The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals

Dryolestes leiriensis is a Late Jurassic fossil mammal of the dryolestoid superfamily in the cladotherian clade that includes the extant marsupials and placentals. We used high resolution micro‐computed tomography (µCT) scanning and digital reconstruction of the virtual endocast of the inner ear to show that its cochlear canal is coiled through 270°, and has a cribriform plate with the spiral cochlear nerve foramina between the internal acoustic meatus and the cochlear bony labyrinth. The cochlear canal has the primary bony lamina for the basilar membrane with a partially formed (or partially preserved) canal for the cochlear spiral ganglion. These structures, in their fully developed condition, form the modiolus (the bony spiral structure) of the fully coiled cochlea in extant marsupial and placental mammals. The CT data show that the secondary bony lamina is present, although less developed than in another dryolestoid Henkelotherium and in the prototribosphenidan Vincelestes. The presence of the primary bony lamina with spiral ganglion canal suggests a dense and finely distributed cochlear nerve innervation of the hair cells for improved resolution of sound frequencies. The primary, and very probably also the secondary, bony laminae are correlated with a more rigid support for the basilar membrane and a narrower width of this membrane, both of which are key soft‐tissue characteristics for more sensitive hearing for higher frequency sound. All these cochlear features originated prior to the full coiling of the therian mammal cochlea beyond one full turn, suggesting that the adaptation to hearing a wider range of sound frequencies, especially higher frequencies with refined resolution, has an ancient evolutionary origin no later than the Late Jurassic in therian evolution. The petrosal of Dryolestes has added several features that are not preserved in the petrosal of Henkelotherium. The petrosal characters of dryolestoid mammals are essentially the same as those of Vincelestes, helping to corroborate the synapomorphies of the cladotherian clade in neural, vascular, and other petrosal characteristics. The petrosal characteristics of Dryolestes and Henkelotherium together represent the ancestral morphotype of the cladotherian clade (Dryolestoidea + Vincelestes + extant Theria) from which the extant therian mammals evolved their ear region characteristics. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 433–463.     

Trophic convergence drives morphological convergence in marine tetrapods

Marine tetrapod clades (e.g. seals, whales) independently adapted to marine life through the Mesozoic and Caenozoic, and provide iconic examples of convergent evolution. Apparent morphological convergence is often explained as the result of adaptation to similar ecological niches. However, quantitative tests of this hypothesis are uncommon. We use dietary data to classify the feeding ecology of extant marine tetrapods and identify patterns in skull and tooth morphology that discriminate trophic groups across clades. Mapping these patterns onto phylogeny reveals coordinated evolutionary shifts in diet and morphology in different marine tetrapod lineages. Similarities in morphology between species with similar diets—even across large phylogenetic distances—are consistent with previous hypotheses that shared functional constraints drive convergent evolution in marine tetrapods.     

Vocal coselection in rat pup ultrasonic vocalizations

Selective breeding and natural selection that select for one trait often bring along other correlated traits via coselection. Selective breeding for an infantile trait, high or low call rates of isolation‐induced ultrasonic vocalization of rat pups, also alters functions of some brain systems and emotional behaviors throughout life. We examined the effect of breeding for call rate on acoustic parameters that are of communicative significance. Selecting for higher call rate produced calls of significantly increased amplitude and bandwidth relative to a randomly bred line. Selecting for lower rate produced calls of decreased duration. These nonmorphological, functional trait changes demonstrate enhanced communicatory potential and energy expenditure for the High line and the opposite for the Low line. This demonstration of coselection in a communicatory system suggests an underlying heritable suite of linked acoustic vocalization characteristics that in noisy environments could enhance dam–pup communication and lead to selection of emotionality traits with beneficial responses to stress.     

Generic species richness and body mass in North American mammals: Support for the inverse relationship of body size and speciation rate

Generic species richness, the number of species per genus, is examined as a function of mean generic body mass for extant North American mammals. Species richness decreases as an inverse power function with increased mass, and the Spearman rank correlation coefficient of the logio transformed data is significant (r_s= ‐0.37). When the data are partitioned by trophic level, the relationship is not statistically significant for carnivores but strengthens for herbivores (r_s= ‐0.46). This interesting but incidental effect is due to the negligible number of diminutive and excessively large carnivores, which is in turn determined by foraging strategies. Alternate hypotheses for the “right‐skewed”; size distribution of modern North American mammals, such as disproportionate extinction of large species, differential species longevity, and a geographical scaling function, are rejected in favor of the proposition that elevated levels of speciation are restricted to animals of small body mass, as originally proposed by Gould and Eldredge (1977). This phenomenon is explained as a function of habitat restriction and particularly in herbivores, limited home range size. Aquatic mammals, regardless of body size, speciate rarely. Cope's Rule, the tendency of many animal groups to evolve towards large size, is understood as a probabilistic statement reflecting the phylogenetic tendencies of a disproportionately high number of small species alive at any given point in time.     

