Modeling Fertilization Outcome in a Changing World.

Marine organisms have complex life histories. For broadcast spawners, successful continuation of the population requires their small gametes to make contact in the water column for sufficiently long periods for fertilization to occur. Anthropogenic climate change has been shown to impact fertilization success in various marine invertebrates, including sea urchins which are key grazers in their habitats. Gamete performance of both sexes declined when exposed to elevated temperature and/or pCO2 levels. Examples of reduced performance included slower sperm swimming speed and thinning egg jelly coat. However, such responses to climate change stress were not uniform between individuals. Such variations could serve as the basis for selection. Fertilization kinetics has long been modeled as a particle collision process. Here, we present a modified fertilization kinetics model that incorporates individual variations in performance in a more environmentally-relevant regime, and which the performance of groups with different traits can be separately tracked in a mixture. Numerical simulations highlight that fertilization outcome is influenced by changes in gametes traits as they age in sea water and the presence of competition groups (multiple dams or sires). These results highlight the importance of considering multiple individuals and at multiple time points during in-vivo assays. We also applied our model to show that interspecific variation in climate stress vulnerabilities elevates the risk of hybridization. By making a numerical model open-source, we aim to help us better understand the fate of organisms in the face of climate change by enabling the community to consider the mean and variance of the response to capture adaptive potential.

Parentage influence on gene expression under acidification revealed through single-embryo sequencing.

The dissolution of anthropogenic carbon dioxide (CO2 ) in seawater has altered its carbonate chemistry in the process of ocean acidification (OA). OA affects the viability of marine species. In particular, calcifying organisms and their early planktonic larval stages are considered vulnerable. These organisms often utilize energy reserves for metabolism rather than growth and calcification as supported by bulk RNA-sequencing (RNA-seq) experiments. Yet, transcriptomic profiling of a bulk sample reflects the average gene expression of the population, neglecting the variations between individuals, which forms the basis for natural selection. Here, we used single-embryo RNA-seq on larval sea urchin Heliocidaris crassispina, which is a commercially and ecologically valuable species in East Asia, to document gene expression changes to OA at an individual and family level. Three paternal half-sibs groups were fertilized and exposed to 3 pH conditions (ambient pH 8.0, 7.7 and 7.4) for 12 h prior to sequencing and oxygen consumption assay. The resulting transcriptomic profile of all embryos can be distinguished into four clusters, with differences in gene expressions that govern biomineralization, cell differentiation and patterning, as well as metabolism. While these responses were influenced by pH conditions, the male identities also had an effect. Specifically, a regression model and goodness of fit tests indicated a significant interaction between sire and pH on the probability of embryo membership in different clusters of gene expression. The single-embryo RNA-seq approach is promising in climate stressor research because not only does it highlight potential impacts before phenotypic changes were observed, but it also highlights variations between individuals and lineages, thus enabling a better determination of evolutionary potential.

The Whole Is Greater Than The Sum of Its Parts: Large-scale Phenomena Arising from Small-Scale Biophysical Processes.

The symposium "Large-scale biological phenomena arising from small-scale biophysical processes" at the SICB 2023 Annual General Meeting focused on the cross-disciplinary exploration of emergent phenomena in biology. Interactions between cells or organisms at small scales within a system can govern patterns occurring at larger scales in space, time, or biological complexity. This theme recurs in many sub-disciplines of biology, including cell and developmental biology, evolution, and ecology. This symposium, and the associated special issue introduced here, showcases a wide range of cross-disciplinary collaborations among biologists, physicists, and engineers. Technological advancements in microscopy and microfluidics, as well as complementary advances in mathematical modelling and associated theory demonstrate the timeliness of this issue. This introduction seeks to provide useful background information to place the studies within this issue in a broader biophysical context and highlight similarities in ideas and approaches across systems and sub-disciplines. We hope to demonstrate that cross-disciplinary research linking small-scale biophysics to larger-scale emergent phenomena can help us understand problems ranging from single-cell behaviors to tissue formation and function, evolution of form, and the dynamics of communities.

Effect of pH on the Early Development of the Biofouling Ascidian Ciona robusta.

