Female‐biased dispersal alone can reduce the occurrence of inbreeding in black grouse (Tetrao tetrix)

Although inbreeding depression and mechanisms for kin recognition have been described in natural bird populations, inbreeding avoidance through mate choice has rarely been reported suggesting that sex‐biased dispersal is the main mechanism reducing the risks of inbreeding. However, a full understanding of the effect of dispersal on the occurrence of inbred matings requires estimating the inbreeding risks prior to dispersal. Combining pairwise relatedness measures and kinship assignments, we investigated in black grouse whether the observed occurrence of inbred matings was explained by active kin discrimination or by female‐biased dispersal. In this large continuous population, copulations between close relatives were rare. As female mate choice was random for relatedness, females with more relatives in the local flock tended to mate with genetically more similar males. To quantify the initial risks of inbreeding, we measured the relatedness to the males of females captured in their parental flock and virtually translocated female hatchlings in their parental and to more distant flocks. These tests indicated that dispersal decreased the likelihood of mating with relatives and that philopatric females had higher inbreeding risks than the actual breeding females. As females do not discriminate against relatives, the few inbred matings were probably due to the variance in female dispersal propensity and dispersal distance. Our results support the view that kin discrimination mate choice is of little value if dispersal effectively reduces the risks of inbreeding.     

Lack of behavioural evidence for kin avoidance in mate choice in a hymenopteran parasitoid (Hymenoptera: Braconidae)

Mechanisms for inbreeding avoidance should be prevalent in insects that reproduce by arrhenotokous haplodiploidy because of the higher potential production of unviable diploid males in inbred matings. Few studies have focused on mating strategies in insect parasitoids and even less on kinship relationships during mate choice. In this study we tested avoidance of kin as mate in the parasitic wasp Aphidius matricariae (Hymenoptera: Braconidae) using an ethological approach. Key mating parameters, such as male wing fanning, latent period before genitalia contact and duration of copulation were measured. No evidence for kin avoidance in mate choice in both A. matricariae males and females was observed in our behaviour (no choice or choice tests) tests. This lack of ethological sib mating avoidance could be due to different factors such as sex determination rule different than the single locus complementary sex determination, making lower the proportion of diploid males in case of sib matings and thus its negative consequence. The existence of other inbreeding avoidance strategies and mechanisms that reduce the probability of 2 receptive relatives meeting in nature may be common, for example, inbred mating may be rare through differential dispersal, delayed maturation, or protandry.     

Premating Avoidance of Inbreeding Absent in Female Guppies (Poecilia reticulata)

The recognition and avoidance of kin during mating can be an important means of reducing the potential for inbreeding depression in offspring. We report here that premating mechanisms to avoid inbreeding, either innate or learnt through juvenile experience, are at best weak in female guppies (Poecilia reticulata). Guppies are small, ovoviviparous, neo‐tropical freshwater fish, with a polygamous mating system where males actively court females and females are selective of their mates. In a series of mate‐choice experiments, naïve, virgin females of the Quare River population in Trinidad were given a choice between a brother and a non‐sib male from the same population. Initially, females were only provided olfactory cues upon which to base their choice and then subsequently both olfactory and visual cues. Despite the females displaying mate choice, we found no evidence of them discriminating between the male types in either experiment. There was thus no indication of inbreeding avoidance, suggesting that experiences after maturation or with mature males (e.g. rare male preference), dispersal and/or post‐mating mechanisms may be evolutionarily more important avoidance mechanisms.     

No Inbreeding Avoidance by Female Burying Beetles Regardless of Whether They Encounter Males Simultaneously or Sequentially

Inbreeding avoidance reduces the probability that an individual will mate with a related partner, thereby lowering the risk that it produces inbred offspring suffering from inbreeding depression. Inbreeding avoidance can occur through several mechanisms, including active mate choice, polyandry and sex‐biased dispersal. Here, we focus on the role of active mate choice as a mechanism for inbreeding avoidance. Recent evidence suggests that the experimental design used in mate choice experiments (i.e. simultaneous versus sequential choice) can have a strong impact on the strength of the reported mating preferences. In this study, we examine whether similar effects of experimental design also apply in the context of inbreeding avoidance. To this end, we designed two experiments on the burying beetle Nicrophorus vespilloides that matched two different contexts under which females encounter potential mates in the wild; that is, when females encounter males simultaneously and sequentially. We found that females were as likely to mate with related and unrelated males regardless of whether they encountered male partners simultaneously or sequentially. Thus, our study provides no evidence for inbreeding avoidance in this species, and suggests that the number of mates present did not influence the degree of inbreeding avoidance. We discuss potential explanations for the lack of inbreeding avoidance through mate choice, including lack of mechanisms for recognizing close relatives, low costs and/or low risks of inbreeding and the presence of other inbreeding avoidance mechanisms, such as sex‐biased dispersal and polyandry coupled with post‐copulatory mate choice.     

