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PubMed2000

Genetic compatibility, mate choice and patterns of parentage: invited review.

There is growing interest in the possibility that genetic compatibility may drive mate choice, including gamete choice, particularly from the perspective of understanding why females frequently mate with more than one male. Mate choice for compatibility differs from other forms of choice for genetic benefits (such as 'good genes') because individuals are expected to differ in their mate preferences, changing the evolutionary dynamics of sexual selection. Recent experiments designed to investigate genetic benefits of polyandry suggest that mate choice on the basis of genetic compatibility may be widespread. However, in most systems the mechanisms responsible for variation in compatibility are unknown. We review potential sources of variation in genetic compatibility and whether there is any evidence for mate choice driven by these factors. Selfish genetic elements appear to have the potential to drive mate compatibility mate choice, though as yet there is only one convincing example. There is abundant evidence for assortative mating between populations in hybrid zones, but very few examples where this is clearly a result of selection against mating with genetically less compatible individuals. There are also numerous cases of inbreeding avoidance, but little evidence that mate choice or differential fertilization success driven by genetic compatibility occurs between unrelated individuals. The exceptions to this are a handful of situations where both the alleles causing incompatibility and the alleles involved in mate choice are located in a chromosome region where recombination is suppressed. As yet there are only a few potential sources of genetic compatibility which have clearly been shown to drive mate choice. This may reflect limitations in the potential for the evolution of mate choice for genetic compatibility within populations, although the most promising sources of such incompatibilities have received relatively little research.

Animals↗

PubMed2002

A conserved mitogen-activated protein kinase pathway is required for mating in Candida albicans.

Candida albicans had been thought to lack a mating process until the recent discovery of a mating type-like locus and mating between MTLa and MTL(alpha) strains. To elucidate the molecular mechanisms that regulate mating in C. albicans, we examined the function of Cph1 and its upstream mitogen-activated protein (MAP) kinase pathway in mating, as they are homologues of the pheromone-responsive MAP kinase pathway in Saccharomyces cerevisiae. We found that overexpressing CPH1 in MTLa, but not in MTLa/alpha strains, induced the transcription of orthologues of S. cerevisiae pheromone-induced genes and also increased mating efficiency. Furthermore, cph1 and hst7 mutants were completely defective in mating, and cst20 and cek1 mutants showed reduced mating efficiency, as in S. cerevisiae. The partial mating defect in cek1 results from the presence of a functionally redundant MAP kinase, Cek2. CEK2 complemented the mating defect of a fus3 kss1 mutant of S. cerevisiae and was expressed only in MTLa or MTL(alpha), but not in MTLa/alpha cell types. Moreover, a cek1 cek2 double mutant was completely defective in mating. Our data suggest that the conserved MAP kinase pathway regulates mating in C. albicans. We also observed that C. albicans mating efficiency was greatly affected by medium composition, indicating the potential involvement of nutrient-sensing pathways in mating in addition to the MAP kinase pathway.

Amino Acid Sequence↗

PubMed1998

Polyandrous females discriminate against previous mates.

In most animal species, particularly those in which females engage in polyandry, mate choice is a sequential process in which a female must choose to mate or not to mate with each male encountered. Although a number of theoretical and empirical investigations have examined the effects of sequential mate choice on the operation of sexual selection, how females respond to solicitation by previous mates has received little attention. Here, we report the results of a study carried out on the polyandrous pseudoscorpion, Cordylochernes scorpioides, that assessed the sexual receptivity of once-mated females presented after a lapse of 1.5 hr or 48 hr with either their first mate or a different male. Females exhibited a high level of receptivity to new males, irrespective of intermating interval. By contrast, time between matings exerted a strong effect on female receptivity to previous mates. After a lapse of 48 hr, females did not differ significantly in their receptivity toward previous mates and different males, whereas at 1.5 hr after first mating, females were almost invariably unreceptive to males from whom they had previously accepted sperm. This result could not be attributed to male size or mating experience or to male sexual receptivity. Indeed, males were as willing to transfer sperm to a previous mate as they were to a new female. This difference between males and females in their propensity to remate with the same individual may reflect a conflict between the sexes, with males seeking to minimize postcopulatory sexual selection and females actively keeping open the opportunity for sperm competition and female choice of sperm by discriminating against previous mates.

Animals↗

PubMed2006

The effect of length of use of teaser rams prior to mating and individual liveweight on the reproductive performance of ewe hoggets.