Ocean acidification (OA) impacts the survival, fertilization, and community structure of marine organisms across the world. However, some populations or species are considered more resilient than others, such as those that are invasive, globally distributed, or biofouling. Here, we tested this assumption by investigating the effect of pH on the larval development of one such tunicate, Ciona robusta, which is currently exposed to a wide range of pH levels. Consistent with our hypothesis, C. robusta larvae developed and metamorphosed at a rate comparable to control (pH 8.0) at modest near-future conditions (pH 7.7) over a 58-hour period. However, development was stunted at the extreme low pH of 6.8 such that no embryo progressed beyond late cleavage after 58 hours. Interestingly, piecewise regression of the proportion of embryos at the most advanced stage at a given time point against pH identified a breakpoint with the highest pH (~pH 7.6) at around hatching. The variation in breakpoint pH throughout ontogeny highlighted that the sensitivity to decreasing pH differs significantly between developmental stages. More broadly, our results show that even a cosmopolitan, biofouling, invasive species could be negatively impacted by decreasing pH.

Common Interests Without Common Expertise: Reflections on Early-career Experiences in Cross-Disciplinary Research.

Cross-disciplinary research enables us to tackle complex problems that require expertise from different fields. Such collaborations involve researchers who have different perspectives, communication styles, and knowledge bases, and can produce results far greater than the sum of their parts. However, in an era of increasing scientific specialization, there exist many barriers for students and early-career researchers (ECRs) interested in training and undertaking interdisciplinary research endeavors. This perspective examines the challenges that students and ECRs perceive and experience in cross-disciplinary work and proposes pathways to create more inclusive and welcoming research environments. This work emerges from a National Science Foundation (NSF)-funded workshop held during the Society for Integrative and Comparative Biology (SICB) Annual Meeting in January 2023 in Austin, TX. The workshop brought together seasoned interdisciplinary scientists with undergraduate and graduate students to identify and discuss perceived challenges through small group discussions and experience sharing. Through summarizing a range of student concerns about embarking on careers as interdisciplinary scientists and identifying ways to dismantle institutional and lab management-level barriers, we aim to promote an inclusive and collaborative problem-solving environment for scientists of all experience levels.

Thermal Limits Determination for Zooplankton Using a Heat Block.

Thermal limits and breadth have been widely used to predict species distribution. As the global temperature continues to rise, understanding how thermal limit changes with acclimation and how it varies between life stages and populations are vital for determining the vulnerability of species to future warming. Most marine organisms have complex life cycles that include early planktonic stages. While quantifying the thermal limit of these small early developmental stages (tens to hundreds of microns) helps identify developmental bottlenecks, this process can be challenging due to the small size of target organisms, large bench space requirement, and high initial fabrication cost. Here, a setup that is geared toward small volumes (mL to tens of mL) is presented. This setup combines commercially available components to generate a stable and linear thermal gradient. Production specifications of the setup, as well as procedures to introduce and enumerate live versus dead individuals and compute lethal temperature, are also presented.

Microplastics impede larval urchin selective feeding.

Microplastics are emergent threats to marine organisms as ingestion can cause a multitude of physiological problems. Suspension feeders, including marine invertebrate larvae, are particularly susceptible to ingesting microplastics due to similarities in physical appearance to algal cells. Larval feeding involves multiple stages: the capture and subsequent selection of particles followed by ingestion from the mouth to the stomach, digestion, and finally, egestion. Yet, little is known about which aspect of the feeding process is disrupted by microplastics. Here, we determine if prior exposure to microplastics alters the feeding behavior of the larval sea urchin Heliocidaris crassispina. We conducted two experiments: a food handling experiment studied larval survival, growth, and time required to fill and vacate the stomach; and a particle selection experiment analyzed changes in the ability of the larvae to selectively ingest algal cells over microplastics. In both experiments, larvae were pre-exposed to algae only (control), the addition of 10 µm polystyrene beads at 1 bead mL-1 or 1000 beads mL-1 until 3- or 7-days post-fertilization. Previous exposure to microplastics lengthened stomach filling time and impaired particle selection. While there was no significant change in survivorship and larval arm length, these sub-lethal impacts on larval feeding likely have more severe ramifications in vivo where food is limited, and thus, potentially threaten post-settlement success.

Near future ocean acidification modulates the physiological impact of fluoxetine at environmental concentration on larval urchins.