Consequences of genetic incompatibility on fitness and mate choice: the male point of view

Hymenopterans under single‐locus complementary sex determination (sl‐CSD) face inbreeding costs due to this sex determination mode. Under sl‐CSD, homozygote eggs at the sl‐CSD locus usually develop into unviable or sterile diploid males. Production of such costly males increases when sib‐mating happens because related individuals share half of their genome. In the hymenopteran Venturia canescens (a solitary parasitoid wasp), diploid males are sterile, leading to fitness costs through genetic incompatibility between parents. Whereas the costs of producing diploid males and behavioural strategies that would reduce such costs have been studied in females, the potential fitness costs faced by males have not. Here, we aimed to investigate fitness costs that males endure after a single sib‐mating and tested whether they have the ability to avoid sib‐mating through kin recognition. Our results show that males have a reduced fitness (i.e. they produce fewer daughters) when mating with their sibs. We also show that males have the ability to distinguish between non‐sib and sib females (i.e. kin). They use chemical marks emitted by the females to discriminate kin from non‐kin. We discuss the evolution of kin recognition in males in the context of mate choice for genetic compatibility. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 279–286.     

Has inbreeding depression led to avoidance of sib mating in the Glanville fritillary butterfly (Melitaea cinxia)?

Previous work on the Glanville fritillary butterfly (Melitaea cinxia) shows substantial inbreeding depression in both of our two study regions, Finland and southern France. The influence of inbreeding depression on population dynamics should depend on the strength of inbreeding avoidance. We conducted mate choice experiments to ascertain whether and to what extent butterflies avoid mating with their sibs. Experiments with similar design were done in the laboratory with Finnish butterflies and in the field with French butterflies. Each female was given a choice of mates with equal opportunity to mate with a sib or with a non-sib. In neither experiment was there a trend towards avoidance of sib mating. 95% confidence intervals for the proportion of non-sib matings were 12–62% in the laboratory experiment and 28–69% in the field experiment. Any preference for non-sibs must be slight, and can provisionally be ignored in modelling the dynamics of M. cinxia populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of sex‐biased dispersal on opposite‐sexed spatial genetic structure and inbreeding risk

Natal sex‐biased dispersal has long been thought to reduce the risk of inbreeding by spatially separating opposite‐sexed kin. Yet, comprehensive and quantitative evaluations of this hypothesis are lacking. In this study, we quantified the effectiveness of sex‐biased dispersal as an inbreeding avoidance strategy by combining spatially explicit simulations and empirical data. We quantified the extent of kin clustering by measuring the degree of spatial autocorrelation among opposite‐sexed individuals (FM structure). This allowed us to systematically explore how the extent of sex‐biased dispersal, generational overlap, and mate searching distance, influenced both kin clustering, and the resulting inbreeding in the absence of complementary inbreeding avoidance strategies. Simulations revealed that when sex‐biased dispersal was limited, positive FM genetic structure developed quickly and increased as the mate searching distance decreased or as generational overlap increased. Interestingly, complete long‐range sex‐biased dispersal did not prevent the development of FM genetic structure when generations overlapped. We found a very strong correlation between FM genetic structure and both F_IS under random mating, and pedigree‐based measures of inbreeding. Thus, we show that the detection of FM genetic structure can be a strong indicator of inbreeding risk. Empirical data for two species with different life history strategies yielded patterns congruent with our simulations. Our study illustrates a new application of spatial genetic autocorrelation analysis that offers a framework for quantifying the risk of inbreeding that is easily extendable to other species. Furthermore, our findings provide other researchers with a context for interpreting observed patterns of opposite‐sexed spatial genetic structure.     

