Edaphic and climatic history has driven current dung beetle species pool and assemblage structure across a transition zone in central South Africa

We investigate biogeographical, regional and sub‐regional‐scale responses of scarabaeine dung beetles to late Cenozoic changes in edaphic and climatic character that created a Savanna/Karoo transition zone in the Northern Cape, South Africa. Across a 50 200 km² study area, the Northern Cape species pool comprised six biogeographical groups defined from distribution across southern Africa. These species groups contributed in different proportions to five regional assemblages defined from structural differences across the transition zone. Towards transition zone peripheries, regional assemblage structure was more strongly correlated to sandiness dating from Miocene to Pliocene deposition (Kalahari), aridity dating from Pliocene to Pleistocene climatic change (Bushmanland Karoo), or cooler temperatures dating from Miocene to Pliocene uplift (Upper Karoo). Correlates of sub‐regional assemblages trended to intensification of dominant drivers towards regional peripheries. Drivers of central transition zone, regional assemblages (‘Gariep Karoo’, ‘Gariep Stony Karoo’) showed no dominance. Biogeographically, endemism dominates the Northern Cape transition zone: south‐west arid groups in Nama Karoo regions; Kalahari plus north‐east savanna groups in the Kalahari. Regionally, transition drives assemblage structure: unique variance, 60% in the Kalahari, 21–30% in four Nama Karoo regions; shared variance (overlap), 25–65% between Kalahari and warmer Karoo regions, 11–71% between mainly cooler Karoo regions.     

Causes of perceived faunal change in the later Neogene of East Africa

African terrestrial vertebrate faunas change over the time range from 14 my to 4 my, the period during which hominids are presumed to have diverged from other hominoids. The most complete local sequence showing this is provided by the Tugen Hills, west of Lake Baringo in Kenya. A large component of the pattern of faunal changes seen there, and at other relevant sites, could be explained by local environmental alterations, or by sampling properties of fossil assemblages and collections. It is hard to justify global climatic change as the sole explanation of observed faunal shifts, although such external factors cannot be ruled out and on general grounds are likely to be involved. As yet there is no convincing demonstration of synchronicity in faunal turnover. Evidence of a simple shift from forest conditions to grasslands, an event that has been correlated with the origins of hominid bipedalism, is hard to detect. Existing data suggest a more patchy distribution of forest and grassland in both space and time.     

Genotypic diversity of a dominant C4 grass across a long-term fire frequency gradient

Aims and Methods Diversity-disturbance research has focused on community diversity, but disturbance frequency could impact diversity within species as well, with important consequences for community diversity and ecosystem function. We examined patterns of genetic diversity of a dominant grass species, Andropogon gerardii, in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments (burned every 1, 2, 4 or 20 years) since the 1970s. In addition, we were able to assess the relationships between genetic diversity of A. gerardii, species diversity and productivity across this range of fire frequencies.Important findings We found no significant relationships between genetic diversity of A. gerardii at the local scale (1 m 2 plot level) and disturbance frequency (burned 2 to 32 times over a 38-year period). However, at the site level (i.e. across all plots sampled within a site, ~100 m 2) there were differences in genotype richness and composition, as well as genomic dissimilarity among individuals of A. gerardii. Genotype richness was greatest for the site burned at an intermediate (4-year) frequency and lowest for the infrequently (20-year) burned site. In addition, genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites. Genotype composition of A. gerardii was not significantly different between the frequently burned sites (annual vs. 2 year) but did differ between frequently burned and infrequently burned sites (1 and 2 year vs. 4 and 20 year, etc.). Together, these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies, likely driven by alterations in environmental conditions. Frequent fire promotes the abundance of dominant grass species, reduces plant community diversity and impacts ecosystem processes such as productivity. Our study suggests that genetic diversity within dominant grass species also may be affected by disturbance frequency, which could have important implications for how species are able to respond to disturbance.     

