Outbreeding Depression Varies Among Cohorts of Ipomopsis Aggregata Planted in Nature

Abstract

Outbreeding depression in progeny fitness may arise from disruption of local adaptation, disruption of allelic coadaptation, or a combination of these "environmental" and "physiological" mechanisms. Thus the minimum spatial scale over which outbreeding depression arises should depend on the spatial scale of gene dispersal and (with an environmental mechanism) of change in selection regimes. We previously reported substantial outbreeding depression in lifetime fitness of progeny resulting from crosses among parents separated by 100 m in natural populations of the herbaceous plant Ipomopsis aggregata. In this paper we explore the effect of crossing distance on fitness in two additional experiments begun in 1987 and 1990. We planted seed progeny derived from partial diallel crossing designs in randomized blocks in maternal environments and scored emergence of seedlings, survival, and eventual flowering of individuals over the subsequent six to eight years. Nested within each diallel design were crossing distances of 1 m, 10 m, and 100 m. Compared to 1-m and 10-m progeny, 100-m progeny of the 1987 diallel suffered a significant reduction in seedling emergence, and both 1-m and 100-m progeny that survived to flower achieved lower lambda-values on average than 10-m progeny. Total outbreeding depression suffered by 100-m relative to 10-m progeny was approximately 10%, compared to approximately 30% in our earlier study of I. aggregata. Progeny of 10-m crosses also outperformed 1-m and 100-m progeny of the 1990 diallel by approximately 5%, but no difference among crossing distance treatments was significant. Thus, the magnitude of outbreeding depression in 100-m crosses varied among experiments. This is not surprising given likely spatial and temporal variation in gene flow and selection regimes, different population histories, and different parental and progeny environments. Characterizing outbreeding depression on the shortest spatial scales over which it is expressed, as well as its variation and causes, is worthwhile because it promises to shed light on the earliest stages of angiosperm speciation.

Does pollination limit tolerance to browsing in Ipomopsis aggregata ?

“…In the vicinity of the Rocky Mountain Biological Laboratory, Colorado, USA (RMBL, 2,900 m elevation) seeds germinate soon after snowmelt or the onset of summer rains and establish a single vegetative rosette that grows for 2-6 years before sending up a single flowering stalk and dying. Multiple flowering stalks and iteroparity are rare, and are generally restricted to instances where multiple rosettes form after the primary rosette has been damaged while the plant is a vegetative rosette (Juenger and Bergelson 2000b;Waser et al 2000;M. Price, N. Waser, A. Brody, and D. Campbell, unpublished data).…”

Gene-flow through space and time: dispersal, dormancy and adaptation to changing environments

“…This may be expected because both provide the possibility of risk reduction by averaging genotype fitness over spatial or temporal environmental variation. Additionally, dispersing away from the parent in either time or space also permits escape from crowding and sib competition and reduces the probability of inbreeding (Waser et al 2000;Ronce 2007;Vitalis et al 2013). Because of these shared effects on the fitness and the demographic dynamics of lineages, the spatial and temporal components of dispersal experience correlated evolutionary pressures.…”

Fluorescent dye particles as pollen analogues for measuring pollen dispersal in an insect-pollinated forest herb

“…As a result, dye dispersal might not accurately reflect realized pollen dispersal. For instance, discrimination against pollen of genetically related neighbours can lead to an increase in the distance of effective pollen flow (Campbell 1991), and discrimination against pollen from genetically dissimilar individuals can lead to a decrease in the distance of effective gene flow (Waser et al 2000). However, whether dye dispersal patterns can be used to estimate realized pollen dispersal has rarely been examined (Campbell 1991).…”