There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change ...through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels (Glaucomys volans) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel (Glaucomys sabrinus). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans. There was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Tree cavities likely vary in their thermal quality for cavity-nesting animals, which could be especially important during winter. We conducted a winter field experiment to test whether cavities vary ...either in their buffering capacity or in their mean temperature according to predictable characteristics. We found that cavities buffered temperature and that there was a lag effect in temperature that appeared to be related to heating and cooling. Diameter at breast height was the most important variable influencing cavity temperature during the day, with smaller trees warming up more. During the night, diameter at breast height and tree decay class were important, such that larger, live trees cooled down less. Maintaining live trees with cavities in managed forests should be considered in addition to snag retention, because live trees appear to provide warmer structures during winter.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
SUMMARY
Triacylglycerols have important physiological roles in photosynthetic organisms, and are widely used as food, feed and industrial materials in our daily life. Phospholipid:diacylglycerol ...acyltransferase (PDAT) is the pivotal enzyme catalyzing the acyl‐CoA‐independent biosynthesis of triacylglycerols, which is unique in plants, algae and fungi, but not in animals, and has essential functions in plant and algal growth, development and stress responses. Currently, this enzyme has yet to be examined in an evolutionary context at the level of the green lineage. Some fundamental questions remain unanswered, such as how PDATs evolved in photosynthetic organisms and whether the evolution of terrestrial plant PDATs from a lineage of charophyte green algae diverges in enzyme function. As such, we used molecular evolutionary analysis and biochemical assays to address these questions. Our results indicated that PDAT underwent divergent evolution in the green lineage: PDATs exist in a wide range of plants and algae, but not in cyanobacteria. Although PDATs exhibit the conservation of several features, phylogenetic and selection‐pressure analyses revealed that overall they evolved to be highly divergent, driven by different selection constraints. Positive selection, as one major driving force, may have resulted in enzymes with a higher functional importance in land plants than green algae. Further structural and mutagenesis analyses demonstrated that some amino acid sites under positive selection are critically important to PDAT structure and function, and may be central in lecithin:cholesterol acyltransferase family enzymes in general.
Significance Statement
Phospholipid:diacylglycerol acyltransferase (PDAT) is a pivotal enzyme catalyzing the acyl‐CoA‐independent biosynthesis of triacylglycerols and has essential functions in plant and algal growth, development and stress response. While several features are conserved in PDAT enzymes across the green lineage, positive selection appears to have been a major driving force resulting in a high level of divergence in these enzymes overall, leading to their greater functional significance in land plants than green algae.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Phenotypic plasticity enables rapid responses to environmental change, and could facilitate range shifts in response to climate change. What drives the evolution of plasticity at range edges, and the ...capacity of range-edge individuals to be plastic, remain unclear. Here, we propose that accurately predicting when plasticity itself evolves or mediates adaptive evolution at expanding range edges requires integrating knowledge on the demography and evolution of edge populations. Our synthesis shows that: (i) the demography of edge populations can amplify or attenuate responses to selection for plasticity through diverse pathways, and (ii) demographic effects on plasticity are modified by the stability of range edges. Our spatially explicit synthesis for plasticity has the potential to improve predictions for range shifts with climate change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Animal movement patterns, whether related to dispersal, migration, or ranging behaviors, vary in time. Individual movements reflect the outcomes of interactions between an individual's condition and ...a multitude of underlying ecological processes. Theory predicts that when competition for breeding territories is high, individuals should arrive at breeding sites earlier than what would otherwise be optimal for breeding in the absence of competition. This is because priority at a site can confer significant competitive advantages leading to better breeding outcomes. Empirical data from long-distance migrants support this theory. However, it has not been tested within the context of fine-scale movements in nonmigratory populations. We assessed the effect of arrival time at a breeding site on reproductive outcomes in an intensively monitored resident population of Great Tits (
Parus major
). The population was monitored passively, via passive integrated transponder (PIT) tag loggers, and actively, via catching, during breeding and nonbreeding seasons. We developed new capture-recapture-resight models that use both data types to model breeding outcome conditional on the unknown individual arrival times. In accordance with theory, individuals arrived at the woods synchronously in waves that were large at the beginning of the nonbreeding season and small toward the end, with very few arrivals in the intervening period. There was a strong effect of arrival time on the probability of breeding; the earlier an individual arrived, the more likely it was to successfully establish a nest that reached the incubation period. However, once nests were established, they had equal probabilities of failing early, regardless of arrival time. Finally, there was moderate evidence of a negative effect of arrival time on the probability of successfully fledging nestlings. These empirical findings are consistent with theoretical models that suggest an important role for competition in shaping fine-scale seasonal movements. Our capture-recapture-resight models are extensible and suitable for a variety of applications, particularly when the goal is to estimate the effects of unobservable arrival times on subsequent ecological outcomes.
