A preliminary analysis of correlations between chewing motor patterns and mandibular morphology across mammals

The establishment of a publicly-accessible repository of physiological data on feeding in mammals, the Feeding Experiments End-user Database (FEED), along with improvements in reconstruction of mammalian phylogeny, significantly improves our ability to address long-standing questions about the evolution of mammalian feeding. In this study, we use comparative phylogenetic methods to examine correlations between jaw robusticity and both the relative recruitment and the relative time of peak activity for the superficial masseter, deep masseter, and temporalis muscles across 19 mammalian species from six orders. We find little evidence for a relationship between jaw robusticity and electromyographic (EMG) activity for either the superficial masseter or temporalis muscles across mammals. We hypothesize that future analyses may identify significant associations between these physiological and morphological variables within subgroups of mammals that share similar diets, feeding behaviors, and/or phylogenetic histories. Alternatively, the relative peak recruitment and timing of the balancing-side (i.e., non-chewing-side) deep masseter muscle (BDM) is significantly negatively correlated with the relative area of the mandibular symphysis across our mammalian sample. This relationship exists despite BDM activity being associated with different loading regimes in the symphyses of primates compared to ungulates, suggesting a basic association between magnitude of symphyseal loads and symphyseal area among these mammals. Because our sample primarily represents mammals that use significant transverse movements during chewing, future research should address whether the correlations between BDM activity and symphyseal morphology characterize all mammals or should be restricted to this "transverse chewing" group. Finally, the significant correlations observed in this study suggest that physiological parameters are an integrated and evolving component of feeding across mammals.     

The evolution of feeding motor patterns in vertebrates

Despite considerable skepticism, researchers have found that the patterns of muscle activation that control feeding behaviors of lower vertebrates have been surprisingly conserved during evolution. This tendency for conservation among taxa appears in the face of marked flexibility of motor patterns within individuals. One interpretation of these apparently conflicting trends is that the most effective motor pattern for any given feeding situation is the same across substantial phylogenetic distances and morphological differences. The novel evolutionary insight provided by this research is that historical changes to motor patterns are a relatively infrequent source of trophic innovation. The spectacular diversity of feeding abilities and feeding ecology in lower vertebrates is based mostly on axes of variation, and on the innovations in the organization of muscles and the skeletal linkage systems that they drive.     

The evolution of the cortico-cerebellar complex in primates: anatomical connections predict patterns of correlated evolution

Investigations into the evolution of the primate brain have tended to neglect the role of connectivity in determining which brain structures have changed in size, focusing instead on changes in the size of the whole brain or of individual brain structures, such as the neocortex, in isolation. We show that the primate cerebellum, neocortex, vestibular nuclei and relays between them exhibit correlated volumetric evolution, even after removing the effects of change in other structures. The patterns of correlated evolution among individual nuclei correspond to their known patterns of connectivity. These results support the idea that the brain evolved by mosaic size change in arrays of functionally connected structures. Furthermore, they suggest that the much discussed expansion of the primate neocortex should be re-evaluated in the light of conjoint cerebellar expansion.     

Biogeography explains cophylogenetic patterns in toucan chewing lice

Historically, comparisons of host and parasite phylogenies have concentrated on cospeciation. However, many of these comparisons have demonstrated that the phylogenies of hosts and parasites are seldom completely congruent, suggesting that phenomena other than cospeciation play an important role in the evolution of host-parasite assemblages. Other coevolutionary phenomena, such as host switching, parasite duplication (speciation on the host), sorting (extinction), and failure to speciate can also influence host-parasite assemblages. Using mitochondrial and nuclear protein-coding DNA sequences, I reconstructed the phylogeny of ectoparasitic toucan chewing lice in the Austrophilopterus cancellosus subspecies complex and compared this phylogeny with the phylogeny of the hosts, the Ramphastos toucans, to reconstruct the history of coevolutionary events in this host-parasite assemblage. Three salient findings emerged. First, reconstructions of host and louse phylogenies indicate that they do not branch in parallel, and their cophylogenetic history shows little or no significant cospeciation. Second, members of monophyletic Austrophilopterus toucan louse lineages are not necessarily restricted to monophyletic host lineages. Often, closely related lice are found on more distantly related but sympatric toucan hosts. Third, the geographic distribution of the hosts apparently plays a role in the speciation of these lice. These results suggest that for some louse lineages biogeography may be more important than host associations in structuring louse populations and species, particularly when host life history (e.g., hole nesting) or parasite life history (e.g., phoresis) might promote frequent host switching events between syntopic host species. These findings highlight the importance of integrating biogeographic information into cophylogenetic studies.     

