Summary: Biological Journal of the Linnean Society (1997), 60: 365379.
The evolution of animal genitalia: distinguishing
between hypotheses by single species studies
GO¨ RAN ARNQVIST
Dept. of Animal Ecology, University of Umea°, S-901 87 Umea°, Sweden
Received 26 March 1996; accepted for publication 1 July 1996
Rapid evolution of genitalia is one of the most general patterns of morphological diversification in
animals. Despite its generality, the causes of this evolutionary trend remain obscure. Several alternative
hypotheses have been suggested to account for the evolution of genitalia (notably the lock-and-key,
pleiotropism, and sexual selection hypotheses). Here, I argue that thorough intraspecific studies are the
key to gaining insight into the patterns and processes of genitalic evolution. Critical assumptions and
predictions that may be used to distinguish between the different hypotheses are identified and discussed.
However, current knowledge of selection on genitalia, or even of the degree of phenotypic and genotypic
variability of genital morphology, is highly limited, allowing only a very tentative assessment of the
various hypotheses. In-depth single species studies of current patterns and processes of selection on
genitalia are badly needed, and a single species research program is briefly outlined.
© 1997 The Linnean Society of London
ADDITIONAL KEY WORDS:--sexual selection cryptic female choice evolutionary radiation -
phenotypic selection intraspecific studies genetic variation reproductive isolation reproduction.