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PubMed1997

Effects of paced mating on c-fos gene expression in the female rat brain.

When estrous female rats control or pace (P) their sexual contacts with males, several neuroendocrine and behavioral responses to mating occur that are not observed or are greatly attenuated after nonpaced mating. The present study examined whether the distribution and amount of FOS immunoreactivity (FOS-IR) induced in brain by mating would be altered in females receiving paced rather than nonpaced mating stimulation. In the first experiment, females received 5 or 15 intromissions during paced mating tests (5P and 15P), 5 or 15 intromissions during nonpaced mating tests (5NP and 15NP), 15 mounts-without-intromission (MO) or remained in their homecages (HC). Selective increases 1 h after paced mating stimulation were observed in the posterodorsal medial amygdala (MePD), where significantly more FOS-IR cells were present in the 5P and 15P groups than in the respective NP groups. The 5P, 5NP and 15NP had significantly more FOS-IR than the HC, MO, and 5NP groups, and the 5P group had levels of FOS-IR which were equivalent to that seen in the 15NP group. In the posteromedial portion of the bed nucleus of the stria terminalis (BNSTpm) and the ventrolateral portion of the ventromedial nucleus of the hypothalamus (VMHvl), paced mating induced significantly greater numbers of FOS-IR cells than did either MO or HC treatments; increases induced by nonpaced mating were not statistically greater than HC controls. No differences between groups were seen in the medial preoptic area (mPOA). In the second experiment, experimentally lengthening the interintromission interval (III) as well as increasing the intromission duration to mimic the characteristics of paced mating, resulted in significant increases in FOS-IR in the MePD but not in the other three brain regions. These results demonstrate that paced mating is more effective in inducing c-fos expression than nonpaced mating, and that the MePD is particularly sensitive to differing characteristics of the mating stimuli received.

Animals↗

PubMed1998

Olfactory contribution to Fos expression during mating in inexperienced male hamsters.

Male hamsters are very dependent on chemosensory cues for normal mating behavior. We have previously reported that central, vomeronasal pathways are intensely and selectively activated during mating or pheromonal stimulation. The contribution of main olfactory sensory input to the patterns of c-fos activation was investigated in this study. Sexually inexperienced male hamsters were either made anosmic by intranasal infusion of zinc sulfate or remained intact. Fos protein immunoreactivity was analyzed in main olfactory and vomeronasal pathways of the zinc sulfate-treated, anosmic animals after mating with receptive females for 45 min, and compared with Fos patterns seen in intact mating animals, some of which have been described in a previous publication. The zinc sulfate-treated anosmic males described here all mated when given access to receptive females. Whether mated or unstimulated, anosmic males had little or no Fos expression in main olfactory pathways; significantly less even than in unstimulated intact animals. Mating did not increase Fos expression in main olfactory pathways of intact animals over that of unstimulated intact controls. However, Fos expression in central vomeronasal pathways was significantly higher in mating anosmic males, as in intact males, compared with appropriate non-mating controls. Fos expression was significantly different between intact and zinc sulfate-treated anosmic mating males in only one area studied. The rostral anterior medial amygdala, known to receive a small olfactory terminal field, had significantly lower Fos expression in zinc sulfate-treated anosmic males that mated when compared with intact-mating animals. Thus, functional main olfactory input to the rostral vomeronasal amygdala can be demonstrated but does not appear to be critical for mating behavior in previously inexperienced male hamsters with intact vomeronasal organs. Other main olfactory input appears to have a negligible contribution to Fos-patterns in such animals.

Animals↗

PubMed2000

Sperm precedence in a novel context: mating in a sessile marine invertebrate with dispersing sperm.

