Climate change alters the reproductive phenology and investment of a lacustrine fish, the three-spine stickleback

Reproductive phenology and behaviour of endangered redside dace (Clinostomus elongatus) in urban streams

Investigation of the reproductive phenology and spawning behaviour of imperilled species in relation to environmental variability is needed to understand a critical component of species life history. In this study, we used redside dace (Clinostomus elongatus), a freshwater leuciscid listed as Endangered under Canada's Species at Risk Act, to model spawning phenology and make predictions about spawning initiation using historical and climate change projected thermal cues (measured as cumulative growing degree days), and provide an ethological description of spawning behaviour. Logistic regression models applied to 4 years of average daily stream water temperature data and field behavioural observations of the onset of spawning activity indicated a 50% probability of spawning initiation when cumulative growing degree days reached 214°C days and a 95% probability of spawning initiation at 288°C days. Using two climate change scenarios (i.e., a mid-century 1.6°C increase and an end of century 3.6°C increase), spawning initiation was predicted to advance 3 days by the year 2050 and 7 days by the year 2100. Underwater video cameras placed at two sites within an urban stream captured 73 unique spawning events revealing that redside dace spawn in pairs as well as in dense, tightly packed groups (more than 20 individuals). Moreover, there is evidence of redside dace having a polygynandrous mating system, as female redside dace spawned with multiple males in 45.2% of the total spawning events recorded. Taken together, this study provides important insights into redside dace spawning initiation and behaviour, key life-history traits having conservation implications for future reproductive success and, ultimately, population dynamics.

Investigating effects of climate-induced changes in water temperature and diet on mercury concentrations in an Arctic freshwater forage fish

The amount of mercury (Hg) in Arctic lake food webs is, and will continue to be, affected by rapid, ongoing climate change. At warmer temperatures, fish require more energy to sustain growth; changes in their metabolic rates and consuming prey with potentially higher Hg concentrations could result in increased Hg accumulation. To examine the potential implications of climate warming on forage fish Hg accumulation in Arctic lakes, we quantified growth and Hg accumulation in Ninespine Stickleback Pungitius pungitius under different temperature and diet scenarios using bioenergetics models. Four scenarios were considered that examined the role of climate, diet, climate × diet, and climate × diet × elevated prey Hg. As expected, annual fish growth increased with warmer temperatures, but growth rates and Hg accumulation were largely diet dependent. Compared to current growth rates of 0.3 g⋅y^-1, fish growth increased at least 200% for fish consuming energy-dense benthic prey and decreased at least 40% for fish consuming pelagic prey. Compared to baseline levels, the Hg burden per kilocalorie of Ninespine Stickleback declined up to 43% with benthic consumption - indicating strong somatic growth dilution - but no more than 4% with pelagic consumption; elevated prey Hg concentrations led to moderate Hg declines in benthic-foraging fish and Hg increases in pelagic-foraging fish. Bioenergetics models demonstrated the complex interaction of water temperature, growth, prey proportions, and prey Hg concentrations that respond to climate change. Further work is needed to resolve mechanisms and rates linking climate change to Hg availability and uptake in Arctic freshwater systems.

Geothermal stickleback populations prefer cool water despite multigenerational exposure to a warm environment

Given the threat of climate change to biodiversity, a growing number of studies are investigating the potential for organisms to adapt to rising temperatures. Earlier work has predicted that physiological adaptation to climate change will be accompanied by a shift in temperature preferences, but empirical evidence for this is lacking. Here, we test whether exposure to different thermal environments has led to changes in preferred temperatures in the wild. Our study takes advantage of a "natural experiment" in Iceland, where freshwater populations of threespine sticklebacks (Gasterosteus aculeatus) are found in waters warmed by geothermal activity year-round (warm habitats), adjacent to populations in ambient-temperature lakes (cold habitats). We used a shuttle-box approach to measure temperature preferences of wild-caught sticklebacks from three warm-cold population pairs. Our prediction was that fish from warm habitats would prefer higher water temperatures than those from cold habitats. We found no support for this, as fish from both warm and cold habitats had an average preferred temperature of 13°C. Thus, our results challenge the assumption that there will be a shift in ectotherm temperature preferences in response to climate change. In addition, since warm-habitat fish can persist at relatively high temperatures despite a lower-temperature preference, we suggest that preferred temperature alone may be a poor indicator of a population's adaptive potential to a novel thermal environment.

