Rainfall seasonality predicts the germination behavior of a tropical dry‐forest vine

Abstract

Seed dormancy is considered to be an adaptive strategy in seasonal and/or unpredictable environments because it prevents germination during climatically favorable periods that are too short for seedling establishment. Tropical dry forests are seasonal environments where seed dormancy may play an important role in plant resilience and resistance to changing precipitation patterns. We studied the germination behavior of seeds from six populations of the Neotropical vine Dalechampia scandens (Euphorbiaceae) originating from environments of contrasting rainfall seasonality. Seeds produced by second greenhouse‐generation plants were measured and exposed to a favorable wet environment at different time intervals after capsule dehiscence and seed dispersal. We recorded the success and the timing of germination. All populations produced at least some dormant seeds, but seeds of populations originating from more seasonal environments required longer periods of after‐ripening before germinating. Within populations, larger seeds tended to require longer after‐ripening periods than did smaller seeds. These results indicate among‐population genetic differences in germination behavior and suggest that these populations are adapted to local environmental conditions. They also suggest that seed size may influence germination timing within populations. Ongoing changes in seasonality patterns in tropical dry forests may impose strong selection on these traits.

Is There More to Within-plant Variation in Seed Size than Developmental Noise?

“…Assuming that seasonality in precipitation is an important source of selection on seed dormancy and germination behaviour, the weak tendency for seed size to increase with seasonality tends to support the conclusion that seed size in D. scandens is correlated with dormancy and germination behaviour (Martins et al, 2019). However, even taken at face value, this effect remains limited, with an increase in seed size of ca.…”

“…Previous experiments have shown that neither seed size nor within-blossom variation in seed size is detectably affected by the number of fathers siring the clutch (Pélabon et al, 2015). Furthermore, within populations, seed size correlates positively with the duration of seed after-ripening required before germination, and among populations, the duration of the after-ripening period correlates positively with environmental seasonality (Martins et al, 2019). Once dormancy is broken, however, larger seeds have a higher probability of germinating (Pélabon et al, 2005).…”

“…In such environments, mature seeds are expected to delay their germination so as to avoid germinating before the dry season. We thus expect seeds from population occurring in highly seasonal environments to have evolved long duration of afterripening (Martins et al, 2019). If seed size is correlated with Table 1 Description of the populations and environmental characteristics a Experiment 1: variance components analysis; experiment 2: drought treatment b Greenhouse gener.…”

“…Assuming that the after-ripening duration necessary for seeds to germinate is positively correlated with seed size, we first tested if seed size increases with environmental seasonality (Martins et al, 2019). We also tested whether variation in seed size increases with short-term environmental unpredictability as suggested by the diversifying bet-hedging hypothesis.…”

“…Among species, time to germination generally increases with seed mass (Harel et al, 2011;Norden et al, 2009), while within species, several studies report that larger seeds germinate earlier, or are more likely to germinate than smaller ones (Biere, 1991;Simons & Johnston, 2000;Galloway, 2001;Pélabon et al, 2005, but see Susko & Lovett-Doust, 2000 for the opposite pattern). Furthermore, in seeds exhibiting dormancy, the time necessary to break dormancy and induce germination under favorable conditions sometimes increases with seed mass (Martins et al, 2019). Variation in seed size may thus provide a mechanism for producing seeds with different germination times, and diversifying bet-hedging could therefore represent an adaptive explanation for the unexpected within-individual and within-inflorescence variation in seed size often observed in angiosperms.…”