Hybrid chickadees found deficient at learning and memory

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."

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Is a new chickadee on the horizon?

Date: June 8, 2016

Source: Lehigh University

Class is in session for a group of chickadees at their temporary quarters inside an aviary in Lehigh's department of biological sciences.

Today, the students are beginning a 10-day lesson on spatial memory. A wooden board hanging on one of the aviary's walls contains 60 small holes, each covered with a ball of cotton. One of those cotton balls conceals a worm. One at a time, each bird must find the hole hiding the worm.

Over the next nine days, the test will be repeated daily, with a new worm hidden each day inside the same hole.

The experiment, says Michael McQuillan, is designed to measure each bird's ability to remember where it has stored food -- a trait vital for chickadees and other animals that scatter and hoard their food to survive in the wild.

It is also designed to shed light on speciation, the process by which new species arise over time.

McQuillan, a Ph.D. candidate in biological sciences, is particularly interested in hybridization, which occurs when parents from two different species mate. Their offspring, called a hybrid, may or may not become a new species.

McQuillan's chickadees include the black-capped chickadee, whose range covers Alaska, Canada and the northern United States, and the Carolina chickadee, which lives in the southeastern U.S. The two species of songbirds do not migrate and are similar, but distinguishable, in appearance. The black-capped variety is darker and larger, its tail is longer, and its black bib has sharper edges.

The ranges of the two purebred species overlap in the Lehigh Valley. The intermingling has led to interbreeding and produced hybrid chickadees, which McQuillan is also testing.

Hybridization occurs in about 10 percent of animals and 25 percent of plants, says McQuillan. Some hybrids thrive, but most do not. The mule, a cross between a horse and donkey, is valued for its strength and endurance but is unable to reproduce and thus to speciate. And roughly 60,000 years ago, says McQuillan, scientists believe human beings interbred with Neanderthal men.

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Brainy birds stash stores

We know that squirrels make the most of fall's plenty by hoarding nuts for the winter, but the fact that birds also store, or cache, food goes largely unappreciated. Through clever observation and experiments, biologists have found that food caching (from the French cacher, "to hide") has developed to a high art in some birds.

Take the chickadee, for instance. Chickadees put tens of thousands of food items a year into short-term storage. They usually retrieve and eat the food in the space of several days. Each food item is cached in a different place to make it difficult for thieves to steal all the food at once. When hiding a new item, they remember their previous storage sites and avoid placing caches too close together. Chickadees remember each hiding place for around a month, even though they may be scattered widely across a bird's territory. Research shows they use visual cues to navigate back to each of their cache sites by a combination of larger landscape features, particularly verticals, and use of the sun as compass. Smaller local details are not as critical, probably because these often change in a forest. When retrieving food, they remember which sites have been emptied, either by them or by robbers, to avoid fruitless searching.

How does a tiny bird have such brain power?

Read on:  http://www.benningtonbanner.com/opinion/ci_21849128/brainy-birds-stash-stores