DOI: 10.5061/dryad.f4qrfj78r
title: An ecological-evolutionary investigation of phenotypic, genetic, and environmental variation and correlations among reproductive traits of tall goldenrod (<em>Solidago altissima</em>)

description: Although fitness-related traits are expected to be under strong selection,
 traits related to reproduction are often quite variable within plant
 populations. We used data from two large greenhouse experiments to
 quantify phenotypic, genetic, and environmental variation, as well as
 genetic tradeoffs that might help explain the maintenance of
 within-population variation in four traits related to sexual or vegetative
 reproduction in tall goldenrod (Solidago altissima). The goldenrod
 population exhibited high levels of both phenotypic and genetic variation
 for capitulum (flower head) number and size, seed production, and rhizome
 growth. Significant negative genetic correlations were present between the
 number of capitula and size of capitula—but only at high-nutrient
 levels—and between seed production and rhizome growth when nutrients were
 more limiting. In total, negative genetic correlations may act to maintain
 variation in fitness-related traits in goldenrod populations—a phenomenon
 we suspect may be shared by other herbaceous plant species as their
 populations experience variation in environmental factors, such as
 nutrient levels, among sites or over the course of ecological succession
 within a site.
description: <strong>Plant source and propagation
 methods</strong> In the early spring of 2003, I
 excavated rhizome samples from 26 widely separated <em>Solidago
 altissima</em> (“tall goldenrod”) genets from a 3-ha old-field
 population in Union County, Pennsylvania, USA (40°57.9´ N, 76°57.3´ W).
 The rhizomes were located by the presence of clumps of senesced goldenrod
 stems (ramets) from the previous year. Different genets were inferred by
 large gaps between the clumps of stems. I transplanted rhizomes into 27-cm
 diameter plastic pots in commercial growing medium (ProMix
 BX<sup>TM</sup>; Premier Horticulture Ltd, Dorval, QC, Canada)
 in a greenhouse at Bucknell University in Lewisburg, Pennsylvania. New
 sections of rhizomes from these pot-grown genets were stored in
 refrigeration over winter and repotted in the same fashion each year
 through 2009. Vegetative progeny (from new rhizome growth) from these
 genets were used in experiments at Bucknell from 2003-2009. These
 procedures enabled my colleagues and me to use multiple ramets from each
 of multiple genets to estimate broad-sense heritabilities in a number of
 different traits. <strong>Experiment 1
 (2005):</strong> In late April of 2005, rhizomes
 of 26 goldenrod genets were removed from cold storage to begin plant
 propagation. For each genet, healthy rhizomes were cut into at least 20
 equal-sized (2 cm<sup>3</sup>) segments, as measured by water
 displacement of 2 mL in a 100 mL-graduated cylinder containing 98 mL of
 water. Rhizome segments were planted into plastic flats containing ProMix
 BXTM, and shoots (ramets) began emerging within about one week. In late
 May, 18 ramets from each genet were transplanted individually from the
 flats into 16.5-cm diameter plastic azalea pots containing ProMix BXTM.
 These 468 pots were placed in two randomized blocks on greenhouse benches
 at Bucknell University (representing east and west sides of the
 greenhouse), with one ramet per genet per each of nine spittlebug
 treatments per block. The spittlebug treatments consisted of placing 0, 1,
 2, 3, 4, 5, 6, 7, or 8 nymphs on a ramet. Early-instar spittlebug nymphs
 were transferred to ramets on 3 June and removed upon eclosion to adults,
 which concluded on 29 June. Plants were fertilized
 monthly using Peters Professional 15-16-17 NPK water-soluble fertilizer
 (J.R. Peters, Allentown, PA). This fertilizer was mixed to a concentration
 of 3.9 mL per liter of water (i.e., 1 tablespoon per gallon), and 59 mL
 (1/4 cup) of the mixture was applied to each pot. In elemental terms, this
 rate works out 34.5 mg of N, 16.0 mg of P, and 32.5 mg of K per
 application. Once a ramet finished flowering and
 setting seeds, its capitula were counted by hand, one inflorescence branch
 at a time (from 12 October to 14 November). In addition, ten capitula for
 each ramet were collected across different locations in the inflorescence.
 These capitula were dissected to count achenes and obtain a mean number of
 seeds per capitulum for each ramet. This mean was multiplied by the number
 of capitula to estimate the total number of seeds produced by each ramet.
 In late winter, each pot was emptied and the underground plant material
 was cleaned of growing medium. Roots were removed from the rhizomes, and
 the new rhizomes (initiated and grown in 2005) were collected into paper
 bags, dried to a constant mass in a drying oven at 60 °C, and weighed to
 the nearest mg. <strong>Experiment 2
 (2006):</strong> In April of 2006, a random
 subset of 15 of the 26 goldenrod genets from the 2005 experiment were
 randomly selected for a follow-up study to investigate the effects of
 nutrient levels on the expression of phenotypic and genetic variation and
 potential correlations among the same four fitness-related traits as were
 examined in the previous experiment (viz., number of capitula, seeds per
 capitula, seed production per ramet, an rhizome mass). Goldenrod ramets
 were propagated from cold-stored rhizomes using the same procedures as
 detailed for Experiment 1. For the current study, twelve ramets per genet
 were grown in 16.5 cm plastic azalea pots in ProMix BXTM. These plants
 were assigned randomly to a two-way factorial design with nutrient level
 (n = 2) crossed by spittlebug treatment (n = 2). Each genet had three
 ramets per treatment combination, for a total of 180 ramets in the
 experiment. The high-nutrient treatment received weekly
 fertilization at the dosage described above for the plants in Experiment
 1. The low-nutrient ramets received no fertilizer for the duration of the
 experiment. On 2 June, 10 field-collected, early-instar spittlebug nymphs
 were placed on half of the ramets. Each spittlebug was removed upon adult
 eclosion, which took as short as one week to as long as nearly three weeks
 of feeding. Measurements of capitula number, capitulum size, seed number,
 and rhizome mass were taken with the same procedures as described above
 for Experiment 1.
