The evolutionary history of Stomatopoda (Crustacea: Malacostraca) inferred from molecular data

Molecular Evolution of Malacostracan Short Wavelength Sensitive Opsins

Investigations of the molecular mechanisms behind detection of short, and particularly ultraviolet, wavelengths in arthropods have relied heavily on studies from insects due to the relative ease of heterologous expression of modified opsin proteins in model organisms like Drosophila. However, species outside of the Insecta can provide information on mechanisms for spectral tuning as well as the evolutionary history of pancrustacean visual pigments. Here we investigate the basis of spectral tuning in malacostracan short wavelength sensitive (SWS) opsins using phylogenetic comparative methods. Tuning sites that may be responsible for the difference between ultraviolet (UV) and violet visual pigment absorbance in the Malacostraca are identified, and the idea that an amino acid polymorphism at a single site is responsible for this shift is shown to be unlikely. Instead, we suggest that this change in absorbance is accomplished through multiple amino acid substitutions. On the basis of our findings, we conducted further surveys to identify spectral tuning mechanisms in the order Stomatopoda where duplication of UV opsins has occurred. Ancestral state reconstructions of stomatopod opsins from two main clades provide insight into the amino acid changes that lead to differing absorption by the visual pigments they form, and likely contribute the basis for the wide array of UV spectral sensitivities found in this order.

Increasing complexity of opsin expression across stomatopod development

Stomatopods are well studied for their unique visual systems, which can consist of up to 16 different photoreceptor types and 33 opsin proteins expressed in the adults of some species. The light-sensing abilities of larval stomatopods are comparatively less well understood with limited information about the opsin repertoire of these early-life stages. Early work has suggested that larval stomatopods may not possess the extensive light detection abilities found in their adult counterparts. However, recent studies have shown that these larvae may have more complex photosensory systems than previously thought. To examine this idea at the molecular level, we characterized the expression of putative light-absorbing opsins across developmental stages, from embryo to adult, in the stomatopod species Pullosquilla thomassini using transcriptomic methods with a special focus on ecological and physiological transition periods. Opsin expression during the transition from the larval to the adult stage was further characterized in the species Gonodactylaceus falcatus. Opsin transcripts from short, middle, and long wavelength-sensitive clades were found in both species, and analysis of spectral tuning sites suggested differences in absorbance within these clades. This is the first study to document the changes in opsin repertoire across development in stomatopods, providing novel evidence for light detection across the visual spectrum in larvae.

Investigation of the ultrastructures and retinal arrangements of larval stomatopod eyes

Though the transparent apposition eyes of larval stomatopod crustaceans lack most of the unique retinal specializations known from their adult counterparts, increasing evidence suggests that these tiny pelagic organisms possess their own version of retinal complexity. In this paper, we examined the structural organization of larval eyes in six species of stomatopod crustaceans across three stomatopod superfamilies using transmission electron microscopy. The primary focus was to examine retinular cell arrangement of the larval eyes and characterize the presence of an eighth retinular cell (R8), which is typically responsible for UV vision in crustaceans. For all species investigated, we identified R8 photoreceptor cells positioned distal to the main rhabdom of R1-7 cells. This is the first evidence that R8 photoreceptor cells exist in larval stomatopod retinas, and among the first identified in any larval crustacean. Considering recent studies that identified UV sensitivity in larval stomatopods, we propose that this sensitivity is driven by this putative R8 photoreceptor cell. Additionally, we identified a potentially unique crystalline cone structure in each of the species examined, the function of which is still not understood.

Sexual selection and predation drive the repeated evolution of stridulation in Heteroptera and other arthropods

