Which preposition to use with specialising

in Occurrences 16%

Here two Englishmen, soldiers of fortune or misfortune, as the case might be, who had specialised in recent Mexican revolutions, till the fall of Huerta brought them, too, to unemployment; an Irishman there, for whom the President of Costa Rica had promised a swift death against a blank wall.

to Occurrences 3%

Murphy, but the way, seems to have specialised to some extent in saint's Lives and to have imbued his disciples with something of the same taste.

into Occurrences 2%

It is this Mesozoic continent (which may well have lain in the neighbourhood of what are now the shores of the North Pacific Ocean) which I suppose to have been occupied by the Mesozoic Monodelphia; and it is in this region that I conceive they must have gone through the long series of changes by which they were specialised into the forms which we refer to different orders.

Which preposition to use with  specialising