Mating preferences in a species flock of Mexican pupfishes (Cyprinodon, Teleostei)

Female mating preferences were examined in three members of an evolutionarily young Cyprinodon lineage from Laguna Chichancanab, Yucatan, Mexico. In separate experiments, females of C. beltrani and C. labiosus , and C. beltrani and C. maya were simultaneously presented with conspecific and heterospecific males and given the opportunity to spawn with either or both. These three species showed different degrees of conspecific mate recognition: complete for C. maya , intermediate for C. labiosus , and indiscriminate for C. beltrani. We conclude that only C. maya is reproductively isolated and that C. beltrani and C. labiosus still hybridize in nature. Whereas between C. beltrani and C. maya mate choice is symmetric, it is asymmetric between C. beltrani and C labiosus. The results of the mating trials are consistent with mitochondrial DNA data which indicate that C. maya is genetically the most distinct species in the flock. They are also supported by experiments on visually and chemically mediated mate preferences.     

Mate Choice by Both Sexes Maintains Reproductive Isolation in a Species Flock of Pupfish (Cyprinodon spp) in the Bahamas

Female and male mate choices can reinforce reproductive isolation after sympatric speciation. Using a binary choice design, we examine the importance of visual cues in female mate choice in all three sympatric species of pupfish on San Salvador Island. We also examine the importance of olfactory cues in female choice of the hard‐shelled invertebrate specialist (Cyprinodon brontotheroides). We examine male mate choice in two of the three species, the scale eater (C. desquamator) and the detritivore (C. variegatus). Females of all three species use visual cues and prefer conspecific males. C. brontotheroides females do not use olfactory cues to discriminate between conspecific and heterospecific males. Males of C. desquamator and C. variegatus also preferentially court conspecific females. Thus, mutual mate choice, where both females and males exhibit mate choice, acts as a strong behavioral pre‐mating isolation mechanism in these sympatrically speciated pupfish.     

Female preference for conspecific males based on olfactory cues in a Lake Malawi cichlid fish

Research on reproductive isolation in African cichlid fishes has largely focused on the role of nuptial colours, but other sensory modes may play an important role in mate choice. Here, we compare the relative importance of visual and olfactory cues in mate recognition by females of a Lake Malawi cichlid species. Female Pseudotropheus emmiltos were given a choice of spawning next to a conspecific male or a male of the closely-related sympatric Pseudotropheus fainzilberi. Significant preference for conspecific males only occurred when olfactory cues were present. This suggests that divergence of olfactory signals may have been an important influence on the explosive radiation of the East African species flock.     

Lack of species discrimination based on chemical cues by male sailfin mollies, <Emphasis Type="Italic">Poecilia latipinna</Emphasis>

When making mating decisions, individuals may rely on multiple cues from either the same or multiple sensory modalities. Although the use of visual cues in sexual selection is well studied, fewer studies have examined the role of chemical cues in mate choice. In addition, few studies have examined how visual and/or chemical cues affect male mating decisions. Male mate choice is important in systems where males must avoid mating with heterospecific females, as is found in a mating complex of Poecilia. Male sailfin mollies, Poecilia latipinna, are sexually parasitized by gynogenetic Amazon mollies, P. formosa. Little is known about the mechanism by which male sailfin mollies base their mating decisions. Here we tested the hypothesis that male sailfin mollies from an allopatric and a sympatric population with Amazon mollies use multiple cues to distinguish between conspecific and heterospecific females. We found that male sailfin mollies recognized the chemical cues of conspecific females, but we found no support for the hypothesis that chemical cues are by themselves sufficient for species discrimination. Lack of discrimination based on chemical cues alone may be due to the close evolutionary history between P. latipinna and P. formosa. Males from populations sympatric with Amazon mollies did not differentially associate with females of either of the two species when given access to both visual and chemical cues of the females, yet males from the allopatric population did associate more with conspecific females than with heterospecific females in the presence of both chemical and visual cues. The lack of discrimination by males from the sympatric population between conspecific and heterospecific females based on both chemical and visual cues suggests that these males require more complex combinations of cues to distinguish species, possibly due to the close relatedness of these species.     

