Allometry, bilateral asymmetry and sexual differences in the vocal tract of common eiders Somateria mollissima and king eiders S. spectabilis

Intraspecific sexual differences, high variation, and positive allometry of sexually-selected external display structures are common. Many sexually-selected anatomical specializations occur in the avian vocal tract but intraspecific variation and allometry have been investigated little. The tracheal bulla bulla syringealis occurs in males of most duck species. We quantified variation and size-scaling of the bulla, plus sexual differences in size of trachea, bronchi, and vocal muscles, for 62 common eiders Somateria mollissima and 51 king eiders S. spectabilis. Trends were similar in both species. Bullar ossification and definitive size occurred early in life: bullar size did not differ between first-year and older males. Bullar size did not vary more than size of other body parts (CVs of 3.4–7.0% for bullar length and breadth). Bullar size scaled to body size with negative allometry or isometry. Vocal muscles were 10–50% thicker in males than females, a much greater sexual difference than in body size (CVs of 3–6% on linear body-size variables). Vocal muscles were larger on the left side in both sexes and bilateral asymmetry was slightly more pronounced in males. Low variation and a trend towards negative allometry suggest that bullar size is under stabilizing selection; if bullar size affects vocal attributes of voice, then the latter cannot be condition-dependent. We recommend comparative research on vocal communication, vocal individuality and vocal-tract anatomy and function in eiders and other ducks.     

Molecular systematics of gerbils and deomyines (Rodentia: Gerbillinae,Deomyinae) and a test of desert adaptation in the tympanic bulla

Recent molecular studies in gerbils found multiple instances of discordance between molecular and morphological phylogenies. In this study, we analyse the largest molecular data set to date of gerbils and their sister group the deomyines to estimate their phylogenetic relationships. Maximum‐likelihood and Bayesian analyses were largely concordant, and both generally had high levels of node support. For gerbils, the results were generally concordant with previous molecular phylogenies based on allozymes, chromosomes, DNA/DNA hybridization and DNA sequences, and discordant with morphological phylogenies. None of the traditional gerbil tribes and subtribes were monophyletic. In addition, paraphyly was found in the genera Gerbillus, Gerbilliscus and Meriones as well as in five subgenera within Dipodillus, Gerbillurus and Meriones. Short branches separating taxa in small clusters within Dipodillus and Meriones suggest synonymy. Within deomyines, all genera and subgenera were monophyletic; however, two species groups within Acomys appear to contain synonymous taxa. We also find support for the discordance between molecular and morphological phylogenies in gerbils being partly due to convergent adaptations to arid environments, primarily in the suite of traits associated with inflation of the tympanic bullae. Relative bullar size does appear to be a desert adaptation and is correlated with aridity independent of phylogeny. Further, it varies more strongly along bioclimatic clines than between binary habitat classifications (desert versus mesic).     

新疆准噶尔盆地北缘铁尔斯哈巴合晚渐新世两种啮形类耳区的形态研究

我们曾描述过一块与本文描述的标本产自同一地点和层位、可能为Ａｍｐｈｅｃｈｉｎｕｓ的猬类岩骨标本（孟津等,１９９９）。后来新发现的与牙齿属同一个体的Ａｍｐｈｅｃｈｉｎｕｓ岩骨标本证明我们根据单体岩骨的分类鉴定无误。此例说明,在一定的条件下,耳区标本在某些哺乳动物类群中可以鉴定到属,甚至种。因此在形态学、生物地层学上都有一定的意义,而且会因有关标本的不断积累而越来越重要。本文记述了另外两块产自新疆准噶尔盆地北缘铁尔斯哈巴合晚渐新世地层中的岩骨。有关地层、地点资料及所用术语见孟津等（１９９９）以及其中…     

A New Species of Ctenomys (Rodentia: Ctenomyidae) from Patagonia Related to C. sociabilis

