Issue with spray.io and json marshallers

compiler error

could not find implicit value for parameter marshaller: spray.httpx.marshalling.ToResponseMarshaller[scala.concurrent.Future[Animal]]
        (zoo ? GetRandomAnimal).mapTo[Animal]
                                     ^

testcase.scala

import spray.routing.HttpService
import spray.json.{RootJsonWriter, DefaultJsonProtocol}
import akka.actor.{Props, Actor, ActorSystem}
import akka.util.Timeout
import akka.pattern.ask
import scala.concurrent.duration._
import scala.util.Random
import reflect.ClassTag
import spray.httpx.SprayJsonSupport._
import Zoo._

sealed trait Animal
case class Dog(name: String, color: String) extends Animal
case class Cat(name: String, age: Int) extends Animal

class Zoo extends Actor {
  val random = new Random
  def receive: Actor.Receive = {
    case GetRandomAnimal =>
      if (random.nextBoolean()) Dog("puppy", "black")
      else Cat("sylvester", 5)
  }
}
object Zoo {
  case object GetRandomAnimal
}
trait AnimalService extends HttpService {
  object JsonImplicits extends DefaultJsonProtocol {
    implicit val CatJsonWriter = jsonFormat2(Cat)
    implicit val DogJsonWriter = jsonFormat2(Dog)

    implicit val animalFormat = lift {
      new RootJsonWriter[Animal] {
        def write(c: Animal) = c match {
          case cat: Cat => CatJsonWriter.write(cat)
          case dog: Dog => DogJsonWriter.write(dog)
        }
      }
    }
  }
  val system = ActorSystem()
  val zoo = system.actorOf(Props(classOf[Zoo]))
  case object GetRandomAnimal

  implicit val timeout = Timeout(3.seconds)
  import JsonImplicits._
  val routes = path("/randomAnimal") {
    post {
      complete {
        (zoo ? GetRandomAnimal).mapTo[Animal]
      }
    }
  }
}