title: Geographic patterns of seed mass are associated with climate factors, but relationships vary between species.
abstract: OBJECTIVE
  Seed size is a critical life history attribute with fitness effects that cascade throughout the lifespan of plants. Interspecific studies repeatedly report a negative correlation between seed mass and latitude. Yet, despite its importance, little is known about geographic variation in seed size within species' ranges.
  
  
  METHODS
  To improve our understanding of intraspecific geographic variation in seed size, we collected and weighed seeds by maternal line from 8 to 17 populations of seven herbaceous plant species spanning large geographic areas, and measured a dispersal trait, awn length, for two grass species. We examined the overall relationship between seed mass and latitude, then divided the data into species-specific subsets to compare the fit of three models to explain seed mass and awn length: (1) latitude and longitude, (2) long-term climate, and (3) collection-year weather.
  
  
  RESULTS
  Like previous work, we found a negative relationship between interspecific seed mass and latitude. However, the best-fit models explaining seed size and awn length differed between individual species and often included significant interaction terms. For all species, the best model was either long-term or collection-year climate data instead of latitude and longitude.
  
  
  CONCLUSIONS
  Intraspecific geographic patterns for seed traits were remarkably inconsistent, covarying both negatively and positively with temperature and precipitation. The only apparent generalization is that annual species' seed mass corresponded more with collection-year weather while perennial species covaried more with long-term climate. Overall, this study suggests that the scale of climate variation that molds seed traits is highly species-specific.
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA nsopergorden@mhu.edu.
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Soper Gorden
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
authors.forename: Katharine J
authors.initials: KJ
authors.lastname: Winkler
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Jahnke
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Marshall
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: Horky
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
authors.forename: Colton
authors.initials: C
authors.lastname: Huddelson
authors.affiliation: Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
authors.forename: Julie R
authors.initials: JR
authors.lastname: Etterson
mesh_terms: D002980:Climate; D019684:Magnoliopsida / Q000235:genetics / Q000502:physiology*; D063148:Plant Dispersal; D012639:Seeds / Q000502:physiology; D013045:Species Specificity
keywords: awn length; climate; geographic patterns; interspecific; intraspecific; latitude; longitude; precipitation; seed size; temperature