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Effects of crossing distance on offspring fitness and developmental stability in Dalechampia scandens (Euphorbiaceae)¹

²Dept. of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway; ³Alaska Natural Heritage Program, Environment and Natural Resources Inst., University of Alaska, Anchorage, Alaska 99501 USA; ⁴Dept. of Biological Science, Florida State University, Tallahassee, Florida 32306 USA; ⁵Inst. of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775 USA; ⁶School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, UK

ABSTRACT

Crosses between genetically close and distant populations of Dalechampia scandens (Euphorbiaceae) were made to test whether the responses of various fitness components and measurements of developmental stability were affected by the outcrossing distance (level of outbreeding). Two fecundity traits, seed set and seed mass, decreased consistently with increasing level of outbreeding, and hybrids between the most divergent populations were sterile. Effects of the genetic distance between parental populations on viability traits, survival and vigor at 1 month of age, were highly idiosyncratic. Hybrids of one long-distance combination had no reduction in survival and vigor, while both traits were greatly reduced in the other long-distance combination. The expression of outbreeding depression on fecundity traits differed between reciprocal crosses in some hybrids but not others; thus, hybrid breakdown may have been due to cytoplasmic-by-nuclear gene interactions, reduced endosperm formation, or an interaction between progeny and maternal genotype. None of the measures of developmental stability had a consistent relationship with either genetic distance between parental populations or seedling vigor. These results suggest that fecundity and viability traits may be differentially affected by hybridization, probably due to differences in genetic architecture among populations. This study also confirms that developmental stability, as measured by the level of fluctuating asymmetry, is not a reliable index of genetic stress.

Key Words: cytonuclear interactions • Dalechampia scandens • Euphorbiaceae • fluctuating asymmetry • genetic distance • interpopulation hybridization • outbreeding depression • outcrossing distance

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