The influence of landscape, climate and history on spatial genetic patterns in keystone plants (Azorella) on sub‐Antarctic islands

Abstract

The distribution of genetic variation in species is governed by factors that act differently across spatial scales. To tease apart the contribution of different processes, especially at intermediate spatial scales, it is useful to study simple ecosystems such as those on sub‐Antarctic oceanic islands. In this study, we characterize spatial genetic patterns of two keystone plant species, Azorella selago on sub‐Antarctic Marion Island and Azorella macquariensis on sub‐Antarctic Macquarie Island. Although both islands experience a similar climate and have a similar vegetation structure, they differ significantly in topography and geological history. We genotyped six microsatellites for 1,149 individuals from 123 sites across Marion Island and 372 individuals from 42 sites across Macquarie Island. We tested for spatial patterns in genetic diversity, including correlation with elevation and vegetation type, and clines in different directional bearings. We also examined genetic differentiation within islands, isolation‐by‐distance with and without accounting for direction, and signals of demographic change. Marion Island was found to have a distinct northwest–southeast divide, with lower genetic diversity and more sites with a signal of population expansion in the northwest. We attribute this to asymmetric seed dispersal by the dominant northwesterly winds, and to population persistence in a southwestern refugium during the Last Glacial Maximum. No apparent spatial pattern, but greater genetic diversity and differentiation between sites, was found on Macquarie Island, which may be due to the narrow length of the island in the direction of the dominant winds and longer population persistence permitted by the lack of extensive glaciation on the island. Together, our results clearly illustrate the implications of island shape and geography, and the importance of direction‐dependent drivers, in shaping spatial genetic structure.

EST‐SSR‐based landscape genetics ofPseudotaxus chienii, a tertiary relict conifer endemic to China

“…It can determine and quantify the relationship between complex and dynamic landscape and various genetic evolutionary processes (Storfer et al., 2007). Effects of geographical distance or environmental configuration on among‐population gene flow and genetic differentiation (e.g., IBD or IBE) have been revealed by using landscape genetics approaches (Chau et al., 2019; González‐Martínez et al., 2010; Hübner et al., 2009; Tóth et al., 2019). Importantly, adaptive genetic differentiation and local adaptation processes are found to be possibly associated with multiple environmental variables (Hancock et al., 2011; Manel et al., 2012; Mosca et al., 2014; Pal et al., 2020; Shih et al., 2018).…”

An open access geospatial database for the sub-Antarctic Prince Edward Islands

“…Similarly, studies that focus on indigenous or invasive species can now investigate the potential control of topographical and/or hydrological factors on their distribution at a larger scale. This can be applied to, for example, burrow-nesting bird species 13 , microorganisms 12,14 or plant communities. The effect of these topographic controls on variations in Table 1: A summary of the geospatial data and downloadable maps which can be accessed through the open access dataset.…”

“…9 Geospatial information of Marion Island's topography has aided scientific investigations by not only providing the backdrop for site selection and planning of sampling strategies but also interpreting and modelling landscape and ecosystem evolution. [11][12][13][14] Since the introduction of handheld Global Positioning Systems (GPS) in early 2000s, terrestrial multi-and transdisciplinary research on Marion Island has increasingly started to include assessment of fine-scale interactions within the landscape to understand ecosystem responses to past and present climate change, as well as the impacts of invasive species. [15][16][17][18] Individual-based population studies focusing on various animal species have, by necessity, also been structured around specific geographical localities at the Islands to aid in experimental design.…”

A spatial model of Marion Island's palaeo-ice extent

“…Scott 1985, Haussmann et al 2010, Rudolph et al 2020), whereas the distribution of various species and abiotic features can directly be related to the extent of palaeo-ice cover (e.g. Sumner & Meiklejohn 2004, Boelhouwers et al 2008, Hedding 2008, Chau et al 2019). A thorough understanding of Marion Island's glacial history, therefore, provides the baseline for the majority of ongoing terrestrial investigations (Nel et al 2021).…”