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1. Ultrastructural and elemental characterization of the extracorporeal tube of the sessile rotifer Floscularia conifera (Rotifera: Gnesiotrocha)

   https://doi.org/10.1111/ivb.12230  

   Yang, Hui ; Hochberg, Rick ( December 2018 , Invertebrate Biology)

   Rotifers are aquatic microinvertebrates that live in the plankton or in the benthos, which may include a variety of macrophytes. Among these periphytic forms of rotifers, some have taken up a sessile existence and secrete protective tubes around their bodies. One type of tube common to species ofFlosculariais made of small round pellets. To date, the building process and some fine structural details are known forFloscularia ringens, but many questions about the composition of the tube and its ultrastructure still remain unanswered. Here, we use transmission electron microscopy and scanning electron microscopy–energy dispersive X‐ray spectroscopy (SEM–EDS) to study the ultrastructure of the pellets and their elemental composition, respectively, in the putative sister species,Floscularia conifera. We revealed several new details that add important information about the physiology of tube‐making in species ofFloscularia. First, we note an inner secretory membrane that is thin, electron lucent, and supports the external pellets. The pellets are relatively consistent in size and have a small depression on their inner surface. All pellets are individually wrapped in a secretory membrane that completely encapsulates suspended materials collected from the surrounding water. Elemental signatures of pellets reveal they consist mostly of carbon (C), nitrogen (N), and oxygen (O), with some silicon (Si) content that is likely the result of diatom shells. Other trace elements such as iron (Fe) and sodium (Na) are also present and likely the result of incorporated bacteria and suspended materials. When larval rotifers are cultured in filtered pond water, the pellets consist mostly of C and O, with little N and no Si; Fe is present in smaller amounts. These new discoveries provide a better understanding of the physiology of rotifer tube construction and tube composition, and their future utility in understanding if and how changes in freshwater environments might impact these factors.

    

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2. The biomechanical, chemical and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

   https://doi.org/10.1111/jmi.12572  

   GRELLET‐TINNER, G. ; LINDSAY, S. ; THOMPSON, M. B. ( May 2017 , Journal of Microscopy)

   Megapodes are galliform birds endemic to Australasia and unusual among modern birds in that they bury their eggs for incubation in diverse substrates and using various strategies.Alectura lathamiandLeipoa ocellataare Australian megapodes that build and nest in mounds of soil and organic matter. Such unusual nesting behaviours have resulted in particular evolutionary adaptations of their eggs and eggshells. We used a combination of scanning electron microscopy, including electron backscatter diffraction and energy‐dispersive X‐ray spectroscopy, to determine the fine structure of the eggshells and micro‐CT scanning to map the structure of pores. We discovered that the surface of the eggshell ofA. lathamidisplays nodes similar to those of extinct titanosaur dinosaurs from Transylvania and Auca Mahuevo egg layer #4. We propose that this pronounced nodular ornamentation is an adaptation to an environment rich in organic acids from their nest mound, protecting the egg surface from chemical etching and leaving the eggshell thickness intact. By contrast,L. ocellatanests in mounds of sand with less organic matter in semiarid environments and has eggshells with weakly defined nodes, like those of extinct titanosaurs from AM L#3 that also lived in a semiarid environment. We suggest the internode spaces in both megapode and titanosaur species act as funnels, which concentrate the condensed water vapour between the nodes. This water funnelling in megapodes through the layer of calcium phosphate reduces the likelihood of bacterial infection by creating a barrier to microbial invasion. In addition, the accessory layer of both species possesses sulphur, which reinforces the calcium phosphate barrier to bacterial and fungal contamination. Like titanosaurs, pores through the eggshell are Y‐shaped in both species, butA. lathamidisplays unique mid‐shell connections tangential to the eggshell surface and that connect some adjacent pores, like the eggshells of titanosaur of AM L#4 and Transylvania. The function of these interconnections is not known, but likely helps the diffusion of gases in eggs buried in environments where occlusion of pores is possible.

    

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3. Fine structure of the retrocerebral organ in the rotifer Trichocerca similis (Monogononta)

   https://doi.org/10.1111/ivb.12396  

   Hochberg, Rick ; Araújo, Thiago Q. ; Walsh, Elizabeth J. ; Mohl, Jonathon E. ; Wallace, Robert L. ( March 2023 , Invertebrate Biology)

   The retrocerebral organ (RCO) is a complex glandular system that is widely distributed across species of phylum Rotifera (sensu stricto). This system is hypothesized to secrete mucus that aids in benthic locomotion, adhesion, and/or reproduction. Unfortunately, the ultrastructure of the RCO is mostly unknown, having only been partially examined in one species. We used transmission electron microscopy and confocal laser scanning microscopy to describe the RCO in the planktonic freshwater rotiferTrichocerca similis. Results reveal the RCO to be a singular syncytial organ composed of a posterior glandular region, an expansive reservoir, and an anterior duct. The glandular portion has an active synthetic cytoplasm with paired nuclei, abundant rER, ribosomes, Golgi, and mitochondria. Electron‐dense secretion granules accumulate at the anterior end of the gland and undergo homotypic fusion to create larger, more electron‐lucent granules with numerous mesh‐like contents that gradually fuse into tubular secretions that accumulate in the reservoir. Ultrastructure of these secretions suggests they may be hydrated glycoproteins. Cross‐striated longitudinal muscles form a partial sleeve around the reservoir and may function to squeeze the secretions through the single cytoplasmic duct that penetrates the cerebral ganglion. A review of the RCOs from other rotifers suggests that further ultrastructural analyses are required before attempting to discern their functions and homologies.

