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Yan C, Ma H, Yang Y, Mi Z. Sexual Dimorphism in the Limb Bones of Asiatic Toad ( Bufo gargarizans) in Relation to Sexual Selection. Animals (Basel) 2023; 13:2638. [PMID: 37627429 PMCID: PMC10451170 DOI: 10.3390/ani13162638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 08/05/2023] [Accepted: 08/14/2023] [Indexed: 08/27/2023] Open
Abstract
Sexual dimorphism is often considered to be the result of differences in the intensity of sexual selection between sexes. From this point of view, the sexual dimorphism of the limb bones of the Bufo gargarizans in southwest China was studied. Results showed that the fore- and hindlimb skeletons of this species were sexually dimorphic in anatomy. The humerus, radioulna, and total lengths of the forelimb skeleton of males were substantially longer than those of females, but the hand length of males was smaller than that of females. Several other features of males, such as deltoid and medial crest areas and humerus and radioulnar weights, were also significantly larger than those of females. The femoris, tibiofibula, talus-calcaneus, and foot lengths; total hindlimb skeleton length; and femoral upper crest areas of males were significantly greater than those of females. However, no significant intersexual difference in femoris and tibiofibular weights was observed. These findings suggested that robust forelimb bones and long hindlimb bones could contribute to the mating success of males; if so, sexual selection promotes the evolution of sexual size and shape dimorphism in the limb bones of the B. gargarizans.
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Affiliation(s)
| | | | | | - Zhiping Mi
- Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education), China West Normal University, Nanchong 637009, China; (C.Y.); (H.M.); (Y.Y.)
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Powell AR, Deban SM, Lappin AK. Sustained force production by the jaw-adductor muscles of a megalophagous frog, Ceratophrys cranwelli. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY 2023; 339:437-445. [PMID: 36855228 DOI: 10.1002/jez.2690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Revised: 01/11/2023] [Accepted: 02/14/2023] [Indexed: 03/02/2023]
Abstract
Most frogs have weak jaws that play a relatively minor role in tongue-mediated prey capture. Horned frogs (Ceratophrys spp.), however, follow the projection of a large tongue with a vice-like grip of their jaws to hold and immobilize prey. Prey include relatively large vertebrates, which they may restrain for minutes to possibly hours. High endurance behaviors, such as prolonged biting, require that muscles be capable of sustained force production. The feeding behavior of Ceratophrys suggests that their jaw-adductor muscles may be capable of powering sustained bites for long periods. We examined the capacity for sustained bite force by conducting an in situ experiment during which we measured bite force while bilaterally and supramaximally stimulating the jaw-adductor muscles of euthanized Cranwell's horned frogs (C. cranwelli). Muscles were stimulated for at least 60 min with a series of tetanic trains, with one experiment lasting over 6 h. We found that a significant sustained force develops during the first few minutes of the experiment, and this force is present between tetanic trains when the muscles are not being stimulated. The sustained force persists long after tetanic forces are barely detectable. The observed sustained force phenomenon parallels that observed for the jaw-adductor muscles of alligator lizards (Elgaria), another animal capable of sustained biting. The ability to bite with sustained and significant force by C. cranwelli may be facilitated by a configuration of different muscle fiber types, such as slow tonic fibers, as well as specializations in the muscle fibers that mitigate the effects of fatigue.
