Invertebrate Biology最新文献

Negative interaction between alleles that arise independently in diverging populations (i.e., Dobzhansky–Muller incompatibilities) can cause reduction of fitness in their hybrids. However, heterosis in hybrids can emerge if hybridization breaks down detrimental epistatic interaction within parental lineages. In this study, we examined the life history fitness of the interspecific F₁s of two recently diverged microcrustacean species, Daphnia pulex and D. pulicaria, as well as intraspecific crosses of D. pulex. We identified heterosis in two of five life history traits in the interspecific F₁s. According to theories that heterosis can transiently emerge in early speciation, the observation of heterosis in these life history traits suggests that there are no major genetic incompatibilities between these two species affecting these traits and that D. pulex and D. pulicaria are at an early stage of speciation.

Invertebrates in polar and deep-sea environments that have complex life histories are exposed to unique environmental conditions that may favor non-pelagic development and K-strategist reproduction. Although many polar species follow this strategy, the numerically most abundant species tend to have more r-strategist life-history characteristics. We deployed artificial substrata over 3 years in the Arctic deep sea and collected hundreds of specimens of the athecate hydroid Bouillonia cornucopia. While this species has previously been described as rare, we report dense, patchy recruitment on artificial substrata, suggesting that B. cornucopia is highly opportunistic. This species has rapid growth compared to other sessile invertebrates in the study area, high fecundity, and continuous reproduction—all characteristics of an r-selected life history. The species’ gonophores are simple, lacking an obvious spadix or radial canals. We observed nurse cells in histological sections of female gonophores, but no male gonophores were observed. Gonophores break away from the blastostyles in mature specimens and appear to have fertilization envelopes, suggesting that each gonophore is composed of a single oocyte and that embryological development occurs in the water column. Hydroids are typically the first invertebrates to recruit to substrata in the Arctic but are easily overgrown. The opportunistic life histories of B. cornucopia and other hydroids may be adaptive for maintaining populations in the face of high mortality. Our study demonstrates the utility of artificial substrata for collections of otherwise rare opportunistic species.

Sthenelanella is an unusual genus of tube-dwelling scale worms, with fine fibrous threads that appear on either side of the body. These fibers emerge dorsally in long silvery bundles that are then tightly interwoven to construct the felt-like material of the tube. In the literature, these fibers are described as the products of so-called “spinning glands.” In this article, we investigated the ultrastructure of these notopodial fibers and show that they are annelid chaetae. Three or four dynamic microvilli of a basal chaetoblast form each of these feltage chaetae, making them the thinnest known annelid bristles. Our results show that the spinning glands of Sthenelanella uniformis are additional, highly modified notopodial chaetal sacs. We also show that the follicle cells, by their secretion of the enamel layer, play an active role in shaping the final chaeta. These findings not only increase the known morphological diversity of chaetae but also demonstrate the apparent plasticity of the machinery that form these chitinous structures. Our results are compared with chaetae in other annelids, with a particular focus on similar fibrous chaetae in Aphroditiformia.

As suspension feeders, freshwater bryozoans (Phylactolaemata) ingest a wide variety of particles. After this material is processed in the gut, the remaining wastes are ejected in a pellet. Curiously, fecal pellet contents appear perfectly intact, often still alive, and apparently unharmed. This raises questions about the true sources of bryozoan nutrition and the entire digestive process itself. This article summarizes the results of controlled feeding experiments as well as findings from gut examination by scanning electron microscopy. Extensive feeding tests with bryozoan species in three families show that colonies ingesting protozoans and small rotifers grow much faster than those on any other diet. There is no evidence for digestion of green algae or bacteria, including cyanobacteria. Close observations reveal muscular contractions of the stomach crushing and abrading fragile prey organisms, with possible assistance from indigestible algal particles. A dense carpet of microvilli lines the walls of the stomach and intestine. In most instances, these are organized in a three-dimensional matrix that offers an extensive surface area. Because all food is handled in sequential batches, there is limited time for many particles to be digested.

