Solid Hardwood, Engineered and Laminate Flooring - Gaps in wood floor

I have a tongue and grove oak plank floor glued to concrete floor. The oak expands and contracts width-wise with the weather and often times there's a 1/8 gap between some of the boards. Is there anything I can do to fill in these gaps permanently? Is there anything I can do to prevent or minimize the expansion/contraction? I've tried caulk but it gets pushed out when joints expand. Wood fill works better but pulls apart when joint contracts. Would replacing select boards with larger boards that were custom fit help? Thanks.

Where is floor location nationally? Width and thickness of T&G? Temperature and relative humidity of room?

Thanks. Located in Jacksonville, Fl. Each board is 2" wide 12 " long. and 3/8" thick. Room temp varies between 68 in winter and 78 in summer. Don't know the humidity. House is located about 15 miles in shore from ocean.

How old is the floor and how much do you know about the installation? It seems like the wood was not acclimated enough before installation or the concrete still had to much moisture. For that size T&G the 1/8" gaps must not close up after normal expansion. What is the normal variation from max. to min.?

Because wood tends to expand and contract as temp and humidity levels change, filling gaps tends to produce less than desirable results as you have experienced. Keeping temp and humidity levels as near constant as possible year round tends to minimize expansion/contraction problems.

House and concrete slab are 15 years old. Wood floor approx. 3 years old. Gaps are not appearing between all boards but rather along lines where it looks like installer may have stopped one evening and then picked up again the next morning. Gaps appear worse in the winter, less humidity, than in spring/summer/fall. I appreciate the suggestions!