Anatomy of the cecum of the gerbil Meriones unguiculatus (Mammalia,Rodentia, Cricetidae)

Summary The macroscopic and microscopic anatomy of the cecum of the gerbil was investigated using dissections, dried specimens and vascular injections as well as light-, scanning- and transmission electron microscopy.The cecum of the gerbil is a voluminous organ, possessing slight sacculations and only poorly developed taeniae. The base or ampulla ceci is slightly dilated and more voluminous than the corpus ceci, which decreases gradually in diameter to the blind-end, the apex ceci. A half ring-fold limits the entrance to the proximal colon from the ampulla. A wide-opened communication exists between ampulla and corpus ceci. The scanning microscopical appearance of the cecal wall takes the form of raised elevations circumventing a central depression. The cecum is lined internally by a tall columnar epithelium displaying a well-developed microvillar border and possessing numerous cellular organelles.     

Microscopic anatomy and fine structure of the skeleton-heart-kidney complex in <Emphasis Type="Italic">Saccoglossus mereschkowskii</Emphasis> (Hemichordata,Enteropneusta): 1. Stalk skeleton

This is the first paper of the series devoted to the microscopic anatomy and fine structure of the skeleton-heart-kidney complex in the acorn worm Saccoglossus mereschkowskii Wagner 1885. The skeleton of S. mereschkowskii consists of the unpaired anterior plate (lamina imparis) and two posterior horns (corni). The anterior plate bears a pair of lateral wings (alae laterales), the midventral keel (carina ventralis), the central fossa (fossa centralis) with the bordering ridge (crista circumflexa fossae centralis), two symmetrical supporting saucers (subiculi), and the conical rostrum (rostrum). The skeleton is an accretion (overgrowth) of the basal lamina between the epidermis and the endodermal epithelium of the buccal diverticulum (in the anterior part) and between the endodermal epithelia of the buccal diverticulum and the gut (in the posterior part) and consists of collagen fibers, mostly longitudinal. In all representatives of the Enteropneusta studied to date, the skeleton is a wishbone-like structure with the unpaired anterior plate and paired posterior horns, but its components widely vary in shape between species. In the family Harrimaniidae, the horns are long, and the anterior plate is rod-shaped. In the Ptychoderidae, the horns are short, and the anterior plate is rectangular. In the Spengelidae, the skeleton has an intermediate shape.     

Volatile fatty acid concentrations in the digestive tract of the West Indian manatee, Trichechus manatus

1. Digesta samples were collected from five West Indian manatees, Trichechus manatus, for volatile fatty acid (VFA) analysis. 2. Mean total VFA concentrations were low in the stomach and duodenum (18.6 and 12.3 mM/l, respectively). Mean VFA concentrations were considerably higher in the cecum and colon (220.6 and 307.3 mM/l, respectively). 3. The relative proportions of the individual VFA's shifted from predominantly acetic acid in the foregut to a mixture of acetic, butyric and propionic acids in the hindgut. 4. The VFA concentrations in the manatee are similar to those in the dugong, Dugong dugon, and the green sea turtle, Chelonia mydas. 5. The mean total VFA concentrations indicate that the cecum and colon of the manatee are sites of microbial cellulose fermentation. The contribution of VFAs to the manatees' total energy requirements could not be calculated, but it is probably considerable.     

Genetic evidence for the existence of cryptic species in theAnopheles albitarsis complex in Brazil: Allozymes and mitochondrial DNA restriction fragment length polymorphisms

