Pollen‐mediated gene dispersal within continuous and fragmented populations of a forest understorey species, Trillium cuneatum

Abstract

Pollen movement plays a critical role in the distribution of genetic variation within and among plant populations. Direct measures of pollen movement in the large, continuous populations that characterize many herbaceous plant species are often technically difficult and biologically unreliable. Here, we studied contemporary pollen movement in four large populations of Trillium cuneatum. Three populations, located in the Georgia Piedmont, are exposed to strong anthropogenic disturbances, while the fourth population, located in the Southern Appalachian Mountains, is relatively undisturbed. Using the recently developed TwoGener analysis, we extracted estimates of the effective number of pollen donors (N(ep)), effective mating neighbourhood size (A(ep)) and the average distance of pollen movement (delta) for each population. We extended the TwoGener method by developing inference on the paternal gametic contribution to the embryo in situations where offspring genotypes are inferred from seeds and elaiosomes of species with bisporic megagametogenesis. Our estimates indicate that maternal plants do not sample pollen randomly from a global pool; rather, pollen movement in all four populations is highly restricted. Although the effective number of pollen donors per maternal plant is low (1.22-1.66) and pollen movement is highly localized in all populations, N(ep) in the disturbed Piedmont populations is higher and there is more pollen movement than in the mountains. The distance pollen moves is greater in disturbed sites and fragmented populations, possibly due to edge effects in Trillium habitats.

Restricted pollen flow of Dieffenbachia seguine populations in fragmented and continuous tropical forest

“…We have recorded density of flowering ramets in each population and assumed that the effective number is only 10% of the census number of flowering adults at any specific time (Gonzales et al, 2006). We used a t-test to compare the average A ep -values of population fragments (as a group) and continuous forest populations (as a group).…”

“…Populations of D. seguine are large, but each population has only a few reproductive individuals at any one time. This species is pollinated by small beetles with limited tolerance of open conditions (Cuartas-Hernández, 2006), so the situation provides an interesting opportunity to study mating and pollen dispersal (Robledo-Arnuncio and Gil, 2005;Gonzales et al, 2006). We have reported earlier that natural populations of D. seguine at the Los Tuxtlas Reserve are genetically highly structured and diverse, but fragmented populations, while having higher population density, exhibit reduced arrays of multilocus genotypes (CuartasHernández and Nú ñ ez-Farfán, 2006).…”

A fragmented future for the forest flora

“…There is growing evidence that trees distributed among forest fragments can maintain some degree of genetic integration (Bittencourt and Sebbenn, 2007;Dunphy and Hamrick, 2007;Bacles and Ennos, 2008;Andrianoelina et al, 2009), and the same appears to be true of understory plant species (Gonzales et al, 2006;Cibrian-Jaramillo et al, 2009). However, maintaining gene flow and maintaining local population sustainability are two different things.…”

Effective range of reproductive interference exerted by an alien dandelion, Taraxacum officinale, on a native congener

“…While some studies of other plants, mainly woody or wind-pollinated species, have shown that more distant individuals may contribute pollen (e.g., Dow and Ashley 1998;Dick et al 2003;García et al 2007;Busi et al 2008), short-range pollination has been reported in some herbaceous and animal-pollinated plants (Waser 1988;Campbell and Waser 1989;Godt and Hamrick 1993;Gonzales et al 2006). In dandelions, longdistance pollination from more than several meters away probably does occur.…”