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Affiliation(s)
- Anthony R Powell
- Biological Sciences Department, California State Polytechnic University, Pomona, California, USA
| | - Stephen M Deban
- Department of Integrative Biology, University of South Florida, Tampa, Florida, USA
| | - A Kristopher Lappin
- Biological Sciences Department, California State Polytechnic University, Pomona, California, USA
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Li H, Chen S, Jiang J, He B, Zhang M. Exploring sexual differences in external morphology and limb muscles of
Hylarana guentheri
(Anura: Ranidae) during non‐breeding season. ACTA ZOOL-STOCKHOLM 2022. [DOI: 10.1111/azo.12448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Hui Li
- College of Life Sciences Sichuan Normal University Chengdu China
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization and Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province Chengdu Institute of Biology, Chinese Academy of Sciences Chengdu China
| | - Shunde Chen
- College of Life Sciences Sichuan Normal University Chengdu China
| | - Jianping Jiang
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization and Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province Chengdu Institute of Biology, Chinese Academy of Sciences Chengdu China
| | - Bing He
- College of Life Sciences Sichuan Normal University Chengdu China
| | - Meihua Zhang
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization and Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province Chengdu Institute of Biology, Chinese Academy of Sciences Chengdu China
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4
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Yang YJ, Jiang Y, Mi ZP, Liao WB. Testing the Role of Environmental Harshness and Sexual Selection in Limb Muscle Mass in Anurans. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.879885] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Sexual dimorphism is regarded as the consequence of differential responses by males and females to selection pressures. Limb muscle plays a very important role during amplexus, which is likely to be under both natural and sexual selection in anurans. Here, we studied the effects of natural and sexual selection on limb muscle mass in males and females across 64 species of anurans. The results showed that there were non-significant differences in relative limb muscle mass between the sexes among species, exhibiting no sexual dimorphism in limb muscle. Absolute and relative limb muscle mass positively displayed correlations with snout-vent length (SVL)for both sexes. However, neither male-biased operational sex ratio (OSR) nor environmental harshness [e.g., coefficient of variation (CV) in temperature and CV in rainfall] can explain relative limb muscle mass (e.g., forelimb, hindlimb, and total limb muscle) within each sex. The findings suggest that environmental harshness and sexual selection cannot play important roles in promoting variations in limb muscle among anuran species.
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5
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Antipredator responses of the morphs of an amphibian species match their differential predation pressures. Behav Ecol Sociobiol 2022. [DOI: 10.1007/s00265-022-03140-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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6
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Leung KW, Yang S, Wang X, Tang K, Hu J. Ecogeographical Adaptation Revisited: Morphological Variations in the Plateau Brown Frog along an Elevation Gradient on the Qinghai-Tibetan Plateau. BIOLOGY 2021; 10:biology10111081. [PMID: 34827074 PMCID: PMC8614741 DOI: 10.3390/biology10111081] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/11/2021] [Revised: 10/18/2021] [Accepted: 10/18/2021] [Indexed: 11/16/2022]
Abstract
Simple Summary A number of studies have explored how the body size and extremities of frogs vary in response to the changing environmental conditions across different geographical gradients, but the outcomes remain controversial. Here, we studied the morphological variations of the plateau brown frog (Rana kukunoris) along an elevation gradient (~1800–3500 m) on the eastern margin of the Qinghai–Tibetan Plateau to understand how environmental and biological factors affect them, and to assess whether these variations help to improve thermoregulation. Although we found that male and female frogs showed different variations in body size and extremities along the elevational gradient, both of them showed a significant decrease in the ratio of extremities to body size with increasing elevation. The decreasing ratio implies a gain of thermoregulatory benefits based on the ecogeographical rules. Moreover, the morphological variations were found to be strongly related to both environmental and biological factors. These results suggest that ecogeographical adaptation in frogs may be more complicated than other terrestrial vertebrate species. Most importantly, the adaptation should be viewed as a result of both environmental and biological factors, while it may also appear as an interactive change between body size and extremities. Abstract Several anurans have broad elevational and latitudinal distribution ranges; distinct species and populations may face various environmental and selection stresses. Due to their environmental sensitivity, adaptation is critical for the long-term persistence of anurans. Previous studies have tried to identify the ecogeographical pattern and its mechanism in anurans, suggesting different patterns, but the related explanatory mechanisms are yet to be generally supported and are suggested to be complicated. To explore the elusive mechanisms, we studied the morphological variation of the plateau brown frog (Rana kukunoris) along an elevational gradient on the eastern margin of the Qinghai–Tibetan Plateau. Using body size, extremity length, and the ratio between them (extremities/body size) as testing indicators, we examined potential ecogeographical adaptations and investigated how environmental and biological factors could shape the morphological development in R. kukunoris. We found that males and females showed different variations in body size and extremities along the elevational gradient, whereas both of them showed a decreasing extremities/body size ratio along elevation. Together with the strong correlations between environmental and biological factors and the morphometrics, we identified ecogeographical adaptation and a sexual difference in the selective pressures on the extremities and body size of the plateau brown frog. Our results imply that geographic variations in anuran morphological traits should be understood as an outcome of environmental and biological factors. Furthermore, ecogeographical adaptation in anurans can manifest as an interactive change between body size and extremities.
