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Consistent behavioural responses of individuals (i.e. personality) have been linked with reproductive output and success across a range of taxa. In species with biparental care, the behavioural compatibility of breeding partners may also affect reproductive output, perhaps because it allows greater pair coordination during breeding attempts. The aim of this study was to investigate whether pairs of greylag geese are assortatively paired for personality, and whether these traits within pairs affect reproductive output. We used repeated behavioural assays in the field to quantify three personality traits: activity (focal observations), boldness (flight initiation distance) and aggressiveness (response to mirror image). We assessed their correlation with three measures of reproductive output (clutch size, hatching success and fledging success). All three personality traits were significantly repeatable; however, we found no evidence that pairs within the flock routinely assortatively paired for any trait, regardless of the pair bond duration. Nevertheless, there may still be fitness benefits associated with pair compatibility. Pairs in which the partners were similar in average boldness had higher hatching success, although this trend was not found for clutch size or fledging success. These results suggest that the benefits of having similar predator defence strategies within pairs differ across the breeding cycle, resulting in no overall selection for assortative mating for boldness. • Personality of both parents and their similarity in personality can affect fitness. • Greylag geese were not assortatively paired for personality at the flock level. • Similarity in parental personality correlated with hatching success. • Similarity in personality within pairs did not affect fledging success. [ABSTRACT FROM AUTHOR]

Mate choice is a key driver of evolutionary phenomena such as sexual dimorphism. Social mate choice is studied less often than reproductive mate choice, but for species that exhibit biparental care, choice of a social mate may have important implications for offspring survival and success. Many species make pairing decisions based on size that can lead to population-scale pairing patterns such as assortative and disassortative mating by size. Other size-based pairing patterns, such as females pairing with males larger than themselves, have been commonly studied in humans, but less often studied in nonhuman animal systems. Here we show that sexually size-dimorphic mountain chickadees, Poecile gambeli , appear to exhibit multiple self-referential pairing patterns when choosing a social mate. Females paired with males that were larger than themselves more often than expected by chance, and they paired with males that were slightly larger than themselves more often than they paired with males that were much larger than themselves. Preference for slightly larger males versus much larger males did not appear to be driven by reproductive benefits as there were no statistically significant differences in reproductive performance between pairs in which males were slightly larger and pairs in which males were much larger than females. Our results indicate that self-referential pairing beyond positive and negative assortment may be common in nonhuman animal systems. • The factors influencing social mate choice remain unclear. • Some species, including humans, make self-referential pairing decisions. • Mountain chickadees are sexually size dimorphic and socially monogamous. • Females paired with males that were larger but not too much larger than themselves. • Reproductive performance was not related to whether a pair followed this pattern. [ABSTRACT FROM AUTHOR]

Individually consistent behavioural phenotypes persist in a diversity of populations, despite the expectation that selection would reduce their prevalence. The life-history trade-off between current and future reproduction, combined with individual variation in age or condition and therefore in residual reproductive value, may explain this apparent paradox. Specifically, individuals that are old or of low condition and therefore of low residual reproductive value should take risks and thus elevate current reproduction at the expense of future reproduction. The opposite should be true for individuals that are young or of high condition and therefore of high residual reproductive value, which should be risk averse. Over the course of a long-term study on Lincoln's sparrows, Melospiza lincolnii , we discovered a behavioural phenotype based on trappability that predicts both condition (but not age) and current reproductive success but, surprisingly, in a way that was not expected based on our assumption of how this phenotype is associated with risk taking. We found that, relative to individuals that did not enter traps (the nontrap phenotype, assumed as risk averse), those of the trap phenotype (assumed as risk taking) showed elevated indices of energetic condition and, for females, reduced reproductive success. Assortative mating may be a proximate mechanism for the populationwide maintenance of multiple behavioural phenotypes, and we found that assortative pairings based on trappability phenotype occurred more frequently than random pairing would predict. However, assortative pairing, when compared to disassortative pairing, did not affect reproductive success. Nevertheless, the contrasting relationships between current reproductive success and condition that we found for each phenotype are consistent with life-history theory. However, our results are not consistent with the assumption that the trap phenotype is a manifestation of risk-taking behaviour and may, in fact, arise from just the opposite: a risk-averse, shy or neophobic behaviour for the trap phenotype. • Two phenotypes in a bird species coexist and differ in their life-history strategy. • The trap phenotype (assumed as risk taking) had higher energetic condition. • The nontrap phenotype (assumed as risk averse) had higher reproductive success. • Members of a breeding pair were correlated in phenotype. [ABSTRACT FROM AUTHOR]

