Divergent pathways shape climatic niches and body size evolution across terrestrial vertebrates

Divergent pathways shape climatic niches and body size evolution across terrestrial vertebrates | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 24 November 2025 V1 Latest version Share on Divergent pathways shape climatic niches and body size evolution across terrestrial vertebrates Authors : Matheus de T. Moroti 0000-0002-2645-9130 [email protected] , Mario Moura 0000-0002-7369-7502 , Mathias Pires 0000-0003-2500-4748 , and Diogo Provete 0000-0002-0097-0651 Authors Info & Affiliations https://doi.org/10.22541/au.176400956.64170283/v1 390 views 199 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Understanding how phenotypic and niche evolution interact is central to macroevolution, yet their causal direction remains uncertain. We contrasted predictions from Adaptive Landscape Theory, where phenotypes track environmental shifts, with those from Niche Construction Theory, which expects reciprocal feedback between organisms and environments. Using body size, climate, phylogeny, and microhabitat data for terrestrial vertebrates, we applied causal models to contrast these hypotheses. Overall, climatic niche shifts most often drove body size evolution, whereas microhabitat showed weaker effects. Endotherms exhibited the strongest bidirectional relationships, with body size also facilitating exploration of new climatic regimes. In contrast, amphibians and squamates displayed opposite unidirectional patterns: climate primarily shaped body size in amphibians, while body size influenced climatic niche evolution in squamates. These clade-specific outcomes indicate that both theoretical frameworks capture real macroevolutionary processes, but their relative importance varies across vertebrates, highlighting the value of explicitly testing causal direction. Introduction Understanding the causal relationship between phenotypic evolution and niche evolution is central to macroevolution. However, the directionality of this relationship remains debatable (Folk et al. 2019; Quintero 2025). According to the Adaptive Landscape Theory (ALT), species distribution in climatic space is guided by shifts between pre-existing adaptive peaks, determined by environmental gradients and novel ecological opportunities (Simpson, 1944; 1953). Under this theoretical framework, evolution occurs when new opportunities arise—such as the acquisition of key innovations, dispersal to novel environments, or the release of competitors—allowing species to colonize new adaptive zones (Drury et al. 2024; Folk et al. 2019). In this view, organisms are largely passive entities, shaped by external pressures that delimit the available paths for diversification. Accordingly, the phenotype is expected to be a response to abiotic constraints or biotic interactions (as proposed by the Court Jester and Red Queen hypotheses; Benton 2009), resulting in relatively predictable and stable adaptive trajectories. In contrast, the Niche Construction Theory (NCT) argues that organisms not only respond to, but also actively shape the environments in which they inhabit, creating dynamic feedback between the phenotype and position in niche space (Quintero 2025). Under this theory, phenotypic or behavioral changes may enable the exploitation of novel ecological opportunities, giving organisms an active role in determining their own evolutionary trajectories (Odling-Smee et al. 2013; Odling-Smee 2024). In this context, species could alter how they use and perceive the environment, generating divergent selective pressures among populations and, consequently, accelerating or decelerating evolutionary rates that contribute to adaptive diversification (Alencar et al. 2017; Lapiedra et al. 2013; Quintero 2025). These two theories represent contrasting macroevolutionary paradigms, with organisms shaped by either environmental constraints (ALT) or as active constructors of their own niches (NCT). Determining which theory is best supported requires testing the relationship between the rates of phenotypic and climatic niche evolution within a causal framework. While ALT proposes minimal association with the phenotype responding to niche shifts (Simpson, 1944; 1953), NCT predicts reciprocal influence between phenotypes and the niche, as mutual feedback drives coevolutionary dynamics (Odling-Smee et al. 2013; Odling-Smee 2024; Quintero 2025). Evolutionary rates are shaped by a complex interplay between intrinsic factors, such as life-history traits (Cássia-Silva et al. 2020), habitat (Huang et al. 2022), or microhabitat use (Alencar et al. 2017), and extrinsic factors, such as environmental pressures (Clavel & Morlon 2017; Moreira et al. 2024). Such