Social Correlates of Variation in Male Calling Behavior in Blanchard's Cricket Frog,Acris crepitans blanchardi

I studied variation in male calling behavior and its social correlates in Blanchard's cricket frog, Acris crepitans blanchardi. Calls were produced in distinct call groups, and they increased in duration and complexity from the beginning to end of a call group. Dominant frequency was the only character of 18 quantified consistently correlated with male snout-vent length. Calls from the beginning of a call group varied independently of calls from the middle and end of a call group, and only calls from the beginning of a call group exhibited significant variation among males, thus relative consistency within males. Other characters varied greatly within individual males. Unlike most other anurans, dominant frequency also exhibited tremendous within-male variation. The relative influence of caller density, local caller density, nearest neighbor distance, and nearest neighbor sound pressure level on variation in male calling behavior was examined. Nearest neighbor distance, mediated through the sound-pressure level of neighbor calls, appeared to have the greatest influence on variation in male calling behavior. The most profound changes in calling behavior occurred during aggressive encounters; males altered their calling behavior in a manner suggesting that they respond to competitors with graded aggressive signals. Furthermore, the structure of the communication system suggests that calls are graded not only in response to the level of social competition, but graded over a call group as well.     

Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardi

In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females.     

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.     

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.     

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.     

Agonistic Encounters in a Cricket Frog (Acris crepitans) Chorus: Behavioral Outcomes Vary with Local Competition and within the Breeding Season

Male cricket frogs ( Acris crepitans ) gather in breeding choruses and call to attract females. The call also serves to maintain an individual's calling space. When an intruder invades a resident male's space, the resident will display one of three behavior patterns. He will either attack the intruder, abandon calling, or tolerate the intruder's presence and continue calling. We simulated an intruder by broadcasting a stimulus from a speaker and categorized the response of the resident male. We recorded social variables relevant to local competition among males, specifically, local caller density (within 2 m) and the amplitude of the nearest neighbor's calls. In addition we recorded the size of the subject, the amplitude of the stimulus, and the time of night and the season. We used a multivariate approach to assess the relative importance of these variables. Local caller density and nearest neighbor call amplitude were the best predictors of a resident's response to the intruder; higher levels of local competition resulted in more males tolerating the intruder. In addition, behavior changed over the season: males were more likely to abandon or ignore the intruder early in the season and more likely to attack later in the season. No other variables were related to the outcome of the agonistic encounter. This study suggests that the most important variables impinging on a male's decision to fight, flee, or ignore an intruder are influences external to the individuals involved in the conflict.     

A comparison of energy substrates and reproductive patterns of two anurans. Acris crepitans and Bufo woodhousei

The seasonal pattern of carcass, liver and ovary lipid and liver non-lipid mass was examined in the cricket frog, Acris crepitans, and Woodhouse's toad, Bufo woodhousei. Reproductive patterns were also studied. The over-winter reduction of body lipid and liver non-lipid material was attributed to metabolism in Acris crepitans. Male, but not female, Bufo woodhousei exhibited seasonal variation in lipid stores that was attributable to metabolism. Females, but not males, showed seasonal variation in liver non-lipid mass and quantified liver glycogen. Females of both species mobilized body lipid during the period of ovarian development; however, an inverse relationship between fatbody mass and ovary mass was evident for Acris, only. Female Acris crepitans depleted all ovarian follicles prior to brumation; however, Bufo woodhousei retained enlarged follicles throughout the year. Variation in metabolic substrate use between species was related to the differences in reproductive patterns exhibited by the two anurans. These variations in reproductive strategy represent adaptations that enhance the survivability of different species in dissimilar habitats.     

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.     

Morphological Evolution of Coexisting Amphipod Species Pairs from Sulfidic Caves Suggests Competitive Interactions and Character Displacement,but No Environmental Filtering and Convergence

