Plant controls on Late Quaternary whole ecosystem structure and function

Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; however, their relative importance remains unclear. We assessed the extent to which mega‐herbivore species controlled plant community composition and nutrient cycling, relative to other factors during and after the Late Quaternary extinction event in Britain and Ireland, when two‐thirds of the region's mega‐herbivore species went extinct. Warmer temperatures, plant–soil and plant–plant interactions, and reduced burning contributed to the expansion of woody plants and declining nitrogen availability in our five study ecosystems. Shrub biomass was consistently one of the strongest predictors of ecosystem change, equalling or exceeding the effects of other biotic and abiotic factors. In contrast, there was relatively little evidence for mega‐herbivore control on plant community composition and nitrogen availability. The ability of plants to determine the fate of terrestrial ecosystems during periods of global environmental change may therefore be greater than previously thought.     

Using human case studies to teach evolution in high school A.P. biology classrooms

Background

While recent research indicates that using human examples can be an engaging way to teach core evolutionary concepts such as natural selection and phylogenetic thinking, teachers still face potential conflicts and challenges that arise from cultural barriers to teaching and learning about evolution. The “Teaching Evolution through Human Examples” (TEtHE) project developed (1) a set of four curriculum mini-units for advanced placement (A.P.) biology that use human examples to teach evolutionary principles (Adaptation to Altitude, Evolution of Human Skin Color, Malaria, and What Does It Mean To Be Human?), and (2) a cultural and religious sensitivity (CRS) teaching strategies resource that includes background materials and two in-class activities to help teachers create a classroom environment to increase student willingness to engage the topic.

Methods

This paper reports on the development and field test of the TEtHE materials in A.P. biology classes in 10 schools in 8 states during the 2012–2013 school year using a design-based research framework (cf. Anderson and Shattuck in Educ Res 41:16–25, 2012). We chose A.P. classrooms to study the potential impacts of the materials in a “best case scenario” and analyzed data about understanding and acceptance of evolution from pre-post assessments in the 10 classrooms separately to mitigate potential validity concerns arising from the design (Anderson and Shattuck in Educ Res 41:16–25, 2012; Shadish et al. in Experimental and quasi-experimental designs for generalized causal inference. Houghton Mifflin, Boston, 2002). These data were treated as a secondary source of formative data to add additional perspective to teacher self-reports, observations, student and teacher questionnaires, teacher interviews, and student focus groups.

Results

Results indicate that the use of the three curriculum mini-units which focus on natural selection and the CRS classroom activities generally increased A.P. biology students’ understanding and acceptance of evolution. Students whose teachers used one of the CRS activities showed generally larger increases in understanding of evolution than those whose teachers did not use one of the CRS activities.

Conclusions

Although the utility of using human examples to teach evolution in college-level classes has been demonstrated in a few previous studies, this is the first national project of which we are aware to systematically explore the effect of a similar approach in high school biology classes. While we recognize that the results may be mitigated by the limitations of design-based research, particularly the absence of a comparison or control group, the general effectiveness of this approach suggested by qualitative and quantitative data in increasing student understanding and acceptance of evolution suggests that using human examples and explicitly creating a classroom environment to help students engage the topic of evolution are worth considering for further development and more robust testing.

     

Response to joint selection on germination and flowering phenology depends on the direction of selection

Flowering and germination time are components of phenology, a complex phenotype that incorporates a number of traits. In natural populations, selection is likely to occur on multiple components of phenology at once. However, we have little knowledge of how joint selection on several phenological traits influences evolutionary response. We conducted one generation of artificial selection for all combinations of early and late germination and flowering on replicated lines within two independent base populations in the herb Campanula americana. We then measured response to selection and realized heritability for each trait. Response to selection and heritability were greater for flowering time than germination time, indicating greater evolutionary potential of this trait. Selection for earlier phenology, both flowering and germination, did not depend on the direction of selection on the other trait, whereas response to selection to delay germination and flowering was greater when selection on the other trait was in the opposite direction (e.g., early germination and late flowering), indicating a negative genetic correlation between the traits. Therefore, the extent to which correlations shaped response to selection depended on the direction of selection. Furthermore, the genetic correlation between timing of germination and flowering varies across the trait distributions. The negative correlation between germination and flowering time found when selecting for delayed phenology follows theoretical predictions of constraint for traits that jointly determine life history schedule. In contrast, the lack of constraint found when selecting for an accelerated phenology suggests a reduction of the covariance due to strong selection favoring earlier flowering and a shorter life cycle. This genetic architecture, in turn, will facilitate further evolution of the early phenology often favored in warm climates.     

