Biology subjects

Wells, C. D.

Publications and source records attributed to Wells, C. D..

13 recordsLinked to original sources

bioRxiv2026

Species identity rather than colony size partitions shape variation in six Caribbean octocorals

Caribbean reefs are increasingly dominated by arborescent octocorals as scleractinian cover declines. The physical structure of these octocoral forests is established by the manner in which octocoral species generate and modify colony form as they grow. We tested whether colony shape exhibited species-specific architecture and whether it changed allometrically with size. Two-dimensional projections of colony form were modeled as a series of stacked bands, whose areas were measured from scaled in situ images of colonies of six sympatric Caribbean octocorals from St John, US Virgin Islands. Principal component analysis (PCA) of relative band areas resolved a single dominant axis, accounting for 67.9% of the variation, that separated top-heavy from bottom-heavy colony profiles. Species identity explained 42% of the total variation in relative form, whereas colony height only explained 2% and had no detectable effect on either PCA axis. The proportion of the colony outline occupied by branches increased with height, from a predicted 41% at 20 cm to 52% at 100 cm. Colonies therefore grew without a detectable redistribution of area along their vertical axis, filling a species-specific outline more densely rather than moving along a common allometric trajectory. The vertical geometry of an octocoral canopy may therefore depend more on which species are present than on the sizes its colonies have reached.

ecology↗

bioRxiv2026

Feeding frequency sets the rhythm of asexual reproduction in the sea anemone Cylista elegans

Many sea anemones reproduce asexually by pedal laceration, shedding fragments of the pedal disk that regenerate into polyps. How feeding affects the amount of this reproduction differs among species, but whether feeding also sets its timing has rarely been examined. We fed the sea anemone Cylista elegans (formerly Sagartia elegans) daily, every second day, every fourth day, or not at all, measured growth, laceration, and survival over 35 days, then reassigned anemones to new schedules to test whether laceration follows the current or previous schedule. Growth rose with feeding but saturated, animals fed daily and every second day growing at similar rates. Total laceration depended on whether an anemone was fed rather than how often. Every fed schedule produced more lacerates than starvation. The timing, by contrast, tracked the schedule closely. Laceration was suppressed for about a day after each meal and recovered before the next, so anemones fed every second or every fourth day lacerated on matching two- and four-day rhythms, while daily-fed animals were arrhythmic. When moved to a new schedule, the period shifted to match it, not the old one. Only starvation caused death. Asexual reproduction in C. elegans is therefore bound closely to feeding, which fuels laceration yet suppresses it during digestion, confining it between meals. This coupling distinguishes C. elegans from anemones with symbiotic microalgae, where starvation rather than feeding drives reproduction, and links it to the feeding-driven clonal proliferation of the invasive sea anemone Diadumene lineata.

ecology↗

bioRxiv2026

Behavioral metabolic suppression confounds thermal performance estimates and climate vulnerability assessments in a marine ectotherm