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BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
Information on wildlife population structure, demographic history, and adaptations are fundamental to understanding species evolution and informing conservation strategies. To study this ecological ...context for a cetacean of conservation concern, we conducted the first genomic assessment of the northern bottlenose whale, Hyperoodon ampullatus, using whole‐genome resequencing data (n = 37) from five regions across the North Atlantic Ocean. We found a range‐wide pattern of isolation‐by‐distance with a genetic subdivision distinguishing three subgroups: the Scotian Shelf, western North Atlantic, and Jan Mayen regions. Signals of elevated levels of inbreeding in the Endangered Scotian Shelf population indicate this population may be more vulnerable than the other two subgroups. In addition to signatures of inbreeding, evidence of local adaptation in the Scotian Shelf was detected across the genome. We found a long‐term decline in effective population size for the species, which poses risks to their genetic diversity and may be exacerbated by the isolating effects of population subdivision. Protecting important habitat and migratory corridors should be prioritized to rebuild population sizes that were diminished by commercial whaling, strengthen gene flow, and ensure animals can move across regions in response to environmental changes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Landscape genetic analyses assess the influence of landscape structure on genetic differentiation. It is rarely possible to collect genetic samples from all individuals on the landscape and thus it ...is important to assess the sensitivity of landscape genetic analyses to the effects of unsampled and under-sampled sites. Network-based measures of genetic distance, such as conditional genetic distance (cGD), might be particularly sensitive to sampling intensity because pairwise estimates are relative to the entire network. We addressed this question by subsampling microsatellite data from two empirical datasets. We found that pairwise estimates of cGD were sensitive to both unsampled and under-sampled sites, and F(ST), D(est), and d(eucl) were more sensitive to under-sampled than unsampled sites. We found that the rank order of cGD was also sensitive to unsampled and under-sampled sites, but not enough to affect the outcome of Mantel tests for isolation by distance. We simulated isolation by resistance and found that although cGD estimates were sensitive to unsampled sites, by increasing the number of sites sampled the accuracy of conclusions drawn from landscape genetic analyses increased, a feature that is not possible with pairwise estimates of genetic differentiation such as F(ST), D(est), and d(eucl). We suggest that users of cGD assess the sensitivity of this measure by subsampling within their own network and use caution when making extrapolations beyond their sampled network.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Arctic is the fastest‐warming region on the planet, and the lengthening ice‐free season is opening Arctic waters to sub‐Arctic species such as the killer whale (Orcinus orca). As apex predators, ...killer whales can cause significant ecosystem‐scale changes. Setting conservation priorities for killer whales and their Arctic prey species requires knowledge of their evolutionary history and demographic trajectory. Using whole‐genome resequencing of 24 killer whales sampled in the northwest Atlantic, we first explored the population structure and demographic history of Arctic killer whales. To better understand the broader geographic relationship of these Arctic killer whales to other populations, we compared them to a globally sampled dataset. Finally, we assessed threats to Arctic killer whales due to anthropogenic harvest by reviewing the peer‐reviewed and gray literature. We found that there are two highly genetically distinct, non‐interbreeding populations of killer whales using the eastern Canadian Arctic. These populations appear to be as genetically different from each other as are ecotypes described elsewhere in the killer whale range; however, our data cannot speak to ecological differences between these populations. One population is newly identified as globally genetically distinct, and the second is genetically similar to individuals sampled from Greenland. The effective sizes of both populations recently declined, and both appear vulnerable to inbreeding and reduced adaptive potential. Our survey of human‐caused mortalities suggests that harvest poses an ongoing threat to both populations. The dynamic Arctic environment complicates conservation and management efforts, with killer whales adding top‐down pressure on Arctic food webs crucial to northern communities' social and economic well‐being. While killer whales represent a conservation priority, they also complicate decisions surrounding wildlife conservation and resource management in the Arctic amid the effects of climate change.
Killer whales are moving northward into the Arctic as sea ice melts from a warming climate. Using genetics, we identified two highly distinct Canadian Arctic populations with origins from the western and eastern North Atlantic that appear to be at risk from both inbreeding and harvest. Although these killer whales are threatened, they may also disrupt the Arctic food chain by their increased access to Arctic prey, which presents a complex case for conservation in the Arctic ecosystem.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Both social and ecological factors influence population process and structure, with resultant consequences for phenotypic selection on individuals. Understanding the scale and relative contribution ...of these two factors is thus a central aim in evolutionary ecology. In this study, we develop a framework using null models to identify the social and spatial patterns that contribute to phenotypic structure in a wild population of songbirds. We used automated technologies to track 1053 individuals that formed 73 737 groups from which we inferred a social network. Our framework identified that both social and spatial drivers contributed to assortment in the network. In particular, groups had a more even sex ratio than expected and exhibited a consistent age structure that suggested local association preferences, such as preferential attachment or avoidance. By contrast, recent immigrants were spatially partitioned from locally born individuals, suggesting differential dispersal strategies by phenotype. Our results highlight how different scales of social decision-making, ranging from post-natal dispersal settlement to fission–fusion dynamics, can interact to drive phenotypic structure in animal populations.
Competition is a driving factor in shaping ecological communities and may act directly or indirectly through apparent competition. We examined a classic example of parasite-mediated competition ...between northern (Glaucomys sabrinus) and southern flying squirrels (G. volans) via the intestinal nematode, Strongyloides robustus, and tested whether it could act as a species barrier in a flying squirrel hybrid zone. We live-trapped flying squirrels (G. sabrinus and G. volans), grey squirrels (Sciurus carolinensis), red squirrels (Tamiasciurus hudsonicus), and chipmunks (Tamias striatus) from June–September 2019 at 30 woodlots in Ontario, Canada. Fecal samples from squirrels were collected and analyzed for the presence of endoparasite eggs. For each individual, we calculated Scaled Mass Index (SMI) as a measure of body condition to assess the effect of S. robustus on squirrels. We found eggs of S. robustus in all species except chipmunks. Infection with S. robustus did not appear to affect body condition of southern flying squirrels and grey squirrels, but we did find a weak negative effect on northern flying squirrels and red squirrels. Despite a weak asymmetric effect of S. robustus on flying squirrels, we did not find any evidence that parasite-mediated competition could lead to competitive exclusion from woodlots. Furthermore, S. robustus eggs were common in feces of the red squirrel, a species largely sympatric with northern flying squirrel.
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•Strongyloides robustus was detected in 4 squirrel species.•The highest prevalence of S. robustus was found in red squirrels and northern flying squirrels.•Body condition was lowest in red squirrels and northern flying squirrels infected with S. robustus.•No evidence of parasite-mediated competition between sympatric flying squirrels leading to competitive exclusion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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