Prof. Dr. U. Kutschera wishes to alert Annelida listers to his forthcoming
leech paper. Reprints will be available from his address (below).
The Evolution of Parental Care in Freshwater Leeches*
(Theory Biosci. 2001, in press)
U. Kutschera (1) and P. Wirtz (2)
(1) Fachbereich Biologie, Universität Kassel, Germany
(2) Departmento de Oceanografia e Pesces, Universidade dos Açores,
Portugal
Address for correspondence: U. Kutschera, FB 19 Biologie, Universität
Kassel, Heinrich-Plett-Str. 40, D-34109 Kassel, Germany, Fax:
(0561)804-4009, e-mail: kut at hrz.uni-kassel.de
Key words: hirudinea, life history, natural selection, parental investment
*Dedicated to Professor Dr. G. Osche on the occasion of his 75th
birthday.
Summary: The life-history strategies of a selection of the most common
European freshwater leeches (Euhirudinea) are described. On the basis
of this information and results from the literature, the probable
phylogenetic development of parental care in the Euhirudinea is
reconstructed. The jawless worm leeches (Erpobdellidae) secrete a
protective cocoon, cement it to the substrate and sometimes ventilate it
before they leave the egg capsules. This behaviour represents the most
ancient state in leech evolution. Members of the jawed Hirudinidae
deposit desiccation-resistant cocoons on land. All known Glossiphoniidae
(leeches equipped with a proboscis) have evolved the habit of brooding
the eggs and young. These unique parental care patterns within one
family of extant freshwater leeches can be arranged schematically in a
series of increasing complexity which may reflect the evolution of
brooding behaviour. Glossiphoniid leeches of the genus Helobdella,
which have a world-wide distribution, display the most highly developed
parental care system: they not only protect but also feed the young they
carry. This results in the young being much larger when they leave the
parent and, presumably, in higher subsequent survival. Isolated cocoons
of all aquatic leeches are rapidly destroyed by predators, primarily water
snails. In erpobdellids (but not glossiphoniids, which protect the cocoons)
a large portion of the cocoons are lost due to predatory attacks. We
conclude that the major selective pressure driving the evolution of
parental care in leeches may have been predation on eggs and juvenile
stages.
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