interactions provide an empirical basis for testing ALT and NCT predictions. For instance, in terrestrial mammals, transitions among habitats and variation in resource availability have played key roles in the evolution of body size (Huang et al. 2022), whereas past climatic shifts—particularly cold periods—accelerated body size evolution in mammals and birds (Clavel & Morlon 2017). In vipers, arboreal habits impose strong constraints on the evolution of body size and shape, while terrestrial lineages diversify toward a wider array of forms (Alencar et al. 2017). However, in ectotherms, the relationship between body size and climate is less consistent (Slavenko & Meiri 2015; Slavenko et al. 2019), lacking support for the effect of latitude on body size evolution (Caron & Pie 2024). Although evidence for a link between latitude and morphological evolution in reptiles is mixed (e.g., Hipsley et al. 2014), latitude influences diversification rates in amphibians and squamates (García-Rodríguez et al. 2025; Pyron 2014), suggesting that climate may still act as a key predictor of evolutionary rates across vertebrates. Evidence from diverse vertebrate groups suggests that diversification is tightly coupled to both morphological and climatic niche evolution. Phenotypic and speciation rates are frequently correlated (Cooney & Thomas 2021; Rabosky & Adams 2012; Rabosky et al. 2013 but see Adams et al. 2009; Folk et al. 2019). Similarly, the rate of climatic niche evolution —reflecting changes in both positional and niche breadth—is positively associated with diversification rates, with niche divergence emerging as a major driver of speciation across lineages (Cooney et al. 2016; Gómez‐Rodríguez et al. 2015; Moreira et al. 2024). Despite these advances, the relationships between the rates of phenotypic and climatic niche evolution themselves remain poorly understood. Most research has been focused on the separate association between diversification rates and climatic niche (Moreira et al. 2024) or phenotypic evolution (Cooney & Thomas 2021), leaving the direction and causal pathways between them largely unexplored (but see Folk et al. 2019). Clarifying this relationship requires considering how intrinsic constraints vary across major vertebrate groups. Endotherms and ectotherms differ in their thermal tolerances and energetic requirements, which are likely to shape both phenotypic evolution and climatic niche dynamics in distinct ways (Rolland et al. 2018). Dispersal ability varies from amphibians, with limited dispersal ability and strong dependence to local climatic conditions (Lin et al. 2021), to birds capable of long-distance movements and broad niche ranges (Rodrigues & Botero 2025; Stevens et al. 2014). These contrasts create distinct selective regimes across lineages. Amphibians may respond to climatic shifts through passive rather than active mechanisms, whereas birds can actively track favorable conditions across broader spatial scales. Yet, most studies on climate niche evolution have focused on single taxonomic groups (e.g., Clavel & Morlon 2017; Slavenko & Meiri 2015; Slavenko et al. 2019), potentially limiting the generalization (but see Caron & Pie 2024). A multi-lineage perspective is therefore needed to test whether links between phenotype, climatic niches, and microhabitat-use are taxon-dependent or reflect common evolutionary principles. Given their wide diversity of life-history strategies, physiological constraints, and dispersal abilities (Rodrigues & Botero 2025; Rolland et al. 2018; Stevens et al. 2014), terrestrial vertebrates offer a powerful system to evaluate whether climatic niche shifts drive phenotypic evolution or, conversely, whether phenotypic innovations facilitate the occupation of new climatic spaces. Here, we test these alternative expectations using the most comprehensive dataset of terrestrial vertebrates to date, combining body size, climatic, phylogenetic, and ecological trait data to evaluate the causal links between body size evolution, climatic niche (niche position and breadth), and microhabitat-use (verticality). According to the Adaptive Landscape Theory (ALT), we expect that shifts in the climatic niche would act as external forces driving body size evolution and microhabitat use, where the body size of species would respond unidirectionally to environmental changes (Folk et al. 2019). Although the ALT also predicts that key phenotypic innovations enable the occupation of new climatic or ecological niches, the causal direction remains one-way (Fig. 1A). In contrast, under the Niche Construction Theory (NCT), phenotypic innovations may both precede and facilitate shifts in microhabitat use—such as the occupation of novel vertical strata or the exploration