TY - JOUR
T1 - Change in offspring sex ratio over a very short season in Lincoln’s Sparrows: the potential role of bill development
AU - Graham, E.B.
AU - Caro, S.P.
AU - Sockman, K.W.
N1 - Reporting year: 2011
Metis note: 4951; WAG; AnE
PY - 2011
Y1 - 2011
N2 - The sex ratios of offspring are targets of natural selection that can affect parental energy
expenditure and fitness, adult sex ratios, and population dynamics. Parents may manipulate offspring sex ratios
based on sex differences in potential reproductive success. In Lincoln’s Sparrows (Melospiza lincolnii), male bill shape
is associated with the quality of songs, and song quality predicts female preferences in a reproductive context.Males
and females that hatch later relative to brood mates or later in the breeding season tend to develop bill shapes that
are, for males, associated with low-quality song. Because females do not sing and do not experience this selection
pressure, we predicted that the sex of offspring produced late relative to their brood mates or relative to the season
should be biased toward females. Using a molecular technique to sex nestlings, we found no effects of hatching
order or any interaction between date of clutch initiation and hatching order on offspring sex. However, we found
a seasonal decline in the proportion of male offspring, from approximately 0.8 at the beginning to 0.4 at the end
of a clutch initiation season only 19 d in duration. To our knowledge, this is the shortest period over which the
offspring sex ratio has been shown to change in a bird population. Moreover, these findings are consistent with the
hypothesis that sex differences in the potential attractiveness of offspring ultimately influence offspring sex ratios.
AB - The sex ratios of offspring are targets of natural selection that can affect parental energy
expenditure and fitness, adult sex ratios, and population dynamics. Parents may manipulate offspring sex ratios
based on sex differences in potential reproductive success. In Lincoln’s Sparrows (Melospiza lincolnii), male bill shape
is associated with the quality of songs, and song quality predicts female preferences in a reproductive context.Males
and females that hatch later relative to brood mates or later in the breeding season tend to develop bill shapes that
are, for males, associated with low-quality song. Because females do not sing and do not experience this selection
pressure, we predicted that the sex of offspring produced late relative to their brood mates or relative to the season
should be biased toward females. Using a molecular technique to sex nestlings, we found no effects of hatching
order or any interaction between date of clutch initiation and hatching order on offspring sex. However, we found
a seasonal decline in the proportion of male offspring, from approximately 0.8 at the beginning to 0.4 at the end
of a clutch initiation season only 19 d in duration. To our knowledge, this is the shortest period over which the
offspring sex ratio has been shown to change in a bird population. Moreover, these findings are consistent with the
hypothesis that sex differences in the potential attractiveness of offspring ultimately influence offspring sex ratios.
U2 - 10.1111/j.1557-9263.2010.00306.x
DO - 10.1111/j.1557-9263.2010.00306.x
M3 - Article
SN - 0273-8570
VL - 82
SP - 44
EP - 51
JO - Journal of Field Ornithology
JF - Journal of Field Ornithology
IS - 1
ER -