Temperature and the development rates of thrips: evidence for a constraint on local adaptation?

Typically, the relationship between insect development and temperature is described by two characteristics: the minimum temperature needed for development to occur (T-min) and the number of day degrees required (DDR) for the completion of development. We investigated these characteristics in three English populations of Thrips major and T tabaci [Cawood, Yorkshire (N53degrees49', W1degrees7'); Boxworth, Cambridgeshire (N52degrees15', W0degrees1'); Silwood Park, Berkshire (N51degrees24', W0degrees38')], and two populations of Frankliniella occidentalis (Cawood; Silwood Park). While there were no significant differences among populations in either T-min (mean for T major = 7.0degreesC; T tabaci = 5.9degreesC; F. occidentalis = 6.7degreesC) or DDR (mean for T major = 229.9; T tabaci = 260.8; F occidentalis = 233.4), there were significant differences in the relationship between temperature and body size, suggesting the presence of geographic variation in this trait. Using published data, in addition to those newly collected, we found a negative relationship between T-min. and DDR for F occidentalis and T tabaci, supporting the hypothesis that a trade-off between T-min and DDR may constrain adaptation to local climatic conditions.

A 45 kyr palaeoclimate record from the lowland interior of tropical South America

We present a well-dated, high-resolution, ~ 45 kyr lake sediment record reflecting regional temperature and precipitation change in the continental interior of the Southern Hemisphere (SH) tropics of South America. The study site is Laguna La Gaiba (LLG), a large lake (95 km2) hydrologically-linked to the Pantanal, an immense, seasonally-flooded basin and the world's largest tropical wetland (135,000 km2). Lake-level changes at LLG are therefore reflective of regional precipitation. We infer past fluctuations in precipitation at this site through changes in: i) pollen-inferred extent of flood-tolerant forest; ii) relative abundance of terra firme humid tropical forest versus seasonally-dry tropical forest pollen types; and iii) proportions of deep- versus shallow-water diatoms. A probabilistic model, based on plant family and genus climatic optima, was used to generate quantitative estimates of past temperature from the fossil pollen data. Our temperature reconstruction demonstrates rising temperature (by 4 °C) at 19.5 kyr BP, synchronous with the onset of deglacial warming in the central Andes, strengthening the evidence that climatic warming in the SH tropics preceded deglacial warming in the Northern Hemisphere (NH) by at least 5 kyr. We provide unequivocal evidence that the climate at LLG was markedly drier during the last glacial period (45.0–12.2 kyr BP) than during the Holocene, contrasting with SH tropical Andean and Atlantic records that demonstrate a strengthening of the South American summer monsoon during the global Last Glacial Maximum (~ 21 kyr BP), in tune with the ~ 20 kyr precession orbital cycle. Holocene climate conditions occurred as early as 12.8–12.2 kyr BP, when increased precipitation in the Pantanal catchment caused heightened flooding and rising lake levels in LLG. In contrast to this strong geographic variation in LGM precipitation across the continent, expansion of tropical dry forest between 10 and 3 kyr BP at LLG strengthens the body of evidence for widespread early–mid Holocene drought across tropical South America.

Modelling fire and the terrestrial carbon balance

Four CO2 concentration inversions and the Global Fire Emissions Database (GFED) versions 2.1 and 3 are used to provide benchmarks for climate-driven modeling of the global land-atmosphere CO2 flux and the contribution of wildfire to this flux. The Land surface Processes and exchanges (LPX) model is introduced. LPX is based on the Lund-Potsdam-Jena Spread and Intensity of FIRE (LPJ-SPITFIRE) model with amended fire probability calculations. LPX omits human ignition sources yet simulates many aspects of global fire adequately. It captures the major features of observed geographic pattern in burnt area and its seasonal timing and the unimodal relationship of burnt area to precipitation. It simulates features of geographic variation in the sign of the interannual correlations of burnt area with antecedent dryness and precipitation. It simulates well the interannual variability of the global total land-atmosphere CO2 flux. There are differences among the global burnt area time series from GFED2.1, GFED3 and LPX, but some features are common to all. GFED3 fire CO2 fluxes account for only about 1/3 of the variation in total CO2 flux during 1997–2005. This relationship appears to be dominated by the strong climatic dependence of deforestation fires. The relationship of LPX-modeled fire CO2 fluxes to total CO2 fluxes is weak. Observed and modeled total CO2 fluxes track the El Niño–Southern Oscillation (ENSO) closely; GFED3 burnt area and global fire CO2 flux track the ENSO much less so. The GFED3 fire CO2 flux-ENSO connection is most prominent for the El Niño of 1997–1998, which produced exceptional burning conditions in several regions, especially equatorial Asia. The sign of the observed relationship between ENSO and fire varies regionally, and LPX captures the broad features of this variation. These complexities underscore the need for process-based modeling to assess the consequences of global change for fire and its implications for the carbon cycle.