of novel climatic regimes—thereby creating feedback loops in which ecological change and phenotypic evolution reinforce one another (Fig. 1B) (Laland et al. 2016; Odling-Smee et al. 2013; Quintero 2025). Microhabitat illustrates this contrast particularly well, as it can be interpreted either as a response to environmental shifts (ALT) or as an active driver of evolutionary dynamics (NCT; Alencar et al. 2017; Huang et al. 2022; Lapiedra et al. 2013). Our results suggest that both theories may be compatible, with their applicability varying among groups depending on their life history traits, such as physiology, dispersal ability, and survival strategies. Figure 1. Causal models contrasting the predictions of the Adaptive Landscape Theory (ALT) and the Niche Construction Theory (NCT) . Under the ALT, climatic niche shifts act as external drivers of body size evolution, with species responding to environmental gradients in a predominantly unidirectional manner. Although key phenotypic innovations allow the occupation of novel climatic or ecological niches, feedback between phenotype and environment is limited. Conversely, the Niche Construction Theory (NCT) predicts reciprocal causation between organisms and their environments. Changes in body size can both precede and facilitate the exploration of novel climatic regimes or microhabitats, modifying environmental conditions and generating feedback loops in which ecological, physiological change, and body size evolution mutually reinforce each other. Material and Methods Phylogenetic and ecological data We took advantage of the recently developed TetrapodTraits 1.0 database, which provides ecological and spatial data for 33,281 tetrapods globally (Moura et al. 2024) readily harmonized with phylogenetic trees available in VertLife (https://vertlife.org). We filtered TetrapodTraits to include only non-marine tetrapods, because marine species face distinct evolutionary pressures and environmental conditions not captured by standard bioclimatic variables. Furthermore, they represent the majority of vertebrate species in the dataset (Fig. S1). Our final species dataset included 7,082 species of amphibians, 9,635 squamates, 8,632 birds, and 5,198 mammals, totaling 30,665 non-marine tetrapods, covering ~95% of tetrapod genera and ~94% of tetrapod families (Moura et al. 2024). Phylogenetic relationships for each tetrapod class were represented by a set of 100 trees from the fully-sampled phylogenies available at VertLife for amphibians (Jetz & Pyron 2018), squamates (Tonini et al. 2016), mammals (Upham et al. 2019), and birds (Jetz et al. 2012). To estimate body size evolution, we used direct measurements of body length (mm) for amphibians and squamates, and body mass (g) for mammals and birds (Moura et al. 2024). We exclusively used observed, instead of imputed trait values to avoid circularity in our phylogenetic rates estimation, which would occur if missing trait values were imputed using the same phylogeny, leading to the exclusion of 155 amphibians (~2.1%), 27 squamates (~0.3%), 557 birds (~5.9%), and 479 mammal species (~8%). Sensitivity analysis of missing body size data revealed that they are not random in the phylogenies, but the phylogenetic signal is weak in amphibians, birds, and mammals, while squamates with missing data are randomly distributed across the phylogeny (Table S1). We performed this analysis using the sensiPhy R package (Paterno et al. 2018). To inform each species’ spatial niche and microhabitat use, we used a verticality index, scoring each species according to its predominant microhabitat use: 0 = strictly fossorial, 0.25 = fossorial and terrestrial, 0.5 = terrestrial or aquatic, 0.75 = terrestrial and arboreal, and 1 = strictly arboreal or aerial. These categories reflect ecological strategies associated with space use across tetrapods (e.g., Alencar et al. 2017; Lapiedra et al. 2013; Moura et al. 2024). For 1,301 species (7.9% amphibians, 6.1% squamates, 0.7% birds, and 5.5% mammals), microhabitat information represents imputed data rather than direct observation. However, we retained species with imputed data in our analysis because microhabitat was treated as a predictor rather than a trait to which we estimated evolutionary rate, and the imputation procedure showed high accuracy (see Moura et al. 2024). We repeated the path analysis excluding imputed data and obtained consistent results, confirming the robustness of our findings. The main difference was that body size evolution in mammals had a weak and positive effect on verticality (Fig. S2). We used the spatial distribution data available in Moura et al. (2024), which represents the overlay of combined expert-based range maps onto an equal-area global grid