Evol Ecol Res 5: 1133-1149 (2003)     Full PDF if your library subscribes.

Optimal growth model for the latitudinal cline of shell morphology in cowries (genus Cypraea)

Takahiro Irie and Yoh Iwasa*

Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan

Author to whom all correspondence should be addressed.
e-mail: yiwasscb@mbox.nc.kyushu-u.ac.jp


The marine Indo-Pacific cowry, Cypraea caputserpentis, shows geographic variation of life history and shell morphology. Adult body size increases with latitude, but shell thickness decreases with latitude. To explain the clinal variations, we study a mathematical model of the optimal growth schedule. The life history of cowries consists of three stages: shell volume increases in the juvenile stage, which is followed by the callus-building stage in which shell thickness increases, and then reproduction starts without further growth in the adult stage. We calculate the lengths of juvenile and callus-building stages that maximize lifetime reproduction. By considering latitudinal change in the mortality and growth-promoting factors, the observed clinal patterns of juvenile traits can be explained by a negative latitudinal gradient of shell-crushing predators. This suggests the importance of a latitudinal gradient of predation pressure for body-size clines in marine ectotherms. On the other hand, latitudinal clines of shell thickness can be explained by a latitudinal gradient of either shell-crushing predation pressure or one of the environmental factors promoting shell thickening, such as seawater temperature.

Keywords: Cypraea caputserpentis, latitudinal gradient, optimal growth schedule, phenotypic plasticity, shell thickness.

IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.


        © 2003 Yoh Iwasa. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

       Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.

       All copies of abstracts and articles must preserve their copyright notice without modification.