Biology subjects

Machado, F. A.

Publications and source records attributed to Machado, F. A..

10 recordsLinked to original sources

bioRxiv2026

Conserved covariance structure underlies 60 million years of morphological diversification in primates

Evolvability, the capacity of populations to respond to selection, is shaped by the structure and amount of variation transmitted from generation to generation. Whether the heritable covariance structure itself remains stable or evolves rapidly is a central, yet unresolved, question in phenotypic evolution. Competing hypotheses suggest that trait covariation may be constrained by developmental and genetic architectures or, alternatively, reshaped by persistent directional selection. Here, we test whether covariance structure and evolvability are stable over macroevolutionary timescales by applying a comparative evolutionary quantitative genetics framework on primates. We quantified cranial variation using over ten thousand specimens representing 309 species and compared phenotypic covariance matrices for 57 genera within a Bayesian framework. Our results show that despite extensive morphological divergence, primates show remarkably conserved patterns of variation, modular organization, and capacity to respond to selection. Reconstruction of selection gradients across the primate radiation revealed that selection was highly structured, with preferential directions aligned with major axes of cranial variation. These results suggest that the stability of evolvability does not reflect evolutionary stasis, but rather emerges from the alignment between conserved developmental architecture and selection. Our findings demonstrate that covariance structure and the evolutionary potential it provides can persist over deep evolutionary timescales, providing a mechanistic framework for understanding how developmental systems shape the trajectories of major radiations.

evolutionary biology↗

bioRxiv2026

Sociality Drives Sex Differences in Auditory Brainstem Processing Across Rodent Species

Although social behavior has been predicted to correlate with increased complexity in vocal signals, its relationship with auditory sensitivity between the sexes remains poorly understood. Here, we used phylogenetic comparative analyses to examine sex-specific differences in auditory processing across rodent species representing different social lifestyle strategies. We detected significant sex differences in click and frequency evoked auditory brainstem response (ABR) thresholds across sociality, with social female rodents exhibiting lower thresholds than solitary males. Males generally exhibited higher ABR wave I and IV amplitude ratios than females, whereas interpeak latencies were similar between the sexes across social groups. Females exhibited significantly higher binaural interaction component (BIC) relative amplitudes and faster BIC normalized latencies than males across tested interaural time differences (ITDs). Together, these findings demonstrate that sociality plays an important role in shaping differences in auditory physiology between male and female rodents and highlights the potential influence of social behavior on the evolution of mammalian auditory systems.

physiology↗

bioRxiv2025

Invasion of new adaptive zones retains telltale signs of directional selection at macroevolutionary scales in mammals

Directional selection is often viewed as a transient force in macroevolution, with its signal eroded over time by stabilizing and fluctuating selection. Yet, transitions into new adaptive zones are predicted to impose strong and sustained selective pressures that may leave a detectable signature even across deep timescales. We test this prediction by comparing the rates of multivariate skull morphological evolution required to traverse the boundaries between adaptive zones against genetic drift expectations. Our dataset includes 11,793 specimens spanning 231 species from 12 mammalian clades, each containing unique ecological transitions into new adaptive zones. Using a quantitative genetics framework, we estimated the phenotypic distances between ancestral and derived adaptive zones and contrasted them with null expectations under genetic drift. While a few adaptive zone invasions (e.g., marsupials and rodents) are consistent with drift, most exhibit substantially elevated rates of evolution. These results suggest that directional selection has recurrently shaped mammalian cranial evolution during major ecological shifts. We propose that adaptive zone transitions represent evolutionary contexts in which adaptation leaves a persistent macroevolutionary signal, challenging the prevailing view that long-term patterns are dominated by static forces.

evolutionary biology↗

bioRxiv2025

When morphology stands still: constrained floral evolution in a mega diverse legume genus

