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Traditionally it has been suggested that sexual selection can cause sexual size dimorphism (SSD). However, a recent review in gastropods shows that SSD itself can also cause sexual selection (Ng et al. 2019). This may be the case if mate choice exist, with males preferring to mate with females similar in body size but somewhat larger than themselves (female-biased preference). This verbal explanation is formally investigated here by computer simulations using a Gaussian mating preference function. Parameters of that function are also estimated from empirical data. Our results suggest that sexual selection (estimated as selection differential) is strong when mate choice is high and exerted by only one of the sexes, being influenced by SSD and the magnitude of the female-biased preference. All these factors cause a negative relationship between SSD and the (sexual) selection differential, similar to the one observed in the previous review on gastropods. Empirical estimates of the male mate choice from wild-captured mating pairs of different gastropod species confirm that male mate-choice is biased towards females slightly larger than themselves. Our results also illustrate that if mate choice is truly involved in determining SSD, presentday sexual selection cannot be used to estimate the past magnitude of mate choice, as SSD influences present day patterns of sexual selection.

DMSO is not equivalent to liquid nitrogen for the preservation of olive ridley scales to be used for isotopic analysis. If DMSO has to be used for logistical reasons a replicate sample should also be collected to be able to estimate a correction factor. Copyright © 2016 John Wiley & Sons, Ltd.

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