Acoustic and substrate-borne vibrations are among the most widely used signalling modalities in animals. Arthropods display a staggering diversity of vibroacoustic organs generating acoustic sound and/or substrate-borne vibrations, and are fundamental to our broader understanding of the evolution of animal signalling. The primary mechanism that arthropods use to generate vibroacoustic signals is stridulation, which involves the rubbing together of opposing body parts. Although stridulation is common, its behavioural context and evolutionary drivers are often hard to pinpoint, owing to limited synthesis of empirical observations on stridulatory species. This is exacerbated by the diversity of mechanisms involved and the sparsity of their description in the literature, which renders their documentation a challenging task. Here, we present the most comprehensive review to date on the systematic distribution and behavioural context of stridulation. We use the megadiverse heteropteran insects as a model, together with multiple arthropod outgroups (arachnids, myriapods, and selected pancrustaceans). We find that stridulatory vibroacoustic signalling has evolved independently at least 84 times and is present in roughly 20% of Heteroptera, representing a remarkable case of convergent evolution. By studying the behavioural context of stridulation across Heteroptera and 189 outgroup lineages, we find that predation pressure and sexual selection are the main behaviours associated with stridulation across arthropods, adding further evidence for their role as drivers of large-scale signalling and morphological innovation in animals. Remarkably, the absence of tympanal ears in most Heteroptera suggests that they typically cannot detect the acoustic component of their stridulatory signals. This demonstrates that the adoption of new signalling modalities is not always correlated with the ability to perceive those signals, especially when these signals are directed towards interspecific receivers in defensive contexts. Furthermore, by mapping their morphology and systematic distribution, we show that stridulatory organs tend to evolve in specific body parts, likely originating from cleaning motions and pre-copulatory displays that are common to most arthropods. By synthesising our understanding of stridulation and stridulatory organs across major arthropod groups, we create the necessary framework for future studies to explore their systematic and behavioural significance, their potential role in sensory evolution and innovation, and the biomechanics of this mode of signalling.

Colour vision in stomatopod crustaceans

The stomatopod crustaceans, or mantis shrimps, are colourful marine invertebrate predators. Their unusual compound eyes have dorsal and ventral regions resembling typical crustacean apposition designs separated by a unique region called the midband that consists of from two to six parallel rows of ommatidia. In species with six-row midbands, the dorsal four rows are themselves uniquely specialized for colour analysis. Rhabdoms of ommatidia in these rows are longitudinally divided into three distinct regions: an apical ultraviolet (UV) receptor, a shorter-wavelength middle tier receptor and a longer-wavelength proximal tier receptor. Each of the total of 12 photoreceptors has a different spectral sensitivity, potentially contributing to a colour-vision system with 12 channels. Mantis shrimps can discriminate both human-visible and UV colours, but with limited precision compared to other colour-vision systems. Here, we review the structure and function of stomatopod colour vision, examining the types of receptors present in a species, the spectral tuning of photoreceptors both within and across species, the neural analysis of colour and the genetics underlying the multiple visual pigments used for colour vision. Even today, after many decades of research into the colour vision of stomatopods, much of its operation and its use in nature remain a mystery. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'.

Diversity and distribution of mantis shrimps (Arthropoda: Crustacea: Stomatopoda) in the Gulf of Kachchh, Gujarat, India

Diversity and distribution study of Stomatopoda has been carried out in selected locations of Gulf of Kachchh from 2014 to 2020. Four species belonging to four genera in two families were recorded from Gulf of Kachchh, Gujarat. Carinosquilla multicarinata (White, 1848) was recorded for the first time from the west coast of India. Cloridina ichneumon (Fabricius, 1798) was recorded for the first time from Gujarat coast. Gonodactylellus demanii (Henderson, 1893) was reported after 50 years from Gulf of Kachchh, Gujarat, and Gonodactylus smithii Pocock, 1893 is a commonly occurring species in the intertidal zone of the Gulf of Kachchh. Species are described and illustrated with key characters and distributional status in Gulf of Kachchh. An annotated checklist of nine species of Stomatopoda occurring in Gujarat is presented.

Phylogenetic Appraisal of Lysiosquillidae Giesbrecht, 1910, and a New Species of Lysiosquilloides Manning, 1977, from Taiwan (Crustacea: Stomatopoda: Lysiosquilloidea)

The mantis shrimp family Lysiosquillidae includes the largest known stomatopods and presently includes three genera: Lysiosquilla Dana, 1852, Lysiosquillina Manning, 1995, and Lysiosquilloides Manning, 1977. Since 1995, new species assigned to all three lysiosquilloid genera have been recognised: Lysiosquilla manningi Boyko, 2000, Lysiosquillina lisa Ahyong & Randall, 2001, Lysiosquilla colemani Ahyong, 2001, Lysiosquilla suthersi Ahyong, 2001, and Lysiosquilloides mapia Erdmann & Boyer, 2003, and Lysiosquilla isos Ahyong, 2004. Lysiosquillina lisa, Lysiosquilla campechiensis Manning, 1962 and Lysiosquilla suthersi, however, proved problematical to assign to genera owing to the possession of characters intermediate between Lysiosquilla sensu stricto and Lysiosquillina sensu stricto. In particular, species that are transitional between Lysiosquilla and Lysiosquillina challenge the validity of the latter genus. Here, we reassess the status and composition of the lysiosquillid genera by cladistic analysis of all known species in the family. Lysiosquillina is synonymized with Lysiosquilla and a new species of Lysiosquilloides is described from Taiwan. A key to the species of Lysiosquilloides is provided.

