Mary V. Ashley

Microsatellite analysis of seed dispersal and parentage of saplings in bur oak, Quercus macrocarpa

Microsatellite analysis was used to examine parentage and spatial distributions of 62 adult bur oaks Quercus macrocarpa, and 100 saplings in a single stand. Using genotypes scored by PCR products at four microsatellite loci, we determined that 94 saplings matched at least one parent in the stand. Saplings often occur as dense clusters of half‐sibs around the presumed maternal parent, and only four adults were seed parents to a large proportion of the saplings sampled. A stump apparently was the seed parent of the largest cluster of half‐sibs, which occupied a sizeable light gap opened up by the death of their maternal tree. Approximately half of the saplings appeared to have grown from seeds that had not been removed after falling from the tree, and half from seeds that were dispersed beyond the crown of their maternal parent. Long‐distance seed dispersal may be more common than has been previously reported. Extremely high levels of long‐distance pollination were indicated, and pollen donors within the stand were generally distributed randomly around maternal trees. More than half of the saplings had paternal parents outside of the stand. This study demonstrates the utility of microsatellite analysis for studying mating systems, seed dispersal and seedling establishment in natural plant populations.

Noninvasive paternity assignment in Gombe chimpanzees

The relative success of chimpanzee male mating strategies, the role of male dominance rank and the success of inbreeding avoidance behaviour can only be assessed when paternities are known. We report the probable paternities of 14 chimpanzees included in a long‐term behavioural study of chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania. DNA samples were collected noninvasively from shed hair and faeces and genotyped using 13–16 microsatellite loci characterized in humans. All 14 offspring could be assigned to fathers within the community. While there is a positive relationship between male rank and reproductive success, we demonstrate that a range of male mating strategies (possessiveness, opportunistic mating and consortships) can lead to paternity across all male ranks. Several adult females were at risk of breeding with close male relatives. Most successfully avoided close inbreeding but in one case a high‐ranking male in the community mated with his mother and produced an offspring. In contrast to recent data on chimpanzees (P. t. verus) from the Taï forest, Côte d’Ivoire, no evidence of extra‐group paternity was observed in our study. Reanalysis of Taï data using a likelihood approach casts doubt on the occurrence of extra‐group paternity in that community as well.

Evolutionarily enlightened management

Here we review growing evidence that microevolutionary changes may often be rapid and, in many cases, occur on time frames comparable to human disturbance and anthropogenic change. Contemporary evolutionary change has been documented in relatively pristine habitats, in disturbed populations, under captive management, and in association with both intentional and inadvertent introductions. We argue that evolutionary thinking is thus relevant to conservation biology and resource management but has received insufficient consideration. Ignoring evolution may have a variety of consequences, including unpredicted evolutionary responses to disturbance and naive or inappropriate management decisions. Philosophically, we must also grapple with the issue of whether the evolution of adaptations to disturbance and degraded habitats is sometimes beneficial or something to be rigorously avoided. We advocate promoting evolutionarily enlightened management [Lecture Notes in Biomathematics 99 (1994) 248], in which both the ecological and evolutionary consequences of resource management decisions are considered.

The paradox of forest fragmentation genetics

Theory predicts widespread loss of genetic diversity from drift and inbreeding in trees subjected to habitat fragmentation, yet empirical support of this theory is scarce. We argue that population genetics theory may be misapplied in light of ecological realities that, when recognized, require scrutiny of underlying evolutionary assumptions. One ecological reality is that fragment boundaries often do not represent boundaries for mating populations of trees that benefit from long-distance pollination, sometimes abetted by long-distance seed dispersal. Where fragments do not delineate populations, genetic theory of small populations does not apply. Even in spatially isolated populations, where genetic theory may eventually apply, evolutionary arguments assume that samples from fragmented populations represent trees that have had sufficient time to experience drift, inbreeding, and ultimately inbreeding depression, an unwarranted assumption where stands in fragments are living relicts of largely unrelated predisturbance populations. Genetic degradation may not be as important as ecological degradation for many decades following habitat fragmentation.

Characterization of highly variable (GA/CT)n microsatellites in the bur oak, Quercus macrocarpa

The objective of this study was to ascertain the usefulness of polymerase chain reaction (PCR)-based microsatellite analysis for studying pollination and parentage in a wind-pollinated temperate tree. A small insert genomic library of the bur oak (Quercus macrocarpa) was constructed and screened for the presence of (CA/GT)n and (GA/CT)n repeats. The proportion of positive clones yielded estimates of 3×105 such dinucleotide repeats per genome, roughly comparable to abundances reported in other eukaryotic genomes. Thirteen positive clones were sequenced. In contrast to mammalian genomes, the (GA/CT)n motif was more abundant than the (CA/GT)n motif in these clones. The (GA/CT)n repeats also showed longer average repeat length (mean n=16.2 versus 7.3), suggesting that they are better candidates for yielding polymorphic genetic markers in oak genomes. Indeed, a survey of adult bur oaks and offspring in a small stand in northern Illinois at 3 of these (GA/CT)n microsatellite loci revealed Mendelian inheritance and extremely high levels of polymorphism, with the number of alleles at each locus ranging from 11–20 and heterozygosity ranging from 0.66 to 0.75. These results, indicating that (GA/CT)n microsatellites are both abundant and highly polymorphic in the bur oak genome, suggest that such genetic markers have tremendous potential for applications for studies of parentage, pollination and dispersal in temperate trees.

