A New Model for the Origin of Bipedality

Scholars have long thought that bipedality evolved gradually in response to the opening of the savanna. Recently, both parts of this concept have come into question. A variety of benefits of bipedality have been posited as responsible, but a trait can not evolve unless a useful mutation appears. Perhaps we need to stop wondering about selective pressures and consider what kind of mutation might be involved in forming a bipedal pelvis. Work on the evolution of development has shown that there are segmental control genes, alterations in which have large effects. These include the hox genes, of which there are four sets in humans, referred to as the HOX A, B, C, and D sequences. Changes in their activation in embryogenesis alter the identity of vertebrae and limb structure. An alteration in the control region of certain of the distal HOX D genes may well be responsible for the sudden appearance of bipedality by moving the boundary between the lumbar and sacral vertebrae, and so moving the position of the pelvis and lower limb origin. Pongids usually have three lumbar vertebrae; early hominids, 6. Pongids also have 48 chromosomes while we have 46. HOX D is located on our 2nd chromosome, the one that is a fusion of two pongid chromosomes. If that fusion altered the onset of perhaps HOX D 10, so that it switched on a couple of segments later, then the sacrum would form further down the vertebral column and might be shorter. In this paper I look at the chromosomal location of HOX D and examine the likelihood that the fusion of two panid chromosomes could have given rise to alterations in its control resulting in the abrupt appearance of bipedality and accompanying changes in the limbs and in the chela in which the HOX sequences are reused.     

A host-host-pathogen model with free-living infective stages, applicable to microbial pest control

A model has been investigated of the dynamics of the interaction between two hosts which are both attacked by a common pathogen, where the pathogen has free-living infective stages the population size of which must itself be modelled explicitly, and where the host species do not interact with one another except through their shared pathogen. If either host interacted with the pathogen alone, three broad classes of dynamics would be possible: host regulation, pathogen persistence and pathogen extinction. Here, all possible types of combinations of hosts are examined: regulation-regulation (both hosts would be regulated if they interacted with the pathogen alone), regulation-persistence, regulation-extinction, persistence-persistence persistence-extinction and extinction-extinction. A wide range of dynamics is generated, including a number of patterns quite unlike those found in the one-host pathogen case (e.g. persistence in one host, elimination of the other host) and behaviour contingent on initial densities in the system. For clarity and pertinence, attention is focused on the case where one host is a pest, the pathogen is a potential microbial control agent, and the other host is a non-target species which it is undesirable to harm. The model suggests, broadly, that non-targets are unlikely to be seriously threatened in such cases, and also that non-targets, far from undermining pest control, are quite likely to contribute to its efficacy.     

Inhibition of ecdysteroid production in nymphs of Rhodnius prolixus treated with ethoxyprecocene II

Rhodnius prolixus nymphs fed 7-ethoxy-6-methoxy-2,2-dimethylchromene (ethoxyprecocene II, EPII) show a variety of responses, including precocious molting to diminutive adults, severe retardation of molting, or a condition of permanent ecdysial stasis. The latter two conditions are reversible by subsequent treatment with 20-hydroxyecdysone. Ecdysteroid titers in the hemolymph of individual insects, determined by radioimmunoassay (RIA), show that the ecdysteroid cycle in nymphs undergoing precocious metamorphosis is similar to that of untreated fifth stage nymphs during normal imaginal molting. Nymphs in ecdysial stasis, following EPII treatment, were found to have very low ecdysteroid titers. Analysis of ecdysteroid synthesis by the prothoracic glands (PG), cultured in vitro, showed that: 1) only traces of ecdysteroid were detectable in PG from nymphs treated in vivo with EPII; 2) the PG from untreated nymphs incubated in culture medium with EPII possessed significantly lower ecdysteroid synthesis compared with controls. These studies sought to determine if the inhibition of ecdysteroid biosynthesis observed in Rhodnius, following exposure to EPII in vivo and in vitro, is due to a direct action on the PG or result as an indirect effect perhaps mediated by the neuroendocrine system.     