The mitochondrial genome of Faughnia haani (Stomatopoda): novel organization of the control region and phylogenetic position of the superfamily Parasquilloidea

BACKGROUND

Stomatopod crustaceans are aggressive marine predators featuring complex compound eyes and powerful raptorial appendages used for "smashing" or "spearing" prey and/or competitors. Among them, parasquilloids (superfamily Parasquilloidea) possess eyes with 2-3 midband rows of hexagonal ommatidia and spearing appendages. Here, we assembled and analyzed the complete mitochondrial genome of the parasquilloid Faughnia haani and explored family- and superfamily-level phylogenetic relationships within the Stomatopoda based on mitochondrial protein coding genes (PCGs).

RESULTS

The mitochondrial genome of F. haani is 16,089 bp in length and encodes 13 protein coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes, and a control region that is relatively well organized, containing 2 GA-blocks, 4 poly-T stretches, various [TA(A)]n-blocks, and 2 hairpin structures. This organized control region is likely a synapomorphic characteristic in the Stomatopoda. Comparison of the control region among superfamilies shows that parasquilloid species are more similar to gonodactyloids than to squilloids and lysiosquilloids given the presence of various  poly-T stretches between the hairpin structures and [TA(A)]n-blocks. Synteny is identical to that reported for other stomatopods and corresponds to the Pancrustacea ground pattern. A maximum-likelihood phylogenetic tree based on PCGs revealed that Parasquilloidea is sister to Lysiosquilloidea and Gonodactyloidea and not to Squilloidea, contradicting previous phylogenetic studies.

CONCLUSIONS

The novel phylogenetic position of Parasquilloidea revealed by our study indicates that 'spearing' raptorial appendages are plesiomorphic and that the 'smashing' type is either derived (as reported in previous studies) or apomorphic. Our results raise the possibility that the spearing raptorial claw may have independently evolved twice. The superfamily Parasquilloidea exhibits a closer relationship with other stomatopod superfamilies with a different raptorial claw type and with dissimilar numbers of midband rows of hexagonal ommatidia. Additional studies focusing on the assembly of mitochondrial genomes from species belonging to different genera, families, and superfamilies within the order Stomatopoda are warranted to reach a robust conclusion regarding the evolutionary history of this iconic clade based on mitochondrial PCGs.

The complete mitochondrial genome of Purple Spot Mantis Shrimp Gonodactylus smithii (Pocock, 1893)

In this study, the whole mitochondrial genome of the Purple Spot Mantis Shrimp Gonodactylus smithii from the South China Sea was determined using next-generation sequencing. The circular mitogenome of G. smithii is 16,260 bp long and consists of 13 protein-coding genes (PCGs), 22 tRNA genes, and two rRNA genes. The base composition is AT-rich and has an overall AT content of 67.76% (composition of A, G, T, and C was 35.30%, 12.41%, 32.46%, and 19.83%, respectively). Among 13 PCGs, 12 PCGs shared a common ATN as the start codon except COX1 gene using an abnormal putative first codon GCG. 11 PCGs ended with TAA or TAG, while ND6, COX2 gene terminated with a single T and ND3 gene used a special “GAT” as the stop codon. The phylogenetic tree showed that G. smithii was clustered with Gonodactylus chiragra, then together with Gonodactylaceus randalli.

Scaling and development of elastic mechanisms: the tiny strikes of larval mantis shrimp

Latch-mediated spring actuation (LaMSA) is used by small organisms to produce high acceleration movements. Mathematical models predict that acceleration increases as LaMSA systems decrease in size. Adult mantis shrimp use a LaMSA mechanism in their raptorial appendages to produce extremely fast strikes. Until now, however, it was unclear whether mantis shrimp at earlier life-history stages also strike using elastic recoil and latch mediation. We tested whether larval mantis shrimp (Gonodactylaceus falcatus) use LaMSA and, because of their smaller size, achieve higher strike accelerations than adults of other mantis shrimp species. Based on microscopy and kinematic analyses, we discovered that larval G. falcatus possess the components of, and actively use, LaMSA during their fourth larval stage, which is the stage of development when larvae begin feeding. Larvae performed strikes at high acceleration and speed (mean: 4.133×105 rad s-2, 292.7 rad s-1; 12 individuals, 25 strikes), which are of the same order of magnitude as for adults - even though adult appendages are up to two orders of magnitude longer. Larval strike speed (mean: 0.385 m s-1) exceeded the maximum swimming speed of similarly sized organisms from other species by several orders of magnitude. These findings establish the developmental timing and scaling of the mantis shrimp LaMSA mechanism and provide insights into the kinematic consequences of scaling limits in tiny elastic mechanisms.

