Dwarf males.
Dwarf males are often found in species with sedentary females, where they typically cohabit in varying degrees of intimacy. This is short of true parasitism because, in return for room and board, males provide the benefit of sperm. Sexual selection rarely seems to be an option to explain male dwarfing, whereas natural selection often can.
Dept of Zoology, University of Aarhus, 8000 Aarhus C, Denmark; Dept of Zoology, Oxford University, Oxford, UK OX1 3PS.
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Vollrath