The compound ascidian Diplosoma listerianum releases aquatic sperm which are dispersed passively to potential mates as individual gametes prior to storage of sperm, internal fertilization and brooding of embryos. The storage of exogenous sperm enables D. listerianum to produce a lengthy series of progeny following a brief period of mating. Molecular paternity analysis following sequential mating of colonies in laboratory culture revealed a consistent pattern with a clear initial bias in paternity towards the first of two acting males. The sites of sperm storage and fertilization and the morphology of the ovary in D. listerianum suggest that this bias reflects first-in-first-out use of individual stored gametes. The proportion of second-male paternity subsequently increased with time within the progeny arrays. This may have reflected the ageing or passive loss of first-male sperm. It is also possible that the modular nature of the organism contributed to this temporal trend: any recently budded colony modules maturing in the interval between matings would have been available exclusively to second-male sperm as virgin zooids. Two sets of mating trials were run. In the first, the collection of progeny suffered an interruption of 13 days and each male gained a larger proportion of recorded paternity within the progeny analysed when mating first rather than when mating second. In one mating combination, the first male obtained almost 100% of recorded paternity. In the second set of trials, with different clonal combinations, the complete sequence of progeny was collected and the estimated overall proportion of second-male paternity (P2) was consistently > 0.5. Taken as a whole, the results suggest that the overall P2-value can vary widely within the population studied. Proposed mechanisms of mating-order effects in species with copulatory mating include several which can have no counterpart in indirect aquatic mating since they involve the active removal, sealing off, volumetric displacement or incapacitation of first-male ejaculates. It is nevertheless clear that mating-order effects can be pronounced during the type of non-copulatory mating examined here, which is widespread in marine invertebrates.

Animals↗

PubMed2006

Lonely hearts or sex in the city? Density-dependent effects in mating systems.

Two very basic ideas in sexual selection are heavily influenced by numbers of potential mates: the evolution of anisogamy, leading to sex role differentiation, and the frequency dependence of reproductive success that tends to equalize primary sex ratios. However, being explicit about the numbers of potential mates is not typical to most evolutionary theory of sexual selection. Here, we argue that this may prevent us from finding the appropriate ecological equilibria that determine the evolutionary endpoints of selection. We review both theoretical and empirical advances on how population density may influence aspects of mating systems such as intrasexual competition, female choice or resistance, and parental care. Density can have strong effects on selective pressures, whether or not there is phenotypic plasticity in individual strategies with respect to density. Mating skew may either increase or decrease with density, which may be aided or counteracted by changes in female behaviour. Switchpoints between alternative mating strategies can be density dependent, and mate encounter rates may influence mate choice (including mutual mate choice), multiple mating, female resistance to male mating attempts, mate searching, mate guarding, parental care, and the probability of divorce. Considering density-dependent selection may be essential for understanding how populations can persist at all despite sexual conflict, but simple models seem to fail to predict the diversity of observed responses in nature. This highlights the importance of considering the interaction between mating systems and population dynamics, and we strongly encourage further work in this area.

Animals↗

PubMedDate not supplied

Genetic and environmental factors affecting mating type frequency in natural isolates of Tetrahymena thermophila.

In Tetrahymena thermophila mating type alleles specify temperature sensitive frequency distributions of multiple mating types. A-like alleles specify mating types I, II, III, V and VI, whereas B-like alleles specify mating types II through VII. We have characterized the mating type distributions specified by several A- and B-like genotypes segregated by genomic exclusion from cells isolated from a pond in northwestern Pennsylvania. The B-like genotypes are alike in specifying very low frequencies of mating type III, but differ with respect to the frequencies of other mating types, particularly II and VII. An A-like genotype specifies a high frequency of mating type III and is unstable in successive generations for the expression of mating type II, suggesting a possible modifier. Inter se crosses performed at 18 degrees C, 28 degrees C and 34 degrees C showed that each genotype specifies a frequency distribution that is uniquely affected by temperature. No mating type was affected the same way by temperature in all genotypes. In A/B heterozygotes, the B-like genotype exhibited partial dominance. The genotypes described here differ significantly from previously described genotypes from the same pond, indicating that there are numerous mating type alleles. For frequency-dependent selection to equalize mating type frequencies, it must act not only on complex multiple alleles but also on the response of mating type alleles to temperature.

Alleles↗

PubMed1990

Effects of breeding season and mating on total number and distribution of spermatozoa in the epididymis of the brown marsupial mouse, Antechinus stuartii.