The characterization of early life-history strategies of soft corals is important in understanding population maintenance, replenishment, and recovery in disturbed coral reefs. This study examined the sexual reproduction of the soft coral Lobophytum schoedei in the Bolinao-Anda Reef Complex (BARC), a degraded reef in northwestern Philippines. Reproductive strategies such as sexuality, sex ratio, fecundity, and reproductive timing were examined. Random colonies of L. schoedei were sampled a few weeks before the predicted time of spawning to assess fecundity (n = 73 colonies), and sexuality and sex ratio (n = 221 colonies). Monthly sampling of tagged colonies of L. schoedei (n = 20) was done over 13 months to determine the reproductive timing through polyp dissection. Peak of annual spawning was inferred based on the presence of large gametes and their absence in the next sampling period. Results showed that L. schoedei is a gonochoric broadcast spawner with 1:1.1 sex ratio. Although oogenesis and spermatogenesis exhibited overlapping cycles, both gametes matured and spawned in April, coinciding with increasing sea surface temperature. Prior to spawning, oocytes and spermaries ranged 300–633 µm and 150–337 µm in diameter, respectively. Mean female fecundity was 6.7 ± 3.9 oocytes per polyp and male fecundity was 39.2 ± 22.5 (±SD) spermaries per polyp. Some of these results, including the low number of oocytes produced by female polyps, may be caused by sexual reproduction in a degraded reef environment. Understanding these reproductive traits may be useful for predicting the resiliency of populations of L. schoedei in response to ongoing and future environmental change.

Challenging students to independently design and implement experiments is a powerful way to teach the scientific method while engaging with STEM-related course material. For ecology and organismal biology, such experiences often take the form of field work. The COVID-19 pandemic presented formidable challenges for instructors of such courses: How can students conduct any experiments, much less ones of their own design, when they might not even have access to campus? Here we describe a student-led field project exploring invertebrate herbivory in terrestrial plant systems. Designed to flexibly accommodate student groups working either in-person, remotely, or both, the project would be suitable for invertebrate biology, plant biology, or general ecology courses at the college or high school level. We describe our implementation in two sections of a sophomore-level course, provide specific advice based on our experiences, make suggestions for future improvements or adaptations, and provide all the written materials that instructors would need to implement this in their own teaching.

Close observation is central to both art and science as practitioners in both disciplines describe, compare, and seek to understand or interpret the natural world. Indeed, as the artist and writer Guy Davenport noted, “The vision by which we discover the hidden in nature is sometimes called science, sometimes called art.” In the last decade, the movement to integrate science, technology, engineering, and mathematics with arts and humanities (i.e., STEAM learning) has gained traction in K–12 education. A recent National Academies report (2018) examines the case for integrating humanities and the arts in undergraduate STEM education. Microscopy provides an excellent vehicle for engaging all kinds of students in integrative (STEAM) learning about biology and for encouraging them to observe the world closely. In this essay adapted from my keynote address to the American Microscopical Society in 2020, I highlight activities and approaches that use microscopy to engage learners of all kinds, examine how using microscopes changes students’ attitudes about science and biology, and explore the intersection of microscopy and visual art.

The COVID-19 global pandemic caused instructors to pivot to remote and online teaching, an especially challenging task in hands-on classes such as invertebrate biology. In this special 25th anniversary issue of Invertebrate Biology, the authors present a variety of clever and effective ways to help invertebrate biology instructors adapt to teaching in an online environment. Student-centered research and learning are essential in all biology classes, and we explore scientific writing, field trips, do-it-yourself laboratories, and more. These techniques will be useful for classes of varying sizes and types, from non-major undergraduates to graduate students, even after the pandemic is over. Innovation for teaching invertebrate biology online may help facilitate more inclusive courses that serve diverse students more equitably. Ideas for how to best move traditionally hands-on laboratories into online or remote formats are currently also being informally discussed in a collaborative online space for instructors.

Our understanding of how sea anemones reproduce in the equatorial Central Indo-Pacific region remains poor compared to other marine regions. Here we report the gametogenic cycles of Phymanthus pinnulatus, a zooxanthellate sea anemone found throughout the Indo-Pacific tropics. Observations were based on 41 individuals collected in Singapore. We found P. pinnulatus to be gonochoric, with an equal sex ratio of 1:1. Phases of oogenesis and spermatogenesis were detailed for the first time in P. pinnulatus, and were consistent with phases in other actiniarians. Females with pedal disc diameters <10 mm were found to asynchronously produce oocytes. We also found that trophonemata were associated with both oocytes and spermaries during gametogenesis. In Singapore, the periods during which gametes matured in each sex of P. pinnulatus appeared to overlap. We were unable distinguish whether spawning was annual or continuous in P. pinnulatus. Our observations on the occurrence of maturing and matured gametes in P. pinnulatus were similar to those reported for other species within the Central Indo-Pacific. It also coincided with the multispecies spawning of scleractinian corals in Singapore. This study contributes to the growing body of work focused on the biology of tropical actiniarians in the Central Indo-Pacific region.