Distortion-product otoacoustic emissions from the tympanic organ in two noctuoid moths

Distortion-product otoacoustic emissions were measured from the tympanic organ of Ascalapha odorata (Noctuidae, Erebinae) and Empyreuma affinis (=pugione) (Arctiidae, Ctenuchinae) during stimulation with two pure tones of different frequency ( f1, f2) within a frequency range between 5 and 60 kHz. The cubic distortion-product that appears at a frequency of 2f1-f2 showed the largest amplitude and could be used to obtain “distortion audiograms”. In such audiograms, the maximal distortion-product otoacoustic emission levels were measured for stimulus frequencies that correspond to lowest A1-cell thresholds in each of the two species. Newly emerged E. affinis showed very low levels of the 2f1-f2 distortion, most of which were within the noise range. In contrast to vertebrate distortion-product otoacoustic emissions, in neither of the species could an optimum f2/f1 ratio be easily defined, and small ratios were sufficient to induce the distortions. We conclude that the ears of the two moth species exhibit distinctly non-linear mechanical properties. Distortion-product otoacoustic emissions are a good non-invasive method for studying the spectral response characteristics of the mechanics of their auditory organs, despite the fact that their morphological characteristics are very different from those in vertebrates. Accepted: 3 July 1998     

Otoacoustic emissions from insect ears having just one auditory neuron

Sensitive hearing organs often employ nonlinear mechanical sound processing which produces distortion-product otoacoustic emissions. Such emissions are also recorded from insect tympanal organs. Here we report high frequency distortion-product emissions, evoked by stimulus frequencies up to 95 kHz, from the tympanal organ of a notodontid moth, Ptilodon cucullina, which contains only a single auditory receptor neuron. The 2f1–f2 distortion-product emission reaches sound levels above 40 dB SPL. Most emission growth functions show a prominent notch of 20 dB depth (n = 20 trials), accompanied by an average phase shift of 119°, at stimulus levels between 60 and 70 dB SPL, which separates a low- and a high-level component. The emissions are vulnerable to topical application of ethyl ether which shifts growth functions by about 20 dB towards higher stimulus levels. For the mammalian cochlea, Lukashkin and colleagues have proposed that distinct level-dependent components of nonlinear amplification do not necessarily require interaction of several cellular sources but could be due to a single nonlinear source. In notodontids, such a physiologically vulnerable source could be the single receptor cell. Potential contributions from accessory cells to the nonlinear properties of the scolopidial hearing organ are still unclear.     

Comparison of sandbathing and grooming in two species of kangaroo rat

Sandbathing and grooming behaviours of two species of kangaroo rat (Dipodomys merriami and D. microps) were compared after zero and three days of sand deprivation. Results showed that D. merriami sandbathed and groomed at higher frequencies and over a longer time period than D. microps. Comparison of hair lipids revealed that D. merriami produced more oils. The data support the hypothesis that lipids in the hair are removed by sandbathing and suggest that D. merriami requires more pelage maintenance than D. microps. Three hypotheses about the function of lipids in the pelage of kangaroo rats are discussed.     

Mechanisms for the keystone status of kangaroo rats: graminivory rather than granivory?

Graminivory by kangaroo rats (Dipodomys spp.) was investigated as a potential mechanism for the keystone role of these rodents in the dynamics of desert grasslands. Experiments confirmed that Ord's kangaroo rats (Dipodomys ordii) cut and consumed a large proportion of the tillers of three Chihuahuan Desert tussock-forming grass species. Field observations indicated that the characteristically cut grass tillers were absent from all-rodent and medium-sized kangaroo rat exclosures, but were frequent in large-sized kangaroo rat and rabbit exclosures, indicating that the medium-sized kangaroo rats (D. ordii, D. merriami) were responsible for grass cutting. Tiller waste as a percentage of peak standing crop ranged from 7% in grassland habitats to 0.7% in Flourensia cernua shrubland. Of the 13 species of perennial, tussock-forming grasses measured, only one, Muhlenbergia porteri, had no tillers cut by kangaroo rats. This study demonstrates that the keystone role of kangaroo rats in Chihuahuan Desert grassland ecosystems is probably the result of their graminivory. Received: 28 October 1996 / Accepted: 26 February 1997     

