Mate Recognition System Research Articles

A modular circuit coordinates the diversification of courtship strategies.

Mate recognition systems evolve rapidly to reinforce the reproductive boundaries between species, but the underlying neural mechanisms remain enigmatic. Here we leveraged the rapid coevolution of female pheromone production and male pheromone perception in Drosophila1,2 to gain insight into how the architecture of mate recognition circuits facilitates their diversification. While in some Drosophila species females produce unique pheromones that act to arouse their conspecific males, the pheromones of most species are sexually monomorphic such that females possess no distinguishing chemosensory signatures that males can use for mate recognition3. We show that Drosophila yakuba males evolved the ability to use a sexually monomorphic pheromone, 7-tricosene, as an excitatory cue to promote courtship. By comparing key nodes in the pheromone circuits across multiple Drosophila species, we reveal that this sensory innovation arises from coordinated peripheral and central circuit adaptations: a distinct subpopulation of sensory neurons has acquired sensitivity to 7-tricosene and, in turn, selectively signals to a distinct subset of P1 neurons in the central brain to trigger courtship. Such a modular circuit organization, in which different sensory inputs can independently couple to parallel courtship control nodes, may facilitate the evolution of mate recognition systems by allowing novel sensory modalities to become linked to male arousal. Together, our findings suggest how peripheral and central circuit adaptations can be flexibly coordinated to underlie the rapid evolution of mate recognition strategies across species.

Genetic Coupling of Mate Recognition Systems in the Genomic Era.

The concept of "genetic coupling" in mate recognition systems arose in the 1960s as a potential mechanism to maintain coordination between signals and receivers during evolutionary divergence. At its most basic it proposed that the same genes might influence trait and preference, and therefore mutations could result in coordinated changes in both traits. Since then, the concept has expanded in scope and is often used to include linkage or genetic correlation between recognition system components. Here we review evidence for genetic coupling, concentrating on proposed examples of a common genetic basis for signals and preferences. Mapping studies have identified several examples of tight genetic linkage between genomic regions influencing signals and preferences, or assortative mating. Whether this extends as far as demonstrating pleiotropy remains a more open question. Some studies, notably of Drosophila, have identified genes in the sex determination pathway and in pheromonal communication where single loci can influence both signals and preferences. This may be based on isoform divergence, in which sex- and tissue-specific effects are facilitated by alternative spicing, or on regulatory divergence. Hence it is not clear that such examples provide compelling evidence of pleiotropy in the sense that "magic mutations" could maintain trait coordination. Rather, coevolution may be facilitated by regulatory divergence but require different mutations or coevolution across isoforms. Reconsidering the logic of genetic coupling, it may be that pleiotropy could actually be less effective than linkage if distinct but associated variants allow molecular coevolution to occur more readily than potentially "unbalanced" mutations in single genes. Genetic manipulation or studies of mutation order effects during divergence are challenging but perhaps the only way to disentangle the role of pleiotropy versus close linkage in coordinated trait divergence.

Swarming and mate selection in Anopheles gambiae mosquitoes (Diptera: Culicidae).

Treating both male and female Anopheles gambiae as if they are "boids" (a computer program that mimics flocking in birds) explains much of the swarming and mating behavior in this important group of malaria vectors. It is suggested that species specific swarm sites act as the mate recognition system in anophelines and it is proposed that virgin females respond to the swarm site per se rather than the swarm itself. Given the high operational sex ratio and the inability of any male to dominate all females within the swarm, it is considered that chance, rather than sexual selection, is the most important determinant of mating. The male being in the swarm may be a sufficiently strong signal to the female of his fitness, so that more elaborate sexual selection is unnecessary. The possibility of alternative mechanisms for mating may also exist but need to be investigated further. Given the importance of swarms as the isolating mechanism between species, emphasis should be placed on determining the characteristics of swarm sites and markers between them.

Differences in Male Mate Recognition between the Invasive Anoplophora glabripennis (Coleoptera: Cerambycidae) and Japanese Native A. malasiaca.

