March 26, 2018, Lehigh University
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."