Many animals have the ability to learn, and some taxa have shown learned mate preference, which may be important for speciation. The butterfly Heliconius melpomene is a model system for several areas of research, including hybridization, mate selection and speciation, partially due to its widespread diversity of wing patterns. It remains unclear whether social experience shapes realized mating preferences in this species. Here we test whether previous experience with a female influences male mate preference for two H. melpomene subspecies, H. m. malleti and H. m. rosina. We conducted no-choice assays to determine whether male courtship (versus no courtship) and latency to court differed between naïve males and males with previous exposure to a sexually mature, virgin female. To test whether assortative courtship preference is learned in H. melpomene , males were either paired with a female who shared their phenotype or one who did not. Naïve H. m. malleti males courted assortatively, while naïve H. m. rosina males did not. When data were pooled across subspecies, experienced males reduced their courting relative to naïve males, suggesting that social experience with a female sans copulation may be perceived as a negative experience. This effect was likely driven by experienced H. m. malleti males, who reduced their courting relative to naïve males when analysed independently, while experienced H. m. rosina males did not. Our results suggest that social experience can influence male mating behaviour in H. melpomene and has the potential to contribute to the high rate of diversification observed in Heliconius butterflies. • Learning whom to court may be either adaptive or maladaptive when around heterospecifics. • Using no-choice assays, we tested for courtship learning in male H. melpomene. • Male H. melpomene reduced courtship after encountering but not copulating with a female. • H. melpomene males can use past experience to inform current mating decisions. • This may be adaptive if encounters with heterospecific, unreceptive females are common. [ABSTRACT FROM AUTHOR]

Assortative mating depends on species distinctiveness in mating traits and preferences, which can be challenging to maintain when traits and/or preferences are learned. This is because learning may cause individuals to copy heterospecific signals. Juvenile songbirds possess innate sensory biases favouring them to learn and to prefer conspecific songs, but the effectiveness of these biases relies on consistent and sufficient differences between the songs produced by different species. However, mating signals, including learned songs, sometimes converge in sympatry, and the species-specific cues that individuals use to shape their preferences are often unknown. In Ficedula flycatchers, a stereotyped and highly species-specific alarm call is often incorporated as the first syllable of their songs. However, where the two species co-occur, pied flycatchers, Ficedula hypoleuca , learn to incorporate the introductory calls of the closely related collared flycatcher, Ficedula albicollis , into their songs. In this study, we investigated the role of introductory alarm calls for song discrimination in collared flycatchers, using playback experiments of both manipulated and unmanipulated songs on adults and nestlings within the hybrid zone of Öland, Sweden. We predicted that the introductory alarm call would be sufficient to trigger song responses, such that adults and nestlings would respond similarly to song phrases including the call, whether it is followed by conspecific or heterospecific notes. Our results provide evidence that the introductory alarm call is sufficient to trigger song discrimination in nestlings, but not in adult males, potentially due to their greater experience with songs and, therefore, subtler discrimination. Altogether, this study highlights the often-overlooked importance of calls within or associated with songs. • Collared flycatchers often start their songs with an alarm call. • The alarm call seems sufficient to drive song responses in nestlings. • We argue that the call could guide learning onto appropriate songs. • However, the call alone is unlikely to be sufficient for discrimination in adults. • We discuss the broader implication of incorporation of calls into songs. [ABSTRACT FROM AUTHOR]

