A major goal of speciation research is to understand the processes involved in the earliest stages of the evolution of reproductive isolation. One important challenge has been to identify systems where lineages have very recently diverged and opportunities for hybridization are present. We conducted a comprehensive examination of the components of reproductive isolation across the life cycle of two subspecies of Clarkia xantiana, which diverged recently (ca. 65,000 bp). One subspecies is primarily outcrossing, but self-compatible, whereas the other is primarily selfing. The subspecies co-occur in a zone of sympatry but hybrids are rarely observed. Premating barriers resulted in nearly complete isolation in both subspecies with flowering time and pollinator preference (for the outcrosser over the selfer) as the strongest barriers. We found that the outcrosser had consistently more competitive pollen, facilitating hybridization in one direction, but no evidence for pollen-pistil interactions as an isolating barrier. Surprisingly, postzygotic isolation was detected at the stage of hybrid seed development, but in no subsequent life stages. This crossing barrier was asymmetric with crosses from the selfer to outcrosser most frequently failing. Collectively, the results provide evidence for rapid evolution of multiple premating and postzygotic barriers despite a very recent divergence time.
Ecogeography populations_Briscoe Runquist et al
This file contains all known populations of both subspecies of Clarkia xantina. The file also contains numbers assigned to the populations used in manuscripts, a short description of the site and UTM coordinates (Zone 11S).
F1 pollen viab and pollen prod_Briscoe Runquist et al
This file contains pollen counts and pollen viability determinations for both parental subspecies and F1 reciprocal hybrids from greenhouse grown plants. Pollen was counted for 2 aliquots and summed.
F1 polle viab and pollen prod_Briscoe Runquist et al .csv
F1 seed viab_Briscoe Runquist et al
This file contains the number of viable seeds (germinated + tetrazolium) for parental and F1 reciprocal crosses. FOr each fruit we assessed 20 seeds.
F1-growth_Briscoe Runquist et al
In this file, we have the growth of parentals and F1 reciprocal crosses from a greenhouse common garden. We counted the number of fully formed leaves on plants at the beginning of the initial growth phase and then 2 weeks later. Growth was determined by the number of leaves added. Plants were in different blocks which were measured on different days (noted).
Gametophyte_comp_Briscoe Runquist et al
We performed crosses using intra- and intersubspecific pollen (alternating the first pollen donor subspecies identity) in the greenhouse. We then counted the number of offspring that were hybrid from the total.
Phenology Data and RI calcs_Briscoe Runquist et al
This file contains the phenological and reproductive isolation calculations (using Sobel and Chen 2014) for each site at 4 different sites. We walked semi-permanent transects at each site for the flowering season and counted the number of flowers of each subspecies on the date noted.
Pollen tube growth_Briscoe Runquist et al
We performed intra- and intersubspecific crosses in a greenhouse for 2 sympatric populations of Clarkia xantiana. We applied single-donor pollen and noted the time that we pollinated and the time at which we fixed the style (4-6 hours). We then measured the length of the longest pollen tube and the length of the style and used the data to obtain growth rates and proportional distance.
Pollinator_transitions-constancy_Briscoe Runquist et al
This file contains all of the pollinator bouts that contained intersubspecific transitions in pollinator arrays of greenhouse grown sympatric plants that were placed out into the field. We noted the number of visits to each subspecies. We also noted the different numbers of each transition type. Transition categories are detoed "from_to" (i.e. "x_p" transition was from a xantiana to a parviflora). We also noted that parviflora may have different colors (pp = pink; wp = white; up = unknown) and the should sum to the category with only a "p". We also have separate entries using all flowers or plants only (no geitnogamy). The entries with all flowers used end in "_f".
Pollinator-pref-data_Briscoe Runquist et al
In pollinator arrays of greenhouse grown plants in the field, we watched plants in the arrays (position) and at each observation time noted the number of visits to a flower subspecies and the number of each type of flower subspecies. The file also contains information on the date of observation, the observer, and whether the observation took place in the morning or afternoon.
Single-donor crosses_Briscoe Runquist et al
We performed intra- and intersubspecific crosses in sympatric populations (crosses were only within populations) or allopatric populations (crosses were preformed in all combinations of all allopatric populations). There were 4 crosstypes (treatments) (1 = xantiana to xantiana), 2 = xantiana to parviflora; 3 = parviflora to xantiana; 4 = parviflora to parviflora). We counted the number of fully formed seeds, number of fertilized but aborted ovules, and the number of unfertilized ovules for each fruit collected.