    

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4. Anemochory of diapausing stages of microinvertebrates in North American drylands

   https://doi.org/10.1111/fwb.13306  

   Rivas, Jr., Jose A. ; Schröder, Thomas ; Gill, Thomas E. ; Wallace, Robert L. ; Walsh, Elizabeth J. ( May 2019 , Freshwater Biology)

   Dry, ephemeral, desert wetlands are major sources of windblown sediment, as well as repositories for diapausing stages (propagules) of aquatic invertebrates. Zooplankton propagules are of the same size range as sand and dust grains. They can be deflated and transported in windstorm events. This study provides evidence that dust storms aid in dispersal of microinvertebrate propagules via anemochory (aeolian transport).

   We monitored 91 windstorms at six sites in the southwestern U.S.A. over a 17‐year period. The primary study site was located in El Paso, Texas in the northern Chihuahuan Desert. Additional samples were collected from the Southern High Plains region. Dust carried by these events was collected and rehydrated to hatch viable propagules transported with it.

   Using samples collected over a 6‐year period, 21 m above the ground, which included 59 storm events, we tested the hypothesis that transport of propagules is correlated with storm intensity by monitoring meteorological conditions such as storm duration, wind direction, wind speed, and particulate matter (PM₁₀; fine dust concentration). An air quality monitoring site located adjacent to the dust samplers provided quantitative hourly measurements.

   Rehydration results from all events showed that ciliates were found in 92% of the samples, rotifers in 81%, branchiopods in 29%, ostracods in 4%, nematodes in 13%, gastrotrichs in 16%, and tardigrades in 3%. Overall, four bdelloid and 11 monogonont rotifer species were identified from rehydrated windblown dust samples.

   Principal component analysis indicated gastrotrichs, branchiopods, nematodes, tardigrades, and monogonont rotifer occurrence positively correlated withPM₁₀and dust event duration. Bdelloid rotifers were correlated with amount of sediment deposited. Non‐metric multidimensional scaling showed a significant relationship betweenPM₁₀and occurrence of some taxa. Zero‐inflated, general linear models with mixed‐effects indicated significant relationships with bdelloid and nematode transport andPM₁₀.

   Thus, windstorms with highPM₁₀concentration and long duration are more likely to transport microinvertebrate diapausing stages in drylands.

    

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5. Vertically transmitted microbiome protects eggs from fungal infection and egg failure

   https://doi.org/10.1186/s42523-021-00104-5  

   Bunker, M. E. ; Elliott, G. ; Heyer-Gray, H. ; Martin, M. O. ; Arnold, A. E. ; Weiss, S. L. ( December 2021 , Animal Microbiome)

   Abstract Background Beneficial microbes can be vertically transmitted from mother to offspring in many organisms. In oviparous animals, bacterial transfer to eggs may improve egg success by inhibiting fungal attachment and infection from pathogenic microbes in the nest environment. Vertical transfer of these egg-protective bacteria may be facilitated through behavioral mechanisms such as egg-tending, but many species do not provide parental care. Thus, an important mechanism of vertical transfer may be the passage of the egg through the maternal cloaca during oviposition itself. In this study, we examined how oviposition affects eggshell microbial communities, fungal attachment, hatch success, and offspring phenotype in the striped plateau lizard, Sceloporus virgatus , a species with no post-oviposition parental care. Results Relative to dissected eggs that did not pass through the cloaca, oviposited eggs had more bacteria and fewer fungal hyphae when examined with a scanning electron microscope. Using high throughput Illumina sequencing, we also found a difference in the bacterial communities of eggshells that did and did not pass through the cloaca, and the diversity of eggshell communities tended to correlate with maternal cloacal diversity only for oviposited eggs, and not for dissected eggs, indicating that vertical transmission of microbes is occurring. Further, we found that oviposited eggs had greater hatch success and led to larger offspring than those that were dissected. Conclusions Overall, our results indicate that female S. virgatus lizards transfer beneficial microbes from their cloaca onto their eggs during oviposition, and that these microbes reduce fungal colonization and infection of eggs during incubation and increase female fitness. Cloacal transfer of egg-protective bacteria may be common among oviparous species, and may be especially advantageous to species that lack parental care. 

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