Size-assortative mating and sexual selection on size are common across species. Since both may be a result of mate choice, mate choice based on size should also be a widespread process. This behaviour is, however, rarely studied directly and thus the biological causes that determine size-based mate choice are poorly understood. To address this, we studied the size-based mate choice in an intertidal snail, Echinolittorina malaccana , that has been used as a model to understand this process. Previous studies, assuming a quantitative Gaussian mating preference function, have inferred that mate choice in this snail is caused by a size similarity mechanism (males prefer to mate with females slightly larger than themselves). To further test and quantify this proposed mechanism, we conducted mate choice experiments with alternative designs (single, male and multiple choice) in the laboratory and compared the results to mate choice data observed in natural populations. This integrated approach allowed us to elucidate the mechanism of mate choice by evaluating alternative mating models that best fitted the observed data of various designs. Results confirmed the similarity-based mechanism but showed deviations at extreme size classes. The single choice design indicated that mate choice was exercised during one-on-one male–female interactions, but the strength of mate choice increased with the presence of additional individuals (males in the male choice design, and both males and females in the multiple-choice design). Multiple-choice experiments are, therefore, the most valuable and useful design to infer how males choose mates in the wild, as they best mimic the natural scenario and the results are the most similar to those observed in natural populations. To elucidate the mechanisms causing this male choice for particular female sizes, the next steps are to identify the genetic basis as well as potential physiological benefits associated with choosing slightly larger females. • Mating behaviour was used to infer size-based mate choice in a littorinid snail. • Single-, male and multiple-choice designs were compared to infer mate choice. • All designs deviated from random mating, being strongest for multiple choice. • On-shore, wild data showed similar patterns to the multiple-choice laboratory data. • Choice parameters were based on a similarity-like preference with few deviations. [ABSTRACT FROM AUTHOR]

Traditionally it has been suggested that sexual selection can cause sexual size dimorphism (SSD). However, a recent review in gastropods shows that SSD itself can also cause sexual selection (Ng et al., 2019. Animal Behaviour , 148, 53–62). This may be the case if mate choice exists, with males preferring to mate with females similar in body size but somewhat larger than themselves (female-biased preference). We formally investigated this verbal explanation by computer simulations using a Gaussian mating preference function. Parameters of that function were also estimated from empirical data. Our results suggest that sexual selection (estimated as selection differential) is strong when mate choice is high and exerted by only one of the sexes, being influenced by SSD and the magnitude of the female-biased preference. All these factors cause a negative relationship between SSD and the (sexual) selection differential, similar to that observed in Ng et al.'s review on gastropods. Empirical estimates of male mate choice from wild-captured mating pairs of different gastropod species confirm that mate choice by males is biased towards females slightly larger than themselves. Our results also illustrate that if mate choice is truly involved in determining SSD, present-day sexual selection cannot be used to estimate the past magnitude of mate choice, as SSD influences present-day patterns of sexual selection. • Dimorphism is negatively correlated with sexual selection differential in gastropods. • Dimorphism plus similarity-based mate choice can cause strong sexual selection. • Preference bias can have the opposite effect than dimorphism on sexual selection. • Past mate choice causing dimorphism cannot be estimated from present sexual selection. [ABSTRACT FROM AUTHOR]

In monogamous mating systems, pair mates frequently share similar characteristics, such as size or ornamentation, a pattern suggesting mutual mate choice. When pairs persist across multiple seasons, preferences for familiar pair mates can either reinforce or disrupt patterns of assortative pairing. Snapping shrimp (Alpheus angulosus) are socially monogamous shrimp that can be found in size-assortative pairs year-round; both sexes could benefit from pairing with larger individuals. To determine the role of pair mate preferences for either size or established pair mates in size-assortative pairing, we performed simultaneous choice trials to test whether (1) either or both sexes prefer larger pair mates, (2) females prefer males with larger claws, or (3) either or both sexes prefer current pair mates over size-matched unfamiliar potential mates. Males, but not females, preferred larger potential pair mates in both the reproductive and nonreproductive seasons; males also showed more mate-searching behaviour, switching more frequently between choice options than females. Females, but not males, preferred their current pair mate over a novel potential pair mate; females also engaged in more frequent switching between pair mates and novel males, but only during the nonreproductive season. Thus, while both males and females exhibit preferences in pairing, size-assortative pairing in snapping shrimp does not result from mutual mate choice for size, but rather preferences for size in one sex, with size-assortative pairing reinforced by preferences for established pair mates in the other. Furthermore, pairing behaviour may be dynamic, shifting across seasons even in a year-round socially monogamous species. • Male snapping shrimp preferred larger females, even during the nonreproductive season. • Females preferred their current pair mate over size-matched novel males. • Females increased mate sampling during the nonreproductive season. • Males showed no preference for current mates; females showed no size preferences. • Sex differences in preferences led to year-round size-assortative monogamy. [ABSTRACT FROM AUTHOR]