The genus Ctenomys includes a high number of taxa, with at least ten species from Patagonia and three recently described species for northeastern Chubut Province (Argentina). Ctenomys sociabilis is a social species of the genus Ctenomys and is currently distributed in the surrounding area of Sierra Cuyin Manzano (Neuquén Province), with a recently extinct population that occurred in Laguna Nahuelquir (Cushamen, Chubut Province). Molecular analyses have placed C. sociabilis at the base of Ctenomys clade, as the sister species to all other Ctenomys. Based on a morphological assessment (qualitative and quantitative) and DNA sequencing, we describe a new species of Ctenomys from Esquel, Chubut Province. Phylogenetic analysis shows the new species to be closely related to C. sociabilis, with evidence of solitary behavior. This new species is the first reported to be closely related phylogenetically to Ctenomys sociabilis at the base of the Ctenomys phylogeny. We provide anatomical comparisons between the new species and other species of Ctenomys from Patagonia, especially C. sociabilis.

     

Chromosome multiformity in the genus Ctenomys (Rodentia,Octodontidae)

The karotypes of eleven species of the South American burrowing rodents, genus Ctenomys are described, and information on the somatic number of two other species of the same genus is given. The studied species are: C. torquatus (2n =68), C. tuconax (2n =61), C. minutus (2n=50), C. talarum (2n= 48), C. porteousi (2n=48), C. cf. minutus (2n=48), C. australis (2n=46), C. azarae (2n=48), C. latro (2n=42), C. magellanicus fueguinus (2n=36), C. tucumanus (2n=28), C. opimus luteolus (2n=26), and C. occultus (2n =22). This extreme intrageneric variation in somatic number is also reflected by a great amount of diversity in chromosome structure. Karyotypes seem to be rather constant at the species level. Autosomal polymorphism has been found in two of the species, namely C. talarum and C. latro. The hypothesis of the superimposition of Robertsoman rearrangements, pericentric inversions and translocations in the evolution of the karyotype of Ctenomys is advanced. The direction of chromosome change, either toward increase or decrease in chromosome number, is discussed. It is emphasized that high chromosome multiformity is correlated in Ctenomys with a rapid and explosive pattern of species diversification; the meaning of the small size of populations in enhancing the role of chromosome rearrangements in the evolution of Ctenomys is discussed.     

New notharctine (primates,adapiformes) skull from the Uintan (middle Eocene) of San Diego County,California

A new genus and species of notharctine primate, Hesperolemur actius, is described from Uintan (middle Eocene) aged rocks of San Diego County, California. Hesperolemur differs from all previously described adapiforms in having the anterior third of the ectotympanic anulus fused to the internal lateral wall of the auditory bulla. In this feature Hesperolemur superficially resembles extant cheirogaleids. Hesperolemur also differs from previously known adapiforms in lacking bony canals that transmit the internal carotid artery through the tympanic cavity. Hesperolemur, like the later occurring North American cercamoniine Mahgarita stevensi, appears to have lacked a stapedial artery. Evidence from newly discovered skulls of Notharctus and Smilodectes, along with Hesperolemur, Mahgarita, and Adapis, indicates that the tympanic arterial circulatory pattern of these adapiforms is characterized by stapedial arteries that are smaller than promontory arteries, a feature shared with extant tarsiers and anthropoids and one of the characteristics often used to support the existence of a haplorhine-strepsirhine dichotomy among extant primates. The existence of such a dichotomy among Eocene primates is not supported by any compelling evidence. Hesperolemur is the latest occurring notharctine primate known from North America and is the only notharctine represented among a relatively diverse primate fauna from southern California. The coastal lowlands of southern California presumably served as a refuge area for primates during the middle and later Eocene as climates deteriorated in the continental interior. Hesperolemur probably was an immigrant taxon that entered California from either the northern (Wyoming/Utah) or southern (New Mexico) western interior during the middle Eocene © 1995 Wiley-Liss, Inc.     

Geomorphometric differences among four species of Microtus in Turkey (Mammalia: Rodentia)

In order to determine the phenotypic associations of four morphologically similar species of Microtus occurring in Turkey, we applied landmark-based shape analysis. The skulls of Microtus anatolicus, M. dogramacii, M. guentheri and M. levis (= M. rossiaemeridionalis) were found to differ significantly in terms of both size and shape. M. guentheri had the biggest skull, while M. levis had the smallest. Sexual dimorphism was found in the shape of the skull in M. dogramacii and M. levis. The tympanic bulla area is enlarged in M. anatolicus compared to the other species. Mahalanobis distances (the distance between a point and the group mean, taking into account the within-group covariance-variance matrix) confirm the distinction of the arvalis group (M. levis) and socialis group (Microtus anatolicus, M. dogramacii, M. guentheri).     

