Geographic variation and divergence of songs in the Olive Sparrow species complex

Phenotypic traits such as songs are important in species recognition. Variation in acoustic traits can form barriers to gene flow and promote speciation. Therefore, understanding song divergence is crucial in groups with controversial taxonomy such as Olive Sparrows (Arremonops rufivirgatus), a widespread Neotropical species of songbird with multiple allopatric populations. Taxonomic authorities disagree on the number of Olive Sparrow subspecies, placing them into either two or three main groups. These groups may represent separate species based on morphological traits, but trait divergence within the complex has not been examined. We studied geographic variation in the characteristics of the songs of Olive Sparrows at two geographical levels: among three proposed groups and among five allopatric populations. In a second analysis, we evaluated the strength of acoustic divergence within the complex by comparing acoustic distances among groups and allopatric populations of Olive Sparrows with the acoustic distance among three recognized species in the genus Arremonops. We analyzed 802 songs from 174 individuals across 81 locations and measured 12 variables to describe the fine structural characteristics of the songs of Olive Sparrows, Green-backed Sparrows (A. chloronotus), Black-striped Sparrows (A. conirostris), and Tocuyo Sparrows (A. tocuyensis). We found significant acoustic variation in the Olive Sparrow complex at both geographical levels. Our divergence analysis also revealed that vocal divergence within the complex is similar to or greater than that found between recognized species in the genus. Together, these results suggest that acoustic diversity within the Olive Sparrow complex probably originated by isolation in tandem with selective and/or non-selective factors.     

The best of both worlds: cicada males change costly signals to achieve mates while females choose a mate based on both calling and courtship songs

Cicadas usually sing and mate in the higher parts of trees. Studies addressing the effects of different acoustic signals on mate choice in Cicadidae are very limited. We investigated the effects of both acoustical features and morphological traits on mate choice in an East Asian cicada Platypleura kaempferi. Males produce high-rate calling songs that attract females, then produce low-rate courtship songs to secure mating when a female is attracted. Higher calling song rate (CR), shorter single-pulse duration, and shorter pulse period of the calling song, together with lower courtship song rate and longer echeme period of the courtship song, are the most desirable traits used by females to choose a mate. These traits indicate that the more a male can raise the rate of song production, the higher the probability he is sexually selected by the female. No correlation was found between morphological traits and mating success. After mating, a minority of males started emitting calling songs again, but the CR was significantly lower than before mating and none of them attracted a new mate later. This promotes females mating with unmated males. We hypothesize that P. kaempferi may have the best of both worlds due to the unique song modulation and the mechanism of female mate choice: males change energetically, costly acoustic signals to achieve mates, while females choose a mate based on males’ acoustic properties. Our results contribute to better understanding the diversity of mating preference and enrich the mechanism of mate choice in acoustic insects.     

Specificity of cicada calling songs in the genus Tibicina (Hemiptera: Cicadidae)

Abstract.  Males of Tibicina cicada species produce a sustained and monotonous calling song by tymbal activity. This acoustic signal constitutes the first step in pair formation, attracting females at long range, and is involved in male–male interactions. The specificity of this signal was investigated for the first time for seven species and one subspecies of Tibicina occurring in France. This analysis was achieved by describing tymbal anatomy, tymbal mechanism and calling song structure. Male calling songs are emitted following the same general scheme: tymbals are activated alternately and the successive buckling of the sclerotized ribs that they bear produces a regular succession of groups of pulses. The structural and mechanical properties shared by Tibicina species and subspecies lead to a considerable uniformity of the signal shape. Nevertheless, a principal component analysis applied to eight temporal and three frequency parameters revealed differences between the signals of the species studied. In particular, calling songs differed in groups of pulse rate and/or in peak of the second frequency band (carrier frequency). These acoustic differences are probably linked to differences in the numbers of tymbal ribs and body size. Groups of pulse rate and/or peak of the second frequency band could encode specific information. However, Tibicina calling songs may not act as distinct specific-mate recognition systems and may not play a leading role in the mating isolation process; rather, they might merely belong to a complex set of specific spatial, ecological, ethological and morphological characters that ensure syngamy.     