试论动物考古中的小哺乳动物研究

小哺乳动物种类及其数量,在哺乳动物中占据大多数。它们是自然界生态链中非常重要的、不可缺少的环节。它们体质进化较快,大部分种类居住区域选择性强,种群活动范围比较小。所以研究小哺乳动物种群面貌及其生态特征,可以帮助我们判断古遗址相对时代,解析历史时期的生态演变。小哺乳动物的生态指示性,能够帮助我们准确复原和研究古遗址环境背景。它们的分布状况及很多生态规律,在帮助我们研究古遗址环境卫生及古居民住房条件等方面有独特作用。小哺乳动物种群变化与人类经济生产的互动性,以及它们与人类的伴栖关系、人类对小哺乳动物资源的开发和利用等,均是动物考古工作中应该重视和积极开展研究的内容。开展小哺乳动物研究,需要必要的工作计划、专业技术和实验设备。我国旧石器时代的小哺乳动物考古已取得丰硕成果,新石器时代及其以后的小哺乳动物考古尚有待加强。小哺乳动物研究工作的拓展,将会有力促进动物考古学进展,促使动物考古在考古学实践中发挥出更大作用。     

Ultrasonic vocalizations in mouse models for speech and socio‐cognitive disorders: insights into the evolution of vocal communication

Comparative analyses used to reconstruct the evolution of traits associated with the human language faculty, including its socio‐cognitive underpinnings, highlight the importance of evolutionary constraints limiting vocal learning in non‐human primates. After a brief overview of this field of research and the neural basis of primate vocalizations, we review studies that have addressed the genetic basis of usage and structure of ultrasonic communication in mice, with a focus on the gene FOXP2 involved in specific language impairments and neuroligin genes (NL‐3 and NL‐4) involved in autism spectrum disorders. Knockout of FoxP2 leads to reduced vocal behavior and eventually premature death. Introducing the human variant of FoxP2 protein into mice, in contrast, results in shifts in frequency and modulation of pup ultrasonic vocalizations. Knockout of NL‐3 and NL‐4 in mice diminishes social behavior and vocalizations. Although such studies may provide insights into the molecular and neural basis of social and communicative behavior, the structure of mouse vocalizations is largely innate, limiting the suitability of the mouse model to study human speech, a learned mode of production. Although knockout or replacement of single genes has perceptible effects on behavior, these genes are part of larger networks whose functions remain poorly understood. In humans, for instance, deficiencies in NL‐4 can lead to a broad spectrum of disorders, suggesting that further factors (experiential and/or genetic) contribute to the variation in clinical symptoms. The precise nature as well as the interaction of these factors is yet to be determined.     

Oligosaccharides of milk and colostrum in non-human mammals

Mammalian milk or colostrum usually contains, in addition to lactose, a variety of neutral and acidic oligosaccharides. Although the oligosaccharides of human milk have been reviewed in several recent publications, those of non-human mammals have received much less attention. This paper reviews the chemical structures and the variety of milk oligosaccharides in species other than humans, including placental mammals (e.g. primates, domestic herbivores, bears and other carnivores, the rat and the elephant) as well as monotremes (platypus and echidna) and marsupials (e.g. wallaby). The gastrointestinal digestion and absorption and the possible biological functions of these oligosaccharides are also discussed.     

The maximal body mass–area relationship in island mammals

Aim A positive power relationship between maximal body mass and land area has previously been reported of the form M_max ∝ Area^0.5 whilst allometric scaling theory predicts either M_max ∝ Area^1.33 or M_max ∝ Area¹. We provide an analysis of the maximal mass–area relationship for four island systems, to test the hypothesis that community relaxation following isolation converges in each case to a slope of Area^0.5. Location Islands of the Japanese archipelago, the western Mediterranean, the Sea of Cortés and Southeast Asia. Methods We calculated the relationship between island area and the maximal body mass of the largest mammal species on the island using linear regression models with log‐transformed variables, and tested the hypothesis that the slopes were not significantly different from 0.5. Results We found a slope of 0.47 within the Japanese archipelago, 0.42 for western Mediterranean islands, 0.73 for the Sea of Cortés islands and 0.50 for Southeast Asian islands. None of these slopes were significantly different from 0.5. Main conclusions Our results provide further empirical support for previous findings of a general maximal body mass–area relationship of M_max ∝ Area^0.5, but they deviate from theoretical predictions. We hypothesize that this mass–area relationship was the ultimate end point of community relaxation initiated by the isolation of the mammal communities. Maximal body mass on each island today probably reflects the interaction between energetic constraints, home range size and island area.     

