Communication via Biotremors in the Veiled Chameleon (Chamaeleo calyptratus): Part II-Social Contexts.

This study extends recent research demonstrating that the veiled chameleon (Chamaeleo calyptratus) can produce and detect biotremors. Chameleons were paired in various social contexts: dominance (male-male; female-female C. calyptratus); courtship (male-female C. calyptratus); heterospecific (C. calyptratus + C. gracilis); and inter-size class dominance (adult + juvenile C. calyptratus). Simultaneous video and accelerometer recordings were used to monitor their behavior and record a total of 398 biotremors. Chamaeleo calyptratus produced biotremors primarily in conspecific dominance and courtship contexts, accounting for 84.7% of the total biotremors recorded, with biotremor production varying greatly between individuals. Biotremors were elicited by visual contact with another conspecific or heterospecific, and trials in which chameleons exhibited visual displays and aggressive behaviors were more likely to record biotremors. Three classes of biotremor were identified-hoots, mini-hoots, and rumbles, which differed significantly in fundamental frequency, duration, and relative intensity. Biotremor frequency decreased with increasing signal duration, and frequency modulation was evident, especially in hoots. Overall, the data show that C. calyptratus utilizes substrate-borne vibrational communication during conspecific and possibly heterospecific interactions.

Communication via Biotremors in the Veiled Chameleon (Chamaeleo calyptratus): Part I- Biotremor Production and Response to Substrate-Borne Vibrations.

Biotremors are vibrations, usually surface waves along the boundary of a medium, produced by an organism. While substrate-borne vibrations are utilized by different reptile species, true conspecific communication via biotremors has not yet been demonstrated in lizards. Recent research revealed that the veiled chameleon (Chamaeleo calyptratus) produces biotremors. The prerequisites for any communication system are the ability of an organism to produce and detect a signal. We tested C. calyptratus behavioral responses to vibrations by placing them on a dowel attached to a shaker, emitting vibrations of 25, 50, 150, 300, and 600 Hz and compared their locomotory velocity before and after the stimulus. Adult chameleons exhibited a freeze response to 50 and 150 Hz, while juveniles exhibited a similar response to frequencies between 50 and 300 Hz. In a second experiment, chameleons were induced to produce biotremors via experimenter contact. These biotremors ranged in mean fundamental frequency from 106.4 to 170.3 Hz and in duration from 0.06 to 0.29 s. Overall, two classes of biotremors were identified, "hoots" and "mini-hoots," which differed significantly in mean relative signal intensity (-7.5 and -32.5 dB, respectively). Juvenile chameleons 2 months of age were able to produce biotremors, suggesting this behavior may serve a wide range of ecological functions throughout ontogeny. Overall, the data demonstrate that C. calyptratus can both produce and detect biotremors that could be used for intraspecific communication.

Extreme Morphology, Functional Trade-offs, and Evolutionary Dynamics in a Clade of Open-Ocean Fishes (Perciformes: Bramidae).

When novel or extreme morphologies arise, they are oft met with the burden of functional trade-offs in other aspects of anatomy, which may limit phenotypic diversification and make particular adaptive peaks inaccessible. Bramids (Perciformes: Bramidae) comprise a small family of 20 extant species of fishes, which are distributed throughout pelagic waters worldwide. Within the Bramidae, the fanfishes (Pteraclis and Pterycombus) differ morphologically from the generally stout, laterally compressed species that typify the family. Instead, Pteraclis and Pterycombus exhibit extreme anterior positioning of the dorsal fin onto the craniofacial skeleton. Consequently, they possess fin and skull anatomies that are radically different from other bramid species. Here, we investigate the anatomy, development, and evolution of the Bramidae to test the hypothesis that morphological innovations come at functional (proximate) and evolutionary (ultimate) costs. Addressing proximate effects, we find that the development of an exaggerated dorsal fin is associated with neurocrania modified to accommodate an anterior expansion of the dorsal fin. This occurs via reduced development of the supraoccipital crest (SOC), providing a broad surface area on the skull for insertion of the dorsal fin musculature. While these anatomical shifts are presumably associated with enhanced maneuverability in fanfishes, they are also predicted to result in compromised suction feeding, possibly limiting the mechanisms of feeding in this group. Phylogenetic analyses suggest craniofacial and fin morphologies of fanfishes evolved rapidly and are evolutionarily correlated across bramids. Furthermore, fanfishes exhibit a similar rate of lineage diversification as the rest of the Bramidae, lending little support for the prediction that exaggerated medial fins are associated with phylogenetic constraint. Our phylogeny places fanfishes at the base of the Bramidae and suggests that nonfanfish bramids have reduced medial fins and re-evolved SOCs. These observations suggest that the evolution of novel fin morphologies in basal species has led to the phylogenetic coupling of head and fin shape, possibly predisposing the entire family to a limited range of feeding. Thus, the evolution of extreme morphologies may have carryover effects, even after the morphology is lost, limiting ecological diversification of lineages.

