Collinsia

Abstract: Collinsia verna, blue-eyed Mary, has floral attributes of an outcrossing species, yet most flowers readily self-pollinate under greenhouse conditions. Here we describe the mechanism of self-pollination in C. verna via changes in relative positions of the stigma and anthers and late timing of receptivity, resulting in delayed selfing. Each flower contains four anthers that dehisce sequentially over -1 wk. Pollen that is not collected by pollinators accumulates in the keel petal and retains high viability (>80% pollen germination) up to the time of corolla abscission. The stigmatic surface does not become receptive until after the third anther dehisces. This overlap in the sexual phases is concurrent with a change in herkogamy during floral development. In most flowers (70%), the stigma has moved to the front of the keel and is positioned near the anthers when the third anther dehisces. Under field conditions, fruiting success of plants within pollinator exclosures was -75% of the fruiting success in open-pollinated plants (33% fruiting success via autogamy vs. 44% fruiting success, respectively). Collinsia iverna plants in pollinator exclosures exhibit variation in autogamy rates within natural populations (range 0-80%). In addition, only half of naturally pollinated, receptive flowers examined had pollen tubes growing in their styles. In contrast, shortly after corolla abscission, nearly all flowers examined (96%) had pollen tubes in their styles. Thus we find that in C. verna, autogamy occurs late in floral development, which has the potential to provide substantial reproductive assurance, and that individuals vary in their ability to set fruit through this mechanism. We suggest that delayed selfing mechanisms may be overlooked in other species and that variable pollinator availability may play a significant role in the maintenance of mixed mating in species with delayed selfing, such as C. verna.

Abstract: †Background and Aims How and why plants evolve to become selfing is a long-standing evolutionary puzzle. The transition from outcrossing to highly selfing is less well understood in self-compatible (SC) mixed-mating (MM) species where potentially subtle interactions between floral phenotypes and the environment are at play. We examined floral morphological and developmental traits across an entire SC MM genus, Collinsia, to determine which, if any, predict potential autonomous selfing ability when pollinators are absent (AS) and actual selfing rates in the wild, sm, and to best define the selfing syndrome for this clade. †Methods Using polymorphic microsatellite markers, we obtained 30 population-level estimates of sm across 19 Collinsia taxa. Species grand means for the timing of herkogamy (stigma‐anther contact) and dichogamy (stigmatic receptivity, SR), AS, floral size, longevity and their genetic correlations were quantified for 22 taxa. †Key Results Species fell into discrete selfing and outcrossing groups based on floral traits. Loss of dichogamy defines Collinsia’s selfing syndrome. Floral size, longevity and herkogamy also differ significantly between these groups. Most taxa have high AS rates (.80 %), but AS is uncorrelated with any measured trait. In contrast, sm is significantly correlated only with SR. High variance in sm was observed in the two groups. †Conclusions Collinsia species exhibit clear morphological and developmental traits diagnostic of ‘selfing’ or ‘outcrossing’ groups. However, many species in both the ‘selfing’ and the ‘outcrossing’ groups were MM, pointing to the critical influence of the pollination environment, the timing of AS and outcross pollen prepotency on sm. Flower size is a poor predictor of Collinsia species’ field selfing rates and this result may apply to many SC species. Assessment of the variation in the pollination environment, which can increase selfing rates in more ‘outcrossing’ species but can also decrease selfing rates in more ‘selfing’ species, is critical to understanding mating system evolution of SC MM taxa.

Abstract: The effects of one and two generations of inbreeding were studied in plants from four natural populations of the annual plant, Collinsia heterophylla, using inbred and outcrossed plants generated by hand pollinations to create expected inbreeding coefficients ranging from 0-0.75. The selfing rates of the populations were estimated using allozyme markers to range from 0.37-0.69. Inbreeding depression was mild, ranging from 5-40%, but significant effects were detected for characters measured at all stages of the life cycle. Fitness components declined significantly with the inbreeding coefficient, and regression of fitness characters on inbreeding coefficients gave no evidence of any strongly synergistic effects attributable to the different genetic factors that contribute to decline in fitness under inbreeding. The magnitude of inbreeding depression did not clearly decrease with the populations' levels of inbreeding. This is not surprising because the selfing rates are similar enough that it is unlikely that the populations have been characterized for long periods of time by these different inbreeding levels.