Jump to: Botany; Developmental Biology; Ecology; Environmental; Evolution; Geology; Historical Geology; Human Evolution; Palaeontology; Zoology.
Now that we’re done with the top books of the year, let’s look at the top research of the year. I re-examined a total of 412 papers published this year, sorted in the following categories: Arthropods; Botany; Developmental Biology; Ecology; Environmental; Evolution; Geology; Historical Geology; Human Evolution; Palaeontology; and Zoology. As with the books, every day, I will do a top 10 research for each category. The top 10s will be inverted like a proper countdown. As with any top 10 lists, your mileage may vary; these picks and the rankings are all subjective and prone to my own biases.
Let’s start off with the arthropods. The top 10 papers were chosen from a master list of 74 papers. [OA] indicates open access papers. The topic listing, from 10 to 1: spider intelligence; spider silk; fossil insect behaviour; fossil pupation chambers; caste-specific neuroanatomy; early arthropod evolution; evolutionary dynamics; early fossil insect; earliest amber arthropods; treehopper helmet.
10. The discerning predator: decision rules underlying prey classification by a mosquito-eating jumping spider.
Jumping spiders’ excellent eyesight has led to their also having high intelligence, being able to observe and filter what they see to the point that the African jumping spider Evarcha culicivora can differentiate their prey, female Anopheles mosquitoes, from all other insects flying around just by looking at their antennae. This is what Nelson & Jackson showed with this elegant experiment.
By combining parts from male and female mosquitoes and using the resultant Frankenmosquitoes as lures for the spiders to attack, they identified the two clues that led to the most attacks: a red, blood-engorged abdomen, and slender antennae. Both of these are female mosquito features: male mosquitoes don’t feed on blood (they’re nectar feeders), and males have bushy antennae. As for the specificity for Anopheles mosquitoes, that’s explained by their posture – other mosquitoes rest with their body parallel to the ground, while Anopheles rest with a 45° angle.
For showing that such a tiny spider is capable of such complex prey-distinction and thus giving even more credence to the notion that intelligence is not a function of brain size, as well as for having a great experimental design, Nelson & Jackson get the #10 place.
9. Post-secretion processing influences spider silk performance.
Spider silk is not a simple strand that’s the same in every species. There’s many different types of silk that come out of different glands, and the silk is also modified after it’s secreted. The study focuses on major ampullate silk, the type of silk that makes up the framework of an orb web and whose stiffness is responsible for the strength of the webs. The researchers examined natural silk, and silk that they supercontracted to remove any post-secretion modifications. What they found was that these supercontracted silks lost the stiff properties of their natural counterparts, meaning that their properties come from whatever modification is made to them, not from the actual structure and composition of the silk. I find this discovery significant because it adds a new dimension to the study of spider silk, a field that has quite a lot of technological and biomimetic research ahead of it.
Other significant spider silk and web-related research this year include:
The role of capture spiral silk properties in the diversification of orb webs: how various silk types affect the web’s properties.
Nonlinear material behaviour of spider silk yields robust webs: This research provides more insight into the factors mentioned above, finding that it isn’t just the type of and modification of silks that affect the web’s properties, but that the geometry of the web is as important in determining its strength and behaviour.
Early Events in the Evolution of Spider Silk Genes [OA]: A phylogeny of genes from the silk-producing glands reveals gene duplications associated with more diverse ecological use of silk and webs.
Functional values of stabilimenta in a wasp spider, Argiope bruennichi: support for the prey-attraction hypothesis: research into the use of stabilimenta, UV-reflective strands of silk that orb-weavers have.
8. Jurassic mimicry between a hangingfly and a ginkgo from China. [OA]
This is cool more than anything else, and the mimicry is shown in the picture above, from the original paper: A, B, E, and F are gingko leaves; C and H are the described specimen and its wing, D and I are a closely-related species which also exhibits mimesis with gingkos; J and K are gingko leaf closeups. As you can see, the similarities are striking, and the artist’s conception in G shows how well the hangingfly would have blended in. The paper has more details on the coevolution of mimesis between this group of hangingflies and gingkos. In all, a neat piece of work with evolutionary insights as well as cool fossil preservation.