AIM: To determine the effects of liveweight (LW) and duration of teasing with vasectomised rams prior to breeding on both the mating performance and pregnancy rate of ewe hoggets. METHODS: Five hundred and forty-six (1/2) Romney x (1/4) Texel x (1/4) Finnish Landrace ewe hoggets were weighed and randomly assigned to one of three treatment groups: either exposed to five harnessed vasectomised (teaser) rams for 17 days prior to the breeding period (T17; n =181); exposed to five harnessed teaser rams for 8 days prior to the breeding period (T8; n = 184); or not exposed to teasers (unteased; n = 181). Harnessed entire rams of the same breed were then introduced for the duration of two oestrous cycles. Using crayon marks, hoggets were identified as having been mated in the first 5 days, Days 6-10, Days 11-17, during the first 17 days only, during both 17-day periods, during the second 17 days only, or not mated. All hoggets that were mated were scanned for pregnancy, using ultrasound, 48 days after the end of the breeding period, and identified as being either non-pregnant, or as singleton- or twin-bearing. RESULTS: Hoggets mated in the second 17-day period only were significantly lighter than those mated in either the first 17-day period only (p < 0.001), or in both the first and second 17-day periods (p < 0.02). At Day 1, twin-bearing hoggets were heavier than singleton-bearing hoggets (p < 0.001) and tended to be heavier (p = 0.06) than non-pregnant hoggets. At Day 18, twin-bearing hoggets were heavier than non-pregnant (p = 0.01) and singleton-bearing (p < 0.01) hoggets. A lesser proportion (p < 0.001) of unteased hoggets was mated in the first 17-day period only, compared to T17 hoggets. Conversely, a greater proportion of unteased hoggets was mated in the second 17-day period only, compared to either T8 (p < 0.01) or T17 (p < 0.001) hoggets. A lesser proportion of unteased hoggets was mated in the first 17 days of breeding, regardless of whether they returned to oestrus or not, in comparison to either T8 (p = 0.001) or T17 (p < 0.001) hoggets. Of those mated in the first 17 days of the breeding period, T8 hoggets were less likely (p < 0.05) to be mated in the first 5 days of that period but more likely to be mated in the last 7 days, compared to unteased and T17 hoggets. T17 hoggets had higher pregnancy rates to the first 17 days of breeding compared with either unteased (p = 0.01) or T8 hoggets (p = 0.06), and were more likely (p < 0.05) to be twin-bearing. In addition, the scanning percentage of T17 hoggets was higher than either unteased or T8 hoggets (p < 0.05). CONCLUSIONS: Heavier hoggets at breeding are more likely to be mated during the first 17 days of breeding and to be twin-bearing. While teasing for just 8 days increased the numbers mated in the first 17 days of breeding it did not increase the numbers of hoggets pregnant to that period. In contrast, teasing for 17 days did increase the numbers pregnant to the first 17 days of breeding and also increased the overall scanning percentage. It is recommended that farmers use a 17-day period of teasing before the breeding of ewe hoggets.

Animals↗

PubMedDate not supplied

Mating-type differentiation by transposition of controlling elements in Saccharomyces cerevisiae.

The nonfunctional mutation of the homothallic gene HML alpha, designated hml alpha, produced two mutant alleles, hml alpha-1 and hml alpha-2. Both mutant clones were mixed cultures consisting of a mating-type cells and nonmating haploid cells. The frequencies of the two cell types were different, and a few diploid cells able to sporulate were found in the hml alpha-2 mutant. Conversions of an a mating-type cell to nonmater, and vice versa, were observed in both mutants. The conversion of an a mating phenotype to nonmating is postulated to occur by alteration of the a mating type to the sterile mating-type allele in the hml alpha-1 mutant. In tetrad dissection of prototrophic diploids that were obtained by rare mating of hml alpha-1 mutants with a heterothallic strain having the MATa ho HMRa HMLa genotype, many mating-deficient haploid segregants were found, while alpha mating-type segregants were observed in a similar diploid using an hml alpha-2 mutant. The mating-type-deficient haploid segregants were supposed to have the sterile alpha mating-type allele because the nonmating genetic trait always segregated with the mating-type locus. Sporogenous diploid cells obtained in the hml alpha-2 mutant clone had the MATa/MAT alpha HO/HO HMRa/HMRa hml alpha-2/hml alpha-2 genotype. These observations suggested that the hml alpha-1 allele produces a transposable element that gives rise to the sterile alpha mating type by transposition into the mating-type locus, and that the hml alpha-2 allele produces an element that provides alpha mating-type information, but is defective in the structure for transposition.