The Asian longicorn beetle Anoplophora glabripennis is a recently arrived invasive species to Japan. The Japanese native A. malasiaca shows an extensive overlap with A. glabripennis with host plants, niches, and emergence season. Hybridization between these two species is suspected in Japan. The surface of the female is covered with contact sex pheromones that elicit male mating behavior within species. We evaluated the contact pheromonal activity of crude extract and fractions of female A. glabripennis coated on a black glass model and revealed a hydrocarbon fraction and a blend of fractions to show activity but relatively weak, suggesting the presence of other unknown active compounds. Few male A. glabripennis showed mating behavior when they were exposed to a crude extract of female A. malasiaca. However, a considerable number of A. malasiaca males mounted and showed abdominal bending behavior when presented with glass models that were coated with each extract of female A. glabripennis and A. malasiaca. Gomadalactones are essential contact pheromone components that elicit mating behavior in male A. malasiaca; however, we could not detect them in female A. glabripennis extract. Here, we investigated the possible reasons for this phenomenon and the difference in male mate recognition systems between these two species.

Molecular evidence for introgressive hybridization in New Zealand masked gulls

We used mitochondrial DNA (mtDNA) gene sequences and nuclear microsatellite loci to investigate the extent and outcome of hybridization between the Black‐billed Gull Chroicocephalus bulleri and the Red‐billed Gull Chroicocephalus novaehollandiae scopulinus in New Zealand. Six of 26 sampled Black‐billed Gulls possessed mtDNA typical of Red‐billed Gulls, but allele frequencies at six polymorphic microsatellites provided little evidence of mixed ancestry expected in very recent hybrids. None of the Red‐billed Gulls sampled from different colonies possessed Black‐billed Gull mtDNA expected in the reciprocal cross, suggesting that hybridization in the two species typically occurs between female Red‐billed Gulls and Black‐billed Gull males. The lack of any hybrid signal in the nuclear loci indicates that there has been extensive backcrossing with Black‐billed Gulls, effectively diluting the Red‐billed Gull nuclear DNA contribution. Divergence of Red‐billed Gulls and Black‐billed Gulls occurred approximately 250 000 years ago, indicating that unsorted ancestral polymorphism is an unlikely alternative to hybridization. Comparing demographic models within an approximate Bayesian computation (ABC) framework, we confirm that the observed patterns cannot result from incomplete lineage sorting. Using an ABC random forest approach, we determined that the most likely model explaining the data is a recent introgression scenario, whereby unidirectional gene flow is re‐established following a period of strict isolation. The ability of Black‐billed and Red‐billed Gulls to successfully interbreed shows that despite significant differentiation (FST > 0.3), there has been insufficient time for the two species to develop complete reproductive isolation. The apparent one‐way transfer of Red‐billed Gull mtDNA into Black‐billed Gulls and extensive backcrossing argues against cytoplasmic–nuclear genome incompatibilities between the two species. We hypothesize that the specific mate recognition system cued on colours of soft parts normally functions to prevent hybridization, but that it can break down under demographic conditions where there is a shortage of available mates and a surplus of females in the Red‐billed Gull population. The high incidence of introgression in Black‐billed Gulls conflicts with field observations that interbreeding is extremely rare.

No pre-zygotic isolation mechanisms between Schistosoma haematobium and Schistosoma bovis parasites: From mating interactions to differential gene expression.

Species usually develop reproductive isolation mechanisms allowing them to avoid interbreeding. These preventive barriers can act before reproduction, "pre-zygotic barriers", or after reproduction, "post-zygotic barriers". Pre-zygotic barriers prevent unfavourable mating, while post-zygotic barriers determine the viability and selective success of the hybrid offspring. Hybridization in parasites and the underlying reproductive isolation mechanisms maintaining their genetic integrity have been overlooked. Using an integrated approach this work aims to quantify the relative importance of pre-zygotic barriers in Schistosoma haematobium x S. bovis crosses. These two co-endemic species cause schistosomiasis, one of the major debilitating parasitic diseases worldwide, and can hybridize naturally. Using mate choice experiments we first tested if a specific mate recognition system exists between both species. Second, using RNA-sequencing we analysed differential gene expression between homo- and hetero-specific pairing in male and female adult parasites. We show that homo- and hetero-specific pairing occurs randomly between these two species, and few genes in both sexes are affected by hetero-specific pairing. This suggests that i) mate choice is not a reproductive isolating factor, and that ii) no pre-zygotic barrier except spatial isolation "by the final vertebrate host" seems to limit interbreeding between these two species. Interestingly, among the few genes affected by the pairing status of the worms, some can be related to pathways affected during male and female interactions and may also present interesting candidates for species isolation mechanisms and hybridization in schistosome parasites.