Correlations between hearing and sound production in piranhas

Summary In order to determine whether correlations exist between hearing and the known soundproduction abilities in piranhas (Serrasalmus nattereri), behavioral auditory thresholds were obtained with continuous tones and tone pulses. A new avoidance conditioning method was developed, where fin movements of caged animals were taken as response to a tone. The mean values of the far-field audiogram ranged from –26 dB re. 0.1 Pa at 80 Hz to a low point of about –43 dB between 220–350 Hz and rose to –14 dB at 1500 Hz. The frequency spectrum of typical drumming sounds (barks) covers the range of best hearing (100–600 Hz).Piranhas are able to integrate temporally acoustic signals: in threshold investigations with repeated tone pulses, the thresholds rose approximately exponentially with decreasing pulse duration and repetition rate; thresholds of single pulses were higher with shorter pulses. The temporal patterning of the calls and the temporal integration ability are well correlated in piranhas, optimizing intraspecific detectability and total length of sound production with respect to the fatigue characteristics of drumming muscles and habituation of the neural pacemaker.The lagenae of the piranhas were found to face laterofrontally; this is thought to be a morphological adaptation to sound production, saving the lagenae from excessive strain during activation of the drumming muscles.Abbreviations Cl acoustic condition 1, where a board with the air loudspeaker rested on the experimental tank upon a layer of felt - C2 acoustic condition 2, where the loudspeaker was freely mounted 20 cm above the water surface - d _p pulse duration - f _p pulse repetition rate - D duty cycle     

Genetic consequences of postglacial range expansion in two codistributed rodents (genus Dipodomys) depend on ecology and genetic locus

How does range expansion affect genetic diversity in species with different ecologies, and do different types of genetic markers lead to different conclusions? We addressed these questions by assessing the genetic consequences of postglacial range expansion using mitochondrial DNA (mtDNA) and nuclear restriction site‐associated DNA (RAD) sequencing in two congeneric and codistributed rodents with different ecological characteristics: the desert kangaroo rat (Dipodomys deserti), a sand specialist, and the Merriam's kangaroo rat (Dipodomys merriami), a substrate generalist. For each species, we compared genetic variation between populations that retained stable distributions throughout glacial periods and those inferred to have expanded since the last glacial maximum. Our results suggest that expanded populations of both species experienced a loss of private mtDNA haplotypes and differentiation among populations, as well as a loss of nuclear single‐nucleotide polymorphism (SNP) private alleles and polymorphic loci. However, only D. deserti experienced a loss of nucleotide diversity (both mtDNA and nuclear) and nuclear heterozygosity. For all indices of diversity and differentiation that showed reduced values in the expanded areas, D. deserti populations experienced a greater degree of loss than did D. merriami populations. Additionally, patterns of loss in genetic diversity in expanded populations were substantially less extreme (by two orders of magnitude in some cases) for nuclear SNPs in both species compared to that observed for mitochondrial data. Our results demonstrate that ecological characteristics may play a role in determining genetic variation associated with range expansions, yet mtDNA diversity loss is not necessarily accompanied by a matched magnitude of loss in nuclear diversity.     

Interspecific interactions between three sympatric species of kangaroo rats (Dipodomys)

Interspecific interactions between Dipodomys merriami, D. ordii, and D. panamintinus were observed in the laboratory. The largest species, D. panamintinus, was the most dominant while the smallest species, D. merriami, was the least dominant. All interactions were characterized by extreme fighting. Laboratory and field evidence indicate that interspecific aggression in the field may be one mechanism keeping these sympatric species of kangaroo rats ecologically separate.     

An analysis of sandbathing and grooming in the kangaroo rat (Dipodomys merriami)

The sandbathing and grooming behaviour of ten kangaroo rats (Dipodomys merriami) were recorded on sand and woodchip substrates after periods of 0,1,5 and 10 days without sand. Sandbathing is restricted to the sandy substrate. Grooming occurs on both, but with a higher frequency on sand. Increases in both grooming and sandbathing occur with increasing sand deprivation, but the temporal patterning does not change. D. merriami tends to alternate sandbathing components in contrast to other Dipodomys species. Lipid on the pelage increases noticeably with sand deprivation and decreases during a sandbathing bout; sand appears to be removed from the pelage by shaking and grooming. These findings suggest a three-process system for care of the body surface.     

Does urbanization ameliorate the effect of endoparasite infection in kangaroo rats?

