In their latest public display of friendship, Serena Williams and Caroline Wozniacki posted a photo of getting their nails done before the Australian Open. The camaraderie, in a sport better known for its rivalries, has prompted discussion among players on what it's like in the locker room and behind-the-scenes with top women's tennis stars.

Is everyone friends? The answer: it depends who you ask.

The No. 1-ranked Williams, who plays her fourth-round match Sunday and is known for having some of the highest-profile rivalries on the tour, says the mood has changed since she joined the professional ranks way back in the 90s.

"It's like a big family now," said Williams, who at 33 is pushing for her 19th Grand Slam title and shows no sign of easing her dominance. She came of age during a different era, recalling that rivals Steffi Graf and Monica Seles "never spoke."

"When you're young, you really idolize those people. I wanted to do what they did. I was really quiet. I did my own thing," Serena told a news conference at the Australian Open. "I just tried to copy them."

Now, things are different, partly because players spend more time together due to the packed schedule of tournaments year-round.

"I definitely think people talk a little bit more now than back in the 90s," said Williams, who faces No. 24 Garbine Muguruza in the quarterfinals. "We travel 10, 11 months of the year together. So you just know everyone."

Social media has played a big role in opening a window into the players' private lives, with many posting comments to each other or photographs of their off-court friendships.

The former No. 1-player Wozniacki, who exited in the second round of this year's Australian Open, shared the picture of herself and Williams getting pedicures the weekend before the tournament started.

Asked about competing against a friend at the top level, Wozniacki later said: "Whenever you're on court, you just want to win. It doesn't matter who is on the other side."

The two friends faced off in a Grand Slam final at last year's U.S. Open, which Williams won. Two days later, Wozniacki showed up to support Williams at her first runway show during New York Fashion Week. Williams then live tweeted from the New York City Marathon as she cheered on Wozniacki, who ran an impressive 3 hours and 26 minutes.

"Is it normal to cry when someone finished (a) marathon? So proud of you Caro," Williams tweeted after the race. The two have been spotted at the beach, hockey games, basketball games and concerts.

Williams has been quoted as saying that Wozniacki is her closest friend on the circuit other than her sister, Venus.

Naturally, though, tense rivalries remain, and Williams doesn't like to talk about them. There was great speculation about Williams' apparently icy relationship with Sloane Stephens, after the young American upset the No. 1-ranked player in the 2013 Australian Open quarterfinal.

No. 2 Maria Sharapova, who advanced to the quarterfinals on Saturday, has publicly said she has no friends on the women's tour. She and Williams have long had a not-so-friendly rivalry that made headlines in 2013 when the pair traded personal barbs relating to their romantic relationships.

Williams could face Sharapova in the final. To have any chance of that happening, Sharapova has to clear a quarterfinal hurdle against rising star Eugenie Bouchard, a rematch of last year's French Open semifinal that Sharapova won en route to the title.

The No. 7-ranked Bouchard also prefers to keep competitors at a distance.

"I don't want to become really good friends with any of the girls on the tour," said the Wimbledon finalist. "I come here, do my job, and leave. I think that's the best way for me to stay focused and not really have distractions."

Asked what it's like in the locker room, Bouchard laughed.

"I'm sure you imagine 'Mean Girls' or something. It's not like that," said the 20-year-old Canadian, referring to Hollywood's take on a mean-spirited high school clique. "It's pretty chill, pretty relaxed. We're all friendly and talking to each other."

For what it's worth, "Mean Girls" happens to be Bouchard's favorite movie.

Two-time champion Victoria Azarenka says her perspective has changed over the years, and she wants to get to know more players.

"Not that I wasn't friendly, but it's nice to get to know girls," said Azarenka, unseeded here because her ranking fell late last year during an injury layoff. She faces No. 11 Dominika Cibulkova in the quarterfinals.

"On the court there are no friends, unless there are umpires you try to be nicer to," the 25-year-old Azarenka said. But off the court, she would like to "make an effort" and build friendships — possibly with Sharapova or other players who have residences near her in the Los Angeles area.

"I haven't hit with any girls yet," Azarenka said. "I know Maria lives there. But we haven't hit yet. Hopefully, maybe one day it will happen."