Strange, I was taught that sex that determines whether a sexually reproducing organism produces male or female gametes. You're describing anisogamy. Large male

Strange, I was taught that sex that determines whether a sexually reproducing organism produces male or female gametes. You're describing anisogamy. Large males are sexually selected for in elephant seals because they can fight off other males, but small males are sexually selected for in spiders for they can mate with the female quickly while avoiding being eaten.