Kristine L. Grayson

I study the variable migration tactics of red-spotted newts (Notophthalmus viridescens) to test predictions from life history and partial migration theory. I conduct my research at Mountain Lake Biological Station (MLBS).

The newt populations at MLBS are partially migratory, where one portion of the population winters in the pond while the other portion migrates to the forest to overwinter. Migrant adults change their physiology for the terrestrial habitat, reabsorbing the tail fin and developing granular skin more resistant to desiccation. Essentially, migrant adults are similar in appearance to efts (the terrestrial juvenile stage) but without the bright red color (adults are approximately ten times less toxic than efts). Partially migratory newts may vary migration tactics over their lifetime. An individual that overwinters in the pond one year may migrate the following year.

In 2007, I examined the effects of habitat quality and sex on migration decision by manipulating population density and sex ratio in aquatic enclosures (Grayson and Wilbur, 2009, Ecology). This past year I used the enclosures to test for differences in reproductive phenology between migrant females and resident females.

Mark-recapture work to understand migration dynamics in two natural populations:

In 2005, I built drift fences around Horton and Sylvatica Ponds at MLBS and have been censusing and checking pitfall traps every day from March to October. In order to avoid the fence being a barrier to winter movements for all species, a gate with a sliding door was installed between each pitfall trap pair. This gate is opened when the lids are covering the pitfall traps. Red-spotted newts are the dominant pond-breeding salamander (400 – 700 adults in each small pond). I use photographs of the dorsal pattern of red spots as an individual unique mark.

I am investigating questions on both the individual level, (i.e. How much temporal variation in migration tactics exists within individuals?), and population level (i.e. What are the costs and benefits for current and future survival of alternate migration tactics?)