Male-mediated early maturation unlikely to evolve via adaptive evolution.

The Vandenbergh effect, or male-mediated maturation, occurs when females reach sexual maturation upon exposure to a novel male. Male-mediated maturation is found across mammals, including in geladas, Theropithecus gelada, where it may be an adaptive counterstrategy to infanticide that follows the immigration of a new male; maturing after male immigration maximizes a female's chances of weaning her first offspring before the next infanticidal male immigrates (the 'optimal timing hypothesis'). Alternatively, the nonadaptive 'Bruce effect by-product hypothesis' posits that male-mediated maturation in geladas (and possibly other mammals) is triggered by the same physiological changes that, in pregnant females, produce spontaneous abortion (the Bruce effect). We test both hypotheses using theory and observational data. We show that neither male-mediated maturation nor its associated hormonal changes occur in baboons (Papio cynocephalus × P. anubis), a primate without the Bruce effect. An individual-based model suggests that male-mediated maturation should not evolve via adaptive evolution in either geladas or baboons. Finally, we derive the selection coefficient for male-mediated maturation and show it is likely to be very small because male-mediated maturation yields only marginal potential benefits unless the system is extremely fine-tuned. We conclude that male-mediated maturation in geladas is a by-product of the Bruce effect and more broadly that the Vandenbergh effect may be nonadaptive.

Still little evidence sex differences in spatial navigation are evolutionary adaptations.

A putative male advantage in wayfinding ability is the most widely documented sex difference in human cognition and has also been observed in other animals. The common interpretation, the sex-specific adaptation hypothesis, posits that this male advantage evolved as an adaptive response to sex differences in home range size. A previous study a decade ago tested this hypothesis by comparing sex differences in home range size and spatial ability among 11 species and found no relationship. However, the study was limited by the small sample size, the lack of species with a larger female home range and the lack of non-Western human data. The present study represents an update that addresses all of these limitations, including data from 10 more species and from human subsistence cultures. Consistent with the previous result, we found little evidence that sex differences in spatial navigation and home range size are related. We conclude that sex differences in spatial ability are more likely due to experiential factors and/or unselected biological side effects, rather than functional outcomes of natural selection.

Low internal air space in plants with crassulacean acid metabolism may be an anatomical spandrel.

Crassulacean acid metabolism (CAM) is a photosynthetic adaptation found in at least 38 plant families. Typically, the anatomy of CAM plants is characterized by large photosynthetic cells and a low percentage of leaf volume consisting of internal air space (% IAS). It has been suggested that reduced mesophyll conductance (gm) arising from low % IAS benefits CAM plants by preventing the movement of CO2 out of cells and ultimately minimizing leakage of CO2 from leaves into the atmosphere during day-time decarboxylation. Here, we propose that low % IAS does not provide any adaptive benefit to CAM plants, because stomatal closure during phase III of CAM will result in internal concentrations of CO2 becoming saturated, meaning low gm will not have any meaningful impact on the flux of gases within leaves. We suggest that low % IAS is more likely an indirect consequence of maximizing the cellular volume within a leaf, to provide space for the overnight storage of malic acid during the CAM cycle.

Thank Martin Luther that ciprofloxacin could cure your gonorrhoea? Ecological association between Protestantism and antimicrobial consumption in 30 European countries.

Background: Higher consumption of antimicrobials plays an important role in driving the higher prevalence of antimicrobial resistance in Southern compared to Northern Europe. Poor controls on corruption (CoC), high uncertainty avoidance (UA) and performance vs. cooperation orientation (POCO) of societies have been found to explain much of this higher consumption in Southern European countries.  We hypothesized that these predictors were in turn influenced by the Protestant Reformation in the 16 th century onwards. Methods: We used structural equation modelling (SEM) to assess the relationships between country-level proportions being Protestant, CoC, UA, POCO and four markers of antimicrobial consumption in the community (all antibacterials, cephalosporin, macrolides and fluoroquinolones). Results: The proportion of a country that was Protestant was negatively correlated with the consumption of all antibacterials. SEM revealed that UA predicted all antibacterial consumption (direct effect coef. 0.15, 95% Confidence Interval [CI] 0.04-0.26). The proportion Protestant exerted an indirect effect on consumption (coef. -0.13, 95% CI -0.21- -0.05). This effect was mediated predominantly via its effect on UA (direct effect coef. 0.15, 95% CI 0.04-0.26). The model explained 37% of the variation in consumption.  Similar results were obtained for each of the other three classes of antimicrobials investigated. Conclusions: Our results are compatible with the theory that contemporary differences in antimicrobial consumption in Europe stem in part from cultural differences that emerged in the Reformation. These findings may explain the differential efficacy of similar antibiotic stewardship campaigns in Northern and Southern European populations.

