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).     

Relationship between the Social Structure and Potential Reproductive Success in Muroid Rodents (Rodentia,Myomorpha)

Biology Bulletin - In many systematic groups of mammalian species, the evolution of sociality leads to the formation of large social groups (group-size evolution). In rodents, however, the most...     

Evolutionary and developmental dynamics of the dentition in Muroidea and Dipodoidea (Rodentia, Mammalia)

SUMMARY When it comes to mouse evo‐devo, the fourth premolar–first molar (P4–M1) dental complex becomes a source of longstanding controversies among paleontologists and biologists. Muroidea possess only molar teeth but with additional mesial cusps on their M1. Developmental studies tend to demonstrate that the formation of such mesial cusps could result from the integration of a P4 germ into M1 during odontogenesis. Conversely, most Dipodoidea conserve their fourth upper premolars and those that lost these teeth can also bear additional mesial cusps on their first upper molars. The aim of this study is to assess this developmental model in both Muroidea and Dipodoidea by documenting the morphological evolution of the P4–M1 complex across 50 Ma. Fourteen extinct and extant species, including abnormal and mutant specimens were investigated. We found that, even if their dental evolutionary pathways strongly differ, Dipodoidea and Muroidea retain common developmental characteristics because some of them can present similar dental morphological trends. It also appears that the acquisition of a mesial cusp on M1 is independent from the loss of P4 in both superfamilies. Actually, the progressive decrease of the inhibitory effect of P4, consequent to its regression, could allow the M1 to lengthen and mesial cusps to grow in Muroidea. Apart from these developmental explanations, patternings of the mesial part of first molars are also deeply constrained by morpho‐functional requirements. As there is no obvious evidence of such mechanisms in Dipodoidea given their more variable dental morphologies, further developmental investigations are needed.     

Ecomorphological diversification following continental colonization in muroid rodents (Rodentia: Muroidea)

The emergence of exceptionally diverse clades is often attributed to ecological opportunity. For example, the exceptional diversity in the most diverse superfamily of mammals, muroid rodents, has been explained in terms of multiple independent adaptive radiations. If multiple ecological opportunity events are responsible for generating muroid diversity, we expect to find evidence of these lineages ecologically diversifying following dispersal into new biogeographical areas. In the present study, we tested the trait‐based predictions of ecological opportunity using data on body size, appendages, and elevation in combination with previously published data on biogeographical transitions and a time‐calibrated molecular phylogeny. We identified weak to no support of early ecological diversification following the initial colonizations of all continental regions, based on multiple tests, including node height tests, disparity through time plots, evolutionary model comparison, and Bayesian analysis of macroevolutionary mixtures. Clades identified with increased diversification rates, not associated with geographical transitions, also did not show patterns of phenotypic divergence predicted by ecological opportunity, which suggests that phylogenetic diversity and phenotypic disparity may be decoupled in muroids. These results indicate that shifts in diversification rates and biogeographically‐mediated ecological opportunity are poor predictors of phenotypic diversity patterns in muroids.     

Simimys and origin of the cricetidae (Rodentia: Muroidea)

Simimys is a late Eocene and earliest Oligocene genus that shares dipodoid (zygoma) and muroid (dental) characters. The Oligocene record of dipodoid rodents includes Plesiosminthus from middle Oligocene deposits of Asia and late Oligocene deposits of Europe. The Oligocene record of muroid rodents includes at least two genera (Eucricetodon and (Cricetops)) from Asia, six genera (Eucricetodon, Pseudocricetodon, Melissiodon, Paracricetodon, Heterocricetodon and Adelomyorion)) from Europe, and three genera (Eumys, Scottimus and Nonomys)) from North America. The known record, as given above, suggests that Siminys is the earliest and most primitive genus with muroid affinities; it also implies that muroid rodents were derived from unknown Eocene dipodoid rodents.The Oligocene cricetid rodents display progressive expansion and inclination of the anterior plate of the zygoma. These changes in the zygoma probably reflect evolutionary stages in the development of a myomorphous zygoma from an hystricomorphous zygoma. Changes in the zygoma apparently took place at different rates and times in Asia. Europe, and North America; they probably reflect differenciation of Cricetodontinae in Palaearctica, and Eumyinae in Nearctica during the Oligocene.     