DNA Transposable Elements↗

PubMed2002

Influence of mating ratio and group size on indicators of fearfulness and stress of hens and cocks.

The effects of the male to female mating ratio on the heterophil to lymphocyte ratio and duration of tonic immobility (indicators of stress and fearfulness, respectively) were analyzed in two different experiments with different group sizes. In Experiment 1, four different mating ratios (1:11, 1:5, 1:3, and 1:1) and 10 different Spanish breeds of chickens were used; each breeding pen had 12 birds. In Experiment 2, two different mating ratios (1:11 and 1:1) and four breeds were analyzed; 60 birds were used. There were significant differences among mating ratios (P < 0.001) for the heterophil to lymphocyte ratio in females of both group sizes. Hens housed with a mating ratio of 1:1 had higher heterophil to lymphocyte ratios than did hens housed with a 1:11 mating ratio in the group with 12 birds (0.53 vs. 0.35) or that with 60 birds (0.76 vs. 0.37). Hens in a mating ratio of 1:1 had significant heterophilia and lymphopenia (P < 0.001). The 1:5 and 1:3 male to female mating ratios did not differ significantly from the 1:11 mating ratio. The effect of the group size was significant when the mating ratio was 1:1 but not when it was 1:11. There was no significant difference among mating ratios in terms of tonic immobility for hens. Cocks housed with a mating ratio of 1:1 and a group size of 60 birds showed shorter duration of tonic immobility (P < 0.05) than did cocks housed with a 1:11 mating ratio (203 vs. 296 s). The results suggest that very high mating ratios should not be used in conservation populations because it increases physiological and psychological stress responses.

Animals↗

PubMed2000

Dynamic mate-searching tactic allows female satin bowerbirds Ptilonorhynchus violaceus to reduce searching.

Females can maximize the benefits of mate choice by finding high-quality mates while using search tactics that limit the costs of searching for mates. Mate-searching models indicate that specific search tactics would best optimize this trade-off under different conditions. These models do not, however, consider that females may use information from previous years to improve mate searching and reduce search costs in subsequent years. We followed female satin bowerbirds Ptilonorhynchus violaceus during mate searching and reconstructed their search patterns. We found that females who chose very attractive males typically mated with the same male in the following year, resulting in these females sampling fewer males than those who switched mates. In contrast, females who mated with less attractive males typically rejected their previous mates and searched longer for more attractive mates in the following mating season. A potential cost to mate searching is suggested by the observed increase in the likelihood of force-copulation attempts from marauding males with increased searching. Our results suggest that by using past experiences to adjust their search tactics, females may obtain high-quality mates while limiting search costs. These results emphasize the need to consider historical effects in studies of sexual selection, especially for long-lived species with stable display sites.

Animals↗

PubMed1976

Two-sided assortative mating for a single locus.

Most models previously considered for assortative mating were such that no change in gene frequencies occurred, or that one-sided assortative mating was occurring. Two-sided assortative mating is more realistic for human populations, and in this paper a model of two-sided assortative mating is analysed for two autosomal alleles with dominance, an important case for human genetics. The concept of a relative probability of matin between two phenotypes is used, and this variable can take into account factors such as different propensities for assortment in the various phenotypes and so forth. It is shown that the gene frequency may vary from generation to generation and conditions for the establishment of a stable polymorphism are given. For instance, Stanton (1947) has considered a special case of two-sided assortative mating with two autosomal alleles and a constant correlation between mates, where the value expressed by the heterozygote is numerically exactly half-way between the values exhibited by the two homozygotes. Also he has considered a special form of assortative mating, where the probability of occurrence of matings between the same homozygotes has been increased in each generation by the same constant factor as the probability of occurrence of matings between different homozygotes has been decreased. The probability of occurrence of matings involving heterozygotes remains the same as if mating were random. For this particular model the frequency of the genotypes in those who mate in generation t is the same as for the general population in generation t, but the genotypic frequencies change from generation to generation, reaching an equilibrium value. Stark (1976) has also considered a similar model to Stanton's (1947), the major difference occurring in the construction of the mating frequencies, which in this case occurs according to the canonical decomposition of the 2-way table of mating frequencies. Stark shows the correspondence between the results for this model and those given by Malécot (1939, 1948). The results for all these models depend on the particular values assigned to the genotypes. Also these models could be extended as outlined in this article for the case of two autosomal alleles with dominance.

