@article{oai:kumadai.repo.nii.ac.jp:00023801,
 author = {曽田, 貞滋 and 田邊, 力 and Tanabe, Tsutomu and Sota, Teiji},
 issue = {5},
 journal = {American Naturalist},
 month = {May},
 note = {application/pdf, 論文(Article), The role of species-specific genitalia in reproductive isolation
is unclear. Males of the millipede genus Parafontaria use gonopods
(modified eighth legs) charged with sperm from the genital
openings of the second legs as intromittent organs. Males perform
both preliminary and true intromission during mating. During preliminary
intromission, a male attempts to insert his gonopods into
the female genitalia before charging the gonopods with sperm. If this
intromission is completed, it is followed by the ejaculation of sperm
to the gonopods and true intromission for insemination. In two
sympatric species of Parafontaria that lack effective precopulatory
isolation, copulation was terminated without insemination because
of preliminary intromission failure caused by mismatched genital
and body sizes. Thus, mechanical isolation between these sympatric
species resulted from morphological differentiation mediated by the
obligatory preliminary intromission. These findings demonstrate the
proximate importance of genital and body size differences for reproductive
isolation within this genus of millipede., http://www.journals.uchicago.edu/toc/an/2008/171/5},
 pages = {692--699},
 title = {Complex Copulatory Behavior and the Proximate Effect of Genital and Body Size Differences on Mechanical Reproductive Isolation in the Millipede Genus Parafontaria},
 volume = {171},
 year = {2008}
}