Palynological evidence for the impact of colonial settlement within lowland fynbos: A high‐resolution study from the Verlorenvlei,southwestern Cape Province,South Africa

The present distribution of lowland fynbos of the southwestern Cape coastal forelands occupies a unique yet threatened existence. Long renowned for its extraordinary species richness, the lowland fynbos now reveals a decline in diversity following the impact of recent European settlement. Fine resolution pollen analysis, conducted on a dated sediment core from the Verlorenvlei, reveals a 250 year pattern of debilitating vegetation transformations. The arrival of European colonists in the area circa 1700 is noted in the sedimentary sequence, not only with respect to changes in the pollen spectra, but also through concomitant changes in the nature and timing of sedimentation. The rapid extermination of large mammalian fauna, overgrazing by domestic stock and decades of agricultural mismanagement in a marginal landscape are considered to be the principal factors responsible for deliterious alterations of the natural disturbance regime.     

Neogene phasianids (Aves: Phasianidae) of Central Asia: 2. Genera <Emphasis Type="Italic">Perdix,Plioperdix</Emphasis>, and <Emphasis Type="Italic">Bantamyx</Emphasis>

The phasianid genera Perdix, Plioperdix, and Bantamyx from the Neogene of Mongolia and Transbaikalia are reviewed. Based on published data and new material, the diagnoses of Late Pliocene Perdix margaritae Kurochkin and Plioperdix ponticus (Tugarinov) and Late Miocene Bantamyx georgicus Kurochkin are emended. It is shown that a tarsometatarsus from the Upper Miocene of the Pavlodar locality belongs to the genus Palaeoperdix rather than Palaeortyx, as was proposed in the previous studies. Small Neogene Asian phasianids are compared in detail with Neogene taxa from Europe and extant genera.     

Bantu language trees reflect the spread of farming across sub-Saharan Africa: a maximum-parsimony analysis

Linguistic divergence occurs after speech communities divide, in a process similar to speciation among isolated biological populations. The resulting languages are hierarchically related, like genes or species. Phylogenetic methods developed in evolutionary biology can thus be used to infer language trees, with the caveat that 'borrowing' of linguistic elements between languages also occurs, to some degree. Maximum-parsimony trees for 75 Bantu and Bantoid African languages were constructed using 92 items of basic vocabulary. The level of character fit on the trees was high (consistency index was 0.65), indicating that a tree model fits Bantu language evolution well, at least for the basic vocabulary. The Bantu language tree reflects the spread of farming across this part of sub-Saharan Africa between ca. 3000 BC and AD 500. Modern Bantu subgroups, defined by clades on parsimony trees, mirror the earliest farming traditions both geographically and temporally. This suggests that the major subgroups of modern Bantu stem from the Neolithic and Early Iron Age, with little subsequent movement by speech communities.     

Fire and the Miocene expansion of C4 grasslands

C₄ photosynthesis had a mid‐Tertiary origin that was tied to declining atmospheric CO₂, but C₄‐dominated grasslands did not appear until late Tertiary. According to the ‘CO₂‐threshold’ model, these C₄ grasslands owe their origin to a further late Miocene decline in CO₂ that gave C₄ grasses a photosynthetic advantage. This model is most appropriate for explaining replacement of C₃ grasslands by C₄ grasslands, however, fossil evidence shows C₄ grasslands replaced woodlands. An additional weakness in the threshold model is that recent estimates do not support a late Miocene drop in pCO₂. We hypothesize that late Miocene climate changes created a fire climate capable of replacing woodlands with C₄ grasslands. Critical elements were seasonality that sustained high biomass production part of year, followed by a dry season that greatly reduced fuel moisture, coupled with a monsoon climate that generated abundant lightning‐igniting fires. As woodlands became more open from burning, the high light conditions favoured C₄ grasses over C₃ grasses, and in a feedback process, the elevated productivity of C₄ grasses increased highly combustible fuel loads that further increased fire activity. This hypothesis is supported by paleosol data that indicate the late Miocene expansion of C₄ grasslands was the result of grassland expansion into more mesic environments and by charcoal sediment profiles that parallel the late Miocene expansion of C₄ grasslands. Many contemporary C₄ grasslands are fire dependent and are invaded by woodlands upon cessation of burning. Thus, we maintain that the factors driving the late Miocene expansion of C₄ were the same as those responsible for maintenance of C₄ grasslands today.     