Evolution of thermal physiology alters the projected range of threespine stickleback under climate change

Species distribution models (SDMs) are widely used to predict range shifts but could be unreliable under climate change scenarios because they do not account for evolution. The thermal physiology of a species is a key determinant of its range and thus incorporating thermal trait evolution into SDMs might be expected to alter projected ranges. We identified a genetic basis for physiological and behavioural traits that evolve in response to temperature change in natural populations of threespine stickleback (Gasterosteus aculeatus). Using these data, we created geographical range projections using a mechanistic niche area approach under two climate change scenarios. Under both scenarios, trait data were either static ("no evolution" models), allowed to evolve at observed evolutionary rates ("evolution" models) or allowed to evolve at a rate of evolution scaled by the trait variance that is explained by quantitative trait loci (QTL; "scaled evolution" models). We show that incorporating these traits and their evolution substantially altered the projected ranges for a widespread panmictic marine population, with over 7-fold increases in area under climate change projections when traits are allowed to evolve. Evolution-informed SDMs should improve the precision of forecasting range dynamics under climate change, and aid in their application to management and the protection of biodiversity.

The influence of thermal cues on the reproductive phenology of Silver Shiner, Notropis photogenis

Reproductive phenology and the length of the growing season vary in response to interannual environmental variability, with implications for population dynamics of freshwater fishes. Understanding the reproductive phenology of imperilled species in relation to environmental conditions is needed to better evaluate potential responses to changing environmental conditions, estimate future population dynamics and develop comprehensive recovery strategies. We examined Silver Shiner, a species listed as "Threatened" under Canada's Species at Risk Act, during spring 2018 and 2019 to better understand the reproductive phenology of the species at the northern edge of its range in Canada. The initiation of Silver Shiner spawning occurred on the descending limb of the hydrograph and was completed before the onset of the extended period of low summer flow. In addition, both the initiation and cessation of spawning occurred in response to a cumulative growing degree day base 5 (GDD₅ ) cue, with logistic regression models indicating a 50% probability the population initiated and ceased spawning when GDD₅ reached 68°C•days and 368°C•days, respectively. Logistic regression incorporating GDD₅ effectively predicted spawning initiation and cessation, providing useful models for examining the impacts of alterations to the thermal regime on reproductive phenology and improving the ability to evaluate changes in the larval growth period. Furthermore, the models can facilitate the development of real-time estimates of spawning activity, and therefore ensure that disturbance to the species is minimized during the sensitive reproductive period.

Demographic Consequences of Phenological Shifts in Response to Climate Change

When a phenological shift affects a demographic vital rate such as survival or reproduction, the altered vital rate may or may not have population-level consequences. We review the evidence that climate change affects populations by shifting species’ phenologies, emphasizing the importance of demographic life-history theory. We find many examples of phenological shifts having both positive and negative consequences for vital rates. Yet, few studies link phenological shifts to changes in vital rates known to drive population dynamics, especially in plants. When this link is made, results are largely consistent with life-history theory: Phenological shifts have population-level consequences when they affect survival in longer-lived organisms and reproduction in shorter-lived organisms. However, there are just as many cases in which demographic mechanisms buffer population growth from phenologically induced changes in vital rates. We provide recommendations for future research aiming to understand the complex relationships among climate, phenology, and demography, which will help to elucidate the extent to which phenological shifts actually alter population persistence.

