publications

Temperature-dependent sex determination occurs when the temperature during development affects gonad determination. Historically, most work on TSD in fishes was conducted under constant temperatures, yet daily fluctuating temperatures can significantly alter fish physiology and life history. Thus, we subjected the Atlantic silverside, Menidia menidia (a TSD species), to 28, 28±2, and 28±4°C — a high, masculinizing temperature — and quantified sex ratios and length. We found that the percentage of females increased by 60-70% when the fish were exposed to daily fluctuating temperatures (from 10% to 16 and 17% under fluctuations).           wordle

Species distribution models predict a poleward migration for marine ectotherms with ocean warming. However, a key limitation in current species distribution models (SDM) is that they do not account for population-specific heterogeneity in physiological responses to temperature change resulting from local adaptations and acclimatization. To address this gap, we developed a novel, Physiology Integrated BioClimate Model (PIBCM) that combines habitat-specific metabolic thermal physiological tolerance of a species into a bioclimate envelope model. Using a downscaling approach, we also established a fine-resolution coastal sea-surface temperature data set for 2050–2080, that showed a high degree of location-specific variability in future thermal regimes. Combining predicted temperature data with the PIBCM model, we estimated habitat distribution for a highly eurythermal intertidal minnow, the Atlantic killifish (Fundulus heteroclitus), a species that likely presents a best-case-scenario for coastal vertebrates. We show that the killifish northern boundary shifts southwards, while distinct habitat fragmentation occurs in the southern sub-population (due to migration of adjacent fish populations to the nearest metabolically optimal thermal habitat). When compared to current SDMs (e.g., AquaMaps), our results emphasize the need for thermal physiology integrated range shift models and indicate that habitat fragmentation for coastal fishes may reshape nursery habitats for many commercially and ecologically important species.           wordle

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6,169 populations in 160 cities globally. Plants were assayed for a Mendelian anti-herbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2,074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale.           wordle

(1) Temperature influences the life of ectotherms in the oceans. (2) Phenotypic plasticity, the ability of a single genotype to produce different phenotypes when exposed to different environments, is ubiquitous in nature. (3) Water temperature varies spatially and temporally at various scales in the oceans, so understanding thermal plasticity is essential to understanding organisms. (4) The thermal performance curve has been used extensively to describe an organism's performance in relation to temperature. (5) Cellular processes that help determine critical thermal extremes and are involved in coping with thermal stress include (i) the rate of biochemical reactions, (ii) the integrity of macromolecular structures, and (iii) the solubility of small molecules. (6) The heart and mitochondria are two critical components of an adequate stress response. (7) There are practical issues that should not be ignored when thinking about (and using) thermal performance curves (e.g. they do change over the life of an organism, they are time-sensitive, they are only one aspect of an integrated phenotype). (8) Developmental plasticity, the capacity of an organism to shape its phenotype based (at least partly) on the early-life environment, is a special case of phenotypic plasticity that is worth exploring in detail. (9) Plasticity can occur across generations ("transgenerational plasticity"), and can be quite important in response to changes over a few generations. (10) Lastly, plasticity can play a role in adaptation to rare or novel environments, a timely consideration as climate change continues to expose populations to these uncommon conditions.           wordle

A formidable challenge for global change biologists is to predict how natural populations will respond to the emergence of conditions not observed at present, termed novel climates. Popular approaches to predict population vulnerability are based on the expected degree of novelty relative to the amplitude of historical climate fluctuations experienced by a population. Here, we argue that predictions focused on amplitude may be inaccurate because they ignore the predictability of environmental fluctuations in driving patterns of evolution and responses to climate change. To address this disconnect, we review major findings of evolutionary theory demonstrating the conditions under which phenotypic plasticity is likely to evolve in natural populations, and how plasticity decreases population vulnerability to novel environments. We outline key criteria that experimental studies should aim for to effectively test theoretical predictions, while controlling for the degree of climate novelty. We show that such targeted tests of evolutionary theory are rare, with marine systems being overall underrepresented in this venture despite exhibiting unique opportunities to test theory. We conclude that with more robust experimental designs that manipulate both the amplitude and predictability of fluctuations, while controlling for the degree of novelty, we may better predict population vulnerability to climate change.           wordle

