Check the other Asian elephant threads for more discussion and information on this but I will say Tucker hasn't been used to breeding since he's related to two of Houston's breeding cows Tess and Tupelo. While he is unrelated to Shanti, Houston's other mature bull Thai is more valuable and much older and they want him breeding her. Tucker will likely breed Shanti and her daughter Joy in the future while his mom Tess and their female relatives (Tupelo, Tilly, Winnie) may be sent out.
I think though it might work the other way around. The reason I think this is because with Tesses bloodline they already have a multigenerational herd and I think the Houston Zoo will want to prioritize sending the bachelors out first (possibly some of them for breeding or for their elephants to join a bachelor herd) and then maybe in the near future send Shanti and her daughter Joy I think to the Smithsonian National Zoo which would be the perfect logical choice because A.) Shanti will be reunited with her mother and B.) Spike will finally have more girls to breed with