Jeff W. Dawson

Bat-deafness in day-flying moths (Lepidoptera, Notodontidae, Dioptinae)

Abstract Assuming that bat-detection is the primary function of moth ears, the ears of moths that are no longer exposed to bats should be deaf to echolocation call frequencies. To test this, we compared the auditory threshold curves of 7 species of Venezuelan day-flying moths (Notodontidae: Dioptinae) to those of 12 sympatric species of nocturnal moths (Notodontidae: Dudusinae, Noctuidae and Arctiidae). Whereas 2 dioptines (Josia turgida, Zunacetha annulata) revealed normal ears, 2 (J. radians, J. gopala) had reduced hearing at bat-specific frequencies (20–80 kHz) and the remaining 3 (Thirmida discinota, Polypoetes circumfumata and Xenorma cytheris) revealed pronounced to complete levels of high-frequency deafness. Although the bat-deaf ears of dioptines could function in other purposes (e.g., social communication), the poor sensitivities of these species even at their best frequencies suggest that these moths represent a state of advanced auditory degeneration brought about by their diurnal life history. The phylogeny of the Notodontidae further suggests that this deafness is a derived (apomorphic) condition and not a retention of a primitive (pleisiomorphic), insensitive state.

Auditory encoding during the last moment of a moth's life

SUMMARY The simple auditory system of noctuoid moths has long been a model for anti-predator studies in neuroethology, although these ears have rarely been experimentally stimulated by the sounds they would encounter from naturally attacking bats. We exposed the ears of five noctuoid moth species to the pre-recorded echolocation calls of an attacking bat (Eptesicus fuscus) to observe the acoustic encoding of the receptors at this critical time in their defensive behaviour. The B cell is a non-tympanal receptor common to all moths that has been suggested to respond to sound, but we found no evidence of this and suggest that its acoustic responsiveness is an artifact arising from its proprioceptive function. The A1 cell, the most sensitive tympanal receptor in noctuid and arctiid moths and the only auditory receptor in notodontid moths, encodes the attack calls with a bursting firing pattern to a point approximately 150 ms from when the bat would have captured the moth. At this point, the firing of the A1 cell reduces to a non-bursting pattern with longer inter-spike periods, suggesting that the moth may no longer express the erratic flight used to escape very close bats. This may be simply due to the absence of selection pressure on moths for auditory tracking of bat echolocation calls beyond this point. Alternatively, the reduced firing may be due to the acoustic characteristics of attack calls in the terminal phase and an acoustic maneuver used by the bat to facilitate its capture of the moth. Although the role of less sensitive A2 cell remains uncertain in the evasive flight responses of moths it may act as a trigger in eliciting sound production, a close-range anti-bat behaviour in the tiger moth, Cycnia tenera.

Why Do Diurnal Moths Have Ears

Ears exist in moths primarily for the purpose of detecting hunting bats at night to avoid predation. The ears of four species of day-flying Nearctic moths are as sensitive as those of a common, night-flying genus to the frequencies emitted by sympatric bats and show no evidence of being vestigial. We determined that all of the day-flying moths spend 44–73% of their 24-hour cycles active at night when bats hunt. Two of the moths tested are sound-emitting species and may use their ears during intraspecific communication. We conclude that the functions of bat detection and social communication are the only selective forces acting on moth ears, and that in their absence these sensory structures degenerate. Most moths have simple ears on various parts of their bodies that they use to detect the echolocation calls of aerially hunting, insectivorous bats [1]. Where bats are numerous and diverse (e.g., the tropics), the ears of sympatric moths are more sensitive to a broader range of frequencies than those that live in areas of lower bat diversity (e.g., temperate regions) [2]. Certain habitats exist that are spatially and/or temporally bat free (i.e., places and/or times that bats do not exist), and some of the moths in these habitats exhibit ears with varying levels of auditory degeneration (e.g., oceanic island moths [3], wintermoths [4]). Other moths experience release from bat predation and corresponding auditory degeneration by means of extreme behavioral changes (e.g., flightlessness [5–8]). For temporal bat release a pronounced example of auditory degeneration exists in certain members of the Dioptinae, a group of diurnal Neotropical moths [9]. If diurnal habits result in bat-free environments, we should expect auditory degeneration in day-flying moths, assuming that they do not use their ears for other purposes (e.g., social communication). We examined the auditory, activity, and acoustic characteristics of four species of Nearctic dayflying moths to test this hypothesis.

