Heterosis may result in selection favouring the products of long-distance pollen dispersal in Eucalyptus

• Published in: PloS one 2014-04, Vol.9 (4), p.e93811-e93811
• Main Authors: Costa E Silva, João, Potts, Brad M, Lopez, Gustavo A
• Format: Article
• Language: English
• Subjects: Adaptation; Age; Analysis; Animal behavior; Biology and Life Sciences; Crosses, Genetic; Dispersal; Dispersion; Ecology; Eucalyptus; Eucalyptus - genetics; Eucalyptus - growth & development; Eucalyptus - physiology; Eucalyptus globulus; Evolution; Extremities; Fitness; Gene flow; Genes; Genetic aspects; Genetic crosses; Genetics; Genomes; Geography; Heterosis; Hybrid Vigor - genetics; Hybrids; Immigration; Inbreeding; Inbreeding depression; Long distance; Mating; Parents; Plant reproduction; Planting; Pollen; Pollen - physiology; Pollination; Probability; Progeny; Seed Dispersal - genetics; Seeds; Selection, Genetic; Survival; Tasmania; Trees; Trees - genetics; Trees - growth & development
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0093811

Using native trees from near the northern and southern extremities of the relatively continuous eastern distribution of Eucalyptus globulus in Tasmania, we compared the progenies derived from natural open-pollination (OP) with those generated from within-region and long-distance outcrossing. Controlled outcrossing amongst eight parents - with four parents from each of the northern and southern regions - was undertaken using a diallel mating scheme. The progeny were planted in two field trials located within the species native range in southern Tasmania, and their survival and diameter growth were monitored over a 13-year-period. The survival and growth performances of all controlled cross types exceeded those of the OP progenies, consistent with inbreeding depression due to a combination of selfing and bi-parental inbreeding. The poorer survival of the northern regional (♀N♂N) outcrosses compared with the local southern regional outcrosses (♀S♂S) indicated differential selection against the former. Despite this mal-adaptation of the non-local ♀N♂N crosses at both southern sites, the survival of the inter-regional hybrids (♀N♂S and ♀S♂N) was never significantly different from that of the local ♀S♂S crosses. Significant site-dependent heterosis was detected for the growth of the surviving long-distance hybrids. This was expressed as mid-parent heterosis, particularly at the more northern planting site. Heterosis increased with age, while the difference between the regional ♀N♂N and ♀S♂S crosses remained insignificant at any age at either site. Nevertheless, the results for growth suggest that the fitness of individuals derived from long-distance crossing may be better at the more northern of the planting sites. Our results demonstrate the potential for early-age assessments of pollen dispersal to underestimate realised gene flow, with local inbreeding under natural open-pollination resulting in selection favouring the products of longer-distance pollinations. Indeed, heterosis derived from long-distance pollinations may be sufficient to counter local mal-adaptation, at least in the first generation.