Allozyme and mitochondrial DNA (mtDNA) restriction studies were undertaken to determine the extent of genetic divergence among field populations ofAnopheles albitarsis in Brazil. Two sympatric species,An. deaneorum andAn. marajoara, were identified in collections from Costa Marques (CM), Rondonia. Genetic evidence includes (1) the presence of two types of individuals, each with diagnostic allelic clusters (forHad-1, Pgi-1, Pep-1, Mpi-1, andIdh-1), (2) a deficiency of heterozygotes, and (3) characteristic mtDNA haplotypes. In addition, two allopatric cryptic species ofAn. marajoara were identified, one from Iguape (An. marajoara form IG), Sao Paulo state, and the other from the Island of Marajo (An. marajoara form MA). Though form IG and form-MA resemble form CM in wing spot morphology, they differ from it in diagnostic allozymes and mtDNA haplotypes.An. marajoara form CM had a higher variability (mean heterozygosity,H=0.22, and percentage of polymorphic loci,P=66.7) than did form IG and form MA (H=0.08 in both, andP=25.0 and 33.3, respectively). Form MA and form IG are genetically more similar to each other than both are to form CM. Based on wing morphology, estimates ofF statistics, and genetic similarities, we propose thatAn. albitarsis in Brazil is a species complex. It comprises at least two morphologically distinguishable species: (1)An. deaneorum (currently one taxon) and (2) theAn. marajoara species complex, which further consists of at least three cryptic forms,marajoara form MA,marajoara form IG, andmarajoara form CM. The views of the authors do not purport to reflect the position of the Department of the Army or the Department of Defense of the United States. This research was conducted when the senior author was on the staff of the USDA-ARS Laboratory in Gainesville, Florida.     

Characterization of kidney epithelial cells from the Florida manatee, Trichechus manatus latirostris

Summary The West-Indian manatee,Trichechus manatus latirostris, is a herbivorous marine mammal found in the coastal waters of Florida. Because of their endangered status, animal experimentation is not allowed. Therefore, a cell line was developed and characterized from tissue collected during necropsies of the manatees. A primary cell culture was established by isolating single cells from kidney tissue using both enzymatic and mechanical techniques. Primary manatee kidney (MK) cells were subcultured for characterization. These cells were morphologically similar to the cell lines of epithelial origin. An immunocytochemistry assay was used to localize the cytokeratin filaments common to cells of epithelial origin. At second passage, epithelial-like cells had an average population-doubling time of 48 h, had an optimum seeding density of 5×10³ cells/cm², and readily attached to plastic culture plates with a high level of seeding efficiency. Although the epithelial-like cells had a rapid growth rate during the first three passages, the cloning potential was low. These cells did not form colonies in agar medium, were serum dependent, had a limited life span of approximately nine passages, and possessed cell-contact inhibition. These data suggest that the cells were finite (noncontinuous growth), did not possess transformed properties, and were of epithelial origin. These cells are now referred to as MK epithelial cells.     

Survival of West Nile virus‐challenged Southern house mosquitoes,Culex pipiens quinquefasciatus,in relation to environmental temperatures

We investigated the effect of West Nile virus (WNV) infection on survival in two colonies of Culex pipiens quinquefasciatus Say (Diptera: Culicidae) originating from Vero Beach and Gainesville, FL. Mosquitoes were fed West Nile virus‐infected blood and checked daily for survival. Exposure to WNV decreased survival among Cx. p. quinquefasciatus from Gainesville relative to unexposed individuals at 31° C. In contrast, exposure to WNV enhanced survival among Cx. p. quinquefasciatus from Vero Beach relative to unexposed individuals at 27° C. These results may suggest that exposure to WNV and associated infection could increase or decrease components of fitness, dependent on environmental temperature and intraspecific variation in Cx. p. quinquefasciatus. The relationship between lifespan (time of death in days) and WNV titer differed in the colonies at 31° C and 27° C, suggesting that intraspecific species variation in response to temperature impacts interactions with WNV. While further work is needed to determine if similar effects occur under field conditions, this suggests intraspecific variation in vector competence for WNV and adult survival of Cx. p. quinquefasciatus, both aspects of vectorial capacity.     