of 110 × 110 km cells (equal-area projection) to derive within-range averages of bioclimatic variables across species. Using the CHELSA v2.1 dataset (Brun et al. 2022), we extracted the median value of the following variables for each grid cell: annual mean temperature (Bio1), temperature seasonality (Bio4), maximum temperature of the warmest month (Bio5), minimum temperature of the coldest month (Bio6), annual precipitation (Bio12), precipitation seasonality (Bio15), precipitation of the wettest quarter (Bio16), and precipitation of the driest quarter (Bio17). We then calculated the within-range average of these eight bioclimatic variables for each species. These bioclimatic variables capture a spectrum of conditions: general climate (Bio1, Bio12), seasonality (Bio4, Bio15), and extremes (Bio5, Bio6, Bio16, Bio17), offering insights into both the baseline environment and physiological limits of species (e.g., Liu et al. 2020; Moreira et al. 2024; Quintero & Wiens 2013). We excluded 11 species (1 amphibian, 8 squamates, and 2 bats) from these computations due to the lack of spatial data (see Moura et al. 2024). All computations were performed in R v. 4.1.1 (R Core Team 2021), using the sf (Pebesma 2018; Pebesma & Bivand 2023) and terra packages (Hijmans 2025). Measuring species climatic niche We used the bioclimatic variables to derive indices representing the centroid and breadth of the climatic niche of each species. Before the computation, we assessed multicollinearity among variables using the Variance Inflation Factor (VIF) and iteratively removed variables with VIF > 10 (Table S2). This procedure selected five bioclimatic variables (Bio4, Bio5, Bio15, Bio16, and Bio17) for subsequent analyses. Using the reduced set of bioclimatic variables, we conducted an Outlying Mean Index (OMI; Dolédec et al. 2000) separately for each tetrapod class. This ordination analysis provides a multivariate representation of the climatic conditions associated with the geographic distribution of species. Specifically, OMI quantifies how much a species’ niche deviates from the mean environmental conditions available in the region (‘OMI’ as a proxy for niche position), and the range of climatic conditions in which the species occurs (‘Tol’ as a proxy for climatic niche breadth). Since our bioclimatic data were derived from regions occupied by species, this approach considers only the climatic conditions effectively used by the species (e.g., Hutchinson’s duality; Colwell & Rangel 2009; Gouveia et al. 2014; Peixoto et al. 2017; Rodrigues et al. 2019)—that is, it reflects the realized rather than the fundamental climatic niche (Soberón 2007; Soberón & Nakamura 2009). For simplicity, we use the term “climatic niche” here to refer to the realized niche. All analyses were conducted using R packages ade4 (Dray & Dufour 2007) and subniche (Karasiewicz 2016). Estimating evolutionary rates To estimate rates of body size and niche evolution across tetrapods, we used BAMM v2.5.0 (Bayesian Analysis of Macroevolutionary Mixtures; Rabosky 2014), a framework that is robust and has been widely used in recent macroevolutionary studies (Barreto et al. 2023; Cooney & Thomas 2021; Moreira et al. 2024). Analyses were implemented in the R package BAMMtools (Rabosky et al. 2014) to set priors and plot results. Imputation can affect trait-based analyses (see in Rabosky 2015), and because some species in these phylogenies are placed using taxonomic rather than genetic information, their exact placement carries inherent uncertainty. To mitigate this, we incorporated phylogenetic uncertainty by analyzing multiple plausible topologies. For each tetrapod group, we randomly selected 10 phylogenetic trees of the posterior distribution to balance replication with computational feasibility and ran BAMM separately on each tree using observed body size data, climatic niche position (OMI), and breadth (Tol). MCMC convergence and effective sample sizes were assessed using the R package coda (Plummer et al. 2006), retaining runs with an effective sample size (ESS) > 200 for key parameters (Table S3). Species-specific evolutionary rates were then calculated as the median across the 10 runs. In addition, we summarized the temporal dynamics of evolutionary rates by computing the median and standard deviations from rate-through-time curves obtained with BAMM analyses, providing an overview of how body size and climatic niche evolution changed across the phylogenetic timescale. Analytical workflow is detailed in Fig. 2. Figure 2. Overview of the analytical workflow from variables to phylogenetic path analysis. (1–3). (1) Evolutionary rates of body size were estimated using body length (amphibians, squamates) and body mass (birds, mammals). (2) Evolutionary