Pheromones and body coloration affect mate recognition in the Japanese nine-spotted moth Amata fortunei (Lepidoptera: Arctiidae)

Adults of the Japanese nine-spotted moth, Amata fortunei, are diurnal and have white-spotted black wings and a black-and-yellow striped body pattern. We evaluated whether this species uses sex pheromones and whether visual cues from the female body are used in mate recognition. We introduced extracts of potentially scent-bearing abdominal tips of females to males. Males responded more to the extracts than to dried female specimens, suggesting the presence of sex pheromones in the extracts. Indeed, no males responded to the dried female specimens. To evaluate the importance of visual cues, we conducted the experiments with crude extract and an additional model stimulant. Males responded more to model females with the same number and similar area of yellow bands to the original conspecific females than to those with more bands and greater total band area, suggesting that dissimilarity in band number and area to conspecific females could interrupt male mating behavior. Males of A. fortunei likely find mating partners using olfactory cues over relatively long distances, while using both olfactory and visual cues over short distances. These results suggest that olfactory cues play a major role in mate recognition, whereas visual cues play a supplementary role.     

Are olfactory cues involved in nest recognition in two social species of estrildid finches?

Reliably recognizing their own nest provides parents with a necessary skill to invest time and resources efficiently in raising their offspring and thereby maximising their own reproductive success. Studies investigating nest recognition in adult birds have focused mainly on visual cues of the nest or the nest site and acoustic cues of the nestlings. To determine whether adult songbirds also use olfaction for nest recognition, we investigated the use of olfactory nest cues for two estrildid finch species, zebra finches (Taeniopygia guttata) and Bengalese finches (Lonchura striata var. domestica) during the nestling and fledgling phase of their offspring. We found similar behavioural responses to nest odours in both songbird species. Females preferred the odour of their own nest over a control and avoided the foreign conspecific nest scent over a control during the nestling phase of their offspring, but when given the own odour and the foreign conspecific odour simultaneously we did not find a preference for the own nest odour. Males of both species did not show any preferences at all. The behavioural reaction to any nest odour decreased after fledging of the offspring. Our results show that only females show a behavioural response to olfactory nest cues, indicating that the use of olfactory cues for nest recognition seems to be sex-specific and dependent on the developmental stage of the offspring. Although estrildid finches are known to use visual and acoustic cues for nest recognition, the similar behavioural pattern of both species indicates that at least females gain additional information by olfactory nest cues during the nestling phase of their offspring. Thus olfactory cues might be important in general, even in situations in which visual and acoustic cues are known to be sufficient.     

INTERSPECIFIC RECOGNITION AND DISCRIMINATION BASED UPON OLFACTORY CUES IN NORTHERN SWORDTAILS

Female Xiphophorus montezumae were attracted to olfactory cues from conspecific and heterospecific (X. cortezi and X. nigrensis) males when given a choice between the stimulus and water. When given a choice between conspecific and heterospecific cues, females only demonstrated a strong preference for the conspecific stimulus when it was matched against X. nigrensis. Female X. nigrensis were attracted to olfactory cues from their close relative, X. cortezi, but did not respond to cues from the more distantly related X. montezumae. They preferred the scent of their own males to the olfactory cues of both heterospecific species. Our results indicate that X. cortezi and X. nigrensis share an apomorphic change in some aspect of their olfactory cue-receiver system that is not shared with X. montezumae. We also uncovered an asymmetry in response based on olfactory stimuli in these fishes: X. montezumae is moderately attracted to the cue from X. nigrensis, whereas X. nigrensis does not respond to the cue from X. montezumae at all.     

Love is in the air: olfaction-based mate-odour identification by jumping spiders from the genus Cyrba

Jumping spiders (Salticidae) are known for having good eyesight, but the extent to which they rely on olfaction is poorly understood. Here we demonstrate for the first time that olfactory pheromones are used by two species from the salticid genus Cyrba (C. algerina and C. ocellata). Using a Y-shape olfactometer, we investigated the ability of adult males and females of both species to discriminate between mate and non-mate odour. A hidden spider or a spider’s draglines (no spider present) were used as odour sources. There was no evident response by females of either Cyrba species to any tested odour. Males of both species chose odour from conspecific females, or their draglines, significantly more often than the no-odour control, but there was no evident response by males to any of the other odours (conspecific male and heterospecific female). Our findings demonstrate that C. algerina and C. ocellata males can make sex- and species-specific discriminations even when restricted to using olfaction alone. Also, by showing that draglines can be a source of olfactory pheromones, our findings illustrate the difficulty of ruling out olfaction when attempting to test for chemotactile cues.     