The valvula cerebelli of the spiny eel,Macrognathus aculeatus,receives primary lateral-line afferents from the rostrum of the upper jaw

Summary In the spiny eel, Macrognathus aculeatus, anterodorsal and (to a lesser degree) anteroventral lateralline nerves project massively to the granular layer of the valvula cerebelli, throughout its rostrocaudal extent. The posterior lateral-line nerve terminates in the corpus cerebelli. Thus, valvula and corpus cerebelli are supplied with mechanosensory input of different peripheral origins. An analysis of the taxonomic distribution of experimentally determined primary lateral-line input to the three parts of the teleostean cerebellum reveals that the eminentia granularis always receives such input, and that the corpus cerebelli is the recipient of primary lateral-line input in many teleosts. The valvula, however, receives primary lateral-line afferents in only two examined species. In M. aculeatus, the massive lateral-line input to the valvula probably originates in mechanoreceptors located in the elongated rostrum of the upper jaw, a characteristic feature of mastacembeloid fishes. This projection to the valvula may therefore represent a unique specialization that arose with the evolution of the peculiar rostrum.     

Dimorphism of both head and prothoracic horn morphologies in male Copris acutidens (Coleoptera: Scarabaeoidea)

Allometric scaling of male horn morphologies of Copris acutidens, including the head and prothoracic horns, was analyzed. The analyses of scaling relationships indicated a discontinuous increase in head horn length and prothoracic horn height but a linear increase in prothoracic horn length relative to body size. The different results for length and height of the prothoracic horn suggest that the height is functionally more important for ensuring mates in the nests. Furthermore, both the head and prothoracic horns were dimorphic, and this characteristic was not found in the scarabaeoid beetle Onthophagus. Similarity in the switch point values for the head and prothoracic horns suggests that the dimorphism of the two kinds of horns may result from the same developmental threshold mechanism.     

Conservation, innovation, and the evolution of horned beetle diversity

Beetle horns represent an evolutionary novelty exhibiting remarkable diversity above and below the species level. Here, we show that four typical appendage patterning genes, extradenticle (exd), homothorax (hth), dachshund (dac), and Distal-less (Dll) are expressed in the context of the development of sexually dimorphic thoracic horns in three Onthophagus species. At least two of these genes, Dll and hth, exhibited expression patterns consistent with a conservation of patterning function during horn development relative to their known roles in the development of insect legs. exd, hth, and dac expression patterns during horn development were largely invariable across species or sexes within species. In contrast, Dll expression was far more discrete and exhibited consistent differences between sexes and species. Most importantly, differences in location and domain size of Dll expression tightly correlated with the degree to which prepupal horn primordia were retained or resorbed before the final adult molt. Our results lend further support to the hypothesis that the origin of beetle horns relied, at least in part, on the redeployment of already existing developmental mechanisms, such as appendage patterning processes and that changes in the exact location and domain size of Dll expression may represent important modifier mechanisms that modulate horn expression in different species or sexes. If correct, this would imply that certain components of genetic basis of horn development may be able to diversify rapidly within lineages and largely independent of phylogenetic distance. We present a first model that integrates presently available data on the genetic regulation of horn development and diversity.     

Histomorphology of the glans penis in Vespertilionidae and Phyllostomidae species (Chiroptera,Mammalia)

The penises of bats are taxonomically distinctive in size and shape. In addition, they are variable in microscopic anatomy, indicating that histomorphological studies of copulatory organs of bats may help understanding their successful reproductive strategies. We studied adult males of 13 species of vespertilionid and phyllostomid bats. Both families exhibited the basic structure of the vascular penis of mammals: the hydrostatic elements of the corpora cavernosa and the corpus spongiosum surrounding the urethra, as well as accessory cavernous tissue. Variation in the position and amount of the tissues were observed in these families. Vespertilionid bats have a small glans penis with abundant accessory cavernous tissue on the prepuce and a highly variable baculum. The baculum varied in size and morphology, even among congeneric species, such as the three Lasiurus species and the two Myotis species. Phyllostomid species possess no bacula, but vascular structures are present to produce penile stiffening, particularly on the glans. Variation in the microscopic anatomy of the phyllostomid prepuce was observed, for example, Artibeus species had accessory cavernous tissue surrounded by a tunica albuginea, but Carollia perspicillata had two bundles of striated musculature and some adipose tissue; abundant pigments were present in the prepuce of most species.     