rates of climatic niches (position and breadth in climatic space) were obtained using Outlying Mean Index (OMI) based on the spatial distribution of terrestrial vertebrates and bioclimatic variables, after VIF selection. (3) For both body size and climatic niche, evolutionary rates (σ²) were estimated with Bayesian Analysis of Macroevolutionary Mixtures (BAMM) and summarized as the median of 10 phylogenetic trees to account for uncertainty (gray rectangle). To inform each species’ microhabitat use, we used a verticality index, scoring each species according to its predominant microhabitat use: 0 = strictly fossorial, 0.25 = fossorial and terrestrial, 0.5 = terrestrial or aquatic, 0.75 = terrestrial and arboreal, and 1 = strictly arboreal or aerial. All these variables were used as input for the phylogenetically adjusted path analyses to assess the directional relationships among body size evolution, climatic niche, and microhabitat use. Phylogenetic path analysis We evaluated alternative causal hypotheses specifically designed to test the predictions of Adaptive Landscape Theory (ALT) and Niche Construction Theory (NCT), using phylogenetic path analysis implemented in the phylopath R package (van der Bijl 2018). This framework allows an explicit comparison of alternative causal models while accounting for shared ancestry and differences in predictor availability among clades. Before the analysis, we log-transformed all variables to reduce skewness and scaled them to have a mean of 0 and a standard deviation of 1, allowing for direct comparison of their effect sizes. We assessed multicollinearity among predictors using Variance Inflation Factor (VIF) analysis, confirming that all variables included in the models had VIF values below 2, indicating low multicollinearity (Table S4). We specified four a priori models describing the causal direction among niche breadth, niche position, body size evolutionary rates, and verticality, differing in terms of which variable was treated as the response in the model. For each of the four models with response variables (A: body size rate, B: niche position, C: niche breadth, V: verticality), we specified eight variants differing in the direction of causality, testing both direct and indirect effects among predictors, totaling 32 alternative models (Fig. S3), besides a null model. We assessed model fit using Shipley’s test of d-separation (Fisher’s C), and competing models were compared using the C-statistic Information Criterion corrected for small sample size (CICc). We ranked models using CICc and model weights. Because several models showed substantial support (Fig. S4), we applied model averaging (conditional averaging for models with CICc ≤ 2) to obtain mean coefficients. All models estimated phylogenetic autocorrelation using Pagel’s lambda. Results We found high heterogeneity in evolutionary rates for body size, climatic niche position, and niche breadth across suborders of terrestrial vertebrates (Figs 3-4). When comparing Sister Ranoidae to other anuran lineages, this clade shows rates approximately 2–7 times higher. Salamanders and newts (Caudata) also display higher rates of body size evolution, approximately 1,5–5 times higher than those of most amphibian clades, although still roughly one third lower than the exceptionally high rates of Sister Ranoidae. Within squamates, snakes (Serpentes) exhibit the highest rates of body size evolution, approximately 1,7–5 times higher than those of other lizard clades. Among birds, non-flying and terrestrial species, such as ostriches (Struthioniformes), kiwis (Apterygiformes), cassowaries, and emus (Casuariiformes), exhibit the highest body size evolutionary rates, about 1–2 times higher than those of volant lineages. In mammals, the highest rates of body size evolution occur in elephants and their relatives (Proboscidea), 9–18 times higher than those of other clades. Notably, the clades with the highest rates of climatic niche position evolution were distinct from those with the highest rates of climatic niche breadth evolution (Figs. S5-S6), reinforcing complex and heterogeneous patterns for evolutionary rates across tetrapods. Analysis of rates through time revealed that the Cretaceous-Paleogene (K–Pg) transition marked a generalized acceleration in rates of body size and climatic niche evolution across all tetrapod groups, although specific patterns varied among clades (Fig. 5). In amphibians, rates of climatic niche evolution remained consistently higher than those of body size, suggesting that phenotypic changes accompanied the expansion into new climatic regimes. In squamates, rates of climatic niche and body size evolution accelerated in a synchronized manner over time, indicating