A closer look at invasiveness and relatedness: life histories, temperature, and establishment success of four congeners

Outside your shell: exploring genetic variation in two congeneric marine snails across a latitude and temperature gradient

Intertidal organisms withstand extreme temperature fluctuations, and theirability to cope with this variation may affect their distributions across the seascape. Genetic variation and local environments likely interact to determine variation in thermal performances across intertidal species' ranges, so characterizing the relationship between temperature variation and population structure is key to understanding the biology of marine invertebrates. Here, we use 2bRAD-sequencing to examine population genetic structure in two congeneric intertidal marine gastropods (Crepidula fornicata, C. plana), sampled from locations along a natural temperature gradient on the Northeast shores of the United States. These two species share similar life histories, yet C. plana exhibits a narrower distribution than C. fornicata. Our results demonstrate that both species show patterns of genetic divergence consistent with isolation by distance, though this pattern was only significant in C. fornicata. Both putatively selected and neutral loci displayed significant spatial structuring in C. fornicata; however, only putatively selected loci showed significant clustering in C. plana. When exploring whether temperature differences explained genetic differentiation, we found that 9-12% of genetic differentiation was explained by temperature variation in each species even when controlling for latitude and neutral population structure. Our results suggest that temperature shapes adaptive variation across the seascape in both Crepidula species and encourages further research to differentiate our results from models of neutral evolutionary drift.

Interactions Between Non-Native Western Mosquitofish and Native Bluegill Sunfish: Mesocosm Experiments

Aquatic ecosystems are often negatively affected by invasive species. However, biotic resistance by native species, either by competition or predation, can reduce the impacts of invasions by non-native species. The Western Mosquitofish (Gambusia affinis) is one of the most impactful invasive species of freshwater fish and cause declines in native fish populations. Using two mesocosm experiments conducted in different years, we examined the ecological interactions between juveniles of the native fish, Bluegill Sunfish (Lepomis macrochirus), and adults of the invasive fish, G. affinis. We found evidence for interactions between L. macrochirus and G. affinis. However, interactions did not appear symmetric, with L. macrochirus generally more affected by intraspecific interactions than interspecific interactions whereas G. affinis was more affected by interspecific interactions than intraspecific interactions. The presence of either species of fish led to a decrease in the number of large zooplankton and a tendency for a decrease in the total number of zooplankton. Based on these results, native L. macrochirus appear to be able to reduce the ability of non-native G. affinis to establish or maintain populations through both competition and predation (i.e., acting as an intraguild predator). The consistency of our results across both experiments, with their different designs and their occurring in different years, gives weight to these conclusions. The reduction of or prevention of establishment of populations of invasive G. affinis would likely benefit the aquatic communities of ponds with fish, especially small-bodied native fish.

Shoals in troubled waters? The impact of rising temperatures on metabolism, foraging, and shoaling behavior in mixed-species shoals

Rising water temperatures across aquatic habitats, in the current global climate change scenario, can directly affect metabolism and food intake in fish species. This can potentially alter their physiological, behavioral, and shoaling properties. In the current study, we examined the effects of high temperatures on metabolism, foraging, and shoaling in tropical fish. Mixed-species (comprising flying barbs, zebrafish, and gambusia) and single-species (flying barbs and zebrafish) shoals were conditioned for 45 days to three kinds of temperature regimes: the current temperature regime (CTR), in which shoals were maintained at water temperature of 24°C (i.e., the current mean temperature of their habitat), the predicted temperature regime (PTR) at 31°C (i.e., simulating conditions projected for their habitat in 2100), and the dynamic temperature regime (DTR), which experienced daily temperature fluctuations between 24 and 31°C (i.e., resembling rapid temperature changes expected in their natural environments). We found species-specific responses to these temperature regimes. Flying barbs exhibited significantly lower body weight at PTR but maintained consistent muscle glycogen content across all temperature regimes. In contrast, zebrafish and gambusia displayed significantly elevated muscle glycogen content at PTR, with similar body weights across all three temperature regimes. Cohesion within flying barb shoals and cohesion/polarization in mixed-species shoals decreased significantly at PTR. Shoals exposed to DTR exhibited intermediate characteristics between those conditioned to CTR and PTR, suggesting that shoals may be less impacted by dynamic temperatures compared to prolonged high temperatures. This study highlights species-specific metabolic responses to temperature changes and their potential implications for larger-scale shoal properties.

Using a metabolomics approach to investigate the sensitivity of a potential Arctic-invader and its Arctic sister-species to marine heatwaves and traditional harvesting disturbances

Coastal species are threatened by fishing practices and changing environmental conditions, such as marine heatwaves (MHW). The mechanisms that confer tolerance to such stressors in marine invertebrates are poorly understood. However, differences in tolerance among different species may be attributed to their geographical distribution. To test the tolerance of species occupying different thermal ranges, we used two closely related bivalves the softshell clam Mya arenaria (Linnaeus, 1758), a cold-temperate invader with demonstrated potential for establishment in the Arctic, and the blunt gaper Mya truncata (Linnaeus, 1758), a native polar species. Clams were subjected to a thermal stress, mimicking a MHW, and harvesting stress in a controlled environment. Seven acute temperature changes (2, 7, 12, 17, 22, 27, and 32 °C) were tested at two harvesting disturbance intensities (with, without). Survival was measured after 12 days and three tissues (gills, mantle, and posterior adductor muscle) collected from surviving individuals for targeted metabolomic profiling. MHW tolerance differed significantly between species: 26.9 °C for M. arenaria and 17.8 °C for M. truncata, with a negligeable effect of harvesting. At the upper thermal limit, M. arenaria displayed a more profound metabolomic remodelling when compared to M. truncata, and this varied greatly between tissue types. Network analysis revealed differences in pathway utilization at the upper MHW limit, with M. arenaria displaying a greater reliance on multiple DNA repair and expression and cell signalling pathways, while M. truncata was limited to fewer pathways. This suggests that M. truncata is ill equipped to cope with warming environments. MHW patterning in the Northwest Atlantic may be a strong predictor of population survival and future range shifts in these two clam species. As polar environments undergo faster rates of warming compared to the global average, M. truncata may be outcompeted by M. arenaria expanding into its native range.