Plant Parentage, Pollination, and Dispersal: How DNA Microsatellites Have Altered the Landscape

DNA microsatellites provide plant ecologists with molecular markers precise enough to assign parentage to seeds and seedlings. This allows the exact distance and trajectory of successful pollen to be traced to characterize pollination patterns. Parentage assignment of established seedlings also allows researchers to accurately determine how far new recruits have traveled from their seed parent. This paper reviews the history and development of molecular parentage assignment in studies of native plants, as well as the limitations and constraints to this approach. This paper also reviews 53 articles published in the past 15 years that use parentage assignment to study pollination and seed dispersal in native plants. These parentage studies have overturned many common assumptions regarding pollen and seed dispersal patterns. They show that long-distance dispersal of pollen is common in both wind and animal dispersed systems, with average pollination distances commonly being hundreds of meters. The pollination neighborhood is often extremely large, and simple dispersal functions based on distance alone fail to make accurate predictions of pollination. Rather than hindering gene flow, fragmentation and isolation sometimes, and perhaps even commonly, results in increased pollination distances. Studies of seed dispersal using parentage assignment have also yielded some surprises. We now know that it may be erroneous to assume that seeds growing under the crown of a conspecific adult are growing beneath their mother, or that seed dispersal distances are more limited than pollen dispersal distances. Taken together, the studies to date demonstrate that both seed and pollen dispersal are quite complex phenomena influenced by many ecological processes.

Global phylogeography and seascape genetics of the lemon sharks (genus Negaprion)

Seascapes are complex environments, and populations are often isolated by factors other than distance. Here we investigate the role of coastal habitat preference and philopatry in shaping the distribution and population structure of lemon sharks. The genus Negaprion comprises the amphiatlantic lemon shark (N. brevirostris), with a relict population in the eastern Pacific, and its Indo‐West Pacific sister species, the sicklefin lemon shark (N. acutidens). Analyzing 138 individuals throughout the range of N. brevirostris (N = 80) and N. acutidens (N = 58) at microsatellite loci (nine and six loci, respectively) and the mitochondrial control region, we find evidence of allopatric speciation corresponding to the Tethys Sea closure (10–14 million years ago) and isolation of the eastern Pacific N. brevirostris population via the emergence of the Isthmus of Panama (~3.5 million years ago). There is significant isolation by oceanic distance (R2 = 0.89, P = 0.005), defined as the maximum distance travelled at depths greater than 200 m. We find no evidence for contemporary transatlantic gene flow (m, M = 0.00) across an oceanic distance of ~2400 km. Negaprion acutidens populations in Australia and French Polynesia, separated by oceanic distances of at least 750 km, are moderately differentiated (FST = 0.070–0.087, P≤ 0.001; ΦST = 0.00, P = 0.99), with South Pacific archipelagos probably serving as stepping stones for rare dispersal events. Migration between coastally linked N. brevirostris populations is indicated by nuclear (m = 0.31) but not mitochondrial (m < 0.001) analyses, possibly indicating female natal site fidelity. However, philopatry is equivocal in N. acutidens, which has the lowest control region diversity (h = 0.28) of any shark yet studied. Restricted oceanic dispersal and high coastal connectivity stress the importance of both local and international conservation efforts for these threatened sharks.

The breeding biology of lemon sharks at a tropical nursery lagoon

Surprisingly little is known about the reproductive behaviour and breeding biology of most shark species, especially in natural populations. Here, we characterize reproductive patterns and use of a natal nursery at Bimini, Bahamas by lemon sharks, Negaprion brevirostris. We systematically and exhaustively sampled young lemon sharks at Bimini annually from 1995 to 2000 and opportunistically sampled adults over the same period. Out of the 897 young sharks sampled, 119 could be assigned to five sampled mothers using microsatellite genotyping. Reproductive females showed strong philopatry to the nursery, returning to Bimini every two years to give birth. Each of these females may rely entirely on the Bimini nursery for recruitment. The protection of known nursery grounds should therefore figure prominently in conservation efforts for large coastal shark species. The reconstruction of paternal genotypes indicates that litters are sired by multiple males, and females mate with different males nearly every breeding cycle. The ubiquitous polyandry reported here raises the possibility that genetic incompatibility and post–copulatory paternity–biasing mechanisms may operate in viviparous sharks.

Is pollen limited? The answer is blowin' in the wind

Abstract Pollen from wind-pollinated trees has traditionally been assumed to be abundant and to travel long distances, resulting in extensive gene flow. However, recent empirical work by Knapp et al. , genetic analysis by Sork et al. , and theoretical models by Satake and Iwasa conclude that short-distance dispersal of limited pollen might be common and play an important role in causing the highly variable seed production (masting) frequently observed in such species. Pollen movement might be sufficiently restricted that increased fragmentation could ultimately bring about reproductive failure in some species.

Population genetic structure of the lemon shark (Negaprion brevirostris) in the western Atlantic: DNA microsatellite variation.

DNA microsatellite markers were used to characterize the population genetic structure of the lemon shark, Negaprion brevirostris, in the western Atlantic. This study demonstrates for the first time the usefulness of microsatellites to study population genetic structure and mating systems in the Chondricthyes. Lemon sharks (mostly juveniles) were sampled non‐destructively from four locations, Gullivan Bay and Marquesas Key in Florida, Bimini, Bahamas, and Atol das Rocas, Brazil. At least 545 individuals were genotyped at each of four dinucleotide loci. The number of alleles per locus ranged from 19 to 43, and expected heterozygosities ranged from 0.69 to 0.90. Relatively little genetic structure was found in the western Atlantic, with small but significant values for estimators of FST and RST among populations, θ (0.016) and ρ (0.026), respectively. No sharp discontinuities were found between the Caribbean sites and Brazil, and most alleles were found at all four sites, indicating that gene flow occurs throughout the western Atlantic with no evidence for distinct stocks.