Jawed vertebrates

Phylogenetic analysis helps us understand the evolutionary history and mechanism of the extraordinary diversity of the vertebrate OR gene family. The phylogenetic tree shows that the OR gene family can be classified into two groups, type 1 and type 2 (Fig. la). The divergence of these two types predated the split between jawed vertebrates and jawless vertebrates (Fig. lb). The phylogenetic analysis revealed at least... 

Apart from sharks, where the upper and lower teeth are relatively similar in shape and number, the upper and lower jaws of modern jawed vertebrates (gnathostomes) generally differ in the shape and number of their teeth or tooth-bearing dermal bones. In bony fishes (osteichthyans), and land vertebrates (tetrapods), this difference disappears as one considers early, Paleozoic groups, whose upper jaw bones are almost a mirror image of those of the lower jaw. This curious symmetry has been pointed out long ago by the American paleontologist A.S. Romer in early... 

Forey, P.L. (1995) Agnathans recent and fossil, and the origin of jawed vertebrates . Reviews in Fish Biology and Fisheries, 5, 267-303. 

Mallatt, J. (1996) Ventilation and the origin of jawed vertebrates a new mouth . Zoological Journal of the Linnean Society, 117, 329-404. 

Figure 9.5 Frequency distribution of LogDet distances among the main lineages of jawed vertebrates. Path lengths from the most recent common ancestor (MRCA) to sharks, the bichir, teleosts, the coelacanth, the lungfishes and tetrapods were calculated across the NJ tree recovered from the 28S rRNA gene data set.A faster evolutionary rate is observed for the lungfishes and the bichir.

In the absence of articulated specimens, it is problematic to prove the presence of jawed vertebrates in the Ordovician based upon scale morphology and histology alone. However, a number of scales recovered from the Harding Sandstone bear a remarkable resemblance to those from accepted stem and crown gnathostomes with jaws. They can be divided into two types Skiichthys halsteadi with scales bearing a... 

In addition to these migrating pheromones, the lampreys produce and use conventional steroid sex hormones such as progesterone, androstenedione and estradiol, but also 15-hydroxysteroids that are generally absent in the jawed vertebrates. Among these are 15a-... 

Abstract This chapter describes what is known about the main components and responses of the innate and adaptive immune system of fish. The chapter first reviews the organs, cells and molecules of the immune system known in a few economically important or model fish species. Molecular evidence suggests a similar immune system exists throughout the jawed vertebrates yet marked differences are also apparent. The innate parameters are at the forefront of fish immune defence and are a crucial factor in disease resistance. The adaptive response of fish is commonly delayed but is essential for long lasting immunity and a key factor in successful vaccination. 

The thymus is considered a key organ of the immune system in jawed vertebrates. It is thought to have evolved in early fish species as a thickening in the epithelium of the pharyngeal area of the gastro-intestinal tract (Bowden et al, 2005), and is identifiable in the Chondrichthyes and the... 

Three isotypes, IgM, IgD and IgT (also called IgZ in zebrafish) have been identified in almost all studied species belonging to the main orders of teleost fish. The main exception is that IgT has not been found thus far in the channel catfish (I. punctatus) (Edholm et al, 2010,2011). IgM is the most ancient and the only isotype functionally conserved in all jawed vertebrates. IgD has been found in all jawed vertebrate groups except birds, indicating that it is also a primordial antibody class despite its highly plastic structure and unclear function in evolution (Edholm et al, 2010, 2011). Other Ig isotypes have evolved to play specialized roles either within mucosal or systemic compartments. In mammals and birds, the IgM, IgG and IgY isotypes have major roles in systemic responses, while IgA is the main player in mucosal areas. In amphibians, IgM and IgY play a prevalent role in systemic immunity whereas IgX is an isotype chiefly expressed in the gut (Flajnik, 2010). The fish IgT is a mucosal-epithelial Ig preferentially... 

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