Anthropogenic alteration of flow, temperature, and light as life-history cues in stream ecosystems

Life history events, from mating and voltinism to migration and emergence, are governed by external and historically predictable environmental factors. The ways humans have altered natural environments during the Anthropocene have created myriad and compounding changes to these historically predictable environmental cues. Over the past few decades, there has been an increased interest in the control temperature exerts on life history events as concern over climate change has increased. However, temperature is not the only life history cue that humans have altered. In stream ecosystems, flow and light serve as important life history cues in addition to temperature. The timing and magnitude of peak flows can trigger migrations, decreases in stream temperature may cause a stream insect to enter diapause, and photoperiod appears to prompt spawning in some species of fish. Two or more of these cues may interact with one another in complex and sometimes unpredictable ways. Large dams and increasing impervious cover in urban ecosystems have modified flows and altered the timing of spawning and migration in fish. Precipitation draining hot impervious surfaces increases stream temperature and adds variability to the general pattern of stream warming from climate change. The addition of artificial light in urban and suburban areas is bright enough to eliminate or dampen the photoperiod signal and has resulted in caddisfly emergence becoming acyclical. The resulting changes in the timing of life history events also have the potential to influence the evolutionary trajectory of an organism and its interactions with other species. This paper offers a review and conceptual framework for future research into how flow, temperature, and light interact to drive life history events of stream organisms and how humans have changed these cues. We then present some of the potential evolutionary and ecological consequences of altered life history events, and conclude by highlighting what we perceive to be the most pressing research needs.

Earlier springs enable high-Arctic wolf spiders to produce a second clutch

Spiders at southern latitudes commonly produce multiple clutches, but this has not been observed at high latitudes where activity seasons are much shorter. Yet the timing of snowmelt is advancing in the Arctic, which may allow some species to produce an additional clutch. To determine if this is already happening, we used specimens of the wolf spider Pardosa glacialis caught by pitfall traps from the long-term (1996-2014) monitoring programme at Zackenberg, NE Greenland. We dissected individual egg sacs and counted the number of eggs and partially developed juveniles, and measured carapace width of the mothers. Upon the discovery of a bimodal frequency distribution of clutch sizes, as is typical for wolf spiders at lower latitudes producing a second clutch, we assigned egg sacs to being a first or second clutch depending on clutch size. We tested whether the median capture date differed among first and second clutches, whether clutch size was correlated to female size, and whether the proportion of second clutches produced within a season was related to climate. We found that assigned second clutches appeared significantly later in the season than first clutches. In years with earlier snowmelt, first clutches occurred earlier and the proportion of second clutches produced was larger. Likely, females produce their first clutch earlier in those years which allow them time to produce another clutch. Clutch size for first clutches was correlated to female size, while this was not the case for second clutches. Our results provide the first evidence for Arctic invertebrates producing additional clutches in response to warming. This could be a common but overlooked phenomenon due to the challenges associated with long-term collection of life-history data in the Arctic. Moreover, given that wolf spiders are a widely distributed, important tundra predator, we may expect to see population and food web consequences of their increased reproductive rates.

The Role of Nest Depth and Site Choice in Mitigating the Effects of Climate Change on an Oviparous Reptile

Climate change is likely to have strong impacts on oviparous animals with minimal parental care, because nest temperature can impact egg development, sex, and survival, especially in the absence of mitigation via parental care. Nesting females may compensate for increasing temperatures by altering how, when, and where they nest. We examined the factors determining nest depth and site choice as well as the effects that nest depth and location have on nest temperature and hatching success in the diamondback terrapin (Malaclemys terrapin). We found that nest depth was not correlated with nesting female size, egg characteristics, or daily temperatures. Nest temperatures and hatching success were correlated with different environmental and nest characteristics between 2004, a cool and wet year, and 2005, a hot and dry year. Females selected nests with lower southern overstory vegetation in 2005. These results suggest that nest depth and location can play an important yet varying role in determining nest temperature and hatching success in more extreme warm and dry environmental conditions and, therefore, may mitigate the impacts of climate change on oviparous reptiles. However, we found minimal evidence that turtles choose nest locations and depths that maximize offspring survival based on short-term environmental cues.

