Why are citrus fruits segmented?

This is commentary on the staff report at:

http://www.straightdope.com/mailbag/mcitrussegment.html

This answer was gutless.

Surely there must be competing evolutionary advantages to segmentation and non-segmentation, and this answer completely sidesteps this question.

I’m not a botanist, but I could see how perhaps each segment of an orange provides a package that could realistically be expected to produce an orange tree, or at least, they probably evolved from something that could have. All the segments share a common skin. The skin, of course, is the first line of defense from parasites and herbivores, but has no other value to the plant. Thus, by covering multiple reproductive packages with a single protective layer, the volume of the fruit is increased, and the relative surface area is decreased. In other words, just one segment per fruit would require a greater skin-to-seed ratio, which would result in worse over-all defense of the seeds.

This could all be wrong of course, but there must be a deeper reason than, “They evolved along different paths, by a combination of accident and
selection over millions of years.” Duh!

Given that we don’t know the details of why they developed that way, I think it is acceptable to just state that it happened that way, the end.

After all, your hypothesis ignores the fact that trees produce many fruits, each a separate reproductive package.

Your hypothesis also doesn’t explain why citris fruit segments are all the way through the fruit, whereas apples are only in the core, and the meat of the fruit is continuous.

Your hypothesis also ignores the reason for the existence of the meat of the fruit. That is not to provide sustenance to the seeds, but rather to entice animals to eat the fruit, and thereby carry the seeds to distant locations and drop them in their feces. If an orangutan is going to eat the whole orange, what difference does it make if the meat is segmented or not? It’s going to the same place - the orangutan.

Wild citrus fruit is fairly sour, isn’t it? And the peel is bitter. So I don’t think citrus fruit would have evolved to be eaten by a large mammal and then deposited somewhere.

http://www.sunkist.com/citrus/growpack.asp

I think it evolved to hang on the tree until it simply started to rot and then fell off, the rotting fruit to be carried off in pieces by various small ground-dwelling critters (rodents, turtles, birds, etc.) In this case it would be handy to have the segments be separate, in individual serving sizes, so to speak.

And I found this discussion. FWIW.
http://www.newscientist.com/lastword/answers/569plants.jsp?tp=plants1

I don’t know if wild citris is extra sour, but yes, the peel is bitter. However, I’ve watched apes (orangutans and gorillas) eat fruit at the zoo, and they eat oranges the way we humans often eat apples - peel and all. So I don’t think it impossible that mammals would eat the wild fruit. (And actually, they eat apples core and all.)

Be that as it may, animals eat the fruit and carry the seeds away in their digestive tract. Or scatter the seeds in the process of eating the fruit.

jawdirk said:

I believe this is the point of the OP. Perhaps the asker of the original question “Why are citrus fruits are segmented?” only wanted a non-technical answer, but I think a “why” question deserves a more complete answer. And in the context of biological species, I think a summary of evolutionary history and functional analysis of the citrus fruits is appropriate.

jawdirk’s hypothesis is only guesswork; Irishman’s orangutan anecnote isn’t really applicable, since modern cultivated citrus fruit has been artificially selected to increase size and sweetness of the fruity flesh. We need to concentrate on the citrus species found in nature. What is the function of the fruit of wild citrus species? What is the local climate? What are the local fruit-eaters?

Irishman said:

In science we don’t have to be only desciptive. We can try to determine the details of why they developed that way.

Pleonast, read the second link by Duck Duck Goose.

So, back to my original response to jawdirk, we do not know. There are numerous guesses on that page, but the essential answer is that it is unknown.

…and, of course, not all evolutionary traits need to provide a competitive advantage. A trait that is neutral can/will still survive; so, the original segmentation may have been neutral but then the further evolution into grapefruits, oranges, etc may have conferred competitive advantage in different local environment.s