Changes in the number and distribution of spermatozoa in the epididymis of the adult brown marsupial mouse were examined during July/August in mated and unmated males. The effects of mating on epididymal sperm populations were studied in 2 groups of males each mated 3 times and compared with the number and distribution of spermatozoa in the epididymides of 4 unmated control groups. One testis and epididymis were removed from each animal (hemicastration) either before or early in the mating season to provide information on initial sperm content and distribution. The contralateral side was removed later in the mating season to examine the effects of mating or sexual abstinence on epididymal sperm distribution. Epididymal sperm number peaked in both the distal caput and distal corpus/proximal cauda epididymidis in late July. The total number of spermatozoa, including those remaining in the testis, available to each male at the beginning of the mating season in early August was approximately 4.4 x 10(6)/side. Although recruitment of spermatozoa into the epididymis from the testis continued until mid-August, sperm content of the epididymis reached a peak of about 3.5 x 10(6)/epididymis in early August. At this time approximately 0.9 x 10(6) spermatozoa remained in the testis which had ceased spermatogenic activity. Throughout the mating season, epididymal spermatozoa were concentrated in the distal corpus/proximal cauda regions of the epididymis and were replenished by spermatozoa from upper regions of the duct. Relatively few spermatozoa were found in the distal cauda epididymidis, confirming a low sperm storage capacity in this region. A constant loss of spermatozoa from the epididymis, probably via spermatorrhoea, occurred throughout the mating season and very few spermatozoa remained in unmated males in late August before the annual male die-off. Mating studies showed that an average of 0.23 x 10(6) spermatozoa/epididymis were delivered per mating in this species, but the number of spermatozoa released at each ejaculation may be as few as 0.04 x 10(6)/epididymis when sperm loss via spermatorrhoea is taken into account. We suggest that the unusual structure of the cauda epididymidis, which has a very restricted sperm storage capacity, may function to limit the numbers of spermatozoa available at each ejaculation and thus conserve the dwindling epididymal sperm reserves in order to maximize the number of successful matings which are possible during the mating season.

Animals↗

PubMed1997

Effects of mating dynamics and crowding on sex ratio variance in mice.

Mating units of six virgin females and one adult stud male were established to test for the effects of timing of mating and crowding of pregnant females on litter sex ratios in mice. Females either copulated during periods when no other female of the mating unit copulated simultaneously (single mating condition) or when more than one female copulated (multiple matings condition). Two crowding conditions were imposed on the animals: the females of 14 mating units were placed into individual cages after mating (isolated condition), while females of the other 13 mating units remained in the original group until shortly before littering (crowded condition). Sex ratio variance did not deviate from random expectation in litters arising from the multiple matings periods. However, in litters arising from single mating periods, extreme sex ratios were found significantly less frequently than expected by chance. Higher sex ratio variance in litters arising from multiple matings periods is attributed to the timing of mating being at higher variance under this condition, which is known to affect sex ratios in other rodents. Crowding significantly reduced sex ratio variance further. Reduced sex ratio variance under single mating and crowded conditions is speculated to follow from competition for resources between preimplantation embryos, which may be further increased by stressful effects of crowding. Loss of embryos after implantation appeared not to be responsible for the above effects.

Animals↗

PubMed2002

Human mate guarding.

Long-term committed mating is a fundamental strategy in the human repertoire. Successful enactment of this strategy requires solving two related adaptive problems--fending off potential mate poachers and preventing a mates from defecting. Mate guarding adaptations evolved to solve these persistent problems. Those who failed in mate guarding risked suffering substantial reproductive costs ranging from genetic cuckoldry to reputational damage to the entire loss of a mate. Because the precise nature of the adaptive problems confronted differed historically for the sexes, men and women evolved corresponding differences in the underlying psychology of mate guarding. Men's mate guarding, relative to that of women's, is strongly triggered as a consequence of being mated to young and physically attractive women, being confronted by interested rivals who have superior economic resources or prospects, and having a mate who displays signs of sexual involvement with a rival. Women's mate guarding, relative to that of men's, is triggered as a consequence of being mated to men high in income and status striving, rivals who are more physically attractive, and having a partner who shows signs of emotional involvement with another woman. Behavioral output of mate guarding adaptations range from vigilance to violence.

Behavior Control↗

PubMed2005

The transition to social inbred mating systems in spiders: role of inbreeding tolerance in a subsocial predecessor.

