Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

Oxidation-reduction properties of the electron acceptors of Photosystem II I. Redox titration of the flash-induced carotenoid band shift,of C550 and of the variable fluorescence yield in spinach chloroplasts

Redox titration of the electrochromic carotenoid band shift, detected at 50 μs after a saturating actinic flash, in spinach chloroplasts, shows that only one electron acceptor in Photosystem II participates in a transmembrane primary electron transfer. This species, the primary quinone acceptor, Q, shows only one midpoint potential (E_m,7.5) of approx. 0 V and is undoubtedly equivalent to the fluorescence quencher, Q_H. A second titration wave is observed at low potential ($\text{E}{}_{\mathrm{<mtext>m</mtext><mtext>,7.5</mtext>}}\text{? ? 240}\text{mV}$) and at greater than 3 ms after a saturating actinic flash. This wave has an action spectrum different from that of Photosystem II centers containing Q and could arise from a secondary but not primary electron transfer. A low-potential fluorescence quencher is observed in chloroplasts which largely disappears in a single saturating flash at ? 185 mV and which does not participate in a transmembrane electron transfer. This low-potential quencher (probably equivalent to fluorescence quencher, Q_L) and Q are altogether different species. Redox titration of C550 shows that if electron acceptor Q_β is indeed characterized by an E_m,7 of + 120 mV, then this acceptor does not give rise to a C550 signal upon reduction and does not participate in a transmembrane electron transfer. This titration also shows that C550 is not associated with Q_L.     

Oxidation-reduction properties of the electron acceptors of Photosystem II. II. Redox titration at various pH values of the flash-induced formation of C550 in Chlamydomonas Photosystem II particles lacking the secondary quinone electron acceptor

Redox titrations of the flash-induced formation of C550 (a linear indicator of Q^?) were performed between pH 5.9 and 8.3 in Chlamydomonas Photosystem II particles lacking the secondary electron acceptor, B. One-third of the reaction centers show a pH-dependent midpoint potential (E_m,7.5) = ? 30 mV) for redox couple $\text{Q}\text{Q}{}^{\mathrm{?}}$, which varies by ?60 mV/pH unit. Two-thirds of the centers show a pH-independent midpoint potential (E_mm = + 10 mV) for this couple. The elevated pH-independent E_m suggests that in the latter centers the environment of Q has been modified such as to stabilize the semiquinone anion, Q^?. The midpoint potentials of the centers having a pH-dependent E_m are within 20 mV of those observed in chloroplasts having a secondary electron acceptor. It appears therefore that the secondary electron acceptor exerts little influence on the E_m of $\text{Q}\text{Q}{}^{\mathrm{?}}$. An EPR signal at g 1.82 has recently been attributed to a semiquinone-iron complex which comprises Q^?. The similar redox behavior reported here for C550 and reported by others (Evans, M.C.W., Nugent, J.H.A., Tilling, L.A. and Atkinson, Y.E. (1982) FEBS Lett. 145, 176–178) for the g 1.82 signal in similar Photosystem II particles confirm the assignment of this EPR signal to Q^?. At below ?200 mV, illumination of the Photosystem II particles produces an accumulation of reduced pheophytin (Ph^?). At ?420 mV Ph^? appears with a quantum yield of 0.006–0.01 which in this material implies a lifetime of 30–100 ns for the radical pair P-680⁺Ph^?.     

Fruiting of ectomycorrhizal basidiomycetes on unburned and prescribed burned hard-pine/hardwood plots after drought-breaking rainfalls on the Allegheny Mountains of southwestern Virginia

A headfire upward along the crest to the peak of a foothill during February 1988 had been prescribed to lower the possibility of a wildfire during the dry season on the Jefferson National Forest. Some surface litter plus annual and perennial stems on one-half of a stand of Pinus pungens/P. rigida had been destroyed. Subsequent development of ectomycorrhizal sporophores of basidiomycetes was recorded regularly within equal areas of burned and unburned portions and within a nearby unburned stand of P. virginiana. Each plot had a few ectomycorrhizal hardwoods, mainly Quercus spp. First fruiting was noted under burned P. pungens 3 weeks after a general rain in mid-July and after 4 weeks under both. By the end of November, when fruiting ceased, 138 separable taxa had been collected of which 95 had been identified. A list of the fungi and data on current and previously reported host associations, occurrence on each of the substrates, times and frequencies of fruiting, periodicity of genera, and variations in weather conditions are presented.     