Another paper this year has preserved evidence of insect behaviour: Wing stridulation in a Jurassic katydid (Insecta, Orthoptera) produced low-pitched musical calls to attract females. The mating call of a katydid has been reconstructed based on the preservation of its stridulatory apparatus, a hard file that the wings strike against to make the music. Related, this paper from this year shows how sensitive the hearing of katydids is: Auditory change detection by a single neuron in an insect.
7. The Earliest Evidence of Holometabolan Insect Pupation in Conifer Wood. [OA]
This paper describes U-shaped burrows in 210 Ma wood from Utah, USA. These were previously assumed to be bee or wasp borings, but the detailed analysis presented in the paper shows that these borings are actually pupation chambers made by a small organism that ate its way into the wood, then emerged from the other side, as presented in the diagram above. From the size of the borings, the authors propose that the organism is a cupedid beetle, showing that these beetles were dominant before the other beetles radiated later.
6. Division of Labor in the Hyperdiverse Ant Genus Pheidole Is Associated with Distinct Subcaste- and Age-Related Patterns of Worker Brain Organization. [OA]
That different castes will have a different brain organisation is expected and has been shown in many papers (e.g. 1, 2, 3). This paper is significant because it’s so thorough: it examines castes of three species of Pheidole ants and their brain anatomy. The diagram above summarises the pattern observed: the colours are species, the shapes are castes; the axes are two variables that together make up 87% of the brain variation seen. The pattern is clear: neuroanatomy is determined by caste, not by species. This is just underlines the incredible amount of plasticity in ants (and other eusocial insects), where the environment can dictate how an individual will function and develop to allow the colony to adapt to changing needs and conditions.
5. A Carboniferous Non-Onychophoran Lobopodian Reveals Long-Term Survival of a Cambrian Morphotype.
This paper has equal relevance to palaeontology as it does to arthropods: like several other papers of the past few years (e.g.), it reinforces the idea that the Cambrian freaks didn’t go extinct, but that the nature of the fossil record changes since the Cambrian to make their preservation much rare (the advent of burrowing made it much harder for such soft-bodied forms to be preserved). This one is the most stirking example yet: a long-legged lobopod, 200 million years after the Cambrian (it comes from the famous Mazon Creek locality in Illinois, USA, 296 Ma)! Lobopods are a wastebasket taxon in which soft-bodied arthropods with stubby legs are dumped, including many fossil-only taxa, tardigrades, and onychophorans. There are two groups: short-legged forms (includes the last two) and long-legged ones, up until this paper known only from the Cambrian.
It was a good year for arthropod evolution, with many excellent studies into the biology and diversity of early arthropods:
Exceptionally preserved crustaceans from western Canada reveal a cryptic Cambrian radiation: These Canadian fossils bring the earliest fossil records of branchiopods, copepods, and ostracods back to the mid-Cambrian.
Silurian horseshoe crab illuminates the evolution of arthropod limbs: A horseshoe crab from Herefordshire, showing a very exciting biramous limb, the significance of which would need an entire post to explain.
A Silurian myodocope with preserved soft-parts: cautioning the interpretation of the shell-based ostracod record is another Herefordshire find that finds that ostracod shells, very abundant fossils with significant stratigraphic and other practical use, are not quite as informative taxonomically as previously thought.
Cambrian lobopodians and extant onychophorans provide new insights into early cephalization in Panarthropoda [OA]: A complete redescription of Onychodictyon‘s head, showing that the arthropod mouth may have originated multiple times.
Cambrian bivalved arthropod reveals origin of arthrodization: A new Burgess Shale arthropod suggests that the key feature of arthropods, the exoskeletal segmentation, was a feature that evolved for swimming.
