Temporal variation in reproductive costs and payoffs shapes the flowering strategy of a neotropical milkweed, Asclepias curassavica

Abstract

AbstractA central goal of evolutionary ecology is to understand the factors that select for particular life history strategies, such as delaying reproduction. For example, environmental variation and reproductive costs to survival and growth often select for reproductive delays in semelparous and iteroparous species. In this study, we examine how variation in reproductive cost, which we define as a reduction to growth, survival, or future reproduction after a reproductive event, may select for reproductive delay in an iteroparous Neotropical milkweed with no obvious reproductive season. We analyzed demographic data collected every 3 months for 3 years from four populations of Asclepias curassavica in Monteverde, Costa Rica. We detected costs of flowering to survival and growth that varied in magnitude between our 12 transition periods without a seasonal pattern. The populations also exhibited temporal variation in reproductive payoffs measured as seedling establishment. We incorporated these reproductive costs into demographic projection models, which predicted a delayed flowering strategy only when we included temporal variation in costs and payoffs. Temporal variation in reproductive costs and payoffs is an important selective force in the evolution of delayed flowering in iteroparous species. Further, a lack of predictable seasonal pattern to reproductive costs and payoffs may contribute to the lack of seasonal reproductive patterns observed in our study species and other Neotropical species.