Urban development can fragment and degrade remnant habitat. Such habitat alterations can have profound impacts on wildlife, including effects on population density, parasite infection status, parasite prevalence, and body condition. We investigated the influence of urbanization on populations of Merriam''s kangaroo rat (Dipodomys merriami) and their parasites. We predicted that urban development would lead to reduced abundance, increased parasite prevalence in urban populations, increased probability of parasite infection for individual animals, and decreased body condition of kangaroo rats in urban versus wildland areas. We live trapped kangaroo rats at 5 urban and 5 wildland sites in and around Las Cruces, NM, USA from 2013 to 2015, collected fecal samples from 209 kangaroo rats, and detected endoparasites using fecal flotation and molecular barcoding. Seven parasite species were detected, although only two parasitic worms, Mastophorus dipodomis and Pterygodermatites dipodomis, occurred frequently enough to allow for statistical analysis. We found no effects of urbanization on population density or probability of parasite infection. However, wildland animals infected with P. dipodomis had lower body condition scores than infected animals in urban areas or uninfected animals in either habitat. Our results suggest that urban environments may buffer Merriam''s kangaroo rats from the detrimental impacts to body condition that P. dipodomis infections can cause.     

Cochlear function in mice following inhalation of brevetoxin-3

Brevetoxin-3 was shown previously to adversely affect central auditory function in goldfish. The present study evaluated the effects of exposure to this agent on cochlear function in mice using the 2f₁-f₂ distortion-product otoacoustic emission (DPOAE). Towards this end, inbred CBA/CaJ mice were exposed to a relatively high concentration of brevetoxin-3 (~400 g/m³) by nose-only inhalation for a 2-h period. Further, a subset of these mice received a second exposure a day later that lasted for an additional 4 h. Mice exposed only once for 2 h did not exhibit any notable cochlear effects. Similarly, mice exposed two times, for a cumulative dose of 6 h, exhibited essentially no change in DPOAE levels.     

Competitive release in microhabitat use among coexisting desert rodents: a natural experiment

Summary Competitive release among desert rodents on sand dunes of differing species richness was examined in the Great Basin and Mohave Deserts, USA. Expansions in microhabitat use were exhibited by the kangaroo rats Dipodomys ordii and D. merriami (granivorous heteromyid rodents, weighing 49 and 42 g, respectively) as the number of coexisting heteromyid species decreased geographically. Perognathus longimembris, the only common small heteromyid species (7 g) exhibited no competitive release. This may be due either to the absence of competitive interactions that affect the use of space by P. longimembris or to an unacceptable increase in risk of predation that precludes the use of more open microhabitats even in the absence of kangaroo rats. The breadth of microhabitat use of an omnivorous cricetid, Peromyscus maniculatus, decreased as the density of Perognathus longimembris increased, and increased as the density of conspecifics increased. The evidence for competitive release in Dipodomys and not in Perognathus is consistent with the hypothesis that species in the same guild and of similar size compete more intensely than species of disparate size.     

The effects of owl predation on the foraging behavior of heteromyid rodents

Summary Researchers have documented microhabitat partitioning among the heteromyid rodents of the deserts of North America that may result from microhabitat specific predation rates; large/bipedal species predominate in the open/risky microhabitat and small/quadrupedal species predominate in the bush/safer microhabitat. Here, we provide direct experimental evidence on the role of predatory risk in affecting the foraging behavior of three species of heteromyid rodents: Arizona pocket mouse (Perognathus amplus; small/quadrupedal), Bailey's pocket mouse (P. baileyi; large/quadrupedal), and Merriam's kangaroo rat (Dipodomys merriami; large/bipedal). Both kangaroo rats and pocket mice are behaviorally flexible and able to adjust their foraging behavior to nightly changes in predatory risk. Under low levels of perceived predatory risk the kangaroo rat foraged relatively more in the open microhabitat than the two pocket mouse species. In response to the presence of barn owls, however, all three species shifted their habitat use towards the bush microhabitat. In response to direct measures of predatory risk, i.e. the actual presence of owls, all three species reduced foraging and left resource patches at higher giving up densities of seeds. In response to indirect indicators of predatory risk, i.e. illumination, there was a tendency for all three species to reduce foraging. The differences in morphology between pocket mice and kangaroo rats do appear to influence their behavioral responses to predatory risk.     