Effects of dietary inositol with sucrose stimulation on chewing and swallowing motor patterns in larvae of the silkworm Bombyx mori

The effects of dietary inositol with sucrose stimulation on chewing and swallowing motor patterns in the larvae of Bombyx mori L. are investigated. Feeding activities of the larvae are significantly enhanced by a test diet containing an inositol–sucrose mixture compared with a test diet of sucrose only. Motor patterns of the mandibular closer muscle are accelerated with shorter burst durations and shorter inter‐burst intervals with the test diet of inositol–sucrose compared with sucrose. In terms of swallowing behaviours, inositol–sucrose shortens the duration of drinking. Motor patterns of the cibarial compressor muscle are accelerated with shorter burst durations and shorter inter‐burst intervals with the inositol–sucrose mixture. Peripheral interactions between inositol‐ and sucrose‐sensitive cells in the maxilla are not detected. Thus, such interactions cannot explain the positive effects of inositol on chewing and swallowing. Responses of inositol‐sensitive cells in the epipharyngeal sensillum are not affected by sucrose. These results suggest that dietary inositol can modify chewing and swallowing motor patterns when coupled with sucrose stimuli. These modifications may occur in the central neural networks involved in chewing and swallowing motor patterns but not in peripheral sensory interactions.     

Telemetric motor activity in children. A preliminary study

A lightweight telemetric mobility sensing system was used to study the relationship between high levels of motor activity during free-play and school performance. Among the 21 normal children, there was a significant correlation between high ankle motor activity during free-play, poor school achievement, the presence of neurological soft signs, and a poor self-image. Those normals whose free-play ankle activity was above the mean, also had significantly more errors and performed at a significantly lower level on the Bender Visual Motor Gestalt Test than children whose activity was below the mean. This preliminary study suggests that the telemetric mobility sensing system can be easily applied to children to assess clinically relevant components of psychomotor activity.     

Plasticity and evolution in correlated suites of traits

When organisms are faced with new or changing environments, a central challenge is the coordination of adaptive shifts in many different phenotypic traits. Relationships among traits may facilitate or constrain evolutionary responses to selection, depending on whether the direction of selection is aligned or opposed to the pattern of trait correlations. Attempts to predict evolutionary potential in correlated traits generally assume that correlations are stable across time and space; however, increasing evidence suggests that this may not be the case, and flexibility in trait correlations could bias evolutionary trajectories. We examined genetic and environmental influences on variation and covariation in a suite of behavioural traits to understand if and how flexibility in trait correlations influences adaptation to novel environments. We tested the role of genetic and environmental influences on behavioural trait correlations by comparing Trinidadian guppies (Poecilia reticulata) historically adapted to high‐ and low‐predation environments that were reared under native and non‐native environmental conditions. Both high‐ and low‐predation fish exhibited increased behavioural variance when reared under non‐native vs. native environmental conditions, and rearing in the non‐native environment shifted the major axis of variation among behaviours. Our findings emphasize that trait correlations observed in one population or environment may not predict correlations in another and that environmentally induced plasticity in correlations may bias evolutionary divergence in novel environments.     