Field evaluation of sex pheromones and binding specificity of pheromone binding protein 4 in Tryporyza intacta (Lepidoptera: Crambidae)

The recognition of chemical signal including volatile odorants and pheromones is very important in the olfactory physiological behaviors of insects, such as avoiding predators, seeking food and mating partners. The sugarcane borer, Tryporyza intacta is the most harmful insect in sugarcane region in Southeast Asia and Southern China, however, the study of their molecular biology and physiology was limited. Here we demonstrated that the sex pheromone (E11-16:Ald: Z11-16:Ald = 7:3) were most effective to T. intacta. In addition, compared the traditional rubber lure, a new microsphere formulation lure can optimize the trapping effect and might be widely used in the sugarcane growing area. To obtain a better understanding of the olfactory molecular mechanism of pheromone-based mate recognition system, we have cloned the full-length gene of the TintPBP4 and expressed in Escherichia coli. Our phylogenetic analysis highlighted that the TintPBP4 was highly conserved among diverse species of Lepidoptera. Furthermore, the results of QRT-PCR demonstrated that TintPBP4 transcripts were abundantly expressed in the antennae of T. intacta, especially in the male adults. The fluorescence binding experiments showed the TintPBP4 exhibited strong binding capacities to the sex pheromone components. These results will not only provide more understanding for the functional analysis of olfactory proteins from T. intacta, but also assist in the exploitation and development of sex pheromones in the integrated biological control of this pest.

Behavioral and Morphological Divergence of Sympatric Morphotypes ofLeptopelis flavomaculatus(Anura, Arthroleptidae) in Northeastern Tanzania

Adult males of the African treefrog species Leptopelis flavomaculatus occur in either brown or green color morphs. In this study, we investigated whether the two color morphs of breeding males of L. flavomaculatus differ in traits other than color. We examined call differences (dominant frequencies and call durations), call-site selection, and body size. Our results show differences in the call durations, dominant frequencies, mean call intensities, as well as in size (body length and body mass) of the two vocally active color morphs of this species. The two morphs were similar in their choice of plant species used as calling sites and the heights of those sites. Given the sensitivity of mate recognition systems for most anurans, our results provide evidence of both call and morphological variation between the two color morphs of this species. Our findings establish a foundation for future phylogenetic and mating system studies to support the contention that the two color morphs of L. flavomaculatus might warrant taxonomic recognition as separate species.

Divergence in Potential Contact Pheromones and Genital Morphology Among Sympatric Song Types of the Bush Cricket Mecopoda elongata

A well-established route to speciation in animals is via the evolution of divergent male mating signals and female preferences within a species. However, an open question is how common it is for near complete isolation to be achieved through a single signal-receiver system or whether multiple aspects of the mate-recognition system diverge simultaneously. The five highly divergent song types of the bush cricket Mecopoda elongata, exemplify reproductive isolation in sympatry through long-distance mating signals. Female preference for their own song type has been established as a strong pre-mating reproductive barrier, but the potential existence of additional isolating mechanisms has not been investigated. We quantify divergence in cuticular lipid profiles and external genital structures between song types. These traits show significant divergence among species of Orthoptera and are known to be used in mate recognition following contact. We show that divergence among sympatric Mecopoda song types in both cuticular lipid profiles and two external genital structures is sufficiently extensive that either of them can be used to identify individual song type with 90% accuracy. Our findings suggest that multiple isolating mechanisms are likely to evolve simultaneously to facilitate a more robust reproductive isolation. This indicates a role for sexual selection in the divergence and potential future speciation of these populations and suggests that reproductive isolation may frequently evolve through simultaneous divergence across different aspects of mate recognition systems.

