Early evolutionary differentiation of morphological variation in the mandible of South American caviomorph rodents (Rodentia, Caviomorpha)

Caviomorphs are a clade of South American rodents recorded at least since the early Oligocene (> 31.5 Ma) that exhibit ample eco-morphological variation. It has been proposed that phylogenetic structure is more important than ecological factors for understanding mandibular shape variation in this clade. This was interpreted as a result of the long-standing evolutionary history of caviomorphs and the early divergence of major lineages. In this work, we test this hypothesis through the analysis of morphological variation in the mandible of living and extinct species and compare this information with that obtained through comparative phylogenetic analyses. Our results support the hypothesis of early origin of mandibular variation; moreover, they suggest the conservation of early differentiated morphologies, which could indicate the existence of constrained evolutionary diversification.     

Arthropod symbiotes of Laonastes aenigmamus (Rodentia:Diatomyidae)

Arthropod symbiotes of the Laotian rock-rat, Laonastes aenigmamus (Rodentia:Diatomyidae), from Laos are examined. This host is a member of Diatomyidae previously thought to have gone extinct >10 million yr ago. Permanent symbiotes are represented by 2 species, a new species of sucking louse, Polyplax sp., near rhizomydis (Phthiraptera:Polyplacidae), and a new species of fur mite, Afrolistrophorus sp., near maculatus (Acariformes:Listrophoridae). The temporary parasites are represented by 18 species, i.e., 1 mesostigmatan species, i.e., a new species of Androlaelaps near casalis (Parasitiformes:Laelapidae); immature stages of 2 tick species, Ixodes granulatus and Haemaphysalis sp. (Parasitiformes:Ixodidae); and a rich fauna of chiggers (Acariformes:Trombiculidae) comprising 8 genera and 15 species. It is hypothesized that this host completely lost its initial fauna of ectosymbiotes and that ancestors of the recorded symbiotes switched to this host from rodents of the superfamily Muroidea.     

Diversification of inflorescence development in the PCK clade (Poaceae: Panicoideae: Paniceae)

In grasses, inflorescence diversification and its correlation with species evolution are intriguing and not well understood. Part of this problem lies in our lack of comprehension about the inflorescence morphological complexity of grasses. We focused our study on the PCK clade (named for phosphoenol pyruvate carboxykinase), a well-supported monophyletic group for which the relationships among its taxa are not well resolved. Interestingly, the PCK clade has an extensive diversity of adult inflorescence forms. A comparative developmental approach can help us to understand the basis of such morphological differences as well as provide characters that can be used in phylogenetic studies of the group. Using SEM studies, we demonstrate that inflorescence morphology in this clade is even more complex than what is typically observed in adult forms. We describe a number of new characters, and some classical features previously used for taxonomic purposes are redefined on the basis of development. We also define four morphological groups combining adult inflorescence form and development, and we discuss some of the evolutionary aspects of inflorescence diversification in the PCK clade. Taxonomic delimitation among genera in the PCK clade remains confusing and unclear where molecular and morphological studies support different classifications.     

Phylogeny and the modalities of acoustic diversification in extant Eneopterinae (Insecta, Orthoptera, Grylloidea, Eneopteridae)

Calling with a tegminal stridulatory apparatus is widespread in crickets. However, the evolution of cricket stridulums has been poorly studied and then only on the basis of prephylogenetic models, which are unable to account for the huge diversity recently documented for acoustic features in crickets. The present paper focuses on the evolution of acoustic devices in the subfamily Eneopterinae. This is the first attempt to reconstruct the phylogeny of a large and diverse cricket clade in order to analyze the evolution of emitting structures using precise homology statements. In the first step, we reconstruct the phylogeny of this clade using a morphological data set of 193 characters and 45 taxa. The resultant phylogeny supports the monophyly of the subfamily and that of the 13 genera represented by at least two species in our taxonomic sample. Phylogenetic relationships within the subfamily also support the definition of five tribes: Eurepini, Eneopterini, Nisitrini, Xenogryllini and Lebinthini. In the second step, the evolution of acoustic devices is studied by optimization of venation characters defined on precise homology statements. As hypothesized by previous authors, losses of acoustic communication occur independently in the course of eneopterine evolution; however, they happen abruptly with no intermediate state. Our results also document for the first time the modalities of forewing evolution: the diversification of male forewing venation originates from two processes, a continuous and regular modification process, responsible for slight venation change; and an irregular, more intense punctuated process, allowing the emergence of different venations. This diversification process with sudden changes could be related to the occurrence of acoustic novelties in advertisement calls.     

