Comparing the population history of Neotropical annual species: The role of climate change and hybridization between Tithonia tubaeformis and T. rotundifolia (Asteraceae).

Historical climate changes and interspecific gene flow have played an important role in shaping the distribution and genetic diversity of the biota in the Neotropics. In this study, we explored the role of both the Pleistocene climate changes and hybridization on the contemporary geographic structure of two Neotropical weedy species: Tithonia tubaeformis and T. rotundifolia. Distribution shifts under past and current climate conditions were explored through ecological niche modelling (ENM). We then tested these hypotheses using chloroplast microsatellite (cpSSR) data in T. tubaeformis and compared the patterns deduced with those previously reported for T. rotundifolia using the same cpSSR loci. Lastly, we searched for shared haplotypes between species. Both species exhibited significant downwards altitudinal shifts during the last interglacial (LIG) and the Last Glacial Maximum (LGM). For instance, T. rotundifolia showed large suitable habitat areas since the LIG at xeric conditions in western Mesoamerica. Tithonia tubaeformis showed a ~five-fold range contraction during the LIG compared to current climate conditions, followed by a range expansion in the LGM. Despite the large shared refugial areas predicted through ENM, we found a low number of shared haplotypes, suggesting a minor role of hybridization in shaping the geographic structure of these species. Our results provide additional patterns of the population history of the northern Neotropics during the Quaternary, and we suggest that weedy widespread species are a well-suited group for the study of the effects of historic climatic changes on the biota of this region.

Natural hybridisation among Quercus glabrescens, Q. rugosa and Q. obtusata (Fagaceae): Microsatellites and secondary metabolites markers.

Natural hybridisation has significant ecological, genetic and evolutionary consequences altering morphological and chemical characters of individuals. Quercus glabrescens, Q. rugosa and Q. obtusata are white oak species well separated by their morphological characters when they occur in allopatry in Mexican temperate forests. However, in sympatry, individuals with atypical morphology have been observed, suggesting hybridisation events. In this study, we determined, with microsatellites and secondary metabolites, if interspecific gene flow occurs when these three oak species coexist in sympatry. In total, 180 individuals belonging to seven populations [three allopatric (one for each parental species) and four sympatric sites] were analysed. Allopatric populations represent well-defined genetic groups and the sympatric populations showed genetic evidence of hybridisation between Q. glabrescens × Q. rugosa and Q. glabrescens × Q. obtusata. The hybridisation percentage varied between sites and combination of involved species. We registered the presence of unique flavonoid compounds for Q. glabrescens (caffeic acid and flavonol 2), Q. rugosa (flavonol 5) and Q. obtusata (flavonol 1). Three compounds (quercetin rhamnoside, flavonol 3 and alkyl coumarate) were expressed in all taxa. Finally, the hybrid genotypes identified in this study (Q. glabrescens × Q. rugosa and Q. glabrescens × Q. obtusata) showed specific chemical profiles, resulting from a combination of those of their parental species. These results show that hybridisation events between these oak species alter chemical expression of secondary metabolites, creating a mosaic of resources and conditions that provide the substrate for different combinations of foliar-associated species such as herbivores, endophytic fungi or epiphyte plants.

Species distribution modelling and cpSSR reveal population history of the Neotropical annual herb Tithonia rotundifolia (Asteraceae).

The impacts of the historical geologic and climatic events on the diversity and genetic structure of Neotropical taxa have recently become a subject of study. However, annual plants associated with tropical dry forests remain under-studied. The exploration of additional taxa in contrasting environments will improve the current understanding of responses of the Neotropical biota to these events. Here, we explore the species distribution and geographic structure of the annual herb Tithonia rotundifolia. We sampled 175 individuals from 19 populations of T. rotundifolia. Species distribution modelling and six microsatellite chloroplast loci were used to infer its population history. We identified areas of historical climate suitability and then tested if there is genetic structuring among these areas. Haplotypes showed strong phylogeographic structure. Historical climatic suitability areas were found along the Pacific coast; however, a gap was found at the Isthmus of Tehuantepec (IT). Although Bayesian analysis showed population structuring, amova revealed that the IT is not its main driver. Instead, a subdivision into a higher number of regions had higher FCT values. Also, populations to the east of the IT showed evidence of recent population expansion and migration in a south-north direction. Pleistocene climate fluctuations partially explain the geographic structure of T. rotundifolia. However, life-history characteristics such as limited seed dispersal and the patchy distribution of suitable habitats explain the high haplotype diversity and population sub-structuring and diversity. Lastly, the absence of geographic structure of some haplotypes may indicate long-distance dispersal, or hybridisation with the closely related T. tubaeformis.

Comparison of two wild rodent species as sentinels of environmental contamination by mine tailings.

BACKGROUND: Contamination with heavy metals is among the most hazardous environmental concerns caused by mining activity. A valuable tool for monitoring these effects is the use of sentinel organisms. Particularly, small mammals living inside mine tailings are an excellent study system because their analysis represents a realistic approach of mixtures and concentrations of metal exposure. PURPOSE: We analyzed metal tissue concentrations and DNA damage levels for comparison between genders of a sentinel (Peromyscus melanophrys) and a nonsentinel (Baiomys musculus) species. Also, the relationship between DNA damage and the distance from the contamination source was evaluated. METHODS: This study was conducted in an abandoned mine tailing at Morelos, Mexico. Thirty-six individuals from both species at the exposed and reference sites were sampled. Metal concentrations in bone and liver of both species were analyzed by atomic absorption spectrophotometry, and DNA damage levels were assayed using the alkaline comet assay. RESULTS: In general, concentrations of zinc, nickel, iron, and manganese were statistically higher in exposed individuals. A significant effect of the organ and the site on all metal tissue concentrations was detected. Significant DNA damage levels were registered in the exposed group, being higher in B. musculus. Females registered higher DNA damage levels than males. A negative relationship between distance from the mine tailing and DNA damage in B. musculus was observed. CONCLUSIONS: We consider that B. musculus is a suitable species to assess environmental quality, especially for bioaccumulable pollutants--such as metals--and recommend that it may be considered as a sentinel species.