O_LIChanges in floral morphology are key for the evolutionary success of flowering plants. However, many species-rich and ecologically diverse groups show low variation in floral traits. Low morphological variation may be associated with selective pressures and constraints to changes. Nonetheless, because our understanding of floral morphological evolution is focused on plant groups with diverse and specialized floral morphology, there has been little progress in identifying factors underlying floral morphological uniformity. C_LIO_LIHerein we addressed this issue by asking whether the morphology of flowers in the mega-diverse legume genus Mimosa is shaped by constraints. By investigating patterns and processes underlying trait variation along floral whorls, we evaluated the role of development and/or function in limiting morphological change. C_LIO_LIOur results showed that floral morphology is remarkably homogeneous and likely shaped by convergent evolution. Morphological variation is unevenly distributed across floral whorls, reflecting differences in the levels of constraints. C_LIO_LIFloral morphology in Mimosa is unlikely to have been primarily driven by pollinator-mediated selection. Instead, we suggest that the development and function of flowers in the mimosoid inflorescence constrained morphological evolution in this megadiverse yet morphologically uniform group. C_LI

evolutionary biology↗

bioRxiv2024

VARIATION IN HEAD AND PINNA MORPHOLOGY OF PRESERVED PEROMYSCUS SPP. SPECIMENS AND IMPLICATIONS FOR AUDITORY FUNCTION

The characteristics of an animals head and pinna mark the beginning of auditory communication. Auditory communication is broadly achieved by receiving sounds from the environment and plays a vital role in an animals ability to perceive and localize sounds. Natural history museums and collections along with their vast repositories of specimens provide a unique resource for examining how the variability in both the size and shape of the head and pinna cause variability in the detection of acoustic signals across species. Using this approach, we measured the dimensions of the head and pinna of over 1,200 preserved specimens of Peromyscus boylii, P. californicus, P. gossypinus, P. leucopus, P. maniculatus, and P. truei, followed by a series of head-related transfer functions (HRTFs) on several individuals to study the relationship between morphology and available auditory information. Our morphological results show significant variation in pinna length and width, as well as in the distance between the two ears across the six species. ITDs and ILDs were calculated and demonstrated consistent results across species, suggesting the differences in head and pinna size do not significantly modify these cues. Not only does this study contribute to existing research on external morphology and auditory function, but it also provides valuable insight into the use of preserved specimens in auditory research, an area that is currently understudied. Summary statementThis work aims to provide insight into using natural history museum specimens for morphological research pertaining to the auditory system in small mammals.

evolutionary biology↗

bioRxiv2024

Rapid adaptive evolution of microbial thermal performance curves

Microbial respiration is a key biotic driver of climate change. Warming boosts microbial population growth, which increases biomass and respiration. This feedback might be disrupted by adaptation in thermal performance curves (TPCs) -whose shape describes how temperature drives growth. In this study, we uncover substantial genetic variation (G) in microbial intrinsic population growth rates (r), demonstrate a causal link between G variation in r and G variation in TPC shape, and show how this variation constrains r-TPC shape evolution along specific evolutionary paths across temperatures. We also uncover Gene-by-Environment (G x E) variation in r, which results in specific signatures in TPC shape and predictable temperature-dependent rapid TPC evolution but also lower G, which could reduce future evolutionary potential. Overall, we show how temperature-dependent evolution in a linchpin of global ecosystem function--microbial TPC shape--is determined by a combination of heritable and non-heritable variation in intrinsic growth rates.

ecology↗

bioRxiv2022

Developmental rules of primate dental evolution align microevolution with macroevolution

Macroevolutionary biologists have classically rejected the notion that higher level patterns of divergence arise through microevolutionary processes acting within populations. For morphology, this consensus partly derives from the inability of quantitative genetics models to correctly predict the behavior of evolutionary processes at the scale of millions of years. Developmental studies (evo-devo) have been proposed to reconcile micro and macroevolution. However, there has been little progress in establishing a formal framework to apply evo-devo models of phenotypic diversification. Here, we reframe this issue by asking if using evo-devo models to quantify biological variation can improve the explanatory power of comparative models, thus helping us bridge the gap between micro- and macroevolution. We test this prediction by evaluating the evolution of primate lower molars in a comprehensive dataset densely sampled across living and extinct taxa. Our results suggest that biologically-informed morphospaces alongside quantitative genetics models allow a seamless transition between the micro and macro scales, while biologically uninformed spaces do not. We show that the adaptive landscape for primate teeth is corridor-like, with changes in morphology within the corridor being nearly neutral. Overall, our framework provides a basis for integrating evo-devo into the modern synthesis, allowing an operational way to evaluate the ultimate causes of macroevolution.

