Abstract
The relative investment of females and males into parental care might depend on the population’s adult sex-ratio. For example, all else being equal, males should be the more caring sex if the sex-ratio is male biased. Whether such outcomes are evolutionary fixed (i.e. related to the species’ typical sex-ratio) or whether they arise through flexible responses of individuals to the current population sex-ratio remains unclear. Nevertheless, a flexible response might be limited by the evolutionary history of the species, because one sex may have lost the ability to care or because a single parent cannot successfully raise the brood. Here, we demonstrate that after the disappearance of one parent, individuals from 8 out of 15 biparentally incubating shorebird species were able to incubate uniparentally for 1–19 days (median = 3, N = 69). Moreover, their daily incubation rhythm often resembled that of obligatory uniparental shorebird species. Although it has been suggested that in some biparental shorebirds females desert their brood after hatching, we found both sexes incubating uniparentally. Strikingly, in 27% of uniparentally incubated clutches - from 5 species - we documented successful hatching. Our data thus reveal the potential for a flexible switch from biparental to uniparental care.
Highlights
Parental care is a tremendously diverse social trait
We found at least one case of uniparental incubation in 8 out of 15 biparental shorebird species (Table 1)
The proportion of nests with uniparental incubation ranged from 4% to 48% (Table 1; median weighted by the total number of nests for a given species = 19%)
Summary
Parental care is a tremendously diverse social trait. The extent of parental cooperation varies along a continuum, from parents sharing all care to uniparental care in which either the female or the male provides all care[1,2]. In some species parents can switch flexibly between breeding attempts from biparental to uniparental care or vice versa[14]. In others such flexibility seems less likely, for example because one sex (often the male) lacks a brood patch and cannot incubate effectively[21]. Flexibility may be limited in species where both sexes possess a brood patch and share incubation roughly because a single parent may not be able to attend the nest enough for embryos to develop until hatching, either because embryos cannot withstand fluctuating temperatures[19,22], or because clutches that are left alone have a high probability of being depredated[23]. Population** Barrow, Alaska Barrow, Alaska Barrow, Alaska Barrow, Alaska Barrow, Alaska Selfoss, Iceland The Netherlands The Netherlands Selfoss, Iceland Barrow, Alaska Selfoss, Iceland Greenland Czech Republic Barrow, Alaska Selfoss, Iceland Selfoss, Iceland Selfoss, Iceland Selfoss, Iceland Barrow, Alaska
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