A PRELIMINARY REPORT ON THE ACOUSTIC COMMUNICATION IN URUGUAYAN CTENOMYS (RODENTIA,OCTODONTIDAE): BASIC SOUND TYPES

ABSTRACT

Subterranean rodents are interesting organisms for communication studies because of their fossorial way of life. Acoustic communication in the South American genus Ctenomys has not yet been studied even though this species is geographically widespread. This paper represents a preliminary survey of Ctenomys vocalizations. Three types of vocal signals were identified: S-, C- and G-signals. Using field, laboratory and literature data, we provide interpretations on the possible functions of these signals. S-signals are harsh and low-pitched putative spatial localization signals that may also encode for sexual identification. C-signals are relatively high-pitched and narrow-banded FM vocalizations that are sexual signals used by females in a copulatory context. Finally, G-signals are harsh and patternless sounds that are aggressive signals used in direct encounters with con- or hetero- specific individuals.     

Cranial variation in Meriones tristrami (Rodentia: Muridae: Gerbillinae) and its morphological comparison with Meriones persicus,Meriones vinogradovi and Meriones libycus: a geometric morphometric study

Jirds (genus Meriones) comprise a group of rodents, of which the biodiversity is still poorly known. Reason for this is that several species of similar morphologies are known to occur sympatrically. In the north‐west of Iran, four such species occur: Meriones tristrami, Meriones persicus, Meriones vinogradovi and Meriones libycus, prone to several issues of taxonomical ambiguity. A proper characterization of morphological distinctiveness between these species, in relation to the variation within species, could provide the required information for species diagnosis and identification. As some cranial characters of M. tristrami, M. persicus and M. vinogradovi are quite similar, demarcations of species‐specific phenotypic variation have proven to be difficult. To tackle this problem, this study involves a geometric morphometric analysis of skull shape and size, incorporating a large representative sample of these four species, originating from most parts of their natural distribution range (especially for M. tristrami). It is first tested whether M. tristrami can be distinguished from the other sympatric species, and if so, to what degree the species shows a geoclimatic pattern in its skull shape and size when comparing different populations. The shape and size analyses show that M. libycus can be distinguished because of its largest skull and the relatively largest tympanic bulla, and that M. tristrami can be distinguished from the other species. At an intraspecific level in M. tristrami, the Iranian groups (Qazvin and west Iran) do not differ in shape among them, but do so in skull size. They could, however, be distinguished in skull shape from the non‐Iranian populations included (Turkey and Jordan). To what degree this continuous data can now be translated into discrete and diagnostic features, useful for taxonomic purposes, remains to be studied.     

Molecular Phylogeny of Tuco-Tucos, Genus Ctenomys (Rodentia: Octodontidae): Evaluation of the mendocinus Species Group and the Evolution of Asymmetric Sperm

The phylogenetic relationships among 23 individuals representing 14 species of underground hystricognath rodents of the genus Ctenomys were studied by analyzing variation of complete cytochrome b gene sequences. Maximum parsimony, neighbor joining, and maximum likelihood analyses were performed, using the octodontine genera Octodon and Tympanoctomys as outgroups. Our analyses support previous studies based on chromosomes and skull morphology that suggested a clade comprised of Argentinean and Uruguayan populations of C. rionegrensis. This clade is closely related to one comprised of C. flamarioni and the C. mendocinus species complex. Our analyses provide evidence that the symmetric sperm morph, which is common to other South American hystricognath rodents, is the plesiomorphic character state in Ctenomys and in Hystricognathi. Our analyses do not support the hypothesis that the sperm morphs define two major lineages of tuco-tuco species, because species with asymmetric sperm are diphyletic on the basis of cytochrome b sequences, and this morphology appears to have evolved twice in Ctenomys.     