mtDNA sequence diversity in Africa.

mtDNA sequences were determined from 241 individuals from nine ethnic groups in Africa. When they were compared with published data from other groups, it was found that the !Kung, Mbuti, and Biaka show on the order of 10 times more sequence differences between the three groups, as well as between those and the other groups (the Fulbe, Hausa, Tuareg, Songhai, Kanuri, Yoruba, Mandenka, Somali, Tukana, and Kikuyu), than these other groups do between one other. Furthermore, the pairwise sequence distributions, patterns of coalescence events, and numbers of variable positions relative to the mean sequence difference indicate that the former three groups have been of constant size over time, whereas the latter have expanded in size. We suggest that this reflects subsistence patterns in that the populations that have expanded in size are food producers whereas those that have not are hunters and gatherers.     

Persistent infection of macaques with simian-human immunodeficiency viruses.

Chimeric simian-human immunodeficiency viruses (SHIV) containing the human immunodeficiency virus type 1 (HIV-1) tat, rev, env, and, in some cases, vpu genes were inoculated into eight cynomolgus monkeys. Viruses could be consistently recovered from the CD8-depleted peripheral blood lymphocytes of all eight animals for at least 2 months. After this time, virus isolation varied among the animals, with viruses continuing to be isolated from some animals beyond 600 days after inoculation. The level of viral RNA in plasma during acute infection and the frequency of virus isolation after the initial 2-month period were higher for the Vpu-positive viruses. All of the animals remained clinically healthy, and the absolute numbers of CD4-positive lymphocytes were stable. Antibodies capable of neutralizing HIV-1 were generated at high titers in animals exhibiting the greatest consistency of virus isolation. Strain-specific HIV-1-neutralizing antibodies were initially elicited, and then more broadly neutralizing antibodies were elicited. env sequences from two viruses isolated more than a year after infection were analyzed. In the Vpu-negative SHIV, for which virus loads were lower, a small amount of env variation, which did not correspond to that found in natural HIV-1 variants, was observed. By contrast, in the Vpu-positive virus, which was consistently isolated from the host animal, extensive variation of the envelope glycoproteins in the defined variable gp120 regions was observed. Escape from neutralization by CD4 binding site monoclonal antibodies was observed for the viruses with the latter envelope glycoproteins, and the mechanism of escape appears to involve decreased binding of the antibody to the monomeric gp120 glycoproteins. The consistency with which SHIV infection of cynomolgus monkeys is initiated and the similarities in the neutralizing antibody response to SHIV and HIV-1 support the utility of this model system for the study of HIV-1 prophylaxis.     

The detritus food-web and the diversity of soil fauna as indicators of disturbance regimes in agro-ecosystems