Acoustic preference functions and sexual selection on the male calling song in the grasshopper Chorthippus biguttulus

Male courtship songs have two functions in species recognition and intraspecific mate choice. Female preference might thus exert different types of selection pressure on male song traits. We used a combination of acoustic mate choice experiments and statistical analyses to examine how traits of the calling songs of male nightingale grasshoppers,Chorthippus biguttulus , are influenced by different sexual selection pressures. We recorded calling songs of males and tested their attractiveness to females in acoustic mate choice experiments. The attractiveness values were a good estimate of the potential male mating success. In experiments with a pair of males, females copulated significantly more often with the male that had the higher attractiveness value. To detect directional, stabilizing, disruptive or correlative selection acting on male song properties we used linear and nonlinear regressions between male song traits and female response behaviour. Three signal traits were revealed to be under directional selection: song loudness, pause to syllable ratio and the mean duration of gaps within syllables. A nonlinear regression testing for correlative selection showed that a fourth song trait, rhythm, in combination with mean gap duration was also important for female mate choice. With these traits and trait combinations we were able to explain 42% of the variance in attractiveness between males. Since we found no evidence for stabilizing selection, but ample evidence for directional selection, we conclude that selection on the traits examined is related to mate choice mainly in the context of intraspecific sexual selection and probably less so in species recognition. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Phylogenetic relationships in the cricket tribe Xenogryllini (Orthoptera,Gryllidae, Eneopterinae) and description of the Indian genus Indigryllus gen. nov.

The subfamily Eneopterinae is known greatly for its diversified acoustic modalities and disjunct distribution. Within Eneopterinae, tribe Lebinthini is the most studied group, due to its highest species diversity (ca. 150 species in 12 genera), endemic distribution on the islands of Southeast Asia and of the South West Pacific, males’ ability to produce high‐frequency calling songs, and evolution of females’ vibrational response. To investigate the distribution pattern and diversification of acoustic and behavioral attributes in a larger frame, clear understanding of phylogenetic relationships within other tribes of Eneopterinae is vital. In this study, we focus on the tribe Xenogryllini, sister group of Lebinthini. Xenogryllini, as opposed to Lebinthini, is known by fewer species (11 species in two genera), distributed widely in continental Asia and Africa, and for producing low‐frequency calling songs. We describe a new genus Indigryllus with a new species of the tribe Xenogryllini, discovered from the southwest of India. We used eight molecular genetic markers to reconstruct the phylogenetic relationships. The resultant phylogenetic tree is used to compare and discuss distribution patterns and acoustic modalities between Lebinthini and Xenogryllini.     

Song frequency correlates with latitude and individual body size in the cicada <Emphasis Type="Italic">Mogannia formosana</Emphasis> Matsumura (Hemiptera: Cicadidae)

Analyses of acoustic variation between and within populations can help to clarify the evolution and diversification of cicada calling songs. In this study, we analyzed the acoustic variation in the calling song of Mogannia formosana within Taiwan and between Taiwan and Green Island to assess the effects of geographic locations. Furthermore, chorusing males in the Green Island population were recorded and collected from the same habitat site during the same time period to investigate the relationship between individual body size and the acoustic features of calling songs. Among populations of M. formosana, we found that most of the acoustic variation in M. formosana calling songs was associated with frequency parameters, in which six frequency parameters changed significantly with latitude on the island of Taiwan. In contrast, temporal parameters, which were associated with principal components corresponding to less acoustic variation than that of the first principal component, were also found to be significant among populations but did not show consistent trends of difference with latitude. However, the geographically isolated Green Island population exhibited the lowest number of short echemes in segment B, which is the diagnostic structure employed to separate M. formosana from other M. species. This finding suggests that the temporal pattern of segment B in the calling songs of M. formosana might be important for both population differentiation and interspecific recognition. In a chorus of the Green Island population, the sound frequency of the last short echeme was found to be significantly correlated with individual body size. The possible role played by sexual selection in shaping sound frequency as a result of its reliable association with body size was discussed. We suggest that, in comparison with temporal elements, the frequency elements of segment B in calling songs of M. formosana in chorus can serve as a more reliable indicator of body size for female mate choice.     