Decoupling of taxonomic diversity and morphological disparity during decline of the Cambrian trilobite family Pterocephaliidae

Although discordance between taxonomic diversity and morphological disparity is common, little is known about the underlying dynamics that drive this decoupling. Early in the history of the Cambrian trilobite family Pterocephaliidae, there was an increase in taxonomic diversity and morphological diversity. As taxonomic diversity declined in the later history of the clade, range of variation stayed high and disparity continued to increase. However, per‐branch rates of morphological evolution estimated from a recent phylogeny decreased with time. Neither within‐trait nor within‐species variation increased or decreased, suggesting that the declining rates of morphological evolution were more likely related to ecological opportunity or niche partitioning, rather than increasing intrinsic constraints. This is further supported by evidence for increased biofacies associations throughout the time period. Thus, the high disparity seen at low taxonomic diversity late in the history of this clade was due to extinction – either random or targeting mean forms – rather than increased rates of morphological evolution. This pattern also provides a scenario that could account for instances of low taxonomic diversity but high morphological disparity in modern groups.     

On the evolution of mimicry in avian nestlings

Batesian mimicry (BM), where a nontoxic species resembles a toxic species with aposematic coloring, has been recently described for a Neotropical species of the suboscine passerine (Laniocera hypopyrra). Understanding the order and series in which these characteristics evolved is unknown and requires character information from closely related taxa. Here, we trace the origin of mimetic traits and how they evolved by examining antipredator characteristics using images and other field‐collected trait data from nest and nestlings along with data available in the literature for the Laniisominae clade and closely related taxa. We found that morphological modifications of the downy feathers appeared first in the broader clade leading to the Laniisominae clade followed by further morphological and behavioral characteristics within the Laniisominae clade leading to the full BM. Images of nestlings in the Laniisominae and closely related clades demonstrated the extent of antipredator and camouflage characteristics. We found a complex set of behavioral and morphological traits in this clade for reducing predation from hiding to camouflage to mimicry. We further propose the evolution of two distinctive mimicry strategies in the Laniisominae clade: (1) Batesian Mimicry, as described above and (2) Masquerade, resemblance to inedible objects commonly found in their local environment. This complex set of antipredator traits shed light on the diversity of antipredator characteristics in avian nestlings, particularly in neotropical areas where the avian diversity is highest. Unfortunately, there are hundreds of species in the neotropics that lack basic natural history information on nesting traits, and therefore, we are likely missing critical information on the diversity of antipredator characteristics across avian nestlings.     

Two- Versus Three-Dimensional Morphometric Approaches in Macroevolution: Insight from the Mandible of Caviomorph Rodents

Morphological variation is one of the most studied dimensions of evolutionary biology, given its close relationship with the ecological aspects of biological diversification. In this work we examine the differences between the use of two- and three-dimensional morphometric techniques for the analysis of macroevolutionary patterns of morphological variation in the mandible of the South American caviomorph rodents, which displays varying degrees of hystricognathy. The variation patterns were similar for 2D and 3D coordinate datasets. However, phylogenetic comparative statistical analyses showed widely different results for mandible variation. Both the phylogenetic signal values and the results of phylogenetic regressions were markedly different between the two macroevolutionary mandible datasets. This suggests that the inclusion of the third coordinate to characterize a hystricognathous mandible may lead to completely different interpretations concerning the processes that could be regulating the morphological diversification of the caviomorph mandible. We also compare these results with the 2D and 3D macroevolutionary patterns of variation in cranial shape and the intra-specific mandible variation. The variation patterns were similar for 2D and 3D coordinate for all these comparative datasets. The differing results obtained at different evolutionary scales, give strength to the statement about careful selection of data not only in studies of morphological variation in caviomorphs but also for other groups of organisms.     

