Why are tropical fruits generally much sweeter than temperate?

[studiot]

1 hour ago, CharonY said:

Not sure whether the distinction is relevant in this context as total water content also differs (though one leads to the other, of course, assuming constant retention). 

Of course it must be.

If the sugar production kept up with the water intake the concentration would be identical.

2 hours ago, CharonY said:

The two fruits with the highest sugar content (date, fig) are from Mediterrenean climates

 

Do you consider the climate in Basra or Muscat to be mediterranean?

Not that I would exclude mediterranean fruits.

 

[CharonY]

1 hour ago, studiot said:

Do you consider the climate in Basra or Muscat to be mediterranean?

Probably not, it is more an arid-desert climate, you are right if you refer to the potential origin of dates.  I was mostly looking at figs, which seem to originate from the Anatolian region and for some reasons my brain  added dates. 

[studiot]

Before the great oil disaster wars of the late 20th/ early 21st centuries the principal exports (to us at any rate)  of Iraq, Muscat and Oman was dates.

[mistermack]

The interaction between plants and their seed dispersers can seemingly get really complicated. The deadly nightshade plant is one of the most poisonous you will find in northern Europe, but it's fruit is described as sweet. As an allotment keeper, I've noticed it growing where it definitely wasn't growing the year before, so something is distributing the seeds, and I'm guessing it's birds. 

The whole plant is poisonous, and even the honey carries the poison, if bees have been visiting a lot of it. Some animals have no immunity to it, but obviously others can eat it no problem. Wikipedia says that cattle and rabbits can apparently eat it without problems. I would say that some birds must also be able to eat the berries. They must have evolved that capability, through lots of animals dying from poisoning, before the immunity was achieved. So the plant was obviously better off remaining toxic, even though animals were getting sick and dying from eating the berries. 

So you have a plant that's very very toxic, but has attractive looking berries with a sweet taste. It's full of contradictions, but it's survived and flourished. 

[John Cuthber]

Some rabbits are substantially immune to deadly nightshade

https://en.wikipedia.org/wiki/Atropa_belladonna#Toxicity

 

[mistermack]

On 9/12/2018 at 10:13 PM, John Cuthber said:

Some rabbits are substantially immune to deadly nightshade

https://en.wikipedia.org/wiki/Atropa_belladonna#Toxicity

 

And cattle too, I mentioned it above. It's surprising that those animals evolved an immunity, rather than an aversion to the plant. You would think that it would be less costly to just evolve a few circuits in the brain, than to evolve the physical ability to cope with the poison. But maybe by evolving the immunity, it gave those animals a food source that other animals are shunning, so they have a more exclusive access to it. It could be a life saver in hard famine times, when every other available scrap of food has been eaten.

[John Cuthber]

If cattle had been "planting" nightshade in your allotment , I think you would have noticed.

Evolving an atropinase enzyme just requires tweaking some other esterase.

It will prevent damage by a range of toxins.

Learning to avoid nightshade would only avoid one.

[mistermack]

I'm still guessing that it's birds that spread it, as well as rabbits. I know what rabbit shit looks like, and I haven't seen any, nor any scrapes. But maybe we've just got some tidy rabbits. I'm not sure if the seeds would pass through a rabbit undamaged either. But I'll avoid eating any rabbit shit, just in case. 

[John Cuthber]

Looking at the data so far, the only gut we can rule out as the delivery mechanism is a human one.

[mistermack]

I read the other day that song thrushes and black caps eat deadly nightshade berries. No more details than that. 

They would make a better seed dispersal candidate, as rabbits would be more likely to chew the seeds up, and they eat their own shit and digest it twice, so the seeds might not survive being eaten.