Contrasting germination responses to vegetative canopies experienced in pre- vs. post-dispersal environments

Abstract

Background Seeds adjust their germination based on conditions experienced before and after dispersal. Postdispersal cues are expected to be more accurate predictors of offspring environments, and thus offspring success, than pre-dispersal cues. Therefore, germination responses to conditions experienced during seed maturation may be expected to be superseded by responses to conditions experienced during seed imbibition. In taxa of disturbed habitats, neighbours frequently reduce the performance of germinants. This leads to the hypotheses that a vegetative canopy will reduce germination in such taxa, and that a vegetative canopy experienced during seed imbibition will over-ride germination responses to a canopy experienced during seed maturation, since it is a more proximal cue of immediate competition. These hypotheses were tested here in Arabidopsis thaliana.Methods Seeds were matured under a simulated canopy (green filter) or white light. Fresh (dormant) seeds were imbibed in the dark, white light or canopy at two temperatures (10 or 22 C), and germination proportions were recorded. Germination was also recorded in after-ripened (less dormant) seeds that were induced into secondary dormancy and imbibed in the dark at each temperature, either with or without brief exposure to red and far-red light.Key Results Unexpectedly, a maturation canopy expanded the conditions that elicited germination, even as seeds lost and regained dormancy. In contrast, an imbibition canopy impeded or had no effect on germination. Maturation under a canopy did not modify germination responses to red and far-red light. Seed maturation under a canopy masked genetic variation in germination.Conclusions The results challenge the hypothesis that offspring will respond more strongly to their own environment than to that of their parents. The observed relaxation of germination requirements caused by a maturation canopy could be maladaptive for offspring by disrupting germination responses to light cues after dispersal. Alternatively, reduced germination requirements could be adaptive by allowing seeds to germinate faster and reduce competition in later stages even though competition is not yet present in the seedling environment. The masking of genetic variation by maturation under a canopy, moreover, could impede evolutionary responses to selection on germination.

Maternal vernalization and vernalization‐pathway genes influence progeny seed germination

“…The environment experienced by the mother plant frequently affects germination of the progeny by modifying dormancy levels (Penfield & Springthorpe, ; He et al ., ; Auge et al ., ; Burghardt et al ., ; Edwards et al ., ; Leverett et al ., ). Changes in the maternal environment can do so even if developing seeds themselves do not experience those changes, as observed here.…”

Context-Dependent Developmental Effects of Parental Shade Versus Sun Are Mediated by DNA Methylation

“…Such context-dependent expression of parental environment effects has been documented in a number of plant and animal taxa (e.g., Schmitt et al, 1992; Galloway, 1995; Hereford and Moriuchi, 2005; Miller et al, 2012; Leverett et al, 2016). In Sheepshead minnow fish ( Cyprinodon variegatus ), for example, the effects of parental temperature treatment were expressed differently depending on the temperature experienced by juvenile offspring (Salinas and Munch, 2012).…”

Adjusting phenotypes via within‐ and across‐generational plasticity

“…temperatures and increased salinity in the offspring environment were only observed when maternal plants were not grown in these environments (Zhang et al, 2012;Vu et al, 2015;Leverett et al, 2016;Moriuchi et al, 2016). This masking can occur when the maternal treatment alone maximized germination or induced such intense dormancy that progeny cues were not able to overcome it.…”

“…1aiii). For instance, seeds may perceive no competitors, but they may be exposed to intense competition later; maternal parents have information on environments likely to be experienced later in the season, at a time when these cues are not yet available to progeny (Leverett et al, 2016). If so, selection could favor a response to maternal rather than progeny environments.…”