Estrogen-dependent trypsin-like activity in the rat uterus. Localization of activity in the 12,000g pellet and nucleus.

Direct evidence was obtained for the presence of hormone-stimulated trypsin-like protease activity in the rat uterus. Ovariectomized rats were either untreated (U), treated with estradiol (E), or estradiol plus progesterone (EP). The uteri were excised and subcellular fractions were prepared. Each fraction was assayed for protease activity using protamine as substrate, the cleavage products being quantitated fluorometrically following reaction with 4-phenylspiro[furan-2(3H),1′-phthalan]-3,3′dione (Fluram). Fractions from U rats yielded negative results, whereas the 12,000g pellets and nuclei from the uteri of E and EP rats exhibited appreciable activities. No significant increase in protease activity was observed in thymus and diaphragm following hormone treatment, indicating organ specificity. The enzyme (or enzymes) from the 12,000g pellet was solubilized and some characteristics were determined. The apparent K_m is about 1.0 × 10^?6m, the temperature optimum is about 44 °C and maximum velocity is achieved in the alkaline range (pH ~ 8.5). The protease is a plasminogen activator and is inhibited by diisopropyl fluorophosphate, Antipain, and Leupeptin. These properties resemble those of trypsin.     

Postglacial recolonization of North America by spadefoot toads: integrating niche and corridor modeling to study species’ range dynamics over geologic time

Understanding the factors that shape species’ distributions is a key topic in biogeography. As climates change, species can either cope with these changes through evolution, plasticity or by shifting their ranges to track the optimal climatic conditions. Ecological niche modeling (ENM) is a widespread technique in biogeography that estimates the niche of the organism by using occurrences and environmental data to estimate species’ potential distributions. ENMs are often criticized for failing to take species’ dispersal abilities into consideration. Here, we attempt to fill this gap by combining ENMs with dispersal and corridor modeling to study the range dynamics of North American spadefoot toads (Scaphiopodidae) over the Holocene. We first estimated the current and past distributions of spadefoot toads and then estimated their past distributions from the Last Glacial Maximum (LGM) to the present day. Then, we estimated how each taxon recolonized North American by using dispersal and corridor modeling. By combining these two modeling approaches we were able to 1) estimate the LGM refugia used by the North American spadefoot toads, 2) further refine these projections by estimating which of the putative LGM refugia contributed to the recolonization of North America via dispersal, and 3) estimate the relative influence of each LGM refugium to the current species’ distributions. The models were tested using previously published phylogeographic data, revealing a high degree of congruence between our models and the genetic data. These results suggest that combining ENMs and dispersal modeling over time is a promising approach to investigate both historical and future species’ range dynamics.     

Recognizing pulses of extinction from clusters of last occurrences

The distribution of last occurrences of fossil taxa in a stratigraphic column are used to infer the pattern, timing and tempo of extinction from the fossil record. Clusters of last occurrences are commonly interpreted as an abrupt pulse of extinction. However, stratigraphic architecture alone can produce clusters of last occurrences that can be misinterpreted as an extinction pulse. These clusters will typically occur in strata that immediately underlie facies changes and sequence‐stratigraphic surfaces. It has been proposed that a basin‐wide analysis of the fossil record within a sequence‐stratigraphic framework can be used to distinguish between clusters of last occurrences caused solely by extinction pulses from those generated by sequence‐stratigraphic architecture. A basin‐wide approach makes it possible to observe lateral facies shifts in response to sea‐level change, mitigating the effects of stratigraphic architecture. Using computer simulations of plausible Late Ordovician mass‐extinction scenarios tuned to an inferred Late Ordovician sea‐level curve, we show that stratigraphically‐generated clusters of last occurrences are observed even in basin‐wide analyses of the simulated fossil records due to the basin‐wide loss of preferred facies for many taxa. Nonetheless, we demonstrate that by coarsening the stratigraphic resolution to the systems‐tract level and identifying facies preferences of simulated taxa, we can filter out taxa whose last occurrences coincide with the basin‐wide loss of their preferred facies. This enables consistent identification of the underlying extinction pattern for a wide variety of extinction scenarios. Applying this approach to empirical field data can help to constrain underlying extinction patterns from the fossil record.     