Differentiation of Mating Vocalizations in Birds: Acoustic Features in Mainland and Island Populations and Evidence of Habitat-Dependent Selection on Songs

Local environments can act as selective agents on some characteristics of birds’ songs, whereas other song traits may not reflect local genetic adaptation. Geographic variation in songs of two Australian bird species (red‐capped robins Petroica goodenovii, western gerygones Gerygone fusca) was studied to examine one component of the ‘habitat‐dependent selection’ hypothesis. This hypothesis suggests that: (1) the detailed spectral characteristics of male songs are an evolved response to local habitat conditions affecting signal propagation and detection and (2) parallel evolution of other fitness traits sets up the potential for assortative mating by female choice. To examine the first part of the hypothesis, I made comparisons among widespread mainland populations and an island population using two levels of analysis: a typological analysis of song morphology (phonology: notes, syllables, syntax, temporal pattern, repertoires) and a spectral analysis of acoustic characteristics of songs (mean frequency, Wiener entropy, frequency modulation) using an automated procedure of feature extraction (Sound Analysis Pro). Spectral analysis was also used to extract values of the same acoustic features from the background sound environment of each recorded population. The typological analysis revealed no differences among mainland populations of either species, but large differences between mainland songs and those on the island. In contrast, the spectral analysis revealed acoustic divergence among populations, both mainland and island. For both species, Wiener entropy of songs correlated negatively with that of the ambient sound environment, consistent with predictions of the habitat‐dependent selection hypothesis of environmental selection on signal design.     

Macrogeographical variation in the song of a widely distributed African warbler

The songs of oscine passerine birds vary on many spatial scales, reflecting the actions of diverse evolutionary pressures. Here we examine the songs of Cisticola erythrops, which effectively signal species identity across a geographical area spanning 6500 km in sub-Saharan Africa. Selection for species identification should promote stability in song traits, while sexual selection and geographical segregation should promote diversity. Cisticola erythrops share syllable types across the entire range of species and structure songs similarly, but individuals sing highly variable songs through improvisational recombination of syllables. Patterns of syllable use change gradually across the range of the species and do not show distinct breaks at subspecies boundaries. The acoustic properties of the most common syllable type also change gradually with distance. The results illustrate how songs can be simultaneously species-specific and highly variable at an individual level. At a larger level, patterns of variation indicate that cultural drift has generated song diversity through an isolation by distance mechanism.     

On the distribution of the bush cricket <Emphasis Type="Italic">Platycleis albopunctata transiens</Emphasis> Zeuner, 1941 (Orthoptera,Tettigoniidae) in the south of European Russia and in Uzbekistan

Based on examination of the morphological characters and comparative analysis of the male calling acoustic signals, distribution of the subspecies Platycleis albopunctata transiens Zeuner, 1941 in the south of European Russia (Crimea and North Caucasus) and in Uzbekistan is proved.     

No Effect of Body Size on the Frequency of Calling and Courtship Song in the Two-Spotted Cricket,Gryllus bimaculatus

The relationship between body size and vocalization parameters has been studied in many animal species. In insect species, however, the effect of body size on song frequency has remained unclear. Here we analyzed the effect of body size on the frequency spectra of mating songs produced by the two-spotted cricket, Gryllus bimaculatus. We recorded the calling songs and courtship songs of male crickets of different body sizes. The calling songs contained a frequency component that peaked at 5.7 kHz. On the other hand, courtship songs contained two frequency components that peaked at 5.8 and 14.7 kHz. The dominant frequency of each component in both the calling and courtship songs was constant regardless of body size. The size of the harp and mirror regions in the cricket forewings, which are the acoustic sources of the songs, correlated positively with body size. These findings suggest that the frequency contents of both the calling and courtship songs of the cricket are unaffected by whole body, harp, or mirror size.     

A taxonomic revision and species delimitation of the genus Purpuraria Enderlein, 1929 (Orthoptera: Pamphagidae) using an integrative approach

Recent studies on the endemic Canarian genus Purpuraria have shown that the taxonomy of its only recognized species (P. erna) is probably erroneous. In this study, an integrative revision of the genus is performed, based on a large number of specimens and geographical sampling. As a result, (1) the diagnostic characters at the genus level are re‐described, (2) Purpuraria magna n. sp. based on morphological, morphometric and genetic data is described and (3) the taxonomic status of a formerly described subspecies is clarified. Intraspecific and interspecific morphometric differences have been found, indicating that the genus is undergoing a process of morphological diversification. Nevertheless, the possibility of interspecific mating between individuals of the two species is suggested, because no significant differences have been found between their respective calling songs. Genetic analyses using mitochondrial and nuclear DNA sequences suggest that P. erna and P. magna are recent species with evidences of secondary contact episodes in the past.     

