Conclusion: The cost of producing and maintaining a resistance-conferring compound is high.

23.18 Producing and Maintaining Resistance Is Costly

Possession of a gene that confers herbicide resistance greatly reduced seed production in Arabidopsis thaliana.

widowbirds, but related studies have been done on males of other species.

In some mammalian species, including deer, lions, and baboons, one male controls reproductive access to many females. These polygynous species tend to be sexually dimorphic— the males appear quite different from the females. Males of these species are significantly larger than females and often bear large weapons (such as horns, antlers, and large canine teeth); size and weaponry are needed to defend a male's multiple mates against other males of the species.

The costs of sexual dimorphism for males of polygynous species were assessed using the comparative method (Figure 23.19). Such males have higher parasite loads and higher mortality rates than females of their own species because maintaining a large size and bearing large weapons makes them more susceptible to parasites. In addition, when compared to parasite loads in males of closely related monogamous species (in which males and females are essentially monomorphic, appearing quite similar), the dimorphic males carried higher parasite loads in almost every case.

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Essentials of Human Physiology

Essentials of Human Physiology

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