Coding of acoustic particle motion by utricular fibers in the sleeper goby, <Emphasis Type="Italic">Dormitator latifrons</Emphasis>

It is unknown whether the fish utricle contributes to directional hearing. Here, we report response properties of single utricular fibers in a teleost fish (Dormitator latifrons) to linear accelerations at various stimulus frequencies and axes. Characteristic frequencies ranged from 50–400 Hz (median=80 Hz), and best frequencies shifted from 50 to 250 Hz with stimulus level. Best sensitivity of utricular fibers was distributed from –70 to –40 dB re: 1 g (mean=–52 dB), which is about 30 dB less sensitive than saccular fibers. Q_50% fell between 0.16 and 11.50 (mean=2.04) at 15 dB above threshold. We observed temporal response patterns of entrained phase-locking, double phase-locking, phase-locked bursting, and non-phase-locked bursting. Most utricular fibers were directionally selective with various directional response profiles, and directional selectivity was stimulus-level dependent. Horizontal best-response axes were distributed in a 152° range while mid-sagittal best-response axes were clustered around the fish longitudinal axis, which is consistent with the horizontal orientation of the utricle and morphological polarizations of utricular hair cells. Therefore, results of this study indicate that the utricle in this vertebrate plays an auditory role in azimuth and that utricular fibers extend the response dynamic range of this species in directional hearing.     

Why do kangaroo rats (Dipodomys spectabilis) footdrum at snakes?

We examined alternative hypotheses for the benefits of footdrummingin the presence of snakes by the banner-tailed kangaroo rat,Dipodomys spectabitis, by testing whether the target of thesignal includes conspecifics, the predator or both. Footdrummingrecorded in the field revealed that rats altered their footdrummingsignatures when drumming at snakes. In playback tests, however,neighbors failed to show any measurable change in behavior tobroadcasts of the snake drumming pattern, but mothers footdrummedsignificantly more than nonmothen in the presence of a tetheredsnake. Gopher snakes, Pituophis melanolsucus affinis, respondedto footdrumming vibrations created by a mechanical thumper.Nonhungry snakes avoided footdrumming, while hungry snakes approachedthe seismic footdrumming. Snakes decreased stalking rates asfootdrumming increased, but they spent more time stalking drummingthan nondnimming rats. We conclude that D. spectabilis footdrumsin individual defense and in parental care, rather than to warnadult conspecfics. Footdrumming deters pursuit by informingthe snake that the rat is alert and the chances of predationare low. We find little evidence that footdrumming startles,confuses, or harasses the snake. Hungry gopher snakes, however,may locate prey by eavesdropping on territorial footdrumming     

Evolution of eusociality in diploid species

Haplodiploid species are naturally biased by their genetic structure toward the evolution of sterile worker castes, as shown by W. D. Hamilton (1964. J. Theoret. Biol., 7, 1–16, 17–52). Diploid species do not have this intrinsic genetic bias toward eusociality. Nonetheless, true sociality has evolved in the diploid ancestors of the modern termites, and varying degrees of quasisociality are not uncommon in diploid species, including mammals. A genetic bias toward investment in relatives rather than offspring can arise in a diploid species as a result of inbreeding. The consequences of several regular incestuous breeding systems are analyzed in detail. It is shown that, under certain conditions, there is a natural bias toward an alternation of inbred and outbred generations. As this alternation proceeds, the genetic bias toward eusociality rapidly approaches an asymptotic value of 4(1 + 2f₀)/3(1 + 3f₀), where f₀ is the average coefficient of relationship for the outbreeding pairs. For f₀ close to zero, the genetic bias toward eusociality is close to 1.33, which is even larger than the genetic bias of 1.25 in haplodiploid species. Under other conditions there may be repeated incestuous matings between successive outbreeding generations. In this case the bias toward eusociality can be as large as 2.     

