One of the clearest differences in how Christian and Muslim society impacted Jewish communities is in the area of marriage and sexuality. The takkanah of Rabbi Gershom prohibiting polygamy was not generally in effect in Spain nor in the Sephardic Diaspora communities following the expulsion.
In fact in Turkey, some Ashkenazim yielded to Sephardic influence and adopted the practice of marrying second wives. Islamic norm and the Bible’s own approbation of such practices allowed them to continue, though curtailing polygamy was attempted through the insertion of a non-polygamy clause in Ketuboth or through an oath taken by the groom.
In the case of Rabbi Gershom, Christianity clearly rejected this practice, kingship perhaps being the exception, and in Ashkenazi circles little if no responsa on the subject was produced. Some Sephardim in Spain also retained concubinage. This was unheard in Ashkenazi circles.
 Ibid., 167-168. There were however communities in Aragon in the 13th century that adopted this prohibition.
 Ibid., 63.
 Ibid., 253.
 Ibid., 253-254.