A. Richard Palmer

Side-resting (pleurothetic) lifestyles evolved independently many times across the Bivalvia in free-lying, byssally attached and cementing lineages. Within some species individuals lie indifferently on either their right or left side (randomly pleurothetic), whereas in others they lie consistently on one side (left-pleurothetic or right-pleurothetic). Morphological differences between valves (asymmetries) typically accompany this behaviour, so it can be studied widely across living and fossil bivalves. Because direction of asymmetry is rarely inherited in cases of random asymmetry, any evolutionary transition from randomly pleurothetic to fixed (left or right) qualifies as a case of ‘genes as followers’. Origins of left-pleurothetic or right-pleurothetic taxa directly from upright (orthothetic) ancestors would represent examples of ‘genes as leaders’. I therefore surveyed pleurothetic lifestyles across the Bivalvia. By mapping pleurothetic states onto a comprehensive phylogenetic tree that included both living and fossil families, I assessed the prevalence of these alternate modes of evolution. Various lines of evidence were also used to hypothesize phylogenetic relations within the Chamidae—the only living bivalve family exhibiting all three pleurothetic states. Randomly pleurothetic forms (direction not inherited) arose from orthothetic ancestors about half as often as fixed pleurothetic forms (direction is inherited). Unlike many other animal groups, fixed pleurothetic forms rarely arose from randomly pleurothetic ancestors, suggesting a ‘genes as leaders’ mode of evolution was most prevalent. However, many fascinating examples of randomly pleurothetic forms among Upper Ordovician and Silurian bivalves suggest that evolutionary transitions from random to fixed may have been more common. Also, randomly pleurothetic forms were short-lived in some fossil lineages, which would reduce the likelihood of them being detected. Hopefully, this preliminary analysis will motivate further study of (1) phylogenetic relations of key groups like the Chamidae, and basal Limida, Ostreida and Pterioidea, and (2) morphological variation among early members of other pleurothetic bivalve groups.

Writing assignments offer valuable student learning experiences in both live and online courses. But concerns about the challenges and extra work of marking, and about plagiarism, often deter instructors from using them. I used a writing assignment successfully over 20 years in a one‐term invertebrate biology course, despite enrolments exceeding 100. Structured to maximally engage students yet minimize marking load, the assignment often yielded gems of stories for use in subsequent lectures. The Annotated Bibliography assignment asks students: (a) to précis the justification, main results, and significance of three papers from the primary scientific literature in under 250 words each, and (b) to provide a short (150 word) summary of the broader story connecting the three papers. Students liked this assignment because they could choose any aspect of the biology of any invertebrate genus. This inspired them to explore the literature out of personal interest. It's appealing for instructors, because annotations are compact and therefore easy to read, mark, and inspect for plagiarism. It is appealing to host universities, because it generates extensive use of library resources and motivates students to learn how to use them, and online taxonomic databases, effectively. Here I provide: (a) instructions for this assignment, (b) a straightforward marking rubric, (c) two examples of excellent submissions, and (d) comments on the risk and extent of plagiarism. Appendices provide: detailed instructions, a sample annotation with comments to guide student writing, an online submission web page, an online administrator web page, and PHP scripts for both web pages. Finally, I summarize topics and taxa from nearly 2,000 submissions. The five most popular taxa were cephalopods, insects, malacostracan crustaceans, gastropods, and arachnids. Although aspects of sex or reproduction, and camouflage or mimicry were the most popular topics, one paper on extreme limb movements in stomatopods was cited the most.

The vertebrate jaw is a versatile feeding apparatus. To function, it requires a joint between the upper and lower jaws, so jaw joint defects are often highly disruptive and difficult to study. To describe the consequences of jaw-joint dysfunction, we engineered two independent null alleles of a single jaw-joint marker gene, nkx3.2, in zebrafish. These mutations caused zebrafish to become functionally jawless via fusion of the upper and lower jaw cartilages (ankylosis). Despite lacking jaw joints, nkx3.2 mutants survived to adulthood and accommodate this defect by: a) having a remodelled skull with a fixed open gape, reduced snout, and enlarged branchial region; and b) performing ram feeding in the absence of jaw-generated suction. The late onset and broad extent of phenotypic changes in the mutants suggest that modifications to the skull are induced by functional agnathia, secondarily to nkx3.2 loss-of-function. Interestingly, nkx3.2 mutants superficially resemble ancient jawless vertebrates (anaspids and furcacaudiid thelodonts) in overall head shapes. Because no homology exists in individual skull elements between these taxa, the adult nkx3.2 phenotype is not a reversal, but convergence due to similar functional requirements of feeding without moveable jaws. This remarkable analogy strongly suggests that jaw movements themselves dramatically influence the development of jawed vertebrate skulls. Thus, these mutants provide a unique model with which to: a) investigate adaptive responses to perturbation in skeletal development; b) re-evaluate evolutionarily inspired interpretations of phenocopies generated by gene knockdowns and knockouts; and c) gain insights into feeding mechanics of the extinct agnathans.

Dr. Tomonari Kaji, an exceptional young evolutionary morphologist at the University of Alberta, passed away unexpectedly in May of this year. His passion for the study of developmental and evolutionary transformations yielded a succession of intriguing papers about how spectacular morphological innovations develop or evolved, including such remarkable structures as crustacean suction cups, squirting heads in termite soldiers, envenomating mandibles in copepods, and shrimp and amphipod claws that create explosive snaps. Significantly, his work is a valuable reminder of how great advances in our understanding of the development and evolution of morphological innovations can be made simply by looking carefully and thinking about what you see, no genetics/genomics or complex statistics required. Long live comparative morphology.

