Biparental Inbreeding and Interremnant Mating in a Perennial Prairie Plant: Fitness Consequences for Progeny in Their First Eight Years

Abstract

Despite fundamental importance to population dynamics, mating system evolution, and conservation management, the fitness consequences of breeding patterns in natural settings are rarely directly and rigorously evaluated. We experimentally crossed Echinacea angustifolia, a widespread, perennial prairie plant undergoing radical changes in distribution and abundance due to habitat fragmentation. We quantified the effects of both biparental inbreeding and crossing between remnant populations on progeny survival and reproduction in the field over the first eight years. Lifetime fitness is notoriously difficult to assess particularly for iteroparous species because of the long sequence and episodic nature of selection events. Even with fitness data in hand, analysis is typically plagued by nonnormal distributions of overall fitness that violate the assumptions of the usual parametric statistical approaches. We applied aster modeling, which integrates the measurements of separate, sequential, nonnormally distributed annual fitness components, and estimated current biparental inbreeding depression at 68% in progeny of sibling-mating. The effect of between-remnant crossing on fitness was negligible. Given that relatedness among individuals in remnant populations is already high and dispersal very limited, inbreeding depression may profoundly affect future dynamics and persistence of these populations, as well as their genetic composition. K E Y W O R D S :Aster life-history analysis, Echinacea angustifolia, genetic rescue, habitat fragmentation, inbreeding depression, outbreeding depression, restoration, self-incompatibility, tallgrass prairie.

Gene flow increases fitness at the warm edge of a species’ range

“…On the contrary, outcrossing may not always be beneficial, and outbreeding depression, resulting from effects of locally maladaptive alleles or gene combinations, can develop in successive generations (25). Little to no benefit of gene flow was shown in an experimentally subdivided population of the selfing species Triticum aestivum (26) and in matings among remnant prairie populations in the outcrossing species Echinacea angustifolia (27). In crosses between nonnative, diverged populations of the selfing plant, Avena barbata, Johansen-Morris and Latta (28) demonstrated that, although early-generation hybrids did not differ from the parental lineages in field and novel greenhouse conditions, late-generation hybrids had lower fitness.…”

Quantitative genetic study of the adaptive process

“…Lifetime fitness is the composite of survival over successive intervals and multiple components of reproduction, within reproductive episodes, as well as over possibly many episodes in a lifetime. Accordingly, fitness has a compound distribution that is far from Gaussian or any other standard sampling distribution (see for example, Figure 4 in Wagenius et al, 2010). Consequently, assumptions of standard methods, such as linear models, are routinely violated, necessitating caveats about statistical inferences and their implications (for example, Shaw, 1986) and sometimes multiple approaches to analysing the data at hand (Antonovics and Ellstrand, 1984).…”

Genetic decline and inbreeding depression in an extremely rare tree

“…Inbred offspring would not have survived during either stage of the life cycle, such as at seed production, germination, seedling growth stages, and so on, whereas outcrossed progeny having relatively higher fitness have a higher probability of survival to the present time. Such a positive relationship between the genetic relatedness of parents and offspring fitness has also been observed in other plants (Hirao 2010;Seltmann et al 2009;Wagenius et al 2010). Our results were inferred from dominant markers, which have lower powers than microsatellites in sibship and parentage assignments (Gerber et al 2000).…”