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Abstract Detail

Tropical Biology Section

Johnson, Melissa [1], Stacy, Elizabeth [2].

Evolution of reproductive barriers within a non-adaptive hyper-species-rich radiation of Hawaiian Cyrtandra (Gesneriaceae).

Purported non-adaptive radiations generate striking species-richness, yet they receive relatively little empirical attention. The Southeast Asian-Pacific angiosperm genus Cyrtandra (Gesneriaceae) comprises ca. 600 species, 58 of which are endemic to Hawaii. Although the genus as a whole is morphologically diverse, Hawaiian Cyrtandra species are markedly uniform, being white-flowered shrubs/trees with white fleshy fruits. The vast majority of species are also narrowly distributed within the understory of wet upland forests. To assess the importance of geographic isolation of small populations followed by reinforcement in secondary contact in the diversification of this group, reproductive barriers were examined among four species of Cyrtandra on Kauai (4.7 Myr) and Hawaii Island (0.6-0 Myr). Sympatric species on Kauai showed strong reproductive isolation at the seed germination stage, while sympatric species on Hawaii Island revealed asymmetric post-zygotic isolation through six-month seedling growth and survivorship (C. platyphylla), or no post-zygotic isolation (C. paludosa var. paludosa). These results are consistent with a model of species emergence in allopatry. However, the absence of reinforcement on either island suggests that evolution of pre-zygotic barriers between sympatric species may require more time, or may not be necessary to complete speciation in Hawaiian Cyrtandra. The current study provides insight into the evolution of reproductive barriers within a young lineage (<5 Myr old) that is still in the process of diversification. Our observations of two pairs of sympatric species revealed the presence of very strong post-zygotic barriers for three of the four species with earlier barriers operating between presumably older species on Kauai, and later barriers between presumably younger species on Hawaii Island. This result may indicate the evolution of significant post-zygotic isolation between allopatric populations relatively early in the divergence process (<1.5 Myr) and the evolution of earlier acting barriers from late-acting barriers. Lastly, our inter-island crosses between species that have been geographically isolated for possibly millions of years revealed a mix of strengths and stages of post-zygotic barriers. These findings likely reflect true variation in reproductive isolation between these Cyrtandra species of unknown phylogenetic relationship.

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1 - Claremont Graduate University, Botany, Rancho Santa Ana Botanic Garden, 1500 N. College Ave., Claremont, CA, 91711, USA
2 - University of Hawaii At Hilo, Department of Biology, 200 West Kawili Street, Hilo, HI, 96720, USA

reproductive isolation
non-adaptive radiation
Allopatric speciation.

Presentation Type: Oral Paper:Papers for Sections
Session: 25
Location: Rosedown/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 11:00 AM
Number: 25004
Abstract ID:702
Candidate for Awards:None

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