Modularity and evolution of flower shape: the role of function, development, and spandrels in Erica.

Flowers have been hypothesized to contain either modules of attraction and reproduction, functional modules (pollination-effecting parts) or developmental modules (organ-specific). Do pollination specialization and syndromes influence floral modularity? In order to test these hypotheses and answer this question, we focused on the genus Erica: we gathered 3D data from flowers of 19 species with diverse syndromes via computed tomography, and for the first time tested the above-mentioned hypotheses via 3D geometric morphometrics. To provide an evolutionary framework for our results, we tested the evolutionary mode of floral shape, size and integration under the syndromes regime, and - for the first time - reconstructed the high-dimensional floral shape of their most recent common ancestor. We demonstrate that the modularity of the 3D shape of generalist flowers depends on development and that of specialists is linked to function: modules of pollen deposition and receipt in bird syndrome, and access-restriction to the floral reward in long-proboscid fly syndrome. Only size and shape principal component 1 showed multiple-optima selection, suggesting that they were co-opted during evolution to adapt flowers to novel pollinators. Whole floral shape followed an Ornstein-Uhlenbeck (selection-driven) evolutionary model, and differentiated relatively late. Flower shape modularity thus crucially depends on pollinator specialization and syndrome.

Genetic Code Error Minimization as a Non-Adaptive But Beneficial Trait.

In a recent Letter, Di Giulio questions the use of the term 'neutral' when describing the process by which error minimization may have arisen as a side-product of genetic code expansion, resulting from the addition of similar amino acids to similar codons (Di Giulio, in J Mol Evol 86(9):593-597, 2018). However, I point out that in this scenario error minimization is non-adaptive, and so 'neutral' is an appropriate term to describe its imperviousness to direct selection. Error minimization is a form of mutational robustness, and so commonly viewed as beneficial. This in turn implies that not all beneficial traits may be adaptations generated by direct selection for that trait.

Oblique human symphyseal angle is associated with an evolutionary rate-shift early in the hominin clade.

The rate of change in primate mandibular symphyseal angles was modeled with particular aim of locating a rate-shift within the hominin clade. Prior work noted that the human symphyseal angle must have experienced a rapid rate of change in order to assume the modern human form, suggestive of the non-random work of natural selection. This study indicates that the rate of symphyseal evolution rose dramatically between Australopithecus anamensis and Australopithecus afarensis and continued throughout the diversification of the hominin clade. Noting the timing of this event, we speculate as to what ecological factors could have been at play in driving this rearrangement of the anterior mandible, contributing to the eventual appearance of the human chin.

Meiotic chromosome stability of a newly formed allohexaploid wheat is facilitated by selection under abiotic stress as a spandrel.

Polyploidy is a prominent route to speciation in plants; however, this entails resolving the challenges of meiotic instability facing abrupt doubling of chromosome complement. This issue remains poorly understood. We subjected progenies of a synthetic hexaploid wheat, analogous to natural common wheat, but exhibiting extensive meiotic chromosome instability, to heat or salt stress. We selected stress-tolerant cohorts and generated their progenies under normal condition. We conducted fluorescent in situ hybridization/genomic in situ hybridization-based meiotic/mitotic analysis, RNA-Seq and virus-induced gene silencing (VIGS)-mediated assay of meiosis candidate genes. We show that heritability of stress tolerance concurred with increased euploidy frequency due to enhanced meiosis stability. We identified a set of candidate meiosis genes with altered expression in the stress-tolerant plants vs control, but the expression was similar to that of common wheat (cv Chinese Spring, CS). We demonstrate VIGS-mediated downregulation of individual candidate meiosis genes in CS is sufficient to confer an unstable meiosis phenotype mimicking the synthetic wheat. Our results suggest that heritable regulatory changes of preexisting meiosis genes may be hitchhiked as a spandrel of stress tolerance, which significantly improves meiosis stability in the synthetic wheat. Our findings implicate a plausible scenario that the meiosis machinery in hexaploid wheat may have already started to evolve at its onset stage.

Causes and evolutionary consequences of primordial germ-cell specification mode in metazoans.