Surf and turf vision: Patterns and predictors of visual acuity in compound eye evolution

Eyes have the flexibility to evolve to meet the ecological demands of their users. Relative to camera-type eyes, the fundamental limits of optical diffraction in arthropod compound eyes restrict the ability to resolve fine detail (visual acuity) to much lower degrees. We tested the capacity of several ecological factors to predict arthropod visual acuity, while simultaneously controlling for shared phylogenetic history. In this study, we have generated the most comprehensive review of compound eye visual acuity measurements to date, containing 385 species that span six of the major arthropod classes. An arthropod phylogeny, made custom to this database, was used to develop a phylogenetically-corrected generalized least squares (PGLS) linear model to evaluate four ecological factors predicted to underlie compound eye visual acuity: environmental light intensity, foraging strategy (predator vs. non-predator), horizontal structure of the visual scene, and environmental medium (air vs. water). To account for optical constraints on acuity related to animal size, body length was also included, but this did not show a significant effect in any of our models. Rather, the PGLS analysis revealed that the strongest predictors of compound eye acuity are described by a combination of environmental medium, foraging strategy, and environmental light intensity.

Complete mitochondrial genome of the mantis shrimp Taku spinosocarinatus (Fukuda, 1909) (Stomatopoda: Gonodactyloidea: Takuidae) in South Korea

The superfamily Gonodactyloidea is polyphyletic because of Hemisquillidae, but to date, mitochondrial genome of that family does not exist. As valuable data that can be compared in the future with that family within this superfamily, we report the first complete mitochondrial genome sequence of Taku spinosocarinatus of the family Takuidae. The mitochondrial genome is 15,960 bp in length and consists of 13 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes, and a non-coding A + T rich region. The overall base composition in the heavy strand was as follows: A: 34.2%, G: 13.4%, C: 19.8%, and T: 32.6%, with a G + C content of 33.2%. Phylogenetic analysis revealed that this species was most closely related to Gonodactylus chiragra of Gonodactylidae, registered with NCBI to date. The result of this study will enable additional comparisons between families in the future.

Using larval barcoding to estimate stomatopod species richness at Lizard Island, Australia for conservation monitoring

Stomatopods (Crustacea, Stomatopoda) are well studied for their aggressive behavior and unique visual system as well as their commercial importance in Asian and European countries. Like many crustaceans, stomatopods undergo indirect development, passing though several larval stages before reaching maturity. Adult stomatopods can be difficult to catch due to their inaccessible habitats and cryptic coloration. By sampling larvae from the planktonic community, less effort is required to obtain accurate measures of species richness within a region. Stomatopod larvae were collected between 2006 and 2015 from the waters around the Lizard Island reef platform in Eastern Australia. Cytochrome oxidase I (COI) mitochondrial DNA sequences were generated from each larval sample and compared to a database of COI sequences tied to adult specimens. Of the 20 species collected from Lizard Island as adults which have COI data available, 18 species were identified from larval sampling. One additional species identified from larval samples, Busquilla plantei, was previously unknown from Lizard Island. Nine larval OTUs were found not to match any published adult sequences. Sampling larval stomatopod populations provides a comparable picture of the adult population to benthic sampling methods and may include species richness beyond what is measurable by sampling adult populations.

The Power of Mantis Shrimp Strikes: Interdisciplinary Impacts of an Extreme Cascade of Energy Release

In the course of a single raptorial strike by a mantis shrimp (Stomatopoda), the stages of energy release span six to seven orders of magnitude of duration. To achieve their mechanical feats of striking at the outer limits of speeds, accelerations, and impacts among organisms, they use a mechanism that exemplifies a cascade of energy release-beginning with a slow and forceful, spring-loading muscle contraction that lasts for hundreds of milliseconds and ending with implosions of cavitation bubbles that occur in nanoseconds. Mantis shrimp use an elastic mechanism built of exoskeleton and controlled with a latching mechanism. Inspired by both their mechanical capabilities and evolutionary diversity, research on mantis shrimp strikes has provided interdisciplinary and fundamental insights to the fields of elastic mechanisms, fluid dynamics, evolutionary dynamics, contest dynamics, the physics of fast, small systems, and the rapidly-expanding field of bioinspired materials science. Even with these myriad connections, numerous discoveries await, especially in the arena of energy flow through materials actuating and controlling fast, impact fracture resistant systems.