Discrimination of conspecific sex and reproductive condition using chemical cues in axolotls (<Emphasis Type="Italic">Ambystoma mexicanum</Emphasis>)

Chemosensory cues play an important role in the daily lives of salamanders, mediating foraging, conspecific recognition, and territorial advertising. We investigated the behavioral effects of conspecific whole-body odorants in axolotls, Ambystoma mexicanum, a salamander species that is fully aquatic. We found that males increased general activity when exposed to female odorants, but that activity levels in females were not affected by conspecific odorants. Although males showed no difference in courtship displays across testing conditions, females performed courtship displays only in response to male odorants. We also found that electro-olfactogram responses from the olfactory and vomeronasal epithelia were larger in response to whole-body odorants from the opposite sex than from the same sex. In males, odorants from gravid and recently spawned females evoked different electro-olfactogram responses at some locations in the olfactory and vomeronasal epithelia; in general, however, few consistent differences between the olfactory and vomeronasal epithelia were observed. Finally, post hoc analyses indicate that experience with opposite-sex conspecifics affects some behavioral and electrophysiological responses. Overall, our data indicate that chemical cues from conspecifics affect general activity and courtship behavior in axolotls, and that both the olfactory and vomeronasal systems may be involved in discriminating the sex and reproductive condition of conspecifics.Abbreviations EOG electro-olfactogram - VNO vomeronasal organ     

Female mate choice and species recognition between two closely related cichlid fish of Lake Malawi,Metriaclima estherae and M. callainos

Cichlids are one of the most diverse and colourful groups of freshwater fishes in the world. Despite much investigation, the factors that promote speciation in these fishes are still uncertain. However, previous studies suggest that sexual selection on male colour is one of the main drivers of speciation among these fishes. Metriaclima estherae is a polymorphic cichlid species from Lake Malawi, and thus provides an ideal model for the investigation of the importance of colour as a species recognition cue. M. callainos is a closely related and morphologically similar species, with male colour pattern very similar to that of M. estherae. We tested female choice by giving females of the two species a choice between conspecific and heterospecific males in the presence and absence of visual (colour) and chemical cues. The results show that females of M. callainos were able to reliably recognize conspecific males, even when colour was eliminated as a cue. However, females of M. estherae did not prefer conspecific males, although they were able to discriminate between red and blue conspecific colour morphs by using chemical cues. These results suggest that species recognition cues may differ even among closely related species of cichlid fish, and that female preferences for male coloration may be weak in certain species.     

Male mate choice relies on major histocompatibility complex class I in a sex‐role‐reversed pipefish

Mate choice for compatible genes is often based on genes of the major histocompatibility complex (MHC). Although MHC‐based mate choice is commonly observed in female choice, male mate choice remains elusive. In particular, if males have intense paternal care and are thus the choosing sex, male choice for females with dissimilar MHC can be expected. Here, we investigated whether male mate choice relies on MHC class I genes in the sex‐role reversed pipefish Syngnathus typhle. In a mate choice experiment, we determined the relative importance of visual and olfactory cues by manipulating visibility and olfaction. We found that pipefish males chose females that maximize sequence‐based amino acid distance between MHC class I genotypes in the offspring when olfactory cues were present. Under visual cues, large females were chosen, but in the absence of visual cues, the choice pattern was reversed. The use of sex‐role reversed species thus revealed that sexual selection can lead to the evolution of male mate choice for MHC class I genes.     

