Is sexual dimorphism an evolutionary dead end?

 So right up front, I’m not an evolutionary biologist. My degrees are in Classical Archaeology and Law. I just am a science and biology enthusiast who is physically disabled, cannot work, and so spends a lot of his time consuming popular science content. I watched a Journey to the Microcosmos video the other day about Ostracods, which are a clade of crustaceans who generally invest very heavily into sexual dimorphism, with males being excessively large compared to females so they can have longer penises and bigger sperm which then translate into greater reproductive success because females prefer males with longer penises, or because its easier to for big sperm to survive or something, I honestly don’t remember the exact reason big penises are good for them. The major point is, being bigger and having a bigger penis and giant sperm are not adaptive beyond their contribution to reproductive success for males. They don’t help any other aspect of survival and are thus essentially evolutionary dead weight from a survival perspective.

Lots of species have traits like this. Peacock tails are the obvious go to, but antlers and horns probably fall into this - although there is likely some survival advantage defensively against predators, not enough to justify the level of investment you see in highly sexually selected species. Fangs in primates is another, as is any species where the male is larger than the female due to male combat or female choice having a hand in sexual selection - which is most mammals and a decent chunk of fish and reptiles and birds. Basically, its all over the natural worlds, traits that species - usually males - invest in which do not convey a direct survival benefit but do convey a reproductive advantage, possibly even though they are in fact detrimental to survival, or at least detrimental when invested in so heavily.

None of this is new, but what was interesting about the video is apparently a study was done on ostracod lineages that showed that those lineages which heavily invest in male size and penis size tend to go extinct at a much faster rate than those which do not. And while I had vaguely wondered how it can actually be advantageous for a peacock to have such a huge useless tail, this really got me wondering - is this true beyond ostracods? Are species which invest heavily in sexual selection shooting themselves in the foot, or perhaps more accurately in the dick? That is apparently true for ostracods, at least according to this one study, and it makes logical sense - investing in sexual selection will have short term dividends for the individual who can survive in their current environment, but without an actual survival advantage, if the species’ niche becomes threatened, the sexually selected traits will be a constant drag on survivability, and while it may continue to provide success to an individuals chances of success at mating when compared to other members of the species, the species as a whole is likely to lose the survival contest against other species without such a drag on them.

Obviously this one study of ostracods doesn’t prove that this does apply to all animals or all life, but it is thought provoking. Specialists of all types tend to go extinct in trying times, and it makes sense that would apply to sexual selection specialists too, probably even more-so, since they are essentially investing evolutionary resources into sucking worse at everything but making ladies fuck you. It even is interesting to think about socially. Might the same be true for societies - societies which invest in patriarchy, which grants men more reproductive control, be less able to survive hard times because they are investing resources in making women less free instead of taking full advantage of all their society’s resources? Anyways, I don’t think any real conclusions can or should be drawn from this, but I would be curious if we can do studies on other groups - or if such studies have already been done - which show a general trend for evolutionary groups with high sexual dimorphism being less successful. I can even imagine reasons why this trend might not stay true beyond ostracods - for instance, having multiple body types could prove an advantage in being able to take advantage of more resources, especially if male and female individuals can niche partition and take advantage of different things, like how male marine iguanas can dive deep for algae but females and juveniles cannot. Anyways, just some random, inexpert musings.