Unusually spine's erect showing determination (11)
I believe the answer is:
persistence
'determination' is the definition.
(persistence is a kind of determination)
'unusually spine's erect' is the wordplay.
'unusually' is an anagram indicator.
'spines'+'erect'='spineserect'
'spineserect' is an anagram of 'PERSISTENCE'.
'showing' is the link.
(Other definitions for persistence that I've seen before include "Determination" , "grit" , "Doggedness" , "Refusal to accept refusal" , "Dogged quality" .)