Karyotypic and molecular polymorphisms in <Emphasis Type="Italic">Ctenomys</Emphasis><Emphasis Type="Italic">torquatus</Emphasis> (Rodentia: Ctenomyidae): taxonomic considerations

The rodent genus Ctenomys (tuco-tucos) comprises more than 60 described species, and shows extraordinary inter- and intraspecific karyotypic variation. The most widely distributed species of Ctenomys in Brazil is C. torquatus. Although several cytogenetic studies have been done, the karyotypic variability of this species is still poorly known. In this paper we report two new diploid numbers for C. torquatus: 2n = 40 and 2n = 42, both showing AN = 72. The new distribution limits of C. torquatus here reported include localities in the southern, central and western parts of Rio Grande do Sul (RS) State in southern Brazil. The phylogenetic relationship between C. torquatus from Alegrete, RS, and Ctenomys sp. from Corrientes, Argentina, is described by means of mtDNA cytochrome b analysis. Although both entities share similar karyotypes and sperm morphology, these two species are not phylogenetically close.     

Population and species boundaries in the South American subterranean rodent Ctenomys in a dynamic environment

Subterranean rodents of the genus Ctenomys are an interesting system to assess the effects of habitat instability on the genetic structure of populations. The perrensi group is a complex of three species (C. roigi, C. perrensi and C. dorbignyi) and several forms of uncertain taxonomic status, distributed in the vicinity of the Iberá wetland in Argentina. Because of limited availability of suitable dry habitat, Ctenomys populations are distributed patchily around a vast mosaic of marshes, swamps and lagoons and become connected or isolated over time, depending particularly on the precipitation regime. Genetic variation at 16 microsatellite loci in 169 individuals collected in the area revealed eight clusters of populations which are thought to be evolutionary units, but which do not fit previous species limits. We interpret this lack of congruence between taxonomy and genetic structure as the result of a dynamic population structure. Where populations become connected, hybridization is possible. Where populations become isolated, rapid genetic divergence may occur. In the perrensi group, it appears that both of these factors disrupt the association between different genetic and morphological characters. The study of multiple characters is crucial to the understanding of the recent evolutionary history for dynamic systems such as this. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 368–383.     

Subterranean rodents of the genus Ctenomys (Caviomorpha, Ctenomyidae) follow the converse to Bergmann's rule

Aim We analysed body‐size variation in relation to latitude, longitude, elevation and environmental variables in Ctenomys (tuco‐tucos), subterranean rodents in the Ctenomyidae (Caviomorpha). We tested the existence of inter‐ and intraspecific size clines to determine if these rodents follow Bergmann's rule, to compare intra‐ and interspecific size trends and to assess the relevance of the subterranean lifestyle on these trends. Location South America, south of 15° latitude. Methods This paper is based on 719 specimens of tuco‐tucos from 133 localities of Argentina, Bolivia, Chile, Paraguay, Peru and Uruguay, representing 47 named species and 32 undescribed forms. Intraspecific analyses were performed for Ctenomys talarum Thomas, 1898 and the Ctenomys perrensi Thomas, 1896 species complex. Head and body length and weight were used for estimating body size. Geographical independent variables included latitude, longitude and altitude. Environmental independent variables were mean minimal and maximal monthly temperature, mean annual temperature, mean minimal and maximal precipitation, and total annual precipitation. To estimate seasonality, the annual variability of the climatic factors was calculated as their coefficients of variation and the difference between maximum and minimum values. Mean annual actual evapotranspiration (AET), and mean annual, January (summer) and July (winter) potential evapotranspiration (PET) values were also calculated for each locality, as well as annual, summer and winter water balance (WB). Statistical analyses consisted of simple and multiple regression and nonparametric correlation. Results Body size of Ctenomys decreases interspecifically from 15°00′ S to 48°15′ S and from 56°33′ W to 71°46′ W, and is positively correlated with ambient temperature and precipitation. The best predictors of body size according to multiple regression analyses were mean annual temperature, the difference between mean maximum and minimum annual temperatures, annual PET, the difference between summer and winter PET, and annual and winter water balance. These patterns are repeated, but not identically, at a smaller geographical scale within the species C. talarum and the superspecies C. perrensi. Main conclusions Tuco‐tucos follow the converse to Bergmann's rule at the interspecific level. At the intraspecific level some parallel trends were observed, but the smaller scale of these analyses, involving a very reduced variation of environmental factors, necessitates caution in interpreting results. The subterranean lifestyle probably insulates these rodents from the external temperature. The observed latitudinal body‐size gradients are more probably related to seasonality, ambient energy, primary productivity and/or intensity of predation.     

