S American native reserved and turned up (5)
I believe the answer is:
coypu
's american native' is the definition.
(rodent native to South America)
'reserved and turned up' is the wordplay.
'reserved' becomes 'coy' (both can mean shy).
'and' says to put letters next to each other.
'turned' is a reversal indicator.
'up' backwards is 'pu'.
'coy'+'pu'='COYPU'
(Other definitions for coypu that I've seen before include "Beaver-like creature" , "aquatic mammal" , "Beaver lookalike" , "Aquatic beaver-like rodent" , "S American rodent inadvertently introduced into Europe" .)