Reproductive isolation between sister species of Iberian pine voles, Microtus duodecimcostatus and M. lusitanicus

Contact zones of recently diverged species provide the ideal opportunity to study the nature of reproductive barriers. The Mediterranean (Microtus duodecimcostatus) and Lusitanian pine voles (M. lusitanicus) are a pair of recently diverged sister species endemic to Western Europe. Recent microsatellite data raised the possibility that hybridisation events, although rare, may still occur in the area of sympatry of both species. Here we evaluated the nature and extent of reproductive isolation between M. duodecimcostatus and M. lusitanicus through a laboratory crossbreeding experiment and two-way mate preference tests on the basis of chemical cues. Crossbreeding of sympatric individuals from the two species was successful and followed Haldane’s rule, revealing hybrid male sterility and reduced fertility of hybrid females. Results from mate preference tests showed males of both pine vole species could discriminate and preferred female conspecifics to heterospecifics or hybrid females on the basis of chemical cues alone. On the contrary, females of both pine vole species did not show a clear preference for conspecific over heterospecific male chemical cues, suggesting females may need additional cues to discriminate between males of the two species. As a whole our results indicate both prezygotic (i.e. species-specific mate recognition systems) and postzygotic barriers (i.e. male hybrid sterility, female reduced fertility and behavioural sterility ― decreased ability to find or attract mates) have evolved, and should make hybridisation of the Iberian pine voles under natural conditions an unlikely event. The role of both species mating preferences and interspecific behavioural interactions in the asymmetric mitochondrial introgression pattern of the Iberian pine voles is discussed.

The influence of developmental environment on courtship song in cactophilic Drosophila.

Closely related species often differ in the signals involved in sexual communication and mate recognition. Determining the factors influencing signal quality (i.e. signal's content and conspicuousness) provides an important insight into the potential pathways by which these interspecific differences evolve. Host specificity could bias the direction of the evolution of sexual communication and the mate recognition system, favouring sensory channels that work best in the different host conditions. In this study, we focus on the cactophilic sibling species Drosophila buzzatii and D.koepferae that have diverged not only in the sensory channel used for sexual communication and mate recognition but also in the cactus species that use as primary hosts. We evaluate the role of the developmental environment in generating courtship song variation using an isofemale line design. Our results show that host environment during development induces changes in the courtship song of D.koepferae males, but not in D.buzzatii males. Moreover, we report for the first time that host rearing environment affects the conspicuousness of courtship song (i.e. song volume). Our results are mainly discussed in the context of the sensory drive hypothesis.

Behavioural elements and sensory cues involved in sexual isolation between Drosophila melanogaster strains.

Sensory cues exchanged during courtship are crucial for mate choice: if they show intraspecific divergence, this may cause or reinforce sexual isolation between strains, ultimately leading to speciation. There is a strong asymmetric sexual isolation between Drosophila melanogaster females from Zimbabwe (Z) and males from all other populations (M). While M and Z flies of both sexes show different cuticular pheromones, this variation is only partly responsible for the intraspecific isolation effect. Male acoustic signals are also partly involved in sexual isolation. We examined strain-specific courtship behaviour sequences to determine which body parts and sensory appendages may be involved in sexual isolation. Using two strains representative of the Z- and M-types, we manipulated sensory cues and the social context; we then measured the consequence of these manipulations on courtship and copulation. Our data suggest that Z females mated best with males whose sensory characteristics matched those of Z males in both quantity and quality. M females were less choosy and much less influenced by the sensory and social contexts. Differences in emission and reception of sensory signals seen between Z and M flies may lead to the concerted evolution of multiple sensory channel, thereby shaping a population-specific mate recognition system.

