Evolutionary Biology最新文献

The goal of evolutionary biology is to explain the diversity of the entire sweep of the natural world; population biology only examines tiny slices of time of a few individuals of single species. What gives the tiny scale of population biology its relevance to evolutionary biology is the following assumption: processes identical or similar to those observed in a given population biology study are operative in unexamined individuals in the same species, have been operative throughout the history of the species, and are operative in other species. Without this assumption, population biology studies are just very detailed descriptions of a handful of individuals of a species. Population biology lacks the means to test its jusifying assumption. It is tested by the comparative method, studies of convergent evolution across species. The comparative method has its own blind spots, mainly its inability to examine intraspecific variation, heritability, and fitness directly, exactly the purview of population biology. Population and comparative biology thus provide complementary sources of direct evidence regarding evolutionary process. Both, along with optimality models, evo-devo studies of the variants that can or can’t be produced in development, together with assumptions about unseeable ancestral populations, make up essential parts of a maximally well-supported evolutionary explanation. Recognizing this essential epistemic interdependence shows why it is necessary to select sources of evidence from across population, comparative, optimality, and developmental studies, leading to collaboration rather than criticism across these fields, and stronger explanations accounting for the evolution of diversity in organismal form and function.

Measurement error is present in all quantitative studies, and ensuring proper biological inference requires that the effects of measurement error are fully scrutinized, understood, and to the extent possible, minimized. For morphometric data, measurement error is often evaluated from descriptive statistics that find ratios of subject or within-subject variance to total variance for a set of data comprising repeated measurements on the same research subjects. These descriptive statistics do not typically distinguish between random and systematic components of measurement error, even though the presence of the latter (even in small proportions) can have consequences for downstream biological inferences. Furthermore, merely sampling from subjects that are quite morphologically dissimilar can give the incorrect impression that measurement error (and its negative effects) are unimportant. We argue that a formal hypothesis-testing framework for measurement error in morphometric data is lacking. We propose a suite of new analytical methods and graphical tools that more fully interrogate measurement error, by disentangling its random and systematic components, and evaluating any group-specific systematic effects. Through the analysis of simulated and empirical data sets we demonstrate that our procedures properly parse components of measurement error, and characterize the extent to which they permeate variation in a sample of observations. We further confirm that traditional approaches with repeatability statistics are unable to discern these patterns, improperly assuaging potential concerns. We recommend that the approaches developed here become part of the current analytical paradigm in geometric morphometric studies. The new methods are made available in the RRPP and geomorph R-packages.

Interspecific hybridization has been historically neglected in research and conservation practice, but it is a common phenomenon in nature, and several models have been developed to characterize it genetically. Even though Trichechus inunguis (Amazonian manatee) and T. manatus (West Indian manatee) exhibit large morphological, karyotypic, and molecular differences, a hybrid zone was identified on the northern coast of South America, from the Amazon River estuary toward the Guianas coastline. Two major populations or evolutionarily significant units (ESUs) within T. manatus, namely, the Caribbean and Atlantic, were separated and their differentiation was likely promoted or reinforced by the interspecific hybridization zone. We used nuclear and mtDNA sequences to reconstruct manatee speciation, population diversification through time and space, and secondary contact, which resulted in a hybrid zone. In this hybrid zone, the genetic contribution of each parental species was estimated, and different models for generating the current scenario were tested using statistical phylogeographic tools. All the results suggest a long hybridization history, during which a stable and structured hybrid swarm is generated. The coastline hybrid zone is composed of individuals with a lesser genomic contribution from T. inunguis; this zone works as a genetic sink that restricts gene flow between neighbouring Atlantic (Brazil) and Caribbean (all others) T. manatus populations, which further reinforces the isolation and differentiation of the Brazilian manatees.

Two macroecological and evolutionary rules are strongly related to the body size of organisms: Bergmann’s and Rensch’s rules. Bergmann’s rule states that organisms are larger in colder regions (high latitudes). Rensch’s rule states that sexual size dimorphism increases when males are larger. Organisms with widespread distribution and resource-mediated growth—such as hermit crabs and their gastropod shells—become excellent models for investigating these patterns. This study is the first to address macroecological and evolutionary patterns in body size among populations and also among sex of the three species of hermit crabs of the genus Clibanarius: C. antillensis, C. sclopetarius and C. symmetricus throughout their distribution. This research included systematic review of data from specialized literature along with primary data by traditional morphometrics of intersexual and populational average body size of the three different species. Regression models were designed to assess the rules separately and altogether. We have observed that the three species of Clibanarius showed interpopulational clines consistent with Bergmann’s rule. Surprisingly, our findings showed a gender-specific divergence from females as a response to latitudinal gradients, suggesting that latitude (as a proxy) increased the interpopulational body effect only in females. We suggest that phenotypic plasticity due to decreased selective pressure with higher latitude (decreased temperature) and greater productivity may affect the bias of these rules. Our data also suggest that female body size variation is modulated by the selection of fecundity in body size.