Time Constraints Do Not Limit Group Size in Arboreal Guenons but Do Explain Community Size and Distribution Patterns

To understand how species will respond to environmental changes, it is important to know how those changes will affect the ecological stress that animals experience. Time constraints can be used as indicators of ecological stress. Here we test whether time constraints can help us understand group sizes, distribution patterns, and community sizes of forest guenons (Cercopithecus/Allochrocebus). Forest guenons typically live in small to medium sized one-male–multifemale groups and often live in communities with multiple forest guenon species. We developed a time-budget model using published data on time budgets, diets, body sizes, climate, and group sizes to predict maximum ecologically tolerable group and community sizes of forest guenons across 202 sub-Saharan African locations. The model correctly predicted presence/absence at 83% of these locations. Feeding-foraging time (an indicator of competition) limited group sizes, while resting and moving time constraints shaped guenon biogeography. Predicted group sizes were greater than observed group sizes but comparable to community sizes, suggesting community sizes are set by competition among guenon individuals irrespective of species. We conclude that time constraints and intraspecific competition are unlikely to be the main determinants of relatively small group sizes in forest guenons. Body mass was negatively correlated with moving time, which may give larger bodied species an advantage over smaller bodied species under future conditions when greater fragmentation of forests is likely to lead to increased moving time. Resting time heavily depended on leaf consumption and is likely to increase under future climatic conditions when leaf quality is expected to decrease.     

Evolutionary and Biological Implications of Dental Mesial Drift in Rodents: The Case of the Ctenodactylidae (Rodentia,Mammalia)

Dental characters are importantly used for reconstructing the evolutionary history of mammals, because teeth represent the most abundant material available for the fossil species. However, the characteristics of dental renewal are presently poorly used, probably because dental formulae are frequently not properly established, whereas they could be of high interest for evolutionary and developmental issues. One of the oldest rodent families, the Ctenodactylidae, is intriguing in having longstanding disputed dental formulae. Here, we investigated 70 skulls among all extant ctenodactylid genera (Ctenodactylus, Felovia, Massoutiera and Pectinator) by using X-ray conventional and synchrotron microtomography in order to solve and discuss these dental issues. Our study clearly indicates that Massoutiera, Felovia and Ctenodactylus differ from Pectinator not only by a more derived dentition, but also by a more derived eruptive sequence. In addition to molars, their dentition only includes the fourth deciduous premolars, and no longer bears permanent premolars, conversely to Pectinator. Moreover, we found that these premolars are lost during adulthood, because of mesial drift of molars. Mesial drift is a striking mechanism involving migration of teeth allowed by both bone remodeling and dental resorption. This dental innovation is to date poorly known in rodents, since it is only the second report described. Interestingly, we noted that dental drift in rodents is always associated with high-crowned teeth favoring molar size enlargement. It can thus represent another adaptation to withstand high wear, inasmuch as these rodents inhabit desert environments where dust is abundant. A more accurate study of mesial drift in rodents would be very promising from evolutionary, biological and orthodontic points of view.     

Zinc Finger Binding Motifs Do Not Explain Recombination Rate Variation within or between Species of Drosophila

In humans and mice, the Cys₂His₂ zinc finger protein PRDM9 binds to a DNA sequence motif enriched in hotspots of recombination, possibly modifying nucleosomes, and recruiting recombination machinery to initiate Double Strand Breaks (DSBs). However, since its discovery, some researchers have suggested that the recombinational effect of PRDM9 is lineage or species specific. To test for a conserved role of PRDM9-like proteins across taxa, we use the Drosophila pseudoobscura species group in an attempt to identify recombination associated zinc finger proteins and motifs. We leveraged the conserved amino acid motifs in Cys₂His₂ zinc fingers to predict nucleotide binding motifs for all Cys₂His₂ zinc finger proteins in Drosophila pseudoobscura and identified associations with empirical measures of recombination rate. Additionally, we utilized recombination maps from D. pseudoobscura and D. miranda to explore whether changes in the binding motifs between species can account for changes in the recombination landscape, analogous to the effect observed in PRDM9 among human populations. We identified a handful of potential recombination-associated sequence motifs, but the associations are generally tenuous and their biological relevance remains uncertain. Furthermore, we found no evidence that changes in zinc finger DNA binding explains variation in recombination rate between species. We therefore conclude that there is no protein with a DNA sequence specific human-PRDM9-like function in Drosophila. We suggest these findings could be explained by the existence of a different recombination initiation system in Drosophila.     

