RESUMEN

Biogeographic disjunction patterns, where multiple taxa are shared between isolated geographic areas, represent excellent systems for investigating the historical assembly of modern biotas and fundamental biological processes such as speciation, diversification, niche evolution, and evolutionary responses to climate change. Studies on plant genera disjunct across the northern hemisphere, particularly between eastern North America (ENA) and eastern Asia (EAS), have yielded tremendous insight on the geologic history and assembly of rich temperate floras. However, one of the most prevalent disjunction patterns involving ENA forests has been largely overlooked: that of taxa disjunct between ENA and cloud forests of Mesoamerica (MAM), with examples including Acer saccharum, Liquidambar styraciflua, Cercis canadensis, Fagus grandifolia, and Epifagus virginiana. Despite the remarkable nature of this disjunction pattern, which has been recognized for over 75 years, there have been few recent efforts to empirically examine its evolutionary and ecological origins. Here I synthesize previous systematic, paleobotanical, phylogenetic, and phylogeographic studies to establish what is known about this disjunction pattern to provide a roadmap for future research. I argue that this disjunction pattern, and the evolution and fossil record of the Mexican flora more broadly, represents a key missing piece in the broader puzzle of northern hemisphere biogeography. I also suggest that the ENA-MAM disjunction represents an excellent system for examining fundamental questions about how traits and life history strategies mediate plant evolutionary responses to climate change and for predicting how broadleaf temperate forests will respond to the ongoing climatic pressures of the Anthropocene.

Asunto(s)

RESUMEN

Climate change represents one of the greatest threats to global biodiversity. We investigate how climate change will affect the future potential distribution of tree species in subtropical high montane habitats in the Atlantic Forest and identify potential climate refuges for these species. The most frequent and exclusive species in this ecosystem were selected and geographic coordinates were compiled. The maximum entropy algorithm was used for climatic niche modeling. Two scenarios for 2061-2080 were considered for future predictions, one low impact (RCP 4.5) and one high impact (RCP 8.5). Isothermality, mean temperature in the driest quarter, mean temperature in the hottest quarter, rainfall in the driest month, and rainfall in the hottest quarter were the variables that best explained the climatic niche of the majority of species. The areas of potential species occurrence were reduced by 48.37 % (± 13.63 %) (RCP 4.5) and 62.49 % (± 21.87 %) (RCP 8.5) on average. The potential area of Crinodendron brasilense Reitz & L.B.Sm. decreased the most, by 82.11 % (RCP 4.5) and 90.06 % (RCP 8.5), respectively. High elevation areas in the south of Brazil were identified as priorities for conservation to ensure that climate refuges for high montane forest species are maintained in the future. Climate change events may significantly affect the species evaluated in this study.(AU)

Asunto(s)

RESUMEN

Three new species of Diplotaxis Kirby are described and illustrated, D. balam sp. nov. from Guatemala, and D. chiapasensis sp. nov. and D. complanatis sp. nov. from Mexico. The new species have a flattened body and are included in the trapezifera species group. An updated key to the trapezifera species group is given.

RESUMEN

BACKGROUND: The Mexican hand tree or Canac (Chiranthodendron pentadactylon) is a temperate tree species of cloud and pine-oak forests of southern Mexico and Guatemala. Its characteristic hand-shaped flower is used in folk medicine and has constituted the iconic symbol of the Sociedad Botánica de México since 1940. Here, the evolutionary history of this species was estimated through phylogeographic analyses of nuclear DNA sequences obtained through restriction site associated DNA sequencing and ecological niche modeling. Total genomic DNA was extracted from leaf samples obtained from a representative number (5 to 10 per sampling site) of individuals distributed along the species geographic range. In Mexico, population is comprised by spatially isolated individuals which may follow the trends of cloud forest fragmentation. By contrast, in Guatemala Chiranthodendron may constitute a canopy dominant species near the Acatenango volcano. The distributional range of this species encompasses geographic provinces separated by the Isthmus of Tehuantepec. The objectives of the study were to: (i) estimate its genetic structure to define whether the observed range disjunction exerted by the Isthmus of Tehuantepec translates into separate populations, (ii) link population divergence timing and demographic trends to historical climate change, and (iii) test hypotheses related to Pleistocene refugia. RESULTS: Patterns of genetic diversity indicated high levels of genetic differentiation between populations separated by the Isthmus. The western and eastern population diverged approximately 0.873 Million years ago (Ma). Demographic analyses supported a simultaneous split from an ancestral population and rapid expansion from a small stock approximately 0.2 Ma corresponding to a glacial period. The populations have remained stable since the LIG (130 Kilo years ago (Ka)). Species distribution modelling (SDM) predicted a decrease in potential distribution in the Last Interglacial (LIG) and an increase during the Last Glacial Maximum (LGM) (22 Ka), Mid-Holocene (6 Ka) and present times. CONCLUSIONS: Divergence time estimations support the hypothesis that populations represent Quaternary relict elements of a species with broader and northernmost distribution. Pleistocene climatic shifts exerted major influence on the distribution of populations allowing dispersion during episodes of suitable climatic conditions and structuring during the first interglacial with a time period length of 100 Kilo years (Kyr) and the vicariant influence of the Isthmus. Limited demographic expansion and population connectivity during the LGM supports the moist forest hypothesis model.