The ability of wildlife to endure the effects of high temperatures is increasingly important for biodiversity conservation under climate change and spreading urbanization. Organisms living in urban heat islands can have elevated heat tolerance via phenotypic or transgenerational plasticity or microevolution. However, the prevalence and mechanisms of such thermal adaptations are barely known in aquatic organisms. Furthermore, males and females can differ in heat tolerance, which may lead to sex-biased mortality, yet it is unknown how sex differences in thermal biology influence urban phenotypic divergence. To address these knowledge gaps, we measured critical thermal maxima (CT_max) in male and female agile frog (Rana dalmatina) tadpoles captured from warm urban ponds and cool woodland ponds, and in a common-garden experiment where embryos collected from both habitat types were raised in the laboratory. We found higher CT_max in urban-dwelling tadpoles compared to their counterparts living in woodland ponds. This difference was reversed in the common-garden experiment: tadpoles originating from urban ponds had lower CT_max than tadpoles originating from woodland ponds. We found no effect of sex on CT_max or its difference between habitats. These results demonstrate that aquatic amphibian larvae can respond to the urban heat island effect with increased heat tolerance similarly to other, mostly terrestrial taxa studied so far, and that phenotypic plasticity may be the main driver of this response. Our findings also suggest that heat-induced mortality may be independent of sex in tadpoles, but research is needed in many more taxa to explore potentially sex-dependent urban thermal responses.

The original exposition of the method of “Cartesian transformations” in D’Arcy Thompson’s On Growth and Form (1917) is still its most cited. But generations of theoretical biologists have struggled ever since to invent a biometric method aligning that approach with the comparative anatomist’s ultimate goal of inferring biologically meaningful hypotheses from empirical geometric patterns. Thirty years ago our community converged on a common data resource, samples of landmark configurations, and a currently popular biometric toolkit for this purpose, the “morphometric synthesis,” that combines Procrustes shape coordinates with thin-plate spline renderings of their various multivariate statistical comparisons. But because both tools algebraically disarticulate the landmarks in the course of a linear multivariate analysis, they have no access to the actual anatomical information conveyed by the arrangements and adjacencies of the landmark locations and the distinct anatomical components they span. This paper explores a new geometric approach circumventing these fundamental difficulties: an explicit statistical methodology for the simplest nonlinear patterning of these comparisons at their largest scale, their fits by what Sneath (1967) called quadratic trend surfaces. After an initial quadratic regression of target configurations on a template, the proposed method ignores individual shape coordinates completely. Those have been replaced by a close reading of the regression coefficients, accompanied by several new diagrams, of which the most striking is a novel biometric ellipse, the circuit of the trend’s second-order directional derivatives around the data plane. These new trend coordinates, directly visualizable in their own coordinate plane, do not conduce to any of the usual Procrustes or thin-plate summaries. The geometry and algebra of the second-derivative ellipses seem a serviceable first approximation for applications in evo-devo studies and elsewhere. Two examples are offered, one the classic growth data set of Vilmann neurocranial octagons and the other the Marcus group’s data set of midsagittal cranial landmarks over most of the orders of the mammals. Each analysis yields intriguing new findings inaccessible to the current GMM toolkit. A closing discussion suggests a variety of ways by which innovations in this spirit might burst the current straitjacket of Procrustes coordinates and thin-plate splines that together so severely constrain the conversion of landmark locations into biological understanding. This restoration of a quantitative diagrammatic style for reporting effects across regions and gradient directions has the potential to enrich landmark-driven comparisons over either developmental or phylogenetic time. Extension of the paper’s quadratic methods to the next polynomial degree, cubics, probably won’t prove generally useful; but close attention to local deviations from globally fitted quadratic trends, however, migh

Body size is a pivotal ecological and evolutionary trait, as it can significantly impact both survival and reproductive success. To understand how human-mediated disturbances influence body size, we conducted a temporal analysis of body mass index (BMI) variations in 2788 individuals spanning six South American rodent species to describe their seasonal and yearly fluctuations between 2005 and 2009. Additionally, we used microsatellite genotyping to estimate genetic pedigrees for individuals from two of these species (Akodon azarae and Calomys musculinus). This enabled us to dissect the phenotypic variation of body size, offering insights into the evolutionary dynamics of that variation. We report significant increments of BMI across years in three species (A. azarae, Calomys venustus, and Oxymycterus rufus). In addition, we observed moderate and similar levels of narrow-sense heritability in A. azarae and C. musculinus, suggesting that part of the variation in this trait is attributable to additive genetic effects. Furthermore, the phenotypic variance, additive genetic variance, and evolvability of BMI were higher in C. musculinus when compared to A. azarae. These findings suggest that BMI in C. musculinus has the potential to exhibit a more rapid response to equivalent selection pressures than in A. azarae. The heritability and evolvability values also imply that the annual changes in BMI may be influenced, at least in part, by natural selection, probably in response to shifting environmental conditions within intensively managed agroecosystems. However, a long-term study is necessary to understand and predict the role of selection in the evolutionary dynamics of body size variation among rodents inhabiting agroecosystems.