Predicting patterns of variation in sexual traits requires understanding how developmental environments influence mate choice. Here, we studied how long-term perceived high predation risk affects mutual mate choice in the cichlid Pelvicachromis taeniatus. From hatching onwards, fish were exposed regularly to either conspecific alarm cues signalling high risk or a control treatment consisting of exposure to water. Alarm cue-exposed and control adult fish were then offered the dichotomous choice between opposite-sex fish from different treatment groups. Under chronic predation risk, lower investment in mate choice and assortative preferences for mates from the same environment may be optimal. As predicted, alarm cue-exposed males assessed potential mates less than controls whereas females did not. Mate preferences differed as well but were independent of sex. While alarm cue-exposed fish were unselective, against expectations, control fish displayed disassortative preferences for alarm cue-exposed fish. This indicates that perceived high predation risk during development may contribute to maintaining variation in mating preferences and sexual traits. • Perceived predation risk during development may affect mate choice patterns. • We let high-risk and control fish choose between high-risk and control mates. • High-risk males but not females assess potential mates for a shorter time. • High-risk fish of both sexes are unselective regarding their mate. • In both sexes, control fish show disassortative preferences for high-risk mates. [ABSTRACT FROM AUTHOR]

Melanin is a common pigment that can indicate individual quality to potential mates and social dominance to competitors. For many avian species, plumage melanism varies within both males and females. If predictive of individual quality, sexual selection may drive contrasting expressions of melanism for each sex, reflecting their different reproductive roles. For an alpine population of horned larks, Eremophila alpestris , we investigated whether plumage ornament size and darkness predicted morphometric traits, parental care and fitness correlates, and we evaluated support for assortative pairing. Males with darker crowns and larger masks were associated with greater wing length and mass, respectively. Males with darker ornaments were paired with females that provisioned nestlings at a higher rate, began nesting earlier in the season, had larger clutch sizes and ultimately had greater nest success. For females, plumage ornaments did not predict morphometric traits (i.e. wing length, mass), provisioning rate of the male partner, clutch initiation date or reproductive success. Instead, females with darker crowns provisioned nestlings more frequently and had larger clutches. Overall darker males tended to pair with darker females, but plumage ornament size did not correlate within mated pairs. We demonstrate that: (1) the darkness of plumage ornaments is a better predictor of fitness than ornament size and (2) darker males are associated with greater individual quality and reproductive investment of the female mate, while female darkness primarily predicts reproductive investment. These results indicate the potential for sex-specific selection pressures and mate choice based on the predictive value of plumage melanism. • Plumage ornament darkness is more predictive of fitness than ornament size. • Male darkness predicts individual quality and parental investment of the female mate. • Female darkness primarily predicts parental care and clutch size. • Individuals demonstrated assortative pairing based on melanin-based plumage ornaments. • Results suggest the potential for sex-specific selection pressures. [ABSTRACT FROM AUTHOR]

Male preference for high-quality females is expected to evolve when male reproductive potential is restricted. However, when there is competition among males, some models predict the evolution of assortative male mate choice, in which good competitors choose high-quality females while poor competitors choose lower quality females to avoid competition. In Trichonephila clavipes spiders, males have limited sperm supply and fight for access to females. We tested whether female quality and male size (a proxy of fighting ability) influence male decisions in T. clavipes. We used field experiments in which males could choose between two available females in a scenario free of competition. We found that males choose their mates based on both female size and female recent pairing status (whether the female was accompanied by a male before the experiment). Importantly, male mate choice was plastic, and varied with male size, as large males preferred larger females that were recently unpaired, medium-sized males showed no preference and small males preferred smaller, recently paired females. Because all females appear to attract males, we predict that variation in male mate choice attenuates sexual selection on females. Our findings confirm the prediction of variable male mate choice when there is male–male competition and male reproductive potential is restricted, a pattern that may be common, but hard to detect. • Trichonephila clavipes males follow a 'choose what you can fight for' rationale. • Large males preferred females that provide the most benefits. • Medium-sized males were unselective towards females. • Small males preferred females that provide the least benefits. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism is widespread among dioecious species, but its underlying driving forces are often complex. A review of sexual size dimorphism in marine gastropods revealed two common patterns: first, sexual size dimorphism, with females being larger than males, and, second, females being larger than males in mating pairs. Both patterns suggest sexual selection and sexual size dimorphism are causally related. To test this hypothesis, we investigated, first, mechanisms driving sexual selection on size in three congeneric marine gastropods with different degrees of sexual size dimorphism, and, second, the correlation between male/female sexual selection and sexual size dimorphism across several marine gastropod species. Male mate choice via mucus trail following (as evidence of sexual selection) was found during the mating process in all three congeneric species, even though not all species showed sexual size dimorphism. There was also a significant and strong negative correlation between female sexual selection and sexual size dimorphism across 16 cases from seven marine gastropod species. These results suggest that sexual selection does not drive sexual size dimorphism. There was, however, evidence of males utilizing a similar mechanism to choose mates (i.e. selecting a female slightly larger than their own size) which may be widespread among gastropods, and, in tandem with sexual size dimorphism varying between species, provides a plausible explanation of the mating patterns observed in marine gastropods. Highlights • Sexual size dimorphism is not driven by sexual selection in marine gastropods. • Female sexual selection is driven by male choice and sexual size dimorphism. • Males prefer to mate with females slightly larger than themselves. • This pattern of male choice may be widespread in marine gastropods. [ABSTRACT FROM AUTHOR]