Immigration prevents inbreeding in a growing colony of a long‐lived and philopatric seabird

Mating between close relatives can have deleterious effects on reproductive success or offspring fitness, which should favour the evolution of active or passive inbreeding avoidance mechanisms. In birds, evidence for active inbreeding avoidance by kin‐discriminative mate choice is scarce; many studies describe random mating in relation to kinship and thus support passive inbreeding avoidance by natal dispersal. However, most studies were conducted in island populations of short‐lived passerines with fast alternation of generations. In this study, we present inbreeding estimates based on pedigree data from a 16‐year study in a coastal colony of Common Terns Sterna hirundo, a long‐lived seabird with delayed sexual maturation and low rates of extra‐pair paternity. Incestuous mating was rare (four of 2387 pairs), even if partially accounting for incomplete pedigrees. Although the average relatedness of observed pairs was lower than would be expected from random pairing, the inbreeding coefficient did not differ from random mating. Hence, we found no clear evidence for active inbreeding avoidance by kin‐discriminative mate choice, and the low level of inbreeding seems to be related to the high immigration rate in the colony and thus to be maintained passively by dispersal.     

Inbreeding avoidance in spiders: evidence for rescue effect in fecundity of female spiders with outbreeding opportunity

Selection by inbreeding depression should favour mating biases that reduce the risk of fertilization by related mates. However, equivocal evidence for inbreeding avoidance questions the strength of inbreeding depression as a selective force in the evolution of mating biases. Lack of inbreeding avoidance can be because of low risk of inbreeding, variation in tolerance to inbreeding or high costs of outbreeding. We examined the relationship between inbreeding depression and inbreeding avoidance adaptations under two levels of inbreeding in the spider Oedothorax apicatus, asking whether preference for unrelated sperm via pre- and/or post-copulatory mechanisms could restore female fitness when inbreeding depression increases. Using inbred isofemale lines we provided female spiders with one or two male spiders of different relatedness in five combinations: one male sib; one male nonsib; two male sibs; two male nonsibs; one male sib and one male nonsib. We assessed the effect of mating treatment on fecundity and hatching success of eggs after one and three generations of inbreeding. Inbreeding depression in F1 was not sufficient to detect inbreeding avoidance. In F3, inbreeding depression caused a major decline in fecundity and hatching rates of eggs. This effect was mitigated by complete recovery in fecundity in the sib-nonsib treatment, whereas no rescue effect was detected in the hatching success of eggs. The rescue effect is best explained by post-mating discrimination against kin via differential allocation of resources. The natural history of O. apicatus suggests that the costs of outbreeding may be low which combined with high costs of inbreeding should select for avoidance mechanisms. Direct benefits of post-mating inbreeding avoidance and possibly low costs of female multiple mating can favour polyandry as an inbreeding avoidance mechanism.     

PROBLEMS WITH TESTING INBREEDING AVOIDANCE: THE CASE OF THE COLLARED FLYCATCHER

Four year's data on collared flycatchers, Ficedula albicollis, breeding in a nestbox plot on the island of Gotland, Sweden, was used to investigate whether individuals avoid mating with close kin (i.e., parents or sibs). Only one case of close inbreeding (0.5% of all pairs) was observed during the years of study. The observed frequency of close inbreeding was compared to expected frequencies based on two different null models. Assuming no inbreeding avoidance behaviors (e.g., dispersal or kin recognition), but taking into account the fact that mortality, and different arrival and pairing times of individuals reduce the probability of mating with close kin, the expected frequency of close inbreeding is 10% and 15% for female and male recruits (i.e., born in the study plot), respectively. However, assuming mating to be random within the study plot reduced the expected frequency of close inbreeding to 1% or less for both males and females. Consequently, conclusions drawn concerning inbreeding avoidance depend on the null model used. Contrasting estimated costs of tolerating close inbreeding with those of avoiding it (by dispersal to other plots), however, suggests that the costs of avoiding close inbreeding are substantially greater than those of tolerating it. Therefore, although inbreeding avoidance cannot be rejected as a cause of dispersal of this species, it is not the primary cause, and particularly not for sex-biased dispersal. The general problems of investigating inbreeding avoidance are discussed. It is argued that all previous null models based on random mating in finite populations produce expected frequencies of close inbreeding that in fact include inbreeding avoidance, since they implicitly assume random dispersal within a finite population. Thus, comparisons between observed and expected frequencies of close inbreeding based on random mating are inadequate. The most promising method of investigating inbreeding avoidance is to experimentally study individual movements and mating preferences in the presence and absence of close kin.     