The heart of the dugong (Dugong dugon) and the west indian manatee (Trichechus manatus) (Sirenia)

Thirty-eight dugong (Dugong dugon) hearts and 28 Florida manatee (Trichechus manatus) hearts were obtained from stranding programs in Australia and the United States. In addition to a double ventricular apex, a feature that has astonished scientists since the eighteenth century, the hearts of both animals have a double subvalvular conus and a dorsal left atrium. The heart lies in a vertical plane at right angles to that of the completely dorsal, symmetrical lungs. The dugong heart has a deeper interventricular cleft and a more conical left ventricle. The latter features may be part of a general morphological trend toward specialization for a more energetic aquatic existence. The presence of a bulbous ascending aorta in the manatee but not in the dugong is without explanation.     

Sexually dimorphic male horns and their use in agonistic behaviors in the horn-headed cricket <Emphasis Type="Italic">Loxoblemmus doenitzi</Emphasis> (Orthoptera: Gryllidae)

Sexual dimorphism, the difference between the sexes in secondary sexual characters, is in general driven by processes of sexual selection. The horn-headed cricket, Loxoblemmus doenitzi, exhibits sexual dimorphism in head shape. Males have flat heads and triangular horns on both sides of their heads, whereas females have rounded heads and no horns. We hypothesized that male horns have evolved due to intra-sexual selection, in which males use these horns as weapons in aggressive interactions. We tested two predictions of this hypothesis by conducting agonistic trials with field-caught males of L. doenitzi: (1) the horns should be used in agonistic interactions between males, and (2) the asymmetry in horn size or horn use may determine contest outcome. Horn length was significantly correlated with thorax length and hind femur length. During agonistic interactions, males aggressively used their horns by beating the opponent’s horns with their own or by poking the opponent’s body. However, logistic regression analysis revealed that neither horn length nor horn use were significant factors for contest outcome. Instead, body size was significant for determining contest outcome. We discuss possible scenarios for evolution of male horns in L. doenitzi.     

Morphology and structural organization of gené's organ in Dermacentor reticulatus (Acari: Ixodidae)

Scanning and transmission electron microscopical investigations revealed that Gené's organ in unfed and ovipositing females of Dermacentor reticulatus is formed as a double-sac-structure consisting of an outer epithelial and an inner cuticular sac. In ovipositing ticks the latter emerges through the camerostomal aperture to the exterior. Gené's organ in unfed ticks consists of a corpus, two posterior horns and a pair of undeveloped glands at each side, which differentiate in ovipositing ticks to compound, branched tubular glands with a main efferent duct for each gland opening into the lumen between the epithelial and the cuticular sac. Gené's organ of egg-laying females corresponds basically in morphology and structural organization to that of unfed ticks. Compared with unfed ticks, however, in ovipositing ticks the corpus and horns are longer and broader, the glands are fully developed and the cuticular sac is evertable. The epithelial sac as the outermost part of Gené's organ is continuous with the hypodermis of the basis capituli and the scutum, arises at the camerostomal aperture, forms the corpus and the two blind-ending horns, passes into the epithelium of the main excretory ducts of the glands and envelops the cuticular sac. The cuticular sac passes into the cuticle of the basis capituli and the scutum, arises at the camerostomal aperture, is folded, expands into the horn tips and consists inwards of a smooth epicuticula and outwards of a fibrous endocuticula. Muscles originating from the scutum pass caudomedially through the epithelial sac and are inserted into the cuticular sac. The entire surface of the maximally everted cuticular sac is covered with an amorphous mass. In cleaned samples, ledge-like structures appear on the lateral surface. These ledges turn into balloon-like structures which extend over the medial and dorsal surface. The entire surface including the balloon-like structures and the ledges are provided with numerous cribrate pits.     