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Affiliation(s)
- Ka Wah Leung
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China; (K.W.L.); (S.Y.); (X.W.); (K.T.)
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shengnan Yang
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China; (K.W.L.); (S.Y.); (X.W.); (K.T.)
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiaoyi Wang
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China; (K.W.L.); (S.Y.); (X.W.); (K.T.)
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ke Tang
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China; (K.W.L.); (S.Y.); (X.W.); (K.T.)
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Junhua Hu
- Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China; (K.W.L.); (S.Y.); (X.W.); (K.T.)
- Correspondence:
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Nguyen A, Balaban JP, Azizi E, Talmadge RJ, Lappin AK. Fatigue resistant jaw muscles facilitate long-lasting courtship behaviour in the southern alligator lizard ( Elgaria multicarinata). Proc Biol Sci 2020; 287:20201578. [PMID: 32962547 PMCID: PMC7542809 DOI: 10.1098/rspb.2020.1578] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The southern alligator lizard (Elgaria multicarinata) exhibits a courtship behaviour during which the male firmly grips the female's head in his jaws for many hours at a time. This extreme behaviour counters the conventional wisdom that reptilian muscle is incapable of powering high-endurance behaviours. We conducted in situ experiments in which the jaw-adductor muscles of lizards were stimulated directly while bite force was measured simultaneously. Fatigue tests were performed by stimulating the muscles with a series of tetanic trains. Our results show that a substantial sustained force gradually develops during the fatigue test. This sustained force persists after peak tetanic forces have declined to a fraction of their initial magnitude. The observed sustained force during in situ fatigue tests is consistent with the courtship behaviour of these lizards and probably reflects physiological specialization. The results of molecular analysis reveal that the jaw muscles contain masticatory and tonic myosin fibres. We propose that the presence of tonic fibres may explain the unusual sustained force properties during mate-holding behaviour. The characterization of muscle properties that facilitate extreme performance during specialized behaviours may reveal general mechanisms of muscle function, especially when done in light of convergently evolved systems exhibiting similar performance characteristics.
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Affiliation(s)
- Allyn Nguyen
- Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768, USA
| | - Jordan P Balaban
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
| | - Emanuel Azizi
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
| | - Robert J Talmadge
- Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768, USA
| | - A Kristopher Lappin
- Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768, USA
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8
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Zamora-Camacho FJ. Locomotor performance in a running toad: roles of morphology, sex and agrosystem versus natural habitat. Biol J Linn Soc Lond 2017. [DOI: 10.1093/biolinnean/blx147] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Lüpold S, Jin L, Liao WB. Population density and structure drive differential investment in pre- and postmating sexual traits in frogs. Evolution 2017; 71:1686-1699. [PMID: 28394412 DOI: 10.1111/evo.13246] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 03/25/2017] [Indexed: 01/01/2023]
Abstract
Sexual selection theory predicts a trade-off between premating (ornaments and armaments) and postmating (testes and ejaculates) sexual traits, assuming that growing and maintaining these traits is costly and that total reproductive investments are limited. The number of males in competition, the reproductive gains from investing in premating sexual traits, and the level of sperm competition are all predicted to influence how males allocate their finite resources to these traits. Yet, empirical examination of these predictions is currently scarce. Here, we studied relative expenditure on pre- and postmating sexual traits among frog species varying in their population density, operational sex ratio, and the number of competing males for each clutch of eggs. We found that the intensifying struggle to monopolize fertilizations as more and more males clasp the same female to fertilize her eggs shifts male reproductive investment toward sperm production and away from male weaponry. This shift, which is mediated by population density and the associated level of male-male competition, likely also explains the trade-off between pre- and postmating sexual traits in our much broader sample of anuran species. Our results highlight the power of such a multilevel approach in resolving the evolution of traits and allocation trade-offs.
