Reaney, LeeannMaurer, GoloBackwell, PatriciaLinde, Celeste2015-12-100340-5443http://hdl.handle.net/1885/64709The fiddler crab Uca mjoebergi mates both underground in male-defended burrows and on the surface near female-defended burrows. The reproductive tract of Uca species facilitates last-male precedence, suggesting that males that do not guard-mated females are likely to gain very little paternity if the female re-mates with another male. Here, we test the reproductive success of burrow and surface matings using paternity analysis. We found that 100 % of the females that mated in burrows extruded a clutch of eggs. Furthermore, we show conclusively, for the first time in a fiddler crab species, that last-male sperm precedence results in the majority of the female's eggs being fertilised by the burrow-mated male. In contrast, surface matings resulted in significantly fewer females extruding eggs (5. 6 %). Paternity analysis also revealed that more than half of the clutches from burrow-mated females showed low levels of extra-pair paternity from previous matings. Although multiple matings appear common in U. mjoebergi, burrow-mated males that guard females are guaranteed a successful mating with extremely high rates of assured paternity. Surface matings therefore appear to be an opportunistic tactic that may increase male reproductive success in a highly competitive environment.Keywords: burrow; clutch size; crab; facilitation; male behavior; marine ecosystem; paternity; reproductive success; sperm; Ocypodidae; Uca Burrow mating; Fiddler crab; Flexible opportunistic tactic; Mate guarding; Paternity; Surface matingPaternity analysis of two male mating tactics in the fiddler crab, Uca mjoebergi201210.1007/s00265-012-1349-92016-02-24