Inference of global HIV-1 sequence patterns and preliminary feature analysis

The epidemiology of HIV-1 varies in different areas of the world, and it is possible that this complexity may leave unique footprints in the viral genome. Thus, we attempted to find significant patterns in global HIV-1 genome sequences. By applying the rule inference algorithm RIPPER (Repeated Incremental Pruning to Produce Error Reduction) to multiple sequence alignments of Env sequences from four classes of compiled datasets, we generated four sets of signature patterns. We found that these patterns were able to distinguish southeastern Asian from nonsoutheastern Asian sequences with 97.5% accuracy, Chinese from non-Chinese sequences with 98.3% accuracy, African from non-African sequences with 88.4% accuracy, and southern African from non-southern African sequences with 91.2% accuracy. These patterns showed different associations with subtypes and with amino acid positions. In addition, some signature patterns were characteristic of the geographic area from which the sample was taken. Amino acid features corresponding to the phylogenetic clustering of HIV-1 sequences were consistent with some of the deduced patterns. Using a combination of patterns inferred from subtypes B, C, and all subtypes chimeric with CRF01_AE worldwide, we found that signature patterns of subtype C were extremely common in some sampled countries (for example, Zambia in southern Africa), which may hint at the origin of this HIV-1 subtype and the need to pay special attention to this area of Africa. Signature patterns of subtype B sequences were associated with different countries. Even more, there are distinct patterns at single position 21 with glycine, leucine and isoleucine corresponding to subtype C, B and all possible recombination forms chimeric with CRF01_AE, which also indicate distinct geographic features. Our method widens the scope of inference of signature from geographic, genetic, and genomic viewpoints. These findings may provide a valuable reference for epidemiological research or vaccine design.     

Broad patterns of speciation are correlated with the evolution of new silk proteins in spiders but not in the lepidoptera

Silk synthesis is an ancestral character of both the Lepidoptera and the Araneae. Araneae evolution is marked by an increased commitment to a silk-producing physiology. At least three major Araneae speciation events are correlated with the evolution of new silk-producing glands and new silk proteins. In contrast, although 98% of the Lepidoptera produce silk, there appears to be no relationship between silk use, protein types, and species numbers. The differences in these two systems, both meeting a need to produce a large volume of protein, may reflect predictable resource availability to herbivorous Lepidoptera larvae but fluctuating resource availability to carnivorous spiders.     

A comparative study of motor patterns during pre-flight warm-up in hawkmoths

Summary Temporal patterns of activation of flight muscles were recorded by means of wires placed extracellularly in thoracic muscles. In the five species of hawkmoths studied, wingstrokes of small amplitude were produced during a preflight warm-up by synchronous contractions of certain groups of muscles which are antagonists in flight. The main depressor muscle, the dorsal longitudinal, was excited in synchrony with some or all of the indirect elevator muscles. Three direct muscles, the subalar, basalar and third axillary muscles, were usually excited out of phase with the dorsal longitudinal muscle. However, details of the motor pattern varied from species to species. During fixed flight phase changes comparable in magnitude to those which occur during the transition from warm-up to flight were observed in Manduca sexta and Smerinthus cerisyi. The results (summarized in Table 2) suggest that a variety of warm-up patterns evolved within the Sphingidae as modifications of a common mechanism generating flight motor patterns.I thank Dr. Harry Lange for assistance in the initial collecting of Manduca sexta and for identifying specimens of this species.     

Bayesian analysis of correlated evolution of discrete characters by reversible-jump Markov chain Monte Carlo

We describe a Bayesian method for investigating correlated evolution of discrete binary traits on phylogenetic trees. The method fits a continuous-time Markov model to a pair of traits, seeking the best fitting models that describe their joint evolution on a phylogeny. We employ the methodology of reversible-jump (RJ) Markov chain Monte Carlo to search among the large number of possible models, some of which conform to independent evolution of the two traits, others to correlated evolution. The RJ Markov chain visits these models in proportion to their posterior probabilities, thereby directly estimating the support for the hypothesis of correlated evolution. In addition, the RJ Markov chain simultaneously estimates the posterior distributions of the rate parameters of the model of trait evolution. These posterior distributions can be used to test among alternative evolutionary scenarios to explain the observed data. All results are integrated over a sample of phylogenetic trees to account for phylogenetic uncertainty. We implement the method in a program called RJ Discrete and illustrate it by analyzing the question of whether mating system and advertisement of estrus by females have coevolved in the Old World monkeys and great apes.     

