Spatial Scales of Pollen and Seed-Mediated Gene Flow in Tropical Rain Forest Trees

University of Michigan Department of Ecology and Evolutionary Biology and Herbarium 830 North University Avenue Ann Arbor MI 48109 USA
Tropical Plant Biology (Impact Factor: 1.52). 04/2008; 1(1):20-33. DOI: 10.1007/s12042-007-9006-6


Gene flow via seed and pollen is a primary determinant of genetic and species diversity in plant communities at different
spatial scales. This paper reviews studies of gene flow and population genetic structure in tropical rain forest trees and
places them in ecological and biogeographic context. Although much pollination is among nearest neighbors, an increasing number
of genetic studies report pollination ranging from 0.5–14km for canopy tree species, resulting in extensive breeding areas
in disturbed and undisturbed rain forest. Direct genetic measures of seed dispersal are still rare; however, studies of fine
scale spatial genetic structure (SGS) indicate that the bulk of effective seed dispersal occurs at local scales, and we found
no difference in SGS (Sp statistic) between temperate (N = 24 species) and tropical forest trees (N = 15). Our analysis did find significantly higher genetic differentiation in tropical trees (F
ST = 0.177; N = 42) than in temperate forest trees (F
ST = 0.116; N = 82). This may be due to the fact that tropical trees experience low but significant rates of self-fertilization and bi-parental
inbreeding, whereas half of the temperate tree species in our survey are wind pollinated and are more strictly allogamous.
Genetic drift may also be more pronounced in tropical trees due to the low population densities of most species.

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    • "The distance over which reproduction occurs defines the local population (Hartl 2000; Conner & Hartl 2004; Waples & Gaggiotti 2006). The spatial extent of gamete and offspring dispersal also determine the degree of inbreeding within and genetic structure among populations of a species (Jain 1976; Hamrick 1982; Dick et al. 2008). Simultaneous hermaphroditism, a common mating system in sessile organisms, may influence the degree of selfing vs. outcrossing (reviewed in (Goodwillie et al. 2005; Jarne & Auld 2006 ), extent of correlatedpaternity (Ritland 1989Ritland , 2002) among siblings from the same mother (i.e., single versus multiple matings/ multiple paternity; Johnson & Yund 2007; Tani et al. 2009), and variation in the extent of biparental inbreeding among close relatives (Ledoux et al. 2010; Li et al. 2012). "
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    ABSTRACT: Within populations of brooding sessile corals, sperm dispersal constitutes the mechanism by which gametes interact and mating occurs, and forms the first link in the network of processes that determine species-wide connectivity patterns. However, almost nothing is known about sperm dispersal for any internally fertilizing coral. In this study, we conducted a parentage analysis on coral larvae collected from an area of mapped colonies, in order to measure the distance sperm disperses for the first time in a reef-building coral and estimated the mating system characteristics of a recently identified putative cryptic species within the Seriatopora hystrix complex (ShA; Warner et al. 2015). We defined consensus criteria among several replicated methods (Colony 2.0, Cervus 3.0, MLTR v3.2) to maximize accuracy in paternity assignments. Thirteen progeny arrays indicated that this putative species produces exclusively sexually-derived, primarily outcrossed larvae (mean tm =0.999) in multiple paternity broods (mean rp =0.119). Self-fertilization was directly detected at low frequency for all broods combined (2.8%), but comprised 23% of matings in one brood. Although over 82% of mating occurred between colonies within 10 m of each other (mean sperm dispersal = 5.5 m ±4.37 SD), we found no evidence of inbreeding in the established population. Restricted dispersal of sperm compared to slightly greater larval dispersal appears to limit inbreeding among close relatives in this cryptic species. Our findings establish a good basis for further work on sperm dispersal in brooding corals and provide the first information about the mating system of a newly identified and abundant cryptic species. This article is protected by copyright. All rights reserved.
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    • "A lack of biparental inbreeding—or any inbreeding (Table 2)—in the studied population can be explained by the absence of SGS in the adult generation and by the occurrence of pollen flow over long distances. This is in contrast to several other fragmented tree species that have shown elevated levels of mating between related individuals (Ismail et al., 2012; Tambarussi, 2013), genetic structuring (Dubreuil et al., 2010; Ismail et al., 2012; Saro et al., 2014) and inbreeding (Fuchs et al., 2003; Jump and Peñuelas, 2006; Kettle et al., 2007; Dick et al., 2008; Vranckx et al., 2011; Zhang et al., 2012; Tambarussi, 2013; Finger et al., 2014). The elevated outcrossing rates, accompanied by moderate values for the estimated paternity correlations observed in this study, strongly corroborate the high number of effective pollen donors involved in seed production in C. estrellensis. "
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    ABSTRACT: Here, we explore the mating pattern and genetic structure of a tropical tree species, Cariniana estrellensis, in a small population in which progeny arrays (n=399), all adults (n=28) and all seedlings (n=39) were genotyped at nine highly informative microsatellite loci. From progeny arrays we were able to identify the source tree for at least 78% of pollination events. The gene immigration rates, mainly attributable to pollen, were high, varying from 23.5 to 53%. Although gene dispersal over long distance was observed, the effective gene dispersal distances within the small population were relatively short, with mean pollination distances varying from 69.9 to 146.9 m, and seed dispersal distances occurring up to a mean of 119.6 m. Mating system analyses showed that C. estrellensis is an allogamous species (tm=0.999), with both biparental inbreeding (tm−ts=−0.016) and selfing rates (s=0.001) that are not significantly different from zero. Even though the population is small, the presence of private alleles in both seedlings and progeny arrays and the elevated rates of gene immigration indicate that the C. estrellensis population is not genetically isolated. However, genetic diversity expressed by allelic richness was significantly lower in postfragmentation life stages. Although there was a loss of genetic diversity, indicating susceptibility of C. estrellensis to habitat fragmentation, no evidence of inbreeding or spatial genetic structure was observed across generations. Overall, C. estrellensis showed some resilience to negative genetic effects of habitat fragmentation, but conservation strategies are needed to preserve the remaining genetic diversity of this population.
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    • "low population density (ca. one reproductive tree × ha -), self-incompatibility systems and their frequent dependence on animals for pollination (Cunningham, 2000; Lowe et al., 2005; Dick et al., 2008). "
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