In monogamous species that provide biparental care, partners with similar behavioural types generally have a better reproductive success than dissimilar ones. The pattern of assortative mating for behavioural type is thus often interpreted as resulting from a mate choice process. However, an alternative process is also possible when the partners become similar through postpairing adjustments (behavioural convergence). The disentanglement of these two nonexclusive mechanisms is an important evolutionary question. Only sexual selection based on behavioural similarity before pairing can explain the maintenance of the behavioural type variability. In a previous study, we reported the existence of behavioural convergence for aggressiveness between partners in convict cichlids Amatitlania siquia , a monogamous tropical fish. We tested herein the assumption of mate choice based on behavioural similarity for aggressiveness using either short-term binary choice or long-term group level pairing. Pairing was not based on behavioural similarity between potential partners. Choosing a behaviourally compatible partner is a complex task because it requires profiling the potential mates. Individuals would thus achieve higher fitness benefits from choosing a partner on more conspicuous criteria (such as size for instance) and then attempt to increase partner similarity by convergence after pairing. Sexual selection does not appear to drive the maintenance of aggressiveness type variability in convict cichlids. [ABSTRACT FROM AUTHOR]

Heterogeneous environments are often associated with differential selection pressures favouring the evolution of local adaptations, and assortative mating is one of the mechanisms that might enhance such local adaptations. Montane environments present an example in which environment changes rapidly and predictably along an elevation gradient, and such variation may be expected to lead to the evolution of local adaptations. In food-caching mountain chickadees, Poecile gambeli, reliance on food stores is likely to increase with elevation, and previous research has shown that individuals living at high elevations cache more food and have superior spatial memory, needed to recover food caches, while also being socially subordinate to low-elevation birds. Here, we asked whether such differences might be associated with assortative mating. Considering that superior spatial memory ability for recovering food caches may be more critical for survival at high elevations because of more severe winter conditions, it should benefit females from high elevations to mate assortatively with males from the same elevation. If spatial memory is costly but not critical at low elevations, females from low elevation should mate assortatively with males from low elevation, especially given their socially dominant status to high-elevation birds. We assessed female preference using a pairwise choice of high- and low-elevation males. We used the amount of time spent in proximity to males from the same versus different elevation to determine female preference. High-elevation females showed significant preference for high-elevation males, however, low-elevation females showed no elevation-related preference. These results suggest that high-elevation females are choosier than low-elevation females, and prefer males from their same elevation. [ABSTRACT FROM AUTHOR]