O_LIThermal performance curves (TPCs) predict species vulnerability to climate change, but standard respirometry assumes that measured oxygen consumption reflects physiological state. Sessile invertebrates that retract their tentacles and contract under thermal stress violate this assumption, with unmeasured consequences for thermal limit estimates. C_LIO_LIWe tested this behavioral confound in an undescribed cold-water intertidal anemone (Urticina sp.) in the Northwest Atlantic by integrating a negative binomial encounter-rate regression, a maximum entropy species distribution model (both from effort-corrected iNaturalist data), and closed-chamber respirometry across seven temperatures (1-30{degrees}C). C_LIO_LIThe strongest distributional predictors were cloud cover and coastal urbanization, with a weaker association with winter minimum SST; direct evidence for warm-edge thermal limitation came from the experiment. Anemone expansion state was variable and without a clear trend across the coldest treatments, declining above 20{degrees}C, and collapsing at the 30{degrees}C treatment, which proved lethal. C_LIO_LIStandard TPC models extrapolated the thermal maximum far beyond the lethal bracket. A Bayesian multiplicative model that separated physiology from behavior showed that physiology continued to track temperature while expansion state declined above 20{degrees}C; a fully expanded anemone respired about twice as fast as a fully closed one at the same temperature. The decline in measured respiration is therefore both behavioral and physiological, and disentangling the two requires recording expansion state alongside oxygen consumption. C_LIO_LIBecause a closed anemone cannot feed or exchange gases, the ecologically relevant thermal limit is the temperature at which the animal can no longer maintain its normal expanded posture, not a curve-fitted thermal maximum. That behavioral threshold leaves warm-edge populations within a few degrees of functional thermal failure. C_LIO_LIFuture thermal physiology studies of organisms capable of modulating oxygen consumption through behavior should incorporate quantitative behavioral covariates to separate physiological from behavioral components of the metabolic response. C_LI ResumeO_LILes courbes de performance thermique (CPT) predisent la vulnerabilite des especes au changement climatique, mais la respirometrie classique postule que la consommation doxygene mesuree reflete letat physiologique. Les invertebres sessiles qui retractent leurs tentacules et se contractent sous stress thermique ne satisfont pas cette hypothese, avec des consequences non quantifiees sur lestimation des limites thermiques. C_LIO_LINous avons teste ce facteur de confusion comportemental chez une anemone intertidale deau froide non decrite (Urticina sp.) de lAtlantique Nord-Ouest, en combinant une regression binomiale negative du taux de rencontre, un modele de distribution despeces a maximum dentropie (tous deux sur donnees iNaturalist corrigees de leffort) et une respirometrie en chambre close a sept temperatures (1 a 30 {degrees}C). C_LIO_LILes principaux predicteurs etaient la couverture nuageuse et lurbanisation cotiere, lassociation au minimum hivernal de temperature de surface de la mer etant plus faible. La preuve directe dune limitation thermique en bordure chaude provient de lexperience. Letat dexpansion variait sans tendance nette aux traitements les plus froids, diminuait au-dela de 20 {degrees}C et seffondrait a 30 {degrees}C, traitement qui sest revele letal. C_LIO_LILes CPT classiques ont extrapole le maximum thermique bien au-dela de lintervalle letal. Un modele bayesien multiplicatif separant physiologie et comportement a montre que la physiologie suivait toujours la temperature alors que letat dexpansion diminuait au-dela de 20 {degrees}C; a temperature egale, une anemone pleinement epanouie respirait environ deux fois plus quune anemone pleinement fermee. La baisse mesuree est donc a la fois comportementale et physiologique, et les dissocier exige denregistrer letat dexpansion avec la consommation doxygene. C_LIO_LIUne anemone fermee ne pouvant ni se nourrir ni assurer ses echanges gazeux, la limite thermique ecologiquement pertinente est la temperature a laquelle lanimal ne peut plus maintenir son expansion normale, et non un maximum issu dun ajustement de courbe. Ce seuil comportemental place les populations de bordure chaude a quelques degres de la defaillance thermique fonctionnelle. C_LIO_LILes futures etudes de physiologie thermique sur des organismes capables de moduler leur consommation doxygene par leur comportement devraient integrer des covariables comportementales quantitatives pour separer les composantes physiologique et comportementale de la reponse metabolique. C_LI

ecology↗

bioRxiv2026

Optimizing calcein marking in the common periwinkle (Littorina littorea) for repeated-measures and mark-recapture studies

Calcein is a fluorescent marker commonly used to label growing calcified structures in marine organisms, but its efficacy is species- and context-specific. We evaluated calcein marking success and survival in the common periwinkle (Littorina littorea) during winter in the Gulf of Maine. Snails were immersed for 24 h in seawater containing 0, 50, or 100 mg L-1 calcein and scored for fluorescent marks 22 days later. Overall marking success was low (12.5% of exposed snails evaluated) but was strongly size-dependent: each 1 mm increase in shell length reduced the odds of acquiring a mark by 27%. Among exposed snails, higher calcein concentration (100 mg L-1) produced significantly brighter marks than the lower concentration (50 mg L-1). Survival was 100% across all treatments. The low overall marking rate likely reflects suppressed shell growth at winter temperatures. We recommend 100 mg L-1 calcein with a 24-h immersion for marking L. littorea and suggest that marking during warmer months would improve efficacy across a broader size range.