Behavioural plasticity and sex differences in host finding of a specialized bee species

Many animals feed on flowers, and visual as well as olfactory cues are considered as most important mediators in animal–plant interactions. However, the relative importance of these cues is not well understood. Bees are the most important animal pollinators worldwide and here, we determined the importance of decoupled and combined visual and olfactory cues of Lysimachia punctata (Primulaceae) for host plant location in both sexes of the specialized, solitary bee, Macropis fulvipes (Melittidae). Lysimachia-inexperienced female bees preferred olfactory over visual cues though visual cues increased the attractiveness of olfactory ones. In experienced females, the importance of visual cues was increased. Both Lysimachia-naive and -experienced males relied more on visual cues as compared to females. This study demonstrates that the relative weighting of cues used for host plant finding depends on the sex and experience of M. fulvipes. The latter finding reveals the presence of learning-induced behavioural plasticity in host plant finding for a bee species. It may allow the bee to forage highly efficient. Visually guided female detection on flowers by males is a likely functional explanation for the differences in the weighting of visual and olfactory cues between the sexes.     

The importance of olfactory signals in the gasterosteid mating system: sticklebacks go multimodal

Stickleback fishes are renowned for the complexity of their nuptial colour signal. In this paper I show that the nuptial signal is in fact multimodal: male-based olfactory cues also transmit information to receptive females. Both female three-spined and brook sticklebacks recognized the scent from each other's males, but discriminated in favour of their own males when asked to choose between conspecific and heterospecific odours. Although females were not attracted to scent from the more distantly related guppy, Poecilia reticulata , changes in their baseline behaviours indicated that they perceived its presence. Olfactory cues act as long distance messages, allowing a female to detect the 'I am here' message from the male before she can actually see him. Studies of interactions between temporally displaced signals indicate that the first cue (in this case chemical) functions to alert the receiver to the presence of the second cue (visual), increasing the probability of its detection and recognition. So, although olfactory cues do not appear to be as species-specific as visual cues, their function as alerting stimuli may not require such fine-tuning. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 555–572.     

Mate recognition systems in a species flock of Mexican pupfish

The pupfishes of Lake Chichancanab (Mexico) provide a unique opportunity to study the evolution of premating reproductive barriers. This group of endemic species is of recent origin and the lineages differ in morphological traits indicating trophic specialization, but show very little genetic change. We studied the function of visual and chemical cues in the mate recognition system of three morphospecies, Cyprinodon beltrani, C. labiosus and C. maya. Only in C. maya, which is genetically the most distinct member of the group, do females show the ability to identify males of their own type, both visually and chemically. C. labiosus females discriminated between their own and C. beltrani males based on chemical but not visual cues. C. beltrani, which is morphologically the least differentiated member of the group, showed no interspecific mate recognition. Females responded more strongly to the visual and chemical cues of their own males than to their own females, but they did not discriminate between their own males and those of the other two morphospecies based upon either type of cue. These results suggest that different levels of behavioural isolation have been established: most isolated is C. maya, and the least is C. beltrani. C. labiosus has an intermediate position. The results also suggest that species recognition cues based on different sensory modalities do not necessarily evolve together, and may evolve at different rates.     

Widespread reliance on olfactory sex and species identification by lyssomanine and spartaeine jumping spiders

Jumping spiders (Salticidae) are renowned for their exceptional vision, but this does not preclude use of other senses. Here we provide evidence that olfactory pheromones are widespread in the Spartaeinae and Lyssomaninae, two subfamilies regarded as basal clades within the Salticidae. Pheromone use by salticids was tested in a series of experiments: males were tested with the odour of conspecific females, heterospecific females, and conspecific males, and females were tested with the odour of conspecific males. With seven of the 29 species tested, we also tested males using the draglines of conspecific females (spider absent) as the odour source. Males of all species tested were attracted to the odour of conspecific females and to the odour of the draglines of conspecific females. There was no evidence of males responding to the odour of heterospecific females or conspecific males, or of females responding to the odour of conspecific males. These findings suggest that it is primarily males that respond to olfactory sex pheromones, consistent with the apparent trend within spiders of males more actively searching for females and females placing greater emphasis on mate‐choice decisions. Compared with most salticid groups, lyssomanines and spartaeines are unusually sedentary and this lifestyle may favour olfactory mate searching. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 664–677.     

