibbons, once thought to form permanent pair bonds, are also subject to change in reproductive and social mating. Gibbons tend to form “nuclear families,” with two adult mates and their offspring sharing a territory until the offspring become old enough to establish their own families in another part of the forest (http://scienceblogs.com/laelaps/2007/11/monogamy_is_much_more_interest.php). In a six-year study, Ryne Palombit determined that gibbon pair bonds are subject to change and desertion; occasionally when the mate of a neighboring gibbon dies, a member of a nearby pair will abandon its mate to join the widow, despite the presence of unattached adults in the vicinity (http://www.jstor.org/stable/pdfplus/4535165.pdf) (And I thought we wouldn’t have to read journal articles for this blog project!)
ReplyDeleteHowever, gibbons do not exactly fit in with Coyne’s description of sexual dimorphism indicating reproductively promiscuous species (159). Since gibbons are highly territorial, there is less chance that they will have contact with other non-family gibbons, although the edges of territories can overlap (http://en.wikipedia.org/wiki/Siamang#Behavior).
Gibbons are not very dimorphic; males and females look very similar, and are about the same size. The Siamang, a species of gibbon found in Southeast Asia, defends its territory through calls and songs which can be heard for miles. The Siamang is unique in that both males and females have a gular sac, or a throat pouch that enables the apes to make extremely loud calls.
Having different social and reproductive mates can be a selective advantage, because social mates help care for the young, while mate competition can potentially result in offspring that have better genes (Coyne 162).
The article that I evaluated about gibbons specifically refers to the theme of “science as a process,” or the forms of inquiry that increase our understanding of nature (Campbell 18). Earlier studies of gibbons seemed to indicate that the apes were exclusively monogamous. Brian Switek, a freelance science writer, explains that this misconception was due to the setup of the experiments; scientists studying gibbons would habituate themselves with one pair, while other gibbons nearby would be frightened off by the researchers. Thus, the researchers would not be able to observe extra-pair matings, since their presence prevented other gibbons from getting closer to the pair (http://scienceblogs.com/laelaps/2007/11/monogamy_is_much_more_interest.php).
However, the experiment of Ryne Palombit was longer term and larger range, allowing the researchers to observe multiple groups/territories. Due to Palombit’s experiments, we now know that gibbons are not exclusively monogamous, and that their mate-pairing system is much more complex and subject to change.
In addition to gibbons and the splendid fairy wrens, starlings are also birds that engage in extra-pair copulation. Similar to the wrens, starlings form monogamous pairs in “[codefending] their territory and [sharing] parental care.” (159) Not only do starlings mate with other starlings that are not their pair, but they also lay eggs in other pairs’ nests, behavior known as “brood parasitism.”
ReplyDeleteStarlings, however, like the gibbons, don’t fit Mr. Coyne’s description of sexual dimorphism. The most common dimorphism in starlings is size disparity, males being a little larger than females. Though their feathers can often be very beautiful in many different colours, the iridescence is mainly caused by the structure of the feathers, instead of the pigments.
I agree with Jaime in that having more than one mate deepens the gene pool, and that the social mate provides more care than a single mother or father. In addition to evolutionary benefits, there is also a debate on how deep animal emotion goes. It’s entirely possible that while instinct drives instances of extra-pair copulation, the need for interaction and support from the other in the pair keeps the two birds or other animals together.
A possibility for how mate pairs developed could be that they were formed by two members of a mostly polygamous species. The altruistic behavior of the two (feeding and caring for the offspring, looking out for the other of the pair), while not necessarily extending to mating, would result in very successful offspring. These offspring, familiar with the way their parents cooperated, would then continue the behavior. The eventual integration of the behavior in the animal’s standard behaviors could be an example of Interdependence in Nature. The two starlings, once a pair, rely on each other to help feed and care for the offspring as well as each other.
(http://depts.alverno.edu/nsmt/441samprev.htm)
(http://en.wikipedia.org/wiki/Starling)
(http://en.wikipedia.org/wiki/Emotion_in_animals)
(http://www.pbs.org/wnet/nature/episodes/inside-the-animal-mind/introduction/2081/)