Parties protecting short seaman forced to follow local conventions (2,2,3,6,2)

'follow local conventions' is the definition.
(to do as the Romans do is to follow local customs)

'parties protecting short seaman forced' is the wordplay.
'parties' becomes 'dodo' ('do' can mean a party).
'protecting' is an insertion indicator (inserted letters are held or protected).
'forced' indicates an anagram.
'short'+'seaman'='shortseaman'
'shortseaman' is an anagram of 'astheromans'.
'dodo' placed around 'astheromans' is 'DO AS THE ROMANS DO'.

'to' is the link.