Pharmaceuticals found in human wastes are emergent pollutants that are continuously released into aquatic systems. While exposure to pharmaceuticals alone could adversely impact aquatic organisms, few studies have considered the interactive effects of pharmaceuticals and the future environmental conditions, such as decreasing pH due to ocean acidification. Given the bioavailability of many pharmaceuticals is dependent on these physical conditions, we investigated the effect of environmentally-relevant concentrations of fluoxetine (10 and 100 ng L-1) under ambient (pH 8.0) and reduced pH conditions (pH 7.7) on physiology, behavior, and DNA integrity of larval sea urchins (Heliocidaris crassispina). Notably, the negative impacts of fluoxetine exposure were attenuated by reduced pH. Larvae exposed to both reduced pH and fluoxetine exhibited lower levels of DNA damage compared to those exposed to only one of the stressors. Similar antagonistic interactions were observed at the organismal level: for example, fluoxetine exposure at 10 ng L-1 under ambient pH increased the percentage of embryos at later developmental stages, but such effects of fluoxetine were absent at pH 7.7. However, despite the modulation of fluoxetine impacts under ocean acidification, control larvae performed better than those exposed to either stressor, alone or in combination. We also observed that pH alone impacted organismal behaviors, as larvae swam slower at reduced pH regardless of fluoxetine exposure. Our findings highlight the need to consider multi-stressor interactions when determining future organismal performance and that multiple metrics are needed to paint a fuller picture of ecological risks.

Parental whole life cycle exposure modulates progeny responses to ocean acidification in slipper limpets.

Multigenerational exposure is needed to assess the evolutionary potential of organisms in the rapidly changing seascape. Here, we investigate if there is a transgenerational effect of ocean acidification exposure on a calyptraeid gastropod such that long-term exposure elevates offspring resilience. Larvae from wild type Crepidula onyx adults were reared from hatching until sexual maturity for over 36 months under three pH conditions (pH 7.3, 7.7, and 8.0). While the survivorship, growth, and respiration rate of F1 larvae were unaffected by acute ocean acidification (OA), long-term and whole life cycle exposure significantly compromised adult survivorship, growth, and reproductive output of the slipper limpets. When kept under low pH throughout their life cycle, only 6% of the F1 slipper limpets survived pH 7.3 conditions after ~2.5 years and the number of larvae they released was ~10% of those released by the control. However, the F2 progeny from adults kept under the long-term low pH condition hatched at a comparable size to those in medium and control pH conditions. More importantly, these F2 progeny from low pH adults outperformed F2 slipper limpets from control conditions; they had higher larval survivorship and growth, and reduced respiration rate across pH conditions, even at the extreme low pH of 7.0. The intragenerational negative consequences of OA during long-term acclimation highlights potential carryover effects and ontogenetic shifts in stress vulnerability, especially prior to and during reproduction. Yet, the presence of a transgenerational effect implies that this slipper limpet, which has been widely introduced along the West Pacific coasts, has the potential to adapt to rapid acidification.

A Tail's Tale: Biomechanical Roles of Dorsal Thoracic Spine of Barnacle Nauplii.

Many marine invertebrates have complex life histories that begin with a planktonic larval stage. Similar to other plankton, these larval invertebrates often possess protruding body extensions, but their function beyond predator deterrence is not well-documented. For example, the planktonic nauplii of crustaceans have spines. Using the epibiotic pedunculate barnacle Octolasmis spp., we investigated how the dorsal thoracic spine affects swimming and fluid disturbance by comparing nauplii with their spines partially removed against those with intact spines. Our motion analysis showed that amputated Octolasmis spp. swam slower, in jerkier trajectories, and were less efficient per stroke cycle than those with intact spines. Amputees showed alterations in limb beat pattern: larger beat amplitude, increased phase lag, and reduced contralateral symmetry. These changes might partially help increase propulsive force generation and streamline the flow, but were insufficient to restore full function. Particle image velocimetry further showed that amputees had a larger relative area of influence, implying elevated risk by rheotactic predator. Body extensions and their interactions with limb motion play important biomechanical roles in shaping larval performance, which likely influences the evolution of form.

Temporal variability modulates pH impact on larval sea urchin development: Themed Issue Article: Biomechanics and Climate Change.