In animals, primordial germ cells (PGCs) give rise to the germ lines, the cell lineages that produce sperm and eggs. PGCs form in embryogenesis, typically by one of two modes: a likely ancestral mode wherein germ cells are induced during embryogenesis by cell-cell signaling (induction) or a derived mechanism whereby germ cells are specified by using germ plasm-that is, maternally specified germ-line determinants (inheritance). The causes of the shift to germ plasm for PGC specification in some animal clades remain largely unknown, but its repeated convergent evolution raises the question of whether it may result from or confer an innate selective advantage. It has been hypothesized that the acquisition of germ plasm confers enhanced evolvability, resulting from the release of selective constraint on somatic gene networks in embryogenesis, thus leading to acceleration of an organism's protein-sequence evolution, particularly for genes expressed at early developmental stages, and resulting in high speciation rates in germ plasm-containing lineages (denoted herein as the "PGC-specification hypothesis"). Although that hypothesis, if supported, could have major implications for animal evolution, our recent large-scale coding-sequence analyses from vertebrates and invertebrates provided important examples of genera that do not support the hypothesis of liberated constraint under germ plasm. Here, we consider reasons why germ plasm might be neither a direct target of selection nor causally linked to accelerated animal evolution. We explore alternate scenarios that could explain the repeated evolution of germ plasm and propose potential consequences of the inheritance and induction modes to animal evolutionary biology.

A General Statistical Method for Identifying Adaptations by Parameterizing Trait Space.

It is obviously useful to think of evolved individuals in terms of their adaptations, yet the task of empirically classifying traits as adaptations has been claimed by some to be impossible in principle. I reject that claim by construction, introducing a formal method to empirically test whether a trait is an adaptation. The method presented is general, intuitive, and effective at identifying adaptations while remaining agnostic about their adaptive function. The test follows directly from the notion that adaptations arise from variation, heritability, and differential fitness in an evolving population: I operationalize these three concepts at the trait level, formally defining measures of individual traits. To test whether a trait is an adaptation, these measures are evaluated, locating the trait within a three-dimensional parameterized trait space. Within this space, I identify a region containing all adaptations; a trait's position relative to this adaptive region of trait space describes its status as an adaptation. The test can be applied in any evolving system where a few domain-specific statistical measures can be constructed; I demonstrate the construction of these measures, most notably a measure of an individual's hypothetical fitness if it were born with a different trait, in Packard's Bugs ALife model. The test is applied in Bugs, and shown to conform with our intuitive classification of adaptations.

The enduring puzzle of the human chin.

Although modern humans are considered to be morphologically distinct from other living primates because of our large brains, dexterous hands, and bipedal gait, all of these features are found among extinct hominins. The chin, however, appears to be a uniquely modern human trait. Probably because of the chin's exclusivity, many evolutionary scenarios have been proposed to explain its origins. To date, researchers have developed adaptive hypotheses relating chins to speech, mastication, and sexual selection; still others see it as a structural artifact tangentially related to complex processes involving evolutionary retraction of the midfacial skeleton. Consensus has remained elusive, partly because hypotheses purporting to explain how this feature developed uniquely in modern humans are all fraught with theoretical and/or empirical shortcomings. Here we review a century's worth of chin hypotheses and discuss future research avenues that may provide greater insight into this human peculiarity.

Selection played a role in the evolution of the human chin.

Chins, which are unique to humans, have generated considerable debate concerning their evolutionary origins, yet a consensus has remained elusive. Many have argued that chins are adaptations for chewing stress, speech, or sexual ornamentation. Alternatively, some have suggested that chins are spandrels-byproducts of selection operating elsewhere in the mandible or face. Lastly, chins could be the product of genetic drift. The questions addressed by this study are: [1] whether chins represent an exceptionally derived morphological condition, and [2] if this can be interpreted as the product of natural selection. These questions are important since the chin is one of the features used to define Homo sapiens in the fossil record. Quantitative measures that capture the degree of chin expression were gathered from a sample of 123 primate taxa, and evolutionary rates associated with these measures were reconstructed in the primate phylogeny. The evolutionary rate associated with these measures was reconstructed to be far higher along the Homo tip (∼77 times greater than the primate background rate of evolution) than elsewhere in the primate phylogeny. These results suggest that human symphyseal morphology is exceptionally derived relative to other primates, and selection has been operational in producing the human chin.

Functionalists and zombis: Sorcery as spandrel and social rescue.

At one level, anthropologists remain functionalists in that they generally see acts and institutions as contributing to a greater social whole only through which they make sense. Thus, sorcery accusations have been traditionally interpreted in terms of maintaining social harmony and cohesion. In the case of Haitian zombification, the zombi seems a locally misidentified victim who is frequently mentally ill. As a hapless non-agent, the zombi cannot initiate the sorcery accusations, so how do we understand the recognition and rescue of the zombi, either in terms of social function or social action?