There is mounting evidence that pathogen threat affects social preferences and responses. In humans, the presence of strangers also elicits heightened sensitivity to pathogen threat, promoting ‘in-group’ bias and ‘out-group’ avoidance. Whether or not a similar effect of social context on responses to pathogen threat occurs in nonhuman animals is unclear. Here we show that the responses of female laboratory mice, Mus muculus , to males are also rapidly affected by the presence of unfamiliar or infected males. In female mice, where odour cues drive appetitive and aversive social responses, brief (1 min) exposure to the urinary odours of an unfamiliar male led to females subsequently discriminating more strongly against the odours of males subclinically infected with the murine nematode parasite, Heligmosomoides polygyrus . Likewise, brief exposure to the odours of infected males attenuated the responses of females to the odours of the normally preferred unfamiliar males and enhanced their preferences for familiar males. These findings are consistent with the concept of ‘assortative’ sociality, whereby the presence of pathogen threat and unfamiliar individuals biases female preferences for uninfected and familiar individuals (‘in-group’ preference and, in human terms, ‘ethnocentrism’) and leads to the avoidance of unfamiliar individuals (‘out-group’ avoidance and ‘xenophobia’). Hence, as in humans, social information associated with infection can rapidly bias the social preferences of female mice. These rapid shifts in social preferences can have implications for our understanding of the evolution of social interactions and group composition. [ABSTRACT FROM AUTHOR]

In sexual communication, partners often form a duet, an exchange of species- and sex-specific signals, and in such systems mate recognition is likely to be reciprocal. We studied the role of vibrational signals in reproductive isolation in the genus Aphrodes (Hemiptera: Cicadellidae) in which mate recognition is based on highly divergent male advertisement calls and similar female replies. We first determined in playback experiments the preferences of females of four Aphrodes species to conspecific and heterospecific male advertisement calls as well as to species-specific elements in these calls. Females of all four species responded preferentially to calls of conspecific males; however, male calls composed of similar elements played only a limited role in mate recognition. In particular, females of Aphrodes aestuarina and Aphrodes bicincta showed higher responsiveness to each other's male calls than to calls of other species. In this species pair we further examined the role of female signals and duet structure in assortative mating using ‘no-choice’ mating experiments. The generally higher responsiveness of A. aestuarina females to male calls of A. bicincta did not translate into higher mating success in this heterospecific cross; lengthy replies of A. aestuarina females resulted in a breakdown of a complex species-specific duet structure and associated difficulties in locating the female reduced the probability of heterospecific mating. Our study shows that in mating systems based on a duet, males may contribute more than females to sexual isolation between species. Males' contribution to assortative mating may stem not only from mate recognition but also from inability to locate the source of the heterospecific female reply. [Copyright &y& Elsevier]

Grouping is a very common outcome of selection that operates on individual animals. Largely considered to be driven by immediate benefits, such as avoiding predators, animal groups often consist of individuals that are phenotypically more similar than expected from the population distribution. This suggests that the distribution and fitness of phenotypes may be shaped by multiple levels of selection operating along different axes of behaviour. Thus, quantifying assortative mixing, or the measure of association between similar individuals in social networks, should be a key component of the biologist's toolbox. Yet, assortment is rarely tested in animal social networks. This may be driven by a lack of tools for robust estimation of assortment, given the reliance of current methods on binary networks. In this paper, I extend existing approaches that calculate the assortativity coefficient of both nominal classes and continuous traits to incorporate weighted associations. I have made these available through a new R package ‘assortnet’. I use simulated networks to show that weighted assortment coefficients are more robust than those calculated on binary networks to added noise that could arise from random interactions or sampling errors. Finally, I demonstrate how these methods differ by applying them to two existing social networks estimated from wild populations, exploring assortment by species, sex and network degree. Given the parallel theoretical developments of the importance of local social structure on population processes, and increasing data on social networks being collected in free-living populations, understanding phenotypic assortment could yield significant insight into social evolution. [ABSTRACT FROM AUTHOR]

Many male signallers convey information to female receivers in multimodal courtship displays. While much is known about how males vary in terms of signalling, variation in female detection of these multimodal signals is relatively unexplored. We suggest that there is a critical, albeit underdeveloped, link between multimodal sensory reception and individual variation in mate choice. This review addresses the potential effects of developmental and conditional factors (e.g. nutrient availability, hormone profiles and age) on female multimodal processing, and illustrates that differences in the (1) source of individual variation and (2) the number of sensory processing modes affected by this variation can influence the receiver''s mate choice patterns. Based on these two factors, we outline novel predictions of preference functions and choosiness in a redundant multimodal signalling context. Moreover, we explore the theoretical implications of individual variation in multimodal signal perception in relation to sensory drive, honest signalling, assortative mating and intrasexual selection. We propose that understanding the role of variation in sensory processing and its relation to mate choice can help us better identify the factors that influence sender and receiver fitness, and subsequently the rate and direction of signal evolution. [Copyright &y& Elsevier]

