Fluctuating asymmetries and advertisement call variation in the cricket frog, Acris crepitans

We used an anuran acoustic communication system to test a predictionof the "fluctuating asymmetries/good genes" hypothesis thatfemales prefer more symmetric mates because symmetry indicatesgenetic quality. Mate preferences of female cricket frogs (Acriscrepitans) can be influenced by three call characters: dominantfrequency, numbers of pulses per call, and number of pulse groupsper call. We tested the hypothesis that these preferences resultin females preferring more symmetric males. We measured fluctuatingasymmetries of characters not involved with the communicationsystem (head and tibia), and those involved in signal production(laryngeal characters) and signal reception (aural characters).We determined whether the asymmetries in these characters wererelated to the three variables that enhance call attractiveness.Most of the multiple regression models showed no significantassociation between the fluctuating asymmetries of charactersand any of the calls. The regression of head and tibia fluctuatingasymmetry on pulse number was significant, but partial regressioncoefficients revealed that more pulses were associated witha more symmetric head length and a less symmetric tibia length.Our findings provide little or no support for the fluctuatingasymmetries/good genes hypothesis. We emphasize, however, thatthis hypothesis should not be abandoned based on negative resultsof a single study, but deserves further scrutiny.     

Evolution of intraspecific variation in the advertisement call of a cricket frog (Acris crepitans, Hylidae)

Advertisement calls of the cricket frog, Acris crepitans , show statistically significant variation among populations in all call variables measured. Call variables show strong clinal variation resulting in calls of lower frequency, longer duration and slower call rates produced by A. c. blanchardi in open habitat in the west of the range, and calls of higher frequency, shorter calls and faster call rates produced by A. c. crepitans in the pine forests in the eastern part of the range. This clinal variation does not result from pleiotropic effects of body size or any other morphological characters we measured.
The two subspecies usually reside in different habitats, but some A. c. blanchardi reside in an isolated pine forest in central Texas. By comparing the calls of this subspecies in open and forest habitat, and by statistically removing the effects of clinal variation for all populations, we determined that habitat explains some of the variation in call structure; this is not true of subspecies.
Our data reject several hypotheses that purport to explain the evolution of mate recognition signals. (1) We reject the notion of Paterson and others that there is strong stabilizing selection on species-specific mate recognition signals. (2) There is no support for the hypothesis that call variation is primarily due to pleiotropic effects of body size or other morphological characters over the geographic range we examined. (3) There is no evidence for reproductive character displacement. (4) Our data, as well as experimental studies of habitat acoustics, support the hypothesis that some differences in calls among habitats result from environmental selection on call structure to enhance call transmission. We suggest that the latter hypothesis does not explain the strong clinal component of call variation. This might result from the passive effects of gene flow between populations at the extremes of the range under selection generated by habitat acoustics.     

Genetic variation and population subdivision in the cricket frog Acris crepitans

Genetic variation at 16 enzyme loci was examined for Acris crepitans, from 14 populations collected along an intermittent creek in north-central Texas and seven populations from separate localities in south-central Texas. Regional genetic differentiation was low. Zygotic distributions for the 14 creek populations were significantly heterogeneous, and genic heterogeneity (F_ST=0.116) was nearly as high as that for widely separated populations (F_ST=0.136). There was no relationship between genetic similarity and proximity of the populations. Gene flow between adjacent populations is minimal, and differentiation appeared to be maintained by a combination of stochastic events and inbreeding.     

Geographic variation of lactate dehydrogenase in the cricket frog,Acris crepitans

Geographic variation is present in what is probably the H subunit of lactate dehydrogenase in Acris crepitans, but not in the M subunit. Electrophoretically different products of two alleles occur in most of the species range. One allele predominates in eastern populations but becomes less common progressively westward from the Middle West. The other allele is the predominant one in the West and in a corridor leading from Nebraska to the western end of Lake Erie. The evidence from this locus suggests genetic continuity over the entire range.This work was supported in part by NSF grants GB-5232 and GB-7749 to S. N. Salthe and by grants-in-aid from Sigma Xi and tenure of a Committee on Evolutionary Biology Traineeship at the Museum of Comparative Zoology, Harvard University, to E. Nevo.     

Habitat-dependent advertisement call variation in the monkey frog Phyllomedusa nordestina

The acoustic adaptation hypothesis (AAH) predicts that acoustic signals are selected to propagate more efficiently in the habitat where they are normally transmitted. Several studies corroborated the AAH for primates and birds, but evidence for frogs is contentious: While most studies failed to support the AAH, recent studies have shown that within-species variation conforms to the predictions of the AAH. Herein, we test the AAH by comparing advertisement calls of Phyllomedusa nordestina from two contrasting habitats (Atlantic Rainforest and Caatinga) and by testing the influence of the amount of vegetation around calling sites on acoustic parameters of frog calls. The interval between pulses was significantly different between individuals from the Atlantic Rainforest and from the Caatinga, and the number of pulses was correlated with the amount of vegetation around calling sites. Hence, our results indicate that multiple evolutionary forces may act simultaneously on the advertisement calls of frogs.     

Sexually transmitted nematodes affect spermatophylax production in the cricket, Gryllodes sigillatus

Parasites can influence various aspects of host reproductionand mating, including spermatophore production. In the cricket,Gryllodes sigillatus, males transfer to females a two-part spermatophorecontaining a sperm-filled ampulla and a gelatinous spermatophylax(nuptial gift). Here we investigate the effects of a sexuallytransmitted nematode on male spermatophylax production. Sexuallytransmitted diseases (STDs) have the potential to reduce hostfertility or fecundity in insect hosts. To our knowledge thisis the first empirical study on the effects of an insect STDon the reproductive physiology of a male host. Our results indicatethat infected males produced significantly smaller spermatophylacesthan healthy males; this effect was more apparent for smallermales. Spermatophylax size was inversely correlated with theintensity of infection. Spermatophylax replacement time, thetime between producing the first and second spermatophylax,did not differ significantly between infected and healthy males.This parasite-mediated reduction in spermatophylax size maybe a direct consequence of the physiological stress of parasitismor parasite manipulation.     

