Molecular and morphological support for a Florida origin of the Cuban oak

Abstract

Aim The origins of the Cuban biota are of long‐standing interest in biogeography, and the source of a small live oak (Quercus series Virentes) population on Cuba remains unresolved. Based on morphological evidence, previous authors have hypothesized a Florida origin from either Q. geminata or Q. virginiana or both; a Mexican origin from Q. oleoides; or a hybrid origin from both sources. We use molecular data and taxonomically informative leaf morphology to identify the source species and timing of colonization. Location Cuba, Central America, Mexico and the south‐eastern United States. Methods We collected representative samples of Cuban oaks and each putative source species and genotyped each sample at 12 nuclear microsatellites and two chloroplast DNA sequences. We estimated population structure using a Bayesian clustering analysis and F‐statistics, pairwise migration rates among taxa, and divergence time using an isolation‐with‐migration model. We measured seven leaf traits and conducted an analysis of similarity (ANOSIM) to determine which putative source species was most similar to Cuban oaks. Results Cuban oak contains one chloroplast DNA haplotype, which is common in southern Florida. Bayesian clustering analysis of microsatellites revealed that the Cuban oak forms a distinct and pure population cluster, and F‐statistics showed that Cuban oaks are differentiated least from Q. virginiana and most from Q. geminata. Migration rates were highest out of Cuba to Q. oleoides. Molecular diversity, the ratio of allelic richness to allele size range, and effective population size of the Cuban oak were relatively low, suggesting a founder effect. Divergence time estimates fell entirely within the Pleistocene (628–6 ka), considering a range of mutation rates and generation times. Cuban oaks were morphologically most similar to Q. virginiana and least similar to Q. geminata. Main conclusions Molecular and morphological data support a Pleistocene dispersal of Q. virginiana from Florida to Cuba, followed by isolation and divergence, then limited dispersal and introgression from Cuba to Q. oleoides in Central America. Birds could have dispersed acorns to Cuba during a glacial period when sea levels were low. These results highlight the varied origin of the Cuban biota and the possible role of Pleistocene glaciations in the establishment of temperate taxa in the tropics.

Phylogeny and biogeography of the American live oaks (QuercussubsectionVirentes): a genomic and population genetics approach

“…These data were combined with previously published data for Quercus geminata, Q. virginiana, Q. oleoides and Q. sagraeana (Cavender‐Bares & Pahlich ; Cavender‐Bares et al . ; Gugger & Cavender‐Bares ) for a total of 672 individuals across all species.…”

“…). Geographic barriers to gene flow were associated with the isolation and formation of the Cuban oak, Q. sagraeana ( Gugger & Cavender‐Bares ), as well as the fixation of a single chloroplast haplotype at the southern range limit of Q. oleoides in Costa Rica (Cavender‐Bares et al . ).…”

Influence of late Quaternary climate change on present patterns of genetic variation in valley oak, Quercus lobata Née

“…To convert these estimates to the per‐locus, per‐year rates required in I Ma 2, per‐generation nSSR mutation rates were multiplied by a mean generation time in oaks of 100 years (Cavender‐Bares et al . ; Gugger & Cavender‐Bares ), and per‐base pair nDNA rates were multiplied by the length of the locus in base pairs.…”

Phylogeography of Neotropical trees

“…Poelchau & Hamrick (2013a), for example, encountered an unexpected phylogeographical structure in two species sampled between El Salvador and Nicaragua – strikingly similar to patterns observed in the same region in Cedrela odorata (Cavers et al ., , ) – which they suggest may derive from genetic isolation on Tertiary islands that coalesced to form the contiguous landscape of modern Central America. Gugger & Cavender‐Bares (), on the other hand, found evidence for a Floridian origin of the Cuban oak, Quercus sagraeana . Oak acorns do not float, suggesting that birds, possibly the extinct passenger pigeon ( Ectopistes migratorius ), deposited the colonizing seeds during periods of lowered sea level, when the water barrier between Cuba and Florida was reduced.…”