Allometric disparity in rodent evolution

In this study, allometric trajectories for 51 rodent species, comprising equal representatives from each of the major clades (Ctenohystrica, Muroidea, Sciuridae), are compared in a multivariate morphospace (=allometric space) to quantify magnitudes of disparity in cranial growth. Variability in allometric trajectory patterns was compared to measures of adult disparity in each clade, and dietary habit among the examined species, which together encapsulated an ecomorphological breadth. Results indicate that the evolution of allometric trajectories in rodents is characterized by different features in sciurids compared with muroids and Ctenohystrica. Sciuridae was found to have a reduced magnitude of inter‐trajectory change and growth patterns with less variation in allometric coefficient values among members. In contrast, a greater magnitude of difference between trajectories and an increased variation in allometric coefficient values was evident for both Ctenohystrica and muroids. Ctenohystrica and muroids achieved considerably higher adult disparities than sciurids, suggesting that conservatism in allometric trajectory modification may constrain morphological diversity in rodents. The results provide support for a role of ecology (dietary habit) in the evolution of allometric trajectories in rodents.     

Ecological and Ecomorphological Specialization Are Not Associated with Diversification Rates in Muroid Rodents (Rodentia: Muroidea)

Multiple diversification rate shifts explain uneven clade richness in muroid rodents. Previous muroid studies have shown that extrinsic factors, notwithstanding ecological opportunity, are poor predictors of clade diversity. Here, we use a 297-muroid species chronogram that is sampled proportional to total clade diversity, along with various trait-dependent diversification approaches to investigate the association between diversification rates with intrinsic attributes—diet, habitat, body mass, and relative tail length. We found some association between both dietary specialization and body mass, as well as between habitat specialization with relative tail lengths using phylogenetic analyses of variance. However, there was no significant association between diversification rates with the evolution of these traits in muroid rodents. We also show that several of the state-dependent diversification approaches are highly susceptible to Type I error—a result that is in accordance with recent criticisms of these methods. Finally, we discuss several potential causes for the lack of association between the examined trait data with diversification rates, ranging from methodological biases (e.g. method conservativism) to biology (e.g. behavioral plasticity and ecological opportunism of muroid rodents).     

Evolutionary dynamics of complex biomechanical systems: an example using the four-bar mechanism

Like many phenotypic traits, biomechanical systems are defined by both an underlying morphology and an emergent functional property. The relationship between these levels may have a profound impact on how selection for functional performance is translated into morphological evolution. In particular, complex mechanical systems are likely to be highly redundant, because many alternative morphologies yield equivalent functions. We suggest that this redundancy weakens the relationship between morphological and functional diversity, and we illustrate this effect using an evolutionary model of the four-bar lever system of labrid fishes. Our results demonstrate that, when traits are complex, the morphological diversity of a clade may only weakly predict its mechanical diversity. Furthermore, parallel or convergent selection on function does not necessarily produce convergence in morphology. Empirical observations suggest that this weak form-function relationship has contributed to the morphological diversity of labrid fishes, as functionally equivalent species may nevertheless possess morphologically distinct jaws. We suggest that partial decoupling of morphology and mechanics due to redundancy is a major factor in morphological diversification.     