Structural Features of Spines in Some Rodents (Rodentia: Myomorpha, Hystricomorpha)

The architectonics of spines and hair was studied in Neacomys spinosus, Tokudaia osimensis, Arvicanthis somalicus, Leopoldamys sabanus, L. edwardsi, Maxomys moi, M. surifer, Niviventer fulvescens, N. confucianus, N. cremoriventer, Acomys cahirinus, A. somalica, Hystrix indica, H. cristata, Atherurus macrourus, Erethizon dorsatum, Proechimys steerei, and Lonchotrix emiliae. The presence of a dorsal longitudinal furrow covered by a modified cuticle is a common structural feature of spines in all studied species except E. dorsatum, H. indica, and H. cristata. The frontal surface of the mosaic (scales located side by side) and terrace cuticle (steps between scales) varies in different species from smooth to rib-folded. A terminology has been proposed to describe the main structures of spine and hair. The adaptive significance of the spine architectonics in rodents is discussed.     

A Dated Phylogeny Complements Macroecological Analysis to Explain the Diversity Patterns in Geonoma (Arecaceae)

Integrating phylogenetic data into macroecological studies of biodiversity patterns may complement the information provided by present‐day spatial patterns. In the present study, we used range map data for all Geonoma (Arecaceae) species to assess whether Geonoma species composition forms spatially coherent floristic clusters. We then evaluated the extent to which the spatial variation in species composition reflects present‐day environmental variation vs. nonenvironmental spatial effects, as expected if the pattern reflects historical biogeography. We also examined the degree of geographic structure in the Geonoma phylogeny. Finally, we used a dated phylogeny to assess whether species richness within the floristic clusters was constrained by a specific historical biogeographic driver, namely time‐for‐diversification. A cluster analysis identified six spatially coherent floristic clusters, four of which were used to reveal a significant geographic phylogenetic structure. Variation partitioning analysis showed that 56 percent of the variation in species composition could be explained by spatial variables alone, consistent with historical factors having played a major role in generating the Geonoma diversity pattern. To test for a time‐for‐diversification effect, we correlated four different species richness measures with the diversification time of the earliest large lineage that is characteristic of each cluster. In support of this hypothesis, we found that geographic areas with higher richness contained older radiations. We conclude that current geographic diversity patterns in Geonoma reflect the present‐day climate, but to a larger extent are related to nonenvironmental spatial constraints linked to colonization time, dispersal limitation, and geological history, followed by within‐area evolutionary diversification. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

First Potwarmus from the Miocene of Saudi Arabia and the early phylogeny of murines (Rodentia: Muroidea)

Potwarmus is recorded for the first time in Saudi Arabia. The material comes from the Middle Miocene of the Hofuf Formation at Al‐Jadidah. This species, Potwarmus flynni sp. nov. , is described and compared with all species currently placed in the genera Potwarmus, Dakkamys, Paradakkamys, Vallaris, and some species of ‘Myocricetodon’ (i.e. the so‐called ‘primitive dendromurids’) as well as with two of the most primitive definitive murines (namely Antemus chinjiensis and Progonomys debruijni). Potwarmus flynni sp. nov. differs from the above‐mentioned species in having the anterior part of the m1 strongly reduced. A cladistic analysis provides evidence that this new Arabian taxon is close to Potwarmus primitivus and Potwarmus sp. nov. from Jebel Zelten (Libya), and also that this genus is unlikely to be the sister taxon to Antemus. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 664–679.     

Morphological Variation of the Forelimb and Claw in Neotropical Sigmodontine Rodents (Rodentia: Cricetidae)

The limbs of mammals exhibit a variety of morphologies that reflect the diversity of their habitats and their functional needs, including subtle structural differences in their distal limb integumentary appendages (hooks, claws, adhesive pads). Little is known about structure and function of claws of sigmodontine rodents. Here, we analyze claw shape and forelimb skeleton morphology of 25 species of sigmodontine rodents with different locomotory types (ambulatory, fossorial, natatorial, quadrupedal saltatorial, and scansorial), taking into account their phylogenetic affinities. Qualitative differences in claw shape were examined using digital photographs, and quantitative measurements were made for length, height, and curvature of the claws of all digits, and dimensions of other forelimb skeletal elements. Our results show that both phylogeny and ecological categories explain substantial components of the morphological variation in sigmodontine rodents. Qualitative analysis reveals that non-specialized forms (ambulatory, quadrupedal saltatorial, and scansorial) tend to have high and strongly curved claws, whereas highly specialized forms (fossorial and natatorial) tend to have elongate and smoothly curved claws. However, the quantitative analysis differentiated the fossorial and scansorial by variables related to claw, and natatorial by variables related to bones of the forelimb. No variables that could differentiate ambulatory or quadrupedal saltatorial forms were found, demonstrating that these forms show a generalized morphological pattern. This study indicates that both historical and ecological factors contribute to the evolution of claw length in these groups.     

