In fact, I - cisgender, straight, female - have been known to blurt out a "great idea" without realizing I was lifting it from someone else's mouth. Likewise, it's possible your colleagues are not deliberately poaching your proposals, but are, as you say, so focused on impressing the new boss that they're not actively listening. Not ill-intentioned, just inattentive.
Of course, that doesn't excuse your boss's - or anyone' - inability to hear ideas pitched at feminine frequencies.
A simple "Er, I just said that" might be worth a try. But if you struggle with being that direct - or suspect your colleagues can't handle your being that direct - you can try some subtler theatrics to keep others from stealing your act:
- Claim the spotlight: Announce, "I have an idea about that . . .," and then wait a beat until the majority of eyes are on you before you deliver your line.
- Borrow the "Yes, and . . ." prompt from improv theatre: "Yes, I was thinking that, too, and furthermore . . . ." This works especially well if you've refrained from sharing your entire idea at once. With email, you can forward your original message with an updated subject line and lead: "To build on this idea we've been discussing . . . ." The intro makes your message collaborative; the time-stamped email chain makes clear whose idea it was first.
- Assemble an ensemble. In the Obama administration, female White House aides who were tired of being verbally trampled in meetings made a point of amplifying each other - immediately repeating each other's ideas with attribution. They got their credit - and, most important, the president's ear. Maybe you can reach a similar signal-boosting arrangement with like-minded colleagues.
- This reader question was answered by the Washington Post's Karla Miller.