The clues are color and size, although bigger birds don't necessarily lay larger eggs.
Breeders choose chickens that produce larger eggs, cows that yield more milk, and corn with higher protein content.
Larger eggs, emblazoned with an "A," start at $60 for one that weighs 7.5 ounces, and go up to $145 for one that weighs 24.7 ounces.
The company -- which buys two billion eggs a year -- has also told its egg suppliers to stop the practice of temporarily withholding food and water to induce hens to lay larger eggs.
The tamer birds grew faster, laid larger eggs, and were bossier than their more fearful counterparts.
An egg parasitoid, Baeus cyclosae, attacked C. morretes more often than C. fililineata, possibly as a consequence of its greater clutch size and/or larger eggs.
While larger eggs generally result in larger, higher-quality offspring, the relationship between egg size and offspring phenotype is complicated because offspring can evolve to be more or less responsive to variation in yolk provisions.
Female body size is positively correlated with egg size in bean beetles (Fox 1994b), and offspring from larger eggs develop more quickly and emerge at larger sizes than offspring from smaller eggs (Fox 1994a).
Eggs obtained from naturally foraging broodfish should contain a biochemical composition that is suitable for producing larger eggs and larvae with higher viability of offspring (Kjørsvik et al. 1989).
Now, animal behaviorists have shown that domestication was a two-for-one deal: Not only did the birds become fearless, they also got bigger and produced more and larger eggs.
Each time they start laying again, they will lay fewer, but larger, eggs.