Cranial shape and correlated characters in crocodilian evolution

Crocodilians show a high degree of cranial variation and convergence throughout their 80 million-year fossil record that complicates their phylogenetic reconstruction. Conflicting phylogenetic results from different data partitions and character homoplasies typify crocodilian phylogeny, and differences between molecular and morphological phylogenetic hypotheses are believed to be associated with the slender-snout skull shape of Gavialis gangeticus and Tomistoma schlegelii. Slender-snout skulls are one of five identified eusuchian cranial ecomorph shape categories (ESCs) thought to reflect functional or ecological specialization. This paper tested the effect of transitions among general, blunt and slender ESCs on cranial character-state distributions in phylogeny using the concentrated changes test. In addition, 'tree-free' character compatibility analysis of character independence was conducted on the morphological character matrix to determine if character correlations are observed independent of specific tree topologies. Results suggest cranial ESCs do affect cranial character-state gains in phylogeny. Concentrated changes identify a broad suite of character-state changes that significantly correlate with transitions to slender, general and blunt ESCs on morphological, molecular and combined-data tree topologies, but numbers of correlated characters for each category differ according to topology. Character compatibility analysis results do not mirror the concentrated changes test results and reflect hierarchically distributed support throughout the data. As cranial ESCs affect character-state transitions, it is possible that nonphylogenetic variables could affect inferences of crocodilian phylogeny by affecting cranial morphology.     

Adaptive diversification of bitter taste receptor genes in Mammalian evolution

The diversity and evolution of bitter taste perception in mammals is not well understood. Recent discoveries of bitter taste receptor (T2R) genes provide an opportunity for a genetic approach to this question. We here report the identification of 10 and 30 putative T2R genes from the draft human and mouse genome sequences, respectively, in addition to the 23 and 6 previously known T2R genes from the two species. A phylogenetic analysis of the T2R genes suggests that they can be classified into three main groups, which are designated A, B, and C. Interestingly, while the one-to-one gene orthology between the human and mouse is common to group B and C genes, group A genes show a pattern of species- or lineage-specific duplication. It is possible that group B and C genes are necessary for detecting bitter tastants common to both humans and mice, whereas group A genes are used for species-specific bitter tastants. The analysis also reveals that phylogenetically closely related T2R genes are close in their chromosomal locations, demonstrating tandem gene duplication as the primary source of new T2Rs. For closely related paralogous genes, a rate of nonsynonymous nucleotide substitution significantly higher than the rate of synonymous substitution was observed in the extracellular regions of T2Rs, which are presumably involved in tastant-binding. This suggests the role of positive selection in the diversification of newly duplicated T2R genes. Because many natural poisonous substances are bitter, we conjecture that the mammalian T2R genes are under diversifying selection for the ability to recognize a diverse array of poisons that the organisms may encounter in exploring new habitats and diets.     

The repeated evolution of stripe patterns is correlated with body morphology in the adaptive radiations of East African cichlid fishes

Color patterns are often linked to the behavioral and morphological characteristics of an animal, contributing to the effectiveness of such patterns as antipredatory strategies. Species‐rich adaptive radiations, such as the freshwater fish family Cichlidae, provide an exciting opportunity to study trait correlations at a macroevolutionary scale. Cichlids are also well known for their diversity and repeated evolution of color patterns and body morphology. To study the evolutionary dynamics between color patterns and body morphology, we used an extensive dataset of 461 species. A phylogenetic supertree of these species shows that stripe patterns evolved ~70 times independently and were lost again ~30 times. Moreover, stripe patterns show strong signs of correlated evolution with body elongation, suggesting that the stripes’ effectiveness as antipredatory strategy might differ depending on the body shape. Using pedigree‐based analyses, we show that stripes and body elongation segregate independently, indicating that the two traits are not genetically linked. Their correlation in nature is therefore likely maintained by correlational selection. Lastly, by performing a mate preference assay using a striped CRISPR‐Cas9 mutant of a nonstriped species, we show that females do not differentiate between striped CRISPR mutant males and nonstriped wild‐type males, suggesting that these patterns might be less important for species recognition and mate choice. In summary, our study suggests that the massive rates of repeated evolution of stripe patterns are shaped by correlational selection with body elongation, but not by sexual selection.     

