DOI: 10.5061/dryad.ghx3ffbzf
title: Locoweed biomass and fecundity +/- fungal endophyte in field 2011-2020

description: Locoweeds (mostly Astragalus and Oxytropis) are legumes that contain
 swainsonine, a toxic alkaloid produced by the vertically-transmitted,
 fungal endophyte Alternaria section Undifilum. These plants cause economic
 losses through livestock poisoning, yet there is little evidence that
 swainsonine plays a role in anti-herbivory. Similarly, while swainsonine
 synthesis relies on nitrogen from the plant, and many fungal endophytes
 are thought to be mutualists, the ecological role of this endophyte across
 the mutualism-commensalism-parasitism continuum is yet unknown. We
 examined the fitness of A. mollissimus and O. sericea plants with and
 without the endophyte by measuring growth and fecundity parameters, and
 potential transgenerational effects, in a multi-year, common garden
 experiment located in or beyond the northern range of locoweeds. We
 hypothesized that field-grown plants with the endophyte would possess a
 fitness advantage over plants without the endophyte under growing
 conditions different from their maternal source. Oxytropis sericea and
 Astragalus mollissimus var. mollissimus and var. thompsoniae plants
 germinated from seeds collected in New Mexico, symbiosed with the
 Alternaria section Undifilum fungal endophyte (E+) and with the fungal
 endophyte mechanically removed (E-) by removal of the seed coat, were
 established in an outdoor, common garden in southwest Montana. To evaluate
 the ability of this vertically-transmitted endophyte to mediate
 transgenerational effects in progeny, two successive generations of E+ and
 E- plants were also established in the garden. We measured overwinter
 survival, photosynthetic gas exchange, flower and seed production, and
 progeny seed germination on these pairs of plants over nine years, and
 compared final above and below-ground biomass. Both A. mollissimus
 varieties grew as annuals under common-garden field conditions, ca. 1500
 km north of their native range, with A. mollissimus var. mollissimus
 plants producing more reproductive stems, flowers, and seed pods, and
 surviving longer than A. mollissimus var. thompsoniae, regardless of
 endophyte presence or swainsonine production. The more broadly distributed
 Oxytropis sericea plants grew as perennials with survival unaffected by
 endophyte status; however, E+ O. sericea plants produced slightly more
 reproductive stems, flowers/reproductive stems, and reproductive stem and
 log crown biomass. Maternal effects detected in the parental generation,
 Gen 0, were highly variable, but this variation disappeared in subsequent
 generations, with no endophyte transgenerational effects detected across
 most variables. Astragalus and Oxytropis gas exchange, fecundity,
 and seed germination also were unaffected by endophyte status when grown
 under environmental conditions differing from the collection sites.
 Contrary to our initial hypothesis of mutualism, the Undifilum endophyte
 did not appear to improve locoweed survival or fecundity, and the presence
 or absence of the endophyte had no detectable transgenerational effects.
 However, the endophyte did slightly increase the number of reproductive
 stems and flowers/stem and the weight of the crown and reproductive stem
 tissue in the perennial O. sericea, suggesting more work is
 needed to examine endophyte effects on carbohydrate biochemistry and
 pollination parameters. Our findings highlight the importance of
 evaluating putative commensal host-endophyte relationships under field
 conditions.
description: Three locoweed taxa were compared because of their different life
 histories and ability to produce swainsonine. <em>Astragalus
 mollissimus </em>varieties have short life histories for perennials,
 including sometimes growing as annuals or biennials (Soltani et al.,
 2021), while <em>O. sericea</em> typically lives much longer
 (Fox et al., 1998; Welsh, 2007). <em>Astragalus
 mollissimus</em> var. <em>mollissimus</em>
 (<em>A.m.m.</em>)<em> </em>is a high producer of
 swainsonine, whereas A. <em>mollissimus</em> var<em>.
 thompsoniae </em>(<em>A.m.t.</em>)<em>
 </em>produces little if any swainsonine, barely reaching PCR
 detection limits of &lt;0.001% (Cook et al., 2016a; Ralphs et al.,
 2008; Vallotton et al., 2012); we included <em>A.m.t.</em> in
 this study to allow separate examination of any swainsonine effect.
 <em>Oxytropis sericea</em> produces intermediate levels of
 swainsonine (Vallotton et al., 2012). Seeds used to establish this study
 were collected from northern New Mexico as described in Delaney et al.
