Wood floors will expand and contract based on variables such as temperature and humidity. As the wood dries out, it shrinks. As the temperature falls, it retains its moisture and swells.
There are 2 things that you can do. One, look into adding humidifier/dehumidifier system to your HFAC system, especially if it's forced, hot air. Otherwise, depending on where you live, you may need a humidifier or dehumidifier. Once you can 'stabilize' the environmental conditions in the house, you go to step Two.
Two, consider re-laying the wood floor. It would have to be gently uninstalled, then reinstalled. This will allow you to bring the planks closer to each other. And by controlling the environmental conditions in the house, you should have very minimal expansion and contractions. You would re-install it as any normal, solid hardwood floor.
DO NOT attempt to fill the gaps! If you do, when the floor decides to expand, the gap-material will get pushed up and out. And if IT doesn't get pushed up and out, then an adjoining, or latter, plank WILL get pushed up. After that, when the wood eventually shrinks, you'll have a new set of gaps along with planks that may be pushed up.
My best to ya and hope this helps.
PS: If you're able to better control the environmental conditions in the house, leave the planks staked like a bon-fire would be stacked, for a week or so. This will allow the planks to get 'acclimated' to the house's conditions. Don't forget about a vapor barrier and proper subflooring BEFORE re-installing.