Alleles↗

PubMed1994

[Hypothalamo-pituitary-testicular function in male Japanese monkeys (Macaca fuscata) in non-mating season].

We examined seasonal changes in serum testosterone and LH, and investigated mechanisms of reduction of testicular function in non-mating season in male Japanese monkeys. Blood samples were collected monthly throughout one year in 5 males, and hCG and LH-RH were administered to 5 and 3 animals, respectively, in non-mating and mating season. Serum testosterone and LH were measured by RIA. Serum testosterone showed the obvious seasonal changes, being low in March to August and high in October to February. Also we found the seasonal changes in LH being low in May to August and high in September to February. When hCG was administered to 5 monkeys in mating season (January), serum testosterone levels increased markedly 30 to 180 min after single administration and showed further increases after continuous administrations for four days. However, in non-mating season (August), serum testosterone showed a little increase for the same treatment as in mating season. These data showed that the reserve ability of testosterone secretion in testis in non-mating season decreased obviously in contrast to mating season. The increase of serum LH and testosterone levels in 3 males in non-mating season (July) after LH-RH single administration were less than those in mating season (December). In intermediate period (September) between non-mating season and mating season, LH showed higher level than that in mating season but the testosterone level was the same extent as in non-mating season.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2002

Chemo-enzymatic synthesis of the glycosylated alpha-mating factor of Saccharomyces cerevisiae and analysis of its biological activity.

The effect of glycosylation on a bioactive peptide was studied using yeast Saccharomyces cerevisiae alpha-mating factor, which is composed of 13 amino acids. In this study, we prepared glycosylated alpha-mating factor by chemo-enzymatic synthesis. At first, N-acetylglucosaminyl alpha-mating factor (Trp-His-Trp-Leu-Gln(GlcNAc)-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr) was chemically synthesized by the solid-phase method. Then, using the transglycosylation activity of Mucor hiemalis endo-beta-N-acetylglucosaminidase, we synthesized glycosylated alpha-mating factor with a glutamine-linked sialo complex type oligosaccharide. The biological activity of alpha-mating factor derivatives was examined by means of a growth arrest assay using secreted-protease-defective a cells of S. cerevisiae. The results showed that the bioactivity of glycosylated alpha-mating factor was lower than that of native alpha-mating factor. However, when sialic acid was removed from the complex type sugar chain of glycosylated alpha-mating factor, its bioactivity was recovered. Glycosylated alpha-mating factor exhibited higher resistance against proteolysis than native alpha-mating factor. It was found that the bioactivity of N-acetylglucosaminyl alpha-mating factor was higher than that of alpha-mating factor. Circular dichroism studies indicated that a slight change in the structure of alpha-mating factor may influence its activity.

Acetylglucosamine↗

PubMed2005

Female mate preference and sexual conflict: females prefer males that have had fewer consorts.

Different aspects of male quality as a mate can vary independently. When this is the case, females may need to use multiple cues to accurately assess overall mate quality. We examined the pattern of mating preference in the cockroach Nauphoeta cinerea. Sexual conflict occurs in this species because male manipulation of female mating receptivity can result in reduced female fitness. We predicted that since females cannot remate within a single reproductive bout because of male manipulation, females should assess male mating history to avoid mating with males with low fertility caused by sperm exhaustion. In a mate-preference experiment, we found that females discriminated against males who had mated multiple times. Females also discriminated against males who had consorted with several females but had been prevented from mating with those females. Thus, females appeared to be able to detect cues on males that were derived from previous mates and to use this information to avoid mating with sperm-exhausted males. We suggest that females may commonly use multiple cues to assess different aspects of mate quality, especially when male quality changes over time. This is an under-studied phenomenon that could help explain individual variation in female mating preferences.

Animals↗

PubMed1994

Isolation of the mating-type genes of the phytopathogenic fungus Magnaporthe grisea using genomic subtraction.

Using genomic subtraction, we isolated the mating-type genes (Mat1-1 and Mat1-2) of the rice blast fungus, Magnaporthe grisea. Transformation of M. grisea strains of one mating type with a linearized cosmid clone carrying the opposite mating-type gene resulted in many "dual maters," strains that contain both mating-type genes and successfully mate with Mat1-1 and Mat1-2 testers. Dual maters differed in the frequency of production of perithecia in pure culture. Ascospores isolated from these homothallic crosses were either Mat1-1 or Mat1-2, but there were no dual maters. Most conidia from dual maters also had one or the other of the mating-type genes, but not both. Thus, dual maters appear to lose one of the mating-type genes during vegetative growth. The incidence of self-mating in dual maters appears to depend on the co-occurrence of strains with each mating type in vegetative cultures. In rare transformants, the incoming sequences had replaced the resident mating-type gene. Nearly isogenic pairs produced from three M. grisea laboratory strains were mated to investigate their fertility. One transformant with switched mating type appears to have a mutation that impairs the development of asci when its mating partner has a similar genetic background. The M. grisea Mat1-1 and Mat1-2 genes are idiomorphs approximately 2.5 and 3.5 kb in length, respectively.