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Affiliation(s)
- Stefan Lüpold
- Department of Evolutionary Biology and Environmental Studies, University of Zurich-Irchel, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Long Jin
- Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education), China West Normal University, Nanchong, 637009, P. R. China
| | - Wen Bo Liao
- Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education), China West Normal University, Nanchong, 637009, P. R. China
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10
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Petrović TG, Vukov TD, Tomašević Kolarov N. Morphometric ratio analyses: Locomotor mode in anurans. C R Biol 2017; 340:250-257. [DOI: 10.1016/j.crvi.2017.02.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 02/10/2017] [Accepted: 02/23/2017] [Indexed: 11/16/2022]
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Petrović TG, Vukov TD, Kolarov NT. Sexual dimorphism in size and shape of traits related to locomotion in nine anuran species from Serbia and Montenegro. FOLIA ZOOLOGICA 2017. [DOI: 10.25225/fozo.v66.i1.a4.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
| | - Tanja D. Vukov
- Institute for Biological Research, Department of Evolutionary Biology, University of Belgrade, 11000 Belgrade, Serbia;,
| | - Nataša Tomašević Kolarov
- Institute for Biological Research, Department of Evolutionary Biology, University of Belgrade, 11000 Belgrade, Serbia;,
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12
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Kampe AR, Peters SE. Effects of testosterone on contractile properties of sexually dimorphic forelimb muscles in male bullfrogs (Rana catesbeiana, Shaw 1802). Biol Open 2013; 2:932-40. [PMID: 24143280 PMCID: PMC3773340 DOI: 10.1242/bio.20133798] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Accepted: 06/17/2013] [Indexed: 11/22/2022] Open
Abstract
This study examined the effects of testosterone (T) on the contractile properties of two sexually dimorphic forelimb muscles and one non-dimorphic muscle in male bullfrogs (Rana catesbeiana, Shaw 1802). The dimorphic muscles in castrated males with testosterone replacement (T+) achieved higher forces and lower fatigability than did castrated males without replaced testosterone (T0 males), but the magnitude of the differences was low and many of the pair-wise comparisons of each muscle property were not statistically significant. However, when taken as a whole, the means of seven contractile properties varied in the directions expected of masculine values in T+ animals in the sexually dimorphic muscles. Moreover, these data, compared with previous data on male and female bullfrogs, show that values for T+ males are similar to normal males and are significantly different from females. The T0 males tended to be intermediate in character between T+ males and females, generally retaining masculine values. This suggests that the exposure of young males to T in their first breeding season produces a masculinizing effect on the sexually dimorphic muscles that is not reversed between breeding seasons when T levels are low. The relatively minor differences in contractile properties between T+ and T0 males may indicate that as circulating T levels rise during breeding season in normal males, contractile properties can be enhanced rapidly to maximal functional levels for breeding success.
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Affiliation(s)
- Aaron R Kampe
- Department of Biology, The University of North Carolina at Charlotte , Charlotte, NC 28223 , USA
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Zhang L, Zhao Y, Yang J, Lu X, Chen X. No sexual dimorphism in limb muscles of a frog not engaging in amplexus. ANIM BIOL 2013. [DOI: 10.1163/15707563-00002421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Sexual dimorphism in limb muscles is widespread among anurans, with males having stronger limbs than females. This phenomenon has been interpreted in the context of intrasexual selection: 1) the robust forelimb muscles in males are associated with amplexus, in which the male tries to grasp the female tightly, and also with rejection of rivals’ attempts at taking over, and 2) massive hindlimb muscles favor the ability to kick away rivals during scramble competition. However, in a few species, fertilization occurs without any form of amplexus and in these species the limb muscle dimorphism is expected to be absent. We tested this prediction inFeirana taihangnicus: a species without amplexus. As expected, we detected non-significant sexual differences in the mass of both forelimb and hindlimb muscles after accounting for body size and age. Our findings represent an interesting example of coevolution of form and function.
