Plasma mammalian leptin analogue predicts reproductive phenology, but not reproductive output in a capital‐income breeding seaduck
Résumé
To invest in energetically demanding life history stages, individuals require a substantial
amount of resources. Physiological traits, particularly those related to energetics,
can be useful for examining variation in life history decisions and trade‐offs because
they result from individual responses to environmental variation. Leptin is a protein
hormone found in mammals that is proportional to the amount of endogenous fat
stores within an individual. Recently, researchers have confirmed that a mammalian
leptin analogue (MLA), based on the mammalian sequence of leptin, is present with
associated receptors and proteins in avian species, with an inhibitory effect on foraging
and body mass gain at high circulating levels. While MLA has been both quantified
and manipulated in avian species, little is currently known regarding whether
plasma MLA in wild‐living species and individuals is associated with key reproductive
decisions. We quantified plasma MLA in wild, Arctic‐nesting female common eiders
(Somateria mollissima) at arrival on the breeding grounds and followed them to determine
subsequent breeding propensity, and reproductive phenology, investment, and
success. Common eiders are capital‐income breeding birds that require the accumulation
of substantial fat stores to initiate laying and successfully complete incubation.
We found that females with lower plasma MLA initiated breeding earlier and in a
shorter period of time. However, we found no links between plasma MLA levels and
breeding propensity, clutch size, or reproductive success. Although little is still known
about plasma MLA, based on these results and its role in influencing foraging behaviors
and condition gain, plasma MLA appears to be closely linked to reproductive
timing and is therefore likely to underlie trade‐offs surrounding life history
decisions.