Simultaneous inbreeding and outbreeding depression in reintroduced Arabianoryx

In most species the offspring of closely related parents have reduced fitne ss compared with the offspring of unrelated parents, a phenomenon known as inbreeding depression. However if parents are very distantly related, their offspring may also have reduced fitness. This pattern, outbreeding depress ion, has been most commonly observed in plants and only rarely in animals. Here we examine the consequences of inbreeding and outbreeding on juvenile survival of reintroduced Arabian oryx (Oryx leucoryx) in Oman, a population with a small number of founders drawn from a number of sources. Using micr osatellite-based measures of inbreeding and outbreeding, there was no appar ent relationship between inbreeding or outbreeding and survival when inbree ding and outbreeding were tested in separate statistical models. However wh en inbreeding and outbreeding were tested in the same statistical model, we found simultaneous inbreeding depression and outbreeding depression acting on juvenile survival. Outbreeding depression may be more common in vertebr ates than previously supposed, and conservation strategies that seek to max imize the genetic diversity of managed populations may risk mixing lineages that are sufficiently differentiated to cause outbreeding depression among descendants.