Phenotypically similar species coexisting in extreme environments like sulfidic water are subject to two opposing eco-evolutionary processes: those favoring similarity of environment-specific traits, and those promoting differences of traits related to resource use. The former group of processes includes ecological filtering and convergent or parallel evolution, the latter competitive exclusion, character displacement and divergent evolution. We used a unique eco-evolutionary study system composed of two independent pairs of coexisting amphipod species (genus Niphargus) from the sulfidic caves Movile in Romania and Frasassi in Italy to study the relative contribution and interaction of both processes. We looked at the shape of the multifunctional ventral channel as a trait ostensibly related to oxygenation and sulfide detoxification, and at body size as a resource-related trait. Phylogenetic analysis suggests that the sulfidic caves were colonized separately by ancestors of each species. Species within pairs were more dissimilar in their morphology than expected according to a null model based on regional species pool. This might indicate competitive interactions shaping the morphology of these amphipod species. Moreover, our results suggest that the shape of the ventral channel is not subject to long-term convergent selection or to the process of environmental filtering, and as such probably does not play a role in sulfide tolerance. Nevertheless, the ancestral conditions reconstructed using the comparative method tended to be more similar than null-model expectations. This shift in patterns may reflect a temporal hierarchy of eco-evolutionary processes, in which initial environmental filtering became later on superseded by character displacement or other competition-driven divergent evolutionary processes.     

Hummingbird-Syndrome Traits, Breeding System, and Pollinator Effectiveness in Two Syntopic Penstemon Species

Red-flowered, tubular Penstemon barbatus and Penstemon pinifolius, which have probably adapted independently to hummingbird pollinators, coflower on recently burned high-elevation slopes in the Chiricahua Mountains in Arizona. Hummingbirds visit both species but visit P. barbatus at a higher rate. We compared several traits and asked whether the species differed in specialization for hummingbird pollination. The corollas of P. pinifolius were 30% narrower than those of P. barbatus, but they were similar in tube length. Although a narrower corolla appeared to decrease access by large insects, small halictid bees were the only common insect visitors, and they gathered nectar from both species. Species differences in nectar production rate and concentration were minor, being smaller than within-species differences between dry and rainy periods. Taller inflorescences and a wider corolla tube may contribute to greater hummingbird use of P. barbatus. Penstemon pinifolius was fully self-compatible and weakly autogamous, whereas P. barbatus was strongly self-incompatible and had a longer flower life. Exclusion of hummingbirds reduced seed set fourfold in both species, supporting the inference from morphology and rewards that hummingbirds are the primary pollinators. In the absence of hummingbirds, halictids increased the seed set of P. barbatus relative to exclusion of all visitors, but they did not increase the seed set of P. pinifolius. Despite sharing the basic set of hummingbird-syndrome traits, the two species differed in degree of investment in individual flowers and in adaptations for outcrossing.     

A forty-three year museum study of northern cricket frog (Acris crepitans) abnormalities in Arkansas: upward trends and distributions

The northern cricket frog (Acris crepitans) is a resident of streams, rivers, and wetlands of eastern North America. We documented abnormalities in A. crepitans housed in the Arkansas State University Museum of Zoology Herpetology Collection. Abnormality frequency increased from 1957 to 2000 (chi 2 = 43.76, df = 3, P < 0.001). From 1957 through 1979 only 3.33% of specimens were unusual. This rate was 6.87% during the 1990s, and in 2000 it was 8.48%. High frequencies of abnormalities were identified in the following Ozark highland counties: Sharp, Lawrence, and Randolph. We observed 104 abnormalities among 1,464 frogs (7.10%). The differential abnormality frequencies observed between the Arkansas lowlands and highlands are striking. The Ozarks had significantly higher frequencies of abnormalities than other Arkansas regions (chi 2 = 59.76, df = 4, P < 0.001). The Ouachita Mountains had significantly higher frequencies than the Gulf Coastal Plain, Delta, or Arkansas River Valley (chi 2 = 13.172, df = 3, P < 0.01). There was no difference in abnormality frequency between the Gulf Coastal Plain, Delta, and Arkansas River Valley (chi 2 = 0.422, df = 2, P > 0.70). Proposed hypotheses for distributions include: 1) A. crepitans might possess naturally high abnormality levels, and land use practices of the Delta may reduce this variability; 2) an unknown xenobiotic may be in Ozark streams causing increased numbers of abnormalities; 3) the museum's collection effort may be skewed; 4) Delta habitat might be more favorable for green tree frogs (Hyla cinerea) allowing this species to drive out A. crepitans through competition; here, abnormal metamorphs are not detected because they are even less competitive than normal individuals.     

