Evolution of Bird Song May Affect Speciation

Speciation
is the formation of new species of organisms.  Often, the term
is used to describe an event in the course of evolution in which one
species gets divided into two groups, after which the process of
genetic change occurs differently in each group.  When the
differences are so great, that representatives from one group do not
interbreed successfully with members of the other, then a new species
has formed.



I know, when you get down to the details, it is tough to come up with a
universally acceptable way to define a species, but that is href="http://www.philosophynow.org/issue50/50pigliucci.htm">another
story.  It is not my intention to discuss the
process of speciation in detail. Rather, I'm going to mention one
little bit of it, one little part of how behavior may play a role.



From an OnlineEarly Article in the journal, Evolution:

href="http://www.blackwell-synergy.com/doi/abs/10.1111/j.1558-5646.2007.00154.x">EVOLUTION
OF BIRD SONG AFFECTS SIGNAL EFFICACY: AN EXPERIMENTAL TEST USING
HISTORICAL AND CURRENT SIGNALS

doi:10.1111/j.1558-5646.2007.00154.x

Elizabeth P.
Derryberry

Duke University, Biology Department, P.O. Box 90338, Durham, North
Carolina 27708

Mating
signals act as behavioral barriers to gene flow in many animal taxa,
yet little is known about how signal evolution within populations
contributes to the formation of these barriers. Although variation in
mating signals among populations is known to affect mating behavior,
there is no direct evidence that the evolution of mating signals
changes signal effectiveness within a natural population. Making use of
historical recordings of bird song, I found that both male and female
white-crowned sparrows (Zonotrichia leucophrys) respond more strongly
to current than to historical songs, indicating that historical songs
are less effective as signals in the current contexts of both mate
choice and male–male competition. Finding that historical
signals are less effective suggests that signal evolution within
populations may ultimately contribute to the formation of behavioral
barriers to gene flow between populations.

The idea here is that one type of behavior -- in this case, singing --
can change over time, leading to changes in mate selection.  



Previous work has shown that different species often have different
mating signals, and these differences are used by the members of the
species to figure out with whom they should mate.  There is
not a lot of empirical evidence regarding the amount of time it would
take for making signals to change enough to have such an effect.



Dr. Derryberry used recordings of birdsong from

 white-crowned sparrows (Zonotrichia leucophrys)
in a particular location in California.  In her study, she
used recordings from 1979 and from 2003.  The recorded songs
were used in a copulation solicitation assay.  This showed
that females responded preferentially to contemporaneous recordings;
less to the older recordings. (The sound quality was standardized).



The males were tested using a territorial playback test.  This
simulates an intrusion on the mating territory that the male has
claimed.  Males showed more territory-defending behavior in
response to contemporaneous songs.  That is, they did not
perceive the (simulated) intrusions by other males singing
old-fashioned songs as being as much of a threat.  



The results show that significant behavioral changes can occur in as
little as 14 years.  The changes are large enough to affect
mating behavior, such that a mating barrier of sorts is created.
 



Although the author does not extend her hypothesis this far, I suspect
that this study helps explain why kids these days always choose music
that annoys their parents.  (Disco? Yuk!)