Differential gene expression in the evolution of sex pheromone communication in New Zealand\u2019s endemic leafroller moths of the genera Ctenopseustis and Planotortrix

BackgroundSex pheromone communication in moths has attracted the attention of evolutionary biologists due to the vast array of pheromone compounds used, addressing questions of how this diversity arose and how male reception has evolved in step with the female signal. Here we examine the role of changing gene expression in the evolution of mate recognition systems in leafroller moths, particularly focusing on genes involved in the biosynthetic pathways of sex pheromones in female pheromone glands and the peripheral reception repertoire in the antennae of males. From tissue-specific transcriptomes we mined and compared a database of genes expressed in the pheromone glands and antennae of males and females of four closely related species of leafroller moths endemic to New Zealand, Ctenopseutis herana and C. obliquana, and Planotortrix excessana and P. octo. The peculiarity of this group, compared to other Lepidoptera, is the use of (Z)-5-tetradecenyl acetate, (Z)-7-tetradecenyl acetate, and (Z)-8-tetradecenyl acetate as sex pheromone components.ResultsWe identify orthologues of candidate genes from the pheromone biosynthesis pathway, degradation and transport, as well as genes of the periphery olfactory repertoire, including large families of binding proteins, receptors and odorant degrading enzymes. The production of distinct pheromone blends in the sibling species is associated with the differential expression of two desaturase genes, deast5 and desat7, in the pheromone glands. In male antennae, three odorant receptors, OR74, OR76a and OR30 are over-expressed, but their expression could not be clearly associated with the detection of species-specific pheromones components. In addition these species contain duplications of all three pheromone binding proteins (PBPs) that are also differentially expressed among species.ConclusionsWhile in females differences in the expression of desaturases may be sufficient to explain pheromone blend differences among these New Zealand leafroller species, in males differential expression of several genes, including pheromone binding proteins, may underpin differences in the response by males to changing pheromone components among the species.

Cladistic classification of Mecyclothorax Sharp (Coleoptera, Carabidae, Moriomorphini) and taxonomic revision of the New Caledonian subgenus Phacothorax Jeannel

The 15 species of Mecyclothorax Sharp precinctive to New Caledonia are revised and shown by cladistic analysis to comprise a monophyletic lineage, here treated as subgenus Phacothorax Jeannel. The New Caledonian species of subgenus Phacothorax include Mecyclothorax fleutiauxi (Jeannel), M. najtae Deuve, and 13 newly described species: M. jeanneli sp. n., M. laterobustus sp. n., M. laterorectus sp. n., M. laterosinuatus sp. n., M. laterovatulus sp. n., M. manautei sp. n., M. megalovatulus sp. n., M. octavius sp. n., M. paniensis sp. n., M. picdupinsensis sp. n., M. plurisetosus sp. n., and two jointly authored species; M. kanak Moore & Liebherr sp. n., and M. mouensis Moore & Liebherr sp. n.. subgenus Phacothorax is one of five subgenera recognized within genus Mecyclothorax based on cladistic analysis of 65 exemplar taxa utilizing information from 137 morphological characters. The four other monophyletic subgenera include the precinctive Australian Eucyclothorax subgen. n. (type species Mecyclothorax blackburni [Sloane]), the precinctive Queensland Qecyclothorax subgen. n. (type species Mecyclothorax storeyi Moore), the precinctive New Zealand Meonochilus Liebherr & Marris status n., and the geographically widespread and very diverse nominate subgenus, distributed from St. Paul and Amsterdam Islands, eastward across Australia and New Guinea, and in the Sundas, Timor Leste, Lord Howe and Norfolk Islands, New Zealand, and the Society and Hawaiian Islands. The biogeographic history of Mecyclothorax can be derived from the parsimony cladogram time-calibrated by times of origin of particular geographic areas inhabited by resident representative species. Based on sister-group status of subgenus Phacothorax and subgenus Mecyclothorax, and occupation of Lord Howe Island–an island originating no earlier than 6 Ma–by the earliest divergent lineage within subgenus Mecyclothorax, the ancestor of present-day Phacothorax spp. is hypothesized to have colonized New Caledonia 6 Ma, subsequent both to Cretaceous Gondwanan vicariance as well as any Oligocene submergence. Area relationships among the New Caledonian Phacothorax point to earliest diversification incorporating the northern massifs, and most recent diversification on the ultramafic volcanic substrates in the south of Grand Terre. Flight wing loss has played an important role in shaping the various island faunas, both in their morphology as well as their diversity. The retention of flight capability in only a few of the many hundred Mecyclothorax spp. is presented in light of how populations evolve from macropterous colonizing propagules to vestigially winged specialists. Interspecific differences in genitalic structures for the sister-species pair M. fleutiauxi + M. jeanneli are shown to involve functional complementarity of male and female structures. Extensive geographic variation of male genitalia is demonstrated for several New Caledonian Mecyclothorax spp. This variation deviates from the geographically uniform male genitalia exhibited by species in the hyperdiverse Mecyclothorax radiation of Haleakalā volcano, Maui, suggesting that extensive sympatry occurring among species in that diverse species swarm selects for stability within this mate recognition system. Conversely, lower levels of sympatry characterizing the depauperate New Caledonian radiation permit the presence of more extensive male genitalic variation, this variation not selected against due to the lower likelihood of interspecific mating mistakes.

