Effects of environmental heterogeneity on phenotypic variation of the endemic plant Lilium pomponium in the Maritime and Ligurian Alps

Abstract

Geographical limits of species’ distributions are assumed to be coincident with ecological margins, although this assumption might not always be true. Indeed, harsh environments such as Alpine and Mediterranean ecosystems may favour high phenotypic variability among populations, especially those in peripheral sites. Floral traits are often found to be less variable and less affected by environmental heterogeneity than vegetative traits because variation in the former may have negative effects on fitness. For this reason, it is important to quantify variation in floral traits and plant fecundity in study range limits. The objective of the study is to examine phenotypic variation and differences in reproduction in endemic Lilium pomponium in the Maritime and Ligurian Alps in relation to environmental variation across its distribution range. In this species, marginal climatic populations occur both in the peripheral and central geographical locations of the distribution range; hence, geographical and ecological gradients are not concordant. Floral trait variation is related to local environmental conditions with an array of interactions among resource availability, potential pollen limitation and population size that are differentially related to floral traits. Contrary to the general expectation, all central and peripheral populations had similar, moderate seed production with each group limited by different factors acting on different stages of the life-history strategy. Our results are in line with the idea that general expectations are confirmed only when its assumptions are met and that the differences in pollination environment along an environmental gradient may not be the main determinant of the distribution limit.

Niche Variation in Endemic Lilium pomponium on a Wide Altitudinal Gradient in the Maritime Alps

“…These results provide a parallel with the previous studies of genetic variability in relation to distribution limits and potential ecologically marginality [ 27 , 28 ]. Casazza et al [ 28 ] insist on the probable effects of local topographic variation that blur any possible relation between genetic variation and distribution limits.…”

“…This may affect population dynamics and genetics irrespective of distance from the geographical centre of the range. Furthermore, Macrì et al [ 27 ] found no direct relationship between the presence near range limits and phenotypic performance.…”

“…The Turban lily, Lilium pomponium L. is endemic to the Maritime and Ligurian Alps ( Figure 1 ) and occupies a wide altitudinal gradient [ 26 ]. There is no apparent link between gradients of climatic conditions and trait variation other than a shift towards smaller flowers at high elevation [ 27 ]. In a study of genetic variability, Casazza et al [ 28 ] found no decline in genetic variability in peripheral populations of this species relative to those in the centre of its distribution, as would be predicted by the so-called centre–periphery hypothesis [ 29 ].…”

When ecological marginality is not geographically peripheral: exploring genetic predictions of the centre-periphery hypothesis in the endemic plantLilium pomponium

“…This may explain why some small-sized populations near the geographical center but far from environmental center (i.e., P04, P05 and P08 in Table 3) have high F ST and Jost'D values and low Rho values. In fact, the high number of flowers per inflorescence detected in these small populations may favor geitonogamous pollination among flowers on the same plant (Macrì et al, 2021). In small sized populations of facultative-autogamous species, like L. pomponium (Casazza et al, 2018), geitonogamy may assure the production of a small, but regular number of seeds (Roberts et al, 2014), but at the cost in terms of reduced outcrossing (Lloyd, 1992;Harder & Barrett, 1995).…”

“…Moreover, in L. pomponium population connectivity may be further reduced by a decrease in suitable habitat due to (i) shrubland or forest expansion in mid-elevation of high elevation sites (Carlson et al, 2014) and/or (ii) urbanization in peripheral coastal lowland areas (Noble & Diadema, 2011). Given that gene flow in perennial plants mainly occurs by pollen transfer (Levin & Kerster, 1974;Ennos, 1994;Tarayre et al, 1997), pollen limitation detected in the southernmost populations of L. pomponium may further drive the genetic differentiation among these populations (Macrì et al, 2021).…”