The influence of environmental factors on breeding system allocation at large spatial scales

Abstract

Plant breeding systems can vary widely among populations, yet few studies have investigated abiotic factors contributing to variation across a broad geographic range. Here we investigate variation in reproductive traits of Triodanis perfoliata (Campanulaceae), a species that exhibits dimorphic cleistogamy, a condition in which individual plants have both closed (selfing: cleistogamous: CL) and open (selfing or outcrossing: chasmogamous: CH) flowers. Chasmogamous production is theorized to be more costly because CH flowers have a larger exposed surface area and thus are more likely to lose more water than CL flowers. We examine relationships between abiotic conditions (temperature, precipitation and soil characteristics) and variation in breeding systems across 14 widespread populations using ordinary least squares models. We found that a large proportion of breeding system variation was described by climate and soil variables (R2 = 0.65–0.92). These results support the hypothesis that variation in the environment drives variation in breeding system allocation. Our broad geographic analyses provide a framework for mechanistic studies of cleistogamy, and employ a novel approach for examining reproductive traits and environmental variation at large scales. Given that two major components of our models were temperature and precipitation, our study further emphasizes the potential for ongoing climate change to alter plant breeding systems.

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

“…In other words, the occurrence of obligately selfing CL flowers in environments with high temperature and low precipitation suggests a desiccating effect of high temperature in environments that are already water limited. This supports previous findings that CL flowers in other dimorphic cleistogamic species are more likely to be produced in environments with limited water and high temperature (Jones et al, 2013;Ansaldi et al, 2018).…”

“…For example, in Viola (Violaceae)—a genus in which cleistogamy commonly occurs (Culley and Klooster, 2007)—CH flowers are often produced as temperatures rise in the spring, with CL flower production continuing as canopy closure reduces light availability (Culley, 2002). Furthermore, while interspecific variability exists in species with dimorphic cleistogamy (e.g., Campbell et al, 2016; Seguí et al, 2021), obligately selfing CL flowers are often produced in environments with low water availability and high temperature, suggesting that drought conditions are climatically stressful for many dimorphic cleistogamic species (e.g., Brown, 1952; Jones et al, 2013; Miranda and Vieira, 2016; Ansaldi et al, 2018).…”

“…This is vital to understand because reduced outcrossing rates can lead to inbreeding depression and increased extinction risk in changing environments (Stebbins, 1957; Beattie, 1976; Solbrig, 1976). Experimental climate manipulations (Jones et al, 2013) and environmental associations across spatial gradients (Ansaldi et al, 2018) have suggested that reproductive strategy allocation may be labile under a temporally changing climate. Nonetheless, a lack of long‐term time series data across the 20th century has precluded documentation of whether climate change is associated with shifts in reproductive strategy allocation in species with mixed mating systems.…”

“…Compared to hermaphroditic species with monomorphic flowers, dimorphism between CL and CH flowers allows reproductive strategy allocation to be readily quantified as the proportion of CL flowers that a plant produces. A higher proportion of CL flowers indicates greater investment in selfing relative to potential outcrossing (Eckert et al, 2010; Campbell et al, 2016; Ansaldi et al, 2018). Fitting with the hypothesis that selfing evolved as an adaptive strategy in stressful environments (Campbell et al, 1983; Lloyd, 1984; Berg and Redbo‐Torstensson, 1998; Oakley et al, 2007), environmental correlates of CL and CH flower production have been found in numerous species (e.g., Brown, 1952; Antlfinger et al, 1985; Bell and Quinn, 1986; Culley, 2002; Cortés‐Palomec and Ballard, 2006; Culley and Klooster, 2007; Campbell et al, 2016; Miranda and Vieira, 2016; Ansaldi et al, 2018).…”

“…A higher proportion of CL flowers indicates greater investment in selfing relative to potential outcrossing (Eckert et al, 2010; Campbell et al, 2016; Ansaldi et al, 2018). Fitting with the hypothesis that selfing evolved as an adaptive strategy in stressful environments (Campbell et al, 1983; Lloyd, 1984; Berg and Redbo‐Torstensson, 1998; Oakley et al, 2007), environmental correlates of CL and CH flower production have been found in numerous species (e.g., Brown, 1952; Antlfinger et al, 1985; Bell and Quinn, 1986; Culley, 2002; Cortés‐Palomec and Ballard, 2006; Culley and Klooster, 2007; Campbell et al, 2016; Miranda and Vieira, 2016; Ansaldi et al, 2018). For example, in Viola (Violaceae)—a genus in which cleistogamy commonly occurs (Culley and Klooster, 2007)—CH flowers are often produced as temperatures rise in the spring, with CL flower production continuing as canopy closure reduces light availability (Culley, 2002).…”