For a long time,
hybridization—when distinct species mate and produce offspring—was thought to
be a mistake. Yet, advancements in genomic testing tools have revealed
naturally occurring hybridization as a fairly common phenomenon—with a role in
natural selection, in some cases.
Scientists estimate that as much
as 10% of animals—and 25% of plants—engage in hybridization in nature. Genetic
data has even shed light on modern-day humans' hybrid ancestry, with most
Europeans and Asians thought to have approximately 2 percent Neanderthal DNA.
Sterility is common in hybrids
and is thought to be a key factor in keeping two hybridizing species distinct. This is
true for a particular hybrid chickadee population in the U.S., the result of
mating between the northern Black-capped Chickadee and a southern species
called the Carolina Chickadee. A lower percentage of the hybrid chickadees'
eggs hatch compared to their pure-species parents—a key selective disadvantage.
The results of a new behavioral
study out of Lehigh University and Franklin & Marshall College add a
wrinkle to this paradigm: scientists found that hybrid chickadees have marked
deficiencies in learning and memory compared to their pure species parents,
which may be another selective disadvantage.
This discovery is the first time
that learning and memory deficiencies have been identified in any hybrid of any
species, opening up a new area of inquiry for understanding hybrids' selective
disadvantage. The study results appear in the journal Evolution in an
article that appears online today by Michael A. McQuillan, Amber M. Rice and
Alex V. Huynh of Lehigh University and Timothy C. Roth II of Franklin &
Marshall College called: "Hybrid Chickadees are Deficient in Learning and
Memory."
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