Disparity and Evolutionary Rate Do Not Explain Diversity Patterns in Muroid Rodents (Rodentia: Muroidea)

A positive correlation between diversity and disparity/evolutionary rate is predicted by multiple evolutionary theories. However, recent empirical studies in various taxa do not always find such an association. Similarly, we find no correlation between these two levels of variation, based on cranial morphometric data and molecular phylogenetic data from 317 muroid rodent species and dipodoid outgroups, analyzed using three-dimensional geometric morphometrics. This disassociation was found using both phylogenetic and non-phylogenetic approaches, indicating that an increase in clade richness is not necessarily followed by an increase in morphological divergence and vice versa. Furthermore, the distribution of muroid families in morphospace is highly overlapping suggesting greater variation within than between clades. Taken together with the observation that families with the most distinctive cranial morphologies (nesomyids, dipodids, and spalacids) are the least diverse, indicates that evolution of new cranial morphologies may not play an important role in the diversification of muroid rodents.     

The impact of digging on the evolution of the rodent mandible

There are two main (but not mutually exclusive) methods by which subterranean rodents construct burrows: chisel-tooth digging, where large incisors are used to dig through soil; and scratch digging, where forelimbs and claws are used to dig instead of incisors. A previous study by the authors showed that upper incisors of chisel-tooth diggers were better adapted to dig but the overall cranial morphology within the rodent sample was not significantly different. This study analyzed the lower incisors and mandibles of the specimens used in the previous study to show the impact of chisel-tooth digging on the rodent mandible. We compared lower incisors and mandibular shape of chisel-tooth digging rodents with nonchisel-tooth digging rodents to see if there were morphological differences between the two groups. The shape of incisors was quantified using incisor radius of curvature and second moment of area (SMA). Mandibular shape was quantified using landmark based geometric morphometrics. We found that lower incisor shape was strongly influenced by digging group using a Generalized Phylogenetic ancova (analysis of covariance). A phylogenetic Procrustes anova (analysis of variance) showed that mandibular shape of chisel-tooth digging rodents was also significantly different from nonchisel-tooth digging rodents. The phylogenetic signal of incisor radius of curvature was weak, whereas that of incisor SMA and mandibular shape was significant. This is despite the analyses revealing significant differences in the shape of both mandibles and incisors between digging groups. In conclusion, we showed that although the mandible and incisor of rodents are influenced by function, there is also a degree of phylogenetic affinity that shapes the rodent mandibular apparatus.     

RELATIONSHIP BETWEEN SPECIES CO-OCCURRENCE AND RATE OF MORPHOLOGICAL CHANGE IN PERCINA DARTERS (PERCIDAE: ETHEOSTOMATINAE)

When the morphological diversity of a clade of species is quantified as the among-species variance in morphology, that diversity is a joint consequence of the phylogenetic structure of the clade (i.e., temporal pattern of speciation events) and the rates of change in the morphological traits of interest. Extrinsic factors have previously been linked to variation in the rate of morphological change among clades. Here, we ask whether species co-occurrence is positively correlated with the rate of change in several ecologically relevant morphological characters using the North American freshwater fish clade Percina (Teleostei: Etheostomatinae). We constructed a time-calibrated phylogenetic tree of Percina from mtDNA sequence data, gathered data on eight morphological characters from 37 species, used a principal components analysis to identify the primary axes of morphological variation, and analyzed 16,094 collection records to estimate species co-occurrence. We then calculated standardized independent contrasts (SIC) of the morphological traits (rate of change) at each node, estimated ancestral species co-occurrence, and quantified the correlation between species co-occurrence and rate of morphological change. We find that morphology changes more quickly when co-occurrence is greater in Percina . Our results provide strong evidence that co-occurrence among close relatives is linked to the morphological diversification of this clade.     

