Development of the skull and pectoral girdle in Siberian sturgeon,Acipenser baerii, and Russian sturgeon,Acipenser gueldenstaedtii(Acipenseriformes: Acipenseridae)

Abstract

The head is considered the major novelty of the vertebrates and directly linked to their evolutionary success. Its form and development as well as its function, for example in feeding, is of major interest for evolutionary biologists. In this study, we describe the skeletal development of the cranium and pectoral girdle in Siberian (Acipenser baerii) and Russian sturgeon (A. gueldenstaedtii), two species that are commonly farmed in aquaculture and increasingly important in developmental studies. This study comprises the development of the neuro-, viscero- and dermatocranium and the dermal and chondral components of the pectoral girdle, from first condensation of chondrocytes in prehatchlings to the early juvenile stage and reveals a clear pattern in formation. The otic capsules, the parachordal cartilages, and the trabeculae cranii are the first centers of chondrification, at 8.4mm TL. These are followed by the mandibular, then the hyoid, and later the branchial arches. Teeth form early on the dentary, dermopalatine, and palatopterygoid, and then appear later in the buccal cavity as dorsal and ventral toothplates. With ongoing chondrification in the neurocranium a capsule around the brain and a strong rostrum are formed. Dermal ossifications start to form before closure of the dorsal neurocranial fenestrae. Perichondral ossification of cartilage bones occurs much later in ontogeny. Our results contribute data bearing on the homology of elements such as the lateral rostral canal bone that we regard homologous to the antorbital of other actinopterygians based on its sequence of formation, position and form. We further raise doubts on the homology of the posterior ceratobranchial among Actinopteri based on the formation of the hyoid arch elements. We also investigate the basibranchials and the closely associated unidentified gill-arch elements and show that they are not homologous. J. Morphol. 278:418-442, 2017. © 2017 Wiley Periodicals, Inc.

Sequence and timing of early cranial skeletal development in Xenopus laevis

“…Parachordals are one of the earliest appearing elements during X. laevis development. This is also the case in Oryzias latipes (Langille & Hall, 1987), sturgeons (Warth et al, 2017) and various anurans (St€ ohr, 1882). Investigations of Rana fusca (now Rana temporaria) indicate similarities in the developmental pattern of anurans (Gaupp, 1906;St€ ohr, 1882).…”

“…The development of the visceral skeleton in X. laevis does not follow the pattern observed in other vertebrates. It has been shown that the viscerocranium of chondrichtyans, sturgeons, and teleosts, as well as anurans, develop in an antero-posterior direction (Gaupp, 1906; Gillis, LUKAS AND OLSSON | 71 Modrell, & Baker, 2012;Langille & Hall, 1987;St€ ohr, 1882;Warth, Hilton, Naumann, Olsson, & Konstantinidis, 2017). In contrast, the ceratohyal is the first cartilage to appear in X. laevis development immediately followed by the palatoquadrate (Figure 3a).…”

Development of the muscles associated with the mandibular and hyoid arches in the Siberian sturgeon, Acipenser baerii (Acipenseriformes: Acipenseridae)

“…The first skeletal elements appear as small aggregations of chondrocytes of the trabecula cranii and the otic capsule (see figure a in Warth et al, ). No obvious chondrocytes are present in the viscerocranium.…”

“…Material used for clsm analysis is listed in Table . Additionally, cleared and stained material as listed in Warth et al () was consulted regarding skeletal anatomy and we dissected a specimen of Acipenser gueldenstaedtii (female, 1,280 mm TL) and Acipenser baerii (male, 1,200 mm TL); specimens were not retained.…”

“…The morphology of Acipenseriformes has been studied intensely since the late 19th and early 20th century (Parker, 1881;Pehrson, 1944;van Wijhe, 1882). To date, special emphasis has been put on their skeletal structures (Dillman & Hilton, 2015;Findeis, 1993Findeis, , 1997Hilton, Grande, & Bemis, 2011), especially the large dermal scutes of sturgeons (Lepr evost, Aza € Is, Trichet, & Sire, 2016), the development of the pectoral girdle (Dillman & Hilton, 2015), and the development of the head skeleton (e.g., de Beer, 1925;Jollie, 1980;Sewertzoff, 1928;Warth, Hilton, Naumann, Olsson, & Konstantinidis, 2017). Soft tissues have been studied to a lesser extent (Edgeworth, 1929;Sewertzoff, 1928;Stengel, 1962), in part because the study of soft tissue generally has been limited by methodological difficulties (Hilton, Schnell, & Konstantinidis, 2015;Konstantinidis et al, 2015).…”