Mating system and early viability resistance to habitat fragmentation in a bird-pollinated eucalypt

Abstract

Habitat fragmentation has been shown to disrupt ecosystem processes such as plant-pollinator mutualisms. Consequently, mating patterns in remnant tree populations are expected to shift towards increased inbreeding and reduced pollen diversity, with fitness consequences for future generations. However, mating patterns and phenotypic assessments of open-pollinated progeny have rarely been combined in a single study. Here, we collected seeds from 37 Eucalyptus incrassata trees from contrasting stand densities following recent clearance in a single South Australian population (intact woodland ¼ 12.6 trees ha À1 ; isolated pasture ¼ 1.7 trees ha À1 ; population area ¼ 10 km 2 ). 649 progeny from these trees were genotyped at eight microsatellite loci. We estimated genetic diversity, spatial genetic structure, indirect contemporary pollen flow and mating patterns for adults older than the clearance events and open-pollinated progeny sired post-clearance. A proxy of early stage progeny viability was assessed in a common garden experiment. Density had no impact on mating patterns, adult and progeny genetic diversity or progeny growth, but was associated with increased mean pollen dispersal. Weak spatial genetic structure among adults suggests high historical gene flow. We observed preliminary evidence for inbreeding depression related to stress caused by fungal infection, but which was not associated with density. Higher observed heterozygosities in adults compared with progeny may relate to weak selection on progeny and lifetime-accumulated mortality of inbred adults. E. incrassata appears to be resistant to the negative mating pattern and fitness changes expected within fragmented landscapes. This pattern is likely explained by strong outcrossing and regular long-distance pollen flow.

Constraints to and conservation implications for climate change adaptation in plants

“…However there is evidence that gene flow dynamics may also be relatively robust to habitat fragmentation (e.g. Lowe et al 2005a;Wang et al 2011;Breed et al 2012b). In a study into the effects of habitat fragmentation on genetic structure of the wind-pollinated, gravity seed-dispersed chinquapin tree (Castanopsis sclerophylla) no significant difference was observed in genetic diversity or inbreeding between pre-and post-fragmented populations, and this was attributed to extensive pollen dispersal .…”

Mating patterns and pollinator mobility are critical traits in forest fragmentation genetics

“…A subset of the genotype data included in this study has been included in previous studies. This includes E. socialis data from Yookamurra Sanctuary and Monarto (n ¼ 47 maternal plants; Breed et al, 2012b) and E. incrassata data from Monarto (n ¼ 37 maternal plants; Breed et al, 2015).…”

“…As a consequence of reduced numbers of pollen sources, the correlated paternity within a given progeny array should increase. The effect of density on correlated paternity should again be a function of pollinator mobility, as more mobile pollinators should overcome greater distances between canopies more easily than less mobile pollinators, resulting in larger pollination neighbourhoods (Bianchi and Cunningham, 2012;Breed et al, 2015).…”

Paternity analysis reveals wide pollen dispersal and high multiple paternity in a small isolated population of the bird-pollinated Eucalyptus caesia (Myrtaceae)

“…As a bird-pollinated species with accentuated persistence in small, insular populations (Moran and Hopper, 1983;Byrne and Hopper, 2008), E. caesia is a model system to assess the generality of near-random mating patterns identified in some bird-pollinated banksias, and to test for beneficial genetic consequences of bird pollination, as predicted by the James Effect hypothesis (Krauss et al, 2009;Ritchie and Krauss, 2012). Furthermore, E. caesia presents an opportunity to study mating system and pollination in an intact, natural setting, whereas previous studies of pollen movement in bird-pollinated species in Australia have largely focussed on populations affected by recent habitat fragmentation Breed et al, 2012;Llorens et al, 2012;Ritchie and Krauss, 2012).…”