a strong coupling between morphological diversification and the exploration of new niches. However, both amphibians and squamates show a slowdown in more recent lineages. In birds, we observed an initial simultaneous peak in body size and niche position rates, followed by a slowdown in evolutionary rates of body size that coincides with an increase in the rate of niche breadth expansion. In mammals, we detected a pronounced acceleration in body size rates that clearly precedes the peak acceleration in climatic niche expansion. Across terrestrial vertebrates, we found clade-dependent support for both the Adaptive Landscape Theory (ALT) and the Niche Construction Theory (NCT). In amphibians, climatic niche position was the main driver of body size evolution, supporting ALT (Fig. 6A). In contrast, in squamates, body size evolution more strongly influenced changes in climatic niche position than the reverse, suggesting that phenotypic change can be a primary driver of climatic niche evolution in this group (Fig. 6B). Birds and mammals exhibited strong bidirectional effects between body size and niche position, indicating reciprocal feedback, supported by NCT (Fig. 6 C-D). Patterns involving climatic niche breadth also varied across clades. In squamates, birds, and mammals, body size evolution had a stronger effect on niche breadth than the reverse, suggesting that body size evolution facilitates niche expansion in these groups. Conversely, in amphibians, climatic niche breadth had a more pronounced influence on body size evolution. However, reciprocal feedback was also evident, indicating that they are more responsive to climatic constraints and environmental variability. In contrast to climate, verticality played a secondary role in the evolutionary dynamics of terrestrial vertebrates (Fig. 6). Its effects were mixed and clade specific. Verticality was constrained by body size evolution in amphibians. On the other hand, verticality itself accelerated the evolution of climatic niche position in mammals. not-yet-known not-yet-known not-yet-known unknown Figure 3. Phylogenetic trees showing evolutionary rates (log-transformed) for amphibians and squamates. The inner heatmap (adjacent to the tree) depicts the evolutionary rate of body size, followed by niche position in the mid position, and the outer heatmap depicts the evolutionary rate of climatic niche breadth. In all cases, lower values are shown in blue and higher values in yellow. Figure 4. Phylogenetic trees showing evolutionary rates (log-transformed) for birds and mammals. Tip colors represent the body size evolutionary rate. The inner heatmap (adjacent to the tree) depicts the evolutionary rate of body size, followed by niche position in the mid position, and the outer heatmap depicts the evolutionary rate of climatic niche breadth. In all cases, lower values are shown in blue and higher values in yellow. Figure 5. Median evolutionary rates (lines) and their standard deviations (shaded areas) for body size (orange), climatic niche position (blue), and climatic niche breadth (green) over time. Rates and uncertainties were estimated from 10 phylogenetic trees for each vertebrate group: amphibians (top left), squamates (top right), birds (bottom left), and mammals (bottom right). To enable relative comparisons across groups, the y-axis ranges from zero to the maximum median rate among all groups, and the x-axis is expressed in million years. Geological periods are shown using colors and abbreviations following the International Chronostratigraphic Chart (ICS): P = Paleozoic, Tr = Triassic, J = Jurassic, K = Cretaceous, Pg = Paleogene, and Ng = Neogene. Figure 6. Causal models corrected for phylogenetic autocorrelation for each group of terrestrial vertebrates (A. Amphibians; B. Squamates; C. Birds; D. Mammals). Changes in climatic niche position were the main predictor of body size evolution and climatic niche breadth; in birds and squamates, a reciprocal cycle is observed between changes in body size and increases in niche breadth, whereas verticality shows only a secondary effect across all groups. Arrows indicate directional effects between variables; arrow thickness is proportional to effect size, and numbers next to arrows represent standardized coefficients. The displayed coefficients correspond to the mean of models with cCIC < 2. Blue indicates a positive effect, red indicates a negative effect, while gray indicates a non-significant effect. Discussion We demonstrated that shifts in climatic niche position were the primary driver of body size evolution across terrestrial vertebrates, consistent with the Adaptive Landscape Theory (ALT, Simpson, 1944; 1953). Yet the pathways of change are distinctly shaped by class-specific