DOI: 10.5061/dryad.6t1g1jx16
title: Data from: Transgenerational genetic effects help explain latitudinal variation in seed mass and germination timing in Plantago lanceolata

description: We know little about the underlying genetic control of phenotypic patterns
 of seed traits across large-scale geographic and environmental gradients.
 Such knowledge is important for understanding the evolution of populations
 within species and for improving species conservation. Therefore, to test
 for genetic variation in P. lanceolata, we made reciprocal crosses between
 northern and southern genotypes that span the species’ range in Europe.
 Results provide evidence of transgenerational genetic effects on seed mass
 and germination timing. Northern mothers produced larger seeds with
 delayed germination, in contrast to southern mothers, which produced
 smaller seeds with accelerated germination. Maternal latitude affected
 both the seed coat, solely maternal tissue, and embryo/endosperm tissues.
 Thus, latitudinal variation in seed size and germination timing can be
 explained, in part, by the direct influence of maternal genotype,
 independent of zygotic genes that parents pass directly to the embryo and
 endosperm. Data suggest that researchers exploring the existence and
 evolution of large-scale geographic variation within species test for
 transgenerational genetic effects. Also, data suggest that
 transgenerational control of seed traits should be considered when
 developing procedures designed to facilitate species conservation and
 restoration.
description: Our two experiments derive from a QTL experiment in which
 Marshall et al. (2020) [92] explored the genetic architecture of
 differences in thermal plasticity in flower color and flowering time
 between northern and southern European populations. Because we used F1
 seeds from this experiment, we summarize aspects of the QTL experiment and
 refer readers to Marshall et al. (2020) [92] and to an earlier experiment
 describing the latitudinal variation in thermal plasticity in flower color
 [97] for more details. The northern and southern parents used in the QTL
 study displayed high and low thermal plasticity, respectively, and
 represented plasticity extremes found in a sample of 29 European P.
 lanceolata populations. Parents in the QTL study were themselves progeny
 of genotypes that had been collected from wild European populations
 differing in thermal regime and duration of the growing season (Fig. 2,
 See also [97]). To reduce maternal environmental effects, Lacey et al.
 (2010) [97] had induced genotypes to flower and set seed while keeping the
 wild populations separated but in similar controlled environments. Plants
 grew vegetatively in a greenhouse until flowering began, at which time
 populations were isolated in growth chambers and separate greenhouse rooms
 set at 22oC, 16-h day/17oC, 8-h night to allow for random
 within-population wind pollination and seed production. In 2012, Marshall
 et al. (2020) [92] reciprocally crossed combinations of genotypes derived
 from northern and southern source populations (i.e., hereafter referred to
 as the parental generation) to produce F1 seeds (Fig. 2). Multiple clones
 of parental genotypes were used to produce F1 seeds. For all crosses, the
 single growth chamber was set at 20°C, 16-hr day/15°C, 8-hr night. Thus,
 the seeds that we examined were products of two generations of crosses
 made in similar environments, which further reduced remnant parental
 environmental effects that might have persisted after the first
 generation. F1 seeds were harvested, counted and stored at room
 temperature in the lab for several months, which allowed time for
 after-ripening to be completed. Then we sampled seeds for the two
 experiments, described below. For both, we chose seeds that were brown and
 shiny and avoided seeds that were black and flat, which indicated that the
 seeds had been aborted. Experiment 1: Five northern
 parental genotypes (one per population) were reciprocally crossed with
 five southern genotypes (one from a French population and four from an
 Italian population). The four genotypes from the Italian population were
 descended from different grandmothers. For each reciprocal cross, we
 randomly sampled 20 seeds per clonal cross (1-3 clonal cross per
 reciprocal) and weighed seeds, each to the nearest 0.001 mg.
 Experiment 2: We sampled 4 pairs of reciprocal crosses again, but
 this time we collected data on total seed mass, coat mass,
 endosperm/embryo mass, and days to germination. Fifteen seeds per
 reciprocal cross were selected randomly and independently of clone. After
 weighing each seed individually per reciprocal cross, we placed 3 seeds in
 each of 5 petri dishes lined with filter paper that was saturated with
 water. The petri dishes were placed in a growth chamber set at 20°C, 16-hr
 day/15°C, 8-hr night, and water was added as needed to keep the filter
 paper moist. Seeds were checked daily. We recorded the day of appearance
 of a radicle protruding from the seed coat. As germination continued, we
 collected the seed coats, which drop off after germination. Coats were
 dried and stored at room temperature for a week after all germination had
 ceased. All seeds germinated within 7 days from the day of placement in
 the growth chamber.
description: Instructions for reading and understanding the datafiles are in
 the README document.