Twins peak

For 25-year-old Tegan Quin, the memory remains sharp as a bee sting. She and her identical twin sister, Sara, were watching ''Twin Falls Idaho," a surreal movie about conjoined twin brothers made by real-life twin brothers Michael and Mark Polish.

''At one point the twins are fighting and pushing against one another, and they're screaming, rolling around, and crying," Tegan recalls over the phone from Vancouver, where she lives. ''And Sara turned to me in the middle of the scene and whispered, 'That's how I feel when I'm with you.' " Tegan was taken aback, but deep down, she knew she felt the same way, too.

In addition to sharing the same face and past, the twins continue, for better and worse, to be entangled in each other's lives. Together they constitute the indie-pop duo Tegan and Sara, who've been recording and touring together for seven years. They headline the Somerville Theatre tonight.

The latest fruit of the sisters' fiery, fraught partnership is ''So Jealous" (Vapor/Sanctuary), a deliciously taut, jagged little pill of an album full of compressed neo-new-wave hooks, buzzing guitars, and burbling synths, the latter courtesy of ex-Weezer bassist/Rentals frontman Matt Sharp. Tegan and Sara's interlocking voices and curiously claustrophobic harmonies deliver sharply focused songs -- they each write separately -- about doubt, devotion, and tempestuous relationships teetering on the edge of collapse. If an album can sound simultaneously despairing and exuberant, ''So Jealous" is it.

''They're quite a pair," Sharp says. ''Individually and together, they have an original voice that stands apart from everything else that's going on right now. The best thing that could happen is that they get a chance to be heard by more people because they deserve the chance to be heard."

Two years ago, Sharp toured with Tegan and Sara as both an opening act and as their keyboard player. A self-described ''huge fan" of their previous disc, 2002's ''If It Was You," he offered to contribute to the Quins' next album. They took Sharp up on his proposal, tempting him with promises of home-cooked meals and lodging on Sara's ''awesome couch."

Tegan estimates that about 80,000 copies of ''So Jealous" have sold since its release last autumn, which easily makes it the duo's best-selling record to date. Now, after years of opening for artists such as Neil Young (who signed the sisters as 18-year-olds to his Vapor records imprint), the Pretenders, Ryan Adams, and Hot Hot Heat, the band -- which also includes drummer Rob Chursinoff and bassist Chris Carlson -- finds itself headlining festivals and ever-larger venues.

''Things are looking up," says Tegan, who with her sister manages nearly every aspect of the duo's career and shares Sara's assessment that they're ''control freaks." ''I think the songs are better and we're creating a better picture of who we are. It's not like we expected to be huge or anything -- we just wanted to get our foot in the door, and with this record, I think we've been able to shove ourselves halfway through."

That's no small feat considering what the sisters say has been a pervasive climate of sexism and homophobia that has dogged them since both came out as gay shortly after releasing their indie-folk-flavored debut, 1999's ''Under Feet Like Ours."

''Everybody wanted to know about our personal lives because we were women," Sara says. ''And I was not going to lie. I would say I'm in a relationship and it's not with a boy. And then it was like, 'Oh, they're gay artists,' and that's how we got pigeonholed. And I struggled with that and wondered, why do we have to talk about our homosexuality when nobody talks about their heterosexuality? But I want to be aligned and in solidarity with the gay community, and want queer youth to be able to look up to us and not be ashamed."

Armed with their new album's clutch of irrepressible melodies and resonant, universal themes -- love, anger, spite, jealousy, heartache -- Tegan and Sara appear poised to smash through whatever labels narrow minds assign them. But the singer-guitarists aren't averse to helping their own cause.

''A music journalist called us because he was doing a 'Women in Rock' issue and asked us, 'What do you think will make the industry change?' " Sara says. ''And I said, 'When people like you stop doing 'Women in Rock' issues and just put us on the cover during a regular week instead of tokenizing us. Being women and being queer and wanting to make quality pop music, you're always in this place where you're not really talking about your art. You're setting the record straight. But I think the longer you stand up, the more people you'll find standing up around you."

Tegan and Sara perform at the Somerville Theatre, 55 Davis Square, Somerville, tonight at 8. Tickets $17. Call box office at 617-625-4088 for more information.