Overcoming Drag at the Water-Air Interface Constrains Body Size in Whirligig Beetles

Whirligig beetles (Coleoptera: Gyrinidae) are among the best swimmers of all aquatic insects. They live mostly at the water’s surface and their capacity to swim fast is key to their survival. We present a minimal model for the viscous and wave drags they face at the water’s surface and compare them to their thrust capacity. The swimming speed accessible is thus derived according to size. An optimal size range for swimming at the water’s surface is observed. These results are in line with the evolutionary trajectories of gyrinids which evolved into lineages whose members are a few milimeter’s long to those with larger-sized genera being tens of millimeters in length. The size of these beetles appears strongly constrained by the fluid mechanical laws ruling locomotion and adaptation to the water-air interface.

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Evidence of morphological adaptation to life underwater: Sternal keel affects swimming speed in giant water scavenger beetles (Coleoptera: Hydrophilidae: Hydrophilini)

Canadian Journal of Zoology ◽

10.1139/cjz-2020-0247 ◽

2021 ◽

Author(s):

Ryosuke Matsushima

Keyword(s):

Body Size ◽

Gas Exchange ◽

Body Mass ◽

Swimming Speed ◽

Aquatic Insects ◽

Morphological Traits ◽

Aquatic Environments ◽

Morphological Adaptation ◽

Ecological Traits ◽

Oscillatory Movement

Fundamentally, insects evolved on land and secondarily inhabited aquatic environments multiple times. To live underwater, aquatic insects have acquired enormously variable morphological, developmental, physiological, and ecological traits, such as gas exchange systems and swimming-related characteristics. Giant water scavenger beetles of the tribe Hydrophilini (Coleoptera: Hydrophilidae) are characterized by the presence of sternal keel, which often extends posteriorly. Despite being a conspicuous morphological trait, its function remains unclear. Here, I verified two hypotheses: keel affects (1) submergence time following air replacement as well as (2) speed and oscillatory movement during forward swimming in Hydrophilus acuminatus Motschulsky, 1854. Submergence time was affected by body mass rather than keel removal; in other words, larger individuals replaced their gas gills more frequently. Keel removal reduced swimming speed by 12.5%. These observations support hypothesis (2) and are also consistent with previous speculations that sternal keel is a key adaptation to swim, but the results showed that the degree of oscillation was closely related to body mass but not keel removal. Further studies are warranted to elucidate precise factors through which the presence of keel increases swimming speed. Such studies would provide clues into understanding the associations amongst body size, swimming methods, and morphological traits.

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Mountain colonisation, miniaturisation and ecological evolution in a radiation of direct-developing New Guinea Frogs (Choerophryne, Microhylidae)

PeerJ ◽

10.7717/peerj.3077 ◽

2017 ◽

Vol 5 ◽

pp. e3077 ◽

Cited By ~ 9

Author(s):

Paul M. Oliver ◽

Amy Iannella ◽

Stephen J. Richards ◽

Michael S.Y. Lee

Keyword(s):

Body Size ◽

Small Body ◽

Strong Support ◽

New Guinea ◽

Ancestral State ◽

Tropical Mountains ◽

Climatic Oscillations ◽

Evolutionary Trajectories ◽

Montane Biodiversity ◽

Male Calling

AimsMountain ranges in the tropics are characterised by high levels of localised endemism, often-aberrant evolutionary trajectories, and some of the world’s most diverse regional biotas. Here we investigate the evolution of montane endemism, ecology and body size in a clade of direct-developing frogs (Choerophryne,Microhylidae) from New Guinea.MethodsPhylogenetic relationships were estimated from a mitochondrial molecular dataset using Bayesian and maximum likelihood approaches. Ancestral state reconstruction was used to infer the evolution of elevational distribution, ecology (indexed by male calling height), and body size, and phylogenetically corrected regression was employed to examine the relationships between these three traits.ResultsWe obtained strong support for a monophyletic lineage comprising the majority of taxa sampled. Within this clade we identified one subclade that appears to have diversified primarily in montane habitats of the Central Cordillera (>1,000 m a.s.l.), with subsequent dispersal to isolated North Papuan Mountains. A second subclade (characterised by moderately to very elongated snouts) appears to have diversified primarily in hill forests (<1,000 m a.s.l.), with inferred independent upwards colonisations of isolated montane habitats, especially in isolated North Papuan Mountains. We found no clear relationship between extremely small body size (adult SVL less than 15 mm) and elevation, but a stronger relationship with ecology—smaller species tend to be more terrestrial.ConclusionsOrogeny and climatic oscillations have interacted to generate high montane biodiversity in New Guinea via both localised diversification within montane habitats (centric endemism) and periodic dispersal across lowland regions (eccentric endemism). The correlation between extreme miniaturisation and terrestrial habits reflects a general trend in frogs, suggesting that ecological or physiological constraints limit niche usage by miniaturised frogs, even in extremely wet environments such as tropical mountains.

