Sex allocation biology is one of the historically most important
and currently most active fields of evolutionary ecology. The extended
Trivers-Willard hypothesis states that females will produce the
sex that is most likely to benefit from maternal or current environmental
effects. This includes female mating patterns (e.g., in relation
to male quality) and female traits (e.g., condition). Consequently,
maternal effects are likely to be sex-specific, with potential
for joint evolution of sex ratio adjustment and maternal effects.
There are conflicting opinions on the state of sex allocation
in vertebrates, and even if (facultative) sex ratio adjustment
occurs
at all. This could be because multiple, conflicting, selection
pressures act simultaneously in natural populations. Things
become even more complicated when sibling interactions are sex-specific,
because sex ratio adjustment itself will affect fitness for
individual
offspring within the brood. All this suggests that some taxa
may be more likely to show sex ratio adjustment than others.
Some literature on the subject
Uller, T. 2003. Viviparity as a constraint on sex ratio evolution.
Evolution 57: 927-931.
Uller, T., Massot, M., Richard, M., Lecomte, J. & Clobert,
J. 2004. Long-lasting fitness consequences of prenatal sex ratio
in a viviparous lizard. Evolution 58: 2511-2516.
Uller, T. 2006. Sex-specific sibling interactions and offspring
fitness in vertebrates: patterns and implications for maternal
sex ratios. Biological Reviews, 81: 207-217.
Uller, T. & Olsson, M. 2006. No seasonal sex ratio shift
despite sex-specific fitness returns of hatching date in a lizard
with genotypic sex determination. Evolution 60: 2131-2136.
Uller, T., Mott, B., Odierna, G. & Olsson, M. 2006. Consistent
sex ratio bias of individual female dragon lizards. Biology Letters
2: 569-572.
Wapstra, E., Uller, T., Pen, I., Olsson, M., Shine, R. & Komdeur,
J. 2007. Disentangling the complexities of vertebrate sex allocation:
a role for squamate reptiles? Oikos, in press.
Uller, T., Pen, I., Wapstra, E., Beukeboom, L. & Komdeur,
J. 2007. Evolution of sex ratios and sex-determining mechanisms.
Trends in Ecology and Evolution, in press.