A preliminary analysis of distribution patterns in a large, pantropical genus, Barleria L. (Acanthaceae)

Barleria L. (Acanthaceae) is a large, polymorphic, widespread genus of herbs and shrubs comprising about 300 species, occurring mainly in Africa and Asia but with one species, Barleria oenotheroides Dum.Cours., extending to the New World tropics. Recent completion of a monographic infra-generic classification of the genus (in which seven sections are recognised, and the names of four of these validated in this paper—see Appendix 1), has facilitated a comprehensive analysis of distribution patterns on a global scale. The richest representation of Barleria is in Africa where there are two centres of diversity, one in tropical East Africa (about eighty species) and the other in southern Africa (about seventy species). The number of species tails off rapidly to both the Far East and the West. Barleria shows a marked trans-Atlantic disjunction between West Africa and the Neotropics, with B. oenotheroides shared by these two regions. This type of disjunction, which is known in other genera of the family, cannot be adequately explained in Barleria on the basis of long-distance dispersal or past continental movements. There is a high degree of regional endemism (e.g. 75% for the Indian subcontinent) at both the species and sectional levels within this genus. The degree of similarity between regions is correspondingly low. The endemics in each region tend to belong to only one or a few of the sections. There are few truly widespread taxa within the genus. East and West Africa are the only regions in which all sections are represented. Sections Barleria and Prionitis C.B. Cl. are the most widespread in the genus; Sections Somalia (Oliv.) Lindau, Fissimura M. Balkwill and Stellatohirtae M. Balkwill are mainly restricted to Africa and Sections Chrysothrix M. Balkwill and Cavirostrata M. Balkwill are the most restricted, occurring mainly in India and Sri Lanka. On a local scale, many of the species show highly restricted, clumped distributions; this is apparently related to particular soil types and possibly to the short-distance, ballistic mode of seed dispersal. This account of the biogeography of Barleria is to be regarded as preliminary, as much taxonomic work at the species level remains to be done before a full-scale cladistic biogeographic account can be undertaken. Particular areas worthy of future investigation include establishing the centre of origin of the genus and investigating the basis for the high degree of endemism shown by many of the species.     

Behavioral syndromes and the evolution of correlated behavior in zebrafish

Studies of "behavioral syndromes" in different populations andspecies of animals can be used to shed light on the underlyingmechanisms of evolution. For example, some personality syndromessuggest the existence of an underlying hormonal link, whereasother relationships between boldness and aggression appear tobe the result of similar selective pressures. Here, we used1 wild-derived and 2 laboratory strains of zebrafish (Daniorerio) to examine relationships among 5 behavioral measures:shoaling, activity level, predator approaches, latency to feedafter a disturbance, and biting to a mirror stimulus. We foundevidence of an activity syndrome, as if underlying metaboliccosts influence variation in multiple forms of behavior. Evidencefor a relationship between boldness and aggression was alsoapparent but depended both on strain and which specific behaviorpatterns were identified as measures of "boldness." Althoughsome comparisons of laboratory and wild-derived strains wereconsistent with a domestication syndrome, others were not. Mostobserved relationships were relatively weak and occasionallyinconsistent, arguing against strong underlying genetic linkagesor pleiotropic effects relating any of the behavioral measures.Instead, it may be more important to study the details of selectivecontext or the long-term impact of linkages between some, butnot all, of a large set of genes influencing complex behavioraltraits. We found profound differences among strains in mostbehavior patterns, but few sex differences. One strain (TM1)was consistently different from the others (SH and Nadia) beingmore social, more likely to approach predators, and taking lesstime to recover from disturbance than were the other 2 strains.     

Sleep in amphibians and reptiles: a review and a preliminary analysis of evolutionary patterns

Despite the ubiquitous nature of sleep, its functions remain a mystery. In an attempt to address this, many researchers have studied behavioural and electrophysiological phenomena associated with sleep in a diversity of animals. The great majority of vertebrates and invertebrates display a phase of immobility that could be considered as a sort of sleep. Terrestrial mammals and birds, both homeotherms, show two sleep states with distinct behavioural and electrophysiological features. However, whether these features have evolved independently in each clade or were inherited from a common ancestor remains unknown. Unfortunately, amphibians and reptiles, key taxa in understanding the evolution of sleep given their position at the base of the tetrapod and amniote tree, respectively, remain poorly studied in the context of sleep. This review presents an overview of what is known about sleep in amphibians and reptiles and uses the existing data to provide a preliminary analysis of the evolution of behavioural and electrophysiological features of sleep in amphibians and reptiles. We also discuss the problems associated with analysing existing data, as well as the difficulty in inferring homologies of sleep stages based on limited data in the context of an essentially mammalian‐centric definition of sleep. Finally, we highlight the importance of developing comparative approaches to sleep research that may benefit from the great diversity of species with different ecologies and morphologies in order to understand the evolution and functions of sleep.