Evolution of the craniate middle ear

Abstract Among the major distance senses of vertebrates, the ear is unique in its complex morphological changes during evolution. Conceivably, these changes enable the ear to adapt toward sensing various physically well-characterized stimuli. This review develops a scenario that integrates sensory cell with organ evolution.

Evolution of the craniate middle ear

Figure 3 Pharyngeal arch primordia and CNC condensation patterns that form craniofacial cartilages in zebrafish. Lateral views at 28 hours A,B and 72 hours C,D postfertilization. The zebrafish lockjaw low mutant disrupts the transcription factor AP-2 alpha tfap2awhich also regulates Hox gene expression.

Like moz, homozygous low mutants exhibit segment-specific changes in CNC fate in the arches, but not in the hindbrain.

Evolution and development of the vertebrate ear. Author links open Ultimately we will come up with a more plausible scenario of molecular evolution of hair cell development of the vertebrate ear and its invertebrate sensory relatives that will be based on hundreds and not a few genes. the evolution and development of the middle ear is a. Start studying Bio - Ch. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Search. Which of the following represents the strongest evidence that two of the three middle ear bones of mammals are homologous to certain reptilian jawbones? The craniate clade is synonymous with the vertebrate clade. 4. The evolution of mammalian auditory ossicles was an evolutionary event in which bones in the jaw of reptiles were co-opted to form part of the hearing apparatus in mammals. The event is well-documented [1] and important [2] [3] as a demonstration of transitional forms and exaptation, the re-purposing of existing structures during evolution.

This CNC-specific requirement for tfap2a in hoxa2 regulation is conserved with mammals; the mouse Hoxa2 promoter contains an AP-2 binding site essential for expression in the CNC but not in the hindbrain.

These correlate with early defects in the specification of the premigratory neural crest expression of foxd3 and sox9a is reduced in tfap2a mutants and cell survival in low mutants. These studies in low and moz support the paradigm of independent regulation of hox2 genes in CNC and the hindbrain and reveal that the final fate of the CNC is not dictated simply by its hindbrain level of origin, but requires signals from adjacent tissues.

However this CNC, perhaps more than any other, possesses an identity independent of adjacent tissues once it has migrated into the head periphery. This was dramatically demonstrated by Noden 19 in a classical series of transplantation experiments in avian embryos, in which midbrain CNC Hox negative was grafted to more posterior hindbrain Hox positive regions.

Evolution of the mammalian middle ear.

Surprisingly, grafted cells retained the identity appropriate for their original positions in the donor embryo and formed an ectopic mandibular skeleton. Notably, these grafts reorganized the surrounding mesoderm to form an ectopic set of mandibular muscles, indicating that CNC is instructive for muscle development.

How do CNC cells that form the skeleton interact with the muscles to which they attach? In the head, this coordination appears to be regulated by specialized attachment cells putative tendon or ligament precursors that are also derived from CNC fig. These resemble attachment cells in the limb, which derive from lateral plate mesoderm and are able to assemble a correct spatial pattern in the complete absence of myocytes.

Fate mapping studies of CNC in chick-quail chimeras revealed a striking correlation in the embryonic origins of these two tissues. Tendon precursors attaching a muscle to a particular bone originated from the same A-P location in the CNC as the precursors of that bone.

Through this process, CNC-derived skeletal and tendon precursors may coordinate the formation of the entire functional skeletomuscular system. Mutant studies in zebrafish also support the model that CNC cells play instructive roles in patterning cranial muscles.

Evolution of the craniate middle ear

Histological analysis of the chinless chn mutant revealed that the pharyngeal skeleton and cranial muscles fail to form entirely. Rescued myocytes were confined to regions immediately adjacent to CNC derived from the donor, demonstrating the local nature of the interaction.

Evolution of mammalian auditory ossicles - Wikipedia

These in turn are surrounded by endodermal and ectodermal epithelia. Separate dorsal and ventral condensations proximal and distal in mice form in the CNC and these are serially reiterated in every arch fig.These represent key events in the evolution of the craniate ear and in the elaboration of audition.

enlarge figure Figure 1 Schematic illustrations of the left inner ear of various vertebrates in lateral view. Evolution of the craniate middle ear The evolution of the auditory structures of the middle ear began with the recycling of the second gill arches in primitive fish (Braxeau and Jeffery ).

While the first set of gill arches became the upper and lower jaws, the upper portion of the second gill arch, the hyoid arch, became a support structure for the cranium as the hyomandibula (Manley ).

•gill pouches and arches, teeth, parts of skull, jaws, middle ear, sensory organs and more 2.


1st duplication of hox gene complex- code for more complex bodies What happened in the evolution of jawed vertebrates or the gnathostomes? Jun 11,  · In conclusion, the evolution of the mammalian middle ear and jaw joint were pivotal steps in the evolution of mammals.

It is also a great example of how classical comparative anatomy, paleontology and developmental biology have come together to piece together how this remarkable transformation of jaw joint to ear ossicles was able to come about. The Craniata, or craniates, include all animals having a skull (or cranium, hence their name), be it cartilaginous or bony.

A skull is a box of hard tissues which encloses the . C) Humans represent the pinnacle of evolution and have escaped from being affected by natural selection. D) Humans evolved from chimpanzees. E) Humans and apes are the result of disruptive selection in a species of chimpanzee.