The huge antlers of the extinct Irish elk have invited evolutionary speculation since Darwin. In the 1970s, Stephen Jay Gould presented the first extensive data on antler size in the Irish elk and combined these with comparative data from other deer to test the hypothesis that the gigantic antlers were the outcome of a positive allometry that constrained large-bodied deer to have proportionally even larger antlers. He concluded that the Irish elk had antlers as predicted for its size and interpreted this within his emerging framework of developmental constraints as an explanatory factor in evolution. Here we reanalyze antler allometry based on new morphometric data for 57 taxa of the family Cervidae. We also present a new phylogeny for the Cervidae, which we use for comparative analyses. In contrast to Gould, we find that the antlers of Irish elk were larger than predicted from the allometry within the true deer, Cervini, as analyzed by Gould, but follow the allometry across Cervidae as a whole. After dissecting the discrepancy, we reject the allometric-constraint hypothesis because, contrary to Gould, we find no similarity between static and evolutionary allometries, and because we document extensive non-allometric evolution of antler size across the Cervidae.

Components of the same structure or characters of the same individual might respond differently to natural and sexual selective pressures, showing complex morphological patterns. Besides, studying interactions between species plays a crucial role in understanding the diversification of sex-linked phenotypes. Specifically, when two closely related species coexist and exhibit interspecific sexual interactions (reproductive interference—IR), key traits for mating can diverge in sympatric areas to prevent interbreeding and ensure reproductive isolation (reproductive character displacement—RCD). RCD is primarily driven by natural selection, although sexual selection pressures can alter the pattern of phenotypic variation. Additionally, to gain a comprehensive understanding of the patterns of morphological diversification, it is essential to consider changes related to phenotypic plasticity across environmental gradients. To date, there are no studies evaluating this topic in scorpions, and two sympatric species (Urophonius brachycentrus and U. achalensis) with RI, provide an ideal model for evaluating phenotypic variation across environmental gradients and the presence of RCD. In this study, we compared intra-specific variation, as well as the size and shape of multiple characters involved in courtship and sperm transfer, between individuals from sympatric and allopatric populations using geometric morphometrics. Our findings revealed an increase in the size of various characters at lower temperatures (higher altitudes) for U. brachycentrus, making them more similar to heterospecifics in sympatric areas, resulting in a pattern of morphological convergence between these species. Increased similarity between species combined with a scramble competition mating system could intensify sexual selection pressures on particular characters. Furthermore, we identified asymmetric RCD in the shape of several sexual characters crucial for mating success (grasping structures) and sperm transfer (genital characters), which could potentially be significant for mechanical isolation during interspecific interactions. Our results highlight significant morphological variability in the size and shape of somatic and genital characters in two scorpion species. This variability may reflect different evolutionary responses, driven in part by natural selection pressures associated with geographic and environmental variations and species recognition mechanisms, and in part by sexual selection pressures at both the intra- and interspecific levels. This comprehensive study reveals the complexity of evolving multifunctional traits in an understudied model and offers valuable insights into traits subject to multiple selective pressures in animal systems experiencing RI.

Adaptive radiations garner considerable interest from evolutionary biologists. Lizard radiations diversifying along structural niche space often exhibit distinct changes in body and limb proportions. One prediction is that terrestrial species inhabiting open habitats will have relatively longer hindlimbs, associated with faster running speeds, while scansorial species will have relatively shorter limbs to keep the centre of mass closer to the substratum. Alternatively, terrestrial species in densely vegetated habitats could benefit from relatively shorter limbs to prevent entanglement with more frequently encountered obstacles, whereas scansorial species could benefit from longer limbs promoting greater limb spans and static stability. Cyrtodactylus, an ecologically diverse gekkonid genus, includes numerous specialists with narrow structural niches, but the degree of morphological diversification exhibited by these specialists is largely unknown. We investigated associations between locomotor morphology and structural microhabitat use in Cyrtodactylus to test if either of the opposing predictions can be corroborated for this radiation. We measured body length and relative limb dimensions of 87 species, covering multiple independent transitions among structural microhabitat preferences. Using these data, we reconstructed the phylomorphospace and tested for associations between structural microhabitat niche and limb morphology. We found strong separation between structural niche groups in accordance with the second hypothesis, although overlap is evident among functionally related niches such as those of granite and karst specialists.