Acoustically induced call modification in the white-lipped frog,Leptodactylus albilabris

The vocalization behaviour of Leptodactylus albilabris was investigated using field playback experiments. To assess the response of males to pre-recorded natural ‘chirp’ (advertisement call) and natural ‘chuckle” (aggressive call) stimuli of gradually increasing broadcast intensity, three parameters (intensity, dominant frequency and repetition rate) of the chirp call were analysed. Of the males tested, 69% showed a significant increase in chirp intensity with increased levels of both stimulus types. In response to playback of the chirp stimulus, males actively modified the dominant frequency of their chirp calls over a mean range of 91·42 Hz, and in one case as much as 400 Hz. Moreover, 12 of 17 males shifted the frequency of their call towards the dominant frequency of the chirp stimulus (2175 Hz) by either increasing or decreasing the dominant frequency of their chirp calls. In response to the natural chuckle stimulus, 83% of the males showed either a decrease or no significant change in the dominant frequency of their chirps. All eight males for which both the chirp frequency and intensity were analysed and that showed an increase in chirp intensity also showed a concomitant increase in chirp dominant frequency. These results are the first to document quantitatively the plasticity of advertisement call intensity and dominant frequency in an anuran. The possible effects of advertisement call modification on male mating success in L. albilabris is discussed.     

Temporal changes in motor variability during prolonged lifting/lowering and the influence of work experience

Existing research indicates that repetitive motions are strongly correlated with the development of work-related musculoskeletal disorders (WMSDs). Resulting from the redundant degrees-of-freedom in the human body, there are variations in motions that occur while performing a repetitive task. These variations are termed motor variability (MV), and may be beneficial for reducing WMSD risks. To better understand the potential role of MV in preventing injury risk, we evaluated the effects of fatigue on MV using data collected during a lab-based prolonged, repetitive lifting/lowering task. We also investigated whether experienced workers used different motor control strategies than novices to adapt to fatigue. MV of the whole-body center-of-mass (COM) and box trajectory were quantified using cycle-to-cycle standard deviation, sample entropy, and goal equivalent manifold (GEM) methods. In both groups, there were significantly increased variations of the COM with fatigue, and with a more substantial increase in a direction that did not affect task performance. Fatigue deteriorated the task goal and made it more difficult for participants to maintain their performance. Experienced workers also had higher MV than novices. Based on these results, we conclude that flexible motor control strategies are employed to reduce fatigue effects during a prolonged repetitive task.     

Individual differences affect honest signalling in a songbird

Research in the past decade has established the existence of consistent individual differences or ‘personality’ in animals and their important role in many aspects of animal behaviour. At the same time, research on honest signalling of aggression has revealed that while some of the putative aggression signals are reliable, they are only imperfectly so. This study asks whether a significant portion of the variance in the aggression-signal regression may be explained by individual differences in signalling strategies. Using the well-studied aggressive signalling system of song sparrows (Melospiza melodia), we carried out repeated assays to measure both aggressive behaviours and aggressive signalling of territorial males. Through these assays, we found that aggressive behaviours and aggressive signalling were both highly repeatable, and moreover that aggressive behaviours in 2009–2010 predicted whether the birds would attack a taxidermic mount over a year later. Most significantly, we found that residual variation in signalling behaviours, after controlling for aggressive behaviour, was individually consistent, suggesting there may be a second personality trait determining the level of aggressive signalling. We term this potential personality trait ‘communicativeness’ and discuss these results in the context of honest signalling theories and recent findings reporting prevalence of ‘under-signalling’.     

The vocal sac increases call rate in the Tungara frog Physalaemus pustulosus

In most anurans, the production of advertisement calls is accompanied by the inflation of a vocal sac. Current functions of the vocal sac, however, are not fully understood, although several hypotheses have been proposed. One hypothesis suggests that the vocal sac decreases the intercall interval (i.e., increases call rate) by reinflating the lungs more rapidly than is possible with the buccal pump. We investigate this hypothesis by analyzing audio and video recordings of calling tungara frogs. We compare the first two call bouts emitted by an originally uninflated male. The first call bout requires lung inflation via buccal pumping, but in the second, the male is already inflated because of capture of air and reinflation of the lungs by the vocal sac. Lung inflation to typical field levels requires 26-51 buccal pumps, which takes at least 4.4 s. This estimate is more than 2.5 times the typical intercall interval with lung reinflation via a vocal sac (ca. 1.7 s). Evidence from phonotaxis tests demonstrates that these differences in intercall intervals are salient to females and that female Physalaemus pustulosus prefer the shorter intercall interval/higher call rate. Acoustic analyses demonstrate that the first call of bout 1, which requires buccal pumping, is usually shorter, of lower amplitude, and spans a smaller frequency range than the first call of bout 2, which does not require buccal pumping. Because females prefer longer, more intense calls, these results suggest that the vocal sac not only increases call rate but also allows males to produce more calls of increased attractiveness to females.     

Acoustic interference limits call detection in a Neotropical frog Hyla ebraccata

Problems1999 The Association for the Study of Animal Behaviourassociated with communication in noisy environments include detection, discrimination, and localization of appropriate signals. I investigated the effects of broadband background noise on call detection by female Copyright 1999 The Association for the Study of Animal Behaviour.