Abstract Detail

Population Genetics/Genomics

Trapnell, Dorset [1], Smallwood, Patrick [2], Dixon, Kingsley [3], Phillips, Ryan [4].

Persistence of a rare orchid in the past, present and future: insights from phylogeography and species distribution modeling.

Many species of orchids are naturally rare, raising questions regarding their levels of genetic diversity and structure within and among populations, and long-term persistence despite small population sizes. Rarity may have arisen in part through preferences exhibited by many orchids for spatially restricted habitats, as well as reliance on one or a few ecological partners, namely pollinators and/or mycorrhizal symbionts. Resolving how rare species persist is important for understanding the ecology of this hyper-diverse family, many members of which are of conservation concern. Eight populations of the rare terrestrial orchid Drakaea micrantha from Southwest Australia, that relies on sexually deceived male thynnine wasps for pollination, were genotyped with ten nuclear and five chloroplast simple sequence repeat (SSR) markers. We also constructed species distribution models (SDMs) using a maximum entropy (Maxent) approach for the last glacial maximum (LGM: ~22,000 YBP), Holocene (~6,000 YBP), present and future (2050 and 2070). For model construction we used post-1969 species occurrence records and 19 bioclimatic variables obtained from Worldclim.
Contrary to expectations, we found high nuclear (He = 0.776) and plastid (HHe = 0.640) genetic diversity and moderate genetic structure (G’STn = 0.172). We detected 32 private nuclear alleles and 15 private plastid haplotypes. Estimated effective population sizes (Ne) exceeded the census sizes of all populations. Drakaea micrantha is unusual in that it has a pronounced range disjunction within apparently suitable habitat. Extant populations are clustered in two regions separated by 149 km. A mp /ms value of 1.1 between these two regions indicates that pollinators and seeds have contributed equally to gene flow. At small spatial scales, within the western and eastern regions, mp /ms values are 10.2 and 10.6 respectively, suggesting that pollinators are more effective at moving genes within regions. SDMs for the past and present offer insights that allow broader interpretation of the genetic data. Suitable habitat for D. micrantha during the LGM (~22,000 YBP) was more extensive than at any time since, encompassing ca. 7,230,605 hectares. By ~6,000 YBP, habitat had shifted southward and contracted by ca. 34% but was still continuous. Some of this habitat loss was caused by rising seas that resulted from the warming climate. By the present however, suitable habitat had contracted another 70% into two regions that correspond with the current distribution of the species. Predictions for the future distribution are grim with little or no suitable habitat remaining. The high levels of genetic diversity in extant populations is likely a legacy of a species that was historically more common, and both widely and continuously distributed. Preservation of D. micrantha in the future will likely have to rely on human intervention and ex situ conservation measures.

1 - University Of Georgia, Plant Biology, 2502 Miller Plant Sciences Bldg , Athens, GA, 30602, United States
2 - University of Georgia, Plant Biology Department, 2502 Miller Plant Sciences Bldg, Athens, Georgia, 30602, United States
3 - Curtin University, Department of Environment and Agriculture, Kent Street, Bentley, 6102 WA, Australia
4 - La Trobe University, Department of Ecology, Environment and Evolution, Melbourne, Victoria 3086, Australia

none specified

Presentation Type: Oral Paper
Number: PGG1002
Abstract ID:74
Candidate for Awards:Margaret Menzel Award

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