A New Species of Praying Mantis from Peru Reveals Impaling as a Novel Hunting Strategy in Mantodea (Thespidae: Thespini)

A new species of lichen-mimicking praying mantis, Carrikerella simpira n. sp., is described from Tingo María region in Peru. The new species differs from its congeners in having reduced tergal lobes, a relatively sinuous pronotum, and it is found in the highland tropical rainforest of the Central Andes. Behavioral observations conducted on captive individuals revealed that juveniles and adults hunt by impaling prey using modified foretibial structures. Anatomical examinations of the incumbent trophic structures revealed functional adaptations for prey impaling in the foretibiae, primarily consisting of prominent, forwardly oriented, barbed spines. We provide an overall description of this novel hunting behavior in Mantodea and hypothesize on its evolutionary origin and adaptive significance for the Thespidae.

Mushroom body evolution demonstrates homology and divergence across Pancrustacea

Descriptions of crustacean brains have focused mainly on three highly derived lineages of malacostracans: the reptantian infraorders represented by spiny lobsters, lobsters, and crayfish. Those descriptions advocate the view that dome- or cap-like neuropils, referred to as 'hemiellipsoid bodies,' are the ground pattern organization of centers that are comparable to insect mushroom bodies in processing olfactory information. Here we challenge the doctrine that hemiellipsoid bodies are a derived trait of crustaceans, whereas mushroom bodies are a derived trait of hexapods. We demonstrate that mushroom bodies typify lineages that arose before Reptantia and exist in Reptantia thereby indicating that the mushroom body, not the hemiellipsoid body, provides the ground pattern for both crustaceans and hexapods. We show that evolved variations of the mushroom body ground pattern are, in some lineages, defined by extreme diminution or loss and, in others, by the incorporation of mushroom body circuits into lobeless centers. Such transformations are ascribed to modifications of the columnar organization of mushroom body lobes that, as shown in Drosophila and other hexapods, contain networks essential for learning and memory.

Evolution of mantis shrimp telson armour and its role in ritualized fighting

Mantis shrimp possess both formidable weapons and impact-resistant armour that clash during ritualized combat. The telson is one of few biological structures known to withstand the repeated high impact forces of smashing mantis shrimp strikes, and it is hypothesized that this pairing of armour and weapon is associated with the evolution of telson sparring. We carried out a comparative analysis of telson impact mechanics across 15 mantis shrimp species to assess if the telsons of sparring species (i) are consistently specialized for impact-resistance, (ii) are more impact-resistant than those of non-sparring species, and (iii) have impact parameters that correlate with body size, and thereby useful for assessment. Our data from ball drop tests show that the telsons of all species function like a stiff spring that dissipates most of the impact energy, but none of the measured impact parameters are correlated with the occurrence of sparring behaviour. Impact parameters were correlated with body mass for only some species, suggesting that it is not broadly useful for size assessment during ritualized fighting. Contrary to expectation, sparring mantis shrimp do not appear to have coevolved telson armour that is more robust to impact than non-sparring species. Rather, telson structure is inherently impact-resistant.

Combining morphological and molecular data resolves the phylogeny of Squilloidea (Crustacea : Malacostraca)

The mantis shrimp superfamily Squilloidea, with over 185 described species, is the largest superfamily in the crustacean order Stomatopoda. To date, phylogenetic relationships within this superfamily have been comprehensively analysed using morphological data, with six major generic groupings being recovered. Here, we infer the phylogeny of Squilloidea using a combined dataset comprising 75 somatic morphological characters and four molecular markers. Nodal support is low when the morphological and molecular datasets are analysed separately but improves substantially when combined in a total-evidence phylogenetic analysis. We obtain a well resolved and strongly supported phylogeny that is largely congruent with previous estimates except that the Anchisquilloides-group, rather than the Meiosquilla-group, is the earliest-branching lineage in Squilloidea. The splits among the Anchisquilloides- and Meiosquilla-groups are followed by those of the Clorida-, Harpiosquilla-, Squilla- and Oratosquilla-groups. Most of the generic groups are recovered as monophyletic, with the exception of the Squilla- and Oratosquilla-groups. However, many genera within the Oratosquilla-group are not recovered as monophyletic. Further exploration with more extensive molecular sampling will be needed to resolve relationships within the Oratosquilla-group and to investigate the adaptive radiation of squilloids. Overall, our results demonstrate the merit of combining morphological and molecular datasets for resolving phylogenetic relationships.