An ongoing study initiated in August 1990 investigated the effects of disturbances (organic mulching, cultivation, herbicides) on the detritus food-web in annual (maize) and perennial (asparagus) cropping systems. In this paper we attempt to simultaneously assess the functional and taxonomic structure of various components of this food-web. Biota in the perennial system was the most responsive to disturbance. The microflora was strongly influenced by mulching, and through tritrophic effects caused increases in top predatory but not most microbe-feeding nematodes. These effects have become increasingly apparent as the study has progressed and, in the asparagus site, have worked their way down the soil profile over time. Cultivation in the asparagus site caused large increases in bacterial-feeding nematodes, probably due to the high weed levels which developed during the winter months under that treatment. Evidence appears to exist for a cascade effect operating due to top down effects of nematodes on lower trophic levels. Ordination analysis of the nematode data demonstrated that nematode populations were more closely related to the state of environmental factors at earlier samplings than at contemporary samplings, and that the linkages between the nematode and environmental data sets strengthened over time. For both the nematode and soil-associated beetle data distinct assemblages of organisms were found in the mulched plots; distinct assemblages of nematode genera also emerged in the cultivated asparagus plots after two years. The soil-associated macrofauna was usually linked to high weed and surface organic residue levels. Species diversity of soil associated nematodes was not particularly responsive to disturbance while that of the soil-associated beetles was strongly enhanced by mulching and (sometimes) high weed levels. Approaches based on either functional group or species composition data emerged in our study as reasonably sensitive indicators for assessing the response of the soil biota to disturbance.     

GABA and glutamate-like immunoreactivity at synapses received by dorsal unpaired median neurones in the abdominal nerve cord of the locust

Dorsal unpaired median (DUM) neurones in the abdominal ganglia of the locust were impaled with microelectrodes and some were injected intracellularly with horseradish peroxidase so that their synapses could be identified in the electron microscope. Simultaneous recordings from DUM neurones in different abdominal ganglia revealed that they received common postsynaptic potentials from descending interneurones. Post-embedding immunocytochemistry using antibodies against GABA and glutamate was carried out on ganglia containing HRP-stained neurones. GABA-like immunoreactivity was found in 39% (n=82) of processes presynaptic to abdominal DUM neurones and glutamate-like immunoreactivity in 21% (n=42) of presynaptic processes. Output synapses from the DUM neurites were rarely observed within the neuropile. Structures resembling presynaptic dense bars but not associated with synaptic vesicles, were seen in some large diameter neurites.     

Mutation detection using immobilized mismatch binding protein (MutS).

An accurate and highly sensitive mutation detection assay has been developed. The assay is based on the detection of mispaired and unpaired bases by immobilized mismatch binding protein (Escherichia coli MutS). The assay can detect most mismatches and all single base substitution mutations, as well as small addition or deletion mutations. The assay is simple to use and does not require the use of either radioactivity or gel electrophoresis.     

Characterization of a five-cluster required for the biogenesis of type 4 fimbriae in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa produces type 4 fimbriae which promote adhesion to epithelial cells and are associated with a form of surface translocation called twitching motility. Transposon mutagenesis was used to identify loci required for fimbrial assembly or function by screening for mutants that lack the spreading colony morphology characteristic of twitching motility. Six mutants were isolated that contain transposon insertions upstream of the previously characterized gene pilQ. This region contains four genes: pilM-P, which encode proteins with predicted sizes of 37.9, 22.2, 22.8 and 19.0 kDa, respectively, pilM-P appear to form an operon and to be expressed from a promoter in the intergenic region between pilM and the divergently transcribed upstream gene ponA. PilM-P were found to be required for fimbrial biogenesis by complementation studies using twitching motility and sensitivity to fimbrial-specific phage as indicators of the presence of functional fimbriae. This was confirmed by electron microscopy. PilO and PilP did not have homologues in the sequence databases, but the predicted PilN amino acid sequence displayed similarity to XpsL from Xanthamonas campestris, a protein required for protein secretion. PilP contained a hydro-phobic leader sequence characteristic of lipoproteins, while PilN and PilO have long internal hydrophobic domains which may serve to localize them to the cytoplasmic membrane. PilM has shared sequence motifs with the cell division protein FtsA from Bacillus subtilis and Escherichia coli, as well as the rod-shapedetermining protein MreB from E. coli. These motifs are also conserved in eukaryotic actin, in which they are involved in forming an ATPase domain. Deletion mutants of pilM and pilQ displayed a dominant negative phenotype when transformed into wild-type cells, suggesting that these genes encode proteins involved in multimeric structures.