Developmental integration cannot explain major features of stomatal anatomical evolution in seed plants

Developmental integration can cause traits to covary over macroevolutionary time and in some cases prevent populations from reaching their adaptive optima. Developmental integration between stomatal size and density may contribute to two major features of stomatal anatomical evolution: inverse size-density scaling and bimodal stomatal ratio. If these patterns result from developmental integration, we predicted that in amphistomatous leaves 1) stomatal size and density should covary similarly on both abaxial and adaxial surfaces and 2) stomatal traits (size and density) on each surface should covary isometrically. We synthesized data on stomatal density and length from amphistomatous leaves of 711 terrestrial seed plant taxa mostly from the literature. We estimated the covariance in divergence between stomatal traits from 327 phylogenetically independent contrasts using a robust Bayesian model. Adaxial stomatal density, but not length, is evolutionarily labile and not strongly integrated with stomatal length or abaxial stomatal density. Hence, developmental integration alone cannot explain inverse size-density scaling nor bimodal stomatal ratio. Quasi-independent evolution of stomatal anatomical traits facilitates largely unfettered access to fitness optima. If stomatal anatomical traits are near their current fitness optimum, this implies that limits on trait (co)variance result from selective rather than developmental constraints. However, we cannot rule out that developmental integration is important in some lineages. Future research should identify the mechanistic basis of(dis)integration in stomatal development.

Correlated evolution of leaf and root anatomic traits in Dendrobium (Orchidaceae)

The whole-plant economic spectrum concept predicts that leaf and root traits evolve in coordination to cope with environmental stresses. However, this hypothesis is difficult to test in many species because their leaves and roots are exposed to different environments, above- and below-ground. In epiphytes, both leaves and roots are exposed to the atmosphere. Thus, we suspect there are consistent water conservation strategies in leaf and root traits of epiphytes due to similar selection pressures. Here, we measured the functional traits of 21 species in the genus Dendrobium, which is one of the largest epiphytic taxa in the family Orchidaceae, and used phylogenetically independent contrasts to test the relationships among traits, and between traits and the environment. Our results demonstrate that species with a thicker velamen tended to have thicker roots, a thicker root cortex and vascular cylinder, and a larger number of vessels in the root. Correspondingly, these species also had higher leaf mass per area, and thicker leaf lower cuticles. Leaf and root traits associated with water conservation showed significantly positive relationships. The number of velamen layers, leaf density and the ratio of vascular cylinder radius to root radius were significantly affected by the species’ differing environments. Thus, traits related to water conservation and transport may play an important role in helping Dendrobium cope with the cool and dry conditions found at high elevations. These findings confirmed the hypothesis that leaf and root traits have evolved in coordination, and also provide insights into trait evolution and ecological adaptation in epiphytic orchids.

First evidence for a latitudinal body mass effect in extant Crocodylia and the relationships of their reproductive characters

Relationships between distribution patterns and body size have been documented in many endothermic taxa. However, the evidence for these trends in ectotherms generally is equivocal, and there have been no studies of effects in crocodylians specifically. Here, we examine the relationship between latitudinal distribution and body mass in 20 extant species of crocodylians, as well as the relationships between seven important reproductive variables. Using phylogenetically independent contrasts to inform generalized linear models, we provide the first evidence of a latitudinal effect on adult female body mass in crocodylians. In addition, we explore the relationships between reproductive variables including egg mass, hatchling mass and clutch size. We report no correlation between egg mass and clutch size, upholding previously reported within-species trends. We also find no evidence of a correlation between measures of latitudinal range and incubation temperature, contrasting with the trends found in turtles.