Transgenerational plasticity (TGP) occurs when phenotypes are shaped by the environment in both the current and preceding generations. Transgenerational responses to rainfall, CO2, and temperature suggest that TGP may play an important role in how species cope with climate change. However, little is known about how TGP will evolve as climate change continues. Here we provide a quantitative test of the hypothesis that the predictability of the environment influences the magnitude of the transgenerational response. To do so, we take advantage of the latitudinal decrease in predictability of temperatures in nearshore waters along the US East Coast. Using sheepshead minnows (Cyprinodon variegatus) from South Carolina, Maryland, and Connecticut we found the first evidence for a latitudinal gradient in thermal TGP. Moreover, the degree of TGP in these populations depends linearly on the decorrelation time for temperature, providing support for the hypothesis that thermal predictability drives the evolution of these traits.           wordle

Many populations have evolved in response to laboratory environments (lack of predators, continual food availability, etc.). Another potential agent of selection in the lab is exposure to constant thermal environments. Here, we examined changes in growth, critical thermal maximum (CTmax), and food consumption under constant (25°C) and fluctuating (22-28°C and 19-31°C) conditions in two populations of fathead minnows, Pimephales promelas: one that has been kept in a laboratory setting for over 120 generations (~40 years) and a corresponding wild one. We found that under thermal fluctuations, domesticated fathead minnows grew faster than their wild counterparts, but also exhibited lower thermal tolerance. Food consumption was significantly higher in the lab population under the constant and large fluctuation thermal treatments. Our results suggest that the lab population has adjusted to the stable conditions in the laboratory and that we should carefully apply lessons learned in the lab to wild populations.           wordle

Transgenerational plasticity (TGP) is increasingly recognized as a mechanism by which organisms can respond to environments that change across generations. Although recent empirical and theoretical studies have explored conditions under which TGP is predicted to evolve, it is still unclear whether the effects of the parental environ- ment will remain beyond the offspring generation. Using a small cyprinodontid fish, we explored multigenerational thermal TGP to address two related questions. First (experiment 1), does the strength of TGP decline or accumulate across multiple gen- erations? Second (experiment 2), how does the experience of a temperature novel to both parents and offspring affect the strength of TGP? In the first experiment, we found a significant interaction between F1 and F2 temperatures and juvenile growth, but no effect of egg diameter. The strength of TGP between F0 and F1 generations was similar in both experiments but declined in subsequent generations. Further, experience of a novel temperature accelerated the decline. This pattern, although similar to that found in other species, is certainly not universally observed, suggesting that theoretical and empirical effort is needed to understand the multigenerational dynamics of TGP.           wordle

Climate change is increasingly exposing populations to rare and novel environmental conditions. Theory suggests that extreme conditions will expose cryptic phenotypes, with a concomitant increase in trait variation. Although some empirical support for this exists, it is also well established that physiological mechanisms (e.g., heat shock protein expression) change when organisms are exposed to constant vs. fluctuating temperatures. To determine the effect of common, rare, and novel temperatures on the release of hidden variation, we exposed fathead minnows, Pimephales promelas, to five fluctuating and four constant temperature regimes (constant treatments: 23.5, 25, 28.5, and 31°C; all fluctuating treatments shared a minimum temperature of 22°C at 00:00 and a maximum of 25, 28, 31, 34, or 37°C at 12:00). We measured each individual’s length weekly over 60 days, critical thermal maximum (CTmax), 5 morphometric traits (eye anterior-posterior distance, pelvic fin length, pectoral fin length, pelvic fin ray count, and pectoral fin ray count), and fluctuating asymmetry (FA, absolute difference between left and right morphometric measurements; FA is typically associated with stress). Length-at-age in both constant and fluctuating conditions decreased with temperature, and this trait’s variance decreased with temperature under fluctuating conditions but increased and then decreased in constant temperatures. CTmax in both treatments increased with increasing water temperature, while its variance decreased in warmer waters. No consistent pattern in mean or variance was found across morphometric traits or fluctuating asymmetry. Our results suggest that, for fathead minnows, variance can decrease in important traits (e.g., length-at-age, CTmax) as the environment becomes more stressful, so it may be difficult to establish comprehensive rules for the effects of rarer or stressful environments on trait variation.           wordle

