title: Development of the nasolacrimal apparatus in the Mongolian gerbil (Meriones unguiculatus), with notes on network topology and function.
abstract: The nasolacrimal apparatus (NLA) is a multicomponent functional system comprised of multiple orbital glands (up to four larger multicellular exocrine structures), a nasal chemosensory structure (vomeronasal organ: VNO), and a connecting duct (nasolacrimal duct: NLD). Although this system has been described in all tetrapod vertebrate lineages, albeit not always with all three main components present, considerably less is known about its ontogeny. The Mongolian gerbil (Meriones unguiculatus) is a common lab rodent in which the individual components of the adult NLA have been well studied, but as yet nothing is known about the ontogeny of the NLA. In this study, serial sections of 15 fetal and three adult Mongolian gerbil heads show that the development of the NLA falls into three fetal stages: inception (origin of all features), elongation (lengthening of all features), and expansion (widening of all features). No postnatal or juvenile specimens were observed in this study, but considerable growth evidently occurs before the final adult condition is reached. The development of the orbital glands and the VNO in the Mongolian gerbil is largely consistent with those in other mammals, despite a slight nomenclatural conundrum for the anterior orbital glands. However, the Mongolian gerbil NLD follows a more circuitous route than in other tetrapods, due mainly to the convoluted arrangement of the narial cartilages, the development of a pair of enlarged incisors as well as an enlarged infraorbital foramen. The impact of these associated features on the ontogeny and phylogeny of the NLA could be examined through the approach of network science. This approach allows for the incorporation of adaptations to specific lifestyles as potential explanations for the variation observed in the NLA across different tetrapod clades.
authors.affiliation: Department of Biology, Slippery Rock University, Slippery Rock, Pennsylvania, 16057.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Rehorek
authors.affiliation: Department of Biology, Slippery Rock University, Slippery Rock, Pennsylvania, 16057.
authors.forename: Jayna
authors.initials: J
authors.lastname: Cunningham
authors.affiliation: Department of Biology, Slippery Rock University, Slippery Rock, Pennsylvania, 16057.
authors.forename: Amanda E
authors.initials: AE
authors.lastname: Bruening
authors.affiliation: Department of Biology, Slippery Rock University, Slippery Rock, Pennsylvania, 16057.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Johnson
authors.affiliation: Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, Louisville, Kentucky, 40292.
authors.forename: Kunwar P
authors.initials: KP
authors.lastname: Bhatnagar
authors.affiliation: School of Physical Therapy, Slippery Rock University, Slippery Rock, Pennsylvania, 19057.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Smith
authors.affiliation: Department of Biology, College of Charleston, Charleston, South Carolina, 29424.
authors.forename: Willem J
authors.initials: WJ
authors.lastname: Hillenius
mesh_terms: D000818:Animals; D005849:Gerbillinae / Q000196:embryology* / Q000254:growth & development; D006257:Head / Q000196:embryology / Q000254:growth & development; D019147:Vomeronasal Organ / Q000254:growth & development* / Q000502:physiology
keywords: Harderian; ontogeny; vertebrate; vomeronasal organ