Elevation‐induced climate change as a dominant factor causing the late Miocene C4 plant expansion in the Himalayan foreland

During the late Miocene, a dramatic global expansion of C₄ plant distribution occurred with broad spatial and temporal variations. Although the event is well documented, whether subsequent expansions were caused by a decreased atmospheric CO₂ concentration or climate change is a contentious issue. In this study, we used an improved inverse vegetation modeling approach that accounts for the physiological responses of C₃ and C₄ plants to quantitatively reconstruct the paleoclimate in the Siwalik of Nepal based on pollen and carbon isotope data. We also studied the sensitivity of the C₃ and C₄ plants to changes in the climate and the atmospheric CO₂ concentration. We suggest that the expansion of the C₄ plant distribution during the late Miocene may have been primarily triggered by regional aridification and temperature increases. The expansion was unlikely caused by reduced CO₂ levels alone. Our findings suggest that this abrupt ecological shift mainly resulted from climate changes related to the decreased elevation of the Himalayan foreland.     

The age of the grasses and clusters of origins of C4 photosynthesis

At high temperatures and relatively low CO₂ concentrations, plants can most efficiently fix carbon to form carbohydrates through C₄ photosynthesis rather than through the ancestral and more widespread C₃ pathway. Because most C₄ plants are grasses, studies of the origin of C₄ are intimately tied to studies of the origin of the grasses. We present here a phylogeny of the grass family, based on nuclear and chloroplast genes, and calibrated with six fossils. We find that the earliest origins of C₄ likely occurred about 32 million years ago (Ma) in the Oligocene, coinciding with a reduction in global CO₂ levels. After the initial appearance of C₄ species, photosynthetic pathway changed at least 15 more times; we estimate nine total origins of C₄ from C₃ ancestors, at least two changes of C₄ subtype, and five reversals to C₃. We find a cluster of C₄ to C₃ reversals in the Early Miocene correlating with a drop in global temperatures, and a subsequent cluster of C₄ origins in the Mid‐Miocene, correlating with the rise in temperature at the Mid‐Miocene climatic optimum. In the process of dating the origins of C₄, we were also able to provide estimated times for other major events in grass evolution. We find that the common ancestor of the grasses (the crown node) originated in the upper Cretaceous. The common ancestor of maize and rice lived at 52 ± 8 Ma.     

Microanatomical traits track climate gradients for a dominant C4 grass species across the Great Plains,USA

Background and AimsAndropogon gerardii is a highly productive C₄ grass species with a large geographic range throughout the North American Great Plains, a biome characterized by a variable temperate climate. Plant traits are often invoked to explain growth rates and competitive abilities within broad climate gradients. For example, plant competition models typically predict that species with large geographic ranges benefit from variation in traits underlying high growth potential. Here, we examined the relationship between climate variability and leaf-level traits in A. gerardii, emphasizing how leaf-level microanatomical traits serve as a mechanism that may underlie variation in commonly measured traits, such as specific leaf area (SLA).MethodsAndropogon gerardii leaves were collected in August 2017 from Cedar Creek Ecosystem Science Reserve (MN), Konza Prairie Biological Station (KS), Platte River Prairie (NE) and Rocky Mountain Research Station (SD). Leaves from ten individuals from each site were trimmed, stained and prepared for fluorescent confocal microscopy to analyse internal leaf anatomy. Leaf microanatomical data were compared with historical and growing season climate data extracted from PRISM spatial climate models.Key ResultsMicroanatomical traits displayed large variation within and across sites. According to AICc (Akaike’s information criterion adjusted for small sample sizes) selection scores, the interaction of mean precipitation and temperature for the 2017 growing season was the best predictor of variability for the anatomical and morphological traits measured here. Mesophyll area and bundle sheath thickness were directly correlated with mean temperature (annual and growing season). Tissues related to water-use strategies, such as bulliform cell and xylem area, were significantly correlated with one another.ConclusionsThe results indicate that (1) microanatomical trait variation exists within this broadly distributed grass species, (2) microanatomical trait variability appears likely to impact leaf-level carbon and water use strategies, and (3) microanatomical trait values vary across climate gradients, and may underlie variation in traits measured at larger ecological scales.     