Cladistic classification of Mecyclothorax Sharp (Coleoptera, Carabidae, Moriomorphini) and taxonomic revision of the New Caledonian subgenus Phacothorax Jeannel

The 15 species of Mecyclothorax Sharp precinctive to New Caledonia are revised and shown by cladistic analysis to comprise a monophyletic lineage, here treated as subgenus Phacothorax Jeannel. The New Caledonian species of subgenus Phacothorax include Mecyclothoraxfleutiauxi (Jeannel), M.najtae Deuve, and 13 newly described species: M.jeanneli sp. n., M.laterobustus sp. n., M.laterorectus sp. n., M.laterosinuatus sp. n., M.laterovatulus sp. n., M.manautei sp. n., M.megalovatulus sp. n., M.octavius sp. n., M.paniensis sp. n., M.picdupinsensis sp. n., M.plurisetosus sp. n., and two jointly authored species; M.kanak Moore & Liebherr sp. n., and M.mouensis Moore & Liebherr sp. n.. subgenus Phacothorax is one of five subgenera recognized within genus Mecyclothorax based on cladistic analysis of 65 exemplar taxa utilizing information from 137 morphological characters. The four other monophyletic subgenera include the precinctive Australian Eucyclothorax subgen. n. (type species Mecyclothoraxblackburni [Sloane]), the precinctive Queensland Qecyclothorax subgen. n. (type species Mecyclothoraxstoreyi Moore), the precinctive New Zealand Meonochilus Liebherr & Marris status n., and the geographically widespread and very diverse nominate subgenus, distributed from St. Paul and Amsterdam Islands, eastward across Australia and New Guinea, and in the Sundas, Timor Leste, Lord Howe and Norfolk Islands, New Zealand, and the Society and Hawaiian Islands. The biogeographic history of Mecyclothorax can be derived from the parsimony cladogram time-calibrated by times of origin of particular geographic areas inhabited by resident representative species. Based on sister-group status of subgenus Phacothorax and subgenus Mecyclothorax, and occupation of Lord Howe Island–an island originating no earlier than 6 Ma–by the earliest divergent lineage within subgenus Mecyclothorax, the ancestor of present-day Phacothorax spp. is hypothesized to have colonized New Caledonia 6 Ma, subsequent both to Cretaceous Gondwanan vicariance as well as any Oligocene submergence. Area relationships among the New Caledonian Phacothorax point to earliest diversification incorporating the northern massifs, and most recent diversification on the ultramafic volcanic substrates in the south of Grand Terre. Flight wing loss has played an important role in shaping the various island faunas, both in their morphology as well as their diversity. The retention of flight capability in only a few of the many hundred Mecyclothorax spp. is presented in light of how populations evolve from macropterous colonizing propagules to vestigially winged specialists. Interspecific differences in genitalic structures for the sister-species pair M.fleutiauxi + M.jeanneli are shown to involve functional complementarity of male and female structures. Extensive geographic variation of male genitalia is demonstrated for several New Caledonian Mecyclothorax spp. This variation deviates from the geographically uniform male genitalia exhibited by species in the hyperdiverse Mecyclothorax radiation of Haleakalā volcano, Maui, suggesting that extensive sympatry occurring among species in that diverse species swarm selects for stability within this mate recognition system. Conversely, lower levels of sympatry characterizing the depauperate New Caledonian radiation permit the presence of more extensive male genitalic variation, this variation not selected against due to the lower likelihood of interspecific mating mistakes.

