Sex determination systems are highly variable in vertebrates, although neither the causes nor the implications of this diversity are fully understood. Theory suggests that sex determination is expected to relate to sexual size dimorphism, because environmental sex determination promotes sex-specific developmental bias in embryonic growth rates. Furthermore, selection for larger size in one sex or the other has been proposed to drive the evolution of different genetic sex determination systems. Here, we investigate whether sex determination systems relate to adult sexual size dimorphism, using 250 species of reptiles (Squamata, Testudines and Crocodylia) representing 26 families. Using phylogenetically informed analyses, we find that sexual size dimorphism is associated with sex determination: species with TSDIa sex determination (i.e. in which the proportion of female offspring increases with incubation temperature) have more female-biased size dimorphism than species with TSDII (i.e. species in which males are produced at mid temperatures). We also found a trend that species with TSD ancestors had more male-biased size dimorphism in XY sex chromosome systems than in ZW sex chromosome systems. Taken together, our results support the prediction that sexual size dimorphism is linked to sex-dependent developmental variations caused by environmental factors and also by sex chromosomes. Since the extent of size dimorphism is related to various behavioural, ecological and life-history differences between sexes, our results imply profound impacts of sex determination systems for vertebrate diversity.

Original languageEnglish
Pages (from-to)594-603
Number of pages10
JournalJournal of Evolutionary Biology
Issue number4
Early online date17 Feb 2021
Publication statusPublished - 6 Apr 2021

Bibliographical note

Funding Information:
The study was supported by the National Research, Development and Innovation Office of Hungary (grants PD 132819 to BV; K 116310 and ?LVONAL KKP-126949 to TS and K-115402 to VB). On behalf of Project 'TetraClim', we thank for the usage of ELKH Cloud (https://science-cloud.hu/) that significantly helped us achieving the results published in this paper. We thank the two anonymous reviewers whose comments helped improve this manuscript.

Publisher Copyright:
© 2021 The Authors. Journal of Evolutionary Biology published by John Wiley & Sons Ltd on behalf of European Society for Evolutionary Biology.

Copyright 2021 Elsevier B.V., All rights reserved.


  • development
  • environmental sex determination
  • genetic sex determination
  • phylogenetic comparative methods
  • sexual size dimorphism

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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