Environmental factors determining the phylogenetic structure of C4 grass communities

Aim To determine how the distribution of species richness is associated with environmental factors for the four major C₄ grass lineages in South Africa, as a means to explore the mechanisms responsible. Location South Africa, Lesotho and Swaziland. Methods The geographical distributions of species richness for four major C₄ grass lineages (Aristidoideae, Chloridoideae, Andropogoneae and Paniceae) were sourced from a recently published flora that divided the study region into different vegetation types. Mean values of potential environmental correlates were calculated for each vegetation type, and the relative importances of these were determined using single‐ and multiple‐predictor generalized linear models, with and without control for spatial autocorrelation. Model selection of the multiple‐predictor generalized linear models was conducted using an Akaike’s information criterion–information theoretic approach. Association with wet, intermediate or dry, shady or open, and disturbed or undisturbed habitats was also determined for each C₄ grass clade using habitat data for all the grass species, and analysed using chi‐square tests of independence. Results Andropogoneae and Paniceae are most species‐rich in areas of high precipitation and in mesic habitats. Andropogoneae are associated with high fire frequencies. Species richness in Andropogoneae decreases and in Paniceae increases in relation to livestock density. Chloridoideae species richness is relatively constant across South Africa, but is highest where there are infrequent fires, high temperatures and basic soils, and in mesic and disturbed habitats. Aristidoideae are most species‐rich in arid regions and in habitats with high temperatures, and are associated with disturbed habitats. Main conclusions Environmental variables other than precipitation, including temperature, fire frequency and grazing pressure, are strongly associated with the contrasting distributions of species richness for the various C₄ grass clades in South Africa. Our results suggest that ecological sorting is an important determinant of phylogenetic patterns in the species richness of these C₄ grass lineages.     

The photosynthetic response of C3 and C4 bioenergy grass species to fluctuating light

Bioenergy grass species are a renewable energy source, but their productivity has not been fully realized. Improving photosynthetic efficiency has been proposed as a mechanism to increase the productivity of bioenergy grass species. Fluctuating light, experienced by all field grown crops, is known to reduce photosynthetic efficiency. This experiment aimed to evaluate the photosynthetic performance of both C₃ and C₄ bioenergy grass species under steady state and fluctuating light conditions by examining leaf gas exchange. The fluctuating light regime used here decreased carbon assimilation across all species when compared to expected steady state values. Overall, C₄ species assimilated more carbon than C₃ species during the fluctuating light regime, with both photosynthetic types assimilating about 16% less carbon than expected based on steady state measurements. Little diversity was observed in response to fluctuating light among C₃ species, and photorespiration partially contributed to the rapid decreases in net photosynthetic rates during high to low light transitions. In C₄ species, differences among the four NADP-ME species were apparent. Diversity observed among C₄ species in this experiment provides evidence that photosynthetic efficiency in response to fluctuating light may be targeted to increase C₄ bioenergy grass productivity.     

Responsiveness of developing dental tissues to fibroblast growth factors: expression of splicing alternatives of FGFR1, -2, -3, and of FGFR4; and stimulation of cell proliferation by FGF-2, -4, -8, and -9

