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Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
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Humerus shape evolved in cetaceans under relaxed selection and random drift.

Maria Ghazali1, Svitozar Davydenko2, Valeriia Telizhenko3

  • 1Schmalhausen Institute of Zoology, National Academy of Sciences of Ukraine, Kyiv, Ukraine. ghazali.maria@gmail.com.

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Summary
This summary is machine-generated.

Cetacean humerus shape evolved independently of mechanical loading, revealing aquatic adaptations and phylogenetic patterns. Gene evolution in cetaceans shows relaxed selection and novel mutations, illustrating evolutionary innovation.

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Area of Science:

  • Evolutionary biology
  • Comparative anatomy
  • Paleontology

Background:

  • Mammalian humerus shape is typically dictated by biomechanical loading.
  • Cetaceans (whales and dolphins) present a unique case where this constraint is relaxed, allowing for other evolutionary drivers to influence bone morphology.

Purpose of the Study:

  • To investigate the three-dimensional (3D) shape of the humerus in extinct and extant cetaceans.
  • To determine if humerus shape evolution in cetaceans reflects specific evolutionary trends independent of allometry and mechanical loading.

Main Methods:

  • Analysis of the 3D humerus shape of 36 cetacean taxa, encompassing both fossil and living species.
  • Comparative morphological analysis to identify shape variations and their correlation with evolutionary divergence and phylogeny.

Main Results:

  • Humerus shape variance correlates with the evolutionary divergence of baleen and toothed whales, independent of allometric scaling.
  • Observed anatomical traits include humeral head twist, shortened and straightened diaphysis, and enlarged epiphyses, indicative of aquatic locomotion.
  • Phylogenetic analysis reveals associations between humeral head and greater tubercle anatomy, modularity, and integration patterns.

Conclusions:

  • Relaxed negative selection and random drift are proposed as key evolutionary mechanisms shaping cetacean humerus morphology.
  • Genetic analysis indicates relaxed selection, positive selection, and nonsense mutations in genes regulating humerus shape in cetaceans.
  • The study supports a
  • fly in a tube model
  • framework for understanding evolutionary innovations.