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Affiliation(s)
- Lixia Zhang
- 1Department of Zoology, College of Life Sciences, Henan Normal University, Xinxiang 453007, China
| | - Yunyun Zhao
- 1Department of Zoology, College of Life Sciences, Henan Normal University, Xinxiang 453007, China
| | - Jie Yang
- 1Department of Zoology, College of Life Sciences, Henan Normal University, Xinxiang 453007, China
- 2Xinxiang Medical University, Xinxiang 453003, China
| | - Xin Lu
- 3Department of Zoology, College of Life Sciences, Wuhan University, Wuhan 430072, China
| | - Xiaohong Chen
- 1Department of Zoology, College of Life Sciences, Henan Normal University, Xinxiang 453007, China
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Akella T, Gillis GB. Hopping isn't always about the legs: forelimb muscle activity patterns during toad locomotion. ACTA ACUST UNITED AC 2010; 315:1-11. [DOI: 10.1002/jez.643] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2010] [Revised: 07/22/2010] [Accepted: 08/13/2010] [Indexed: 11/11/2022]
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Ishii Y, Tsuchiya T. Prolonged relaxation after stimulation of the clasping muscle of male frog, Rana japonica, during the breeding season. Zoolog Sci 2010; 27:595-601. [PMID: 20608849 DOI: 10.2108/zsj.27.595] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We investigated the mechanical properties of the flexor carpi radialis muscle (FCR), a forelimb muscle used mainly for amplexus in the breeding season (February to March), of the male Japanese brown frog, Rana japonica. In the present experiment, the changes in force and stiffness of the FCR before, during, and after contraction were measured at 4 degrees C. The total time from the end of stimulation to the end of relaxation was about 30 min. The time course of this prolonged relaxation was fitted by two exponential decay processes. Stiffness decreased during prolonged relaxation, but stayed higher than force, when normalized to peak values. These mechanical properties of the FCR were different from those of the glutaeus magnus muscle (GM) in the hindlimb, used for jumping. When a quick release was applied to the FCR during relaxation, the force recovered gradually after a sudden decrease. The time course of this force recovery was fitted by a single exponential term, and the rate constant decreased as the prolonged relaxation proceeded. The possible involvement of active process(es) in the prolonged relaxation is discussed.
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Affiliation(s)
- Yoshiki Ishii
- Department of Physical Therapy, Faculty of Health care Sciences, Himeji Dokkyo University, Kamiono 7-2-1, Himeji, Hyogo 670-8524, Japan.
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Navas CA, James RS. Sexual dimorphism of extensor carpi radialis muscle size, isometric force, relaxation rate and stamina during the breeding season of the frog Rana temporaria Linnaeus 1758. ACTA ACUST UNITED AC 2007; 210:715-21. [PMID: 17267656 DOI: 10.1242/jeb.000646] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mating success of individual male frogs within explosive breeding species can depend on their ability to compete for a mate and to hold onto that mate during amplexus. Such importance of amplexus has resulted in the evolution of sexual dimorphism in the morphology and contractile characteristics of the anuran forelimb muscles used during amplexus. The aims of our study were to use an explosive breeding frog (Rana temporaria) during the breeding season to compare extensor carpi radialis (ECR) muscle length, mass, isometric activation times, relaxation times, absolute force, relative force (stress) and fatigue between male and female frogs. We found that ECR muscle mass and length were greater (tenfold and 1.4-fold, respectively), absolute tetanic muscle force and relative tetanic force (stress) were greater (16-fold and 2.2-fold, respectively) and relaxation times were slower in males than in females. Male ECR muscles incompletely relaxed during fatigue tests and showed less fatigue than female muscles. These sex differences are likely to be beneficial to the male frogs in allowing them to produce relatively high absolute muscle forces for prolonged periods of time to hold onto their mate during amplexus.
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Affiliation(s)
- Carlos A Navas
- Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão-Travessa 14 No 321, CEP 05508-900, São Paulo, SP, Brasil.
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