Genetic variation among populations of, and evidence of deep divergence within, the Rio Grande Chirping Frog, Eleutherodactylus campi (Anura: Eleutherodactylidae).

Herein we report the first molecular assessment of intra-species genetic variation and interrelationships within the Rio Grande Chirping frog, Eleutherodactylus campi. We analyzed 548 base pairs of 16S rRNA gene for 71 ingroup individuals belonging to the genus Eleutherodactylus (including 42 E. campi sampled from 15 localities in the United States and Mexico) and four outgroup samples. By unveiling two highly divergent and geographically structured clades within E. campi this study provides a novel phylogenetic placement of E. campi populations north and south of the Rio Grande Valley as sister groups to each other. The observed level of genetic divergence between these two clades (5.8%) is, on average, comparable to or greater than the levels of divergence found between several currently valid amphibian species pairs. Estimates of Time to Most Common Ancestor (TMRCA) indicate that the phylogeographic split between the two E. campi clades may have occurred 7.6 MYA (i.e., late Miocene), consistent with the geologic history of southwestern North America. The study also confirms that south Texas served as the source population for populations of E. campi in its introduced range (i.e., Alabama, Louisiana, and Texas). Overall, this molecular study indicates that E. campi consists of two deeply divergent lineages corresponding to its populations north and south of Rio Grande Valley. These results suggest that the recovered lineages may represent independent species and thereby highlight the need for further research to clarify their status.

The role of aquaporins in excretion in insects.

One of the aspects of insect osmoregulation that has most intrigued researchers is the ability of a simple tubular epithelium, such as the Malpighian tubule, to create both hypo- and hyperosmotic urine. Indeed, Ramsay's initial observation that isolated tubules could secrete a hypoosmotic urine led him to attribute the phenomenon to the active transport of water. In the ensuing decades several models for solute recycling have been proposed, but only in the last 15 years has it become clear that tubule water permeability is due to the presence of aquaporins (AQPs), the ubiquitous water transport proteins. There are 13 known human AQPs, and they are tissue and even membrane specific. It is now clear that the number and type of AQPs within a membrane are the major determinants of its water transport capacity. There are many gene homologs for the AQPs, so proof of function requires expression of the protein in a defined system. Within the insects, only seven AQPs have been functionally expressed and, of these, four directly or indirectly function in excretion. In this paper we review the basic structure and general function of AQPs and then examine the source, localization and functional attributes of those isolated from insects.

Differential expression of the mammalian homologue of fasciclin II during olfactory development in vivo and in vitro.

Developing olfactory sensory neurons are guided to the glomeruli of the olfactory bulb by an increasingly stringent process that is influenced by expression of odorant receptors, cell adhesion molecules (CAMs), and other kinds of signaling cascades. A fundamental feature of the projection is the connecting of broad zones in the epithelium to broad zones in the bulb, also termed rhinotopy. One molecule that parallels and may aid neurons in establishing rhinotopy is the mammalian homologue of fasciclin II (OCAM/mamFas II; also known as RNCAM and NCAM-2), an immunoglobulin superfamily CAM that is differentially expressed in the developing and mature olfactory epithelium (OE): Axons elaborated by ventral and lateral epithelium express the protein at high levels, whereas dorsomedial axons express little or no OCAM/mamFas II. Our investigation has demonstrated that OCAM/mamFas II is detectable early in the development of the rat OE. mRNA is evident on RT-PCR and in situ hybridization by E12.5, and protein is apparent by immunohistochemistry by E13.5. By using a tissue culture system that separates ventral septal epithelium (OCAM/mamFas II-positive) from dorsal (OCAM/mamFas II-negative), we find that explants maintain protein expression levels in vitro that are characteristic of the phenotype at the original location in vivo. At least some neurons are born in culture, suggesting that any cues that direct differential expression are also maintained in vitro. Finally, high OCAM/mamFas II expression correlates with increased growth and fasciculation of olfactory axons in vitro. These data and the similarity between OCAM/mamFas II, on the one hand, and fasciclin II and NCAM, on the other, suggest that OCAM/mamFas II might play a role in growth and fasciculation of primary olfactory axons during development of the projection.