新規または極端な形態が発生すると、解剖学的構造の他の側面で機能的なトレードオフの負担に直面することが多く、表現型の多様化が制限され、特定の適応ピークにアクセスできなくなる可能性があります。ブラミド（スズキ目：シマガツオ科）は、20種の現存する魚の小さな家族で構成されており、世界中の遠洋水域に分布しています。ブラミダエ内では、シマガツオ（PteraclisとPterycombus）は、家族を代表する一般的に頑丈な横方向に圧縮された種と形態学的に異なります。代わりに、PteraclisとPterycombusは、頭蓋顔面骨格への背びれの極端な前方位置を示します。その結果、それらは他のブラミド種とは根本的に異なるひれと頭蓋骨の解剖学的構造を持っています。ここでは、形態学的革新が機能的（近接）および進化的（究極）コストでもたらされるという仮説をテストするために、ブラミダエの解剖学、発達、および進化を調査します。近接効果に対処すると、誇張された背びれの発達は、背びれの前方拡張に対応するように修正された脳頭蓋に関連していることがわかります。これは、後頭上頂（SOC）の発達の低下を介して発生し、背びれの筋肉組織を挿入するための頭蓋骨の広い表面積を提供します。これらの解剖学的変化はおそらくファンフィッシュの操作性の向上に関連していると思われますが、吸引餌の低下をもたらし、このグループの餌のメカニズムを制限する可能性もあると予測されています。系統発生分析は、シマガツオの頭蓋顔面およびヒレの形態が急速に進化し、ブラミド間で進化的に相関していることを示唆しています。さらに、ファンフィッシュは他のブラミダエと同様の系統多様化率を示し、誇張された内側のひれが系統発生の制約に関連しているという予測をほとんど支持していません。私たちの系統発生は、シマガツオをシマガツオ科の根元に配置し、シマガツオ以外のシマガツオが内側のひれを減らし、SOCを再進化させたことを示唆しています。これらの観察結果は、基底種における新しいヒレの形態の進化が、頭とヒレの形状の系統発生的結合をもたらし、おそらく家族全員が限られた範囲の摂食にかかりやすくなっていることを示唆しています。したがって、極端な形態の進化は、形態が失われた後でも持ち越し効果をもたらす可能性があり、系統の生態学的多様化を制限します。.

Cuando surgen morfologías nuevas o extremas, a menudo se encuentran con la carga de compensaciones funcionales en otros aspectos de la anatomía, lo que puede limitar la diversificación fenotípica y hacer inaccesibles los picos adaptativos particulares. Las bramidas (Perciformes: Bramidae) comprenden una pequeña familia de 20 especies de peces existentes, que se distribuyen en las aguas pelágicas de todo el mundo. Dentro de los Bramidae, los fanfishes (Pteraclis y Pterycombus) difieren morfológicamente de las especies generalmente robustas y comprimidas lateralmente que caracterizan a la familia. En cambio, Pteraclis y Pterycombus exhiben una posición anterior extrema de la aleta dorsal sobre el esqueleto craneofacial. En consecuencia, poseen anatomías de aletas y cráneo que son radicalmente diferentes de otras especies de bramidas. Aquí, investigamos la anatomía, el desarrollo y la evolución de Bramidae para probar la hipótesis de que las innovaciones morfológicas tienen un costo funcional (próximo) y evolutivo (último). Al abordar los efectos inmediatos, encontramos que el desarrollo de una aleta dorsal exagerada se asocia con neurocráneo modificado para adaptarse a una expansión anterior de la aleta dorsal. Esto ocurre a través del desarrollo reducido de la cresta supraoccipital (SOC), proporcionando una amplia área de superficie en el cráneo para la inserción de la musculatura de la aleta dorsal. Si bien estos cambios anatómicos presumiblemente están asociados con una mayor maniobrabilidad en los peces fanfishes, también se predice que darán como resultado una alimentación por succión comprometida, lo que posiblemente limite los mecanismos de alimentación en este grupo. Los análisis filogenéticos sugieren que las morfologías craneofaciales y de aletas de los fanfishes evolucionaron rápidamente y están correlacionadas evolutivamente entre las bramidas. Además, los fanfishes exhiben una tasa similar de diversificación de linajes que el resto de los Bramidae, lo que brinda poco apoyo a la predicción de que las aletas mediales exageradas están asociadas con restricciones filogenéticas. Nuestra filogenia coloca a los peces abanico en la base de las Bramidae y sugiere que las bramidas que no son peces abanico tienen aletas mediales reducidas y SOC reevolucionado. Estas observaciones sugieren que la evolución de nuevas morfologías de aletas en especies basales ha llevado al acoplamiento filogenético de la forma de la cabeza y la aleta, lo que posiblemente predisponga a toda la familia a un rango limitado de alimentación. Por lo tanto, la evolución de morfologías extremas puede tener efectos de arrastre, incluso después de que se pierde la morfología, lo que limita la diversificación ecológica de los linajes.