Ontogeny and cranial morphology of the tympanic region of the Tupaiidae, with special reference to Ptilocercus

The structure of the tympanic region of the skull of Ptilocercus lowii was studied in an embryo of 30 mm crown-rump length and in 5 osteocrania. As in Tupaia, the anterior wall of the bulla of Ptilocercus is not completed by a tympanic process of the alisphenoid, contrary to earlier reports. Ptilocercus resembles Tupaia in the following derived characters. The ventral wall of the tympanic cavity is formed by a rostral entotympanic and by a caudal tympanic process of the petrosal. The entotympanic develops in primary connection with the tubal cartilage. The tympanic aperture of the auditory tube is bordered by the entotympanic. The ring-shaped tympanicum is covered by the entotympanicum and is aphaneric. The musculus tensor tympani is lacking. Among mammals, these characters can be regarded as synapomorphic for the Tupaiidae, that is, to have been present in the common ancestor of the two subfamilies. From the evidence of the tympanic region, the Tupaiidae, therefore, form a monophyletic group. Besides these synapomorphies, there are remarkable differences between Ptilocercus and Tupaia in the structure of the bulla. In Ptilocercus the bulla is smaller and less pneumatized than in Tupaia. An anterior intrabullar septum, present in Tupaia, is lacking in Ptilocercus. The epitympanic wing of the alisphenoid is smaller in Ptilocercus than in Tupaia. A lateral prefacial commissure of the tegmen tympani is present in Ptilocercus, but absent in Tupaia. The caudal tympanic process of the petrosal is larger in Ptilocercus than in Tupaia. These characters are autapomorphic for the Ptilocercinae and for the Tupaiinae, respectively. They demonstrate that the auditory bulla of Ptilocercus and that of Tupaia have evolved independently to a considerable extent. An early phylogenetic separation of their respective ancestors seems likely. The tympanic region of the skull provides no evidence for close relationships of the tree shrews to the primates or to any other eutherians. The classification of the Tupaiidae in a separate order, Scandentia, is supported.     

Function‐related Drivers of Skull Morphometric Variation and Sexual Size Dimorphism in a Subterranean Rodent,Plateau Zokor (Eospalax baileyi)

Sexual dimorphism is prevalent in most living organisms. The difference in size between sexes of a given species is generally known as sexual size dimorphism (SSD). The magnitude of the SSD is determined by Rensch's rule where size dimorphism increases with increasing body size when the male is the larger sex and decreases with increasing average body size when the female is the larger sex. The unique underground environment that zokors (Eospalax baileyi) live under in the severe habitat of the Qinghai‐Tibetan Plateau (QTP) could create SSD selection pressures that may or may not be supported by Rensch's rule, making this scientific question worthy of investigation. In this study, we investigated the individual variation between sexes in body size and SSD of plateau zokors using measurements of 19 morphological traits. We also investigated the evolutionary mechanisms underlying SSD in plateau zokors. Moreover, we applied Rensch's rule to all extant zokor species. Our results showed male‐biased SSD in plateau zokors: The body‐ and head‐related measurements were greater in males than in females. Linear regression analysis between body length, body weight, and carcass weight showed significant relationships with some traits such as skull length, lower incisor length, and tympanic bulla width, which might support our prediction that males have faster growth rates than females. Further, the SSD pattern corroborated the assumption of Rensch's rule in plateau zokors but not in the other zokor species. Our findings suggest that the natural underground habitat and behavioral differences between sexes can generate selection pressures on male traits and contribute to the evolution of SSD in plateau zokors.     