If a bird flies in the forest, does an insect hear it?

Birds are major predators of many eared insects including moths, butterflies, crickets and cicadas. We provide evidence supporting the hypothesis that insect ears can function as ‘bird detectors’. First, we show that birds produce flight sounds while foraging. Eastern phoebes (Sayornis phoebe) and chickadees (Poecile atricapillus) generate broadband sounds composed of distinct repetitive elements (approx. 18 and 20 Hz, respectively) that correspond to cyclic wing beating. We estimate that insects can detect an approaching bird from distances of at least 2.5 m, based on insect hearing thresholds and sound level measurements of bird flight. Second, we show that insects with both high and low frequency hearing can hear bird flight sounds. Auditory nerve cells of noctuid moths (Trichoplusia ni) and nymphalid butterflies (Morpho peleides) responded in a bursting pattern to playbacks of an attacking bird. This is the first study to demonstrate that foraging birds generate flight sound cues that are detectable by eared insects. Whether insects exploit these sound cues, and alternatively, if birds have evolved sound-reducing foraging tactics to render them acoustically ‘cryptic’ to their prey, are tantalizing questions worthy of further investigation.

NSERC's HydroNet: A National Research Network to Promote Sustainable Hydropower and Healthy Aquatic Ecosystems

Abstract NSERCs HydroNet is a collaborative national five-year research program initiated in 2010 involving academic, government, and industry partners. The overarching goal of HydroNet is to improve the understanding of the effects of hydropower operations on aquatic ecosystems, and to provide scientifically defensible and transparent tools to improve the decision-making process associated with hydropower operations. Multiple projects are imbedded under three themes: 1) Ecosystemic analysis of productive capacity offish habitats (PCFH) in rivers, 2) Mesoscale modelling of the productive capacity offish habitats in lakes and reservoirs, and 3) Predicting the entrainment risk of fish in hydropower reservoirs relative to power generation operations by combining behavioral ecology and hydraulic engineering. The knowledge generated by HydroNet is essential to balance the competing demands for limited water resources and to ensure that hydropower is sustainable, maintains healthy aquatic ecosystems and a vibr...

Swimming activity and energetic costs of adult lake sturgeon during fishway passage.

ABSTRACT Fish migrations through riverine systems can be energetically demanding, and the presence of fishways to facilitate upstream passage can add an additional energetic cost that may directly affect fitness. Successful fishway passage is a function of the ability of fish to select appropriate paths and swimming strategies that do not exceed their swimming capacity. Triaxial accelerometers were used to estimate the energetic expenditure of adult lake sturgeon (Acipenser fulvescens) swimming through a vertical slot fishway, to determine whether individual behaviour or path selection, resulting in differences in cumulative energy use, explain fishway passage success. Most individuals attempted to pass the fishway (n=30/44; 68%), although successful passage only occurred for a subset of those attempting (n=7/30; 23%). High-speed swimming was rarely observed during upstream passage through fishway basins, and was of short duration. Two turning basins delayed passage, subsequently resulting in a higher energetic cost. The rate at which energy was expended did not differ among successful and unsuccessful individuals, although successful sturgeon exhibited higher costs of transport (42.75 versus 25.85 J kg−1 m−1). Energy expenditure metrics were not predictive of successful fishway passage, leading us to conclude that other endogenous or exogenous factors influence passage success. In a practical application of field measurements of energy expenditure, we demonstrate that fishway passage through a structure designed to facilitate migration does result in an energetic loss for lake sturgeon (3249–16,331 J kg−1), equivalent to individuals travelling 5.8–28.2 km in a lentic system. Highlighted Article: Adult sturgeon energy use during fishway passage reveals location-specific differences in energy use and variable overall net energy costs.

How age influences phonotaxis in virgin female Jamaican field crickets (Gryllus assimilis)

Female mating preference can be a dominant force shaping the evolution of sexual signals. However, females rarely have consistent mating preferences throughout their lives. Preference flexibility results from complex interactions of predation risk, social and sexual experience, and age. Because residual reproductive value should theoretically decline with age, older females should not be as choosy as younger females. We explored how age influences phonotaxis towards a standard mate attraction signal using a spherical treadmill (trackball) and a no-choice experimental protocol. Female Jamaican field crickets, Gryllus assimilis, were highly variable in their phonotaxis; age explained up to 64% of this variation. Females 10 days post imaginal eclosion and older oriented toward the mate attraction signal, with 10- and 13-day females exhibiting the greatest movement in the direction of the signal. Our study suggests 10- and 13-day old females would be most responsive when quantifying the preference landscape for G. assimilis sexual signals.

