What are the absolute must-do conventions (as in, Should one introduce the Hero before the Villain? Must there be a Happy Ever After in SFR?)
By the current publishing definition, a novel isn't a romance (strictly speaking) without a happy ending, defined as a pledge of love between hero and heroine. Not all love stories can be classified as romances; one that ends in tragedy isn't (by today's categorization). Without that “happy ending” feature, it would be an SF or fantasy novel with “romantic elements” or a romantic subplot. I could bend the boundaries so far as to concede that the ending might be “happy for now” rather than “happily ever after.” Other than that principle, which simply restates the essential conditions of the genre, I'd say there aren't any other absolutely required conventions. No, I don't think the hero has to be introduced before the villain. It's not uncommon for romantic suspense to begin with a prologue or opening scene that presents the antagonist in the midst of his villainy before we meet the hero or heroine. For a romance, however, I do think it's almost a required convention that we know from the beginning who the hero is. Yet traditional Gothic romances stretch even that expectation. (The innocent heroine's rakish husband may be under suspicion for villainous deeds.)
What do most have in common?
Besides the journey of the hero and heroine toward the declaration and fulfillment of their love, I see the only universally common feature of speculative romance to be some element that's contrary-to-fact in terms of the primary world we live in. Like the “straight” SF or fantasy author, the SFR writer creates a “secondary world” (as Tolkien puts it), whether a completely different world in a magical realm or on another planet, an alternate-history version of our Earth, or an environment much like ours except for the presence of vampires, werewolves, dragons, magic, psi powers, visiting aliens, etc. The speculative or magical element has to be real within the world of the story, not an illusion or a hoax; the latter would place book in a different subgenre. Other than these elements, we could say most have in common a strong alpha-type hero, but doubtless even this, like almost all other common factors and conventions we might propose, has exceptions. The wonder of this subgenre is the wide variety of stories and characters it encompasses.
What authors inspired the participating authors on this blog?
For me: Suzy McKee Charnas, Chelsea Quinn Yarbro, Jacqueline Lichtenberg and Jean Lorrah (Sime~Gen universe), Marion Zimmer Bradley—I have many other favorite authors, but those are the main ones whose work has directly affected the subject matter and themes I've been inspired to write about.
When did SFR become a recognized sub-genre? And who led the way?
As far as my memory serves, SF, fantasy, and paranormal romance began to be marketed under those terms in the mid- to late-1990s. While I could mention many authors and works that contributed to the prehistory of the subgenre (e.g., myths and fairy tales such as “Cupid and Psyche” and “Beauty and the Beast,” plays and movies such as DEATH TAKES A HOLIDAY and THE GHOST AND MRS. MUIR [based on a novel, of course], some of Bradley's Darkover novels, Yarbro's HOTEL TRANSYLVANIA, etc.), I'm sure of “who led the way” only in the area of vampire romance. That provides a useful boundary marker, I think, because paranormal romance first caught on as a subgenre because of the appeal of vampire romances. The first vampire novel I ever saw marketed as a romance (as opposed to vampire novels with romantic elements marketed under horror) was OBSESSION, by Lori Herter (1991). New readers coming to the field today can have no idea what a thrilling innovation it was to see a romance novel with a black-caped hero and a bat on the cover.
Who were the pioneers?
Again, I can speak with certainty only about my specialty, vampire fiction. Aside from Herter's delightful four-book series (undeservedly neglected and sadly out of print), other pioneers in vampire romance include Linda Lael Miller, Maggie Shayne, Nancy Gideon, and Amanda Ashley.