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Mountain colonisation, miniaturisation and ecological evolution in a radiation of direct developing New Guinea Frogs (Choerophryne, Microhylidae)

10.7287/peerj.preprints.2663v2 ◽

2017 ◽

Author(s):

Paul M Oliver ◽

Amy Iannella ◽

Stephen J Richards ◽

Michael S.Y Lee

Keyword(s):

Body Size ◽

Small Body ◽

Strong Support ◽

New Guinea ◽

Ancestral State ◽

Tropical Mountains ◽

Climatic Oscillations ◽

Evolutionary Trajectories ◽

Montane Biodiversity ◽

Male Calling

Aims. Mountain ranges in the tropics are characterised by high levels of localised endemism, often-aberrant evolutionary trajectories, and some of the world’s most diverse regional biotas. Here we investigate the evolution of montane endemism, ecology and body size in a clade of direct-developing frogs (Choerophryne, Microhylidae) from New Guinea. Methods. Phylogenetic relationships were estimated from a mitochondrial molecular dataset using Bayesian and maximum likelihood approaches. Ancestral state reconstruction was used to infer the evolution of elevational distribution, ecology (indexed by male calling height), and body size, and phylogenetically corrected regression was employed to examine the relationships between these three traits. Results. We obtained strong support for a monophyletic lineage comprising the majority of taxa sampled. Within this clade we identified one subclade that appears to have diversified primarily in montane habitats of the Central Cordillera (> 1000 m. a.s.l), with subsequent dispersal to isolated North Papuan Mountains. A second subclade (characterised by moderately to very elongated snouts) appears to have diversified primarily in hill forests (< 1000 m a.s.l.), with inferred independent upwards colonisations of isolated montane habitats, especially in isolated North Papuan Mountains. We found no clear relationship between extremely small body size (adult SVL less than 15mm) and elevation, but a stronger relationship with ecology – smaller species tend to be more terrestrial. Conclusions. Orogeny and climatic oscillations have interacted to generate high montane biodiversity in New Guinea via both localised diversification within montane habitats (centric endemism) and periodic dispersal across lowland regions (eccentric endemism). The correlation between extreme miniaturisation and terrestrial habits reflects a general trend in frogs, suggesting that ecological or physiological constraints limit niche usage by miniaturised frogs, even in extremely wet environments such as tropical mountains.

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Pectoral fin locomotion in the striped surfperch. II. Scaling swimming kinematics and performance at a gait transition

Journal of Experimental Biology ◽

10.1242/jeb.199.10.2243 ◽

1996 ◽

Vol 199 (10) ◽

pp. 2243-2252 ◽

Cited By ~ 6

Author(s):

E Drucker ◽

J Jensen

Keyword(s):

Body Size ◽

Swimming Speed ◽

Beat Frequency ◽

Small Fish ◽

Maximal Velocity ◽

Pectoral Fin ◽

Gait Transition ◽

Transition Speed ◽

Aspect Ratios ◽

And Performance

In this study, we report the first allometric equations relating gait parameters and swimming speed to body size for fish employing pectoral fin locomotion. Comparisons of locomotor kinematics and performance among striped surfperch (Teleostei: Embiotocidae) are made at the pectoralcaudal gait transition speed (Up-c). Up-c is considered to elicit physiologically equivalent levels of exercise in animals varying over 100-fold in body mass (Mb) by virtue of dynamically similar pectoral fin movements (constant duty factor, length-specific stride length and fin-beat amplitude) and size-independent propulsive efficiency. At Up-c, pectoral fin-beat frequency scales in proportion to Mb-0.12±0.03, a size-dependence consistent with that observed for stride frequency in fishes swimming by axial undulatory propulsion and in many running tetrapods. It is proposed that the similarity in the scaling of frequency in these vertebrate groups reflects an underlying similarity in the allometry of the maximal velocity of muscle shortening. Absolute Up-c (m s-1) generally increases with body size, but the fastest speeds are not exhibited by the largest animals. A pattern of declining performance in fish 23 cm in standard length and longer may be related to their disproportionately small fin areas and aspect ratios. The pronounced negative allometry of Up-c expressed as standard body lengths per second indicates that a given length-specific speed does not induce comparable levels of activity in large and small fish. Thus, normalization of swimming speed to body length may not be a sufficient correction for kinematic comparisons across size.