Genetic differentiation, behavioural reproductive isolation and mixis cues in three sibling species of monogonont rotifers

Many aquatic species usually considered to be 'cosmopolitan' have been identified as cryptic species complexes, based on deep genetic differentiation. However, reproductive isolation among sibling cryptic species has rarely been studied, and interspecific hybridization is common in some taxa.We investigated isolation mechanisms and possible introgression among three cyclical parthenogenetic rotifer species in the Epiphanes senta complex that are found in very different freshwater habitats: temperate floodplains, subtropical desert rock pools and a tropical alpine lake. Whereas Epiphanes ukera is reproductively isolated from E. chihuahuaensis and E. hawaiiensis, the latter hybridize under laboratory conditions.While reproductive isolation is incomplete, RAPD profiles indicated unique genetic signatures and showed no evidence for introgression, indicating that these three species are diverging and have independent evolutionary trajectories.Testing cues for sexual reproduction in these cyclic parthenogens demonstrated that mixis in E. chihuahuaensis and E. ukera is influenced by population density, whereas E. hawaiiensis females rarely produce mictic offspring regardless of density. Different mixis cues are likely to separate sexual periods and effectively cause reproductive isolation between the species. Epiphanes ukera and E. chihuahuaensis males display mate guarding behaviour, and E. ukera males distinguish between conspecific and heterospecific females in mate choice experiments. Geographic isolation, along with different cues for mixis induction and mate recognition, act as reproductive barriers among these sibling species.     

Sex differences in dogfish behaviour: alternative activity patterns and habitat choice

Guppies are highly sexually dimorphic and females have been shown to mate preferentially with males with various visible traits. Guppies, however, have been shown to respond behaviourally to odour cues from conspecifics. Using a specially designed olfactory choice tank, we tested whether females (1) could detect other guppies on the basis of their olfactory cues alone, (2) preferred to associate with males or with females and (3) could distinguish between different males. Female guppies were found to associate preferentially with other guppies when given a choice between water containing cues from another fish and water containing no cues. When females were presented with olfactory cues from a male or a female, they preferred the female initially but most then reversed their decision and swam to the male. Females associated preferentially with certain males based upon olfactory cues alone. Males, however, preferred on the basis of olfactory cues were the least preferred for visual cues.     

Sex Differences in Mate Preference Between Two Hybridizing Species of Poeciliid Fish

When hybridization between two species in secondary contact is costly, natural selection should favor pre‐mating isolation barriers. The invasive Gambusia affinis has been introduced to habitats of a closely related species, the endangered Gambusia nobilis. Although other Gambusia species readily hybridize in secondary contact, previous studies in this system found low abundance of hybrids in sympatry. To examine whether hybridization is limited by behavioral pre‐mating isolation that may have evolved in allopatry, I examined each species’ mating preferences using individuals from allopatric populations in male and female visual/olfactory association preference tests as well as open mating tests with and without male–male competition. Gambusia affinis and G. nobilis males had significant association preference for conspecific females in visual/olfactory tests. Only G. nobilis females had statistically significant preference for conspecific males. In open mating tests, males of both species had lower chase times overall when in competition, but there was no difference in number of copulation attempts. Males of both species had higher copulatory success rates with conspecific females when in competition, suggesting females may exert some control over copulation success of males. These results suggest that there are differences in mating preferences between these species. This mate choice may act as a pre‐mating isolating barrier to reduce hybridization in sympatry, a proposed threat to the endangered G. nobilis.     

Female preferences based on olfactory cues in the guppy (Poecilia reticulata)

Guppies are highly sexually dimorphic and females have been shown to mate preferentially with males with various visible traits. Guppies, however, have been shown to respond behaviourally to odour cues from conspecifics. Using a specially designed olfactory choice tank, we tested whether females (1) could detect other guppies on the basis of their olfactory cues alone, (2) preferred to associate with males or with females and (3) could distinguish between different males. Female guppies were found to associate preferentially with other guppies when given a choice between water containing cues from another fish and water containing no cues. When females were presented with olfactory cues from a male or a female, they preferred the female initially but most then reversed their decision and swam to the male. Females associated preferentially with certain males based upon olfactory cues alone. Males, however, preferred on the basis of olfactory cues were the least preferred for visual cues.