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Abstract:
The Central American seasonally dry tropical (SDT) forest biome is one of the worlds’ most endangered ecosystems, yet little is
known about the genetic consequences of its recent fragmentation. A prominent constituent of this biome is Calycophyllum
candidissimum, an insect-pollinated and wind-dispersed canopy tree of high socio-economic importance, particularly in
Nicaragua. Here, we surveyed amplified fragment length polymorphisms across 13 populations of this species in Nicaragua to
elucidate the relative roles of contemporary vs historical factors in shaping its genetic variation. Genetic diversity was low in all
investigated populations (mean HE= 0.125), and negatively correlated with latitude. Overall population differentiation was
moderate (ΦST =0.109, Po0.001), and Bayesian analysis of population structure revealed two major latitudinal clusters (I:
‘Pacific North’+’Central Highland’; II: ‘Pacific South’), along with a genetic cline between I and II. Population-based cluster
analyses indicated a strong pattern of ‘isolation by distance’ as confirmed by Mantel’s test. Our results suggest that (1) the low
genetic diversity of these populations reflects biogeographic/population history (colonisation from South America, Pleistocene
range contractions) rather than recent human impact; whereas (2) the underlying process of their isolation by distance pattern,
which is best explained by ‘isolation by dispersal limitation’, implies contemporary gene flow between neighbouring populations
as likely facilitated by the species’ efficient seed dispersal capacity. Overall, these results underscore that even tree species from
highly decimated forest regions may be genetically resilient to habitat fragmentation due to species-typical dispersal
characteristics, the necessity of broad-scale measures for their conservation notwithstanding.