Ranging Patterns of Two Syntopic Howler Monkey Species (Alouatta guariba and A. caraya) in Northeastern Argentina

To avoid competition, ecologically similar and closely related species tend to differ in their patterns of habitat use when they live in sympatry. We compared ranging patterns of brown howler (Alouatta guariba) and black and gold howler (A. caraya) monkeys living syntopically, i.e., co-occurring and overlapping their ranges in the same habitat within the zone of sympatry, in the Atlantic Forest of northeastern Argentina with the objective of evaluating whether their use of space contributes to the avoidance of interspecific competition for food resources. During 12 mo we collected data on the ranging behavior of 2 groups of each howler species. We analyzed annual and seasonal daily path lengths and movement rates, home range size, use and overlap, habitat and vertical strata use, and intergroup encounters. Black and gold howlers traveled farther and faster during the time of relative food abundance (abundant season) than during the time of relative food shortage (lean season), and their movement rates were affected by group identity and increased with the proportion of fruits in the diet. Brown howlers’ traveling patterns were not affected by any of these factors. Home ranges for both species (95% fixed kernel; brown howlers: 31–70 ha, black-and-gold howlers: 17–112 ha) were among the largest recorded for Alouatta. For both species, core areas (50% fixed kernel) were larger for larger versus smaller groups, and decreased in the lean season compared to the abundant season. Both species showed similar patterns of habitat use, except for a slight vertical stratification. Groups of different species overlapped their ranging areas consistently more and responded to one another less aggressively during encounters than groups of the same species, suggesting that interspecific spatial niche separation for these two syntopic species is not occurring. The vertical stratification, as well as a day-to-day avoidance strategy, may be the only responses of species to one another that could reduce the potentially high levels of competition for food suggested by their elevated trophic niche overlap. A high degree of niche overlap may explain the parapatric distribution of howlers and other closely related and ecologically similar species of primates.     

褐家鼠声行为的种特性和种族变异

本文比较了不同种类和不同种族的鼠的惊叫声（SC）,给出了鼠类SC的种特异性和种族变异性。褐家鼠（Rattus norvegicus),金黄地鼠（Mesocicetus auratus)和黑线仓鼠（Cricetulus barabensis)的SC呈不同的谱系性状,具有不同的种特性。褐镓鼠（BHR）的变种－大白鼠（WR）（♀）和BHR（♂）的混种鼠（MSR）,其单主音SC（MDTSC）类似于BHR的谱系性状,但主峰频率（MPF）分别平均下降2．2和4．9个半音。其多谱SC（MHSC）的谱系性状虽然类似于BHR,但呈明显的音色变异,不仅基本音的MPF平均下降2．8个半音,而且WR MHSC是以BHR的MPF为2550Hz和5475Hz的隐性分音（RP）为主音,而HR的MPF为3375Hz和6300HZ的主音退化为RP,MSR的MHSC主要继承母本性状,而父本的MPF为4050Hz的RP显性化为次主音,其特有的由MHSC和MDTSC组合的混合SC呈更明显的双亲性状,这些结果为进一步开展动物声行为的种特性和种族变异性的遗传机制和分类上的应用研究提供了依据。     

Roaring Behavior of Two Syntopic Howler Species (Alouatta caraya and A. guariba clamitans): Evidence Supports the Mate Defense Hypothesis

Long-distance calls are loud vocalizations involved in within and between group communication in animals. These calls may maintain cohesion with group members or communicate the ownership of valuable resources such as territory, food, or mates to individuals from other groups. In howlers (Alouatta spp.), three nonmutually exclusive hypotheses suggest that the ultimate function of roaring (howling) behavior is to protect resources from neighboring groups. The space/food defense hypothesis maintains that roars are used to gain exclusive access to food; the mate defense hypothesis holds that roars ensure exclusive access to mates; and the infanticide avoidance hypothesis states that the roaring behavior serves to avoid male takeovers and infanticide. To test these three hypotheses, we conducted a study on black-and-gold howlers (Alouatta caraya) and brown howlers (A. guariba clamitans) living in syntopy at El Pi?alito provincial park in northeast Argentina. We recorded 12 mo of data on the roaring behavior of two groups of each species, along with data on food availability and diet. Although all four groups overlapped extensively in their use of food resources during the study period, roars occurred much more frequently during interactions between groups of the same species than between groups of different species. Roaring frequency was not higher during the lean season, when high-quality food was less abundant. Howlers did not roar more frequently at home range boundaries, nor were roaring bouts spatially associated with valuable feeding resources. Males participated in all of the roaring bouts, whereas females participated in only 29% of them. Adults did not roar more frequently when there were unweaned infants in the group, as expected if roaring behavior decreases infanticide risk. These results provide no support for the food defense or infanticide avoidance hypotheses, but support predictions derived from the mate defense hypothesis.     

