Male elephant seals compete for access to females in limited beach territories. They are on average 4 times bigger than females. Male elephant seals weigh ~3 tons. From “Biological Science” 3 rd ed. by Scott Freeman -fig 25.14
Competition between males is fierce, only a few males father most of the offspring. 90% of males never successfully reproduce 60% of females do not successfully reproduce From “Biological Science” 3 rd ed. by Scott Freeman -fig 25.14
If differences in reproductive behavior and morphology are based on sex roles, what happens when the roles are reversed? Males care for developing eggs
The Measurement of Sexual Selection Using Bateman’s Principles: An Experimental Test in the Sex-Role-Reversed Pipefish Syngnathus typhle (2005) Integrative and Comparative Biology, 45:874–884 Adam G. Jones, Gunilla Rosenqvist, Anders Berglund, and John C. Avise
Jones et al. Fig. 1 frequency number of mates When there are more females than males, many females cannot mate.
frequency number of mates Jones et al. Fig. 1 When the sex ratio is even, most males and females mate.
frequency number of mates Jones et al. Fig. 1 When there are more males than females, most males can mate.
Jones et al. Fig. 1 The sex ratio affects who will successfully reproduce. Pipefish females are more affected by competition.
number of individuals body length (mm) Jones et al. Fig. 4 Excess females: only medium size females can mate
number of individuals body length (mm) Jones et al. Fig. 4 Excess males: many different size males can mate
Jones et al. Fig. 4 medium sized female pipefish are most successful at reproducing while size is less critical for male pipefish
...So when males invest more resources for reproduction, they become the limiting factor and are choosier about mates. Pipefish males care for developing eggs
Different reproductive strategies lead to differences in sexual dimorphism.
In light of differences between male and female resources for reproduction, how does this affect equality between males and females?
Do we want equal treatment of men and women? How should equality be attained, or how should the inequality be regulated?
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