Phenotypic plasticity, both within and across generations, is an important mechanism that organisms use to cope with rapid climate change. While an increasing number of studies show that plasticity across generations (transgenerational plasticity or TGP) may occur, we have limited understanding of key aspects of TGP, such as the environmental conditions that may promote it, its relationship to within- generation plasticity (WGP) and its role in evolutionary potential. In this review, we consider how the detection of TGP in climate change experiments is affected by the predictability of environmental variation, as well as the timing and magnitude of environmental change cues applied. We also discuss the need to design experiments that are able to distinguish TGP from selection and TGP from WGP in multigenerational experiments. We conclude by suggesting future research directions that build on the knowledge to date and admit the limitations that exist, which will depend on the way environmental change is simulated and the type of experimental design used. Such an approach will open up this burgeoning area of research to a wider variety of organisms and allow better predictive capacity of the role of TGP in the response of organisms to future climate change.           wordle

How do scientists decide where to submit manuscripts? Many factors influence this decision, including prestige, acceptance probability, turnaround time, target audience, fit, and impact factor. Here, we present a framework for evaluating where to submit a manuscript based on the theory of Markov decision processes. We derive two models, one in which an author is trying to optimally maximize citations and another in which that goal is balanced by either minimizing the number of resubmissions or the total time in review. We parameterize the models with data on acceptance probability, submission-to-decision times, and impact factors for 61 ecology journals. We find that submission sequences beginning with Ecology Letters, Ecological Monographs, or PLoS ONE could be optimal depending on the importance given to time to acceptance or number of resubmissions. This analysis provides some guidance on where to submit a manuscript given the individual-specific values assigned to these disparate objectives.           wordle

Question: Most of our theoretical and empirical knowledge of phenotypic plasticity is limited to changes in single traits under variation of a single environmental variable. Are insights drawn from this “univariate” world-view different than if we were to study individuals as the integration of many traits in response to many environmental variables? Organisms: Sheepshead minnows, Cyprinodon variegatus, from Gulf Islands National Seashore, Florida.
Methods: We reared individuals at different temperature-food availability combinations (3x3 factorial design) over ~6 months. We measured growth, age and size at maturation, gonadosomatic index, hepatosomatic index, and body shape. We also estimated levels of phenotypic integration and relative fitness for males and females at each of the nine treatments.
Results/conclusions: Most traits responded to temperature and food directly and some exhibited interactions in their response. Phenotypic integration and fitness changed substantially under different environments, and differently for males compared to females. Studying responses from this integrated perspective led to insights that could not have been obtained studying single traits or single environmental variables.           wordle

In some species, parents are always right. In the past few years, we have learned that parents can predict the environment the offspring will experience and get them ready for it—a biological head-start of sorts. As the climate changes rapidly, some ecologists have suggested that these effects may help species along. Not so fast, write Welch and colleagues in this issue of Nature Climate Change, showing that a tropical damselfish cannot help their offspring’s predation-avoidance behavior when exposed to high CO₂ levels. For them, it will have to be adaptation or bust.        

Climate change continues to impact species worldwide. Understanding and predicting how populations will respond is of clear importance. Here, we review a mechanism by which populations may respond rapidly to these changes: Trans-Generational Plasticity (TGP). TGP exists when the environment experienced by the parents affects the shape of the reaction norm in their offspring; that is, the parental and offspring environments interact to determine the offspring phenotype. We survey 80 empirical studies from 63 species (32 orders, 9 phyla) that demonstrate TGP. Overall, TGP is taxonomically widespread and present in response to environmental drivers likely to be impacted by climate change. Although many examples now exist, we also identify areas of research that could greatly improve our understanding of TGP. We conclude that TGP is sufficiently established both theoretically and empirically to merit study as a potential coping tactic against rapid environmental changes.           wordle

