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Abstract The storage effect is a plausible natural mechanism that generates balanced genetic polymorphism in temporally varying environments. Balanced polymorphism may facilitate evolutionary rescue, promoting the persistence of populations otherwise destined for extinction. However, it is unknown whether the storage effect can be established in small populations whose size is allowed to vary, and if so, whether it will lead to evolutionary rescue. In this study, we investigate whether the spatial storage effect emerges and facilitates evolutionary rescue across small populations of variable sizes that inhabit heterogeneous, temporally varying environments and exchange migrants. We use an eco-evolutionary model to examine the phenomenon under a wide set of conditions, including the magnitudes and periods of temporal variation, habitat harshness, migration rates, the degrees of spatial heterogeneity, and increasing fitness oscillations over time, all within the framework of the logistic population growth model. We find that the storage effect emerges and that it increases the persistence of populations in harsh, temporally varying habitats beyond levels expected in the absence of the mechanism. This mechanism demonstrates how rapid evolution broadens the known conditions for population persistence in the face of rapid and continuous environmental changes. 

Abstract An ongoing challenge in macroevolutionary research is identifying common drivers of diversification amid the complex interplay of many potentially relevant traits, ecological contexts, and intrinsic characteristics of clades. In this study, we used geometric morphometric and phylogenetic comparative methods to evaluate the tempo and mode of morphological evolution in an adaptive radiation of Malagasy birds, the vangas, and their mainland relatives (Aves:Vangidae). The Malagasy radiation is more diverse in both skull and foot shape. However, rather than following the classic “early burst” of diversification, trait evolution accelerated well after their arrival in Madagascar, likely driven by the evolution of new modes of foraging and especially of a few species with highly divergent morphologies. Anatomical regions showed differing evolutionary patterns, and the presence of morphological outliers impacted the results of some analyses, particularly of trait integration and modularity. Our results demonstrate that the adaptive radiation of Malagasy vangas has evolved exceptional ecomorphological diversity along multiple, independent trait axes, mainly driven by a late expansion in niche space due to key innovations. Our findings highlight the evolution of extreme forms as an overlooked feature of adaptive radiation warranting further study. 

Abstract Hillieae is a group of ∼30 florally diverse, Neotropical epiphyte species. Species richness peaks in southern Central America and taxa display bat, hawkmoth, or hummingbird pollination syndromes. A phylogenetic framework is needed to understand floral and biogeographic evolution. We used target enrichment data to infer a species tree and a Bayesian time-calibrated tree including ∼83% of the species in the group. We inferred ancestral biogeography and pollination syndromes, described species’ realized bioclimatic niches via a principal component analysis, and estimated significant niche shifts using Ornstein–Uhlenbeck models to understand how different abiotic and biotic variables have shaped Hillieae evolution. We estimated that Hillieae originated in southern Central America 19 Ma and that hawkmoth pollination is the ancestral character state. Multiple independent shifts in pollination syndrome, biogeographic distribution, and realized bioclimatic niche have occurred, though bioclimatic niche is largely conserved. Using generalized linear models, we identify two interactions—between species’ biogeographic ranges and pollination syndromes, and between phylogenetic covariance and pollination syndromes—that additively affect the degree of bioclimatic niche overlap between species. Regional variation in pollination syndrome diversity and patterns of species bioclimatic niche overlap indicate a link between biogeography and species ecology in driving Hillieae diversification and syndrome evolution. 