zoology↗

bioRxiv2025

Blue beats green: Agonistic interactions between Atlantic blue crabs and European green crabs in the Gulf of Maine

As ocean temperatures rise, range expansions and biological invasions are increasingly reshaping marine ecosystems. Warming waters are promoting the northward expansion of the Atlantic blue crab (Callinectes sapidus) into the Gulf of Maine (GoM) where its arrival has resulted in habitat overlap and novel interactions with the invasive European green crab (Carcinus maenas), a pervasive resident of coastal GoM for over a century. Through a series of laboratory trials, we assessed the interactions of paired blue and green crabs sourced from the GoM, specifically investigating the effects of crab size, aggression, and availability of alternative prey on these interactions. Blue crabs were found to be effective predators of green crabs, killing them in half of trials. Blue crabs were more likely to kill smaller green crabs (< 65 mm carapace width), and small to mid-size blue crabs (< 170 mm carapace width) were more likely than large blue crabs to consume green crabs. There was no green crab predation on blue crabs, though larger green crabs (> 65 mm carapace width) displayed more aggressive behavior towards blue crabs. Presence of an alternative prey item had no effect on blue crab predation on green crabs. Blue crab predation on green crabs could shift future ecosystem dynamics, altering community ecology in the GoM. This study highlights how climate-driven range expansions can mediate interactions among introduced species, with implications for ecosystem structure and species management.

ecology↗

bioRxiv2023

Investigating the impact of introduced crabs on the distribution and morphology of littorinid snails: Implications for the survival of the snail Littorina saxatilis

Introduced species can have profound impacts on communities by displacing and consuming native species. The intertidal communities in the Gulf of Maine have been radically altered through a suite of invasions including the herbivorous snail Littorina littorea and the omnivorous crab Carcinus maenas leading to morphological and spatial distribution changes in two native gastropod grazers (Littorina saxatilis and Littorina obtusata). Subsequently, another intertidal omnivorous crab Hemigrapsus sanguineus has become abundant in the intertidal, occurring in areas which were once refuges from crab predation. In order to quantify the potential impact of H. sanguineus on native snails, we conducted both in and ex situ experiments, testing the susceptibility of different sized snails to predation by introduced crabs. Additionally, we measured the distribution, abundance, and morphology of intertidal snails and crabs. Smaller snails of all species were the most susceptible to predation, although susceptibility differed among snail species. Littorina saxatilis was the most vulnerable to predation, with 73 and 64% of the population susceptible to large H. sanguineus and small C. maenas, respectively, while more than 89% of the L. littorea population was resistant to predation. Littorina saxatilis has been relegated to the high intertidal where there is high abiotic stress and poor-quality food, but until the invasion of H. sanguineus, there was little predation risk. Now, it seems that L. saxatilis is at the most risk of all three snail species, and may be at threat of local extirpation at locations with high populations of H. sanguineus.

ecology↗

bioRxiv2022

Grazers and predators mediate the post-settlement bottleneck in Caribbean octocoral forests

Caribbean octocorals have not suffered the decades long decline in abundance that has plagued reef-building scleractinian corals. Their success and the formation of octocoral forests has been attributed to their continuing recruitment to reef habitats. Assessing the processes controlling recruitment is essential to understanding the success of octocorals and predicting their future. Benthic grazers on coral reefs can facilitate the growth and recruitment of corals by reducing the abundance of competitive algal turfs and macroalgae or hinder corals through predation of coral tissue and recruits. We assessed the effects of grazing by fishes and the sea urchin Diadema antillarum and mesofaunal predation on octocoral recruitment in a series of manipulative experiments using varying grazer/predator exclusion and inclusion conditions in in situ and ex situ experiments. Exposure to fish and urchin grazing significantly reduced survival and recruitment of single-polyp octocorals, while turf-associated mesofauna did not significantly affect neither recruitment nor survival. We also found a positive relationship between octocoral recruitment and turf algae, a potential related response to the deleterious effect of grazing exposure. These data suggest that grazers and predators mediate the mortality bottleneck characteristic of recruitment. Thus, the declines in the abundance of grazing fishes and urchins throughout the Caribbean may have contributed to the increase in abundance of octocorals in the Caribbean, concurrent with the loss of scleractinians.

ecology↗

bioRxiv2022

Reconstitution of renal cyst formation in 3D culture reveals a role for AMOT and Yap1 in determining cyst size.

