Abstract
Nest parasitism is a common reproductive strategy used by many species of cavity nesting birds. Among these, the wood duck (Aix sponsa) is known to have evolved very specific strategies of when and whom to parasitize that is often based on population and/or environmental queues. Here, we investigated the genetic relationship of two female wood ducks competing over an artificial nesting box in Delaware, including the continued incubation of one female despite the death and body remains of the other female throughout the incubation process. We test whether such an extreme case of nest parasitism can be explained by relatedness, egg lineage composition, or a combination of other factors. To do so, we extracted genomic DNA from blood and tissue of the females, as well as chorioallantoic membranes of all viable and inviable eggs. Subsequently, we assessed relatedness among females and eggs based on hundreds of nuclear loci and the mitochondrial control region. We concluded that (1) the two incubating females were entirely unrelated, (2) the single clutch is in fact represented by a minimum of four unrelated females, and (3) a single female can lay eggs sired by different males. The latter finding is the first direct evidence for successful extra-pair copulation in wood ducks. With decreasing costs and increasing effectiveness, genomic methods have the potential to provide important insights into more complex ecological and evolutionary tactics of such populations.
Highlights
Avian nest or brood parasitism is a common reproductive strategy utilized by many bird species, and in particular by waterfowl (Anatidae; [1,2,3])
Through the molecular assessment of a single wood duck egg clutch in an artificial nest box and the two females found incubating those eggs, we conclude that (1) the two incubating females were entirely unrelated, (2) the single clutch is represented by a minimum of four unrelated females, and (3) a single female can lay eggs sired by different males (Table 1)
The majority of eggs being identified as full siblings, and having the same father supports this female having a primary male with which she was likely pair-bonded with, the additional paternal lineage suggest this female must have engaged in extra-pair copulation (Fig 2)
Summary
Avian nest or brood parasitism is a common reproductive strategy utilized by many bird species, and in particular by waterfowl (Anatidae; [1,2,3]). Several hypotheses have been proposed to explain the evolution of such reproductive strategies [1,2, 4, 5], including (1) competition for desired nest sites leading to increased parasitism [6]; (2) increasing a female’s reproductive success without incurring the costs of parental care [7]; and (3) maintaining the opportunity for reproduction even if a female is unable to find a suitable nest site or if their personal nest. Genetics and nesting behavior of wood ducks
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