Learning in the context of mate choice is important because it can influence sexual selection and incipient speciation. While fruit flies (Drosophila spp.) have been a key model system for research on sexual selection, speciation and learning, much of the research on fruit fly learning in the context of sexual behaviour has focused on males even though females typically control mating decisions. In a series of experiments, we found no evidence that early experience with either only conspecific males or both conspecific and heterospecific males affected the frequency of heterospecific matings by female Drosophila pseudoobscura. We conducted further experiments to place our results in perspective. First, we tested whether heterospecific matings do not induce female unreceptivity and thus have little cost, in which case learning would be of little benefit. Contrary to our prediction, we found that females that had initially mated heterospecifically remated conspecifically at a lower frequency than females that had first mated conspecifically. Second, we replicated earlier data indicating that male D. pseudoobscura that are rejected by heterospecific females later selectively reduce courtship of heterospecific females. Finally, we tested whether females can learn as well as males in a nonsexual context involving learning to avoid odours associated with danger and found similar learning scores in females and males. Our results indicate that, in spite of the potential benefits from learning in the context of mate choice and possessing a good learning ability in another domain, female D. pseudoobscura either do not learn about potential mates or such learning is not as robust as it is in the males. [Copyright &y& Elsevier]

Rapid speciation has been shown to be plausible without the need for extreme founder events, complete geographical isolation, the existence of distinct adaptive peaks or selection for local adaptation. However, standard theory predicts that extremely low migration rates are enough to hinder divergence between populations, and thus speciation. In this study we asked how low migration rates need to be for divergence to occur and hence for speciation to be possible. We experimentally transferred individual seed beetles, Callosobruchus maculatus, between populations in the laboratory, thus mimicking different rates of migration, and used deviations from Hardy–Weinberg equilibrium as an indicator of assortative mating. We found that assortative mating was upheld for several generations in populations experiencing immigration rates of up to 8% or 13–15 immigrants per generation, despite the lack of adaptive divergence and trade-offs between the exchanging populations. However, after some generations of extensive gene flow and in the absence of selection against hybrids, the system of assortative mating faltered. Based on our results, we conclude that selection is likely to be an important factor in speciation in the face of gene flow and that without it divergence will simply come to a halt. [Copyright &y& Elsevier]

Recent research indicating learning in the context of sexual behaviour in fruit flies suggests that learning could increase levels of assortative mating between partially diverged populations. We present a graphic model examining the role of learning and a series of experiments evaluating assumptions and predictions of the model. We found that male Drosophila persimilis that previously succeeded in mating with females of the sibling species, D. pseudoobscura, did not have a higher heterospecific mating success than males that were either virgin or previously mated with conspecific females. On the other hand, female D. pseudoobscura with apparently strict mating criteria, which rejected heterospecific males, were also more likely to reject conspecific males than were females inexperienced with males. Finally, D. persimilis males previously rejected by heterospecific females courted significantly less and had half as much heterospecific mating success as males previously accepted by heterospecific females. These results, combined with previous evidence demonstrating that males rejected by heterospecific females learn to avoid courting such females, indicate that learning can increase phenotypic divergence between populations with partial pre-mating isolation. [Copyright &y& Elsevier]

Mating preferences depending on Wolbachia infection were studied in two genotypically different strains of Drosophila melanogaster. Females from both strains carry two attached X chromosomes. Males from the red-eyed strain (R) have the wild-type X chromosome compared to males from the white-eyed strain (W), whose X chromosome contains two deleterious mutations (white and singed). Three types of competition tests showed that assortative mating depends on genotype, infection status and their combination in the mating partners. Males of strain R, genetically closer to the wild type, were more successful than males of strain W. Wolbachia infection increased the mating ability of W males but did not affect that of R males. Strain W showed positive assortative mating (preference for ‘self’) with regard to genotype and infection status. In strain R, negative assortative mating (preference for ‘nonself’) was observed. Moreover, the most affected flies (infected W) showed higher preference for ‘self’, while the least affected ones (uninfected R) showed higher preference for ‘nonself’. These results support the idea that mating choice may involve testing the partner for degree of genetic or biochemical similarity with self, based on chemoreception with possible participation of immune system components. [Copyright &y& Elsevier]