Transformation of Baikal sponges (family Lubomirskiidae) after penetration into the Angara River

Genetic and morphological analysis of endemic sponges of the Lubomirskiidae family from Lake Baikal and the upper reaches of the Angara River was performed. Various sponge species acquired a number of similar morphological traits after the transition from the lake into the river. These traits enabled an increase of sponge skeleton strength under the conditions of elevated hydrodynamic activity. The changes significantly impeded morphology-based species identification of Angara sponges. Phylogenetic analysis of ITS regions and noncoding mitochondrial DNA fragments confirmed that the Angara sponges belonged to the Baikalian Lubomirskiidae family and demonstrated the polyphyletic origin of the sponges. The use of combined molecular and morphological data allowed for the clustering of some sponge samples into groups that corresponded to individual species. The absence of genetic isolation between the Baikalospongia intermedia and Lubomirskia baicalensis species was demonstrated, whereas the B. intermedia profundalis subspecies was well separated from B. intermedia. This finding pointed to the necessity of further studies for the clarification of the taxonomic status of this subspecies.     

Genetic Diversity and Population Structure of Tetraploid Wheats (Triticum turgidum L.) Estimated by SSR,DArT and Pedigree Data

Levels of genetic diversity and population genetic structure of a collection of 230 accessions of seven tetraploid Triticum turgidum L. subspecies were investigated using six morphological, nine seed storage protein loci, 26 SSRs and 970 DArT markers. The genetic diversity of the morphological traits and seed storage proteins was always lower in the durum wheat compared to the wild and domesticated emmer. Using Bayesian clustering (K = 2), both of the sets of molecular markers distinguished the durum wheat cultivars from the other tetraploid subspecies, and two distinct subgroups were detected within the durum wheat subspecies, which is in agreement with their origin and year of release. The genetic diversity of morphological traits and seed storage proteins was always lower in the improved durum cultivars registered after 1990, than in the intermediate and older ones. This marked effect on diversity was not observed for molecular markers, where there was only a weak reduction. At K >2, the SSR markers showed a greater degree of resolution than for DArT, with their identification of a greater number of groups within each subspecies. Analysis of DArT marker differentiation between the wheat subspecies indicated outlier loci that are potentially linked to genes controlling some important agronomic traits. Among the 211 loci identified under selection, 109 markers were recently mapped, and some of these markers were clustered into specific regions on chromosome arms 2BL, 3BS and 4AL, where several genes/quantitative trait loci (QTLs) are involved in the domestication of tetraploid wheats, such as the tenacious glumes (Tg) and brittle rachis (Br) characteristics. On the basis of these results, it can be assumed that the population structure of the tetraploid wheat collection partially reflects the evolutionary history of Triticum turgidum L. subspecies and the genetic potential of landraces and wild accessions for the detection of unexplored alleles.     

Testing concordance in species boundaries using acoustic,morphological, and molecular data in the field cricket genus Itaropsis (Orthoptera: Grylloidea,Gryllidae: Gryllinae)

In most taxa, species boundaries are inferred based on differences in morphology or DNA sequences revealed by taxonomic or phylogenetic analyses. In crickets, acoustic mating signals or calling songs have species‐specific structures and provide a third data set to infer species boundaries. We examined the concordance in species boundaries obtained using acoustic, morphological, and molecular data sets in the field cricket genus Itaropsis. This genus is currently described by only one valid species, Itaropsis tenella, with a broad distribution in western peninsular India and Sri Lanka. Calling songs of males sampled from four sites in peninsular India exhibited significant differences in a number of call features, suggesting the existence of multiple species. Cluster analysis of the acoustic data, molecular phylogenetic analyses, and phylogenetic analyses combining all data sets suggested the existence of three clades. Whatever the differences in calling signals, no full congruence was obtained between all the data sets, even though the resultant lineages were largely concordant with the acoustic clusters. The genus Itaropsis could thus be represented by three morphologically cryptic incipient species in peninsular India; their distributions are congruent with usual patterns of endemism in the Western Ghats, India. Song evolution is analysed through the divergence in syllable period, syllable and call duration, and dominant frequency. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 285–303.     

