Ventral Body Regions Research Articles

Transcription factor paralogs orchestrate alternative gene regulatory networks by context-dependent cooperation with multiple cofactors

In eukaryotes, members of transcription factor families often exhibit similar DNA binding properties in vitro, yet orchestrate paralog-specific gene regulatory networks in vivo. The serially homologous first (T1) and third (T3) thoracic legs of Drosophila, which are specified by the Hox proteins Scr and Ubx, respectively, offer a unique opportunity to address this paradox in vivo. Genome-wide analyses using epitope-tagged alleles of both Hox loci in the T1 and T3 leg imaginal discs, the precursors to the adult legs and ventral body regions, show that ~8% of Hox binding is paralog-specific. Binding specificity is mediated by interactions with distinct cofactors in different domains: the Hox cofactor Exd acts in the proximal domain and is necessary for Scr to bind many of its paralog-specific targets, while in the distal leg domain, the homeodomain protein Distal-less (Dll) enhances Scr binding to a different subset of loci. These findings reveal how Hox paralogs, and perhaps paralogs of other transcription factor families, orchestrate alternative downstream gene regulatory networks with the help of multiple, context-specific cofactors.

Conspecifics of the Striped Lava Lizard are able to distinguish sex and male colour morphs in apparently homogeneous dull dorsal colouration

Abstract Animal colouration plays a key role in inter and intraspecific interactions, pre-eminently in mate signalling. When multiple types of colouration occur within sexes it is possible that they show alternative reproductive strategies. In lizards, most colouration studies do not incorporate how colour is perceived by conspecifics. Here, we used unbiased colour analysis methods (spectrophotometry and visual modelling) to test for sexual dimorphism and within male dichromatism in the Striped Lava Lizard. We found that males express two distinct colourations that are different from females in several dorsal and ventral body regions. Our results showed UV reflection at the throat, an important body region for signalling. Ventral patches, the coloured badge seen in adult males of Tropidurus spp., have two distinct colour classes within males (Y and B males). Morphs are best discriminated by blue and yellow chroma, and brightness. Body size had little influence on colouration, suggesting that colour may be linked to inheritance rather than growth. Our study clearly shows sexual dichromatism and the existence of colour morphs in this species. Moreover, morph differences in colouration are perceptible by conspecifics. These differences are not only between ventral patches, but also in other body parts such as the dorsum, previously considered as cryptic by human observers. We suggest that colouration at the ventral patches and throat might play a role in intraspecific interactions. Patches increase colour intensity during breeding season and are likely to be costly by pigment-based expression, whereas throat’s UV reflection might have a cost infringed by conspicuousness.

Ontogenetic trajectories of body coloration reveal its function as a multicomponent nonsenescent signal.

The understanding of developmental patterns of body coloration is challenging because of the multicomponent nature of color signals and the multiple selective pressures acting upon them, which further depend on the sex of the bearer and area of display. Pigmentary colors are thought to be strongly involved in sexual selection, while structural colors are thought to generally associate with conspecifics interactions and improve the discrimination of pigmentary colors. Yet, it remains unclear whether age dependency in each color component is consistent with their potential function. Here, we address lifelong ontogenetic variation in three color components (i.e. UV, pigmentary, and skin background colors) in a birth cohort of common lizards Zootoca vivipara across three ventral body regions (i.e. throat, chest, and belly). All three color components developed sexual dichromatism, with males displaying stronger pigmentary and UV colors but weaker skin background coloration than females. The development of color components led to a stronger sexual dichromatism on the concealed ventral region than on the throat. No consistent signs of late‐life decay in color components were found except for a deceleration of UV reflectance increase with age on the throat of males. These results suggest that body color components in common lizards are primarily nonsenescent sexual signals, but that the balance between natural and sexual selection may be altered by the conspicuousness of the area of display. These results further support the view that skin coloration is a composite trait constituted of multiple color components conveying multiple signals depending on age, sex, and body location.

Early development in the mouth-brooding cichlid fish Satanoperca pappaterra (Perciformes: Cichlidae).