Inferring responses to climate warming from latitudinal pattern of clonal hybridization

Climate warming may affect reproductive isolation between sympatric sister species by modifying reproductive phenology or mate choice. This is expected to result in a latitudinal progression of hybridization in response to the shifting of environmental conditions. The fish species northern redbelly dace (Chrosomus eos) and finescale dace (C. neogaeus) display a wide sympatric distribution in North America. The asexual reproduction of their hybrids allows determining where and when hybridization occurred. The aim of this study was twofold: first, to assess whether temperature affected reproductive isolation, and second, whether the effects of climate warming resulted in a latitudinal progression of hybridization. We performed a 500 km latitudinal survey (51 sites) in southeastern Quebec (Canada) and determined the distribution of clonal hybrid lineages. Results revealed a total of 78 hybrid lineages, including 70 which originated locally. We detected a significant difference between the southern and northern range of the survey in terms of the proportion of sites harboring local hybrids (20/23 vs. 8/28 sites, respectively) and hybrid diversity (57 vs. 13 lineages, respectively). This confirmed that there was more frequent interspecific mating in the warmest sites. In the southern range, diversity of lineages and simulations suggest that hybridization first took place (>7,000 years) in sites characterized by a longer growing season, followed by northerly adjacent sites (ca. 3,500-5,000 years). Moreover, evidence of hybridization occurring in present-day time was detected. This suggests that the current warming episode is going beyond the limits of the previous warmest period of the Holocene.

Climato-environmental influence on breeding phenology of native catfishes in River Ganga and modeling species response to climatic variability for their conservation

The main objectives of the present study were to quantify the environmental, especially temperature and rainfall, effects on breeding phenology of selected catfish species and to predict changes in breeding phenology of the selected species in relation to climatic variability for the Ganga River Basin. The study showed that changes in rainfall pattern may have the most profound effect on gonad maturation and breeding of Mystus tengara and Mystus cavasius followed by the effect of increased water temperature due to rising air temperature. Indication of region-specific adaptation was noticed in reproductive phenology of Eutropiichthys vacha based on local trends of warming climate. The other habitat parameters, such as dissolved oxygen, alkalinity, nitrate, and phosphate, were correlated with gonad maturity and spawning. Climatic variability may bring region-specific changes in breeding phenology of fish species in the Ganga River. Under a warming climate, changes in precipitation pattern manifested into riverine flow pulse may be the key driver in dictating breeding phenology. Our study indicates E. vacha as a climate sensitive species that may be selected as a target species for climate change impact studies.

Phenological mismatch in Arctic-breeding shorebirds: Impact of snowmelt and unpredictable weather conditions on food availability and chick growth

The ecological consequences of climate change have been recognized in numerous species, with perhaps phenology being the most well-documented change. Phenological changes may have negative consequences when organisms within different trophic levels respond to environmental changes at different rates, potentially leading to phenological mismatches between predators and their prey. This may be especially apparent in the Arctic, which has been affected more by climate change than other regions, resulting in earlier, warmer, and longer summers. During a 7-year study near Utqiaġvik (formerly Barrow), Alaska, we estimated phenological mismatch in relation to food availability and chick growth in a community of Arctic-breeding shorebirds experiencing advancement of environmental conditions (i.e., snowmelt). Our results indicate that Arctic-breeding shorebirds have experienced increased phenological mismatch with earlier snowmelt conditions. However, the degree of phenological mismatch was not a good predictor of food availability, as weather conditions after snowmelt made invertebrate availability highly unpredictable. As a result, the food available to shorebird chicks that were 2-10 days old was highly variable among years (ranging from 6.2 to 28.8 mg trap-1 day-1 among years in eight species), and was often inadequate for average growth (only 20%-54% of Dunlin and Pectoral Sandpiper broods on average had adequate food across a 4-year period). Although weather conditions vary among years, shorebirds that nested earlier in relation to snowmelt generally had more food available during brood rearing, and thus, greater chick growth rates. Despite the strong selective pressure to nest early, advancement of nesting is likely limited by the amount of plasticity in the start and progression of migration. Therefore, long-term climatic changes resulting in earlier snowmelt have the potential to greatly affect shorebird populations, especially if shorebirds are unable to advance nest initiation sufficiently to keep pace with seasonal advancement of their invertebrate prey.