Mate recognition systems and species limits in a warbling-finch complex (Poospiza nigrorufa/whitii)

ABSTRACTSpecies limits in the Poospiza nigrorufa/whitii complex are not well understood. Three taxa formally described as species are now considered as subspecies (nigrorufa, whitii and wagneri) of a widespread species. The heavier nigrorufa has longer bill, tarsus and wings, is slightly dimorphic with males showing tawny rufous throat, breast and flanks, and brownish grey upper parts with a slate tinge, while females differ in the orange tinge of ventral parts and in the more olivaceous upper parts; inhabits shrubby open areas and wetlands with reeds and bulrushes in eastern southern South America, and gives a simple three-note pattern that repeats to form the song and diagnostic calls. The lighter whitii (including wagneri as a synonym) has a shorter bill, tarsus and wings, is highly dimorphic with males having dark chestnut throat, breast and flanks, and slate upper parts, while females exhibit tawny pale-orange ventral parts, and olivaceous light-brown upper parts; inhabits closed to semi-closed xerophytic to semi-humid scrub and woodlands in the western highlands, and has a complex multi-noted song and diagnostic calls. Reciprocal playback experiments indicate that both taxa are able to discriminate each other’s songs. Locality data and ecological niche modelling show that nigrorufa and whitii are narrowly allopatric or parapatric in central Córdoba province (Argentina).This integrative evidence and the ~2.5% divergence in mtDNA show that nigrorufa and whitii possess different Specific Mate Recognition Systems and should be afforded full species status under any species concept.

How flies are flirting on the fly

BackgroundFlies have some of the most elaborate visual systems in the Insecta, often featuring large, sexually dimorphic eyes with specialized “bright zones” that may have a functional role during mate-seeking behavior. The fast visual system of flies is considered to be an adaptation in support of their advanced flight abilities. Here, we show that the immense processing speed of the flies’ photoreceptors plays a crucial role in mate recognition.ResultsVideo-recording wing movements of abdomen-mounted common green bottle flies, Lucilia sericata, under direct light at 15,000 frames per second revealed that wing movements produce a single, reflected light flash per wing beat. Such light flashes were not evident when we video-recorded wing movements under diffuse light. Males of L. sericata are strongly attracted to wing flash frequencies of 178 Hz, which are characteristic of free-flying young females (prospective mates), significantly more than to 212, 235, or 266 Hz, characteristic of young males, old females, and old males, respectively. In the absence of phenotypic traits of female flies, and when given a choice between light emitting diodes that emitted either constant light or light pulsed at a frequency of 110, 178, 250, or 290 Hz, males show a strong preference for the 178-Hz pulsed light, which most closely approximates the wing beat frequency of prospective mates.ConclusionsWe describe a previously unrecognized visual mate recognition system in L. sericata. The system depends upon the sex- and age-specific frequencies of light flashes reflecting off moving wings, and the ability of male flies to distinguish between the frequency of light flashes produced by rival males and prospective mates. Our findings imply that insect photoreceptors with fast processing speed may not only support agile flight with advanced maneuverability but may also play a supreme role in mate recognition. The low mating propensity of L. sericata males on cloudy days, when light flashes from the wings of flying females are absent, seems to indicate that these flies synchronize sexual communication with environmental conditions that optimize the conspicuousness of their communication signals, as predicted by sensory drive theory.

Can alternative mating tactics facilitate introgression across a hybrid zone by circumventing female choice?

Reproductive barriers and divergence in species' mate recognition systems underlie major models of speciation. However, hybridization between divergent species is common, and classic mechanisms to explain permeable reproductive barriers rarely consider how an individual may attain reproductive success. Alternative mating tactics (AMTs) exist in various forms across animal taxa. Such tactics may allow poorer quality individuals to gain mating opportunities and facilitate introgression either through asymmetrical positive selection or by circumventing female choice altogether in areas of secondary contact. One such tactic is satellite behaviour in frogs, where silent males perch near advertisers in an attempt to intercept females. To test whether such satellite male tactics are context-dependent and favoured by hybrids, we genotyped and quantified the morphology of 80 male spring peeper (Pseudacris crucifer) individuals involved in caller-satellite associations from a secondary contact zone between two intraspecific mitochondrial lineages. Irrespective of population, satellite behaviour was best predicted by size but not body condition. Within the contact zone, pure individuals showed a significantly greater probability of being active callers, whereas hybrids of one lineage were more likely to adopt the satellite tactic. We suggest that satellite behaviour in P.crucifer promotes introgression, breaks down reproductive isolating barriers and contributes to asymmetrical introgression in this secondary contact zone. AMTs may thus be an underexplored but important alternative to oft-discussed causes of genetic discordance found in hybrid zones.

