Abstract
A.J. Bateman (1948) hypothesized that a metric of sexual selection is in sex differences of intrasexual variance in number of mates (V NM). AJB predicted that (a) males have greater variance in reproductive success (V RS) than females; (b) males have greater V NM than females; and (c) a positive relationship between V NM and V RS is stronger among males. AJB used phenotypically observable mutations in offspring to identify parents and to count subjects' NM and RS. AJB's conclusions matched his predictions, later called “Bateman's Principles.” Empirical challenges to his conclusions guided analyses herein. (a) AJB's analysis pseudo‐replicated sample sizes, violating a sexual selection assumption: That is, individuals must be in the same population to choose and compete. (b) AJB's methods overestimated subjects with no mates while underestimating subjects with one or more. (c) A replication (Gowaty et al., 2012) showed that offspring inheriting nametags from both parents often died before expressing adult phenotypes, proving some of AJB's methods produced biased data. Science historian Thierry Hoquet located AJB's archived, handwritten laboratory notes, photocopied, and transcribed them. We tested each of the 65 unique populations for expected combinations in offspring of parental mutations: 41.5% failed Punnett's tests: Offspring carrying nametags simultaneously from both parents were missing showing estimates of parents' NM and V NM were undercounted. 58.5% of populations met Punnett's expectations providing an unparalleled opportunity to re‐evaluate AJB's predictions. 34 unbiased populations had no sex differences in V RS; 37 had no sex differences in V NM. No sex differences in slopes of RS and NM occurred in any unbiased population. Regressions showed weak, positive, significant associations between V NM and V RS for females and males, contrary to AJB's prediction that the relationship would be positive in males but not in females. AJB's laboratory data are inconsistent with “Bateman's Principles.”
Highlights
To experimentally test this idea, he organized populations of Drosophila melanogaster (Figure 1) to evaluate what became known as Bateman's Principles, which are as follows: (a) Males have greater variance in reproductive success (VRS) than females; (b) variances in number of mates (VNM) for males are greater than for females; and (c) the positive relationship between variance in number of mates (VNM) and VRS is stronger for males than females
Before describing our analysis methods, we review Bateman's original methods in the section What Did Bateman Set Out to Study and What Did He Do? in “Flies in the Ointment: Modern Challenges to Bateman (1948),” we describe the literature of alternative explanations for his results, methodological errors in his published methods, and modern concerns over the implications of his conclusions, and we emphasize that the modern challenges informed our analysis methods of his laboratory notes
Step 1: How we proved which of Angus J. Bateman (AJB)'s populations were robust to evaluation of subjects' NM, VNM, RS, and VRS
Summary
AJB's experiment to test the sex difference in the intensity of selection depended on complex and difficult culturing of 10 mutant fly lines to produce 10 types of heterozygote dominant subjects, each of which carried a unique identifying phenotypic marker, a “nametag,” which, when expressed in offspring, would identify the parents in each population. 355 for a table describing the marker genes), which was a prescient sign of the possibility that double-mutant offspring inheriting two dramatic (different) phenotypes, one from each parent, might not always be any more viable than the homozygous lethal individuals in the originating lines expressing the identifying nametag mutations that AJB used. Despite criticisms of Bateman's study, it was ambitious and it remains perhaps the largest ever on sexual selection His handwritten laboratory notes consist of 65 explicit populations with tables similar to those in Figure 2 showing the counts of inherited offspring phenotypes that identified a parent's NM and their RS. We further characterize the steps we took in our reanalysis of AJB's data
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