Functional morphology of the taste buds of Florida manatee,Trichechus manatus latirostris

The Florida manatee, Trichechus manatus latirostris, is a fully aquatic, threatened marine mammal for which increased understanding of their physiology, reproduction, and nutrition supports management decisions. Manatees may use taste to distinguish saltwater gradients, toxin detection, food assessment, and social interactions. This study sought to locate and characterize manatee taste buds comparing location, structure, number, and size to other species. Entire heads from manatees (6 males, 4 females) of various ages were obtained. The muzzle, tissue surrounding the nares, oral cavity, and epiglottis were examined grossly for pits and papillae. Tissues were examined using light and transmission electron microscopy. Within the predominant taste bud location, the tongue root, taste bud number was estimated using samples from four animals. The average number of taste buds within the tongue root was 11,534 (range 2,711–23,237) with sparse taste buds located on the soft palate and epiglottis. The location along the lateral surface of the tongue root and bordered by grooves, through which tastants could be easily transported, has functional significance. Large numbers of taste buds within the tongue root suggest that taste is an important component of manatee sensory systems and behavioral research would clarify this.     

Phylogenetic Position of Mammoth and Steller's Sea Cow Within Tethytheria Demonstrated by Mitochondrial DNA Sequences

Here we report DNA sequences from mitochondrial cytochrome b gene segments (1,005 base pairs per species) for the extinct woolly mammoth (Mammuthus primigenius) and Steller's sea cow (Hydrodamalis gigas) and the extant Asian elephant (Elephas maximus), the Western Indian manatee (Trichechus manatus), and the hyrax (Procavia capensis). These molecular data have allowed us to construct the phylogeny for the Tethytheria. Our molecular data resolve the trichotomy between the two species of living elephants and the mammoth and confirm that the mammoth was more closely related to the Asian elephant than to the African elephant. Our data also suggest that the sea cow–dugong divergence was likely as ancient as the dugong–manatee split, and it appears to have been much earlier (22 million years ago) than had been previously estimated (4–8 million years ago) by immunological comparison. Received: 8 August 1996 / Accepted: 30 September 1996     

Beetle horns are regulated by the Hox gene,Sex combs reduced,in a species‐ and sex‐specific manner

Discovering the mechanisms that underlie the origin of novel features represents a major frontier in developmental and evolutionary biology. Here we begin to characterize the role of the Hox gene Sex combs reduced (Scr) during the development and evolution of a morphologically novel trait: beetle horns. Beetle horns develop as epidermal outgrowths from the prothorax and/or head, and size and location vary dramatically across species and between sexes. Using both comparative gene expression and larval RNA interference in two species of the horned beetle genus Onthophagus, we show that Scr functions in patterning adult labial mouthpart identity and suppressing wing development in the prothorax. At the same time, however, our results illustrate that Scr has acquired, within its ancestral domain of expression, additional new functions including the regulation of prepupal growth and pupal remodeling of pronotal horn primordia. Furthermore, comparative analyses of our results across both Onthophagus species, which differ in location of horn development (thoracic horns vs. thoracic and head horns) as well as patterns of sexual dimorphism (traditional vs. reversed sexual dimorphism), reveal surprising differences in exactly when, where, and to what degree Scr regulates horn formation in different sexes. These observations suggest that the interactions between Scr and its targets in the regulation of horn development can diversify quickly over remarkably short phylogenetic distances. More generally, our results suggest that the Hox complex can play an integral role in the development and evolution of novel complex traits while maintaining traditional patterning responsibilities.     

PERMANENT GENETIC RESOURCES: Eighteen new polymorphic microsatellite markers for the endangered Florida manatee, Trichechus manatus latirostris

Here we describe 18 polymorphic microsatellite loci for Trichechus manatus latirostris (Florida manatee), isolated using a polymerase chain reaction‐based technique. The number of alleles at each locus ranged from two to four (mean = 2.5) in specimens from southwest (n = 58) and northeast (n = 58) Florida. Expected and observed heterozygosities ranged from 0.11 to 0.67 (mean = 0.35) and from 0.02 to 0.78 (mean = 0.34), respectively. Departures from Hardy–Weinberg equilibrium occurred at two loci. There was no evidence of genotypic disequilibrium for any pair of loci. For individual identification, mean random‐mating and θ‐corrected match probabilities were 9.36 × 10^?7 and 1.95 × 10^?6, respectively.     