Coastal organisms reside in highly dynamic habitats. Global climate change is expected to alter not only the mean of the physical conditions experienced but also the frequencies and/or the magnitude of fluctuations of environmental factors. Understanding responses in an ecologically relevant context is essential for formulating management strategies. In particular, there are increasing suggestions that exposure to fluctuations could alleviate the impact of climate change-related stressors by selecting for plasticity that may help acclimatization to future conditions. However, it remains unclear whether the presence of fluctuations alone is sufficient to confer such effects or whether the pattern of the fluctuations matters. Therefore, we investigated the role of frequency and initial conditions of the fluctuations on performance by exposing larval sea urchin Heliocidaris crassispina to either constant or fluctuating pH. Reduced pH alone (pH 7.3 vs 8.0) did not affect larval mortality but reduced the growth of larval arms in the static pH treatments. Changes in morphology could affect the swimming mechanics for these small organisms, and geometric morphometric analysis further suggested an overall shape change such that acidified larvae had more U-shaped bodies and shorter arms, which would help maintain stability in moving water. The relative negative impact of lower pH, computed as log response ratio, on larval arm development was smaller when larvae were exposed to pH fluctuations, especially when the change was less frequent (48- vs 24-h cycle). Furthermore, larvae experiencing an initial pH drop, i.e. those where the cycle started at pH 8.0, were more negatively impacted compared with those kept at an initial pH of 7.3 before the cycling started. Our observations suggest that larval responses to climate change stress could not be easily predicted from mean conditions. Instead, to better predict organismal performance in the future ocean, monitoring and investigation of the role of real-time environmental fluctuations along the dispersive pathway is key.

Development of the sea urchin Heliocidaris crassispina from Hong Kong is robust to ocean acidification and copper contamination.

Metallic pollution is of particular concern in coastal cities. In the Asian megacity of Hong Kong, despite water qualities have improved over the past decade, some local zones are still particularly affected and could represent sinks for remobilization of labile toxic species such as copper. Ocean acidification is expected to increase the fraction of the most toxic form of copper (Cu2+) by 2.3-folds by 2100 (pH ≈7.7), increasing its bioavailability to marine organisms. Additionally, multiple stressors are likely to exert concomitant effects (additive, synergic or antagonist) on the organisms living in the sea. Here, we tested the hypothesis that copper-contaminated waters are more toxic to sea urchin larvae under future pH conditions. We exposed sea urchin embryos and larvae to two low-pH and two copper treatments (0.1 and 1.0 µM) in three separate experiments. Over the short time typically used for toxicity tests (up to 4-arm plutei, i.e. 3 days), larvae of the sea urchin Heliocidaris crassispina were robust and survived the copper levels present in Hong Kong waters today (≤0.19 µM) as well as the average pH projected for 2100. We, however, observed significant mortality with lowering pH in the longer, single-stressor experiment (Expt A: 8-arm plutei, i.e. 9 days). Abnormality and arm asymmetry were significantly increased by pH or/and by copper presence (depending on the experiment and copper level). Body size (d3; but not body growth rates in Expt A) was significantly reduced by both lowered pH and added copper. Larval respiration (Expt A) was doubled by a decrease at pHT from 8.0 to 7.3 on d6. In Expt B1.0 and B0.1, larval morphology (relative arm lengths and stomach volume) were affected by at least one of the two investigated factors. Although the larvae appeared robust, these sub-lethal effects may have indirect consequences on feeding, swimming and ultimately survival. The complex relationship between pH and metal speciation/uptake is not well-characterized and further investigations are urgently needed to detangle the mechanisms involved and to identify possible caveats in routinely used toxicity tests.

Microplastics reduced posterior segment regeneration rate of the polychaete Perinereis aibuhitensis.

Microplastics are found in abundance in and on coastal sediments, and yet, whether exposure to this emerging pollutant negatively impact whole organism function is unknown. Focusing on a commercially important polychaete, Perinereis aibuhitensis, we demonstrated that presence of microplastics increased mortality and reduced the rate of posterior segment regeneration. The impact of the micro-polystyrene beads was size-dependent with smaller beads (8-12µm in diameter) being more detrimental than those bigger in size (32-38µm). This observed difference suggests microplastic impact could be affected by physical properties, e.g., sinking speed, surface area available for sorption of chemicals and bacteria, and selective feeding behaviors of the target organism.

Negative effects of microplastic exposure on growth and development of Crepidula onyx.

