Trans-Holocene Bayesian chronology for tree and field crop use from El Gigante rockshelter, Honduras.

El Gigante rockshelter in western Honduras provides a deeply stratified archaeological record of human-environment interaction spanning the entirety of the Holocene. Botanical materials are remarkably well preserved and include important tree (e.g., ciruela (Spondias), avocado (Persea americana)) and field (maize (Zea mays), beans (Phaseolus), and squash (Cucurbita)) crops. Here we provide a major update to the chronology of tree and field crop use evident in the sequence. We report 375 radiocarbon dates, a majority of which are for short-lived botanical macrofossils (e.g., maize cobs, avocado seeds, or rinds). Radiocarbon dates were used in combination with stratigraphic details to establish a Bayesian chronology for ~9,800 identified botanical samples spanning the last 11,000 years. We estimate that at least 16 discrete intervals of use occurred during this time, separated by gaps of ~100-2,000 years. The longest hiatus in rockshelter occupation was between ~6,400 and 4,400 years ago and the deposition of botanical remains peaked at ~2,000 calendar years before present (cal BP). Tree fruits and squash appeared early in the occupational sequence (~11,000 cal BP) with most other field crops appearing later in time (e.g., maize at ~4,400 cal BP; beans at ~2,200 cal BP). The early focus on tree fruits and squash is consistent with early coevolutionary partnering with humans as seed dispersers in the wake of megafaunal extinction in Mesoamerica. Tree crops predominated through much of the Holocene, and there was an overall shift to field crops after 4,000 cal BP that was largely driven by increased reliance on maize farming.

Genomic estimation of complex traits reveals ancient maize adaptation to temperate North America.

By 4000 years ago, people had introduced maize to the southwestern United States; full agriculture was established quickly in the lowland deserts but delayed in the temperate highlands for 2000 years. We test if the earliest upland maize was adapted for early flowering, a characteristic of modern temperate maize. We sequenced fifteen 1900-year-old maize cobs from Turkey Pen Shelter in the temperate Southwest. Indirectly validated genomic models predicted that Turkey Pen maize was marginally adapted with respect to flowering, as well as short, tillering, and segregating for yellow kernel color. Temperate adaptation drove modern population differentiation and was selected in situ from ancient standing variation. Validated prediction of polygenic traits improves our understanding of ancient phenotypes and the dynamics of environmental adaptation.

Bacillus tequilensis sp. nov., isolated from a 2000-year-old Mexican shaft-tomb, is closely related to Bacillus subtilis.

A Gram-positive, spore-forming bacillus was isolated from a sample taken from an approximately 2000-year-old shaft-tomb located in the Mexican state of Jalisco, near the city of Tequila. Tentative identification using conventional biochemical analysis consistently identified the isolate as Bacillus subtilis. DNA isolated from the tomb isolate, strain 10b(T), and closely related species was used to amplify a Bacillus-specific portion of the highly conserved 16S rRNA gene and an internal region of the superoxide dismutase gene (sodA(int)). Trees derived from maximum-likelihood methods applied to the sodA(int) sequences yielded non-zero branch lengths between strain 10b(T) and its closest relative, whereas a comparison of a Bacillus-specific 546 bp amplicon of the 16S rRNA gene demonstrated 99 % similarity with B. subtilis. Although the 16S rRNA gene sequences of strain 10b(T) and B. subtilis were 99 % similar, PFGE of NotI-digested DNA of strain 10b(T) revealed a restriction profile that was considerably different from those of B. subtilis and other closely related species. Whereas qualitative differences in whole-cell fatty acids were not observed, significant quantitative differences were found to exist between strain 10b(T) and each of the other closely related Bacillus species examined. In addition, DNA-DNA hybridization studies demonstrated that strain 10b(T) had a relatedness value of less than 70 % with B. subtilis and other closely related species. Evidence from the sodA(int) sequences, whole-cell fatty acid profiles and PFGE analysis, together with results from DNA-DNA hybridization studies, justify the classification of strain 10b(T) as representing a distinct species, for which the name Bacillus tequilensis sp. nov. is proposed. The type strain is 10b(T) (=ATCC BAA-819(T)=NCTC 13306(T)).

Maize diversity and ethnolinguistic diversity in Chiapas, Mexico.

The objective of this study is to investigate whether ethnolinguistic diversity influences crop diversity. Factors suggest a correlation between biological diversity of crops and cultural diversity. Although this correlation has been noted, little systematic research has focused on the role of culture in shaping crop diversity. This paper reports on research in the Maya highlands (altitude >1,800 m) of central Chiapas in southern Mexico that examined the distribution of maize (Zea mays) types among communities of two groups, the Tzeltal and Tzotzil. The findings suggest that maize populations are distinct according to ethnolinguistic group. However, a study of isozymes indicates no clear separation of the region's maize into two distinct populations based on ethnolinguistic origin. A reciprocal garden experiment shows that there is adaptation of maize to its environment but that Tzeltal maize sometimes out-yields Tzotzil maize in Tzotzil environments. Because of the proximity of the two groups and selection for yield, we would expect that the superior maize would dominate both groups' maize populations, but we find that such domination is not the case. The role of ethnolinguistic identity in shaping social networks and information exchange is discussed in relation to landrace differentiation.

Population structure and ecology of a tropical rare rhizomatous species of teosinte Zea diploperennis (Gramineae)

One of the objectives of the Sierra de Manantlán Biosphere Reserve (Jalisco, México) is the conservation in situ of the teosinte Zea diploperennis Iltis, Doebley, Guzman & Pazzi. Zea diploperennis is perennial, shade intolerant and its 1-3 m shoots are architecturally similar to maize. Clonal growth is of the phalanx type. Genets are iteroparous (modules semelparous). The demography of seven module and genet populations was studied in seven sites representing three stages of old-field succession. Seven permanent one-meter-square plots were randomly established in each site. All genets initially present and those that became established during our study were mapped and labeled according to year of establishment. The magnitude of demographic fluctuations was greater in module populations. Genet population dynamics followed a seasonal rhythm with a maximum population size obtained at the onset of the rainy season. A relation was documented between percent annual mortality of a cohort and its age: the younger the cohort, the greater the mortality. This was a statistically significant relationship, Y = [sin(-0.288x + 1.657)]2 (r = 0.92, p < 0.01), where is proportion annual mortality of genets and is the age of the cohort. The maximum rates of genet mortality occurred during the rainy season when population densities were greatest. As a consequence, we postulate that competition occurs principally during the rainy season. Linear relationships were observed between rate of population increase of genets versus old-field successional stage and soil type. Those areas with poor soil (Ultisol), degraded soil or soils with similar physical characteristics could be rehabilitated by introducing Z. diploperennis. Such rehabilitation would achieve two distinct objectives, promote propagation of this rare endemic and reclaim areas that are susceptible to erosion and further degradation.