Acoustic signals in insects: A reproductive barrier and a taxonomic character

In singing insects, the song is an important component of the specific mate recognition system (SMRS). In communities of sympatric singing species, there is a partitioning of communication channels, the so-called “acoustic niches.” Within one community, the songs of different species always differ in temporal or frequency characters, i.e. occupy different acoustic niches. However, conspecific songs do not always act as an interspecific reproductive barrier, despite always being a SMRS component. The species that do not communicate acoustically due to allopatry, different timing of vocalization, inhabiting different biotopes, or unmatched food specializations can produce similar songs while forming reproductively isolated communities. Individuals of different sexes need not only to recognize a conspecific mate but also to evaluate its “quality.” The close-range signal (courtship song) provides more opportunities for choosing the “best” male than does the distant signal (calling song). In many species of Orthoptera, courtship includes not only acoustic but also vibrational, visual, chemical, and mechanical signals. An analysis of cricket songs showed the courtship songs to be on average more elaborate and variable than the calling songs. At the same time, due to the difference in mating behavior between the two groups, the acoustic component of courtship is used for mate quality evaluation to a greater extent in grasshoppers than in crickets. The courtship songs of grasshoppers are generally more elaborate in temporal structure than cricket songs; moreover, they may be accompanied by visual displays such as movements of various body parts. Thus, song evolution in grasshoppers is more strongly driven by sexual selection than that in crickets. According to the reinforcement hypothesis, the premating barrier between hybridizing species becomes stronger in response to reduced hybrid fitness. However, our behavioral experiments with two groups of hybridizing grasshopper species did not confirm the reinforcement hypothesis. We explain this, firstly, by a low level of genetic incompatibility between the hybridizing species and secondly, by high hybrid fitness when attracting a mate. A high competitive capability of hybrids may be accounted for by attractiveness of new elements in hybrid courtship songs. When we divide similar forms based on their songs, we in fact distinguish biological species using the criterion of their reproductive isolation. Acoustic differences between species are usually greater than morphological ones. Therefore, song analysis allows one to determine the real status of doubtful species-rank taxa, to distinguish species in a medley of sibling forms, and to reveal cryptic species in the cases when morphological studies fail to provide a univocal result. At the same time, songs are subject to intraspecific variation the range of which is different in different groups. Therefore, it is necessary to study which degree of difference corresponds to the species level before interpreting the status of some forms based on song comparisons. Besides, song similarities cannot indicate conspecificity of acoustically isolated forms; on the other hand, song differences between these forms prove that they are full-rank species.

Phenotypic plasticity of mate recognition systems prevents sexual interference between two sympatric leaf beetle species.

Maladaptive sexual interactions among heterospecific individuals (sexual interference) can prevent the coexistence of animal species. Thus, the avoidance of sexual interference by divergence of mate recognition systems is crucial for a stable coexistence in sympatry. Mate recognition systems are thought to be under tight genetic control. However, we demonstrate that mate recognition systems of two closely related sympatric leaf beetle species show a high level of host-induced phenotypic plasticity. Mate choice in the mustard leaf beetles, Phaedon cochleariae and P. armoraciae, is mediated by cuticular hydrocarbons (CHCs). Divergent host plant use causes a divergence of CHC phenotypes, whereas similar host use leads to their convergence. Consequently, both species exhibit significant behavioral isolation when they feed on alternative host species, but mate randomly when using a common host. Thus, sexual interference between these syntopic leaf beetles is prevented by host-induced phenotypic plasticity rather than by genotypic divergence of mate recognition systems.