physiology and ecology, with support for Niche Construction Theory (NCT, Odling-Smee 2024; Quintero 2025) in birds and mammals, and to a lesser extent, in squamates. This reflects a reciprocal causation in which innovation in body size not only responds to climatic shifts but also opens ecological opportunities for further niche exploration (Quintero 2025). Amphibians showed a weaker effect of body size on niche expansion toward extreme climates, whose body size appears mostly shaped by climatic conditions, which is a prerequisite for surviving under new climates (Lin et al. 2021; Stevens et al. 2014). Although the high heterogeneity in evolutionary rates across tetrapod clades suggests that distinct ecological strategies play a role in shaping evolutionary dynamics, we observed only a secondary role of verticality. Our findings establish a robust, cross-taxon link between rapid climatic niche evolution and accelerated body size change. While fast climatic niche evolution has been correlated with vertebrate diversification (Castro-Insua et al. 2018; Cooney et al. 2016; Kozak & Wiens 2010; Moreira et al. 2024), we demonstrate that shifts in climatic niche position accelerate body size changes. This implies that shifts into extreme climatic conditions impose direct selective pressures on body size. Species colonizing harsh environments (e.g., highlands, arid zones, or cold climates) may evolve phenotypic adaptations more rapidly relative to their counterparts (Clavel & Morlon 2017; Cooper & Purvis 2010; Lawson & Weir 2014), leading to an expansion of the occupied climate space. This coupling between climatic niche and morphological evolution, also observed in Saxifragales plants (Folk et al. 2019), may represent a shared macroevolutionary pattern for terrestrial organisms. A key next step is to determine whether this niche expansion was driven by dispersal to new areas or by phenotypes that enabled the exploitation of new climatic space within ancestral distributions. Although the relationship between niche position and breadth is well established in vertebrates (Moreira et al. 2024; Pie et al. 2021), here we uncover its directionality relationship. In endotherms and squamates, this evolutionary feedback between body size and niche position can be viewed as an “active” process of niche construction. The high dispersal capacity of endotherms (Rodrigues & Botero 2025; Stevens et al. 2014) and behavioral flexibility of squamates (e.g., thermoregulation, Rivera-Rea et al. 2023) allow phenotypic innovations to directly facilitate the exploration of novel climates, thereby increasing geographic range and environmental tolerance (Rodrigues & Botero 2025), which creates a feedback loop that drives further phenotypic change (Odling-Smee et al. 2013; Odling-Smee 2024; Quintero 2025). However, evolutionary feedback may be stronger between clades with a high capacity for dispersal, such as birds and mammals. Amphibians, with their strict physiological requirements and dispersal abilities, sit closer to the “passive” end of this spectrum, in which body size evolution primarily reflects shifts in climatic niche position (Lin et al. 2021; Stevens et al. 2014). This gradient of “passive” to “active” evolution highlights that organisms are not merely subjects of environmental filtering, but can, to varying degrees (Rodrigues & Botero 2025; Rolland et al. 2018; Weaver et al. 2020), modulate their own selective pressures. Analyses of rates through time indicate that the Cretaceous–Paleogene (K–Pg) transition triggered a synchronized pulse of accelerated evolution in body size and climatic niche across terrestrial vertebrates, highlighting the macroevolutionary coupling of these traits. Our findings align with previous studies identifying the K–Pg as a critical period in the evolutionary history of vertebrates, as the mass extinction profoundly reshaped ecosystems and opened new ecological opportunities (Clavel & Morlon 2017; Ksepka et al. 2017; Procheş et al. 2014; Roelants et al. 2007). However, responses to the event appear to vary in a clade-dependent manner. Based on fossil evidence from mammals, some lineages experienced substantial diversification, whereas others faced intensified extinction rates (Pires et al. 2018). Similarly, the intensity and direction of temporal changes between body size and niche differ among clades, with climatic niche evolution primarily driving body size change in amphibians, whereas in birds these changes appear synchronous, patterns corroborated by our structural equation modeling results. Although our analyses focus primarily on extant taxa, future studies incorporating more complete paleontological and paleoclimatic data will help refine these macroevolutionary rate