 (2011) for <em>O. sericea</em> and
 <em>A.m.m.</em>, and Vallotton et al. (2012) for
 <em>A.m.t</em>. To directly investigate
 endophyte effects on locoweeds, greenhouse-grown seedlings were
 transplanted into a common garden (15.2 m x 4.6 m) in a randomized nested
 design as pairs with endophyte (E+) and without endophyte (E-) within nine
 zones in the garden at the Montana State University Post Farm near
 Bozeman, MT (N 45° 40' 30.5484", W 111° 9' 14.2177";
 elevation 1450 m), in an Amsterdam silty loam (Engel et al., 2007) with pH
 8, 2.1% organic matter, and nitrate-nitrogen at ca. 38 pounds/acre (AgVise
 lab results from 6” soil samples). <em>Astragalus
 mollissimus</em> seedlings were planted in the common garden from
 2011 to 2015 (var. <em>mollissimus</em>, 96 pairs total) and
 2012 to 2015 (var. <em>thompsoniae</em>, 74 pairs total). Most
 <em>O. sericea</em> (New Mexico seed source; Generation 0)
 seedlings were planted in 2011 (18 pairs) and 2013 (24 pairs), with
 additional pairs planted in 2012 (2 pairs), 2014 (3 pairs), and 2015 (3
 pairs) to replace deceased plants (50 pairs total). Most
 <em>Oxytropis</em> plants died, and all
 <em>A.m.m.</em> and <em>A.m.t.</em> plants died
 during the 2013-2014 winter, regardless of endophyte status, and pairs
 were replanted as feasible. To evaluate any
 transgenerational effect of the endophyte in <em>O.
 sericea</em>, 50 E+/E- pairs each of two subsequent generations
 (Post Farm seed source; Generations 1 and 2) were also planted: First
 generation (Gen 1) plants were germinated from seeds collected from 10 E-
 and 10 E+, 1-year-old, parent plants (Gen 0) established in 2013; five
 seedlings from each pair were transplanted into the garden in fall 2015
 (50 pairs). Second generation (Gen 2) plants were germinated in 2016 from
 seeds collected from 5 E- and 5 E+, one-year-old (Gen 1) plants
 established in 2015; ten seedlings from each of two of these five pairs
 were transplanted into the garden in 2017 (50 pairs).
 We measured overwinter survival, photosynthetic gas exchange,
 flower and seed production, and progeny seed germination on these pairs of
 plants over nine years until their death, and compared final above and
 below-ground biomass for surviving plants in July 2020.
description: # Locoweed biomass and fecundity +/- fungal endophyte in field 2011-2020
 [Access this dataset on Dryad](DOI: 10.5061/dryad.ghx3ffbzf) *Oxytropis
 sericea* (Os) and *Astragalus mollissimus* var. *mollissimus* (Amm) and
 var. *thompsoniae* (Amt) plants germinated from seeds collected in New
 Mexico, symbiosed with the *Alternaria* section *Undifilum* fungal
 endophyte (E+) and with the fungal endophyte mechanically removed (E-) by
 removal of the seed coat, were established in an outdoor, common garden in
 southwest Montana. Additionally, two successive generations of Os E+ and
 E- plants were also established in the garden. We measured overwinter
 survival, photosynthetic gas exchange, flower and seed production, and
 progeny seed germination on these pairs of plants over nine years, and
 compared final above and below-ground biomass. Our studies found that both
 *A. mollissimus* varieties grew as annuals under common-garden field
 conditions, with *A. mollissimus* var. *mollissimus* plants producing more
 reproductive stems, flowers, and seed pods, and surviving longer than *A.
 mollissimus* var. *thompsoniae*, regardless of endophyte presence or
 swainsonine production. The more broadly distributed Oxytropis sericea
 plants grew as perennials with survival unaffected by endophyte status;
 however, E+ O. sericea plants produced slightly more reproductive stems,
 flowers/reproductive stems, and reproductive stem and log crown biomass.
 Maternal effects detected in the parental generation, Gen 0, were highly
 variable, but this variation disappeared in subsequent generations, with
 no endophyte transgenerational effects detected across most variables.
 *Astragalus* and *Oxytropis* gas exchange, fecundity, and seed germination
 also were unaffected by endophyte status when grown under environmental
 conditions differing from collection sites. Our findings highlight the
 importance of evaluating putative commensal host-endophyte relationships
 under field conditions. ## Description of the data and file structure Data
 for biological responses measured are provided in Excel data sheets. Each
 data set has a companion PDF file describing the content of each column.
 ## Sharing/Access information NA ## Code/Software NA