Image-forming compound eyes are such a valuable adaptation that similar visual systems have evolved independently across crustaceans. But if different compound eye types have evolved independently multiple times, how useful are eye structures and ommatidia morphology for resolving phylogenetic relationships? Crabs are ideal study organisms to explore these questions because they have a good fossil record extending back into the Jurassic, they possess a great variety of optical designs, and details of eye form can be compared between extant and fossil groups. True crabs, or Brachyura, have been traditionally divided into two groups based on the position of the sexual openings in males and females: the so-called ‘Podotremata’ (females bearing their sexual openings on the legs), and the Eubrachyura, or ‘higher’ true crabs (females bearing their sexual openings on the thorax). Although Eubrachyura appears to be monophyletic, the monophyly of podotreme crabs remains controversial and therefore requires exploration of new character systems. The earliest podotremous lineages share the plesiomorphic condition of ‘mirror’ reflecting superposition eyes with most shrimp, lobsters, and anomurans (false crabs and allies). The optical mechanisms of fossil and extant podotreme groups more closely related to Eubrachyura, however, are still poorly investigated. To better judge the phylogenetic utility of compound eye form, we investigated the distribution of eye types in fossil and extant podotreme crabs. Our findings suggest the plesiomorphic ‘mirror’ eyes—seen in most decapod crustaceans including the earliest true crabs—has been lost in several ‘higher’ podotremes and in eubrachyurans. We conclude that the secondary retention of larval apposition eyes has existed in eubrachyurans and some podotremes since at least the Early Cretaceous, and that the distribution of eye types among true crabs supports a paraphyletic podotreme grade, as suggested by recent molecular and morphological phylogenetic studies. We also review photoreceptor structure and visual pigment evolution, currently known in crabs exclusively from eubrachyuran representatives. These topics are critical for future expansion of research on podotremes to deeply investigate the homology of eye types across crabs.

The vertebrate jaw is a versatile feeding apparatus that facilitated explosive diversification. To function, it requires a joint between the upper and lower jaws, so jaw joint defects - such as osteoarthritis or even ankylosis - are often highly disruptive and difficult to study. To describe consequences of jaw-joint dysfunction, we engineered two independent null alleles of a single jaw-joint marker gene, nkx3.2 , in zebrafish. These mutations caused zebrafish to become functionally jawless via fusion of the upper and lower jaw cartilages (ankylosis). Despite lacking jaw joints, nkx3.2 mutants survive to adulthood and accommodate this defect by: a) remodeling their skulls; and b) altering their behavior from suction feeding to ram feeding. As a result of remodeling, nkx3.2 mutants developed superficial similarities to the skull shapes observed in two lineages of ancient jawless vertebrates (anaspids and furcacaudiid thelodonts), including: a fixed open gape, reduced snout, and enlarged branchial region. However, no homology exists in individual skull elements between these taxa, and most of the modified elements in the mutant zebrafish occur outside known expression domains of nkx3.2 . Therefore, we interpret the adult nkx3.2 phenotype not as a reversal to an ancestral state, but as convergence due to similar functional requirement of feeding without moveable jaws. This remarkable convergence strongly suggests that jaw movements themselves dramatically influence the development of jawed vertebrate skulls, which implies that functionally viable skull morphologies are finite, with or without functional jaws. Because nkx3.2 null zebrafish display prominent joint ankylosis, drastically modified skull shape, and altered feeding behaviors, these mutants provide a unique model with which to investigate mechanisms of skeletal remodeling and joint diseases.

Novel feeding adaptations often facilitate adaptive radiation and diversification. But the evolutionary origins of such feeding adaptations can be puzzling if they require concordant change in multiple component parts. Pelagic, heterorhabdid copepods (Calanoida) exhibit diverse feeding behaviors that range from simple particle feeding to a highly specialized form of carnivory involving piercing mouthparts that likely inject venom. We review the evolutionary history of heterorhabdid copepods and add new high-resolution, 3D anatomical analyses of the muscular system, glands and gland openings associated with this remarkable evolutionary transformation. We examined four heterorhabdid copepods with different feeding modes: one primitive particle-feeder (Disseta palumbii), one derived and specialized carnivore (Heterorhabdus subspinifrons), and two intermediate taxa (Mesorhabdus gracilis and Heterostylites longicornis). We used two advanced, high-resolution microscopic techniques — serial block-face scanning electron microscopy and two-photon excitation microscopy — to visualize mouthpart form and internal anatomy at unprecedented nanometer resolution. Interactive 3D graphical visualizations allowed putative homologues of muscles and gland cells to be identified with confidence and traced across the evolutionary transformation from particle feeding to piercing carnivory. Notable changes included: a) addition of new gland cells, b) enlargement of some (venom producing?) glands, c) repositioning of gland openings associated with hollow piercing fangs on the mandibles, d) repurposing of some mandibular-muscle function to include gland-squeezing, and e) addition of new muscles that may aid venom injection exclusively in the most specialized piercing species. In addition, live video recording of all four species revealed mandibular blade movements coupled to cyclic contraction of some muscles connected to the esophagus. These behavioral and 3D morphological observations revealed a novel injection system in H. subspinifrons associated with piercing (envenomating?) carnivory. Collectively, these results suggest that subtle changes in mandibular tooth form, and muscle and gland form and location, facilitated the evolution of a novel, piercing mode of feeding that accelerated diversification of the genus Heterorhabdus. They also highlight the value of interactive 3D animations for understanding evolutionary transformations of complex, multicomponent morphological systems.