Divergence of developmental mechanisms within populations could lead to hybrid developmental failure, and might be a factor driving speciation in angiosperms. We investigate patterns of endosperm and embryo development in Mimulus guttatus and the closely related, serpentine endemic Mimulus nudatus, and compare them to those of reciprocal hybrid seed. We address whether disruption in hybrid seed development is the primary source of reproductive isolation between these sympatric taxa. M. guttatus and M. nudatus differ in the pattern and timing of endosperm and embryo development. Some hybrid seeds exhibit early disruption of endosperm development and are completely inviable, while others develop relatively normally at first, but later exhibit impaired endosperm proliferation and low germination success. These developmental patterns are reflected in mature hybrid seeds, which are either small and flat (indicating little to no endosperm) or shriveled (indicating reduced endosperm volume). Hybrid seed inviability forms a potent reproductive barrier between M. guttatus and M. nudatus. We shed light on the extent of developmental variation between closely related species within the M. guttatus species complex, an important ecological model system, and provide a partial mechanism for the hybrid barrier between M. guttatus and M. nudatus.
Growth from 1-5 days after pollination of immature seeds
This is a text file with size data from immature seeds derived self-pollination of Mimulus guttatus and M. nudatus accession and sympatric, reciprocal M. guttatus x M. nudatus hybrids. M. guttatus accessions are CSS4 and DHR14; M. nudatus accessions are CSH10 and DHRo22. CSS4 and CSH10 are sympatric; DHR14 and DHRo22 are sympatric. Hybrid seeds either exhibit endopserm development from 2-5 days after pollination ('Hybrid Developing') or exhibit arrested developing starting at 2 days after pollination ('Hybrid Arrested'). CSS4x = self-pollinated CSS4, etc.; DAP = days after pollination; UO = unfertilized ovule. Size is measured from the chalazal to micropylar end and is given in mm. All crosses are female x male.
ImmatureSeedSize
Central cell and putative primary endopserm cell widths
This file contains measurements of the width of the central cell of Mimulus guttatus and M. nudatus accessions and of the putative primary endosperm cell of reciprocal hybrids. M. guttatus accessions are CSS4 and DHR14; M. nudatus accessions are CSH10 and DHRo22. CSS4 and CSH10 are sympatric; DHR14 and DHRo22 are sympatric. CSS4x = self-pollinated CSS4, etc.; DAP = days after pollination; UO = unfertilized ovule. Widths are measured from laser confocal images and are given in um. All crosses are female x male.
CCvsPENConfocalData.csv
Seed set and proportion seed type from self-pollinations and reciprocal M. guttatus x M. nudatus crosses
This file contains seed count data from self-pollinations of Mimulus guttatus and M. nudatus and sympatric, reciprocal M. guttatus x M. nudatus hybrids. In addition to total seed set, proportions of round, shriveled and flat seeds are given. M. guttatus accessions are CSS4 and DHR14; M. nudatus accessions are CSH10 and DHRo22. CSS4 and CSH10 are sympatric; DHR14 and DHRo22 are sympatric.
SeedSetandProportions.csv
Sizes of mature seeds from self-pollinated M. guttatus and M. nudatus accessions
This file contains sizes of the three seed morphs (round, shriveled and flat) derived from self-pollinations of Mimulus guttatus and M. nudatus accessions. M. guttatus accessions are CSS4 and DHR14. M. nudatus accessions are CSH10 and DHRo22. Size data are the length from the chalazal to micropylar end of mature seeds.
SeedMorphSizeData.csv