Physical gills in Elmidae (Coleoptera: Byrrhoidea): Structure and evolutionary pattern of plastron in Stenelmis and related genera

Many species within Elmidae (Coleoptera: Byrrhoidea) have plastrons composed of flattened setae. However, some genera display fine plastrons on the epicuticle, called plastron hairs. In Japanese elmids, members of the genera Stenelmis, Ordobrevia, Nomuraelmis and Leptelmis bear ventral plastron hairs. Based on a maximum likelihood tree including most Japanese genera within Elmidae, we found that these genera are monophyletic and that plastron hairs are a derived character in Elmidae. We also found that the genus Graphelmis bears jigsaw puzzle‐like plastron scales with plastron hair‐like projections, and is sister to the group with plastron hairs.     

Zonation, behaviour and morphology of the intertida coral-treader Hermatobates (Hemiptera: Hermatobatidae) in the south-exst Pacific

The coral-treaders (Hermatobatidae) are the only exclusively marine family of insects. Observations in the Cook Islands, Samoa, Tonga and Fiji show that the insects can be abundant on shores that provide rocks with cavities that remain air-filled during high tide. The zone of suitable habitats for the insects is restricted to a narrow ( c. 20 cm) vertical band roughly centred around Mean Low Water Neaps. Transplant experiments show that the insects are unable to survive above or below this zone. The insects emerge from their rocky crevices about an hour before low tide, swim on the water surface during low tide, and return to their crevices about an hour after the tide has turned. There are only four larval instars, which can be readily separated by their morphology. Electron microscope studies show that the insects are clothed in a layer of micro-hairs of unique design: a short tapering shaft tipped with a sphere. These micro-hairs may act as a plastron: their distribution corresponds precisely to the pattern of the silvery 'air-layer' seen when the insects are submerged, their spherical tips provide a regular array that could support an air-water interface, they occur at high densities (up to 3.5 times 10⁶ mm^-2), and the layer makes connection with the thoracic spiracles. Half the insects were able to survive submergence in recirculated seawater for 12 hours. The adults appear to swim further from shore than the larvae, and they were observed copulating in tidal pools.     

Relating annual increments of the endangered Blanding's turtle plastron growth to climate

This research is the first published study to report a relationship between climate variables and plastron growth increments of turtles, in this case the endangered Nova Scotia Blanding's turtle (Emydoidea blandingii). We used techniques and software common to the discipline of dendrochronology to successfully cross‐date our growth increment data series, to detrend and average our series of 80 immature Blanding's turtles into one common chronology, and to seek correlations between the chronology and environmental temperature and precipitation variables. Our cross‐dated chronology had a series intercorrelation of 0.441 (above 99% confidence interval), an average mean sensitivity of 0.293, and an average unfiltered autocorrelation of 0.377. Our master chronology represented increments from 1975 to 2007 (33 years), with index values ranging from a low of 0.688 in 2006 to a high of 1.303 in 1977. Univariate climate response function analysis on mean monthly air temperature and precipitation values revealed a positive correlation with the previous year's May temperature and current year's August temperature; a negative correlation with the previous year's October temperature; and no significant correlation with precipitation. These techniques for determining growth increment response to environmental variables should be applicable to other turtle species and merit further exploration.     

A review of the North American genus Epimartyria (Lepidoptera, Micropterigidae) with a discussion of the larval plastron

The indigenous North American micropterigid genus Epimartyria Walsingham,1898 is revised. Three species are recognized, including Epimartyria auricrinella Walsingham, 1898 which occurs widely over much of the northeastern United States and Canada, a new species, Epimartyria bimaculella Davis & Landry from northwestern United States and Canada, and Epimartyria pardella (Walsingham, 1880) from northern California to northern Oregon. The larva of Epimartyria auricrinella is described in detail, supplemented with illustrations of the external structure of the larval integument. The larval plastron is described and illustrated for Epimartyria, and this is compared with the plastrons of Neomicropteryx Issiki, 1931 and Micropterix Hübner, 1825. COI barcode sequences show that the three species are genetically distinct, congruent with morphological differences. Marked haplotype divergence within some Epimartyria auricrinella populations appears to be unrelated to morphology, geography or phenology.     