Asunto(s)

RESUMEN

Arhuaco Adams & Bernard (1977) is one of the least known genera of Neotropical Satyrinae. It comprises two species and presents an unusual disjunct distribution, with A. ica Adams & Bernard (1977), endemic to the isolated Colombian Sierra Nevada de Santa Marta, and A. dryadina (Schaus 1913) found in the mountains of Costa Rica and Panama. Here, the female of A. dryadina is described, and a new generic diagnosis is presented. Affinities with other genera of the subtribe Pronophilina, in particular the potential closest relatives, such as Pronophila Doubleday (1849), are investigated based on morphological, molecular, ecological, and behavioral data. Results from molecular and morphological sources are incongruent. Molecular data indicate that Arhuaco is paraphyletic, with A. dryadina segregating within the Pronophila clade. Morphological data, by contrast, indicate a closer affinity between the two species currently placed in Arhuaco, favoring the monophyly of the genus, and show no consistent synapomorphies for Arhuaco + Pronophila. A vicariance biogeographical scenario is evaluated.

Asunto(s)

RESUMEN

Faster growth in tropical trees is usually associated with higher mortality rates, but the mechanisms underlying this relationship are poorly understood. In this study, we investigate how tree growth patterns are linked with environmental conditions and hydraulic traits, by monitoring the cambial growth of 9 tropical cloud forest tree species coupled with numerical simulations using an optimization model. We find that fast-growing trees have lower xylem safety margins than slow-growing trees and this pattern is not necessarily linked to differences in stomatal behaviour or environmental conditions when growth occurs. Instead, fast-growing trees have xylem vessels that are more vulnerable to cavitation and lower density wood. We propose the growth - xylem vulnerability trade-off represents a wood hydraulic economics spectrum similar to the classic leaf economic spectrum, and show through numerical simulations that this trade-off can emerge from the coordination between growth rates, wood density, and xylem vulnerability to cavitation. Our results suggest that vulnerability to hydraulic failure might be related with the growth-mortality trade-off in tropical trees, determining important life history differences. These findings are important in furthering our understanding of xylem hydraulic functioning and its implications on plant carbon economy.

Asunto(s)

RESUMEN

By integrating mitochondrial DNA (mtDNA), microsatellites and ecological niche modelling (ENM), we investigated the phylogeography of Mexican populations of the common bush-tanager Chlorospingus ophthalmicus to examine the relative role of geographical and ecological features, as well as Pleistocene climatic oscillations in driving the diversification. We sequenced mtDNA of individuals collected throughout the species range in Mexico and genotyped them at seven microsatellite loci. Phylogeographic, population genetics and coalescent methods were used to assess patterns of genetic structure, gene flow and demographic history. ENM was used to infer contractions and expansions at different time periods as well as differences in climatic conditions among lineages. The retrieved mitochondrial and microsatellite groups correspond with the fragmented cloud forest distribution in mountain ranges and morphotectonic provinces. Differing climatic conditions between mountain ranges were detected, and palaeodistribution modelling as well as demographic history analyses, indicated recent population expansions throughout the Sierra Madre Oriental (SMO). The marked genetic structure of C. ophthalmicus was promoted by the presence of ecological and geographical barriers that restricted the movement of individuals among mountain ranges. The SMO was mainly affected by Pleistocene climatic oscillations, with the moist forests model best fitting the displayed genetic patterns of populations in this mountain range.

Asunto(s)