Swimming kinematics and temperature effects on spermatozoa from wild and captive shortnose sturgeon (Acipenser brevirostrum)

Computer-assisted semen analysis (CASA) and cluster analysis were used to compare spermatozoa swimming kinematics and milt quality between wild and captive shortnose sturgeon (Acipenser brevirostrum). Milt samples from 27 shortnose sturgeon were collected in May 2016 and June 2017. Of these, 19 were wild caught in the Saint John River, New Brunswick, Canada, and eight were from a captive population at the Mactaquac Biodiversity facility. The following kinematic variables were measured immediately following sperm activation (˜5 s), at 30, 60, and 180 s post-activation; average path velocity (VAP); straight-line velocity (VSL); curvilinear velocity (VCL); amplitude of lateral head displacement (ALH); beat cross frequency (BCF); straightness (STR); linearity (LIN); wobble (WOB); percent motility (MOT). Analyses were conducted at 7, 10, and 14 °C to determine potential effects of temperature on kinematics. Principal components analysis (PCA) of original kinematic variables yielded two main components, a speed/wobble component along with a movement pattern component. Hierarchical cluster analysis (HCPC) indicated there were distinct subpopulations, with composition of clusters the result of fish source (wild-caught or captive). Wild-caught fish had greater sperm densities (P = 0.0064) and sperm swimming speeds compared to captive fish (P < 0.05). Temperature had a significant effect only on captive spermatozoa, and this result was not consistent between time periods. There was no effect of hormonal manipulation on spermatozoa motility kinematics. Results indicate there are significant differences in measures of milt quality between wild and captive shortnose sturgeon, indicating an effect of rearing condition on reproductive potential, which may affect fertilization success.

Susceptibility of European freshwater fish to climate change: Species profiling based on life-history and environmental characteristics

Climate change is expected to strongly affect freshwater fish communities. Combined with other anthropogenic drivers, the impacts may alter species spatio-temporal distributions and contribute to population declines and local extinctions. To provide timely management and conservation of fishes, it is relevant to identify species that will be most impacted by climate change and those that will be resilient. Species traits are considered a promising source of information on characteristics that influence resilience to various environmental conditions and impacts. To this end, we collated life-history traits and climatic niches of 443 European freshwater fish species and compared those identified as susceptible to climate change to those that are considered to be resilient. Significant differences were observed between the two groups in their distribution, life history, and climatic niche, with climate-change-susceptible species being distributed within the Mediterranean region, and being characterized by greater threat levels, lesser commercial relevance, lower vulnerability to fishing, smaller body and range size, and warmer thermal envelopes. Based on our results, we establish a list of species of highest priority for further research and monitoring regarding climate-change susceptibility within Europe. The presented approach represents a promising tool to efficiently assess large groups of species regarding their susceptibility to climate change and other threats, and to identify research and management priorities.

Strong evidence for changing fish reproductive phenology under climate warming on the Tibetan Plateau