Morphology of Cambrian lobopodian eyes from the Chengjiang Lagerstätte and their evolutionary significance shows that Cambrian lobopods had pretty sophisticated eyesight.
Complex brain and optic lobes in an early Cambrian arthropod: Eyes are nice and all, but how about preserved brains and nervous tissue?
Internal Soft-Tissue Anatomy of Cambrian ‘Orsten’ Arthropods as Revealed by Synchrotron X-Ray Tomographic Microscopy [OA] shows more spectacular internal details of long-extinct arthropods.
Exceptionally Preserved Cambrian Trilobite Digestive System Revealed in 3D by Synchrotron-Radiation X-Ray Tomographic Microscopy [OA]: As above.
4. Loss of flight promotes beetle diversification. [OA]
In this study, a molecular phylogeny of Japanese carrion beetles was done, and the result found was that flight loss promotes speciation. Flightless populations have more genetic differences between themselves than do flight-enabled populations. This is to be expected: flight enables greater geographic dispersal, allowing distant populations to reproduce and keep gene flow between them; with flight loss, this doesn’t happen, resulting in more isolation and thus more speciation, as shown in the above bar chart. The authors went further and did a short meta-analysis for other beetle groups and found a similar effect. I look forward to deeper studies examining the precise interplay between diversification and flight loss – does flight loss really directly cause speciation, or is it an indirect knock-on effect. Loss of flight must be related to other factors such as habitat requirements, life history, or feeding preferences, as the authors note; maybe it’s those other factors that actually promote the speciation. The authors checked for this in their carrion beetle dataset, but it’s worth looking into with other taxa.
3. A complete insect from the Late Devonian period.
The fossil doesn’t quite look like an insect until you examine it closely – when I first saw the picture, I thought it was some notostracan. But then it becomes clear that there’s a pair of antennae, then you see the head, then the rest of the body – this is an insect. It’s not the oldest – that honour remains with Rhyniognatha hirsti – but it does come from a time when the fossil record of insects is completely lacking, the Late Devonian, and it’s by far the earliest complete insect – this really is a landmark find.
2. Arthropods in amber from the Triassic Period.
This is not the oldest amber (that’s from the Carboniferous), but it is the oldest fossiliferous amber. Microorganisms have been reported from it before, but this paper records the oldest arthropod inclusions in amber, beating the previous records from the Middle East by some 100 million years. The arthropods are one fly and two mites (one of which is pictured above), with more still to come in future papers.
Some more cool insect preservation papers published this year include:
The original colours of fossil beetles details how preservation of beetle cuticle allows us to reconstruct the colour of fossil beetles – after all, the metallic sheen that some beetles have isn’t due to pigments, but due to the nanostructure of the cuticle playing tricks with the light. THE CONTROLS ON THE PRESERVATION OF STRUCTURAL COLOR IN FOSSIL INSECTS outlines the details of how cuticle preservation affects recovered colour.
WIDESPREAD PYRITIZATION OF INSECTS IN THE EARLY CRETACEOUS JEHOL BIOTA shows that the insects from Jehol – the famous lacustrine fossil locality that has yielded many feathered dinosaurs – are pyritised with the help of bacterial acitvity.
1. On Dorsal Prothoracic Appendages in Treehoppers (Hemiptera: Membracidae) and the Nature of Morphological Evidence. [OA]
In 2011, Prud’homme et al. published an intriguing paper with developmental and some morphological evidence that the helmet of treehoppers, pictured above, is actually a cooption of an ancestral wing-like structure. This is obviously a very extraordinary claim, and this paper reviews all the evidence and comes up with alternative scenarios that show flaws in the Prud’homme et al. paper. It gets the top spot not only for the subject matter, but also for being a prime example of the scientific method in action.
A morphology-only critique of the Prud’homme et al. paper was done very early in the year by Yoshizawa [OA].
Jump to: Botany; Developmental Biology; Ecology; Environmental; Evolution; Geology; Historical Geology; Human Evolution; Palaeontology; Zoology.
