Birth sex ratios relate to mare condition at conception in Kaimanawa horses |
| |
Authors: | Cameron Elissa Z; Linklater Wayne L; Stafford Kevin J; Veltman Clare J |
| |
Institution: | a
Ecology Group, Institute of Natural Resources
b
Institute of Veterinary, Animal and Biomedical Sciences, Massey University,
Private Bag 11222, Palmerston North, New Zealand |
| |
Abstract: | Several hypotheses have been proposed to explain variation inbirth sex
ratios, based on the premise that variation is expectedwhen the profitability
of raising sons and daughters variesbetween individual parents. We tested the
Trivers-Willard hypothesisthat mothers in better condition produce relatively
more sonsand that mothers in poorer condition produce relatively more
daughterswhen male reproductive success is more variable. We examinedbirth
sex ratios in relation to mare body condition at conceptionin horses in which
male reproductive success is differentiallyhelped by slight advantages in
condition. Horses meet the assumptionsof the Trivers-Willard hypothesis
better than many species onwhich it has been tested and in which sex ratio
biases are notconfounded by sexual size dimorphism such that one sex is more
likelyto die in utero in females in poor condition. Mares that hada female
foal were in poorer condition at conception than thosethat had a male foal,
and mares that had foals of differentsexes in different years were in
significantly poorer conditionwhen they conceived their female foal. There
was no relationshipbetween offspring sex and mid-gestation condition, and
therewas no difference in foaling rates in relation to body conditionat
conception. Consequently, sex ratio deviations are not explainedby fetal loss
in utero. Furthermore, differential fetal lossof the less viable sex cannot
explain the greater proportionof males produced by mares in better condition.
Therefore, ourresults suggest that sex ratio modification occurs at
conceptionin wild horses. |
| |
Keywords: | birth sex ratios Equus caballus fetal loss maternal condition Trivers-Willard hypothesis wild horses |
本文献已被 Oxford 等数据库收录! |
|