Updated: 4:36 p.m.

Rep. Lincoln Diaz-Balart (R) announced his retirement on Thursday, touching off an interesting chain reaction in South Florida.

His younger brother, Rep. Mario Diaz Balart (R), immediately announced that he will give up his neighboring 25th district seat to run in Lincoln Diaz-Balart’s slightly more Republican-friendly 21st district.

“This is a natural move for me; in my years of public service at both the federal and state levels, I have had the privilege of representing most of the communities that make up Congressional District 21, including Hialeah, Westchester, Doral, Kendall, Miami Lakes, Hialeah Gardens, Medley and Palmetto Bay,” Mario Diaz-Balart said in a statement. “As the only Broward native in the U.S. House of Representatives, I look forward to the opportunity of representing Broward’s residents.”

With Mario Diaz-Balart making the jump to the 21st district race, the open-seat race in his district becomes a prime pickup opportunity for Democrats.

Mario Diaz-Balart beat longtime Cuban-American activist Joe Garcia by 6 points in 2008, in a race that national Democrats targeted. It was the closest race of his Congressional career. Meanwhile, 25th district voters favored Sen. John McCain (R-Ariz.) by just 1 point over Barack Obama in the presidential contest, just four years after they backed President George W. Bush by 12 points.

While Garcia had passed on a rematch, sources said Democrats would look to Garcia again in the open-seat scenario.

According to a report in the Naples Daily News, Mario Diaz-Balart will endorse state Rep. David Rivera (R), who is currently running for state Senate, in the race to succeed him in Congress.

Meanwhile, in the wake of the Congressmen’s dual announcements, Florida Senate Majority Leader Alex Diaz de la Portilla (R) released a statement expressing interest in a possible Congressional bid — although he did not specify in which district he might run.

“I am seriously considering the opportunity to continue to fight for the people of Florida on a national level in the United States Congress,” Diaz said. “I will make my final decision soon after thoughtful and deliberate consideration.”

Other Republican names that have been mentioned as possible candidates in either the 21st or 25th districts are state Sen. Alex Villalobos and Carlos Curbelo, a Lincoln Diaz-Balart protege who is currently working for appointed Sen. George LeMieux (R-Fla.).

Lincoln Diaz-Balart, who has represented the South Florida-based 21st district since 1992, becomes the 18th Republican to announce plans to leave the House at the end of this Congress. His retirement announcement comes just months after his name was briefly in the mix to temporarily fill then-Sen. Mel Martinez’s (R) seat, which ultimately went to LeMieux.

“Today, I am announcing that I will not seek a 10th term in the United States Congress this November,” Lincoln Diaz-Balart said at a noon news conference in Miami. The Congressman said he plans to return to practicing law.

Lincoln Diaz-Balart reported more than $120,000 in receipts during the fourth quarter of 2009 and about $260,000 in cash on hand on Dec. 31. Mario Diaz-Balart raised just $26,000 during the last three months of 2009 and had about $180,000 in the bank at the end of the year.