Marriott Rewards just announced their latest airline partner Iberia. You can now earn Iberia Avios for your Marriott stays, although this makes very little sense.
Iberia is part of IAG (International Airlines Group), as is British Airways. You have been able to earn BA Avios for your Marriott stays for a long time. You can freely transfer Avios between Avios, BA Avios and Iberia Avios, so there has been a way to earn Iberia Avios for your stays for a long time.