It takes two: Seasonal variation in sexually dimorphic weaponry results from divergent changes in males and females.

Sexually dimorphic weaponry often results from intrasexual selection, and weapon size can vary seasonally when costs of bearing the weapon exceed the benefits outside of the reproductive season. Weapons can also be favored in competition over nonreproductive resources such as food or shelter, and if such nonreproductive competition occurs year-round, weapons may be less likely to vary seasonally. In snapping shrimp (), both sexes have an enlarged snapping claw (a potentially deadly weapon), and males of many species have larger claws than females, although females are more aggressive.

Landmark learning by juvenile salamanders (Ambystoma maculatum).

Learning to use a landmark as a beacon to locate resources is one of the simplest forms of spatial learning. We tested whether landmark learning occurs in a semifossorial salamander that migrates annually to breeding ponds as adults. Juvenile spotted salamanders (Ambystoma maculatum) were tested in square containers with a plastic feeding dish in each corner, and a piece of earthworm was placed in one randomly-chosen dish.