Phylogeny and Evolutionary History of the Ground Squirrels (Rodentia: Marmotinae)

Although ground squirrels (Spermophilus) and prairie dogs (Cynomys) are among the most intensively studied groups of mammals with respect to their ecology and behavior, a well-resolved phylogeny has not been available to provide a framework for comparative and historical analyses. We used complete mitochondrial cytochrome b sequences to construct a phylogeny that includes all 43 currently recognized species in the two genera, as well as representatives of two closely related genera (Marmota and Ammospermophilus). In addition, divergence times for ground squirrel lineages were estimated using Bayesian techniques that do not assume a molecular clock. All methods of phylogenetic analysis recovered the same major clades, and showed the genus Spermophilus to be paraphyletic with respect to both Marmota and Cynomys. Not only is the phylogeny at odds with previous hypotheses of ground squirrel relationships, but it suggests that convergence in morphology has been a common theme in ground squirrel evolution. A well-supported basal clade, including Ammospermophilus and two species in the subgenus Otospermophilus, diverged from all other ground squirrels an estimated 17.5 million years ago. Between 10 and 14 million years ago, a relatively rapid diversification gave rise to lineages leading to marmots and to several distinct groups of ground squirrels. The Eurasian ground squirrels diverged from their North American relatives during this period, far earlier than previously hypothesized. This period of diversification corresponded to warming climate and spread of grasslands in western North America and Eurasia. Close geographic proximity of related forms suggests that most species evolved in or near their current ranges.     

Female Goldeneye Ducks (Bucephala clangula) Do Not Discriminate among Male Precopulatory Display Patterns

Female goldeneyes remain motionless on the surface of the water while single males circle them performing a series of highly stereotyped displays. After performing between eight and 90 of these displays the male either copulates or attempts to copulate with the female. However, females allow only 58% of males to mount them, while rejecting 42%. We have examined 804 of these precopulatory sequences containing 11,841 actions in an effort to determine why females find some display sequences of males unsuitable, while others are accepted. Males have an extraordinarily varied sequence of actions, and sequence variation leading to successful and unsuccessful copulation attempts was similar. Most surprising was the tendency of males to eliminate one of the five actions, whether in successful or unsuccessful attempts. As unlikely as we think it might be as the result of natural selection, the only statistically significant difference we found between successful and unsuccessful attempts was the reduction in the frequency of expression of one or more of the behaviors in successful attempts. These observations, coupled with the large variation seen in most sequences, suggest that there is not a correct sequence, or even a correct set of actions leading to copulation. The male must, however, perform goldeneye species-specific precopulatory behavior as performed by adult males, although it apparently can be performed in a wide variety of patterns.     

Evolutionary history and species diversity of African pouched mice (Rodentia: Nesomyidae: Saccostomus)

We explore diversity of African pouched mice, genus Saccostomus (Rodentia, Nesomyidae), by sampling molecular and morphological variation across their continental‐scale distribution in southern and eastern African savannahs and woodlands. Both mitochondrial (cytochrome b) and nuclear DNA (IRBP, RAG1) as well as skull morphology confirm the distinction between two recognized species, S. campestris and S. mearnsi, with disjunct distribution in the Zambezian and Somali–Maasai bioregions, respectively. Molecular dating suggests the divergence of these taxa occurred in the Early Pliocene, 3.9 Ma before present, whereas the deepest divergences within each of them are only as old as 2.0 Ma for S. mearnsi and 1.4 Ma for S. campestris. Based on cytochrome b phylogeny, we defined five clades (three within S. campestris, two in S. mearnsi) whose species status was considered in the light of nuclear DNA markers and morphology. We conclude that S. campestris group consists of two subspecies S. campestris campestris (Peters, 1846; comprising two cytochrome b clades) and S. campestris mashonae (de Winton, 1897) that are moderately differentiated, albeit distinct in IRBP and skull form. They likely hybridize to a limited extent along the Kafue–Zambezi Rivers. Saccostomus mearnsi group consists of two species, S. mearnsi (Heller, 1910) and S. umbriventer (Miller, 1910), that are markedly differentiated in both nuclear markers and skull form and may possibly co‐occur in south‐western Kenya and north‐eastern Tanzania. Analysis of historical demography suggests both subspecies of S. campestris experienced population expansion dated to the Last Glacial. In the present range of S. campestris group, the distribution modelling suggests a moderate fragmentation of suitable habitats during the last glacial cycle, whereas in the range of S. mearnsi group it predicts substantial shifts of its occurrence in the same period.     

