"We hope that there is more investigation."
Translation:Nós esperamos que haja mais investigação.
There is tonnes of stuff out there. You might find these useful:
http://www.nativlang.com/po/qg_verbs_presentsubjunctive.htm http://www.nativlang.com/po/qg_verbs_imperfectsubjunctive.htm http://www.nativlang.com/po/qg_verbs_futuresubjunctive.htm https://erikspen.wordpress.com/2011/03/02/when-to-not-use-the-subjunctive/
A rule of thumb for the present subjunctive is that you use it for hypothetical situations. This is why you see it being used with 'eu espero que [...]', because you're hoping for something that might happen.
The rule of thumb for the past subjunctive is that it's always paired with the conditional mood as the subclause when you're using the conditional is talking about a hypothetical situation, thus 'eu gostaria se/que [...]'.
I haven't used the future subjunctive enough to get a proper feel for it.
Native speakers, as a general rule, only have a passive understanding of the grammar and syntax of their own language, so I'm not surprised they look at you funny!
And on that topic: http://www.itchyfeetcomic.com/2014/11/uniquely-incapable.html
If you say "We will hope" that implies that at the present time, you are not expressing hope.
It's possible to say: "We will have to hope, but "hope" expresses the future by means of dependent clauses, not in the principal clause. Duolingo is correct.
Literal translations don't always work. "Will" is not used with hope in the main clause to express the future.
I hope that we go tomorrow. or I hope that we will go tomorrow.
http://www.perfect-english-grammar.com/hope.html - section: hope for the future
DL's sentence can be expressed differently:
We hope that there will be more investigation.