This week we are pleased to welcome our own Yihan Wu.
Reconstructing parallel clines in flowering phenology from natural history collections of Lythrum salicaria
Rapid shifts in phenology during biological invasions can increase survival and reproduction of invasive species, contributing to their spread and impact. However, it is not clear how quickly invasive populations can tune their phenology in response to local environmental cues. Global herbarium specimens represent spatial and temporal snapshots of phenology that could be analyzed for environmental tuning by correlating phenological development to local climatic factors. In this study, inflorescence measurements of herbarium specimens were combined with historical weather data to investigate modern and historic clines in flowering phenology throughout the North American distribution of the invasive plant Lythrum salicaria (purple loosestrife).
Inflorescence morphology (i.e. buds, flowers, fruits) was characterized from 3,427 herbarium specimens and interpolated the season length and growing-degree-days from 6,303 unique weather stations by inverse distance weighing. A flowering time index (FTI) was calculated from phenology measurements, which corrected for variation in collection date and local growing conditions.
FTI of herbarium specimens was strongly correlated with genetic differences in time to first flower measured in four common garden experiments. Using a non-linear least squares model, the effects of interpolated season length and time since invasion were compared throughout the North American range. Specimens collected from older populations in locations with short growing seasons reached maturity faster than specimens collected from early populations with short growing seasons. Herbarium specimens can be a valuable resource in reconstructing historical phenological changes due to rapid adaptation.
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