CUCKOLDRY THROUGH STORED SPERM IN THE SEQUENTIALLY POLYANDROUS SPOTTED SANDPIPER

STUDIES of mating systems are often hindered by an inability to determine parentage unequivocally. DNA fingerprinting advanced the field by allowing determination of parentage1-3, especially when alternate mating tactics such as extra-pair fertilizations and parasitic egg-laying are used4-6. A very different, yet essentially unexplored, alternate mating tactic involves fertilization by the sperm of previous mates that is stored for long periods of time. Some birds have the potential to be fertilized by sperm stored in the oviduct for over a month7, but studies of long-term sperm storage among wild birds are limited. In the polyandrous spotted sandpiper (Actitis macularia), territorial females pair with, defend and lay clutches for several males in rapid succession. Here we report that males pairing early in the season cuckold their females' later mates by means of stored sperm. Thus, early-pairing males not only have greater confidence of paternity, but also increase their reproductive success by fertilizing a proportion of eggs laid for, and incubated by, their females' subsequent mates, in addition to those they incubate themselves.