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Effective heritability of targets of sex‐ratio selection under environmental sex determination
Author(s) -
McGAUGH S. E.,
JANZEN F. J.
Publication year - 2011
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/j.1420-9101.2010.02211.x
Subject(s) - heritability , biology , sex ratio , nest (protein structural motif) , selection (genetic algorithm) , population , natural selection , offspring , ecology , avian clutch size , zoology , statistics , evolutionary biology , genetics , demography , reproduction , mathematics , pregnancy , biochemistry , artificial intelligence , sociology , computer science
Abstract Selection is expected to maintain primary sex ratios at an evolutionary equilibrium. In organisms with temperature‐dependent sex determination (TSD), targets of sex‐ratio selection include the thermal sensitivity of the sex‐determining pathway (hereafter, sex determination threshold) and nest‐site choice. However, offspring sex may be canalized for nests located in thermally extreme environments; thus, genetic variance for the sex determination threshold is not expressed and is invisible to direct selection. The concept of ‘effective heritability’ accounts for this dependence and provides a more realistic prediction of the expected evolutionary response to selection in the wild. Past estimates of effective heritability of the sex determination threshold, which were derived from laboratory data, suggested that the potential for the sex determination threshold to evolve in the wild was extremely low. We re‐evaluated original estimates of this parameter by analysing field‐collected measures of nest temperatures, vegetation cover and clutch sex ratios from nests in a population of painted turtles ( Chrysemys picta ). We coupled these data with measurements of broad‐sense heritability of the sex determination threshold in C. picta , using an experiment that splits clutches of eggs between a constant temperature (i.e. typical laboratory incubation) and a daily fluctuating temperature (i.e. similar to natural nests) with the same mean. We found that (i) the effective heritability of the sex determination threshold appears to have been historically underestimated and the effective heritability of nest‐site choice has been overestimated and (ii) significant family‐by‐incubation treatment interaction exists for sex for C. picta between constant‐ and fluctuating‐temperature regimes. Our results suggest that the thermal sensitivity of the sex‐determining pathway may play a larger, more complex role in the microevolution of TSD than traditionally thought.