Allometric Convergence in Savanna Trees and Implications for the Use of Plant Scaling Models in Variable Ecosystems

Theoretical models of allometric scaling provide frameworks for understanding and predicting how and why the morphology and function of organisms vary with scale. It remains unclear, however, if the predictions of ‘universal’ scaling models for vascular plants hold across diverse species in variable environments. Phenomena such as competition and disturbance may drive allometric scaling relationships away from theoretical predictions based on an optimized tree. Here, we use a hierarchical Bayesian approach to calculate tree-specific, species-specific, and ‘global’ (i.e. interspecific) scaling exponents for several allometric relationships using tree- and branch-level data harvested from three savanna sites across a rainfall gradient in Mali, West Africa. We use these exponents to provide a rigorous test of three plant scaling models (Metabolic Scaling Theory (MST), Geometric Similarity, and Stress Similarity) in savanna systems. For the allometric relationships we evaluated (diameter vs. length, aboveground mass, stem mass, and leaf mass) the empirically calculated exponents broadly overlapped among species from diverse environments, except for the scaling exponents for length, which increased with tree cover and density. When we compare empirical scaling exponents to the theoretical predictions from the three models we find MST predictions are most consistent with our observed allometries. In those situations where observations are inconsistent with MST we find that departure from theory corresponds with expected tradeoffs related to disturbance and competitive interactions. We hypothesize savanna trees have greater length-scaling exponents than predicted by MST due to an evolutionary tradeoff between fire escape and optimization of mechanical stability and internal resource transport. Future research on the drivers of systematic allometric variation could reconcile the differences between observed scaling relationships in variable ecosystems and those predicted by ideal models such as MST.     

Copulatory Courtship in Drosophila birchii and D. serrata,Species Recognition and Sexual Selection

Two endemic Australian Drosophila species, D. birchii and D. serrata, have a copulatory courtship, i.e., the males court the female mainly during copulation. In the present study we found the males of both species to mount their prospective mating partners selectively, exhibiting both sex and species recognition. The males began to sing after mounting the female, and they often exhibited also postcopulatory displays typical to copulatory courtship. D. birchii and D. serrata females discriminated against males which did not sing during mounting/copulation, which suggests that the females utilize cryptic female choice. Our findings raise the question of how widespread a phenomenon cryptic female choice is in Drosophila species.     

Pigmentation and spectral absorbance in the deep-sea arctic amphipods Eurythenes gryllus and Anonyx sp.

As for many deep-sea animals, the red colouration of the two amphipods Eurythenes gryllus and Anonyx sp. has an important function providing camouflage, as the attenuation of the red wavelengths in seawater is higher than other colours within the visible range. Variation in colouration between different stages of colour intensity (related to size) is evident in both species. The red colour is caused by carotenoids, and the carotenoid composition was identified and quantified using spectral optical density signatures, high-performance liquid chromatography (HPLC) and liquid chromatography–mass spectrometry (LC–MS). The carotenoid astaxanthin was identified as the major carotenoid in both amphipods, both in pure and in esterified forms. In addition, minor amounts of lutein-like, canthaxanthin-like and several unidentified carotenoids were found in E. gryllus, while diatoxanthin, β,β-carotene and canthaxanthin-like carotenoids were detected in Anonyx sp. Generally, both species displayed an increase in the amount of carotenoids as a function of colour intensity and size. Shifts in λ_max in the OD (Optical density; dimensionless, acronym absorbance) spectra were evident in both species between the different colour stages in both the in vivo and the in vitro material, probably caused by changes in pigment composition. Similar shifts in λ_max were observed between the in vivo and in vitro pigment raw extracts in general, most likely caused by pigment-binding proteins. The differences in pigment composition and wavelength shifts suggest large intra- and inter-specific differences between the two species. Probable reasons for changes in pigment composition could be related to diet, season, moulting patterns, metabolic pathways and reproduction.