Despite substantial progress in identifying and understanding causative mutations in autosomal dominant polycystic kidney disease (ADPKD), little is known about subsequent cellular events leading to cyst formation. In prior studies we reported that Cadherin 8, a type II Cadherin, expression is sufficient to induce cyst emergence from HK-2 cells grown as tubule arrays in collagen matrix (1). However, emergent cysts did not exhibit the luminal enlargement observed in ADPKD. In this communication, we reconstitute cyst emergence with consequent cyst lumen expansion in 3D culture by stable co-expression of Cadherin 8 in combination with a constitutively active mutant of YAP1, the key effector of the HIPPO pathway. Specifically, immortalized cells derived from ADPKD cyst epithelia formed cysts with substantially larger lumen sizes when transduced with YAP1-5SA. Conversely, expression of the YAP1 inhibitor, AMOTL1, in these cells resulted in their forming cysts with smaller lumens than control cells. Our data show that cyst formation results from a sequential two-step process consisting of cyst initiation and subsequent cyst expansion. Taken together, cyst initiation induced by Cadherin 8 expression is proposed to result from decreased cell-cell adhesion while cyst expansion is driven by increased Yap1 activity.

cell biology↗

bioRxiv2020

DNA metabarcoding provides insights into the diverse diet of a dominant suspension feeder, the giant plumose anemone Metridium farcimen

Benthic suspension feeders have significant impacts on plankton communities by depleting plankton or modifying composition of the plankton through prey selectivity. Quantifying diets of planktivorous animals can be difficult because plankton are frequently microscopic, may lack diagnostic characters, and are digested at variable rates. With DNA metabarcoding, the identification of gut contents has become faster and more accurate, and the technique allows for higher taxonomic resolution-n while also identifying rare and highly degraded items that would otherwise not be detected. We used DNA metabarcoding to examine the diet of the giant plumose anemone Metridium farcimen, a large, abundant, competitively-dominant anemone on subtidal rock surfaces and floating docks in the northeast Pacific Ocean. Gut contents of 12 individuals were compared to 80- and 330-m filtered plankton samples collected one hour prior between 0.02 and 1.5 km from the anemones. The objectives of this study were to determine if M. farcimen has a selective diet and compare our findings with traditional gut content analyses. Metridium farcimen captured a wider range of prey than previously suspected and metabarcoding found many more taxa than traditional sampling techniques. Gut contents were less diverse than 80-m filtered plankton samples, but more diverse than 330-m filtered plankton samples. The diet of the anemones was 52% arthropods with a surprisingly high relative abundance of an ant (10%) that has mating flights in August when this study was conducted. The gut contents of M. farcimen likely include all prey that it can detect and that cannot escape. There were no overrepresented taxa in the gut contents compared to the plankton but there were underrepresented taxa. This study highlights the usefulness of the metabarcoding method in identifying prey within the gut of planktivorous animals and the significant terrestrial input into marine food webs.

ecology↗

bioRxiv2020

Polyp bailout and reattachment of the abundant Caribbean octocoral Eunicea flexuosa

Anthozoans exhibit great plasticity in their responses to stressful conditions, including decreasing individual size, detaching from the substratum and relocating, and releasing endosymbiotic microalgae. Another response to stress used by some colonial anthozoans is polyp bailout, in which the coenenchyme breaks down and individual polyps detach from the colony. We observed polyp bailout in the common Caribbean gorgonian Eunicea flexuosa after eight hours of aerial exposure. After nine days, 28% of bailed-out polyps reattached, although none opened to resume feeding. Polyp bailout is a costly and high-risk escape response, but reattachment indicates that this can be a genet-saving behavior in cases where whole-colony mortality is likely. While it has been described in several species of scleractinians and two octocorals, we still do not know how widespread this behavior is in anthozoans.

zoology↗

bioRxiv2020

Welcome to the jungle: Algal turf negatively affects recruitment of a Caribbean octocoral

