Population at the edge: increased divergence but not inbreeding towards northern range limit in Acer campestre

Abstract

Ecological conditions shape natural distribution of plants. Populations are denser in optimal habitats but become more fragmented in the areas of suboptimal environmental conditions. Usually, fragmentation increases towards the limits of species distribution. Fragmented populations are often characterised by decreased genetic variation, and this effect is frequent in peripheral populations, mostly due to the reduced effective population size. Interestingly, the genetic consequences of fragmentation seem to be relatively weak in forest trees. Using microsatellite markers, we assessed the impact of population fragmentation on the genetic structure of a European tree species Acer campestre. Within the study area, this medium-size wind-dispersed and insect-pollinated tree reveals a gradual decrease in population density towards the northern range limit. Over the distance of 150 km, we detected the significant decrease in allelic richness, heterozygosity as well as an increase in the rate of population divergence along with latitude. On the other hand, we failed to show that the observed patterns of genetic structure result from the variation in population densities. Moreover, inbreeding levels revealed no association with both density and geographic location, suggesting that pollen limitation does not occur, even at the range margin. As we showed that there is no difference in a dispersal scale between low-and highdensity populations in the study species, we argue that the genetic structure is a result of postglacial recolonization. However, unlike many other forest trees, A. campestre showed the sharp latitudinal genetic pattern at a very restricted spatial scale. Limited dispersal and high fragmentation are likely the reasons.

Influence of northern limit range on genetic diversity and structure in a widespread North American tree, sugar maple (Acer saccharumMarshall)

“…Large variation was observed in the inbreeding coefficient estimates for sugar maple populations in Québec ( F IS = 0.138, range: −0.051–0.302). Similar results were reported with microsatellites for Acer takesimense ( F IS = 0.28, range: 0.08–0.47; Takayama, Sun, & Stuessy, ) and for A. campestre ( F IS = 0.107, range: 0.015–0.300; Chybicki et al., ; Table ).…”

“…() best supported the range shift model as the determinant of genetic structure for Juglans cinerea L. In a recent study, Chybicki et al. () reported lower genetic variation and higher divergence rates in A. campestre populations that were located closer to the northern margin of the species range. They interpreted this latitudinal genetic gradient as a result of postglacial recolonization because no relationship was found between A. campestre density and genetic structure.…”

“…() ( H E = 0.689), and other species such as Acer mono Maxim. ( H E = 0.80, range: 0.70–0.85; Kikuchi, Shibata, Tanaka, Yoshimaru, & Niiyama, ; Takayama, Sun, & Stuessy, ) and Acer campestre L. ( H E = 0.602, range: 0.509–0.699; Chybicki, Waldon‐Rudzionek, & Meyza, ; Table ).…”

Morphometrical methods as tools for identifying field maple (Acer campestre L.) trees

“…No attempt to discriminate populations or individuals of a single species of Acer L. by morphological means have been published previously. However, Guarino et al (2008) studied the genetic variability and genetic structure of natural populations of several Italian Acer species, including A. campestre and Chybicki et al (2014) used microsatellite markers to assess the impact of population fragmentation on the genetic structure in field maples in Poland. In Sweden the only maple to be studied genetically is Acer platanoides L. represented in a larger survey together with Betula pendula Roth in northern Europe (Rusanen et al 2003).…”

A methodology to determine the maximum value of weighted Gini–Simpson index

“…Considering a simplex of dimension m − 1 defined as , where the numbers p i denote relative extension measures, usually probabilities or proportions, 1 Simpson’s index, originally mentioned as a measure of the concentration of a classification (Simpson 1949 ) is evaluated with the formula and its symmetric form D = 1 − C is usually named 2 Gini–Simpson index (e.g., Rao 1982 ), and used as a measure of biological or phylogenetic diversity until today (e.g., Tryjanowski et al 2015 ; Zaller et al 2015 ; Brocchieri 2015 ), since we can rewrite the correspondent formula as and interpret it associated to the probability that any two random individuals in a population are assigned to different populations or genetic clusters (e.g., Chybicki et al 2014 ). In biological studies, more than seven decades ago, the term p i (1 − p i ) was already mentioned as the contribution to the sampling variance due to any one species being sometimes observed and sometimes not (Fisher et al 1943 ), later stated as the probability of interspecific encounters (Hurlbert 1971 ), or the probability of drawing two individuals of different type from a given collection (Gregorius and Gillet 2008 ).…”