The social spiders are unusual among cooperatively breeding animals in being highly inbred. In contrast, most other social organisms are outbred owing to inbreeding avoidance mechanisms. The social spiders appear to originate from solitary subsocial ancestors, implying a transition from outbreeding to inbreeding mating systems. Such a transition may be constrained by inbreeding avoidance tactics or fitness loss due to inbreeding depression. We examined whether the mating system of a subsocial spider, in a genus with three social congeners, is likely to facilitate or hinder the transition to inbreeding social systems. Populations of subsocial Stegodyphus lineatus are substructured and spiders occur in patches, which may consist of kin groups. We investigated whether male mating dispersal prevents matings within kin groups in natural populations. Approximately half of the marked males that were recovered made short moves (< 5m) and mated within their natal patch. This potential for inbreeding was counterbalanced by a relatively high proportion of immigrant males. In mating experiments, we tested whether inbreeding actually results in lower offspring fitness. Two levels of inbreeding were tested: full sibling versus non-sib matings and matings of individuals within and between naturally occurring patches of spiders. Neither full siblings nor patch mates were discriminated against as mates. Sibling matings had no effect on direct fitness traits such as fecundity, hatching success, time to hatching and survival of the offspring, but negatively affected offspring growth rates and adult body size of both males and females. Neither direct nor indirect fitness measures differed significantly between within patch and between-patch pairs. We tested the relatedness between patch mates and nonpatch mates using DNA fingerprinting (TE-AFLP). Kinship explained 30% of the genetic variation among patches, confirming that patches are often composed of kin. Overall, we found limited male dispersal, lack of kin discrimination, and tolerance to low levels of inbreeding. These results suggest a history of inbreeding which may reduce the frequency of deleterious recessive alleles in the population and promote the evolution of inbreeding tolerance. It is likely that the lack of inbreeding avoidance in subsocial predecessors has facilitated the transition to regular inbreeding social systems.

Animals↗

PubMed2000

Intratetrad mating, heterozygosity, and the maintenance of deleterious alleles in Microbotryum violaceum (=Ustilago violacea).

The mating system of Microbotryum violaceum was investigated in populations that are polymorphic for mating-type bias, where individuals produce viable haploids of only one of the two required mating types. The cause of mating-type bias was identified as deleterious recessive alleles linked to mating type. Maintenance of the deleterious alleles was promoted by early conjugation among products of single meioses, such that the duration of the free-living haploid stage is minimized. This development was also observed in nonbiased isolates. As a consequence, the mating system tends toward mating within the tetrad, which might be expected to reduce heterozygosity. However, complete centromere linkage of mating type ensures conjugation between first division meiotic products, such that mating in M. violaceum is analogous to forms of meiotic parthenogenesis with first division restitution (i.e. automixis with central fusion). This fungus was used to test the prediction that this mating system would maintain heterozygosity in regions of the genome linked to centromeres. Therefore, populations were screened for additional heterozygous lethal recessive alleles linked to centromeres, and several examples were found. Furthermore, the occurrence of intratetrad mating in M. violaceum provides an explanation for low variation among individuals within populations, inconsistent estimates of outcrossing rates, low levels of mating between tetrads of one diploid individual, and high frequencies of haplo-lethal alleles in natural populations.

Alleles↗

PubMed2000

The evolution of polyandry: multiple mating and female fitness in insects.

Theory suggests that male fitness generally increases steadily with mating rate, while one or a few matings are sufficient for females to maximize their reproductive success. Contrary to these predictions, however, females of the majority of insects mate multiply. We performed a meta-analysis of 122 experimental studies addressing the direct effects of multiple mating on female fitness in insects. Our results clearly show that females gain directly from multiple matings in terms of increased lifetime offspring production. Despite a negative effect of remating on female longevity in species without nuptial feeding, the positive effects (increased egg production rate and fertility) more than outweigh this negative effect for moderate mating rates. The average direct net fitness gain of multiple mating was as high as 30-70%. Therefore, the evolutionary maintenance of polyandry in insects can be understood solely in terms of direct effects. However, our results also strongly support the existence of an intermediate optimal female mating rate, beyond which a further elevated mating rate is deleterious. The existence of such optima implies that sexual conflict over the mating rate should be very common in insects, and that sexually antagonistic coevolution plays a key role in the evolution of mating systems and of many reproductive traits. We discuss the origin and maintenance of nuptial feeing in the light of our findings, and suggest that elaborate and nutritional ejaculates may be the result of sexually antagonistic coevolution. Future research should aim at gaining a quantitative understanding of the evolution of female mating rates. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1988

Processes of pair formation leading to assortative mating in biological populations: dynamic interaction model.

A model of pair formation that treats mating between two individuals as a dynamic process rather than an instant event is suggested. A number of cases corresponding to polygamous and monogamous matings of individuals are considered. The individual mating preferences are represented in the model by a set of "compatibility probabilities." It is shown that the mating pattern (the distribution of characters among mating pairs) established in a population as a result of the process of pair formation does not uniquely reflect the pattern of mating preferences. Quite different mating patterns may occur in populations with very similar mating preferences, as well as similar mating patterns may occur in populations with different individual mating preferences. The model demonstrates that not only mating preferences of individuals but also specific mechanisms of pair formation play an important role in determining the mating pattern of a population.

