HowStuffWorks released a video on YouTube on Tuesday all about the science of ‘intersex animals’
The video explores sequential hermaphrodites (animals that start off one gender and then become the other, usually male to female). The last category has a notable member, the clownfish (or ‘Nemo’ in the children’s vernacular), where one fish in a group will be female and mate with all the males. Then when she dies, the oldest and largest male becomes the female.
Being able to switch genders helps some animals maximize mating potential. Meanwhile, some other animals actually “cross-dress” by changing their appearance to resemble the opposite sex to reduce mating. Male market squid, as the video points out, aren’t exactly known for lengthy courtships and gentle love-making. Rather, mating is a frenzied and violent affair that can leave the females worn out and injured. To get away from the craziness, females sometimes cross-dress as males to avoid attention.
The video doesn’t mention the cross-dressing abilities of the Australian giant cuttlefish, cousin to the squid. These molluskan giants meet once a year to mate, and rather than just grabbing any old female and having their way with her, the males compete for female attention. Usually the biggest, brightest cuttlefish win. Smaller males would have no hope against the big guys, so instead they “dress” as females, changing the color of their skin and hiding their extra arm to slip past the males undetected. Then they’ll mate with the female right under the big guy.
The cool thing is that the males just deposit little sacks of sperm into the female. She gets to choose which one of her mates gets to fertilize her eggs later. Paternity tests show that while the big, aggressive males are often the females’ top choice, the second most popular choice us the cross-dressing males. Researchers take this as a sign that the females acknowledge the advantage of being clever by sometimes choosing to pass those genes along to their offspring.
Here’s a video of the cross-dressing in action:
HowStuffWorks also talks about simultaneous hermaphrodites, such as terrestrial slugs. These animals have both sex organs, and usually mate with each other simultaneously to essentially double their output. That’s a great strategy, but it’s a little tame compared to the penis-fencing marine flatworm. These colorful animals will literally fence with their spiky penises until the victor stabs and inseminates the other flatworm, who then has the burden of carrying the new flatworms to term.
All these crazy mating habits boil down to one thing: energy and survival of the species. Given enough time, the selective processes of evolution will lead to some pretty weird mating rituals.