Hi there, I only have limited experience with this but I did successfully introduce my 12 yr old male green iguana to my 2 year old cyclura lewisi cross this past winter.
The key is "neutral territory". Introduce them in a place that neither can claim as "theirs". This will help but you have to watch them very carefully.
In my case I know the personalities of these guys really well. I have had the green ig (9 lbs) for 9 years and I have seen him interact with other iguanas before. I sort of knew he was not an "alpha ig". He is just not a fighter or TOO territorial in my opinion. I was more concerned about the cyclura who only weighed in at about 4 lbs because she was a big bobber and I could just see that she looked like she might be more territorial AND I also know that cycluras of both genders tend to be more territorial.
Armed with this information floating around my head I let them both loose in the living room one day. Sure enough Tashmoo (cyclura) opened her mouth at Pugs and ran at him bobbing and gaping. He just stood there like, "what?" He didnt run away nor defend himself so she just stood there bobbing and bobbing and bobbing. He walked away.
Then a couple of days later he wandered near her room here and I let him in. He saw her basking spot and sat in it. She didnt like that and attempted to chase him away. Again he sat there like, "what exactly is your problem?" She finally had no choice but to bask with him if she wanted to bask.
They kept meeting in the middle between the rooms until it was apparent that they were neither bothered by the other and finally I was able to move her into his room. Like I thought he didnt defend anything from her. He just accepted her.
Will your meeting go like this? I dunno. Know their personalities and try and work with them.
At the moment I am still trying to introduce Pete the new cyclura (3.5 yr old 6.5 lb male) to Tashmoo (2.5 yr old 4.5 lb female) successfully. This is not going as well because unlike Pugsley, Pete ran away from her the first couple of times and he was apparently fun to chase. Now things are changing a bit and Pete has gotten the idea that he should be trying to breed with her and chases her back. I am not sure what the outcome will be.
Neutral territory is your friend tho!
Carole

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