Climate change is associated with increased allocation to potential outcrossing in a common mixed mating species

Abstract

Premise Although the balance between cross‐ and self‐fertilization is driven by the environment, no long‐term study has documented whether anthropogenic climate change is affecting reproductive strategy allocation in species with mixed mating systems. Here, we test whether the common blue violet (Viola sororia; Violaceae) has altered relative allocation to the production of potentially outcrossing flowers as the climate has changed throughout the 20th century. Methods Using herbarium records spanning from 1875 to 2015 from the central United States, we quantified production of obligately selfing cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers by V. sororia, coupled these records with historic temperature and precipitation data, and tested whether changes to the proportion of CL flowers correlate with temporal climate trends. Results We find that V. sororia progressively produced lower proportions of CL flowers across the past century and in environments with lower mean annual temperature and higher total annual precipitation. We also find that both CL and CH flower phenology has advanced across this time period. Conclusions Our results suggest that V. sororia has responded to lower temperatures and greater water availability by shifting reproductive strategy allocation away from selfing and toward potential outcrossing. This provides the first long‐term study of how climate change may affect relative allocation to potential outcrossing in species with mixed mating systems. By revealing that CL flowering is associated with low water availability and high temperature, our results suggest the production of obligately selfing flowers is favored in water limited environments.

Beyond the usual climate? Factors determining flowering and fruiting phenology across a genus over 117 years

“…Understanding phenological responses to different environmental factors requires long‐term data on the timing of plant reproductive events. Herbarium (Davis et al, 2015; Willis et al, 2017; Meineke et al, 2018; Austin et al, 2022) and citizen science records (Belitz et al, 2020; Iwanycki Ahlstrand et al, 2022) can provide a valuable source of such long‐term data. Many herbaria contain records spanning decades, if not centuries, with each record preserving a specimen's unique phenological phase at a certain time and place.…”

Balancing the risks of mating: biogeographic evidence of cleistogamy as a bet hedging strategy

“…However, determining which environmental conditions are optimal for each flower morph has been challenging and often contradictory. For example, increased cleistogamous flower production has been associated with decreases in temperature (Lord [1982], Oakley et al [2007]), but also increases in temperature (Austin et al [2022]); long days (Langer and Wilson [1965]), but also short days (Heslop-Harrison [1962]); higher density (Cheplick and Quinn [1983]), but also no relationship with density (Stølen and Shands [1975]); increased plant size (Joseph Trapp and Hendrix [1988]), but also decreased plant size (Berg and Redbo-torstensson [1998]). Further, there have been opposing observations in which seasons cleistogamous and chasmogamous flowers are favored.…”