
The sperm hook in house mice plays a crucial role in facilitating sperm migration and interactions with the female reproductive tract epithelium, enabling successful sperm transport and self-organized sperm behaviors.


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In most murine species, spermatozoa exhibit a falciform apical hook at the head end. The function of the sperm hook is not yet clearly understood. In this study, we investigate the role of the sperm hook in the migration of spermatozoa through the female reproductive tract in Mus musculus (C57BL/6), using a deep tissue imaging custom-built two-photon microscope. Through live reproductive tract imaging, we found evidence indicating that the sperm hook aids in the attachment of spermatozoa to the epithelium and facilitates interactions between spermatozoa and the epithelium during migration in the uterus and oviduct. We also observed synchronised sperm beating, which resulted from the spontaneous unidirectional rearrangement of spermatozoa in the uterus. Based on live imaging of spermatozoa-epithelium interaction dynamics, we propose that the sperm hook plays a crucial role in successful migration through the female reproductive tract by providing anchor-like mechanical support and facilitating interactions between spermatozoa and the female reproductive tract in the house mouse.

### Competing Interest Statement

The authors have declared no competing interest.

The sperm hook in house mice: a functional adaptation for migration and self-organised behaviour

the-sperm-hook-in-house-mice-its-role-in-sperm-migration-and-self-organized-behavior-within-the-female-reproductive-tract


The Sperm Hook in House Mice: Its Role in Sperm Migration and Self-Organized Behavior within the Female Reproductive Tract


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Contrary to previous assumptions, many undefended poison frog species have measurable levels of alkaloids, suggesting the existence of a phenotypic intermediate between toxin consumption and sequestration - passive accumulation - that differs from active sequestration.


Understanding the origins of novel, complex phenotypes is a major goal in evolutionary biology. Poison frogs of the family Dendrobatidae have evolved the novel ability to acquire alkaloids from their diet for chemical defense at least three times. However, taxon sampling for alkaloids has been biased towards colorful species, without similar attention paid to inconspicuous ones that are often assumed to be undefended. As a result, our understanding of how chemical defense evolved in this group is incomplete. Here we provide new data showing that, in contrast to previous studies, species from each undefended poison frog clade have measurable yet low amounts of alkaloids. We confirm that undefended dendrobatids regularly consume mites and ants, which are known sources of alkaloids. Further, we confirm the presence of alkaloids in two putatively non-toxic frogs from other families. Our data suggest the existence of a phenotypic intermediate between toxin consumption and sequestration—passive accumulation—that differs from active sequestration in that it involves no derived forms of transport and storage mechanisms yet results in low levels of toxin accumulation. We discuss the concept of passive accumulation and its potential role in the origin of chemical defenses in poison frogs and other toxin-sequestering organisms.

### Competing Interest Statement

The authors have declared no competing interest.

Passive accumulation of alkaloids in non-toxic frogs challenges paradigms of the origins of acquired chemical defenses

widespread-passive-accumulation-of-alkaloids-in-putatively-non-toxic-frogs-challenges-paradigms-of-the-origins-of-acquired-chemical-defenses


Widespread Passive Accumulation of Alkaloids in Putatively Non-Toxic Frogs Challenges Paradigms of the Origins of Acquired Chemical Defenses



The Cambrian Explosion, which occurred around 550 million years ago, marked a dramatic shift in the complexity and diversity of life on Earth, transitioning from simple, single-celled organisms to the emergence of large, multicellular plants, animals, and fungi.


For billions of years on Earth, life was limited to simple unicellular, non-differentiated organisms. In a mere flash, that changed…

What was it like when life on Earth became complex?

the-emergence-of-complex-life-on-earth-a-remarkable-transition-in-the-planet-s-evolutionary-history


The Emergence of Complex Life on Earth: A Remarkable Transition in the Planet's Evolutionary History



Comprehensive genomic analysis of 363 bird species across 218 families reveals a well-supported avian phylogenetic tree, but also significant discordance, highlighting the complexity of avian evolution and the rapid radiation of modern birds following the Cretaceous-Paleogene extinction event.


Complexity of avian evolution revealed by family-level genomes - Nature

comprehensive-genomic-analysis-reveals-complexity-and-rapid-diversification-of-avian-evolution


Comprehensive Genomic Analysis Reveals Complexity and Rapid Diversification of Avian Evolution



Ageing is an adaptive evolutionary mechanism that emerges from the mathematical constraints of a system with reproduction and homeostasis, rather than a byproduct of evolution.


Signs of ageing become apparent only late in life, after organismal development is finalized. Ageing, most notably, decreases an individual’s fitness. As such, it is most commonly perceived as a non-adaptive force of evolution and considered a by-product of natural selection.

Building upon the evolutionarily conserved age-related Smurf phenotype, we propose a simple mathematical life-history trait model in which an organism is characterized by two core abilities: reproduction and homeostasis.