Mitochondrial DNA phylogeny of North American field crickets: perspectives on the evolution of life cycles,songs, and habitat associations

North American field crickets (genus Gryllus) exhibit a diversity of life cycles, habitat associations, and calling songs. However, patterns of evolution for these ecological and behavioral traits remain uncertain in the absence of a robust phylogenetic framework. Analyses of morphological variation have provided few clues about species relationships in the genus Gryllus. Here we use comparisons of mitochondrial DNA restriction site maps for 29 individuals representing 11 species (including potential outgroups) to examine relationships among eastern North American field crickets. Initially chosen as likely outgroup taxa, the two European species of Gryllus do not obviously fall outside of an exclusively North American clade and (based on amount of sequence divergence) appear to have diverged from North American lineages at about the same time that major North American lineages diverged from each other. The egg-overwintering crickets comprise a strongly supported monophyletic group, but relationships among these three closely related species cannot be resolved. The mtDNA data are consistent with a single origin of egg diapause and do not support a model of recent life cycle divergence and allochronic speciation for Gryllus pennsylvanicus and G. veletis. The two crickets are not sister species, despite remarkable similarity in morphology, habitat, and calling song. This conclusion is consistent with published data on allozyme variation in North American field crickets. The habitat associations of eastern North American field crickets have been labile, but calling songs sometimes have remained virtually unchanged across multiple speciation events.     

Sharp acoustic boundaries across an altitudinal avian hybrid zone despite asymmetric introgression

Birdsong is a sexually selected trait that could play an important evolutionary role when related taxa come into secondary contact. Many songbird species, however, learn their songs through copying one or more tutors, which complicates the evolutionary outcome of such contact. Two subspecies of a presumed vocal learner, the grey‐breasted wood‐wren (Henicorhina leucophrys), replace each other altitudinally across the western slope of the Ecuadorian Andes. These subspecies are morphologically very similar, but show striking differences in their song. We examined variation in acoustic traits and genetic composition across the altitudinal range covered by both subspecies and between two allopatric populations. The acoustic boundary between the subspecies was found to be highly abrupt across a narrow elevational range with virtually no evidence of song convergence. Mixed singing and use of hetero‐subspecific song occurred in the contact zone and was biased towards the use of leucophrys song types. Hetero‐subspecific song copying by hilaris and not by leucophrys reflected a previously found asymmetric pattern of response to song playback. Using amplified fragment length polymorphisms (AFLP) markers, we detected hybridization in the contact zone and asymmetric introgression in parapatric populations, with more leucophrys alleles present in hilaris populations than vice versa. This pattern may be a trail of introgression due to upslope displacement of leucophrys by hilaris. Our data suggest that song learning may impact speciation and hybridization in contrasting ways at different spatial scales: although learning may speed up population divergence in songs, thereby enhancing assortative mating and reducing gene flow, it may at a local level also lead to the copying of heterospecific songs, therefore allowing some level of hybridization and introgression.     

Acoustic signals in katydids (Orthoptera, Tettigonidae). Communication I

Original and literature data on acoustic signals of katydids of the families Bradyporidae, Conocephalidae, Tettigoniidae, Phaneropteridae, Pseudophyllidae, Mecopodidae and Meconematidae are analyzed. A scheme of possible evolutionary trends in the transformation of the temporal pattern of calling signals in the tribe Platycleidini (Tettigoniidae, Decticinae) is proposed. A comparative analysis of acoustic signals in Phaneropteridae of the world fauna and in Bradyporidae from the Mediterranean, Africa, and Asia is performed. Oscillograms and frequency spectra of calling songs are published for the first time for the following species: some representatives of the genus Mecopoda, Schizonotinus kerketa, Sch. forficalis, Onconotus laxmanni, and O. servillei; oscillograms of calling sounds of Euconocercus iris, Polysarcus zacharovi, and Phaneroptera spinosa, and of other intraspecific signals of representatives of the genus Phaneroptera are also represented for the first time.     

