Evol Ecol Res 2: 337-352 (2000)     Full PDF if your library subscribes.

Cyanogenesis in Turnera ulmifolia L. (Turneraceae): II. Developmental expression, heritability and cost of cyanogenesis

Phillip J. Schappert and Joel S. Shore

Department of Biology, York University, 4700 Keele Street, North York, Ontario M3J 1P3, Canada

Address all correspondence to Phillip J. Schappert, Section of Integrative Biology, School of Biological Science, University of Texas, Austin, TX 78712-1064, USA.
e-mail: philjs@mail.utexas.edu


We examine the cyanogenesis polymorphism in Turnera ulmifolia on Jamaica with respect to our hypothesis that seedlings in some populations have significantly higher levels of cyanogenesis than mature plants because of the developmental loss of cyanogenesis. Furthermore, we provide estimates of among-family variance, as estimates of broad sense heritability, for a number of fitness-related traits, and also examine the potential cost of cyanogenesis in this species. Our data reveal that there is a marked developmental loss of cyanogenesis in some populations of T. ulmifolia. Seedlings have significantly greater levels of cyanogenesis than mature plants in ‘acyanogenic’ populations, but this developmental loss is absent in predominantly cyanogenic populations. This is the first study to document extensive developmental loss of chemical defence in a cyanogenic species. We suggest that, in these populations, there might be selection favouring cyanogenesis in seedlings. There is substantial among-family variance in a number of traits in five T. ulmifolia populations examined, including plant height, time to first flowering, total flower production and cyanogenesis. Phenotypic and, more importantly, negative genetic correlations between total flower production and cyanogenesis provide evidence for a cost of cyanogenesis in three of five populations.

Keywords: chemical defence, genetic variation, life-history trade-offs, natural selection, plant growth, reproduction.

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