Microplastics exposure could be detrimental to marine organisms especially under high concentrations. However, few studies have considered the multiphasic nature of marine invertebrates' life history and investigated the impact of experiencing microplastics during early development on post-metamorphic stages (legacy effect). Many planktonic larvae can feed selectively and it is unclear whether such selectivity could modulate the impact of algal food-sized microplastic. In this two-stage experiment, veligers of Crepidula onyx were first exposed to additions of algae-sized micro-polystyrene (micro-PS) beads at different concentrations, including ones that were comparable their algal diet. These additions were then either halted or continued after settlement. At environmentally relevant concentration (ten 2-µm microplastic beads ml-1), larval and juvenile C. onyx was not affected. At higher concentrations, these micro-PS fed larvae consumed a similar amount of algae compared to those in control but grew relatively slower than those in the control suggesting that ingestion and/or removal of microplastic was/were energetically costly. These larvae also settled earlier at a smaller size compared to the control, which could negatively affect post-settlement success. Juvenile C. onyx receiving continuous micro-PS addition had slower growth rates. Individuals only exposed to micro-PS during their larval stage continued to have slower growth rates than those in the control even if micro-PS had been absent in their surroundings for 65 days highlighting a legacy effect of microplastic exposure.

Resilience of the larval slipper limpet Crepidula onyx to direct and indirect-diet effects of ocean acidification.

Ocean acidification (OA) is known to directly impact larval physiology and development of many marine organisms. OA also affects the nutritional quality and palatability of algae, which are principal food sources for many types of planktonic larvae. This potential indirect effect of OA via trophic interactions, however, has not been fully explored. In this study, veligers of Crepidula onyx were exposed to different pH levels representing the ambient (as control) and low pH values (pH 7.7 and pH 7.3) for 14 days, and were fed with Isochrysis galbana cultured at these three respective pHs. pH, diet, nor their interactions had no effect on larval mortality. Decrease in pH alone had a significant effect on growth rate and shell size. Structural changes (increased porosity) in larval shells were also observed in the low pH treatments. Interactions between acidification and reduced diet quality promoted earlier settlement. Unlike other calcifying molluscs, this population of slipper limpets introduced to Hong Kong in 1960s appeared to be resilient to OA and decreased algal nutritional value. If this robustness observed in the laboratory applies to the field, competition with native invertebrates may intensify and this non-native snail could flourish in acidified coastal ecosystems.

Ocean acidification increases larval swimming speed and has limited effects on spawning and settlement of a robust fouling bryozoan, Bugula neritina.

Few studies to date have investigated the effects of ocean acidification on non-reef forming marine invertebrates with non-feeding larvae. Here, we exposed adults of the bryozoan Bugula neritina and their larvae to lowered pH. We monitored spawning, larval swimming, settlement, and post-settlement individual sizes at two pHs (7.9 vs. 7.6) and settlement dynamics alone over a broader pH range (8.0 down to 6.5). Our results show that spawning was not affected by adult exposure (48h at pH7.6), larvae swam 32% faster and the newly-settled individuals grew significantly larger (5%) at pH7.6 than in the control. Although larvae required more time to settle when pH was lowered, reduced pH was not lethal, even down to pH6.5. Overall, this fouling species appeared to be robust to acidification, and yet, indirect effects such as prolonging the pelagic larval duration could increase predation risk, and might negatively impact population dynamics.

A Cryptic Marine Ciliate Feeds on Progametes of Noctiluca scintillans.

The dinoflagellate Noctiluca scintillans (Noctiluca) has the ability to reproduce sexually, which may help to increase or restore its population size during periods of blooms or environmental stress. Here, we documented for the first time a marine ciliate Strombidium sp. that feeds on Noctiluca's progametes undergoing stages 5 to 9 of nuclear division. This ciliate frequently swam on or around gametogenic and some vegetative Noctiluca cells. The ciliates associated with gametogenic cells had significantly lower swimming speed and changed direction more frequently than those associated with vegetative cells, which overall increased their time spent around the food patches (progametes). This trophic interaction constitutes an upside-down predator-prey link, in which ciliates within the typical size range of Noctiluca prey, become the predators. Based on the phylogenetic tree (maximum-likelihood), there are 14 environmental clones similar to Strombidium sp. found in other coastal waters, where Noctiluca presence or blooms have been reported. This novel predator-prey relationship could therefore be common in other Noctiluca habitats. Additional studies are needed to assess the magnitude of its impacts on Noctiluca population dynamics and plankton bloom succession.