Individuality in the vocalizations of infant and adult coppery titi monkeys (Plecturocebus cupreus)

As social animals, many primates use acoustic communication to maintain relationships. Vocal individuality has been documented in a diverse range of primate species and call types, many of which have presumably different functions. Auditory recognition of one's neighbors may confer a selective advantage if identifying conspecifics decreases the need to participate in costly territorial behaviors. Alternatively, vocal individuality may be nonadaptive and the result of a unique combination of genetics and environment. Pair-bonded primates, in particular, often participate in coordinated vocal duets that can be heard over long distances by neighboring conspecifics. In contrast to adult calls, infant vocalizations are short-range and used for intragroup communication. Here, we provide two separate but complementary analyses of vocal individuality in distinct call types of coppery titi monkeys (Plecturocebus cupreus) to test whether individuality occurs in call types from animals of different age classes with presumably different functions. We analyzed 600 trill vocalizations from 30 infants and 169 pulse-chirp duet vocalizations from 30 adult titi monkeys. We predicted that duet contributions would exhibit a higher degree of individuality than infant trills, given their assumed function for long-distance, intergroup communication. We estimated 7 features from infant trills and 16 features from spectrograms of adult pulse-chirps, then used discriminant function analysis with leave-one-out cross-validation to classify individuals. We correctly classified infants with 48% accuracy and adults with 83% accuracy. To further investigate variance in call features, we used a multivariate variance components model to estimate variance partitioning in features across two levels: within- and between-individuals. Between-individual variance was the most important source of variance for all features in adults, and three of four features in infants. We show that pulse-chirps of adult titi monkey duets are individually distinct, and infant trills are less individually distinct, which may be due to the different functions of the vocalizations.     

Transposable elements and the evolution of genome organization in mammals

All mammalian transposable elements characterized to date appear to be nonrandomly distributed in the mammalian genome. While no element has been found to be exclusively restricted in its chromosomal location, LINE elements and some retrovirus-like elements are preferentially accumulated in G-banding regions of the chromosomes, and in some cases in the sex chromosomes, while SINE elements occur preferentially in R-banding regions. Four mechanisms are presented which may explain the nonrandom genomic distribution of mammalian transposons: i) sequence-specific insertion, ii) S-phase insertion, iii) ectopic excision, and iv) recombinational editing. Some of the available data are consistent with each of these four models, but no single model is sufficient to explain all of the existing data.     

To converge or not to converge in environmental space: testing for similar environments between analogous succulent plants of North America and Africa

Background and Aims

Convergent evolution is invoked to explain similarity between unrelated organisms in similar environments, but most evaluations of convergence analyse similarity of organismal attributes rather than of the environment. This study focuses on the globular succulent plants of the Americas, the cacti, and their counterparts in Africa in the ice-plant, spurge and milkweed families. Though often held up as paragons of convergent morphological evolution, the environmental similarity of these plants has remained largely unexamined from a quantitative perspective.

Methods

Five hotspots (centres of high species diversity of globular succulents) were selected, two in Mexico and three in South Africa. Their environments were compared using niche modelling tools, randomization tests of niche similarity and multivariate analyses to test for environmental similarity.

Key Results

Although the sites selected have ‘similar’ but unrelated life forms, almost all our results highlighted more climate differences than similarities between the hotspots. Interprediction of niches within and between continents, a niche equivalence test, and MANOVA results showed significant differences. In contrast, a niche similarity test showed that the comparisons of Cuatrociénegas–Richtersveld, Huizache–Knersvlakte and Huizache–Richtersveld were similar.

Conclusions

Differences in rainfall and temperature regimes and the potential effect of edaphic factors may be involved in the differences between the hotspots. In addition, differences in structure, morphology and physiology of the globular succulents may coincide with some of the climatic dissimilarities; i.e. given convergence as the evolution of similar morphologies under similar conditions, then it may be that differing environments diagnose inconspicuous morphological differences. Moreover, although fine-scale differences between sites were found, a coarser perspective shows that these sites are clearly similar as drylands with relatively moderate drought and mild temperatures, illustrating how all studies of convergence must address the issue of how similar two entities must be before they are considered convergent.     

