Freshwater fish and the Cretaceous/Palaeogene boundary: a critical assessment of survivorship patterns.

Mass extinctions are major influences on both the phylogenetic structure of the modern biota and our ability to reconstruct broad-based patterns of evolutionary history. The most recent mass extinction is also the most famous-that which implicates a bolide impact in defining the Cretaceous/Palaeogene boundary (K/Pg). Although the biotic effects of this event receive intensive scrutiny, certain ecologically important and diverse groups remain woefully understudied. One such group is the freshwater ray-finned fishes (Actinopterygii). These fish represent 25% of modern vertebrate diversity, yet the isolated and fragmentary nature of their K/Pg fossil record limits our understanding of their diversity dynamics across this event. Here, we address this problem using diversification analysis of molecular-based phylogenies alongside a morphotype analysis of fossils recovered from a unique site in the Denver Basin of western North America that provides unprecedented K/Pg resolution. Our results reveal previously unrecognized signals of post-K/Pg diversification in freshwater clades and suggest that the change was driven by localized and sporadic patterns of extinction. Supported inferences regarding the effects of the K/Pg event on freshwater fish also inform our expectations of how freshwater faunas might recover from the current biodiversity crisis.

Purring Crickets: The Evolution of a Novel Sexual Signal.

Opportunities to observe contemporary signal change are incredibly rare but critical for understanding how diversity is created and maintained. We discovered a population of the Pacific field cricket (Teleogryllus oceanicus) with a newly evolved song (purring), different from any known cricket. Male crickets use song to attract females from afar and to court females once near. Teleogryllus oceanicus is well known for sexual signal evolution, as exemplified by a recent signal loss. In this study, we characterized the new purring sound and investigated the role of the purr in long-distance and short-distance communication. The purring sound differed from typical ancestral calls in peak frequency, amplitude, and bandwidth. Further, the long-distance purring song facilitated mate location, though the role of courtship purring song is less clear. Our discovery of purring male crickets is an unprecedented opportunity to watch the emergence of a newly evolved sexual signal unfold in real time and has potential to illuminate the mechanisms by which evolutionary novelties arise and coevolve between the sexes.

Characterization and Evolution of the Spotted Gar Retina.

In this study, we characterize the retina of the spotted gar, Lepisosteus oculatus, a ray-finned fish. Gar did not undergo the whole genome duplication event that occurred at the base of the teleost fish lineage, which includes the model species zebrafish and medaka. The divergence of gars from the teleost lineage and the availability of a high-quality genome sequence make it a uniquely useful species to understand how genome duplication sculpted features of the teleost visual system, including photoreceptor diversity. We developed reagents to characterize the cellular organization of the spotted gar retina, including representative markers for all major classes of retinal neurons and Müller glia. We report that the gar has a preponderance of predicted short-wavelength shifted (SWS) opsin genes, including a duplicated set of SWS1 (ultraviolet) sensitive opsin encoding genes, a SWS2 (blue) opsin encoding gene, and two rod opsin encoding genes, all of which were expressed in retinal photoreceptors. We also report that gar SWS1 cones lack the geometric organization of photoreceptors observed in teleost fish species, consistent with the crystalline photoreceptor mosaic being a teleost innovation. Of note the spotted gar expresses both exo-rhodopsin (RH1-1) and rhodopsin (RH1-2) in rods. Exo-rhodopsin is an opsin that is not expressed in the retina of zebrafish and other teleosts, but rather is expressed in regions of the brain. This study suggests that exo-rhodopsin is an ancestral actinopterygian (ray finned fish) retinal opsin, and in teleosts its expression has possibly been subfunctionalized to the pineal gland.

Neurodevelopmental implications of COVID-19-induced gut microbiome dysbiosis in pregnant women.

The global public health emergency of COVID-19 in January 2020 prompted a surge in research focusing on the pathogenesis and clinical manifestations of the virus. While numerous reports have been published on the acute effects of COVID-19 infection, the review explores the multifaceted long-term implications of COVID-19, with a particular focus on severe maternal COVID-19 infection, gut microbiome dysbiosis, and neurodevelopmental disorders in offspring. Severe COVID-19 infection has been associated with heightened immune system activation and gastrointestinal symptoms. Severe COVID-19 may also result in gut microbiome dysbiosis and a compromised intestinal mucosal barrier, often referred to as 'leaky gut'. Increased gut permeability facilitates the passage of inflammatory cytokines, originating from the inflamed intestinal mucosa and gut, into the bloodstream, thereby influencing fetal development during pregnancy and potentially elevating the risk of neurodevelopmental disorders such as autism and schizophrenia. The current review discusses the role of cytokine signaling molecules, microglia, and synaptic pruning, highlighting their potential involvement in the pathogenesis of neurodevelopmental disorders following maternal COVID-19 infection. Additionally, this review addresses the potential of probiotic interventions to mitigate gut dysbiosis and inflammatory responses associated with COVID-19, offering avenues for future research in optimizing maternal and fetal health outcomes.