Publishers occasionally send me books to review. I'm now discouraging this, because I have too much to read already.
But I've been enjoying Daphne Fairbairn's "Odd Couples: Extraordinary Differences Between the Sexes in the Animal Kingdom." I knew about species where males are much bigger than females. The females are optimum size, essentially, but the males are bigger to fight over mates. But there are lots of other interesting examples, from fish where the females are tiny (to fit inside discarded snail shells) and the males are much larger (to be big enough to carry those shells) to tiny male octopi who carry jellyfish stingers as weapons -- the females are much bigger and don't need weapons.