Acoustic startle/escape reactions in tethered flying locusts: motor patterns and wing kinematics underlying intentional steering.

We simultaneously recorded flight muscle activity and wing kinematics in tethered, flying locusts to determine the relationship between asymmetric depressor muscle activation and the kinematics of the stroke reversal at the onset of wing depression during attempted intentional steering manoeuvres. High-frequency, pulsed sounds produced bilateral asymmetries in forewing direct depressor muscles (M97, 98, 99) that were positively correlated with asymmetric forewing depression and asymmetries in stroke reversal timing. Bilateral asymmetries in hindwing depressor muscles (M127 and M128 but not M129) were positively correlated with asymmetric hindwing depression and asymmetries in the timing of the hindwing stroke reversal; M129 was negatively correlated with these shifts. Hindwing depressor asymmetries and wing kinematic changes were smaller and shifted in opposite direction than corresponding measurements of the forewings. These findings suggest that intentional steering manoeuvres employ bulk shifts in depressor muscle timing that affect the timing of the stroke reversals thereby establishing asymmetric wing depression. Finally, we found indications that locusts may actively control the timing of forewing rotation and speculate this may be a mechanism for generating steering torques. These effects would act in concert with forces generated by asymmetric wing depression and angle of attack to establish rapid changes in direction.

No neural evidence for dynamic auditory tuning of the A1 receptor in the ear of the noctuid moth, Noctua pronuba

By examining the mechanical properties of the tympanum of the noctuid moth, Noctua pronuba, Windmill et al. (2006) suggested that this insect increases (up-tunes) the frequencies of its best hearing when exposed to high intensity sounds (HIS) resembling the echolocation calls of attacking bats. We tested whether this biophysical phenomenon was encoded in the neural responses of this moth’s most sensitive auditory receptor (A1 cell) before and after exposure to HIS. We measured: (1) the number of A1 action potentials (spikes) per stimulus pulse; (2) the proportion of A1 spike periods below that determined to elicit evasive flight maneuvers and, (3) the change in A1 cell firing (spike number, interspike interval, stimulus/spike latency) over a duration of time similar to that in which up-tuning lasts. We observed no significant spiking response changes in the predicted direction to any of the frequencies tested following exposure to HIS and we observed only two of the 24 predicted time-dependent changes to A1 firing. These results indicate that tympanal up-tuning does not result in a change to this moth’s auditory frequency sensitivity and we suggest either sensillar resonances or increases in thoracic muscle tension following exposure to HIS as alternative explanations.

Design and Manufacturing of Biologically Inspired Micro Aerial Vehicle Wings Using Rapid Prototyping

Micro Aerial Vehicles (MAVs) are an emerging class of uninhabited aerial vehicle (UAV). Their reduced scale (maximum dimension of approximately 150 mm) provides advantages in terms of advanced mission capabilities, such as wildlife monitoring and urban search and rescue. This introduces the design challenge of flying efficiently at very low Reynolds numbers (e.g. Re<10000). To date, three basic MAV design concepts have been developed: fixed, rotary and flapping wings. Each approach has been met with limited success due to gust stability, flight control and propulsive efficiency. The design of both fixed and rotary wing aircraft is relatively mature, whereas flapping wing design is in its infancy and therefore its viability cannot yet be assessed. Nonetheless flapping wing MAVs have the potential to offer advantages such as stealth, manoeuvrability, and improved propulsive efficiencies. This paper focuses on the challenging problem of the manufacture and testing of flapping wings for MAVs. A review of the current state of flapping wing aerodynamics, manufacturing, and wing structures is provided. A detailed assessment of the aerodynamic performance of flexible MAV-scale wings was carried out. Aerodynamic force measurements were collected using a spin rig to assess the effect of design details on lift generation. It was found that a simple three-vein wing structure manufactured using a fused filament fabrication 3D printer could produce lift forces close to those of natural insect wings. The lift and stall performance was found to be sensitive to chordwise stiffness by testing wings without veins. These results demonstrate that it is possible to produce low cost biologically inspired wings with aerodynamic performance equal to or better than natural wings – a critical step on the path to a functional and practical flapping wing MAV.