Abundance and distribution of mammals in Katavi National Park, Tanzania

Ground transects were used to determine densities of 24 larger mammals in Katavi National Park. The Park consists of miombo woodland habitat and two seasonal lakes. Mammalian biomass was extremely high due primarily to large numbers of buffalo. The highest mammal densities were found around Lake Chada to the south-east of the Park. Contrary to earlier reports, species' densities did not differ significantly between dry, wet and intermediate seasons, suggesting that, aside from elephant and warthog, mammals did not enter or leave the Park in large numbers. Similarly, aside from zebra and waterbuck, sightings of species in different vegetation types did not change markedly between seasons. Thus, seasonal lakes in Katavi National Park support very high local concentrations rather than acting as dry season refuges for mammals outside the Park.     

Ultrasonic vocalizations of adult male Foxp2‐mutant mice: behavioral contexts of arousal and emotion

Adult mouse ultrasonic vocalizations (USVs) occur in multiple behavioral and stimulus contexts associated with various levels of arousal, emotion and social interaction. Here, in three experiments of increasing stimulus intensity (water; female urine; male interacting with adult female), we tested the hypothesis that USVs of adult males express the strength of arousal and emotion via different USV parameters (18 parameters analyzed). Furthermore, we analyzed two mouse lines with heterozygous Foxp2 mutations (R552H missense, S321X nonsense), known to produce severe speech and language disorders in humans. These experiments allowed us to test whether intact Foxp2 function is necessary for developing full adult USV repertoires, and whether mutations of this gene influence instinctive vocal expressions based on arousal and emotion. The results suggest that USV calling rate characterizes the arousal level, while sound pressure and spectrotemporal call complexity (overtones/harmonics, type of frequency jumps) may provide indices of levels of positive emotion. The presence of Foxp2 mutations did not qualitatively affect the USVs; all USV types that were found in wild‐type animals also occurred in heterozygous mutants. However, mice with Foxp2 mutations displayed quantitative differences in USVs as compared to wild‐types, and these changes were context dependent. Compared to wild‐type animals, heterozygous mutants emitted mainly longer and louder USVs at higher minimum frequencies with a higher occurrence rate of overtones/harmonics and complex frequency jump types. We discuss possible hypotheses about Foxp2 influence on emotional vocal expressions, which can be investigated in future experiments using selective knockdown of Foxp2 in specific brain circuits.     

Repeated functional convergent effects of NaV1.7 on acid insensitivity in hibernating mammals

Hibernating mammals need to be insensitive to acid in order to cope with conditions of high CO₂; however, the molecular basis of acid tolerance remains largely unknown. The African naked mole-rat (Heterocephalus glaber) and hibernating mammals share similar environments and physiological features. In the naked mole-rat, acid insensitivity has been shown to be conferred by the functional motif of the sodium ion channel Na_V1.7. There is now an opportunity to evaluate acid insensitivity in other taxa. In this study, we tested for functional convergence of Na_V1.7 in 71 species of mammals, including 22 species that hibernate. Our analyses revealed a functional convergence of amino acid sequences, which occurred at least six times independently in mammals that hibernate. Evolutionary analyses determined that the convergence results from both parallel and divergent evolution of residues in the functional motif. Our findings not only identify the functional molecules responsible for acid insensitivity in hibernating mammals, but also open new avenues to elucidate the molecular underpinnings of acid insensitivity in mammals.     

Automated identification and clustering of subunits within delphinid vocalizations

Tonal vocalizations or whistles produced by many species of delphinids range from simple tones to complex frequency contours. Whistle structure varies in duration, frequency, and composition between delphinid species, as well as between populations and individuals. Categorization of whistles may be improved by decomposition of complex calls into simpler subunits, much like the use of phonemes in classification of human speech. We identify a potential whistle decomposition scheme and normalization process to facilitate comparison of whistle subunits derived from tonal vocalizations of bottlenose dolphins (Tursiops truncatus), spinner dolphins (Stenella longirostris), and short‐beaked common dolphins (Delphinus delphis). Network analysis is then used to compare subunits within the vocal corpus of each species. By processing whistles through a series of steps including segmentation, normalization, and dynamic time warping, we are able to automatically cluster selected subunits by shape, regardless of differences in absolute frequency or moderate differences in duration. Using the clustered subunits, we demonstrate a preliminary species classification scheme based on rates of subunit occurrence in vocal repertoires. This provides a potential mechanism for comparing the structure of complex vocalizations within and between species.