Evolutionary Biology最新文献

Enteromius Cope, 1867 is a species-rich genus of small cyprinids endemic to Africa, which includes the ‘sawfin barbs’. This study explored the species diversity of this group within the Lake Edward system, including adjacent areas that belong to the Lakes Albert and Victoria systems. We used a multifaceted approach encompassing mitochondrial and nuclear DNA analyses, including a molecular clock analysis, and morphometrics. Additionally, broader regional relationships were investigated by including ‘sawfin barbs’ from other parts of the East Coast ichthyofaunal province and the Nile Basin, and from the Congo Basin, into the molecular analyses. In contrast to the previously reported three species from the Lake Edward system and adjacent areas, the results showed a fourfold increase in the number of species, thereby indicating that the three species actually constituted species complexes. Within these complexes, a consistent geographic pattern unfolded: if one species occurred at higher altitudes of the Lake Edward system, another closely related species occupied lower altitudes near Lakes Edward and George. This geographic consistency suggested an allopatric mode of speciation. Intriguingly, the revealed Pliocene-Pleistocene origin of nearly all species of ‘sawfin barbs’ from the Lake Edward system and neighbouring regions largely predated the important geological events that reshaped the hydrology in the western rift. This study offers a more detailed insight into the evolutionary patterns of the African small barbs representing a very high and unrecognized species diversity, accompanied by little morphological but high genetic divergence between species, indicating intriguingly old species origins.

Plants have different strategies to avoid selfing and buffer its negative consequences on plant fitness. One strategy is the arrangement of petals and the disposition of the reproductive structures (RS) inside the flowers, allowing the development of different pollination mechanisms. In Calceolaria L. species two possible floral phenotypes can be found: short RS protected by the upper corolla lip (nototribic flowers) and long RS resting in the lower corolla lip (sternotribic flowers), the latter being hypothesized to favor selfing.

We selected 13 Calceolaria taxa and characterized their floral phenotype as nototribic or sternotribic, measured RS length and herkogamy, and performed hand-pollination treatments to determine the number of seeds produced by self- and cross-pollination to test whether floral phenotype influences inbreeding. GLMs analysis was performed to determine the differences between the sizes of RS and both floral phenotypes, and LMM was performed to evaluate the relationship between the RS and inbreeding with both floral phenotypes.

We found a relationship between stamen length and herkogamy in both floral phenotypes, where sternotribic flowers have a higher stamen length and lower herkogamy, whereas the opposite occurred in taxa with nototribic morphology. Stamen length significantly influences the inbreeding with sternotribic flowers having a higher inbreeding depression by geitonogamous self-pollination than nototribic ones.

Our results suggest that plants may evolve different reproductive mechanisms to cope with pollination unreliability. Thus, floral phenotype may favor the development of geitonogamy selfing, which may explain the two floral phenotypes present in this specialized oil-secreting genus.

Geometric Morphometrics can be used to describe morphology as a series of coordinates after the effects of variation in translation, rotation, and scale have been removed. This can be further divided into the notion of shape and form, where the latter excludes the scaling procedure from analyses. Dimensionality reduction in Geometric Morphometrics is necessary for the representation of this data into a reduced, more manageable set of dimensions, while preserving as much of the original variation as possible. The purpose of this study is to explore a new means of performing dimensionality reduction on Procrustes landmark data. Here we present a new mathematical model that can be used to enhance dimensionality reduction techniques such as Principal Component Analyses. Integrated into a new R library, the GraphGMM framework uses elements of geometric learning and graph theory to aggregate and embed (project) morphological information from Procrustes coordinates into a new set of transformed coordinates. We validate this model through the use of theoretically constructed, as well as open source, datasets. We finally present a pilot case study using great ape radii to show how these transformed landmarks efficiently capture morphological information, prior to dimensionality reduction, leading to a more efficient construction of a final representation of a morphological coordinate space. Graph-based Geometric Morphometrics thus provides a new insight into the study of morphological patterns, that can be used as an additional source of information in bioanthropological studies.

The environmental transformations associated with cities are expected to affect organisms at the demographic, phenotypic, and evolutionary level, often negatively. The prompt detection of stressed populations before their viability is compromised is essential to understand species’ responses to novel conditions and to integrate urbanization with biodiversity preservation. The presumably stressful conditions of urban environments are expected to affect organisms’ developmental pathways, resulting in a reduction of the efficacy of developmental stability and canalization processes, which can be observed as increased Fluctuating Asymmetry (FA) and Phenotypic Variance (PV), respectively. Here, we investigated whether patterns of phenotypic variation of urban populations of a fully terrestrial salamander, Salamandra salamandra bernardezi, are affected by urban settings compared to surrounding native forest populations. We sampled populations within and around the city of Oviedo (northern Spain) and used geometric morphometrics to compare morphological differentiation, head shape deviance from the allometric slope, PV, and FA. We also compared morphological patterns with neutral genetic and structure patterns. We observed increased levels of differentiation among urban populations and in PV within certain of them, yet no differences in allometric deviance and FA were detected between habitats, and no morphological measures were found to be correlated with genetic traits. Our results do not support a clear negative impact of urban conditions over salamander populations, but rather suggest that other ecological and evolutionary local processes influence morphological variation in this urban system.

Phenotypic change plays diverse roles in species’ colonization, but most invasion studies target single species. To compare ecomorphological changes among co-invading species with overlapping niches, we examined three lizards on the island of O‘ahu (Anolis carolinensis, A. sagrei, Phelsuma laticauda). Using specimens from three decades of unfolding invasions obtained through museum collections and contemporary field work, we quantified shifts in three traits: snout vent length (SVL), forelimb-, and hindlimb-length (limb lengths relative to SVL). We hypothesized that competition among these three species has led to ecological shifts that will be detectable through morphological change. Overall, we found that unique patterns of phenotypic change were both species-specific and sex-specific within species: (1) male A. sagrei, female A. carolinensis, and male P. laticauda increased in SVL and (2) relative hindlimb length increased in female A. carolinensis since the 1980s. The observed changes involve traits that may be consequential to invasion dynamics. This study illustrates how museum- and field-based research can be integrated to document nuanced temporal patterns in the phenotypes of co-invading species that share similar niches in native ranges, raising questions about the underlying process(es) driving species- and sex-specific change in co-invaded systems.

Abstract

Understanding the evolution of evolvability—the evolutionary potential of populations—is key to predicting adaptation to novel environments. Despite growing evidence that evolvability structures adaptation, it remains unclear how adaptation to novel environments in turn influences evolvability. Here we address the interplay between adaptation and evolvability in the peacock fly Tephritis conura, which recently underwent an adaptive change in ovipositor length following a host shift. We compared the evolvability of morphological traits, including ovipositor length, between the ancestral and the derived host race. We found that mean evolvability was reduced in females of the derived host race compared to the ancestral host race. However, patterns of multivariate evolvability (considering trait covariances) were very similar in both host races, and populations of the derived host race had diverged from the ancestral host race in directions of greater-than-average evolvability. Exploration of phenotypic integration patterns further revealed relatively high levels of independent variation in ovipositor length compared to other measured traits, allowing some degree of independent divergence. Our findings suggest that adaptation to novel environments can reduce mean evolvability without major changes in patterns of variational constraints, and that trait autonomy helps facilitate divergence of functionally important traits.

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.