Quando surgem morfologias novas ou extremas, muitas vezes enfrentam o fardo de compensações funcionais em outros aspectos da anatomia, que podem limitar a diversificação fenotípica e tornar determinados picos adaptativos inacessíveis. Bramids (Perciformes: Bramidae) compreendem uma pequena família de 20 espécies existentes de peixes, que estão distribuídos em águas pelágicas em todo o mundo. Dentro dos Bramidae, os fanfishes (Pteraclis e Pterycombus) diferem morfologicamente das espécies geralmente robustas e comprimidas lateralmente que tipificam a família. Em vez disso, Pteraclis e Pterycombus exibem posicionamento anterior extremo da nadadeira dorsal no esqueleto craniofacial. Conseqüentemente, eles possuem anatomias de barbatana e crânio que são radicalmente diferentes de outras espécies de bramida. Aqui, investigamos a anatomia, o desenvolvimento e a evolução dos Bramidae para testar a hipótese de que as inovações morfológicas têm custos funcionais (proximais) e evolutivos (finais). Abordando os efeitos imediatos, descobrimos que o desenvolvimento de uma nadadeira dorsal exagerada está associado a neurocrania modificada para acomodar uma expansão anterior da nadadeira dorsal. Isso ocorre por meio do desenvolvimento reduzido da crista supraoccipital (SOC), proporcionando uma ampla área de superfície no crânio para a inserção da musculatura da nadadeira dorsal. Embora essas mudanças anatômicas estejam presumivelmente associadas a maior capacidade de manobra em peixes-leque, também se prevê que resultem em alimentação de sucção comprometida, possivelmente limitando os mecanismos de alimentação neste grupo. As análises filogenéticas sugerem que as morfologias craniofaciais e das nadadeiras de fanfishes evoluíram rapidamente e estão evolutivamente correlacionadas entre as bramidas. Além disso, fanfishes exibem uma taxa semelhante de diversificação de linhagem como o resto dos Bramidae, emprestando pouco suporte para a previsão de que nadadeiras mediais exageradas estão associadas a restrições filogenéticas. Nossa filogenia coloca fanfishes na base dos Bramidae e sugere que bramids não fanfish possuem nadadeiras mediais reduzidas e SOCs re-evoluídos. Essas observações sugerem que a evolução de novas morfologias de nadadeiras em espécies basais levou ao acoplamento filogenético da forma da cabeça e da nadadeira, possivelmente predispondo toda a família a uma faixa limitada de alimentação. Assim, a evolução de morfologias extremas pode ter efeitos de transporte, mesmo após a perda da morfologia, limitando a diversificação ecológica das linhagens.

The role of hyoid muscles in biotremor production in Chamaeleo calyptratus.

The production of biotremors has been described in veiled chameleons (Chamaeleo calyptratus), but the mechanism by which they are produced is unknown. We gathered muscle activation data via electromyography (EMG), with simultaneous recordings of biotremors using an accelerometer, to test for the role of hyoid muscles in biotremor production. We recorded a mean biotremor frequency of 150.87 Hz for females and 136.01 Hz for males. The durations of activity and the latencies to onset and offset for the M. sternohyoideus profundus (SP), M. sternohyoideus superficialis (SS), Mm. mandibulohyoideus (MH) and M. levator scapulae (LS) were all significantly correlated with biotremor durations and biotremor onset and offset, respectively. Linear mixed-effect regression model comparisons of biotremor duration indicated that models containing either the MH and/or the SP and LS account for the most variation in biotremor duration. Twitch times for the SP (100 ms) and the SS (132 ms) at field active body temperature, however, were individually too slow to produce the biotremors at the observed frequency without alteration after production by other anatomical structures. These results implicate the SP, SS, MH and LS in the production of biotremors, but the exact mechanism of production requires further study.