Banded mongooses avoid inbreeding when mating with members of the same natal group

Inbreeding and inbreeding avoidance are key factors in the evolution of animal societies, influencing dispersal and reproductive strategies which can affect relatedness structure and helping behaviours. In cooperative breeding systems, individuals typically avoid inbreeding through reproductive restraint and/or dispersing to breed outside their natal group. However, where groups contain multiple potential mates of varying relatedness, strategies of kin recognition and mate choice may be favoured. Here, we investigate male mate choice and female control of paternity in the banded mongoose (Mungos mungo), a cooperatively breeding mammal where both sexes are often philopatric and mating between relatives is known to occur. We find evidence suggestive of inbreeding depression in banded mongooses, indicating a benefit to avoiding breeding with relatives. Successfully breeding pairs were less related than expected under random mating, which appeared to be driven by both male choice and female control of paternity. Male banded mongooses actively guard females to gain access to mating opportunities, and this guarding behaviour is preferentially directed towards less closely related females. Guard–female relatedness did not affect the guard's probability of gaining reproductive success. However, where mate‐guards are unsuccessful, they lose paternity to males that are less related to the females than themselves. Together, our results suggest that both sexes of banded mongoose use kin discrimination to avoid inbreeding. Although this strategy appears to be rare among cooperative breeders, it may be more prominent in species where relatedness to potential mates is variable, and/or where opportunities for dispersal and mating outside of the group are limited.     

Direct Familiarity Does Not Alter Mating Preference for Sisters in Male Pelvicachromis taeniatus (Cichlidae)

In social species, individuals who grew up together are usually relatives. Therefore, direct familiarity is normally a reliable kin recognition mechanism that is used in many species to discriminate kin from non‐kin. It has been shown in animals and in humans that familiar individuals are rejected as mating partners in order to circumvent potential costs of inbreeding. Here, we tested whether direct familiarity also leads to inbreeding avoidance behaviour in male Pelvicachromis taeniatus, a small socially monogamous cichlid with biparental brood care. In mate choice experiments, reproductively active males were given the choice between familiar sisters and unfamiliar, unrelated females. In a previous study, both sexes of P. taeniatus had preferred unfamiliar full‐sibs over unfamiliar unrelated individuals as mating partners. Here, we show that direct familiarity does not alter the male preference for closely related females. This result is in accordance with theoretical predictions, that inbreeding can be advantageous under certain conditions, and confirms previous findings, that active inbreeding is an adaptive strategy in P. taeniatus.     

No evidence for inbreeding avoidance in a great reed warbler population

Inbreeding depression may drive the evolution of inbreedingavoidance through dispersal and mate choice. In birds, manyspecies show female-biased dispersal, which is an effectiveinbreeding avoidance mechanism. In contrast, there is scarceevidence in birds for kin discriminative mate choice, whichmay, at least partly, reflect difficulties detecting it. First,kin discrimination may be realized as dispersal, and this isdifficult to distinguish from other causes of dispersal. Second,even within small, isolated populations, it is often difficultto determine the potential candidates available to a femalewhen choosing a mate. We sought evidence for inbreeding avoidancevia kin discrimination in a breeding population of great reedwarblers (Acrocephalus arundinaceus) studied over 17 years.Inbreeding depression is strong in the population, suggestingthat it would be adaptive to avoid relatives as mates. Detaileddata on timing of settlement and mate search movements madeit possible to identify candidate mates for each female, andlong-term pedigrees and resolved parentage enabled us to estimaterelatedness between females and their candidate mates. We foundno evidence for kin discrimination: mate choice was random withrespect to relatedness when all mate-choice events were considered,and, after correction for multiple tests, also in all breedingyears. We suggest that dispersal is a sufficient inbreedingavoidance mechanism in most situations, although the lack ofkin discriminative mate choice has negative consequences forsome females, because they end up mating with closely relatedmales that lowers their fitness.     

Female‐biased sex allocation and lack of inbreeding avoidance in Cubitermes termites

Sexually reproducing organisms face a strong selective pressure to find a mate and ensure reproduction. An important criterion during mate‐selection is to avoid closely related individuals and subsequent potential fitness costs of resulting inbred offspring. Inbreeding avoidance can be active through kin recognition during mate choice, or passive through differential male and female‐biased sex ratios, which effectively prevents sib‐mating. In addition, sex allocation, or the resources allotted to male and female offspring, can impact mating and reproductive success. Here, we investigate mate choice, sex ratios, and sex allocation in dispersing reproductives (alates) from colonies of the termite Cubitermes tenuiceps. Termites have a short time to select a mate for life, which should intensify any fitness consequences of inbreeding. However, alates did not actively avoid inbreeding through mate choice via kin recognition based on genetic or environmental cues. Furthermore, the majority of colonies exhibited a female‐biased sex ratio, and none exhibited a male‐bias, indicating that differential bias does not reduce inbreeding. Sex allocation was generally female‐biased, as females also were heavier, but the potential fitness effect of this costly strategy remains unclear. The bacterium Wolbachia, known in other insects to parasitically distort sex allocation toward females, was present within all alates. While Wolbachia is commonly associated with termites, parasitism has yet to be demonstrated, warranting further study of the nature of the symbiosis. Both the apparent lack of inbreeding avoidance and potential maladaptive sex allocation implies possible negative effects on mating and fitness.     