The Egyptian fruit bat Rousettus aegyptiacus (Chiroptera: Pteropodidae) in the Palaearctic: Geographical variation and taxonomic status

Two metrically defined subspecies have traditionally been recognised within the Palaearctic distribution range of the Egyptian fruit bat Rousettus aegyptiacus; the larger R. a. aegyptiacus in Egypt and the northern part of the Middle East and the smaller R. a. arabicus in the southern Middle East. An extensive material of R. aegyptiacus from all parts of this area, i.e. the Levant (incl. Turkey and Cyprus), Egypt (incl. Sinai), northern Sudan, Yemen, Oman, Iran, and Pakistan, as well as comparative samples from its sub-Saharan range, were tested using both morphological and genetic approaches in order to revise the species’ taxonomic status. The results indicated two possible processes, depending on the method used. Genetic analysis of the mitochondrial genome (nd1 and cytb) indicated low variation (< 2.0% of genetic distance) and lack of geographical structure while morphometric analysis indicated significant metric differences. Two basic size morphotypes were found within the Palaearctic range, with a rather mosaic-like geographical distribution and a lack of clear size distinction between the two categories, though intermediate types were detected. Thus, we suggest that all Palaearctic populations of R. aegyptiacus represent one form, the nominotypical subspecies, which is uniform in genetic traits but plastic in metric traits.     

Major biogeographic barriers in eastern Australia have shaped the population structure of widely distributed Eucalyptus moluccana and its putative subspecies

We have investigated the impact of recognized biogeographic barriers on genetic differentiation of grey box (Eucalyptus moluccana), a common and widespread tree species of the family Myrtaceae in eastern Australian woodlands, and its previously proposed four subspecies moluccana, pedicellata, queenslandica, and crassifolia. A range of phylogeographic analyses were conducted to examine the population genetic differentiation and subspecies genetic structure in E. moluccana in relation to biogeographic barriers. Slow evolving markers uncovering long term processes (chloroplast DNA) were used to generate a haplotype network and infer phylogeographic barriers. Additionally, fast evolving, hypervariable markers (microsatellites) were used to estimate demographic processes and genetic structure among five geographic regions (29 populations) across the entire distribution of E. moluccana. Morphological features of seedlings, such as leaf and stem traits, were assessed to evaluate population clusters and test differentiation of the putative subspecies. Haplotype network analysis revealed twenty chloroplast haplotypes with a main haplotype in a central position shared by individuals belonging to the regions containing the four putative subspecies. Microsatellite analysis detected the genetic structure between Queensland (QLD) and New South Wales (NSW) populations, consistent with the McPherson Range barrier, an east‐west spur of the Great Dividing Range. The substructure was detected within QLD and NSW in line with other barriers in eastern Australia. The morphological analyses supported differentiation between QLD and NSW populations, with no difference within QLD, yet some differentiation within NSW populations. Our molecular and morphological analyses provide evidence that several geographic barriers in eastern Australia, including the Burdekin Gap and the McPherson Range have contributed to the genetic structure of E. moluccana. Genetic differentiation among E. moluccana populations supports the recognition of some but not all the four previously proposed subspecies, with crassifolia being the most differentiated.     

Divergence in mating signals correlates with genetic distance and behavioural responses to playback

Animals use acoustic signals to defend resources against rivals and attract breeding partners. As with many biological traits, acoustic signals may reflect ancestry; closely related species often produce more similar signals than do distantly related species. Whether this similarity in acoustic signals is biologically relevant to animals is poorly understood. We conducted a playback experiment to measure the physical and vocal responses of male songbirds to the songs of both conspecific and allopatric‐congeneric animals that varied in their acoustic and genetic similarity. Our subjects were territorial males of four species of neotropical Troglodytes wrens: Brown‐throated Wrens (Troglodytes brunneicollis), Cozumel Wrens (T. beani), Clarion Wrens (T. tanneri) and Socorro Wrens (T. sissonii). Our results indicate that birds respond to playback of both conspecific and allopatric‐congeneric animals; that acoustic differences increase with genetic distance; and that genetic divergence predicts the strength of behavioural responses to playback, after removing the effects of acoustic similarity between subjects’ songs and playback stimuli. Collectively, these results demonstrate that the most distantly related species have the most divergent songs; that male wrens perceive divergence in fine structural characteristics of songs; and that perceptual differences between species reflect evolutionary history. This study offers novel insight into the importance of acoustic divergence of learned signals and receiver responses in species recognition.