The Neotropical region exhibits the largest diversity of fish worldwide; however, little is known about the early development of fish species from this region. Therefore, to contribute to this knowledge, this study aimed to morphologically describe the early stages of development (eggs, larvae and juveniles) of S. pappaterra using morphometric and meristic traits, and to assess changes in growth rates throughout larval and juvenile development by analyzing the relationships between various morphometric traits using analytical regression models. Both juvenile and adult individuals with mouth-brooded offspring were collected along the basins of the Cuiaba and Manso Rivers in the state of Mato Grosso, Brazil between March 2000 and March 2004. After the adults were identified, the offspring were classified according to its stage (embryonic, larval or juvenile period), and various morphometric and meristic variables were individually measured (when possible). The eggs of this species are yellow in color, oval shaped, show dendritic pigmentation within their yolk, have small to moderately sized perivitelline spaces and lack a mucous membrane and oil droplets. The horizontal and vertical diameters of the sample yolks ranged from 1.43mm to 2.70mm and 1.05mm to 1.68 mm, respectively. The standard length of the larval period varied from 4.30mm to 7.16mm, and the standard length of the juvenile period varied from 10.29mm to 24.57mm. Larvae exhibit yolk sacs with internal dendritic pigmentation and dark punctate pigmentation in the dorsal and ventral body regions, whereas irregular transverse spots along the flanks are observed during the juvenile period. Adhesive organs are only present during the yolk-sac stage and at the beginning of the flexion stage. The mouth is terminal during all stages of development. The myomere number varied from 22 to 29 (9 to 16 pre-anal and 10 to 16 post-anal), and the maximal numbers of fin rays and spines were as follows: dorsal, XVI+10; anal, IV+8; pectoral, 16; and pelvic, I+8. Growth analyses identified periods of important change in larval morphology (i.e., metamorphosis), particularly during the flexion and post-flexion stages and in juveniles. Therefore, the morphological development of S. pappaterra is consistent with the ecological requirements of this species, which primarily occurs in structured lentic environments with aquatic macrophytes.

Factors shaping the evolution of colour patterns in Australian agamid lizards (Agamidae): a comparative study

Identifying general patterns of adaptive coloration in animals can help to elucidate the evolutionary processes that generate them. We examined the evolution of colour patterns in Australian agamid lizards, a morphologically and ecologically diverse group that relies primarily on visual communication. We tested whether certain types of colour (yellow–reds and black) were likely to be used as sexual signals, as indicated by their association with indices of sexual selection, namely, sexual dichromatism and sexual dimorphism in body size and head shape. We then tested whether sexually dichromatic colours are associated with specific patterns (uniform, mottled, striped, blotched, reticulated) or ecological variables such as habitat openness, arboreality, and substrate type. The presence of yellow–red on lateral and ventral body regions and black on ventral body regions was significantly more common in males than females. Lateral yellow–red in males was associated with the total extent of sexual dichromatism and size dimorphism, whereas ventral yellow–red was associated with sexual dichromatism. Both lateral and ventral yellow–red were associated with uniform patterning, suggesting that sexual signals in male agamid lizards may often comprise uniform patches or flushes of yellow–red. Although ventral black coloration was more prevalent on males (i.e. strongly sexually dichromatic), it was not associated with indices of sexual selection, suggesting that, in agamid lizards, yellow–red coloration is more likely to be sexually selected than black. Sexually dichromatic coloration was not strongly associated with any of the ecological variables measured. We found some associations, however, between female dorsal patterns and ecological variables, suggesting that female patterns are influenced by natural selection. Biological Journal of the Linnean Society, 2013, 109, 101–112.

Striking coat colour variation in tuco-tucos (Rodentia: Ctenomyidae): a role for the melanocortin-1 receptor?

South American tuco-tucos (Ctenomys) are characterized by striking variation in coat colour. A range of phenotypes, from pale blonde to dark black, is observed across species, with some of them matching their local substrate colour. Moreover, phenotypic convergence is evident in some taxa that occupy similar habitats. The present study investigated a role for the melanocortin-1 receptor (Mc1r) in determining coat-colour variation in a wide range of Ctenomys species. We sequenced 1250 bp, including the entire Mc1r coding region and a portion of the adjacent 5′ and 3′ untranslated regions, in 21 species. In total, 20 amino acid replacements were identified in Mc1r. However, our findings suggest that these changes have not contributed to coat-colour differences among tuco-tucos because no amino acid replacement was associated with pigmentation phenotype in a simple way. Levels of Mc1r expression were measured in skin samples from dorsal, flank, and ventral body regions in pale, brown, and melanic individuals. We did not observe any significant difference in transcript abundance among phenotypes, although we identified a significant reduction of expression level from the dorsal to ventral region in both pale and brown morphs but not in the completely melanic form. Thus, a role for Mc1r regulation in tuco-tucos colour pattern cannot be completely ruled out, although further functional assays are needed. Finally, selection analysis suggests that Mc1r, in a majority of lineages, has evolved under purifying selection but with relaxation in functional constraint in some regions, especially in the fourth transmembrane domain. In summary, the results obtained in the present study suggest that this trait may have a complex basis, and that other pigmentation genes are involved in generating the dramatic diversity in coat-colour phenotypes observed among Ctenomys species.

