Abstract
Within-plant variation in seed size may merely reflect developmental instability, or it may be adaptive in facilitating diversifying bet-hedging, that is, production of phenotypically diverse offspring when future environments are unpredictable. To test the latter hypothesis, we analyzed patterns of variation in seed size in 11 populations of the perennial vine Dalechampia scandens grown in a common greenhouse environment. We tested whether population differences in the mean and variation of seed size covaried with environmental predictability at two different timescales. We also tested whether within-plant variation in seed size was correlated with independent measures of floral developmental instability and increased under stressful conditions. Populations differed genetically in the amount of seed-size variation occurring among plants, among infructescences within plants, and among seeds within infructescences. Within-individual variation was not detectably correlated with measures of developmental instability and did not increase under stress, but it increased weakly with short-term environmental unpredictability of precipitation at the source-population site. These results support the hypothesis that greater variation in seed size is adaptive when environmental predictability is low.
Highlights
Despite theoretical models suggesting the existence of an optimal size for propagules produced by an individual (Smith & Fretwell, 1974; Stearns, 1992; de Jong & Klinkhamer, 2005), seed size is surprisingly variable within plants (Herrera, 2009; Michaels et al, 1988; Obeso, 1993; Pélabon et al, 2015; Susko & Lovett-Doust, 2000; Vaughton & Ramsey, 1998)
The size variation of the Dalechampia seeds obtained under greenhouse conditions was relatively small, with a maximum within-population coefficient of variation (CV) in seed diameter of 8%, populations differed both in the magnitude of variation in seed size and how this variation was distributed across individuals, blossoms and seeds (Table 2)
Populations differed in the proportion of variance in seed size expressed at the within-blossom level which ranged from 6 to 25% of the total within-population variance (Table 2)
Summary
Despite theoretical models suggesting the existence of an optimal size for propagules produced by an individual (Smith & Fretwell, 1974; Stearns, 1992; de Jong & Klinkhamer, 2005), seed size is surprisingly variable within plants (Herrera, 2009; Michaels et al, 1988; Obeso, 1993; Pélabon et al, 2015; Susko & Lovett-Doust, 2000; Vaughton & Ramsey, 1998). The production by a single individual of phenotypically variable offspring, each optimal for a different environmental condition, may increase the individual’s fitness by buffering variation in reproductive success and maximizing the long-term fitness. Such a strategy is referred to as diversifying bethedging (Lewontin & Cohen, 1969; Marshall et al, 2008; Philipi & Seger, 1989; Seger & Brockmann, 1987; Simons, 2009; Starrfelt & Kokko, 2012)
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