The sea urchin Lytechinus variegatus lives close to the upper thermal limit for early development in a tropical lagoon.

Thermal tolerance shapes organisms' physiological performance and limits their biogeographic ranges. Tropical terrestrial organisms are thought to live very near their upper thermal tolerance limits, and such small thermal safety factors put them at risk from global warming. However, little is known about the thermal tolerances of tropical marine invertebrates, how they vary across different life stages, and how these limits relate to environmental conditions. We tested the tolerance to acute heat stress of five life stages of the tropical sea urchin Lytechinus variegatus collected in the Bahía Almirante, Bocas del Toro, Panama. We also investigated the impact of chronic heat stress on larval development. Fertilization, cleavage, morula development, and 4-armed larvae tolerated 2-h exposures to elevated temperatures between 28-32°C. Average critical temperatures (LT 50) were lower for initiation of cleavage (33.5°C) and development to morula (32.5°C) than they were for fertilization (34.4°C) or for 4-armed larvae (34.1°C). LT 50 was even higher (34.8°C) for adults exposed to similar acute thermal stress, suggesting that thermal limits measured for adults may not be directly applied to the whole life history. During chronic exposure, larvae had significantly lower survival and reduced growth when reared at temperatures above 30.5°C and did not survive chronic exposures at or above 32.3°C. Environmental monitoring at and near our collection site shows that L. variegatus may already experience temperatures at which larval growth and survival are reduced during the warmest months of the year. A published local climate model further suggests that such damaging warm temperatures will be reached throughout the Bahía Almirante by 2084. Our results highlight that tropical marine invertebrates likely have small thermal safety factors during some stages in their life cycles, and that shallow-water populations are at particular risk of near future warming.

Ontogenetic changes in larval swimming and orientation of pre-competent sea urchin Arbacia punctulata in turbulence.

Many marine organisms have complex life histories, having sessile adults and relying on the planktonic larvae for dispersal. Larvae swim and disperse in a complex fluid environment and the effect of ambient flow on larval behavior could in turn impact their survival and transport. However, to date, most studies on larvae-flow interactions have focused on competent larvae near settlement. We examined the importance of flow on early larval stages by studying how local flow and ontogeny influence swimming behavior in pre-competent larval sea urchins, Arbacia punctulata We exposed larval urchins to grid-stirred turbulence and recorded their behavior at two stages (4- and 6-armed plutei) in three turbulence regimes. Using particle image velocimetry to quantify and subtract local flow, we tested the hypothesis that larvae respond to turbulence by increasing swimming speed, and that the increase varies with ontogeny. Swimming speed increased with turbulence for both 4- and 6-armed larvae, but their responses differed in terms of vertical swimming velocity. 4-Armed larvae swam most strongly upward in the unforced flow regime, while 6-armed larvae swam most strongly upward in weakly forced flow. Increased turbulence intensity also decreased the relative time that larvae spent in their typical upright orientation. 6-Armed larvae were tilted more frequently in turbulence compared with 4-armed larvae. This observation suggests that as larvae increase in size and add pairs of arms, they are more likely to be passively re-oriented by moving water, rather than being stabilized (by mechanisms associated with increased mass), potentially leading to differential transport. The positive relationship between swimming speed and larval orientation angle suggests that there was also an active response to tilting in turbulence. Our results highlight the importance of turbulence to planktonic larvae, not just during settlement but also in earlier stages through morphology-flow interactions.

Acidification reduced growth rate but not swimming speed of larval sea urchins.

Swimming behaviors of planktonic larvae impact dispersal and population dynamics of many benthic marine invertebrates. This key ecological function is modulated by larval development dynamics, biomechanics of the resulting morphology, and behavioral choices. Studies on ocean acidification effects on larval stages have yet to address this important interaction between development and swimming under environmentally-relevant flow conditions. Our video motion analysis revealed that pH covering present and future natural variability (pH 8.0, 7.6 and 7.2) did not affect age-specific swimming of larval green urchin Strongylocentrotus droebachiensis in still water nor in shear, despite acidified individuals being significantly smaller in size (reduced growth rate). This maintenance of speed and stability in shear was accompanied by an overall change in size-corrected shape, implying changes in swimming biomechanics. Our observations highlight strong evolutionary pressure to maintain swimming in a varying environment and the plasticity in larval responses to environmental change.