Morphological and biomechanical disparity of crocodile-line archosaurs following the end-Triassic extinction

Mesozoic crurotarsans exhibited diverse morphologies and feeding modes, representing considerable ecological diversity, yet macroevolutionary patterns remain unexplored. Here, we use a unique combination of morphological and biomechanical disparity metrics to quantify the ecological diversity and trophic radiations of Mesozoic crurotarsans, using the mandible as a morpho-functional proxy. We recover three major trends. First, the diverse assemblage of Late Triassic crurotarsans was morphologically and biomechanically disparate, implying high levels of ecological variation; but, following the end-Triassic extinction, disparity declined. Second, the Jurassic radiation of marine thalattosuchians resulted in very low morphological disparity but moderate variation in jaw biomechanics, highlighting a hydrodynamic constraint on mandibular form. Third, during the Cretaceous terrestrial radiations of neosuchians and notosuchians, mandibular morphological variation increased considerably. By the Late Cretaceous, crocodylomorphs evolved a range of morphologies equalling Late Triassic crurotarsans. By contrast, biomechanical disparity in the Cretaceous did not increase, essentially decoupling from morphology. This enigmatic result could be attributed to biomechanical evolution in other anatomical regions (e.g. cranium, dentition or postcranium), possibly releasing the mandible from selective pressures. Overall, our analyses reveal a complex relationship between morphological and biomechanical disparity in Mesozoic crurotarsans that culminated in specialized feeding ecologies and associated lifestyles.     

Testing for differences in rates of speciation, extinction, and morphological evolution in four tribes of cichlids endemic to Lake Tanganyika, East Africa

Patterns of morphological disparity yield important insight into the causes of diversification and adaptive radiation in East African cichlids. However, comparisons of cichlid disparity have often failed to consider the effects that differing clade ages or stochasticity may have on disparity before making interpretations. Here, a model of branching morphological evolution allows assessment of the relative contributions of differing turnover and morphological change rates, clade ages, and stochastic variation to the observed patterns of disparity in four endemic tribes of Lake Tanganyika cichlids. Simulations compare the likelihood of generating the observed disparity of the four tribes using 200-parameter combinations and four model conditioning variations, which allows inference of evolutionary rate differences among clades. The model is generally robust to model conditioning, the approach to data analysis, and model assumptions. Disparity differences among the first three cichlid tribes, Ectodini, Lamprologini, and Tropheini, can be explained entirely by stochasticity and age, whereas the fourth tribe, Cyprichromini, has likely experienced lower rates of turnover and morphological change. This rate difference is likely related to the low dietary diversity of the Cyprichromini. These results highlight the importance of considering both clade age and stochastic variation when interpreting morphological diversity and evolutionary processes.     

Morphometric variations at an ecological scale: Seasonal and local variations in feral and commensal house mice

The time scales of evolutionary and ecological studies tend to converge, as shown by evidences that contemporary evolution can occur as fast as ecological processes. This opens new questions regarding variation of characters usually considered to change mostly along an evolutionary time scale, such as morphometric traits, including osteological and dental features such as mandibles and teeth of mammals. Using two-dimensional geometric morphometric approach, we questioned whether such features can change on a seasonal and local basis, in relation to the ecological dynamics of the populations. Our model comprised populations of house mice (Mus musculus domesticus) in two contrasted situations in mainland Western Europe: a feral population vs. two close commensal populations. Mitochondrial DNA (D-loop) provided insight into the diversity and dynamics of the populations.The feral population appeared as genetically highly diversified, suggesting a possible functioning as a sink in relation to the surrounding commensal populations. In contrast, commensal populations were highly homogeneous from a genetic point of view, suggesting each population to be isolated. This triggered morphological differentiation between neighboring farms. Seasonal differences in morphometric traits (mandible size and shape and molar size and shape) were significant in both settings, although seasonal variations were greater in the feral than in the commensal population. Seasonal variations in molar size and shape could be attributed to differential wear in young or overwintered populations. Differences in mandible shape could be related to aging in overwintered animals, but also possibly to differing growth conditions depending on the season. The impact of these ecological processes on morphometric traits is moderate compared to divergence over a large biogeographic scale, but their significance nevertheless underlines that even morphological characters may trace populations dynamics at small scale in time and space.     