Ascomycota↗

PubMed1977

A new gene affecting the efficiency of mating-type interconversions in homothallic strains of Saccharomyces cerevisiae.

Homothallic strains of Saccharomyes cerevisiae are able to switch efficiently from one mating genotype to another. From a single haploid spore arise both a and mating type cells, which then self-mate to produce a colony consisting almost exclusively of nonmating a/ diploid cells. We have isolated a mutant homothallic strain that gives rise to colonies that show bisexual mating behavior. The mating reaction is always asymmetric, that is, in some colonies a mating is much stronger than mating, while others show greater than a mating.-This mating phenotype arises from the presence of three cell types in a colony: some a/ nonmating diploids and an unequal number of a and haploid cells. The predominant haploid type is that of the original cell that gives rise to the colony. This mixture of cell types arises from a very reduced efficiency of homothallic mating-type interconversions in the mutant strain.-The mutation, designated switch (swi1-1), behaves as a single genetic locus. The mutation is centromere linked, but not linked to the mating type locus or to any of the homothallism genes: HO, HMa and HM. The switch mutation does not affect the efficiency of self-mating, but rather directly affects the frequency of interconversion of mating types.

Genes, Mating Type, Fungal↗

PubMed1998

How mothers influence the development of litter-mate preferences in Belding's ground squirrels.

We performed three experiments to examine the role of mothers in the development of litter-mate preferences in captive juvenile Belding's ground squirrels, Spermophilus beldingi. First, when observed in the absence of mothers, juveniles did not play preferentially with litter-mates, which suggests that mothers somehow influence the ontogeny of litter-mate preferences. Second, when mothers were present but unable to intervene in social interactions, juveniles displayed litter-mate preferences, which suggests that mothers do not influence their offsprings' social development by directly intervening in social interactions. In another group, mothers were removed daily, a few hours before nocturnal immergence, and returned the following morning. Juveniles in this group did not display litter-mate preferences and at night they occupied burrows with many more non-litter-mates than litter-mates. These results suggest that associating with non-litter-mates can compromise the development of litter-mate preferences, and implies that mothers indirectly influence social development by affecting the identities of sleeping partners. Third, newly emergent juveniles that interacted only with litter-mates for 3 days in the absence of mothers subsequently preferred litter-mates over non-litter-mates as play partners. This result demonstrates that once litter-mate preferences are instilled, due in part to social experiences during juveniles' initial days above-ground, the preferences are expressed even in the absence of mothers. Collectively, the results demonstrate that the presence of S. beldingi mothers is important to juvenile social development, but that mothers do not actively direct the ontogeny of their offsprings' social relationships. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1999

Size-assortative mating, male choice and female choice in the curculionid beetle Diaprepes abbreviatus.

In the beetle Diaprepes abbreviatus (L.) females are larger on average than males, as indicated by elytra length. Size-assortative matings were observed in wild populations in Florida and in laboratory mating experiments. We tested three mechanisms for this size-assortative mating: (1) mate availability; (2) mating constraints; and (3) mate choice. We found that mate choice influenced size-assortative mating by: (1) large and small males preferring to mate with large females; (2) large males successfully competing for large females, leaving small males to mate with small females; and (3) females accepting large males as mates more readily than small males. Males increased their reproductive success by mating with larger, more fecund females. They transferred protein to females during mating. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1986

Ovarian development in red-sided garter snakes, Thamnophis sirtalis parietalis: relationship to mating.

Female red-sided garter snakes (Thamnophis sirtalis parietalis) exhibit a complex array of behavioral patterns. Females may mate once, more than once, or not at all in the spring of the year, and a high percentage of females may mate in late summer before returning to winter hibernacula. The role of mating in the induction of ovarian growth in this species is complicated by this pattern of spring and late summer mating. Females hibernated in the laboratory that mate on emergence in the spring exhibit higher frequencies of ovarian recrudescence than females that do not mate when exposed to males. Yet neither male courtship nor mating in the spring is required for ovarian development. However, mated and unmated females collected in the field in the spring of the year do not differ in frequencies of ovarian recrudescence. Ovarian growth in unmated females collected in the spring parallels the incidence of mating in the previous late summer. Thus, mating may influence the initiation of ovarian growth, but the effect can occur immediately (from spring mating) or be stored over winter (from late summer mating). Large year-to-year variation in reproductive rates of female red-sided garter snakes suggests that other factors such as nutrition and stored energy reserves may modify the effects of mating on ovarian growth.

