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Contributed Poster

Session: Evolution

PS 9-112 - Responses to temperature cycling may explain latitudinal clines in milkweed seed dormancy

Monday, August 7, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
Abstract: Intraspecific variation in recruitment traits may help plant populations adapt to changing environments. Because dormancy and germination timing directly influence the environment experienced by a plant as it continues to develop, these traits have strong impacts across scales, affecting gene expression, individual fitness, population dynamics, and species interactions. As the sole food source for monarch butterflies, milkweed germination phenology is relevant to monarch conservation. In many plants, seeds from high altitudes or latitudes often demonstrate elevated dormancy. However, prior research has demonstrated that for common milkweed, Asclepias syriaca, seeds from high latitude populations express reduced dormancy relative to low latitude populations. We hypothesized that short growing seasons favor faster germination, and we investigated the influence of temperature, temperature cycling, and cold stratification treatments on the germination time of common milkweed seeds collected from 10 different populations across its range (37-46°N). Cold stratification and temperature cycling together were shown to be most effective at reducing dormancy; however, many seeds with no exposure to cold stratification did germinate, especially under 11/21°C temperature cycles. As shown previously, high-latitude populations expressed reduced dormancy, germinating at a higher rate and at lower temperatures. We now hypothesize that seeds from low latitude populations express higher dormancy because, in the absence of reliable snowpack, they are likely to experience regular temperature cycling during winter months. As the climate warms, seeds from high-latitude populations might experience reduced snow cover and increased temperature cycling, increasing risks of early germination.