What does the male function hypothesis claim?


Martin Burd Department of Biological Sciences, P.O. Box 18, Monash University 3800, Melbourne, Victoria, Australia. Tel.: +61 3 9905 5667; fax: +61 3 9905 5613; e-mail: martin.burd@sci.monash.edu.au


Paternal, rather than maternal, fitness consequences of reproductive traits are the lynchpin in many hypotheses about reproductive evolution in hermaphroditic angiosperms. These hypotheses often differ in their predictions, so that supporting or contradictory evidence for one hypothesis may not reflect similarly on another, even though both may be referred to as ‘the male function hypothesis’. We provide graphical representations of four male function hypotheses from the recent literature in order to highlight their differences. We offer and explain two recommendations to reduce ambiguity in terminology: (1) male function hypotheses should address the evolution of excess flowers per se, rather than total flower number, which is usually highly plastic in modular organisms with open growth form; and (2) attention must be given to whole plant fitness, rather than fitness per flower or per inflorescence. In empirical studies, we recommend the use of path analysis to dissect the multiple pathways (through both male and female function) by which selection may act on excess flower number.