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"Living fossils."
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Living fossils : clues to the past
Introduces \"living fossils, or modern-day animals that very closely resemble their ancient relatives. Meet the coelacanth, horseshoe crab, dragonfly, tuatara, nautilus, and Hula painted frog. All are living fossils. Why have they changed so little over time, while other animals evolved or went extinct?\"--Amazon.com.
Book
Genomic insights on the contribution of balancing selection and local adaptation to the long-term survival of a widespread living fossil tree, Cercidiphyllum japonicum
‘Living fossils’ are testimonies of long-term sustained ecological success, but how demographic history and natural selection contributed to their survival, resilience, and persistence in the face of Quaternary climate fluctuations remains unclear.
To better understand the interplay between demographic history and selection in shaping genomic diversity and evolution of such organisms, we assembled the whole genome of Cercidiphyllum japonicum, a widespread East Asian Tertiary relict tree, and resequenced 99 individuals of C. japonicum and its sister species, Cercidiphyllum magnificum (Central Japan).
We dated this speciation event to the mid-Miocene, and the intraspecific lineage divergence of C. japonicum (China vs Japan) to the Early Pliocene. Throughout climatic upheavals of the late Tertiary/Quaternary, population bottlenecks greatly reduced the genetic diversity of C. japonicum. However, this polymorphism loss was likely counteracted by, first, long-term balancing selection at multiple chromosomal and heterozygous gene regions, potentially reflecting overdominance, and, second, selective sweeps at stress response and growth-related genes likely involved in local adaptation.
Our findings contribute to a better understanding of how living fossils have survived climatic upheaval and maintained an extensive geographic range; that is, both types of selection could be major factors contributing to the species’ survival, resilience, and persistence.
Journal Article
Dragonflies lived with the dinosaurs!
Provides information on dragonflies, including their behavior, how they've adapted over the years, and why they survived while dinosaurs became extinct.
Book
Rethinking Living Fossils
Biologists would be mistaken if they relegated living fossils to paleontological inquiry or assumed that the concept is dead. It is now used to describe entities ranging from viruses to higher taxa, despite recent warnings of misleading inferences. Current work on character evolution illustrates how analyzing living fossils and stasis in terms of parts (characters) and wholes (e.g., organisms and lineages) advances our understanding of prolonged stasis at many hierarchical levels. Instead of viewing the concept’s task as categorizing living fossils, we show how its primary role is to mark out what is in need of explanation, accounting for the persistence of both molecular and morphological traits. Rethinking different conceptions of living fossils as specific hypotheses reveals novel avenues for research that integrate phylogenetics, ecological and evolutionary modeling, and evo-devo to produce a more unified theoretical outlook.
Journal Article
Sharks lived with the dinosaurs!
Provides information on sharks, including their behavior, how they've adapted over the years, and why they survived while dinosaurs became extinct.
Book
Plastome data provides new insights into population differentiation and evolution of Ginkgo in the Sichuan Basin of China
Background
Ginkgo biloba
L., an iconic living fossil, challenges traditional views of evolutionary stasis. While nuclear genomic studies have revealed population structure across China, the evolutionary patterns reflected in maternally inherited plastomes remain unclear, particularly in the Sichuan Basin - a potential glacial refugium that may have played a crucial role in
Ginkgo
’s persistence.
Results
Analysis of 227 complete plastomes, including 81 newly sampled individuals from the Sichuan Basin, revealed three distinct maternal lineages differing from known nuclear genome patterns. We identified 170 sequence variants and extensive RNA editing (235 sites) with a bias toward hydrophobic amino acid conversions, suggesting active molecular evolution. A previously undocumented haplotype (IIA2), predominant in western Sichuan Basin populations, showed close genetic affinity with rare refugial haplotypes. Western populations exhibited higher haplotypic diversity and distinctive genetic structure, supporting the basin’s role as both glacial refugium and corridor for population expansion. Ancient trees (314–784 years) provided evidence for interaction between natural processes and historical human dispersal in shaping current genetic patterns.
Conclusions
Our findings demonstrate substantial genetic diversity within Sichuan Basin
Ginkgo
populations and reveal dynamic molecular evolution through plastome variation and RNA editing patterns, challenging the notion of evolutionary stasis in this living fossil. This study provides crucial genomic resources for understanding
Ginkgo
’s evolution and informs conservation strategies for this endangered species.
Journal Article
BOOM AND BUST: ANCIENT AND RECENT DIVERSIFICATION IN BICHIRS (POLYPTERIDAE: ACTINOPTERYGII), A RELICTUAL LINEAGE OF RAY-FINNED FISHES
Understanding the history that underlies patterns of species richness across the Tree of Life requires an investigation of the mechanisms that not only generate young species-rich clades, but also those that maintain species-poor lineages over long stretches of evolutionary time. However, diversification dynamics that underlie ancient species-poor lineages are often hidden due to a lack of fossil evidence. Using information from the fossil record and time calibrated molecular phylogenies, we investigate the history of lineage diversification in Polypteridae, which is the sister lineage of all other ray-finned fishes (Actinopterygii). Despite originating at least 390 million years (Myr) ago, molecular timetrees support a Neogene origin for the living polypterid species. Our analyses demonstrate polypterids are exceptionally species depauperate with a stem lineage duration that exceeds 380 million years (Ma) and is significantly longer than the stem lineage durations observed in other ray-finned fish lineages. Analyses of the fossil record show an early Late Cretaceous (100.5–83.6 Ma) peak in polypterid genus richness, followed by 60 Ma of low richness. The Neogene species radiation and evidence for high-diversity intervals in the geological past suggest a \"boom and bust\" pattern of diversification that contrasts with common perceptions of relative evolutionary stasis in so-called \"living fossils.\"
Journal Article
Extreme survivors : animals that time forgot
Looks at animals that existed in prehistoric times and still exist today and suggests how these creatures managed to survive while other animals are now extinct.
Book
Remarkable morphological stasis in an extant vertebrate despite tens of millions of years of divergence
The relationship between genotypic and phenotypic divergence over evolutionary time varies widely, and cases of rapid phenotypic differentiation despite genetic similarity have attracted much attention. Here, we report an extreme case of the reverse pattern—morphological stasis in a tropical fish despite massive genetic divergence. We studied the enigmatic African freshwater butterfly fish (Pantodon buchholzi), whose distinctive morphology earns it recognition as a monotypic family. We sequenced the mitochondrial genome of Pantodon from the Congo basin and nine other osteoglossomorph taxa for comparison with previous mitogenomic profiles of Pantodon from the Niger basin and other related taxa. Pantodon populations form a monophyletic group, yet their mitochondrial coding sequences differ by 15.2 per cent between the Niger and Congo basins. The mitogenomic divergence time between these populations is estimated to be greater than 50 Myr, and deep genetic divergence was confirmed by nuclear sequence data. Among six sister-group comparisons of osteoglossomorphs, Pantodon exhibits the slowest rate of morphological divergence despite a level of genetic differentiation comparable to both species-rich (e.g. Mormyridae) and species-poor (e.g. Osteoglossidae) families. Morphological stasis in these two allopatric lineages of Pantodon offers a living vertebrate model for investigating phenotypic stability over millions of generations in the face of profound fluctuations in environmental conditions.
Journal Article