Forecasting range expansion into ecological traps: climate‐mediated shifts in sea turtle nesting beaches and human development

Some species are adapting to changing environments by expanding their geographic ranges. Understanding whether range shifts will be accompanied by increased exposure to other threats is crucial to predicting when and where new populations could successfully establish. If species overlap to a greater extent with human development under climate change, this could form ecological traps which are attractive to dispersing individuals, but the use of which substantially reduces fitness. Until recently, the core nesting range for the Critically Endangered Kemp's ridley sea turtle (Lepidochelys kempii) was ca. 1000 km of sparsely populated coastline in Tamaulipas, Mexico. Over the past twenty‐five years, this species has expanded its range into populated areas of coastal Florida (>1500 km outside the historical range), where nesting now occurs annually. Suitable Kemp's ridley nesting habitat has persisted for at least 140 000 years in the western Gulf of Mexico, and climate change models predict further nesting range expansion into the eastern Gulf of Mexico and northern Atlantic Ocean. Range expansion is 6–12% more likely to occur along uninhabited stretches of coastline than are current nesting beaches, suggesting that novel nesting areas will not be associated with high levels of anthropogenic disturbance. Although the high breeding‐site fidelity of some migratory species could limit adaptation to climate change, rapid population recovery following effective conservation measures may enhance opportunities for range expansion. Anticipating the interactive effects of past or contemporary conservation measures, climate change, and future human activities will help focus long‐term conservation strategies.     

Functional analysis and tissue-differential expression of four FAD2 genes in amphidiploid Brassica napus derived from Brassica rapa and Brassica oleracea

Fatty acid desaturase 2 (FAD2), which resides in the endoplasmic reticulum (ER), plays a crucial role in producing linoleic acid (18:2) through catalyzing the desaturation of oleic acid (18:1) by double bond formation at the delta 12 position. FAD2 catalyzes the first step needed for the production of polyunsaturated fatty acids found in the glycerolipids of cell membranes and the triacylglycerols in seeds. In this study, four FAD2 genes from amphidiploid Brassica napus genome were isolated by PCR amplification, with their enzymatic functions predicted by sequence analysis of the cDNAs. Fatty acid analysis of budding yeast transformed with each of the FAD2 genes showed that whereas BnFAD2-1, BnFAD2-2, and BnFAD2-4 are functional enzymes, and BnFAD2-3 is nonfunctional. The four FAD2 genes of B. napus originated from synthetic hybridization of its diploid progenitors Brassica rapa and Brassica oleracea, each of which has two FAD2 genes identical to those of B. napus. The BnFAD2-3 gene of B. napus, a nonfunctional pseudogene mutated by multiple nucleotide deletions and insertions, was inherited from B. rapa. All BnFAD2 isozymes except BnFAD2-3 localized to the ER. Nonfunctional BnFAD2-3 localized to the nucleus and chloroplasts. Four BnFAD2 genes can be classified on the basis of their expression patterns.     

Hemocyanin gene family evolution in spiders (Araneae), with implications for phylogenetic relationships and divergence times in the infraorder Mygalomorphae

Hemocyanins are multimeric copper-containing hemolymph proteins involved in oxygen binding and transport in all major arthropod lineages. Most arachnids have seven primary subunits (encoded by paralogous genes a–g), which combine to form a 24-mer (4 × 6) quaternary structure. Within some spider lineages, however, hemocyanin evolution has been a dynamic process with extensive paralog duplication and loss. We have obtained hemocyanin gene sequences from numerous representatives of the spider infraorders Mygalomorphae and Araneomorphae in order to infer the evolution of the hemocyanin gene family and estimate spider relationships using these conserved loci. Our hemocyanin gene tree is largely consistent with the previous hypotheses of paralog relationships based on immunological studies, but reveals some discrepancies in which paralog types have been lost or duplicated in specific spider lineages. Analyses of concatenated hemocyanin sequences resolved deep nodes in the spider phylogeny and recovered a number of clades that are supported by other molecular studies, particularly for mygalomorph taxa. The concatenated data set is also used to estimate dates of higher-level spider divergences and suggests that the diversification of extant mygalomorphs preceded that of extant araneomorphs. Spiders are diverse in behavior and respiratory morphology, and our results are beneficial for comparative analyses of spider respiration. Lastly, the conserved hemocyanin sequences allow for the inference of spider relationships and ancient divergence dates.