Through the simulation of this model, we observe 1) the convergence of fertility’s end with the onset of senescence, 2) the relative success of ageing populations, as compared to non-ageing populations, and 3) the enhanced evolvability (i.e. the generation of genetic variability) of ageing populations. In addition, we formally demonstrate the mathematical convergence observed in 1).

We thus theorize that mechanisms that link the timing of fertility and ageing have been selected and fixed over evolutionary history, which, in turn, explains why ageing populations are more evolvable and therefore more successful. Broadly speaking, our work suggests that ageing is an adaptive force of evolution.

### Competing Interest Statement

The authors have declared no competing interest.

A scenario for an evolutionary selection of ageing

ageing-as-an-adaptive-evolutionary-mechanism-mathematical-model-reveals-convergence-of-fertility-and-mortality


Ageing as an Adaptive Evolutionary Mechanism: Mathematical Model Reveals Convergence of Fertility and Mortality



Gene expression rate is a fundamental driver of purifying selection in natural populations, maintaining strong selection even in small populations.


Purifying selection is the most pervasive type of selection, as it constantly removes deleterious mutations arising in populations, directly scaling with population size. Highly expressed genes appear to accumulate fewer deleterious mutations between divergent species’ lineages (known as E-R anticorrelation), pointing towards gene expression as an additional driver of purifying selection. However, estimates of the effect of gene expression on segregating deleterious variants in natural populations are scarce, as is an understanding of the relative contribution of population size and gene expression to purifying selection. Here, we analyse genomic and transcriptomic data from two natural populations of closely related sister species with different demographic histories, the Emperor penguin ( Aptenodytes forsteri ) and the King penguin ( A. patagonicus) , and show that purifying selection at the population-level depends on gene expression rate, resulting in very high selection coefficients at highly expressed genes. Leveraging realistic forward simulations, we estimate that the top 10% of the most highly expressed genes in a genome experience a selection pressure corresponding to an average selection coefficient of -0.1, which decreases to a selection coefficient of -0.01 for the top 50%. Gene expression rate can be regarded as a fundamental parameter of protein evolution in natural populations, maintaining selection effective even at small population size. We suggest it could be used as a proxy for gene selection coefficients, which are notoriously difficult to derive in non-model species under real-world conditions.

### Competing Interest Statement

The authors have declared no competing interest.

Gene expression is the main driver of purifying selection in large penguin populations

gene-expression-drives-purifying-selection-in-penguin-populations


Gene Expression Drives Purifying Selection in Penguin Populations



The author proposes a method to estimate traits parameters in a Darwinian evolution model using Fisher's information, highlighting the importance of tracking changes in species traits over time.


information-theory-in-darwinian-evolution-population-dynamics-model


Information Theory in Darwinian Evolution Population Dynamics Model



The author argues that cities are the new engine of evolution, showcasing the rapid emergence of new species. By highlighting urban environments as hotspots for evolutionary change, the author challenges traditional views on biodiversity and adaptation.


Die neue Entstehung der Arten - Science Notes

The-Rapid-Evolution-of-Species-in-Cities


The Rapid Evolution of Species in Cities



The author argues that rapid life-history evolution in response to invasive species can lead to competitive asymmetry, favoring the invader over the resident species. This asymmetry is driven by differences in life-history traits that impact competition outcomes.


Biological invasions by phylogenetically and ecologically similar competitors pose an evolutionary challenge to native species. Cases of character displacement following invasions suggest that they can respond to this challenge by shifting their traits. However, the actual impact of such shifts on competition are seldom studied. Here, we study competition between two freshwater snails from Guadeloupe (French Antilles), the native Aplexa marmorata and the introduced Physa acuta . The former has responded to invasion by rapid life-history evolution towards earlier maturity, higher fecundity and higher juvenile survival, traits that might favor rapid population growth in a noncompetitive context, but not necessarily in a competitive one. We here observe negative impacts of competition by both species on each other, though P. acuta is dominant and over generations largely displaces A. marmorata from co-cultures. In addition, our experiments suggest that A. marmorata populations having experienced competition by P. acuta for sufficient time in nature, have evolved to become even less tolerant to it. Though apparently paradoxical, this result supports the hypothesis that rapid life-history evolution has allowed A. marmorata not to resist competition, but to avoid it by increasing its specialization into the colonizer lifestyle previously documented by long-term field surveys. This example illustrates how evolution, in accordance with metacommunity coexistence theory, sometimes takes other ways than specialization into distinct types of resources or habitats to ensure coexistence between related species inhabiting the same landscape.

### Competing Interest Statement

The authors have declared no competing interest.

Rapid life-history evolution reinforces competitive asymmetry between invasive and resident species

Rapid-Life-History-Evolution-and-Competitive-Asymmetry-Between-Invasive-and-Resident-Species


Rapid Life-History Evolution and Competitive Asymmetry Between Invasive and Resident Species



Reciprocity in humans is based on the idea of mutual benefit, but the evolutionary path to this behavior is complex and may require group cooperation.