Gular pouch diversity in the Chamaeleonidae.

Numerous chameleon species possess an out-pocketing of the trachea known as the gular pouch. After surveying more than 250 specimens, representing nine genera and 44 species, we describe two different morphs of the gular pouch. Species of the genera Bradypodion and Chamaeleo, as well as Trioceros goetzei, all possess a single gular pouch (morph one) formed from ventral expansion of soft tissue where the larynx and trachea meet. Furcifer oustaleti and Furcifer verrucosus possess from one to four gular pouches (morph two) formed by the expansion of soft tissue between sequential hyaline cartilage rings of the trachea. In Trioceros melleri, examples of both morphs of the gular pouch were observed. Morphometric data are presented for 100 animals representing eight species previously known to possess a gular pouch and two additional species, Bradypodion thamnobates and Bradypodion transvaalense. In the species with the absolutely and relatively largest gular pouch, Chamaeleo calyptratus, a significant difference was found between sexes in its width and volume, but not its length. In C. calyptratus, we show that an inflated gular pouch is in contact with numerous hyoid muscles and the tongue. Coupled with the knowledge that C. calyptratus generates vibrations from the throat region, we posit that the tongue (M. accelerator linguae and M. hyoglossus) and supporting hyoid muscles (i.e., Mm. sternohyoideus profundus et superficialis and Mm. mandibulohyoideus) are involved in the production of vibrations to produce biotremors that are amplified by the inflated gular pouch and used in substrate-borne communication.

Muscle architecture and out-force potential of the thoracic limb in the Eastern mole (Scalopus aquaticus).

Moles have modified thoracic limbs with hypertrophied pectoral girdle muscles that allow them to apply remarkably high lateral out-forces during the power stroke when burrowing. To further understand the high force capabilities of mole forelimbs, architectural properties of the thoracic limb muscles were quantified in the Eastern mole (Scalopus aquaticus). Architectural properties measured included muscle mass, moment arm, belly length, fascicle length, and pennation angle, and these were used to provide estimates of maximum isometric force, joint torque, and power. Measurements of muscle moment arms and limb lever lengths were additionally used to analyze the out-force contributions of the major pectoral girdle muscles. Most muscles have relatively long fascicles and little-to-no pennation. The humeral abductor/rotators as a functional group are massive and are capable of relatively high force, power, and joint torque. Of this group, the bipennate m. teres major is the most massive and has the capacity to produce the highest force and joint torque to abduct and axially rotate the humerus. In general, the distal limb muscles are relatively small, but have the capacity for high force and mechanical work by fascicle shortening. The muscle architectural properties of the elbow extensors (e.g., m. triceps brachii) and carpal flexors (e.g., m. palmaris longus) are consistent with the function of these muscles to augment lateral out-force application. The humeral abductor/rotators m. latissimus dorsi, m. teres major, m. pectoralis, and m. subscapularis are calculated to contribute 13.9 N to out-force during the power stroke, and this force is applied in a 'frontal' plane causing abduction of the humerus about the sternoclavicular joint. Moles have several specializations of their digging apparatus that greatly enhance the application of out-force, and these morphological features suggest convergence on limb form and burrowing function between New and Old World moles.

Mega-Bites: extreme jaw forces of living and extinct piranhas (Serrasalmidae).

Here, we document in-vivo bite forces recorded from wild piranhas. Integrating this empirical data with allometry, bite simulations, and FEA, we have reconstructed the bite capabilities and potential feeding ecology of the extinct giant Miocene piranha, Megapiranha paranensis. An anterior bite force of 320 N from the black piranha, Serrasalmus rhombeus, is the strongest bite force recorded for any bony fish to date. Results indicate M. paranensis' bite force conservatively ranged from 1240-4749 N and reveal its novel dentition was capable of resisting high bite stresses and crushing vertebrate bone. Comparisons of body size-scaled bite forces to other apex predators reveal S. rhombeus and M. paranensis have among the most powerful bites estimated in carnivorous vertebrates. Our results functionally demonstrate the extraordinary bite of serrasalmid piranhas and provide a mechanistic rationale for their predatory dominance among past and present Amazonian ichthyofaunas.