Animals↗

PubMed1995

Mating in the monogamous male: behavioral consequences.

In monogamous mammals, males typically show selective affiliation with a single mate, high levels of paternal care, and aggression towards conspecifics to protect male and offspring. We have previously described how selective aggression and affiliation increase after mating in the male prairie vole, Microtus ochrogaster. The current studies further explored the behavioral changes that follow mating in the male of this species. The first set of experiments tested males on several behavioral measures after 24 h of either mating, social (but not sexual) exposure, or no social contact. After 24 h of mating, but not after the other two conditions, aggression and affiliation (partner preference) increased as previously reported. In addition, mated animals showed increased exploration of the open arms of a plus maze, consistent with decreased fearfulness. There were no group differences in paternal behavior (which was high in all three conditions) or analgesia (assessed by tail flick latency). To determine the minimum amount of mating necessary for the induction of aggression, males were tested in a resident-intruder paradigm after 1,6, or 24 h of mating. Although 1 h of mating was associated with a transient increase in the frequency of threats and attacks, the full spectrum of enduring aggression was observed only in the males given 24 h of mating. In a final experiment, the behavioral consequences of mating were studied in males of the closely related montane vole (Microtus montanus) which does not pair bond. Males of this nonmonogamous vole species did not show increased aggression, partner preference, or alterations in plus maze exploration following 24 h of mating. These results demonstrate the importance of prolonged mating for the induction of pair bonding in the monogamous male and they suggest that increases in aggression and affiliation are associated with decreased fearfulness in pair bonded males.

Aggression↗

PubMed2000

Why do females mate multiply? A review of the genetic benefits.

The aim of this review is to consider the potential benefits that females may gain from mating more than once in a single reproductive cycle. The relationship between non-genetic and genetic benefits is briefly explored. We suggest that multiple mating for purely non-genetic benefits is unlikely as it invariably leads to the possibility of genetic benefits as well. We begin by briefly reviewing the main models for genetic benefits to mate choice, and the supporting evidence that choice can increase offspring performance and the sexual attractiveness of sons. We then explain how multiple mating can elevate offspring fitness by increasing the number of potential sires that compete, when this occurs in conjunction with mechanisms of paternity biasing that function in copula or post-copulation. We begin by identifying cases where females use pre-copulatory cues to identify mates prior to remating. In the simplest case, females remate because they identify a superior mate and 'trade up' genetically. The main evidence for this process comes from extra-pair copulation in birds. Second, we note other cases where pre-copulatory cues may be less reliable and females mate with several males to promote post-copulatory mechanisms that bias paternity. Although a distinction is drawn between sperm competition and cryptic female choice, we point out that the genetic benefits to polyandry in terms of producing more viable or sexually attractive offspring do not depend on the exact mechanism that leads to biased paternity. Post-copulatory mechanisms of paternity biasing may: (1) reduce genetic incompatibility between male and female genetic contributions to offspring; (2) increase offspring viability if there is a positive correlation between traits favoured post-copulation and those that improve performance under natural selection; (3) increase the ability of sons to gain paternity when they mate with polyandrous females. A third possibility is that genetic diversity among offspring is directly favoured. This can be due to bet-hedging (due to mate assessment errors or temporal fluctuations in the environment), beneficial interactions between less related siblings or the opportunity to preferentially fertilise eggs with sperm of a specific genotype drawn from a range of stored sperm depending on prevailing environmental conditions. We use case studies from the social insects to provide some concrete examples of the role of genetic diversity among progeny in elevating fitness. We conclude that post-copulatory mechanisms provide a more reliable way of selecting a genetically compatible mate than pre-copulatory mate choice. Some of the best evidence for cryptic female choice by sperm selection is due to selection of more compatible sperm. Two future areas of research seem likely to be profitable. First, more experimental evidence is needed demonstrating that multiple mating increases offspring fitness via genetic gains. Second, the role of multiple mating in promoting assortative fertilization and increasing reproductive isolation between populations may help us to understand sympatric speciation.

Animals↗