Animals↗

PubMed2001

Mating-activated brainstem catecholaminergic neurons in the female rat.

Central catecholaminergic systems play an important role in the control of reproductive activities including sexual behavior, luteinizing hormone (LH) and prolactin secretion. It has been reported that catecholaminergic neurons in the locus coeruleus (A6) are activated by mating in rabbits and ferrets, animals known as reflex ovulators. This study used Fos as a marker of neuronal activity to examine whether brainstem catecholaminergic neurons are activated by mating in the spontaneous ovulator, the female rat. Proestrous rats receiving intromissions (mated group) from males or mounts-without-intromission (mounted group) were sacrificed along with rats taken directly from their home cage (control group) 90 min after the beginning of mating or mounting. Double-label immunocytochemistry was used to examine the expression of c-Fos in catecholaminergic neurons labeled by tyrosine hydroxylase (TH) antibody, or adrenergic neurons labeled by phenylethanolamine-N-methyl transferase (PNMT) antibody. Double label immunofluorescent immunohistochemistry was used to determine the number of neurons containing the estrogen receptor (ERalpha) that were activated by mating in these brain areas. The results showed that mating-with-intromissions induced a significant increase in the percentage of TH/Fos colabeled neurons in both A1 and A2 cells compared to mounting-without-intromission or control. In both these areas, over 50% ERalpha-ir neurons were activated after mating while mounting-without-intromission did not affect the percentage of colabeled Fos/ERalpha neurons. In A6 region, neither the expression of Fos nor the percentage of TH/Fos colabeled cells was influenced by either mating or mounting compared to controls. The percentage of PNMT-containing neurons colabeled with Fos was not different in C1 and C2 among the three experimental groups. The results indicate that catecholaminergic neurons were activated by mating in A1 and A2 but not in adjoining adrenergic C1 and C2 cells. In contrast to the findings that catecholaminergic neurons in A6 are activated by mating in induced ovulators, mating did not affect neuronal activity in A6 neurons in the female rat. In A1 and A2 areas, a high percentage of neurons containing ERalpha were activated by mating suggesting both tactile and hormonal information may converge on these populations of neurons. The activated catecholaminergic neurons in A1 and A2 may be an important pathway by which sensory information generated during sexual interaction modulates both behavior and pituitary function.

Animals↗

PubMed2003

Shared ITS DNA substitutions in isolates of opposite mating type reveal a recombining history for three presumed asexual species in the filamentous ascomycete genus Alternaria.

About 15,000 species of ascomycete fungi lack a known sexual state. For fungi with asexual states in the anamorph genera Embellisia, Ulocladium, and Alternaria, six species have known sexual states but more than 50 species do not. In sexual filamentous ascomycetes, opposite mating type information at the MAT1 locus regulates mating and the opposite mating type genes each have a clonal, non-recombining phylogenetic history. We used PCR to amplify and sequence fragments of the opposite mating type genes from three supposedly asexual species, A. brassicae, A. brassicicola and A. tenuissima. Each haploid fungal isolate had just one mating type, but both mating types were present in all the three species. We sequenced the ribosomal ITS regions for isolates of opposite mating type, for the three asexual species and four known related sexual species. In a phylogenetic analysis including other ITS sequences from GenBank, the three asexual species were not closely related to any of the known sexual species. Isolates of opposite mating type but the same species had identical ITS sequences. During any period of asexual evolutionary history, lineages of each mating type would have had a separate evolutionary history and any ITS substitutions shared between isolates of opposite mating type would have had to accumulate by convergence. Allowing for varying substitution rates and assuming a Poisson distribution of substitutions, the probability that isolates of opposite mating type shared an ITS substitution through convergence was low. This suggests that isolates of opposite mating type of A. brassicae, A. brassicicola and A. tenuissima were exchanging substitutions through sexual or parasexual reproduction while the ITS was evolving. If sexuality was lost, it was lost after the period of evolutionary history represented by the shared substitutions.

Alternaria↗

PubMed2001

Mating behaviour of Rhytidoponera sp. 12 ants inferred from microsatellite analysis.

