This piece is a belated response to a lot of the kerfuffle around SUMO's release especially in regards to Primarina's design. Personally my Primarina, Vincero, was one of my Sun run's best bois, but a lot of people hated it or considered its design inappropriate for a 7:1 male:female pokemon (if there's anything I actively dislike in Pokemon, it's the weird gender ratios). It's important to remember that nature doesn't follow the sensibilities of any one human culture and we have to be careful when interpreting animal behavior and report it objectively. Generally in the animal kingdom, the male of the species is the "pretty" one.
I've sometimes complained that realistic pokemon artists follow real-life animals too slavishly when interpreting pokemon designs, but here I've gone and done just that, pasting a sea lion's top half on a mermaid tail instead of paying attention to canon Primarina's slinky and elongated design. Oh well.
Greetings Pokemon Professor hopefuls, it's time for another helpful infographic from Professor Honeylocust, the world's friendliest Pokemon Professor. cough
Male Primarina have a vivid coloration and a long, flowing mane driven by sexual selection. A healthy and strong Primarina is able to survive despite its bright color and the drag created by its mane, which make it easier for prey to avoid it. Most important, though, is its loud and carrying song, which attracts female Primarina from dozens of kilometers in every direction. Their sacral spikes are actually resonators that help increase their song volume and carrying distance.
Female Primarina choose mates based on their appearance, singing quality, and stamina. Male Primarina often cannot leave to hunt in case other males attract any female Primarina that have initially chosen them in their absence, and so they will often be quite thin and weak by the end of the breeding season.
Female Primarina are duller in color, taking on more natural hues to better sneak up on prey. Male Primarina coloration is still vivid outside of the breeding season but it will dim somewhat. The appearance of the female is less driven by sexual selection, but they have their own markers of health including a mane and symbiotic barnacles. Some males may decline to mate with unhealthy-looking females in order to conserve their energy.
Female Primarina also sing to one another, to males, and to their pups, and are thought to be exchanging information regarding information, identity, territory, or exigent threats, but their songs tend to be far quieter than the breeding males'. Both male and female Primarina are adept battlers, but it is thought that the wild females may be more practiced with using their songs as weapons to defend their pups from predators.
Females are on average larger than males. As with other pokemon whose males do not engage in direct contests of strength to impress potential mates and drive off competitors, the evolutionary pressure on size instead acts on the female. Larger and more nutritive/energy-rich pokemon eggs are more likely to produce strong baby pokemon that survive their earliest and most vulnerable stages.
Now get back to studying! Pokemonology isn't going to pass itself!