The influence of age and sex on the vocal repertoire of the Antillean manatee (Trichechus manatus manatus) and their responses to call playback

Limited information is available regarding the acoustic communication of Antillean manatees, however, studies have shown that other manatee taxa produce vocalizations as a method of individual recognition and communication. Here, the acoustic signals of 15 Antillean manatees in captivity were recorded, aiming to (1) describe their acoustic repertoire, (2) investigate the influence of sex and age on vocalization, and (3) examine manatee responses to call playback. Six acoustic signals ranging in mean fundamental frequencies from 0.64 kHz to 5.23 kHz were identified: squeaks and screeches were common to adult males, adult females, and juveniles; trills were common to adult males and females; whines were specific to males; creaks were specific to females; and rubbing was specific to juveniles. The structure of squeak vocalizations was significantly different between age and sex classes and screech structure was significantly different between age classes. Squeaks and screeches produced by juveniles had higher frequencies of maximum energy when compared to those produced by adult males and females. A significant increase in the vocalization rate following vocalization playbacks was found for all three age/sex groups. Our results introduce the potential of using acoustic signals in identifying and noninvasively monitoring manatees in the wild in Brazil.     

Cranial and chromosomal geographic variation in manatees (Mammalia: Sirenia: Trichechidae) with the description of the Antillean manatee karyotype in Brazil

We employed landmark‐based 3D geometric morphometrics to assess cranial size and shape diversification in Trichechus manatus and T. inunguis to compare it with patterns among all manatee taxa (T. manatus latirostris, T. m. manatus, T. inunguis and T. senegalensis), and to analyse geographic variation within American manatee populations, using a sample of 189 skulls. Chromosome G‐ and C‐banding techniques were performed in T. m. manatus from Brazil. All taxa were statistically discriminated by skull shape. Trichechus m. manatus and T. m. latirostris have larger skulls than T. inunguis. A morphological discontinuity was noted within T. m. manatus, with the Brazilian population south of the Amazon discriminated from the T. m. manatus Caribbean and T. m. latirostris USA populations. Specimens from Suriname and Guyana had a skull shape more similar to the one from the Caribbean population. The Brazil Antillean manatee population exhibited morphological differences similar in magnitude to those found between the Amazonian and African species. Additionally, structural chromosome differences were detected between that population (chromosome pair 4 is metacentric and 10 is submetacentric) and manatees from Puerto Rico and Florida. Based on such morphological discontinuity and chromosomal divergence, we hypothesize that the Amazon River mouth may be acting as a reproductive barrier for the T. m. manatus population in Brazil, thus indicating that its taxonomic status and conservation strategies need an urgent reassessment.     

Mandibular biomechanics of Crocuta crocuta,Canis lupus,and the late Miocene Dinocrocuta gigantea (Carnivora,Mammalia)

The relative simplicity of the mandible and its functional integration with the upper dentition in carnivorans makes it an ideal subject for functional morphological studies. To compare the mandibular biomechanics of two convergently evolved bone‐cracking ecomorphologies, we used finite element modelling to analyse mandibular corpus stress. The bone‐cracking spotted hyena Crocuta crocuta was used as a living analogue to the late Miocene percrocutid Dinocrocuta gigantea, using the grey wolf Canis lupus as a molar bone‐crushing outgroup. Mandibular stress values during p3, p4, and m1 tooth biting are found to be lowest in Cr. crocuta, and elevated in both Ca. lupus and D. gigantea. However, the stress‐dissipation patterns of the pre‐m1 corpus are similar between Cr. crocuta and D. gigantea. Lastly, D. gigantea has a relatively weaker corpus at the post‐m1 position than either Cr. crocuta or Ca. lupus. These findings suggest that even though stress patterns are similar amongst the bone‐cracking ecomorphs, the extinct D. gigantea had a weaker mandibular structure when performing a comparable bone‐cracking task as in Cr. crocuta because of its slender post‐m1 corpus. Ontogeny could potentially play an important role in strengthening the post‐m1 corpus by growth in the dorsoventral axis, and continuous increase in biting performance through adulthood in living Cr. crocuta suggests the possibility of a relatively more delayed development to full bone‐cracking capability in D. gigantea. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 683–696.