The application of evolutionary principles to the management of fisheries has gained considerable attention recently. Harvesting of fish may apply directional or disruptive selection to key life-history traits, and evidence for fishery-induced evolution is growing. The traits that are directly selected upon are often correlated (genetically or phenotypically) with a suite of interrelated physiological, behavioral, and morphological characters. A question that has received comparatively little attention is whether or not, after cessation of fishery-induced selection, these correlated traits revert back to previous states. Here, we empirically examine this question. In experiments with the Atlantic silverside, Menidia menidia, we applied size-selective culling for five generations and then maintained the lines a further five generations under random harvesting. We found that some traits do return to pre-harvesting levels (e.g., larval viability), some partially recover (e.g., egg volume, size-at-hatch), and others show no sign of change (e.g., food consumption rate, vertebral number). Such correlations among characters could, in theory, greatly accelerate or decelerate the recovery of fish populations. These results may explain why some fish stocks fail to recover after fishing pressure is relaxed.           wordle

Transgenerational plasticity (TGP), a generalisation of more widely studied maternal effects, occurs whenever environmental cues experienced by either parent prior to fertilisation results in a modification of offspring reaction norms. Such effects have been observed in many traits across many species. Despite enormous potential importance—particularly in an era of rapid climate change—TGP in thermal growth physiology has never been demonstrated for vertebrates. We provide the first evidence for thermal TGP in a vertebrate: given sufficient time, sheepshead minnows adaptively program their offspring for maximal growth at the present temperature. The change in growth over a single generation (c. 30%) exceeds the single-generation rate of adaptive evolution by an order of magnitude. If widespread, transgenerational effects on thermal performance may have important implications on physiology, ecology and contemporary evolution, and may significantly alter the extinction risk posed by changing climate.           wordle

The mummichog, Fundulus heteroclitus, is a widely distributed fish that has been extensively researched in the southern portion of its range (south of Cape Cod, MA). During the summers of 2003 and 2004, we studied the reproductive ecology of F. heteroclitus in a northern population (Northeast Creek, Mount Desert Island, Maine). Our direct observations show that unlike more southern populations, northern F. heteroclitus spawns daily during its two-month spawning season, with no preference for spring tides over the entire season. However, within consecutive semidiurnal tides significantly more spawning was associated with the higher high tide. Spawning occurred on bare gravel and on mud associated with the grass Spartina patens. Spawning was highly promiscuous with males typically spawning in groups with females in very shallow water during receding tides. These temporal and spatial patterns of oviposition caused eggs to be deposited in a much broader range of habitats than in southern populations of this species. We present and evaluate critically several hypotheses that may explain the variation in spawning patterns observed in this species.           wordle

Many ectotherms exhibit striking latitudinal gradients in lifespan. However, it is unclear whether lifespan gradients in distantly related taxa share a common mechanistic explanation. We compiled data on geographic variation in lifespan in ectotherms from around the globe to determine how much of this intraspecific variation in lifespan may be explained by temperature using the simple predictions of the metabolic theory of ecology. We found that the metabolic theory accurately predicts how lifespan varies with temperature within species in a wide range of ectotherms in both controlled laboratory experiments and free-living populations. After removing the effect of temperature, only a small fraction of species showed significant trends with latitude. There was, however, considerable residual intraspecific variation indicating that other, more local factors are likely to be important in determining lifespan within species. These findings suggest that, given predicted increases in global temperature, lifespan of ectotherms may be substantially shortened in the future.           wordle

The killifish, Fundulus heteroclitus, has been studied intensively, yet little is known about its reproductive behavior in the field. The majority of what is known about its reproductive biology has been done using individuals from populations south of Cape Cod, often with the southern subspecies, and most of the work has been done in the laboratory. During 2003, we studied the reproductive biology of the northern subspecies of F. heteroclitus in a salt marsh habitat (Northeast Creek) and of a congener, F. diaphanus, in a nearby freshwater lake (Lakewood). Specifically, we examined the mating systems of these species, factors affecting time and intensity of spawning, and salinity effects on sperm motility and fertilization ability.           wordle