Freshwater-to-marine transitions may explain the evolution of herbivory in the subgenus Mollienesia (genus Poecilia, mollies and guppies)

The ability of organisms to cross ecosystem boundaries is an important catalyst of evolutionary diversification. The genus Poecilia (mollies and guppies) is an excellent system for studying ecosystem transitions because species display a range of salinity and dietary preferences, with herbivory concentrated in the subgenus Mollienesia. We reconstructed ancestral habitats and diets across a phylogeny of the genus Poecilia, evaluated diversification rates and used phylogenetically independent contrasts to determine whether diet evolved in response to habitat transition in this group. The results suggest that ancestors of subgenus Mollienesia were exclusively herbivorous, whereas ancestral diets of other Poecilia included animals. We found that transitions across euryhaline boundaries occurred at least once in this group, probably after the divergence of the subgenus Mollienesia. Furthermore, increased salinity affiliation explained 24% of the decrease in animals in the gut, and jaw morphology was associated with the percentage of animals in the gut, but not with the percentage of species occupying saline habitats. These findings suggest that in the genus Poecilia, herbivory evolved in association with transitions from fresh to euryhaline habitats, and jaw morphology evolved in response to the appearance of herbivory. These results provide a rare example of increased diet diversification associated with the transition from freshwater to euryhaline habitats.

Functional and Phylogenetic Aspect in Modularity of Palearctic Mustelids (Carnivora, Mustelidae) Mandible

Geometric morphometrics was used to investigate morphological integration and modularity in mustelid mandible. A set of 16 two-dimensional landmarks was digitized on the mandibles of 14 extant species of Palearctic Mustelidae (genera Enhydra, Gulo, Meles, Lutra, Martes, Mustela). The original data size-corrected data and phylogenetically independent contrasts (PICs) were analyzed. Several hypotheses were tested: two and three-modules with the masseteric fossa included in corpus or ramus of the mandible. As a result, the two-module hypothesis (subdivision into the alveolar region and the ascending ramus) with masseteric fossa included in corpus for all sets of data was supported. A clear modularity in mustelid mandible is seen at interspecific level, whereas there was large within species covariation between mandibular corpus and ramus. The allometry correction reduces estimates of covariation for the mustelid mandibles. Due to the analysis of PICs the shape changes with maximum evolutionary covariation were found: elongated, sloped backward ramus and thick corpus.

Long-legged bees make adaptive leaps: linking adaptation to coevolution in a plant–pollinator network

Adaptation is evolution in response to natural selection. Hence, an adaptation is expected to originate simultaneously with the acquisition of a particular selective environment. Here we test whether long legs evolve in oil-collecting Rediviva bees when they come under selection by long-spurred, oil-secreting flowers. To quantify the selective environment, we drew a large network of the interactions between Rediviva species and oil-secreting plant species. The selective environment of each bee species was summarized as the average spur length of the interacting plant species weighted by interaction frequency. Using phylogenetically independent contrasts, we calculated divergence in selective environment and evolutionary divergence in leg length between sister species (and sister clades) of Rediviva . We found that change in the selective environment explained 80% of evolutionary change in leg length, with change in body size contributing an additional 6% of uniquely explained variance. The result is one of four proposed steps in testing for plant–pollinator coevolution.

Genomic evidence of bitter taste in snakes and phylogenetic analysis of bitter taste receptor genes in reptiles

As nontraditional model organisms with extreme physiological and morphological phenotypes, snakes are believed to possess an inferior taste system. However, the bitter taste sensation is essential to distinguish the nutritious and poisonous food resources and the genomic evidence of bitter taste in snakes is largely scarce. To explore the genetic basis of the bitter taste of snakes and characterize the evolution of bitter taste receptor genes (Tas2rs) in reptiles, we identifiedTas2rgenes in 19 genomes (species) corresponding to three orders of non-avian reptiles. Our results indicated contractions ofTas2rgene repertoires in snakes, however dramatic gene expansions have occurred in lizards. Phylogenetic analysis of theTas2rs with NJ and BI methods revealed thatTas2rgenes of snake species formed two clades, whereas in lizards theTas2rgenes clustered into two monophyletic clades and four large clades. Evolutionary changes (birth and death) of intactTas2rgenes in reptiles were determined by reconciliation analysis. Additionally, the taste signaling pathway calcium homeostasis modulator 1 (Calhm1) gene of snakes was putatively functional, suggesting that snakes still possess bitter taste sensation. Furthermore, Phylogenetically Independent Contrasts (PIC) analyses reviewed a significant correlation between the number ofTas2rgenes and the amount of potential toxins in reptilian diets, suggesting that insectivores such as some lizards may require moreTas2rs genes than omnivorous and carnivorous reptiles.

