Could a sapient, animal-like alien reproduce with pollen and ovules, rather than directly producing sperm and eggs?
Reproduction via pollen works. There is no reason why you couldn't imagine an alien using that form of reproduction
But it's very inefficient
This mode of reproduction consumes a lot of energy because you have to disseminate an enormous quantity of pollen in order to get a small result. Moreover, if you want to use other animals to help disseminate your pollen (as trees do), you have to create an incentive in the form of flower nectar, which costs energy.
The reason why trees use this type reproduction is because they cannot move, so they cannot use a more efficient one.
You need a reason why your aliens would evolve that type of reproduction.
- Either they cannot meet their counterparts of the other sex (or lay eggs in some place like fish do) for some reason (or it is difficult for them).
- Or maybe they rapidly evolved from plants (or other lifeform unable to move) that used this method of reproduction, and have not yet evolved another method. But then they would need to have other characterestics of plants
Some plants and some sea creatures like corals and sea urchins spread their gametes and let the chance take care of the reproduction.
Therefore it is in principle possible that also other creatures keep the same way of doing it. However you need a good evolutionary reason for this to happen.
A possible motivation might be that seeking a partner and mating is less favorable than blowing it in the wind: this can be maybe because of a very sparse population and/or an high risk of being eaten during the act, resulting in a more precautionary approach to reproduction.
If it evolved from a pollen wielding ancestor then it could have retained this characteristic. In fact, if a distant common ancestor had been pollen reproducing then perhaps there is an entire class of ambulatory plants which reproduce this way.
Some things to consider might be
- Are they monoecious or dioecious?
- Are they synchronously monoecious or consecutively monoecious?
- Are they wind pollinated or animal pollinated?
Pollination has massive implications for behaviour / culture / society - not least because pollination implies distance reproduction. The above traits will heavily influence culture and behaviour.
Assuming they are dioecious then there is no concept of father as we understand it. Children never meet their genetic father and if they do they don't notice / care. The emergence of gene sequencing is the only thing which would really allow a child to identify their parent but it would have zero cultural relevance as the culture would have evolved to be sexually divergent to the extent that males and females may never meet as adults.
There is no concept of courtship, no romance, no mating displays, no physical competition for partners. Competition takes place at the microscopic level in terms of whose pollen is most effective.
Instead of partnership they might have evolved completely different pollination-specific behaviours, such as they may be compelled to climb to high points outdoors when in season if they are wind pollinators. In this case a completely different form of competition may have evolved revolving around securing the highest point.
If they reproduce in large numbers like seed plants then males may live longer than females because the reproductive burden on females is heavier (heavier than with humans, if you think growing a baby is difficult try growing 80,000 of them at once). Child mortality rate would also be extremely high and children may not begin to have value until they are a certain age. Killing children might not be illegal.
If they are consecutively monoecious wind pollinators then they may have an aggressive climbing "male" phase where they fight over the summit of the nearest hill and a child bearing "female" phase where they stay out of danger and eat a lot.
Many animals essentially do reproduce this way. That is, one or both parents release gametes into the environment, and fertilisation takes place externally. It generally happens underwater (I'm not aware of any land-based animal with airborne sperm), and the parents are usually not very far from each other, but it would obviously be physically possible.
If individuals of a species are able to meet in person, then it is much more evolutionarily favorable for them to exchange gametes directly, because (a) it is more efficient and (b) it allows for mate selection. Even if trees learned to walk around, then you would expect them to almost immediately evolve to only release pollen when they are right next to another tree. So, barring some extremely contrived condition, I'd expect that these aliens release pollen because, for whatever reason, they never actually meet other individuals of their species.
That raises the question of how they could have a civilisation. I'm pretty sure there have been questions here before about how sentience might evolve in a species that never knows its parents, but this is more specific, because not only do these aliens not know their parents, they never know anyone at all.
The obvious suggestion would be that they can encode their experiences in their genome, and are born with their parents' memories. Another possibility is that they are separated by time rather than distance – perhaps fertilised eggs lay dormant until a rare warm season occurs, and when the individual hatches it finds some kind of library left by its long-dead ancestors (although how would it learn to read?).
Or a simpler answer, which the question doesn't rule out, is that these are sessile animals, like sea anemones. They might be able to talk to their neighbors 30 centimeters away, but simply unable to move (like the Skroderiders in Vernor Vinge's A Fire Upon the Deep). Possibly they are also able to use pollen for long-distance communication as well as reproduction.