Patterns of Leaf and Fruit Morphological Variation in Marginal Populations of Acer tataricum L. subsp. tataricum

Abstract

Marginal populations are usually smaller and more isolated and grow in less favourable conditions than those at the distribution centre. The variability of these populations is of high importance, as it can support the adaptations needed for the conditions that they grow in. In this research, the morphological variability of eight Tatar maple (Acer tataricum L. subsp. tataricum) populations was analysed. Tatar maple is an insect-pollinated and wind-dispersed shrub/tree, whose northwestern distribution edge is in southeastern Europe. Morphometric methods were used to analyse the variability of the populations using leaf and fruit morphology. The research revealed significant differences between and within populations. Furthermore, differences in the distribution of the total variability were noted, which suggest that different evolutionarily factors affect different plant traits. Correlation analysis confirmed a weak dependency between the vegetative and generative traits. In addition, no evidence was found for the presence of isolation by environment (IBE). However, the Mantel test for isolation by distance (IBD) was significant for the leaf morphometric traits and non-significant for the fruit morphometric traits. Being the marginal leading-edge populations, they are younger and were less likely to have had time for adaptation to local environments, which would have resulted in the development of IBE. Overall, edge populations of Tatar maple were characterised by great morphological variability, which helps these populations in their response to the intensive selective pressures they face in their environment.

Keywords: environmental differentiation; geographical differentiation; leading-edge populations; morphometric analysis; plant morphology; plant variation; population variability.

Figure 1

Locations of the eight sampled Tatar maple (Acer tataricum L. subsp. tataricum) populations. Populations: P1—Odransko polje; P2—Lipovljani; P3—Veliki Grđevac; P4—Mali Grđevac; P5—Grubišno Polje; P6—Virovitica; P7—Požega; P8—Županja. The blue area represents the natural habitat of Tatar maple according to Bartha [33].

Figure 2

Measured leaf and fruit traits: LA—leaf area; LL—leaf length; MLW—maximum leaf width; PMLW—leaf length, measured from the leaf base to the point of maximum leaf width; LW1—leaf blade width at 50% of leaf blade length; LW2—leaf blade width at 90% of leaf blade length; PL—petiole length; LA1—angle closed by the main leaf vein (the centre of the leaf blade) and the line connecting the leaf blade base to a set point on the leaf margin at 10% of the total leaf blade length; and LA2—angle closed by the main leaf vein (the centre of the leaf blade) and the line connecting the leaf blade base to a set point on the leaf margin at 25% of the total leaf blade length; MA—mericarp area; ML—mericarp length; MMW—maximum mericarp width; PMMW—mericarp length, measured from the mericarp base to the point of maximum mericarp width; NW90—mericarp width at 90% of the fruit length; NL—nut length; NW—nut width; WA—wing angle.

Figure 3

Isolation by distance (IBD) in Tatar maple populations. Scatter plot of simple Mantel test showing the relationship between geographic and leaf phenotypic distances (r = 0.585, p = 0.0092, R² = 0.3421).