The origin of the turtle body plan: evidence from fossils and embryos

The origin of the unique body plan of turtles has long been one of the most intriguing mysteries in evolutionary morphology. Discoveries of several new stem-turtles, together with insights from recent studies on the development of the shell in extant turtles, have provided crucial new information concerning this subject. It is now possible to develop a comprehensive scenario for the sequence of evolutionary changes leading to the formation of the turtle body plan within a phylogenetic framework and evaluate it in light of the ontogenetic development of the shell in extant turtles. The fossil record demonstrates that the evolution of the turtle shell took place over millions of years and involved a number of steps.     

The structure and probable function of the peritreme in intertidal Gamasina (Acarina: Mesostigmata)

The peritremes of the British intertidal Gamasina are structurally similar to those described for species occurring in soil and leaf litter, the highly elaborate peritreme plastrons present in species occurring in low oxygen tension environments are not typical of the fauna. It is shown that elaborate peritremes can form effective gas gills if an airfilm is supported by the peritrematic slit; however, if the airfilm is supported by the micropapillae on the floor of the peritreme, then the respiratory efficiency of the gas gilhbecomes comparable with that of elaborate peritreme plastrons. Evidence is presented reinforcing the theory that the plastron is supported by the micropapillae. The absence of elaborate respiratory peritreme plastrons among the intertidal Gamasina suggests that these mites are preadapted to respiration during tidal inundation. Other preadaptations include the distal parabolic shape of the micropapillae, however in the plastron forming species the micropapillae are shorter and basally thicker to prevent bending under pressure Developmental trends within the peritremes, with respect to plastron formation are discussed.     

Evidence for the neural crest origin of turtle plastron bones

Summary: The migrating cranial neural crest cells of birds, fish, and mammals have been shown to form the membranous bones of the cranium and face. These findings have been extrapolated to suggest that all the dermal bones of the vertebrate exoskeleton are derived from the neural crest ectomesenchyme. However, only one group of extant animals, the Chelonians, has an extensive bony exoskeleton in the trunk. We have previously shown that the autapomorphic carapacial and plastron bones of the turtle shell arise from dermal intramembranous ossification. Here, we show that the bones of the plastron stain positively for HNK‐1 and PDGFRα and are therefore most likely of neural crest origin. This extends the hypothesis of the neural crest origin of the exoskeleton to include the turtle plastron. genesis 31:111–117, 2001. © 2001 Wiley‐Liss, Inc.     

Repeated evolution of underwater rebreathing in diving Anolis lizards

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Marine antifouling from thin air

The dynamic relationship between the settlement behaviour of marine biota (cells, spores, larvae) and the longevity of an entrapped air layer (plastron) on submersed superhydrophobic surfaces was systematically investigated. Plastron lifetime decreased with increasing hydrophobic polymer loadings, and was correlated with the settlement rate of a range of fouling species of varying length scale, motility and hydrophobic/hydrophilic surface preference. The results show that the level of fouling on immersed superhydrophobic surfaces was greater when plastron lifetimes were minimal, regardless of the length scale, motility and the surface preference of the organisms. This is the first direct demonstration of the broad-spectrum attachment-inhibiting properties of a plastron on an immersed superhydrophobic surface.     

The influence of multiple functional demands on morphological diversification: A test on turtle shells

Organismal parts are often involved in the performance of more than one function. The role of trade‐offs in influencing phenotypic evolution of such parts is well‐studied; less well‐understood is their role in influencing phenotypic diversity. Increases in the number of functions a part is involved in may inhibit subsequent diversification, as the number of trade‐offs increases. Alternately, such an increase might promote phenotypic diversification, by increasing adaptive landscape complexity and promoting specialization for different roles. We compare these predictions by testing whether aquatic turtle shells, which resist loads, act as hydrodynamic elements, facilitate self‐righting, and exchange heat with the environment, differ in phenotypic diversity from those of terrestrial species, which perform all the same functions except for hydrodynamics. We used 53 3D landmarks digitized on 2722 specimens of 274 hard‐shelled turtle species to quantify shell shape variation, and a set of phylogenetic hypotheses to examine evolutionary patterns. Terrestrial turtles consistently had higher phenotypic diversity than aquatic species. Differences are not due to differences in the rates of evolution between the two groups, but rather differences in evolutionary mode. Thus this study supports the traditional view of the role of multiple functions in determining phenotypic diversity.