>>47174006it's part of the lore described in a gen 1, jap only encyclopedia with info from Tajiri himself
it came out way earlier than breeding game mechanics were a thing but somehow they felt it was significant enough to reflect that information when that became part of the games
Here's a transcript, if you want to plop it up on google translate for a rough understanding:
ニドラン
小さくても毒針の威力は強烈である。メスの方が角が小さい。毎年春に繁殖期があり、夏の終わりに2個卵を産み、その2週間後、オスとメスが孵化する。ニドラン赤ちゃんの体長は10cm。
ニドリーナ
メスなので性格は温厚だ。口から出す超音波は相手を惑わす力がある。ニドランの進化形だが、ニドリーナになると、卵を産む能力はなくなる。
ニドラン
耳が大きく遠くの音を聞くとき、羽ばたくように動き、怒ると毒針を出す。繁殖期には角の色が七色に発光し、メスにアピールする。大きい角の方がメスにウケるらしい。
ニドリーノ
怒りやすい性格。 発達した角を振りまわして、ダイヤモンドも串刺しにする。ニドランの進化形だが、ニドリーナと違って繁殖能力がある。
Why that seemingly bizarre lore came to be idk, perhaps an obscure reference
We can trace the origin of the Nidoran line back to the Kaiju Baragon and the Bunicorn from Dragon Quest but it explains nothing as neither even have the gender difference concept going on.
Or maybe it's just that, being that at the time they were the Pokémon that represented the male/female biological dichotomy, it just alludes to how in nature males remain fertile all their life while females don't(but if that was the case one would think they would do the loss of fertility for Nidoqueen only, Nidorina doesn't seem like it has hit menopause yet, lol.)