A New Snake Skull from the Paleocene of Bolivia Sheds Light on the Evolution of Macrostomatans

Macrostomatan snakes, one of the most diverse extant clades of squamates, display an impressive arsenal of cranial features to consume a vast array of preys. In the absence of indisputable fossil representatives of this clade with well-preserved skulls, the mode and timing of these extraordinary morphological novelties remain obscure. Here, we report the discovery of Kataria anisodonta n. gen. n. sp., a macrostomatan snake recovered in the Early Palaeocene locality of Tiupampa, Bolivia. The holotype consists of a partial, minute skull that exhibits a combination of booid and caenophidian characters, being the presence of an anisodont dentition and diastema in the maxilla the most distinctive trait. Phylogenetic analysis places Kataria basal to the Caenophidia+Tropidophiidae, and represents along with bolyeriids a distinctive clade of derived macrostomatans. The discovery of Kataria highlights the morphological diversity in the maxilla among derived macrostomatans, demonstrating the relevance of maxillary transformations in the evolution of this clade. Kataria represents the oldest macrostomatan skull recovered, revealing that the diversification of macrostomatans was well under way in early Tertiary times. This record also reinforces the importance of Gondwanan territories in the history of snakes, not only in the origin of the entire group but also in the evolution of ingroup clades.     

Phylogenic Diversity and Taxonomic Problems of the Dictyosphaerium Morphotype within the Parachlorella Clade (Chlorellaceae,Trebouxiophyceae)

The Parachlorella clade was put forward as a group within the family Chlorellaceae in 2004. Recent molecular analyses have revealed that Dictyosphaerium morphotype algae form several independent lineages within the Parachlorella clade, and new genera and species have been established. In this study, we focus on the diversity of Dictyosphaerium morphotype algae within the Parachlorella clade, based on 42 strains from China. We used combined analyses of morphology and molecular data based on SSU and internal transcribed spacer region (ITS) rDNA sequences to characterize these algae. In addition, the secondary structure of ITS2 was compared to delineate new lineages. Our results revealed high phylogenic diversity of Dictyosphaerium morphotype algae, and we describe five distinct lineages. We examined the morphological features of these five lineages, and morphological differences are difficult to find compared with other Dictyosphaerium morphotype algae. The five distinct lineages were not described as new genera currently. We lastly discuss the taxonomic problems regarding the Dictyosphaerium morphotype within the Parachlorella clade, and possible solutions are considered.     

Palynological variation in Balsaminoid Ericales. II. Balsaminaceae, Tetrameristaceae, Pellicieraceae and general conclusions

BACKGROUND AND AIMS: The objective of this study is to examine the palynological diversity of Balsaminaceae (two genera/+/-1000 species), Tetrameristaceae (two genera/two species) and Pellicieraceae (one genus/one species). The diversity found will be used to infer the systematic value of pollen features within the balsaminoid clade. METHODS: Pollen morphology and ultrastructure of 29 species, representing all families of the balsaminoid clade except Marcgraviaceae, are investigated by means of light microscopy, scanning electron microscopy and transmission electron microscopy. KEY RESULTS: Balsaminaceae pollen is small to medium sized with three to four apertures, which can be either colpate or porate, and a sexine sculpturing varying from coarsely reticulate to almost microreticulate. Tetrameristaceae pollen is small sized, 3-colporate, with a heterobrochate reticulate sculpturing and granules present in the lumina. Pellicieraceae pollen is large sized, 3-colporate with long ectocolpi and a perforate sexine sculpturing with large verrucae. Furthermore, Pelliciera is characterized by the occurrence of aggregated orbicules, while orbicules are completely absent in both Balsaminaceae and Tetrameristaceae. Balsaminaceae pollen differs from the other balsaminoid families due to the occurrence of colpate or porate grains with an oblate to peroblate shape, a very thin foot layer and a lamellated endexine. CONCLUSIONS: From a pollen morphological point of view, Balsaminaceae are completely different from the other balsaminoid families. Therefore, no pollen morphological synapomorphies could be defined for the balsaminoid clade. However, various pollen features were observed that could indicate a possible relationship between Tetrameristaceae, Pellicieraceae and Marcgraviaceae. Despite the palynological similarities in the latter three families, it remains unclear to what extent they are related to each other.