Correlation between auditory sensitivity and vocalization in anabantoid fishes

Several anabantoid species produce broad-band sounds with high-pitched dominant frequencies (0.8–2.5 kHz), which contrast with generally low-frequency hearing abilities in (perciform) fishes. Utilizing a recently developed auditory brainstem response recording-technique, auditory sensitivities of the gouramis Trichopsis vittata, T. pumila, Colisa lalia, Macropodus opercularis and Trichogaster trichopterus were investigated and compared with the sound characteristics of the respective species. All five species exhibited enhanced sound-detecting abilities and perceived tone bursts up to 5 kHz, which qualifies this group as hearing specialists. All fishes possessed a high-frequency sensitivity maximum between 800 Hz and 1500 Hz. Lowest hearing thresholds were found in T. trichopterus (76 dB re 1 μPa at 800 Hz). Dominant frequencies of sounds correspond with the best hearing bandwidth in T. vittata (1–2 kHz) and C. lalia (0.8–1 kHz). In the smallest species, T. pumila, dominant frequencies of acoustic signals (1.5–2.5 kHz) do not match lowest thresholds, which were below 1.5 kHz. However, of all species studied, T. pumila had best hearing sensitivity at frequencies above 2 kHz. The association between high-pitched sounds and hearing may be caused by the suprabranchial air-breathing chamber, which, lying close to the hearing and sonic organs, enhances both sound perception and emission at its resonant frequency. Accepted: 26 November 1997     

Reingestion of feces in rodents and its daily rhythmicity

Summary The ingestion of feces is widespread among rodent species and is an extensively employed component of the repertoire of feeding behaviors in some species. Coprophagy is thus a significant consideration in the nutrition and dietary ecology of many rodents. As certain fecal pellets pass from the anus, they are taken up directly into the mouth, chewed, and swallowed. The nocturnally active herbivorous kangaroo rat Dipodomys microps ingests about 1/4 of the feces it produces daily and the daily pattern of reingestion shows a consistent rhythm. For about 8 h of the daytime, during the non-foraging, resting phase of the day, D. microps reingests all fecal pellets produced; during the remainder of the day it leaves all feces produced. The reingested feces contain more nitrogen and water, and less inorganic ions than the non-reingested feces. The extent of reingestion varies among rodent species in relation to diet, and coprophagy is more important in the more herbivorous species. The granivorous kangaroo rat D. merriami ingests feces rarely. The herbivorous vole Microtus californicus ingests about 1/4 of its feces, as does D. microps. However, in contrast to D. microps, M. californicus shows a series of rhythmic, short-term (one to several hour duration) alternations between reingestion and non-reingestion during the course of the day and night. This pattern correlates with the pattern of foraging in M. californicus, which extends over both night and day.     

Neighbor Recognition in a Solitary Desert Rodent (Dipodomys merriami)

Neighbor recognition in the Merriam's kangaroo rat (Dipodomys merriami) was tested in neighbor and nonneighbor pairs of the same and opposite sex in a large enclosure in the field. Mutual tolerance, rather than aggression, occurred in the encounters, and neighbor recognition was more apparent in females than in males. Females tolerated and engaged in nonagonistic contact with familiar males and females; males approached and attempted to contact neighbors and nonneighbors alike. Neighbor recognition is important to both spacing and mating in females. Males' persistent attempts to interact with any conspecific may be important to their mating success.     

Cardiac responses to maximal anisotonic isometric contractions during handgrip and leg extension

A group of 14-healthy men performed anisotonic isometric contractions (AIC), for 60 s, at an intensity of 100% maximal voluntary contraction force (MVC) during handgrip (HG) and leg extension (LE). Heart rate (f _c), stroke volume index (SVI) and cardiac output index (Q_cI) were measured during the last 10 s of both AIC by an impedance reography method. Force (F) exerted by the subjects was recorded continuously and reported as a relative force (F _r) (% MVC). The F generated during MVC was greater for LE than for HG (502.I N compared to 374.6 N, P < 0.001). The rate of decrease in F _r was significantly slower for LE than HG for the first 25 s of the exercise (phase 1 of AIC). The F _r developed by the subjects at the end of AIC was 40% MVC for both LE and HG. The increase in f _c was greater for LE (63 beats · min^–1) than for HG (52 beats · min^–1), P < 0.01. The SVI decreased significantly from the resting level by 17.0 ml · m^–2 and by 18.2 ml · m^–2 for LE and HG, respectively. The Q_cI increased insignificantly for HG by 0.091 · min^–1 · m^–2 andsignificantly forLE by 0.561 · min^–1 · m^–2 (P < 0.001). It was concluded that although both AIC caused a significant decrease in SVI, greater increases in f _c and Q_c were observed for LE than for HG. The greater f _c and Q_c reported during LE was probably related to the greater relative force exerted by LE during phase 1 of AIC. It seems, therefore that central command might have dominated for phase 1 of AIC but that the muscle reflex also contributed significantly to the control of the cardiac response to the high intensity AIC.