Abstract Variation of form–function relationships within populations is the substrate for adaptation at higher levels. Therefore, assessing similarity in form–function relationships within and between species may help reveal the processes shaping functional diversity. Here, we test such similarity across three levels of anuran phenotypic divergence: within a population, among species in a single family (Hylidae; ~60 myr), and across a much broader sample of all anuran species using a single microhabitat (arboreal; ~120 myr). We expected less interspecific divergence to show higher similarity of form–function relationships with the intraspecific level. We analyzed the relationships between locomotor performance (in both swimming and jumping) and several hindlimb traits across these three evolutionary levels. While we found a positive correlation between swimming and jumping velocity at both intra- and interspecific levels, relationships between performance and body form did not match across levels. We suggest that different strengths of functional constraints or trade-offs may have produced more variation in form–function relationships across species, decoupling them from within-species patterns. We conclude that performance landscapes are likely qualitatively different across the different evolutionary scales, potentially reflecting changes in the relative importance of different behaviors across all arboreal species. 

Abstract Plasticity to reduce activity is a common way prey evade predators. However, by reducing activity prey often experience lower individual growth rates because they encounter their own prey less often. To overcome this cost, natural selection should not simply favor individuals generating stronger plasticity to reduce activity rates but also selection to resume activity once the threat of predation subsides. If such plasticity is adaptive, it should vary under environmental conditions that generate stronger selection for greater plasticity, such as predator density. Using a mesocosm experiment and observational study with a damselfly-prey/fish-predator system, we show that fish predation exerts selection for greater plasticity in activity rates of damselflies. Such selection allows damselfly activity levels to initially decrease and then rebound when the threat of predation dissipates, potentially helping to ameliorate a hypothesized growth penalty from activity reductions. We also find that the extent of plasticity in activity to the threat of fish predation increases, albeit slightly (r2 = 0.04%–0.063%), as fish densities increase across natural lakes, consistent with the idea that the magnitude of plasticity is shaped by environmental conditions underlying selection. Collectively, these results demonstrate how selection acts to drive adaptive plasticity in a common predator avoidance strategy. 

Abstract Mountains and islands provide an opportunity for studying the biogeography of diversification and population fragmentation. Aotearoa (New Zealand) is an excellent location to investigate both phenomena due to alpine emergence and oceanic separation. While it would be expected that separation across oceanic and elevation gradients are major barriers to gene flow in animals, including aquatic insects, such hypotheses have not been thoroughly tested in these taxa. By integrating population genomic from subgenomic Anchored-Hybrid Enrichment sequencing, ecological niche modeling, and morphological analyses from scanning-electron microscopy, we show that tectonic uplift and oceanic vicariance are implicated in speciation and population structure in Kapokapowai (Uropetala) dragonflies. Although Te Moana o Raukawa (Cook Strait) is likely responsible for some of the genetic structure observed, speciation has not yet occurred in populations separated by the strait. We find that the altitudinal gradient across Kā Tiritiri-o-te-Moana (the Southern Alps) is not impervious, but it significantly restricts gene flow between the aforementioned species. Our data support the hypothesis of an active colonization of Kā Tiritiri-o-te-Moana by the ancestral population of Kapokapowai, followed by a recolonization of the lowlands. These findings provide key foundations for the study of lineages endemic to Aotearoa. 

Abstract Evolutionary innovations have played an important role in shaping the diversity of life on Earth. However, how these innovations arise and their downstream effects on patterns of morphological diversification remain poorly understood. Here, we examine the impact of evolutionary innovation on trait diversification in tetraodontiform fishes (pufferfishes, boxfishes, ocean sunfishes, and allies). This order provides an ideal model system for studying morphological diversification owing to their range of habitats and divergent morphologies, including the fusion of the teeth into a beak in several families. Using three-dimensional geometric morphometric data for 176 extant and fossil species, we examine the effect of skull integration and novel habitat association on the evolution of innovation. Strong integration may be a requirement for rapid trait evolution and facilitating the evolution of innovative structures, like the tetraodontiform beak. Our results show that the beak arose in the presence of highly conserved patterns of integration across the skull, suggesting that integration did not limit the range of available phenotypes to tetraodontiforms. Furthermore, we find that beaks have allowed tetraodontiforms to diversify into novel ecological niches, irrespective of habitat. Our results suggest that general rules pertaining to evolutionary innovation may be more nuanced than previously thought.