estimates. The marked heterogeneity in evolutionary rates among suborders aligns with the well-documented influence of ecological traits on evolutionary tempo (Rodrigues & Botero 2025; Rolland et al. 2018; Weaver et al. 2020). For instance, large-sized vertebrates tend to exhibit higher rates of phenotypic evolution than small-sized ones (Caron & Pie 2024). Similarly, the greater thermal tolerance of endotherms is often associated with faster climatic niche evolution relative to ectotherms (Rolland et al. 2018). Herein, we found that rapid body size evolution in amphibians restricts behavioral and ecological options, such as verticality. Indeed, arboreal microhabitats require highly specialized morphology, imposing stronger limits on body size evolution and constraining habitat use in vipers (Alencar et al. 2017). Similar patterns are observed in some lizards, in which terrestrial lineages have evolved to extremely large sizes, and those living on rocks have become very small (Collar et al. 2011). The same is likely true for frogs and toads, in which very large frogs may be restricted to non-arboreal environments. In mammals, verticality promotes faster niche position evolution. By enabling active relocation across environmental gradients, verticality allows transitions between environments that modify selective pressures and accelerate changes in climatic niche position (Huang et al. 2022; Lapiedra et al. 2013), consistent with the Niche Construction Theory. We have demonstrated that shifts in climatic niche position are the primary driver of both body size and climatic niche breadth evolution. We also identified a bidirectional relationship between body size and climatic niche, allowing bidirectional evolutionary dynamics that can ultimately expand ecological opportunities in groups with either high vagility or behavioral flexibility. While both ALT and NCT are applicable, their relative influence is shaped by group-specific differences in physiology and ecology. Interactions between morphological innovation and climate shifts across lineages can increase speciation rates and drive adaptive radiation, as novel traits enable lineages to overcome environmental barriers and persist in changing environments (Barreto et al. 2023; Cooney et al. 2016). While studies have shown microhabitat use can explain differences in evolutionary rates at finer taxonomic scales (Alencar et al. 2017; Collar et al. 2011), our analyses reveal it to be a weak predictor of body size and climatic niche evolution at the scale of terrestrial vertebrates. As diversification is often linked to the pace of trait change rather than its absolute value (e.g., Barreto et al. 2023), treating verticality as static likely masks its dynamic evolutionary role, highlighting the need to incorporate temporal trait variation in macroevolutionary analyses. Other unmeasured ecological traits may also explain heterogeneous evolutionary rates at a broad taxonomic scale (e.g., Huang et al. 2022; Weaver et al. 2020). Acknowledgements ─ We would like to thank Renan Maestri, Thais B. Guedes, and Gabriel Nakamura for their constructive comments during the development of this manuscript. This study was funded in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Finance Code 001. MTM was supported by a postdoc fellowship from São Paulo Research Foundation (FAPESP) (#2023/14506-5; #2024/22798-9) during the writing and analysis phase of this study. 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Evolution , 74, 1804–1814. Information & Authors Information Version history V1 Version 1 24 November 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords adaptive landscape eco-evolutionary processes evolutionary dynamics macroecology macroevolution niche-trait relationship phenotypic evolution phylogenetic comparative methods tetrapods trait evolution Authors Affiliations Matheus de T. Moroti 0000-0002-2645-9130 [email protected] Universidade Estadual de Campinas View all articles by this author Mario Moura 0000-0002-7369-7502 Universidade Federal da Paraiba View all articles by this author Mathias Pires 0000-0003-2500-4748 Universidade Estadual de Campinas View all articles by this author Diogo Provete 0000-0002-0097-0651 Universidade Federal de Mato Grosso do Sul View all articles by this author Metrics & Citations Metrics Article Usage 390 views 199 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Matheus de T. Moroti, Mario Moura, Mathias Pires, et al. Divergent pathways shape climatic niches and body size evolution across terrestrial vertebrates. Authorea . 24 November 2025. DOI: https://doi.org/10.22541/au.176400956.64170283/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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