The inbreeding strategy of a solitary primate,Microcebus murinus

Inbreeding depression may be common in nature, reflecting either the failure of inbreeding avoidance strategies or inbreeding tolerance when avoidance is costly. The combined assessment of inbreeding risk, avoidance and depression is therefore fundamental to evaluate the inbreeding strategy of a population, that is how individuals respond to the risk of inbreeding. Here, we use the demographic and genetic monitoring of 10 generations of wild grey mouse lemurs (Microcebus murinus), small primates from Madagascar with overlapping generations, to examine their inbreeding strategy. Grey mouse lemurs have retained ancestral mammalian traits, including solitary lifestyle, polygynandry and male‐biased dispersal, and may therefore offer a representative example of the inbreeding strategy of solitary mammals. The occurrence of close kin among candidate mates was frequent in young females (~37%, most often the father) and uncommon in young males (~6%) due to male‐biased dispersal. However, close kin consistently represented a tiny fraction of candidate mates (< 1%) across age and sex categories. Mating biases favouring partners with intermediate relatedness were detectable in yearling females and adult males, possibly partly caused by avoidance of daughter–father matings. Finally, inbreeding depression, assessed as the effect of heterozygosity on survival, was undetectable using a capture–mark–recapture study. Overall, these results indicate that sex‐biased dispersal is a primary inbreeding avoidance mechanism at the population level, and mating biases represent an additional strategy that may mitigate residual inbreeding costs at the individual level. Combined, these mechanisms explain the rarity of inbreeding and the lack of detectable inbreeding depression in this large, genetically diverse population.     

The Effect of Inbreeding on Mating Behaviour of West Indian Sweet Potato Weevil Euscepes postfasciatus

When there is an inbreeding depression, mating with a kin individual is generally considered maladaptive behaviour. However, in some conditions, the inclusive fitness benefits from inbreeding may outweigh the costs of inbreeding depression, and thus, inbreeding tolerance is often adaptive. Inbreeding depression and the effect of relatedness on mating behaviour in the West Indian sweet potato weevil Euscepes postfasciatus were examined. No significant inbreeding depression was detected as indicated by body weight and number of progeny emerging from sweet potato roots. Male mating performance (i.e. number of mating occurrences per night) was adversely affected by inbreeding depression, but the effect was low (fitness loss was 6.3%). Although there were no significant differences in latency to mounting, pre‐copulatory guarding, copulation and post‐copulatory guarding duration between full‐sib and non‐kin pairs, the copulation rate of full‐sib pairs was significantly higher than that of non‐kin pairs. These results support the theoretical prediction that when inbreeding depression is weak, copulation with close relative individuals is favoured.     

How relatedness between mates influences reproductive success: An experimental analysis of self‐fertilization and biparental inbreeding in a marine bryozoan

Kin associations increase the potential for inbreeding. The potential for inbreeding does not, however, make inbreeding inevitable. Numerous factors influence whether inbreeding preference, avoidance, or tolerance evolves, and, in hermaphrodites where both self‐fertilization and biparental inbreeding are possible, it remains particularly difficult to predict how selection acts on the overall inbreeding strategy, and to distinguish the type of inbreeding when making inferences from genetic markers. Therefore, we undertook an empirical analysis on an understudied type of mating system (spermcast mating in the marine bryozoan, Bugula neritina) that provides numerous opportunities for inbreeding preference, avoidance, and tolerance. We created experimental crosses, containing three generations from two populations to estimate how parental reproductive success varies across parental relatedness, ranging from self, siblings, and nonsiblings from within the same population. We found that the production of viable selfed offspring was extremely rare (only one colony produced three selfed offspring) and biparental inbreeding more common. Paternity analysis using 16 microsatellite markers confirmed outcrossing. The production of juveniles was lower for sib mating compared with nonsib mating. We found little evidence for consistent inbreeding, in terms of nonrandom mating, in adult samples collected from three populations, using multiple population genetic inferences. Our results suggest several testable hypotheses that potentially explain the overall mating and dispersal strategy in this species, including early inbreeding depression, inbreeding avoidance through cryptic mate choice, and differential dispersal distances of sperm and larvae.     