Phylogeographic analysis of the chloroplast DNA variation in wild common bean (Phaseolus vulgaris L.) in the Americas

The wild common bean (Phaseolus vulgaris) is widely but discontinuously distributed from northern Mexico to northern Argentina on both sides of the Isthmus of Panama. Little is known on how the species has reached its current disjunct distribution. In this research, chloroplast DNA polymorphisms in seven non-coding regions were used to study the history of migration of wild P. vulgaris between Mesoamerica and South America. A penalized likelihood analysis was applied to previously published Leguminosae ITS data to estimate divergence times between P. vulgaris and its sister taxa from Mesoamerica, and divergence times of populations within P. vulgaris. Fourteen chloroplast haplotypes were identified by PCR-RFLP and their geographical associations were studied by means of a Nested Clade Analysis and Mantel Tests. The results suggest that the haplotypes are not randomly distributed but occupy discrete parts of the geographic range of the species. The current distribution of haplotypes may be explained by isolation by distance and by at least two migration events between Mesoamerica and South America: one from Mesoamerica to South America and another one from northern South America to Mesoamerica. Age estimates place the divergence of P. vulgaris from its sister taxa from Mesoamerica at or before 1.3 Ma, and divergence of populations from Ecuador-northern Peru at or before 0.6 Ma. As these ages are taken as minimum divergence times, the influence of past events, such as the closure of the Isthmus of Panama and the final uplift of the Andes, on the migration history and population structure of this species cannot be disregarded.

Effects of a sex-ratio distorting endosymbiont on mtDNA variation in a global insect pest

Background: Patterns of mtDNA variation within a species reflect long-term population structure, but may also be influenced by maternally inherited endosymbionts, such as Wolbachia. These bacteria often alter host reproductive biology and can drive particular mtDNA haplotypes through populations. We investigated the impacts of Wolbachia infection and geography on mtDNA variation in the diamondback moth, a major global pest whose geographic distribution reflects both natural processes and transport via human agricultural activities. Results: The mtDNA phylogeny of 95 individuals sampled from 10 countries on four continents revealed two major clades. One contained only Wolbachia-infected individuals from Malaysia and Kenya, while the other contained only uninfected individuals, from all countries including Malaysia and Kenya. Within the uninfected group was a further clade containing all individuals from Australasia and displaying very limited sequence variation. In contrast, a biparental nuclear gene phylogeny did not have infected and uninfected clades, supporting the notion that maternally-inherited Wolbachia are responsible for the mtDNA pattern. Only about 5% (15/306) of our global sample of individuals was infected with the plutWBI isolate and even within infected local populations, many insects were uninfected. Comparisons of infected and uninfected isofemale lines revealed that plutWBI is associated with sex ratio distortion. Uninfected lines have a 1:1 sex ratio, while infected ones show a 2:1 female bias. Conclusion: The main correlate of mtDNA variation in P. xylostella is presence or absence of the plutWBI infection. This is associated with substantial sex ratio distortion and the underlying mechanisms deserve further study. In contrast, geographic origin is a poor predictor of moth mtDNA sequences, reflecting human activity in moving the insects around the globe. The exception is a clade of Australasian individuals, which may reflect a bottleneck during their recent introduction to this region.

Variation in rice cadmium related to human exposure.

Cereal grains are the dominant source of cadmium in the human diet, with rice being to the fore. Here we explore the effect of geographic, genetic, and processing (milling) factors on rice grain cadmium and rice consumption rates that lead to dietary variance in cadmium intake. From a survey of 12 countries on four continents, cadmium levels in rice grain were the highest in Bangladesh and Sri Lanka, with both these countries also having high per capita rice intakes. For Bangladesh and Sri Lanka, there was high weekly intake of cadmium from rice, leading to intakes deemed unsafe by international and national regulators. While genetic variance, and to a lesser extent milling, provide strategies for reducing cadmium in rice, caution has to be used, as there is environmental regulation as well as genetic regulation of cadmium accumulation within rice grains. For countries that import rice, grain cadmium can be controlled by where that rice is sourced, but for countries with subsistence rice economies that have high levels of cadmium in rice grain, agronomic and breeding strategies are required to lower grain cadmium.