Botanic Gardens Trust, Sydney, Australia

Biodiversity adaptation transect Sydney

Marlien van der Merwe & Hannah McPherson - Post Doctoral Fellows

July 2012 saw the start of the second year of the collaborative ARC funded project investigating how floristic diversity changes across an environmental gradient in the Sydney region. The study area is between the coast and the Capertee valley, west of the Great Dividing Range.

In this project we are using a landscape-level approach to investigate taxonomic, functional and genetic turn-over along a natural environmental gradient. The project can roughly be divided into three parts all aiming at improving our knowledge of how and why diversity changes across natural gradients.

Part one is a plot-based study along a transect traversing the sandstone soils of the Sydney region, and exploring species turnover across altitudinal and rainfall gradients. This part of the project is now near completion. Specimen collection and identification, and abundance estimates were obtained for 27, 50 x 50 meter plots. In total, 332 woody species were recorded from the plots, with between 26 and 76 species per plot. Two volunteers, Brendan Molloy and Emma Oldman have helped us finalise species lists and abundance measures across all of the plots. A compilation of relevant functional traits is currently being gathered for each of the species found on the plots. This data will be used for biodiversity measures, in order to assess community diversity (alpha, beta, phylobeta, functional) among plots. In addition, fungal material from Proteaceae and Myrtaceae hosts was collected as surrogate for fungal diversity along the gradient (B. Summerell).

The second part of the project aims at contrasting plastic versus adaptive variation in two species co-occurring along this same environmental gradient. We selected two species found on the majority of the 27 plots, Isopogon anemonifolius and Petrophile pulchella (see figures). Seeds were collected from four environmentally differentiated plots and were germinated in controlled conditions. RNA was extracted from 25 pooled-seedlings representing each plot and each species. Transcriptome (i.e. RNA derived) data is currently being explored bio-informatically to obtain information on adaptive genes that are potentially under local selection.

The third part of the project aims to place genetic turnover across the transect into the broader context of genetic variation across the entire distributional range of these same species. For example, is altitudinal variation similar to latitudinal variation? For this part of the project further collections across the entire distribution of the selected species are in progress. Environmental niche-modelling was implemented to optimise collection from populations that represented the geographical and environmental extremes of the species’ distribution. Samples are currently being analysed using next generation sequencing techniques (the DArT technique) with the aim of discovering possible associations between genetic and environmental variation.





Petrophile pulchella
, one of the species that occur across 90% of the plots that was selected for part two and three of the project. Photograph: Susan Rutherford.
Petrophile pulchella seedlings ready for RNA extraction