Abstract
Variation in leaf morphology is correlated with environmental variables, such as precipitation, temperature and soil composition. Several studies have pointed out that individual plasticity can largely explain the foliar phenotypic differences observed in populations due to climatic change and have suggested that the environment plays an important role in the evolution of plant species by selecting for phenotypic variation. Thus, the study of foliar morphology in plant populations can help us identify the environmental factors that have potentially influenced the process of species diversification. In this study, we analyzed morphological variation in the leaf traits of the Ternstroemia lineata species complex (Penthaphylacaceae) and its relation to climatic variables across the species distribution area to identify the patterns of morphological differentiation within this species complex. Based on the collected leaves of 270 individuals from 32 populations, we analyzed nine foliar traits using spatial interpolation models and multivariate statistics. A principal component analysis identified three main morphological traits (leaf length and two leaf shape variables) that were used to generate interpolated surface maps to detect discrete areas delimited by zones of rapid change in the values of the morphological traits. We identified a mosaic coarse-grain pattern of geographical distribution in the variation of foliar traits. According to the interpolation maps, we could define nine morphological groups and their geographic distributions. Longer leaves, spatulate leaves and the largest foliar area were located in sites with lower precipitation and higher seasonality of precipitation following a northwest–southeast direction and following significant latitudinal and longitudinal gradients. According to the phenogram of the relationships of the nine morphological groups based on morphological similarity, the putative species and subspecies of the T. lineata species complex did not show a clear pattern of differentiation. In this study, we found a complex pattern of differentiation with some isolated populations and some other contiguous populations differentiated by different traits. Further genetic and systematic studies are needed to clarify the evolutionary relationships in this species complex.
Highlights
Intraspecific variation is one of the main sources of information for recognizing evolutionary patterns
The higher loading values were associated with leaf length (TL and LL) and width (DW and MW), and the second and third components were associated with leaf shape (WLR and DWLR, respectively) (Table 2)
The longest leaves occurred in southern Mexico (Sierra Madre del Sur), and the plants with the shortest leaves were mainly located in the southernmost region of the distribution (Sierra Norte y Los Altos de Chiapas and Sierra Madre de Chiapas and Cuchumatanes) and a small area in the western part of the Eje Neovolcánico (Fig. 3A)
Summary
Intraspecific variation is one of the main sources of information for recognizing evolutionary patterns. Identifying the causes of intraspecific variation is essential to understanding the evolutionary processes that maintain diversity and promote speciation (Futuyma, 1998). Variation occurs in populations of species that are separated in space, encompassing both the genotype and phenotype (Thorpe, 2002). The causes of phenotypic variation among individuals across the geographical distribution range of a species can be broadly divided into current environmental conditions within particular habitats and historical processes and phylogenesis (Thorpe, 1987; Peppe et al, 2011). Plant populations of the same species growing under different environmental conditions respond to different selection pressures, producing genetic and phenotypic divergence between populations (Ramsey, Cairns & Vaughton, 1994; Fenster & Stenøien, 2001; Albarrán-Lara et al, 2019). The leaf is the structure in which changes in morphology in response to their environment are more readily acquired by plants (Malhado et al, 2009a; Yang et al, 2015) because leaves are the organs that perform essential functions, such as photosynthesis and regulation of water content (Givnish, 1979; Wright et al, 2004; Adams & Ichiro, 2018; Tsukaya, 2018)
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