Implicaciones de la precipitación sobre la evolución del tamaño corporal y distancia interaxilar en el complejo Aspidoscelis gularis (Squamata: Teiidae)

Life history traits are highly variable attributes that maximize organisms’s adaptation. The relationship of weight and body size with environmental changes and habitat heterogeneity has been documented in previous reports; and size and body shapes are both considered life history attributes that are associated with rainfall, that boost available resources in the environment. While in Aspidoscelis genus, clutch size and relative mass are mainly associated with latitude and altitude, in Aspidoscelis gularis, winter rainfall favors two reproductive seasons, which may determine season variable clutch size. With the aim to study this, samplings were undertaken from May-July 2013, and May-September 2015. A total of 65 individuals lizards of the Southeast clade were obtained, and body length and interaxilar distance measurements were taken; furthermore, hepatic tissue samples were taken for DNA extraction, which allowed us to analyze phylogenetic relationships through a Bayesian Inference analysis, and subsequently, to apply Phylogenetic Comparative Methods (like phylogenetic signal, phylogenetically independent contrasts and reconstruction of ancestral character). Our results showed that there is a low phylogenetic signal regarding body size and shape, while the phylogenetically independent contrasts and reconstruction of ancestral characters suggest that small body sizes are associated to locations with highest rainfall. This can be associated to an establishment of an early sexual maturity, which reflects the maximum size of adults. Furthermore, according to an ANOVA and ANCOVA, there were statistically significant differences in body size and shape respectively, which promote a system for sexual competition for males and a system for fertility in females. These results were important to determine the effect of rainfall on some life history traits, pointing out that lizards of the Southeast clade, belonging to the A. gularis complex were able to face different selection pressures, determined by the environment.

Correlates of ecological-niche diversity and extinction risk of amphibians in China under climate change

In the present study, we measured spatiotemporal properties of ecological niches of amphibians in China and tested the relative importance of various niche-diversity metrics for explaining the evolutionary distinctiveness-weighted extinction risk (EDGE) of amphibian species. We applied the hierarchical partitioning technique on the phylogenetically independent contrasts of the niche covariates and EDGE of amphibians, for the purpose of removing the influence of evolutionary inertia among species. As a comparison, phylogenetic least-square general regression (PLGS) was also conducted. The results showed that EDGE was high for those amphibian species of China identified as Critically Endangered or Endangered on the IUCN Red List. Niche fragmentation dimension (NFD) and niche position (NP) were the top two predictors across partial correlation analyses, hierarchical variation partitioning, PLGS and multiple regression analyses. Most temporal niche properties were not significantly associated with the EDGE index of amphibians. Variation partitioning analysis showed that the spatial component of niche measures explained the largest proportion of total variation in EDGE (~31%), whereas the temporal component of niche properties explained ~8% of the variation. The significantly negative role of NFD and extinction risk of amphibians in China may be attributed to a reduced rescue effect, habitat geometry, and local extinction in species with large and continuous distributional ranges.

Evolutionary patterns of range size, abundance and species richness in Amazonian trees

Amazonian tree species vary enormously in their total abundance and range size, while Amazonian tree genera vary greatly in species richness. Here, we construct a phylogenetic hypothesis that represents half of Amazonian tree genera in order to analyse evolutionary patterns of range size, abundance, and species richness. We find several clear, broad-scale patterns. Firstly, there is significant phylogenetic signal for all three characteristics, i.e. closely related genera tend to have similar numbers of species and similar mean range size and abundance. Additionally, the species richness of genera shows a significant, negative relationship with the mean range size and abundance of their constituent species, while mean range size and abundance are significantly, positively correlated. These correlations are stronger in the raw data, but still significant when using phylogenetically independent contrasts. We suggest that tree stature and/or other phylogenetically related biological traits underlie these results. Lineages comprised of small-statured trees show greater species richness and smaller range sizes and abundances. Lastly, the phylogenetic signal that we evidence for range size suggests that should many small ranged species go extinct, greater phylogenetic diversity may be lost than expected if range size were distributed randomly across the phylogeny.