Abstract
Zygomorphic flower species tend to show lower flower size variation than actinomorphic flower species. Have these differences also brought an association in ovule and seed production that has arisen due to natural selection in these species? Flowers were collected from 29 actinomorphic and 20 zygomorphic flower species, and fruits were collected from 21 actinomorphic and 14 zygomorphic flower species in Miyagi and Aomori prefectures, in Japan. The coefficient of variations (CVs) of flower sizes, mean ovule sizes of flowers, ovule numbers of flowers and mean seed sizes of fruits were calculated. The CV of flower sizes was marginally different between the floral symmetry types; tending to be lower in the zygomorphic flower species than in the actinomorphic flower species. The CVs of mean ovule sizes and ovule numbers of flowers increased with increase in the CV of flower sizes in the actinomorphic flower species but not in the zygomorphic flower species. Mean ovule number of flowers tends to increase with increase in mean flower size in the actinomorphic flower species but not in the zygomorphic flower species. The degrees in variations in ovule size and number of flowers were influenced by the interaction of floral symmetry type and flower size variation, suggesting that floral symmetry also has brought an evolutionary association in ovule production by flowers.
Highlights
Animal-pollinated flowers show several patterns of floral symmetry and two types of floral symmetry, actinomorphy with several symmetry planes, and zygomorphy with one symmetry plane, are typical (Neal et al 1998; Endress 2001)
The coefficient of variations (CVs) of flower sizes was marginally different between the floral symmetry types (Table 2; Fig. 1); it tended to be lower in the zygomorphic flower species than in the actinomorphic flower species
There were no significant differences between the floral symmetry types in the CVs of mean ovule sizes of flowers, ovule numbers of flowers and mean seed sizes of fruits (Table 2; Fig. 1)
Summary
Animal-pollinated flowers show several patterns of floral symmetry and two types of floral symmetry, actinomorphy (radial symmetry) with several symmetry planes, and zygomorphy (bilateral symmetry) with one symmetry plane, are typical (Neal et al 1998; Endress 2001). Actinomorphy is ancestral, and zygomorphy has evolved independently throughout angiosperms (Stebbins 1974; Coen et al 1995; Endress 2011; Reyes et al 2016; Sauquet et al 2017) Despite such parallel evolution, respective species groups with actinomorphic and zygomorphic flowers show functionally similar pollination patterns, exceptions exist; zygomorphic flowers are often visited by a narrower range of pollinator groups than actinomorphic flowers (Richards 1997; Fenster et al 2004; Gong and Huang 2009, 2011). This may be because, in zygomorphic flower species, accuracy of physical fit between flowers and pollinators is necessary, resulting in low flower size variation (several relevant hypotheses are summarized by Nikkeshi et al 2015)
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