To elucidate the roles of fibroblast growth factors (FGF) in tooth development, we have analyzed the expression patterns of fibroblast growth factor receptors (FGFR) in mouse teeth by in situ hybridization and studied the effects of FGF-2, -4, -8, and -9 on cell proliferation in vitro by local application with beads on isolated dental mesenchymes. mRNAs of FGFR-1, -2, and -3 were localized by probes specific for the alternative splice variants IIIb and IIIc. The expression patterns of FGFR1, -2, and -3 were completely different, and the two splicing variants of FGFR1 and 2 exhibited different expression domains. FGFR4 was not expressed in the developing teeth. The IIIb splice forms of FGFR1 and -2 were expressed in the dental epithelium during morphogenesis. The IIIc splice form of FGFR1 was expressed both in epithelium and mesenchyme whereas FGFR2 IIIc was confined to the mesenchymal cells of the dental follicle. Both splice forms of FGFR3 were expressed in dental papilla mesenchyme. None of the FGF-receptors was detected in the primary enamel knot, the putative signaling center regulating tooth morphogenesis. This may explain the fact that enamel knot cells do not proliferate, although they express intensely mitogenic FGFs. Beads releasing FGF-2, -4, -8, or -9 proteins stimulated cell proliferation in cultured dental mesenchymes. These data, together with our earlier data on FGF expression [Kettunen and Thesleff (1998): Dev Dyn 211:256–268] suggest that FGF-8 and -9 mediate epithelial-mesenchymal interactions during tooth initiation. During advancing morphogenesis FGF-3, -4, and -9 may act both on mesenchyme and epithelium. Finally, the intense expression of FGFR1 in odontoblasts and ameloblasts, and FGFR2 IIIb in ameloblasts suggests that FGFs participate in regulation of their differentiation and/or secretory functions. Dev. Genet. 22:374–385, 1998. © 1998 Wiley-Liss, Inc.     

Climate and the U.S. distribution of C4 grass subfamilies and decarboxylation variants of C4 photosynthesis

I compared the C(4) grass flora and climatic records for 32 sites in the United States. Consistent with previous studies, I found that the proportion of the grass flora that uses the NADP malic enzyme (NADP-ME) variant of C(4) photosynthesis greatly increases with increasing annual precipitation, while the proportion using the NAD malic enzyme (NAD-ME) variant (and also the less common phosphoenolpyruvate carboxykinase [PCK] variant) decreases. However the association of grass subfamilies with annual precipitation was even stronger than for the C(4) decarboxylation variants. Analysis of the patterns of distribution by partial correlation analysis showed that the correlations between the frequency of various C(4) types and rainfall were solely due to the association of the C(4) types with particular grass subfamilies. In contrast, there was a strong correlation of the frequency of the different subfamilies with annual precipitation that was independent of the influence of the different C(4) variants. It therefore appears that other, as yet unidentified, characteristics that differ among grass subfamilies may be responsible for their differences in distribution across natural precipitation gradients.     

Evolutionary implications of C3–C4 intermediates in the grass Alloteropsis semialata

C₄ photosynthesis is a complex trait resulting from a series of anatomical and biochemical modifications to the ancestral C₃ pathway. It is thought to evolve in a stepwise manner, creating intermediates with different combinations of C₄‐like components. Determining the adaptive value of these components is key to understanding how C₄ photosynthesis can gradually assemble through natural selection. Here, we decompose the photosynthetic phenotypes of numerous individuals of the grass Alloteropsis semialata, the only species known to include both C₃ and C₄ genotypes. Analyses of δ¹³C, physiology and leaf anatomy demonstrate for the first time the existence of physiological C₃–C₄ intermediate individuals in the species. Based on previous phylogenetic analyses, the C₃–C₄ individuals are not hybrids between the C₃ and C₄ genotypes analysed, but instead belong to a distinct genetic lineage, and might have given rise to C₄ descendants. C₃ A. semialata, present in colder climates, likely represents a reversal from a C₃–C₄ intermediate state, indicating that, unlike C₄ photosynthesis, evolution of the C₃–C₄ phenotype is not irreversible.     

Metabolism of phosphoenolpyruvate in the C4 cycle during photosynthesis in the phosphoenolpyruvate-carboxykinase C4 grass Spartina anglica Hubb.

The aim of this work was to investigate the fate of phosphoenolpyruvate (PEP) produced by decarboxylation of oxaloacetate during photosynthesis in the bundle sheaths of leaves of the PEP-carboxykinase C₄ grass Spartina anglica Hubb. Mesophyll protoplasts and bundle sheath cells were separated enzymically and used to investigate activities and distributions of putative enzymes of the C₄ cycle and the photosynthetic carbon metabolism of bundle sheath cells. The results indicate that neither conversion of PEP to pyruvate nor its conversion to 3-phosphoglycerate can account for all of the carbon flux through the C₄ cycle during photosynthesis. It is likely, therefore, either that PEP moves directly from bundle sheath to mesophyll or that more than one pathway of regeneration of PEP is involved in the C₄ cycle in this plant.Abbreviations Chl chlorophyll - PEP phosphoenolpyruvate - Pi phosphate - RuBP ribulose-1,5-bisphosphate     

Photosynthetic carbon metabolism of the cool-temperate C4 grass Spartina anglica Hubb.