Muscle activity and hydrodynamic function of pelvic fins in trout (Oncorhynchus mykiss)

Contrary to the previous premise that pelvic fins lacked obvious function, recent work on three-dimensional fin motions suggests that pelvic fins actively control stability and speed in slowly swimming trout. This study used electromyography to measure pelvic fin muscle activity and particle imaging velocimetry to quantify flow along the ventral body region to test this hypothesis. Fish swam at slow speeds (0.13-1.36 BL s(-1)) while being filmed with three high speed cameras. Three-dimensional kinematics were captured for all trials. During EMG trials pelvic fin muscle activity was synchronized to kinematic motion, during particle imaging velocimetry trials, a laser light-sheet was used to visualize the flow surrounding the ventral aspect of the fish. Four main conclusions are reached: first, pelvic fins are actively oscillated during slow-speed swimming; antagonistic abductor and adductor muscles contracted simultaneously, their collective action producing a unique contralateral oscillating behaviour in the fins. Second, pelvic fins slow the flow along the ventral side affecting pitch and yaw instabilities; flow upstream of the pelvic fins is slowed by 0.02 m s(-1) and flow downstream of the pelvic fins is slowed by 0.034 m s(-1) compared with free stream flow. Third, pelvic fin wake influences anal fin angle of attack; flow angle in the wake of the pelvic fin was 33.84+/-2.4 deg. (max) and -11.83+/-11.2 deg. (min) compared with the free stream flow angle of 1.27+/-0.1 deg. Fourth, pelvic fins appear to actively damp body oscillation during slow-speed swimming, providing drag to help control speed and stabilize the body position during slow-speed swimming.

Comparative myoanatomy of cycliophoran life cycle stages

The metazoan phylum Cycliophora includes small cryptic epibionts that live attached to the mouthparts of clawed lobsters. The life cycle is complex, with alternating sexual and asexual generations, and involves several sessile and free-living stages. So far, the morphological and genetic characterization of cycliophorans has been unable to clarify the phylogenetic position of the phylum. In this study, we add new details on the muscular anatomy of the feeding stage, the attached Prometheus larva, the dwarf male, and the female of one of the two hitherto described species, Symbion pandora. The musculature of the feeding stage is composed of myofibers that run longitudinally in the buccal funnel (two fibers) and in the trunk (variable number of fibers). The mouth opening is lined by a myoepithelial ring musculature. A complex myoepithelial sphincter is situated proximal to the anus. In the attached Prometheus larva, three longitudinal sets of myofilaments run dorsally, laterally, and ventrally along the entire anterior-posterior body axis. The muscular architecture of the dwarf male is complex, especially close to the penis, in the posterior part of the body. An X-shaped muscle structure is found on the dorsal side, whereas on the ventral side, longitudinal muscles and a V-shaped muscle structure are present. These muscles are complemented by additional dorsoventral muscles. The mesodermal muscle fibers attach to the cuticle via the epidermis in all life cycle stages studied herein. The musculature of the female is similar to that of the Pandora larva of Symbion americanus and includes dorsoventral muscles and longitudinal muscles that run in the dorsal and ventral body region. Overall, our results reveal striking similarities in the muscular arrangement of the life cycle stages of both Symbion species.

FGF-16 is required for embryonic heart development

Fibroblast growth factor 16 (FGF-16) expression has previously been detected in mouse heart at mid-gestation in the endocardium and epicardium, suggesting a role in embryonic heart development. More specifically, exogenously applied FGF-16 has been shown to stimulate growth of embryonic myocardial cells in tissue explants. We have generated mice lacking FGF-16 by targeting the Fgf16 locus on the X chromosome. Elimination of Fgf16 expression resulted in embryonic death as early as day 11.5 (E11.5). External abnormalities, including hemorrhage in the heart and ventral body region as well as facial defects, began to appear in null embryos from E11.5. Morphological analysis of FGF-16 null hearts revealed cardiac defects including chamber dilation, thinning of the atrial and ventricular walls, and poor trabeculation, which were visible at E10.5 and more pronounced at E11.5. These findings indicate FGF-16 is required for embryonic heart development in mid-gestation through its positive effect on myocardial growth.