description: # An ecological-evolutionary investigation of phenotypic, genetic, and
 environmental variation and correlations among reproductive traits of tall
 goldenrod (*Solidago altissima*) Dataset DOI:
 [10.5061/dryad.f4qrfj78r](https://doi.org/10.5061/dryad.f4qrfj78r) ##
 Description of the data and file structure This data package includes two
 spreadsheets. The first provides data from an experiment conducted in 2005
 to assess phenotypic and genetic variation in four traits related to
 reproduction in tall goldenrod (*Solidago altissima*): number of capitula
 (i.e., seed heads), size of the capitula (i.e., average number of seeds
 per capitulum), number of seeds produced per ramet, and production of new
 rhizomes (measured as dry mass). Phenotypic, genetic, and environmental
 correlations were calculated between number and size of capitula and
 between seed production and rhizome production. The effect of feeding by
 nymphs of the meadow spittlebug (*Philaenus spumarius*) was also
 investigated in this experiment. Six ramets died early in the experiment,
 resulting in some blanks in the cells of the spreadsheet. ### Files and
 variables #### File: 2005_Experiment.csv **Description:** This spreadsheet
 provides data from an experiment conducted in 2005 to assess phenotypic
 and genetic variation in four traits related to reproduction in tall
 goldenrod (*Solidago altissima*): number of capitula (i.e., seed heads),
 size of the capitula (i.e., average number of seeds per capitulum), number
 of seeds produced per ramet, and production of new rhizomes (measured as
 dry mass). Phenotypic, genetic, and environmental correlations were
 calculated between number and size of capitula and between seed production
 and rhizome production. The effect of feeding by nymphs of the meadow
 spittlebug (*Philaenus spumarius*) was also investigated in this
 experiment. Six ramets died early in the experiment, resulting in some
 blanks in the cells of the spreadsheet. ##### Variables * **Block**: (Two
 blocks, indicating the east or west half of the greenhouse.) * **Table**:
 (Four greenhouse benches were arranged north-south in each Block.) *
 **Row**: (The pots were arranged in six east-west rows per bench.) *
 **Column**: (Each row contained 10 evenly spaced pots.) * **Genet**: (The
 experiment included plants from 26 different genets.) * **Ramet**: (Each
 genet was represented by 18 ramets—one per pot.) * **Bugs**: (Each ramet
 was assigned to have from 0-8 spittlebug nymphs. The numbers in this
 column represent the actual number of nymphs that ended up feeding on the
 ramet.) * **Height (cm)**: (The final height of a ramet at the end of the
 experiment. Height data are unavailable for eight ramets.) * **Capitula**:
 (The total number of capitula produced by a ramet, from an actual
 count–not an estimate. Capitula counts are unavailable for six ramets.) *
 **Seeds/cap**: (The “size” of an average capitulum, estimated as the mean
 number of seeds per capitulum from ten capitula sampled across the
 inflorescence. Estimates of seeds/cap were unavailable for 16 ramets.) *
 **Seeds**: (The number of seeds produced per ramet, as estimated from the
 number of capitula produced by that ramet multiplied by the size of the
 average capitulum for that ramet. Estimates of seeds production were
 unavailable for six ramets.) * **Rhizome mass**: (The dry weight of
 rhizomes produced by each ramet, in g. Rhizome mass was unavailable for
 six ramets.) #### File: 2006_Experiment.csv **Description:** This
 spreadsheet provides data from a follow-up experiment conducted in 2006
 that examined the effect of nutrient stress on phenotypic and genetic
 variation in the same four reproductive traits measured in the 2005
 experiment described above. Genetic and environmental correlations were
 calculated between number and size of capitula and between seed production
 and rhizome production for fertilized plants and unfertilized (i.e.,
 nutrient-stressed) plants. The effect of feeding by nymphs of the meadow
 spittlebug (*Philaenus spumarius*) was also investigated in this
 experiment. One ramet died early in the experiment, and it is excluded
 from the spreadsheet. ##### Variables * **Bench**: (Three pairs of benches
 were used in this part of the experiment) * **Row**: (The pots were
 arranged in six east-west rows per bench.) * **Column**: (Each row
 contained 10 evenly-spaced pots.) * **Nutrients**: (“High”: half of the
 ramets were fertilized regularly; “Low”: half of the ramets were not
 fertilized.) * **Genet**: (The experiment included plants 15 of the 26
 different genets used in the 2005 experiment.) * **Ramet**: (Each genet
 was represented by 12 ramets—one per pot.) * **Bugs**: (Each ramet was
 assigned to have 0 or 10 spittlebug nymphs. The numbers in this column
 represent the actual number of nymphs that ended up feeding on the ramet.)
 * **Height (cm)**: (The final height of a ramet at the end of the
 experiment.) * **Capitula**: (The total number of capitula produced by a
 ramet, from an actual count–not an estimate.) * **Seeds/cap**: (The “size”
 of an average capitulum, estimated as the mean number of seeds per
 capitulum from ten capitula sampled across the inflorescence. Estimates of
 seeds/cap were unavailable for one ramet.) * **Seeds**: (The number of
 seeds produced per ramet, as estimated from the number of capitula
 produced by that ramet multiplied by the size of the average capitulum for
 that ramet.) * **Rhizome mass**: (The dry weight of rhizomes produced by
 each ramet, in g.)