Female‐biased dispersal in a bat with a female‐defence mating strategy

The ultimate causes for predominant male‐biased dispersal (MBD) in mammals and female‐biased dispersal (FBD) in birds are still subject to much debate. Studying exceptions to general patterns of dispersal, for example, FBD in mammals, provides a valuable opportunity to test the validity of proposed evolutionary pressures. We used long‐term behavioural and genetic data on individually banded Proboscis bats (Rhynchonycteris naso) to show that this species is one of the rare mammalian exceptions with FBD. Our results suggest that all females disperse from their natal colonies prior to first reproduction and that a substantial proportion of males are philopatric and reproduce in their natal colonies, although male immigration has also been detected. The age of females at first conception falls below the tenure of males, suggesting that females disperse to avoid father–daughter inbreeding. Male philopatry in this species is intriguing because Proboscis bats do not share the usual mammalian correlates (i.e. resource‐defence polygyny and/or kin cooperation) of male philopatry. They have a mating strategy based on female defence, where local mate competition between male kin is supposedly severe and should prevent the evolution of male philopatry. However, in contrast to immigrant males, philopatric males may profit from acquaintance with the natal foraging grounds and may be able to attain dominance easier and/or earlier in life. Our results on Proboscis bats lent additional support to the importance of inbreeding avoidance in shaping sex‐biased dispersal patterns and suggest that resource defence by males or kin cooperation cannot fully explain the evolution of male philopatry in mammals.     

Phenotype matching and inbreeding avoidance in African elephants

Perhaps the most important 'decision' made by any animal (or plant) is whether to disperse--leave kith and kin, or remain with the familiar and related. The benefits of staying at home are obvious, so dispersal requires an explanation--and the most popular is that dispersal functions to avoid inbreeding depression. Strong support comes from the observation that dispersal is so often sex biased. Simply put, all else being equal members of both sexes should prefer to remain philopatric, but this would lead to inbreeding depression so members of one sex have to disperse. In principle, this link between inbreeding depression and sex-biased dispersal could be broken if individuals recognize close kin and avoid mating with them. Archie et al. (2007) provide one of the most compelling analyses to date of the interaction among inbreeding avoidance, kin recognition and mating strategies in any mammal, clearly showing that elephants recognize even close paternal kin and avoid mating with them. Their important results illuminate the subtleties of elephant inbreeding avoidance as well as illustrate the difficulty of arriving at definitive answers to questions about the evolution of dispersal behaviour.     

Sex‐biased dispersal: a review of the theory

Dispersal is ubiquitous throughout the tree of life: factors selecting for dispersal include kin competition, inbreeding avoidance and spatiotemporal variation in resources or habitat suitability. These factors differ in whether they promote male and female dispersal equally strongly, and often selection on dispersal of one sex depends on how much the other disperses. For example, for inbreeding avoidance it can be sufficient that one sex disperses away from the natal site. Attempts to understand sex‐specific dispersal evolution have created a rich body of theoretical literature, which we review here. We highlight an interesting gap between empirical and theoretical literature. The former associates different patterns of sex‐biased dispersal with mating systems, such as female‐biased dispersal in monogamous birds and male‐biased dispersal in polygynous mammals. The predominant explanation is traceable back to Greenwood's ( 1980 ) ideas of how successful philopatric or dispersing individuals are at gaining mates or the resources required to attract them. Theory, however, has developed surprisingly independently of these ideas: models typically track how immigration and emigration change relatedness patterns and alter competition for limiting resources. The limiting resources are often considered sexually distinct, with breeding sites and fertilizable females limiting reproductive success for females and males, respectively. We show that the link between mating system and sex‐biased dispersal is far from resolved: there are studies showing that mating systems matter, but the oft‐stated association between polygyny and male‐biased dispersal is not a straightforward theoretical expectation. Here, an important understudied factor is the extent to which movement is interpretable as an extension of mate‐searching (e.g. are matings possible en route or do they only happen after settling in new habitat – or can females perhaps move with stored sperm). We also point out other new directions for bridging the gap between empirical and theoretical studies: there is a need to build Greenwood's influential yet verbal explanation into formal models, which also includes the possibility that an individual benefits from mobility as it leads to fitness gains in more than one final breeding location (a possibility not present in models with a very rigid deme structure). The order of life‐cycle events is likewise important, as this impacts whether a departing individual leaves behind important resources for its female or male kin, or perhaps both, in the case of partially overlapping resource use.