Geographic variation in offspring size: Long‐ and short‐term climate affect mean seed mass ofStreptanthuspopulations

Abstract

Offspring size is a key functional trait that can affect subsequent life history stages; in many species, it exhibits both local adaptation and phenotypic plasticity. Variation among populations in offspring size may be explained by various factors, including local climatic conditions. However, geographic variation in climate may be partitioned into long‐term and interannual sources of variation, which may differ in their effects on population mean offspring size. To assess environmental correlates of offspring size, we evaluated geographic variation in seed mass among 88 populations representing 6 species of Streptanthus (Brassicaceae) distributed across a broad climatic gradient in California. We examined the effects of temperature‐mediated growing season length and precipitation on population mean seed mass to determine whether it is best explained by (1) long‐term mean climatic conditions; (2) interannual climate anomalies (i.e., deviations in climate from long‐term means) during the year of seed development, or (3) interactions between climate variables. Both long‐term mean climate and climate anomalies in the year of collection were associated with population mean seed mass, but their effects differed in direction and magnitude. Relatively large seeds were produced at chronically wet sites but also during drier‐than‐average years. This contrast indicates that these associations may be generated by different mechanisms (i.e., adaptive evolution vs. phenotypic plasticity) and may be evidence of countergradient plasticity in seed mass. In addition, populations occurring in locations characterized by relatively long growing seasons produced comparatively large seeds, particularly among chronically dry sites. This study highlights the need to consider that the responses of seed mass to long‐term versus recent climatic conditions may differ and that climate variables may interact to predict seed mass. Such considerations are especially important when using these patterns to forecast the long‐ and short‐term responses of seed mass to climate change. The results presented here also contribute to our broader understanding of how climate drives long‐term (e.g., local adaptation) and short‐term (e.g., phenotypic plasticity) variation in functional traits, such as offspring size across landscapes.

Geographic Variation in Progeny: Climatic and Soil Changes in Offspring Size and Colour in Four Sorbus spp. (Rosaceae)

“…Larger offspring tend to possess relatively higher energy reserves during the independent phase, possibly explaining their superior performance compared to smaller offspring [9]. Phenotypic variation in seed mass can further influence germination timing, dispersal distance, demography, and ultimately impact population and community dynamics in plant populations [10]. Moreover, seed mass strongly influences plant distribution and is frequently employed as an indicator of disturbance in ecological classification schemes [11].…”

Spatial uncertainty in herbarium data: simulated displacement but not error distance alters estimates of phenological sensitivity to climate in a widespread California wildflower

“…On the other hand, phenological variation explained by climate anomalies may only reflect phenotypic plasticity in response to interannual variation in climate, barring instances of rapid short‐term evolution. Only a handful of studies have estimated biological responses to multiple forms of climatic variation (Bontrager and Angert 2016, Waterton et al 2020, Mazer et al 2021, Love and Mazer 2022), and recent evidence shows that species' phenological sensitivity to climate may depend on the dimension of climatic variation being analyzed (geographic versus interannual) (Munson and Long 2017, Delgado et al 2020, Pearson et al 2021). For traits such as flowering time that may respond to climate change via both adaptive evolution and plasticity (Anderson et al 2012), studying the effects of both normals and anomalies on the estimation of phenological sensitivity can improve our understanding of the causes of phenological shifts in response to ongoing global change.…”