Phenological responses to climate change have been widely observed and have profound and lasting effects on ecosystems and biodiversity. However, compared to terrestrial ecosystems, the long-term effects of climate change on species' phenology are poorly understood in aquatic ecosystems. Understanding the long-term changes in fish reproductive phenology is essential for predicting population dynamics and for informing management strategies, but is currently hampered by the requirement for intensive field observations and larval identification. In this study, a very low-frequency sampling of juveniles and adults combined with otolith measurements (long axis length of the first annulus; LAFA) of an endemic Tibetan Plateau fish (Gymnocypris selincuoensis) was used to examine changes in reproductive phenology associated with climate changes from the 1970s to 2000s. Assigning individual fish to their appropriate calendar year class was assisted by dendrochronological methods (crossdating). The results demonstrated that LAFA was significantly and positively associated with temperature and growing season length. To separate the effects of temperature and the growing season length on LAFA growth, measurements of larval otoliths from different sites were conducted and revealed that daily increment additions were the main contributor (46.3%), while temperature contributed less (12.0%). Using constructed water-air temperature relationships and historical air temperature records, we found that the reproductive phenology of G. selincuoensis was strongly advanced in the spring during the 1970s and 1990s, while the increased growing season length in the 2000s was mainly due to a delayed onset of winter. The reproductive phenology of G. selincuoensis advanced 2.9 days per decade on average from the 1970s to 2000s, and may have effects on recruitment success and population dynamics of this species and other biota in the ecosystem via the food web. The methods used in this study are applicable for studying reproductive phenological changes across a wide range of species and ecosystems.

Warmed Winter Water Temperatures Alter Reproduction in Two Fish Species

We examined the spawning success of Fathead Minnows (Pimephales promelas) and Johnny Darters (Etheostoma nigrum) exposed to elevated winter water temperatures typical of streams characterized by anthropogenic thermal inputs. When Fathead Minnows were exposed to temperature treatments of 12, 16, or 20 °C during the winter, spawning occurred at 16 and 20 °C but not 12 °C. Eggs were deposited over 9 weeks before winter spawning ceased. Fathead Minnows from the three winter temperature treatments were then exposed to a simulated spring transition. Spawning occurred at all three temperature treatments during the spring, but fish from the 16° and 20 °C treatment had delayed egg production indicating a latent effect of warm winter temperatures on spring spawning. mRNA analysis of the egg yolk protein vitellogenin showed elevated expression in female Fathead Minnows at 16 and 20 °C during winter spawning that decreased after winter spawning ceased, whereas Fathead Minnows at 12 °C maintained comparatively low expression during winter. Johnny Darters were exposed to 4 °C to represent winter temperatures in the absence of thermal inputs, and 12, 16, and 20 °C to represent varying degrees of winter thermal pollution. Johnny Darters spawned during winter at 12, 16, and 20 °C but not at 4 °C. Johnny Darters at 4 °C subsequently spawned following a simulated spring period while those at 12, 16, and 20 °C did not. Our results indicate elevated winter water temperatures common in effluent-dominated streams can promote out-of-season spawning and that vitellogenin expression is a useful indicator of spawning readiness for fish exposed to elevated winter temperatures.

Within-lake habitat heterogeneity mediates community response to warming trends

Climate change is rapidly altering many aquatic systems, and life history traits and physiological diversity create differences in organism responses. In addition, habitat diversity may be expressed on small spatial scales, and it is therefore necessary to account for variation among both species and locations when evaluating climate impacts on biological communities. Here, we investigated the effects of temperature and spatial heterogeneity on long-term community composition in a large boreal lake. We used a five-decade time series of water temperature and relative abundance of fish species captured in the littoral zone throughout the summer at 10 discrete locations around the lake. We applied a spatial dynamic factor analysis (SDFA) model to this time series, which estimates the sensitivity of each species to changing water temperature while accounting for spatiotemporal variation. This analysis described the trend in community composition at each sampling location in the lake, given their different trends in temperature over time. The SDFA indicated different magnitude and direction of species responses to temperature; some species increased while others decreased in abundance. The model also identified five unique trends in species abundance across sites and time, indicating residual dynamics in abundance after accounting for temperature effects. Thus, different regions in the lake have experienced different trajectories in community change associated with different rates of temperature change. These results highlight the importance of considering habitat heterogeneity in explaining and predicting future species abundances, and our model provides a means of visualizing spatially-explicit temporal variation in species' dynamics.