In the queenless ponerine ant Rhytidoponera sp. 12, all workers have a spermatheca and functional ovaries and are potentially able to mate and reproduce. Within a colony gamergates may either be full sisters to each other (Type 1 colony), or they may not be full sisters but still be significantly related to each other (Type 2 colony) due to daughter gamergates reproducing in their natal colonies after mating. Despite many studies the mating behaviour of R. sp. 12 has been poorly understood. In this study, we used microsatellite markers to investigate intracolony relatednesses of male mates to the gamergates (bmq) and between male mates (bmm), and mating frequencies and mating patterns, using gamergate DNA and sperm DNA isolated from the spermathecae of gamergates from five colonies. Average bmm and bmq estimates for all five colonies studied were not significantly different from zero, suggesting that on average, within colonies, mating males were unrelated both to each other and to the gamergates. A low frequency (3%) of multiple mating by gamergates was detected. Multiple mating by individual males with sister gamergates within Type 1 colonies was also detected at 3% and could give rise to half-sister nestmate workers. Polygamy in R. sp. 12 might indicate local female-biased operational sex ratios despite the expectation of overall male biases. Our results concur with previous reports that gamergates mate within the colony or nearby, but indicate more diversity in mating patterns than previously indicated for this polygynous ponerine ant species.

Animals↗

PubMed2002

Delayed mating reduces reproductive output of female European grapevine moth, Lobesia botrana (Lepidoptera: Tortricidae).

Virgin females of Lobesia botrana Denis & Schiffermüller were mated at ages of 1, 3, 5, 8, 12 and 16 days and the effect of mating delay on reproductive output assessed. Delayed mating did not affect female mating success but fertilization was reduced in 16-day-old females. Increased mating delays substantially affected daily oviposition pattern and resulted in a significant reduction of both fecundity and fertility, so that mean number of viable eggs laid decreased from 150 to 22 in 1- and 16-day-old mated females, respectively. Heavier females were more constrained than lighter ones by mating delays and female reproductive efficiency (no. viable eggs/female body weight) was also significantly reduced. Female longevity significantly increased and oviposition period gradually declined with mating delay. The number of viable eggs was positively correlated with both female weight and oviposition period; female longevity and female weight were also significantly correlated. However, the significance of these correlations declined with increased mating delay. Results overall indicated that mating delay drastically reduces female L. botrana reproductive output. The implications of delayed mating of females are discussed from an ecological perspective in relation to L. botrana control using mating disruption.

Animals↗

PubMed1992

Compensatory development in preimplantation mouse embryos derived from delayed mating.

Rodent embryos resulting from delayed mating grow relatively faster than those resulting from normal mating. To evaluate this phenomenon quantitatively, in the present study we compared the number of cells at the preimplantation stage of mouse embryos derived from normal mating and those derived from delayed mating (3 and 6 h after ovulation). The mean cell numbers (45.4 and 43.0 for delayed mating at 3 and 6 h postovulation, respectively) of embryos at 77 h postcoitus (hpc) in the delayed mating groups were greater than that (38.4) of the normal mating group. Further, when the mean cell numbers (38.8 and 38.5) in the delayed mating groups were counted at 74 hpc, they were almost equal to that of the normal mating group at 77 hpc. The study demonstrated that preimplantation mouse embryos derived from delayed mating progress more rapidly than their normally mated counterparts. However, a 3-h advance in development seems to be the limit of this increased rate of growth, even when the time interval from ovulation to mating is longer than 3 h. The mechanism(s) of this interesting compensatory phenomenon should be investigated.

Animals↗

PubMed2001

'Good genes as heterozygosity': the major histocompatibility complex and mate choice in Atlantic salmon (Salmo salar).

According to the theory of mate choice based on heterozygosity, mates should choose each other in order to increase the heterozygosity of their offspring. In this study, we tested the 'good genes as heterozygosity' hypothesis of mate choice by documenting the mating patterns of wild Atlantic salmon (Salmo salar) using both major histocompatibility complex (MHC) and microsatellite loci. Specifically, we tested the null hypotheses that mate choice in Atlantic salmon is not dependent on the relatedness between potential partners or on the MHC similarity between mates. Three parameters were assessed: (i) the number of shared alleles between partners (x and y) at the MHC (M(xy)), (ii) the MHC amino-acid genotypic distance between mates' genotypes (AA(xy)), and (iii) genetic relatedness between mates (r(xy)). We found that Atlantic salmon choose their mates in order to increase the heterozygosity of their offspring at the MHC and, more specifically, at the peptide-binding region, presumably in order to provide them with better defence against parasites and pathogens. This was supported by a significant difference between the observed and expected AA(xy) (p = 0.0486). Furthermore, mate choice was not a mechanism of overall inbreeding avoidance as genetic relatedness supported a random mating scheme (p = 0.445). This study provides the first evidence that MHC genes influence mate choice in fish.

Alleles↗