Sperm morphology in the Malagasy rodents (Muroidea: Nesomyinae)

The morphology of the spermatozoon of representative species of the subfamily Nesomyinae (Muroidea: Nesomyidae), a monophyletic group of rodents endemic to Madagascar, was examined by light and electron microscopy to determine the sperm head shape and tail length across the species. Marked interspecific differences were found to occur in both the form of the sperm head and length of the tail. The species that possess a sperm head with an apical hook, which largely contains acrosomal material, generally displayed longer sperm tails, and a species with a spatulate sperm head had the shortest tail. The association between sperm head shape and tail length mirrors that previously found in Eurasian and Australasian murine rodents. Thus, the repeated association between sperm head shape and tail length across these groups of muroid rodents clearly indicates a functional relationship between these two features. A comparison of sperm morphology of the nesomyines to that of related muroid rodents on the mainland of Africa suggests that the possession of an apical hook is the ancestral condition. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Cultural Diversity and Saccade Similarities: Culture Does Not Explain Saccade Latency Differences between Chinese and Caucasian Participants

A central claim of cultural neuroscience is that the culture to which an individual belongs plays a key role in shaping basic cognitive processes and behaviours, including eye movement behaviour. We previously reported a robust difference in saccade behaviour between Chinese and Caucasian participants; Chinese participants are much more likely to execute low latency express saccades, in circumstances in which these are normally discouraged. To assess the extent to which this is the product of culture we compared a group of 70 Chinese overseas students (whose primary cultural exposure was that of mainland China), a group of 45 participants whose parents were Chinese but who themselves were brought up in the UK (whose primary cultural exposure was western European) and a group of 70 Caucasian participants. Results from the Schwartz Value Survey confirmed that the UK-Chinese group were culturally similar to the Caucasian group. However, their patterns of saccade latency were identical to the mainland Chinese group, and different to the Caucasian group. We conclude that at least for the relatively simple reflexive saccade behaviour we have investigated, culture cannot explain the observed differences in behaviour.     

Brachiocephalic Muscular Arrangements in Cavioid Rodents (Caviomorpha): a Functional,Anatomical, and Evolutionary Study

Journal of Mammalian Evolution - In cursorial mammals, reduction or loss of the clavicle is usually associated with the constitution of the m. brachiocephalicus, a continuous muscle that extends...     

Contrasting Phylogenetic and Diversity Patterns in Octodontoid Rodents and a New Definition of the Family Abrocomidae

Octodontoidea is the most species-rich clade among hystricomorph rodents. Based on a combined parsimony analysis of morphological and molecular data of extinct and extant species, we analyze the history of South American octodontoids and propose ages of divergence older than interpreted so far. Early Abrocomidae are recognized for the first time, and a new definition of the family is provided. Traditionally accepted fossil-based times of origin for the southern clades are reinterpreted as later stages of differentiation markedly uncoupled from the origin, differentiation implying specializations for open environments as shown in a morphospace of skull variation. Origin of crown groups is also strongly uncoupled from origin of clades as a consequence of extinction of deep lineages. In the resulting diversity pattern of modern southern clades of octodontoids, the combination of greater disparity, less content of evolutionary history, and lower taxonomic diversity, compared to their northern counterparts, appears at first counterintuitive. We propose that primary components of diversity derived from evolutionary transformation or anagenesis, on the one hand, and from cladogenesis and extinction, on the other, should not be considered associated, or at least not necessarily. Certain patterns of relationships between these distinct components could be driven by environmental dynamics. Like environments, octodontoid diversity would have been more stable in northern South America, whereas in the south, both strong adaptive change and extinction would have been triggered by emerging derived environments.