The importance of the feeding current for oxygen uptake in the water flea daphnia magna

In the planktonic crustacean Daphnia magna (Branchiopoda, Cladocera), different views exist on the mechanism of respiratory gas exchange, ranging from gill breathing to general integumentary respiration. The presumed structures for specialized gas exchange are located ventrally within the filter chamber, which is continuously perfused with the ambient medium for food gathering. To localize respiratory gas exchange in D. magna, we determined the contribution of the feeding current to total oxygen transport. Combining microscopy with special optical techniques, we used a phosphorescent oxygen-sensitive dye for oxygen partial pressure (PO2) measurements and applied fluorescent microspheres for flow-rate analysis. Appendage beat rate was determined by digital image-processing. All experiments were carried out on hypoxia-adapted animals with a body length ranging from 2.3 to 2.7 mm at 20 degreesC. External PO2 measurement revealed oxygen depletion in the ventral body region but essentially no change at posterior, lateral and dorsal positions. The PO2 difference between the inflow and outflow of the feeding current was 13.0 mmHg (1.73 kPa). The flow rate of the feeding current ranged from 1.2 to 5.2 ml h-1 and showed a close correlation with appendage beat rate, which varied from 310.4 to 460.7 beats min-1. Model calculations based on the Fick principle suggest that oxygen extraction from the feeding current satisfies most of the total of oxygen requirement of D. magna.

Attachment-site patterns of adult blacklegged ticks (Acari: Ixodidae) on white-tailed deer and horses.

The attachment site pattern of adult Ixodes scapularis Say on white-tailed deer and horses in Maryland was determined by whole-body examinations during fall and spring periods of tick host-seeking activity. On deer in the fall, both female and male I. scapularis attached largely to anterior dorsal body regions, with attachment to the ears (outside), head, neck, and brisket accounting for 87.9% of females and 86.6% of males. The attachment pattern of females differed between bucks and does during fall, but not in spring, and both females and males were more abundant on bucks than does during fall, but not in spring. Neither female nor male attachment patterns on deer differed between fall and spring seasons. In contrast to deer, the ears and neck of horses were largely devoid of blacklegged ticks, and 84% of the females were attached either on the chest, in the axillae of the fore and rear legs, or under the jawbone. The restricted attachment of female blacklegged ticks to ventral body regions of horses may reflect avoidance of light. An understanding of the attachment patterns of adult I. scapularis, an increasingly abundant and economically important species, enhances sampling of feeding ticks, deticking to limit host irritation or exposure to tick-borne pathogens, and identifies body areas that should be targeted for delivery of repellents or acaricides.

Polkepsilonema mombasae gen. et sp.n. andPternepsilonema servaesae gen. et sp.n. (Nematoda, Epsilonematidae) from East African coasts

Two new genera and species from Kenyan tidal areas,Polkepsilonema mombasae gen. et sp.n. andPternepsilonema servaesae gen. et sp.n., are described. Both are characterized by the presence of at least fourteen subcephalic setae and by thick thorns on the ventral body region of males. In the first genus, eight to ten subcephalic setae are situated anterior to the amphid, and the ambulatory setae are bisinuous. In the second, the subcephalic setae are situated at the posterior edge of the rostrum, and the ambulatory setae are straight. A key to the 13 genera of the Epsilonematidae is presented.

Ultrastructure of epidermal sensory receptors in Amphibolurus barbatus (Lacertilis: Agamidae).

The histological and ultrastructural organisation of the epidermal sensory organs in Amphibolurus barbatus has been described with respect to their position and possible functions. The sensory organs, located at the scale's edge, are most numerous in scales of the dorsal surface of the head. Most other scales of the body surface have two receptors located laterally to the spine or keel of the scale. In the imbricate scales of the ventral body region, the receptors lie just beneath the reinforced scale lip. Scanning electron microscopy has revealed the surface of the organ to be a crater lacking any surface projections. These sensory organs have a dermal papilla consisting of a nerve plexus and loose connective tissue. The nerve fibres arising from the plexus, pass to the epidermal columnar cells, where some form nerve terminals at the base of the cells, while others pass between them to form nerve terminals embedded in a superficial layer of cuboidal cells. The superficial terminals are held against the overlying alpha keratin by masses of tonofilaments. The beta keratin is thickened to form a collar around the periphery of the organ but is only about 0.5 micrometer thick immediately above it. Mechanical deformation of the scale's spine or reinforced scale lip may initiate stimulation of the nerve terminals described.

A Comparative Study of the thickness of the Stratum Corneum in Nigerian Breeds of Cattle

SUMMARY Measurements of the thickness of the stratum corneum of the skin from eleven body regions in four breeds of Nigerian Cattle (White Fulani, Muturu, N’Dama and Keteku) using histological methods are described. The mean thickness of the stratum corneum of the muzzle (98 μm), horn margin (36 μm) and coronary groove (28 μm) was greater than that of the other body regions studied, the thinnest of which was 13 μm thick. The White Fulani and N’Dama had thicker stratum corneum (121 and 104 μm respectively) on the muzzle than the Muturu and Keteku (80 and 87 μm respectively) but there was no significant difference in thickness between breeds in the dorsal and ventral body regions. The possible relation of these findings to the pattern of distribution of lesions of streptothricosis in the various cattle breeds is discussed.