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Pectoral fin locomotion in the striped surfperch. I. Kinematic effects of swimming speed and body size

Journal of Experimental Biology ◽

10.1242/jeb.199.10.2235 ◽

1996 ◽

Vol 199 (10) ◽

pp. 2235-2242 ◽

Cited By ~ 9

Author(s):

E Drucker ◽

J Jensen

Keyword(s):

Body Size ◽

Swimming Speed ◽

Beat Frequency ◽

Limited Range ◽

The Body ◽

Small Fish ◽

Large Fish ◽

Pectoral Fin ◽

Transition Speed ◽

Speed Up

Swimming trials at increasing velocity were used to determine the effects of steady swimming speed on pectoral fin kinematics for an ontogenetic series of striped surfperch Embiotoca lateralis, ranging from 6 to 23 cm in standard length (SL). The fin stroke cycle consisted of a propulsive period, the duration of fin abduction and adduction, and a 'refractory' period, during which the fin remained adducted against the body. Pectoral fin-beat frequency (fp) measured as the inverse of the entire stride period, as in past studies, increased curvilinearly with speed. Frequency, calculated as the reciprocal of the propulsive period alone, increased linearly with speed, as shown previously for tail-beat frequency of fishes employing axial undulation. Fin-beat amplitude, measured as the vertical excursion of the pectoral fin tip during abduction, increased over a limited range of low speeds before reaching a plateau at 0.350.40 SL. Pectoral fin locomotion was supplemented by intermittent caudal fin undulation as swimming speed increased. At the pectoralcaudal gait transition speed (Up-c), frequency and amplitude attained maxima, suggesting that the fin musculature reached a physiological limit. The effects of body size on swimming kinematics differed according to the method used for expressing speed. At a given absolute speed, small fish used higher stride frequencies and increased frequency at a faster rate than large fish. In contrast, the relationship between fp and length-specific speed (SL s-1) had a greater slope for large fish and crossed that for small fish at high speeds. We recommend that comparisons across size be made using speeds expressed as a percentage of Up-c, at which kinematic variables influencing thrust are size-independent.

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Challenges and advances in the study of pterosaur flight

Canadian Journal of Zoology ◽

10.1139/cjz-2013-0219 ◽

2015 ◽

Vol 93 (12) ◽

pp. 945-959 ◽

Cited By ~ 2

Author(s):

K.M. Middleton ◽

L.T. English

Keyword(s):

Body Size ◽

Size Range ◽

Flapping Flight ◽

Flight Mechanics ◽

Wing Membrane ◽

Membrane Function ◽

Aerodynamic Modeling ◽

History Of ◽

Bone Loading

Pterosaurs have fascinated scientists and nonscientists alike for over 200 years, as one of the three known clades of vertebrates to have evolved flapping flight. The smallest pterosaurs were comparable in size to the smallest extant birds and bats, but the largest pterosaurs were vastly larger than any extant flier. This immense size range, coupled with poor preservation and adaptations for flight unknown in extant vertebrates, have made interpretations of pterosaur flight problematic and often contentious. Here we review the anatomical, evolutionary, and phylogenetic history of pterosaurs, as well as the views, perspectives, and biases regarding their interpretation. In recent years, three areas of pterosaur biology have faced challenges and made advances: structure of the wing membrane, function of the pteroid, body size and mass estimates, as well as flight mechanics and aerodynamics. Comparative anatomical and fossil study, simulated bone loading, and aerodynamic modeling have all proved successful in furthering our understanding of pterosaur flight. We agree with previous authors that pterosaurs should be studied as pterosaurs, a diverse but phylogenetically, anatomically, and mechanically constrained clade that can offer new insights into the diversity of vertebrate flight.

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