The aim of this work was to describe the photosynthetic carbon metabolism of the cooltemperate C₄ grass Spartina anglica. With the exception of pyruvate, phosphate dikinase and pyruvate kinase, the maximum catalytic activities in leaves of putative enzymes of the C₄ cycle of a phosphoenolpyruvate-carboxykinase C₄ plant were considerably in excess of the observed, steady-state rate of photosynthesis, and were comparable with the maximum catalytic activities of key enzymes of the reductive pentose-phosphate pathway. Radioactive carbon from ¹⁴CO₂ supplied to attached leaves during steady-state photosynthesis appeared first in malate and aspartate from which it moved to intermediates of the reductive pentose-phosphate pathway, and then to sucrose. These experiments show that photosynthetic carbon metabolism in this cool-temperate C₄ plant is similar to that of C₄ plants of hotter climates.     

Plio-Pleistocene history and phylogeography of Acacia senegal in dry woodlands and savannahs of sub-Saharan tropical Africa: evidence of early colonisation and recent range expansion

Drylands are extensive across sub-Saharan Africa, socio-economically and ecologically important yet highly sensitive to environmental changes. Evolutionary history, as revealed by contemporary intraspecific genetic variation, can provide valuable insight into how species have responded to past environmental and population changes and guide strategies to promote resilience to future changes. The gum arabic tree (Acacia senegal) is an arid-adapted, morphologically diverse species native to the sub-Saharan drylands. We used variation in nuclear sequences (internal transcribed spacer (ITS)) and two types of chloroplast DNA (cpDNA) markers (PCR-RFLP, cpSSR) to study the phylogeography of the species with 293 individuals from 66 populations sampled across its natural range. cpDNA data showed high regional and rangewide haplotypic diversity (h_T(cpSSR)=0.903–0.948) and population differentiation (G_ST(RFLP)=0.700–0.782) with a phylogeographic pattern that indicated extensive historical gene flow via seed dispersal. Haplotypes were not restricted to any of the four varieties, but showed significant geographic structure (G_ST(cpSSR)=0.392; R_ST=0.673; R_ST>R_ST (permuted)), with the major division separating East and Southern Africa populations from those in West and Central Africa. Phylogenetic analysis of ITS data indicated a more recent origin for the clade including West and Central African haplotypes, suggesting range expansion in this region, possibly during the Holocene humid period. In conjunction with paleobotanical evidence, our data suggest dispersal to West Africa, and across to the Arabian Peninsula and Indian subcontinent, from source populations located in the East African region during climate oscillations of the Plio-Pleistocene.     

Drought limitation of photosynthesis differs between C3 and C4 grass species in a comparative experiment

Phylogenetic analyses show that C₄ grasses typically occupy drier habitats than their C₃ relatives, but recent experiments comparing the physiology of closely related C₃ and C₄ species have shown that advantages of C₄ photosynthesis can be lost under drought. We tested the generality of these paradoxical findings in grass species representing the known evolutionary diversity of C₄ NADP‐me and C₃ photosynthetic types. Our experiment investigated the effects of drought on leaf photosynthesis, water potential, nitrogen, chlorophyll content and mortality. C₄ grasses in control treatments were characterized by higher CO₂ assimilation rates and water potential, but lower stomatal conductance and nitrogen content. Under drought, stomatal conductance declined more dramatically in C₃ than C₄ species, and photosynthetic water‐use and nitrogen‐use efficiency advantages held by C₄ species under control conditions were each diminished by 40%. Leaf mortality was slightly higher in C₄ than C₃ grasses, but leaf condition under drought otherwise showed no dependence on photosynthetic‐type. This phylogenetically controlled experiment suggested that a drought‐induced reduction in the photosynthetic performance advantages of C₄ NADP‐me relative to C₃ grasses is a general phenomenon.