O_LIAlgal cover has increased and scleractinian coral cover has steadily declined over the past 40 years on Caribbean coral reefs. In contrast, octocoral abundance has increased at those sites where octocoral abundances have been monitored. The effects of algal cover on recruitment may be a key component in these patterns, as upright octocoral recruits have the potential to escape competition with algae by growing above the ubiquitous algal turfs. However, the impacts of algal turf on octocorals have not been tested. C_LIO_LIWe used laboratory and field recruitment experiments to examine impacts of algal turf on settlement and then survival of newly-settled octocorals. Tiles were preconditioned on a Caribbean reef, allowing algae to settle and grow. Tiles were then partitioned into three treatments: lightly scrubbed (0% turf cover), left alone (19% turf cover), or kept for 15 days in a sea table without fish or large invertebrate herbivores (50% turf cover). Planulae of the common Caribbean octocoral Plexaura homomalla were allowed to settle and metamorphose on the tiles for six days. Tiles were then deployed onto a reef and survival of those recruits was monitored for seven weeks. Settlers that recruited to the tiles after deployment to the reef were also monitored. C_LIO_LILaboratory recruitment rate was significantly higher in lower turf cover treatments. Field survival was significantly reduced by increased turf cover; for every 1% increase in turf cover, polyps died 1.3% faster. In a model parameterized by the observed field survival, polyps exposed to 100% turf cover had a 2% survival rate over 51 days, while polyps exposed to no turf cover had a 32% survival rate over the same time. C_LIO_LISynthesis. We found that high densities of turf algae can significantly inhibit recruitment of octocorals. Octocoral survival rates were similar to those published for scleractinians, but field settlement rates were much higher, which likely contributes to the higher resilience of octocorals to disturbances. The factors that influence recruitment are critical in understanding the dynamics of octocorals on Caribbean reefs as continuing declines in scleractinian cover may lead to more octocoral-dominated communities in the Caribbean. C_LI

ecology↗

bioRxiv2020

Embryogenesis, polyembryony, and settlement in the gorgonian Plexaura homomalla

Understanding the ontogeny and reproductive biology of reef-building organisms can shed light on patterns of population biology and community structure. This knowledge is particularly important for Caribbean octocorals, which seem to be more resilient to long-term environmental change than scleractinian corals and provide some of the same ecological services. We monitored the development of the black sea rod Plexaura homomalla, a common, widely distributed octocoral on shallow Caribbean reefs, from eggs to 3-polyp colonies over the course of 73 days. In aquaria on St John, U.S. Virgin Islands, gametes were released in spawning events three to six days after the July full moon. Cleavage started 3 hours after fertilization and was holoblastic, equal, and radial. Embryos were positively buoyant until becoming planulae. Planulae were competent after 4 days. Symbiodiniaceae began infecting polyps at around 8 days post fertilization. Development was typical for Caribbean octocorals, except for the occurrence of a novel form of asexual reproduction in octocorals: polyembryony. Fragmentation of embryos during development may represent a temporally varied tradeoff between number and size of propagules, in which large eggs have higher fertilization rates followed by polyembryony, which maximizes the number of surviving recruits by generating more, albeit smaller, larvae. Polyembryony may contribute to the success of some gorgonians on Caribbean reefs as other anthozoans are in decline.

developmental biology↗

bioRxiv2019

Alternative transcription cycle for bacterial RNA polymerase

RNA polymerases (RNAPs) transcribe genes through a cycle of recruitment to promoter DNA, initiation, elongation, and termination. After termination, RNAP is thought to initiate the next round of transcription by detaching from DNA and rebinding a new promoter. We used single-molecule fluorescence microscopy to observe individual RNAP molecules after transcript release at a terminator. Following termination, RNAP almost always remained bound to DNA and sometimes exhibited one-dimensional sliding over thousands of basepairs. Unexpectedly, the DNA-bound RNAP often restarted transcription, usually in reverse direction, thus producing an antisense transcript. Furthermore, we report evidence of this \"secondary initiation\" in live cells, using genome-wide RNA sequencing. These findings reveal an alternative transcription cycle that allows RNAP to reinitiate without dissociating from DNA, which is likely to have important implications for gene regulation.

biophysics↗