Size-assortative mating is one of the most common mating patterns in nature. Nevertheless, the underlying behavioural mechanisms have received little attention. Assortment is typically assumed to result from mate choice, which can be coupled with differences in competitive potential. We investigated the behavioural mechanisms underlying size-assortative mating in a monogamous, biparental goby cichlid, where mutual mate choice should be expected. We performed three field experiments with females and males of Eretmodus cyanostictus to test for the existence of mate preferences in general and with regard to size: (1) a sequential presentation of differently sized potential partners; (2) a removal of partners combined with surveillance until re-pairing with a new partner; and (3) the simultaneous release of new and original partners on the experimental territories. In the removal experiment, we found evidence for weak preferences for large partners relative to own size and to the original partner''s size, but pairs were formed irrespective of these preferences. The ecological importance of being paired appears to reduce choosiness and to override mate preferences. Territory ownership was quickly decided by aggressive interactions between original and new partners, and in both sexes the larger contestant won and was immediately accepted as partner by the resident. Our results suggest that strong intrasexual competition can be a powerful promoter of size-assortative mating even in the absence of active mate choice. [Copyright &y& Elsevier]

Recent data indicating that male fruit flies adaptively reduce courtship of heterospecific females, which typically reject them, suggest that learning could contribute to reduced levels of matings between individuals from diverging populations with partial premating isolation. To further examine the robustness of learning in the context of courtship in fruit flies, I wished to broaden the types of experience provided to males prior to testing. In both Drosophila persimilis and D. pseudoobscura, alternating trials of mating with conspecific females and rejection by heterospecific females produced the strongest reduction in heterospecific courtship. Trials of rejection by heterospecific females produced equally strong reduction in heterospecific courtship in D. persimilis but not in D. pseudoobscura, whereas trials of mating with conspecific females did not reduce heterospecific courtship at all. The pattern of strong reduction in heterospecific courtship was also replicated when I simulated the likely natural scenario in which males interact with conspecific females since eclosion and later encounter and experience rejection by heterospecific females. The results indicate that a variety of relevant experiences cause a rapid decrease in the time that male fruit flies spend courting heterospecific females. Such learning in partially reproductively isolated populations could contribute to speciation. [Copyright &y& Elsevier]

In a study of the spider Pholcus phalangioides, we double-mated large or small females with large and small males in all possible combinations to investigate the effects of body size and female mating history on male copulatory behaviour and paternity success. In addition we recorded data on female struggle behaviour. Our aim was to get insights into evolutionary forces that promote and constrain adaptive plasticity in male copulatory behaviour in this species with last-male sperm priority. When mating with virgin females, small males made more movements with both inserted pedipalps (sperm transfer organs) than large males, and males of both size classes showed many more pedipalp movements (PPMs) in large, fecund females. With mated females, in contrast, matings were either very short (5min, 82% of matings), during which PPMs were little affected by male and female size, or as long as matings with virgin females (78min, 18%) with comparably strong size effects on PPMs. Genetic paternity analysis showed that the second male fertilized on average 88% of the eggs, independent of his size and behaviour. Variation in relative fertilization success was solely predicted by the first male''s behaviour. We suggest that this difference in fertilization returns between first and second males may to a large extent explain the contrasting behavioural patterns in virgin versus mated females. The fact that female struggle behaviour contributed to variation in male copulatory behaviour further highlights that females are not merely passive during mating. [Copyright &y& Elsevier]

Age-assortative mating has been documented among birds, but there is little evidence of direct benefits to females that pair with older males. In this study, I examined nest concealment in Darwin''s small tree finch and tested the following predictions: (1) nest concealment increases with male age, (2) females prefer males that build well-concealed nests, and (3) females receive direct benefits through reduced predation at concealed nests. Darwin''s small tree finch has a pattern of annual moult that makes it easy to observe age-related variation in reproductive success. In this species, males build a display nest that is sometimes used by the female for nesting. Controlling for male age, females preferred display nests for nesting that were well concealed by surrounding vegetation, whereas exposed display nests were rarely used for nesting (although occasionally a female paired with the male that built the unused display nest). Using cross-sectional and longitudinal data, this study found evidence of a female pairing preference for older males, as well as increased nest concealment among older males. Females that paired with older males had higher fledging success (using the longitudinal data), mostly due to reduced predation. [Copyright &y& Elsevier]