A dynamic refuge model and population regulation by insect parasitoids

1. The population dynamic effects of refuges, which hosts enter and leave by diffusive movement, in host–parasitoid interactions are explored using simple models in continuous time.
2. This type of refuge has a stabilizing effect on a host–parasitoid interaction, which is contrary to the implications of some previous models.
3. Stability can be explained by considering how depletion processes lead to a refuge proportion (proportion of hosts protected at a given instant) that increases as parasitoid density increases. This effect is synonymous with pseudointerference in the context of the model.
4. Very high rates of movement of host larvae largely destroy this stability process. Stability is greatest at intermediate levels of movement.
5. Density-dependent host movement can alter the effect of these refuges such that they are either more stabilizing, or tend to destabilize, the dynamics of host–parasitoid systems, depending on the type of density dependence assumed. The conclusion that intermediate movement rates are likely to generate stability with this general type of refuge is not altered in the presence of any type of density dependence, unless the density dependence is at levels which we consider unrealistically high and unlikely to be encountered in nature.
6. It is the assumption that larvae do not move into the refuge prior to becoming vulnerable to parasitism that ensures top-down population control in the model. Thus, parasitoids attacking very early instars make good candidates for biological control when faced with a structural refuge.     

Ecological and genomic analyses of candidate phylum WPS-2 bacteria in an unvegetated soil

Members of the bacterial candidate phylum WPS-2 (or Eremiobacterota) are abundant in several dry, bare soil environments. In a bare soil deposited by an extinct iron–sulfur spring, we found that WPS-2 comprised up to 24% of the bacterial community and up to 10⁸ cells per g of soil based on 16S rRNA gene sequencing and quantification. A single genus-level cluster (Ca. Rubrimentiphilum) predominated in bare soils but was less abundant in adjacent forest. Nearly complete genomes of Ca. Rubrimentiphilum were recovered as single amplified genomes (SAGs) and metagenome-assembled genomes (MAGs). Surprisingly, given the abundance of WPS-2 in bare soils, the genomes did not indicate any capacity for autotrophy, phototrophy, or trace gas metabolism. Instead, they suggest a predominantly aerobic organoheterotrophic lifestyle, perhaps based on scavenging amino acids, nucleotides, and complex oligopeptides, along with lithotrophic capacity on thiosulfate. Network analyses of the entire community showed that some species of Chloroflexi, Actinobacteria, and candidate phylum AD3 (or Dormibacterota) co-occurred with Ca. Rubrimentiphilum and may represent ecological or metabolic partners. We propose that Ca. Rubrimentiphilum act as efficient heterotrophic scavengers. Combined with previous studies, these data suggest that the phylum WPS-2 includes bacteria with diverse metabolic capabilities.     

Carrying capacity for species richness as a context for conservation: a case study of North American breeding birds

Aim To demonstrate that the concept of carrying capacity for species richness (S_K) is highly relevant to the conservation of biodiversity, and to estimate the spatial pattern of S_K for native landbirds as a basis for conservation planning. Location North America. Methods We evaluated the leading hypotheses on biophysical factors affecting species richness for Breeding Bird Survey routes from areas with little influence of human activities. We then derived a best model based on information theory, and used this model to extrapolate S_K across North America based on the biophysical predictor variables. The predictor variables included the latest and probably most accurate satellite and simulation‐model derived products. Results The best model of S_K included mean annual and inter‐annual variation in gross primary productivity and potential evapotranspiration. This model explained 70% of the variation in landbird species richness. Geographically, predicted S_K was lowest at higher latitudes and in the arid west, intermediate in the Rocky Mountains and highest in the eastern USA and the Great Lakes region of the USA and Canada. Main conclusions Areas that are high in S_K but low in human density are high priorities for protection, and areas high in S_K and high in human density are high priorities for restoration. Human density was positively related to S_K, indicating that humans select environments similar to those with high bird species richness. Federal lands were disproportionately located in areas of low predicted S_K.