evolutionary biology↗

bioRxiv2021

Morphological integration during postnatal ontogeny: implications for evolutionary biology

How covariance patterns of phenotypes change during development is fundamental for a broader understanding of evolution. There is compelling evidence that mammalian skull covariance patterns change during ontogeny. However, it is unclear to what extent variation in covariance patterns during ontogeny can impact the response to selection. To tackle this question we explored: i) the extent to which covariance patterns change during postnatal ontogeny; ii) in which ontogenetic stages covariance patterns differ the most, and iii) the extent to which the phenotypic covariance pattern at different ontogenetic stages can be explained by the same processes determining additive genetic covariance. We sampled postnatal ontogenetic series for both marsupials, and placentals. Within each ontogenetic series, we compared covariance matrices (P-matrices) at different ontogenetic stages. Furthermore, we compared these P-matrices to two target matrices [adult P-matrix and an additive genetic covariance matrix (G-matrix)]. Our results show that for all ontogenetic series, covariance patterns from weaning onward are conserved and probably shaped by the same processes determining the G-matrix. We conclude that irrespective of eventual differences in how selection operates during most of postnatal ontogeny, the net response to such pressures will probably not be affected by ontogenetic differences in the covariance pattern.

developmental biology↗

bioRxiv2021

The preeminent role of directional selection in generating extreme morphological change in Glyptodonts (Cingulata; Xenarthra)

The prevalence of stasis on macroevolution has been classically taken as evidence of the strong role of stabilizing selection in constraining morphological evolution. Rates of evolution calculated over longer time scales tend to fall below the expected under genetic drift, suggesting that the signal for directional selection is erased at longer time scales. Here we investigated the rates of morphological evolution of the skull in a fossil lineage that underwent extreme morphological modification, the glyptodonts. Contrary to what was expected, we show here that directional selection was the main process during the evolution of glyptodonts. Furthermore, the reconstruction of selection patterns shows that traits selected to generate a glyptodont morphology are markedly different from those operating on extant armadillos. Changes in both direction and magnitude of selection are probably tied to glyptodonts invasion of a specialist-herbivore adaptive zone. These results suggest that directional selection might have played a more important role in the evolution of extreme morphologies than previously imagined.

evolutionary biology↗

bioRxiv2021

Evolution of Drosophila buzzatii wings: Modular genetic organization, sex-biased integrative selection and intralocus sexual conflict

The Drosophila wing is a structure shared by males and females with the main function of flight. However, in males, wings are also used to produce songs, or visual displays during courtship. Thus, observed changes in wing phenotype depend on the interaction between sex-specific selective pressures and the genetic and ontogenetic restrictions imposed by a common genetic architecture. Here, we investigate these issues by studying how the wing has evolved in twelve populations of Drosophila buzzatii raised in common-garden conditions and using an isofemale line design. The between-population divergence shows that sexual dimorphism is greater when sex evolves in different directions. Multivariate Qst-Fst analyses confirm that male wing shape is the target for multiple selective pressures, leading males wings to diverge more than females wings. While the wing blade and the wing base appear to be valid modules at the genetic (G matrix) and among-population (D matrix) levels, the reconstruction of between-population adaptive landscapes ({Omega} matrix) shows selection as an integrative force. Also, cross-sex covariances reduced the predicted response to selection in the direction of the extant sexual dimorphism, suggesting that selection had to be intensified in order to circumvent the limitations imposed by G. However, such intensity of selection was not able to break the modularity pattern of the wing. The results obtained here show that the evolution of D. buzzatii wing shape is the product of a complex interplay between ontogenetic constraints and conflicting sexual and natural selections.

evolutionary biology↗