The Ear Region of the Pen-tailed Treeshrew, Ptilocercus lowii Gray, 1848 (Placentalia, Scandentia, Ptilocercidae)

The ear region of the pen-tailed treeshrew, Ptilocercus lowii Gray, 1848 (Scandentia, Ptilocercidae), is described and illustrated in detail based on five museum specimens from the National Museum of Natural History, two with the auditory bulla removed exposing the intratympanic surfaces. Soft tissues (arteries, veins, nerves, and muscles) are reconstructed onto the adult skulls based on published reports of these elements in a fetal P. lowii. Comparisons are made with four specimens of the common treeshrew, the tupaiid Tupaia glis (Diard, 1820), from the Carnegie Museum of Natural History, including one with the auditory bulla removed. The mammalian ear region widely is regarded to be a rich source of characters for phylogenetic analysis. This study supports this view by identifying numerous features that are shared between the two treeshrews as well as numerous features that distinguish them. Several features used in the past to distinguish tupaiid treeshrews from primates are found to differ between P. lowii and T. glis: the composition of the bony tubes for the internal carotid artery and the composition of the intrabullar septa and spaces. Despite the compositional differences, it seems likely that the bony carotid tubes and intrabullar septa and spaces shared by P. lowii and T. glis occurred in their common ancestor. Evaluating the utility of these and other ear region features awaits future phylogenetic analysis of treeshrews and related Euarchontoglires.     

From Problem Taxa to Problem Solver: A New Miocene Family,Tranatocetidae, Brings Perspective on Baleen Whale Evolution

Miocene baleen whales were highly diverse and included tens of genera. However, their taxonomy and phylogeny, as well as relationships with living whales, are still a subject of controversy. Here, “Mesocetus” argillarius, a poorly known specimen from Denmark, is redescribed with a focus on the cranial anatomy. It was found to represent not only a new genus, Tranatocetus gen. nov., but also a new family; Tranatocetidae. The whales of this family have the rostral bones either overriding or dividing the frontals; the rostral bones are contacting the parietals and nasals dividing the maxillae on the vertex; the occipital shield is dorsoventrally bent. The tympanic bulla is particularly characteristic of this family featuring a short, narrow anterior portion with a rounded or squared anterior end and a wider and higher posterior portion that is swollen in the posteroventral area. A phylogenetic analysis including 51 taxa supports a monophyletic group comprising most Neogene and modern whales, with Tranatocetidae being possibly closer related to Balaenopteridae (rorquals) than to Cetotheriidae. Tranatocetidae exhibit a charahteristic bulla shape. In fact, all Neogene and modern mysticete families examined have a unique shape of the tympanic bulla that is diagnostic at family-level. Inclusion of problematic taxa like Tranatocetus argillarius in phylogenies brings new understanding of the distribution and diagnostic value of character traits. This underlines the need for re-examination of earlier described specimens in the light of the wealth of new information published in later years.     

Partitions in the carnivoran auditory bulla: their formation and significance for systematics

The common notion that the septa in the carnivoran auditory bulla are formed by the growth of bone edges inwards the bullar cavity is a mistaken assumption based on the data of the late 19th century. Intrabullar partitions are in fact a result of the differential resorption of the bulla internal surface during the growth of the external surface. A septum develops at the boundary between local, relatively independent, ‘inflations’ of the bulla wall. This explanation, given by Van Kampen in 1905 for the case of the Canidae and some Mustelidae, can be applied to the whole order, including the aeluroid families with their ‘bilaminar’ septum bullae. Such an approach seems to solve the problem of homology of the intrabullar septa throughout the Carnivora, a question which has long been confused because of insufficient knowledge of septum morphogenesis. The partitions can really be considered as indicators of independent attempts to increase the size of a middle‐ear cavity among the infraorders. This conclusion follows immediately from the difference between major carnivoran taxa in the arrangement of separate inflations on the bulla wall, which can be considered as additional sinuses enlarging the hypotympanic space. It is precisely this difference that conditions the relative contribution of several bones (mainly of the ectotympanic and caudal entotympanic) to the intrabullar septa. Thus, the initial topographies of the above sinuses – whichever subsequent bone modelling of septa occurs – represent unique patterns useful in the higher‐level systematics of the Carnivora.