Check the display percent set in the WIndows Display control panel. Due to a bug in FileMaker, you need to keep this setting at 100% when using FileMaker which can be a problem for many users. If this is not set at 100%, try changing that setting first to see if it makes a difference.
Then, if text is still too small in the drop downs, try selecting the "enlarge window contents to improve visibility" option in Preferences to see what that does for you.
If all else fails, test your system by using the windows machine to add a new copy of one of these fields to your layout and see if you get the same behavior with the new copy of the field.
Thanks! I think it was a combination of that and my retina screen - when I ran the runtime on a true pc (instead of through my virtual pc on the Mac) it worked better.