Seed-mediated connectivity among fragmented populations of Quercus castanea (Fagaceae) in a Mexican landscape.
OBJECTIVE
Anthropogenic fragmentation is an ongoing process in many forested areas that may create loss of connectivity among tree populations and constitutes a serious threat to ecological and genetic processes. We tested the central hypothesis that seed dispersal mitigates the impact of fragmentation by comparing connectivity and genetic diversity of adult vs. seedling populations in recently fragmented populations of the Mexican red oak Quercus castanea.


METHODS
Adult individuals, established before fragmentation, and seedlings, established after fragmentation, were sampled at 33 forest fragments of variable size (0.2 to 294 ha) within the Cuitzeo basin, Michoacán state, and genotyped using seven highly polymorphic chloroplast microsatellite markers (cpSSRs). To test whether seed dispersal retains connectivity among fragmented populations, we compared genetic diversity and connectivity networks between adults and progeny and determined the effect of fragment size on these values.


RESULTS
Seventy haplotypes were identified, 63 in the adults and 60 in the seedlings, with average within-population diversity (hS) values of 0.624 in the adults and 0.630 in the seedlings. A positive correlation of genetic diversity values with fragment size was found in the seedling populations but not in the adult populations. The network connectivity analysis revealed lower connectivity among seedling populations than among adults. The number of connections (edges) as well as other network properties, such as betweenness centrality, node degree and closeness, were significantly lower in the seedlings network.


CONCLUSIONS
Habitat fragmentation in this landscape is disrupting seed-dispersal-mediated genetic connectivity among extant populations.
Centro de Investigaciones en Ecosistemas. Universidad Nacional Autónoma de México UNAM, Antigua carretera a Pátzcuaro no. 8701, Col. Ex-hacienda San José de la Huerta, Morelia 58190 Michoacán, México.
M Luisa
ML
Herrera-Arroyo
Victoria L
VL
Sork
Antonio
A
González-Rodríguez
Víctor
V
Rocha-Ramírez
Ernesto
E
Vega
Ken
K
Oyama
D018742:DNA, Chloroplast / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D017753:Ecosystem; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D006239:Haplotypes; D008800:Mexico; D018895:Microsatellite Repeats / Q000235:genetics; D029963:Quercus / Q000235:genetics* / Q000502:physiology; D058614:Seed Dispersal; D036226:Seedlings / Q000235:genetics / Q000502:physiology; D012639:Seeds / Q000235:genetics* / Q000502:physiology; D014197:Trees
D018742:DNA, Chloroplast; D018744:DNA, Plant
Fagaceae; Quercus castanea; chloroplast DNA; forest fragmentation; genetic connectivity; genetic variation; microsatellites