Strict Monogamy Research Articles

Partner recognition in a perennially monogamous pipefish, Corythoichthys haematopterus

The pipefish Corythoichthys haematopterus, which forms lifelong pair bonds and exhibits strict monogamy, performs a daily ritualized intrapair interaction, called the greeting. Cross-pairing experiments were performed to examine the capacity for partner recognition in C. haematopterus during the greeting. When pair members were released into an artificially constructed greeting arena, they exhibited typical greeting behavior immediately after contact. In contrast, when males and females from different pairs met, almost no displays were exchanged. These results strongly suggest that paired C. haematopterus can recognize their own partners, irrespective of the meeting location.

Male Ornamentation in a Sex‐Role Reversed Pipefish Corythoichthys haematopterus

AbstractSexual selection theory predicts that mating competition in sex‐role reversed animals acts more strongly on females than males and consequently females are expected to develop secondary sexual traits. However, in a sex‐role reversed pipefish Corythoichthys haematopterus (family: Syngnathidae), only males develop an ornamental trait on the thorax, consisting of approx. 3–5 speckles alternated by lateral stripes of brilliant light blue and orange. To understand the function of this male ornament, we examined whether the presence of females affects the expression of this trait, and whether the expression of this trait depends on the male’s physical condition. Individual males were reared in a tank for a month in four different conditions: in high or low food supply and in the presence or absence of a female. After 1 mo, males in better condition expressed larger and deeper blue and yellow speckles, and males maintained with a female expressed larger and deeper blue speckles than solely reared males. These results indicated that the male ornament functions as a signal conveying information on the phenotypic quality of its holder and that females are potential receivers of this signal. Because C. haematopterus exhibits strict monogamy and competition for a mate occurs only among females, we concluded that the male ornament is not displayed in the context of mating competition but rather it is used as a cue for partner recognition to maintain pair bond.

Mediating the Good Life: Prostitution and the Japanese Woman's Christian Temperance Union, 1880s-1920s

This article examines how the Japanese Woman's Christian Temperance Union, in the name of promoting liberty and rights of women in their relations with men, constructed hierarchies to ascribe value to themselves through moral condemnation. The JWCTU used extramarital sex as a political issue to strengthen the position of the legal wife in the household as opposed to the concubine and prostitute. Their efforts to prohibit Japanese women from going abroad as prostitutes, while understood as an attempt to end a system of slavery that violated the inherent rights of Japanese womanhood, was actually a desire to regulate the behaviour of the poor. The JWCTU based its moral reform agenda on the importance of premarital chastity, strict monogamy and the obligation to work for the good of the nation. Its construction of prostitution as evil represents an important strand in the history of the relationship between prostitution and family as a socio-political issue in modern Japan.

Mutual Mate Choice Can Drive Costly Signaling Even Under Perfect Monogamy

Models of sexual selection by mate choice have emphasized the evolution of sexually dimorphic costly signals, such as elaborate plumage or courtship display, in the sex exhibiting higher reproductive skew, usually males. Less well explored is the action of mutual mate choice in driving signal evolution in socially monogamous or near-monogamous populations. We present a simulation model of condition-dependent investment in a signal trait under conditions of perfect monogamy, equal initial offspring number, and differential offspring mortality based on inherited genetic quality minus signal cost. The model demonstrates persistent evolution of high-cost sexual ornaments through mutual mate choice, even under strict monogamy, as long as the phenotypic condition is sufficiently heritable, and the monomorphic ornament reflects condition with sufficient accuracy to allow positive assortative mating. We discuss implications for research on sexual selection, mate choice, mutation-selection balance, and human evolution.

Understanding mating systems: A mathematical model of the pair formation process

Mechanisms generating inequalities among males in reproductive success are key to understanding the evolutionary significance of sexual selection. This paper develops a stochastic model to quantitatively describe and analyze mating systems on a continuous scale from strict monogamy to extreme polygyny. The variance in male mating success is shown to increase with increased differences among males, with decreased interdependence of mating events, with increased population size, and with an increased number of females per male. The latter condition decreases the opportunity for sexual selection. It is found that different combinations of mating system characteristics can lead to the same variance in male mating success, although the distribution differs. This emphasizes the importance of using a model of this type to study mating systems, rather than relying solely on the variance in reproductive success as a descriptor of different systems.

Are parthenogenetic and sexual Ischnura hastata damselflies equally fertile? Testing sexual conflict theories

Recent theories of sexual selection stress the importance of conflicts over reproduction in shaping the reproductive traits of males and females. Except when the reproductive interests of both sexes coincide, which only occurs under strict monogamy, there is a conflict of interests between the sexes over the number of matings and reproductive decisions. It has been suggested that males are selected to “harm” females if this increases male reproductive success, even at the expenses of female fitness. One prediction of such an hypothesis is that sperm is selected to maximize the probability of fertilization, and this sometimes can cause a decrease in fertility due to multispermy, genetic incompatibility, toxic seminal products that harm females, etc. We have tested this hypothesis by comparing the fertility rates of parthenogenetic and sexual Ischnura hastata populations. Our results show that sexual females are less fertile than parthenogenetic ones, which is in agreement with the sexual conflict predictions tested in this study.

Mate Change Reduces the Reproductive Rate of Males in a Monogamous Pipefish Corythoichthys haematopterus: The Benefit of Long‐Term Pair Bonding

AbstractMonogamy has evolved independently in many taxa, and often involves biparental care of the young and/or low defendability of multiple mates. In many teleost fishes, however, strict monogamy is practised without such limitations. In this study, we examined why males of the pipefish Corythoichthys haematopterus (family: Syngnathidae) reproduce monogamously without changing to another mate. For this we examined the time cost associated with mate change by experimentally removing females from mating pairs and compelling the males to change mates. Mate‐changing males needed longer interspawning intervals, an average of 8.5 d, than their monogamous counterparts, which was primarily because of the time needed for the new female to prepare mature eggs. As a result, we assume that mate change entails considerable reproductive costs associated with a decrease in reproductive rate. Monogamy and long‐term pair bonding in C. haematopterus are likely maintained because of high reproductive rates by repeatedly reproducing with the same mate over a lifetime.

Genetic monogamy despite social promiscuity in the pot‐bellied seahorse (Hippocampus abdominalis)

Sexual selection theory predicts a positive correlation between relative parental investment and mate choice. In syngnathid fishes (seahorses and pipefish), males brood offspring in specialized brooding structures. While female-female mating competition has been demonstrated in some pipefishes, all seahorses (genus Hippocampus) studied to date have been found to have conventional sex roles with greater male-male competition for access to mates despite possessing the most complex brood structures in the family. Although multiple mating is common in pipefish, seahorses are again exceptional, exhibiting strict genetic monogamy. Both demographic and behavioural explanations have been offered to explain the lack of multiple mating in seahorse species, but these hypotheses have not yet been explicitly addressed. We investigated mating systems and brood parentage of the pot-bellied seahorse, Hippocampus abdominalis, a temperate-water species that is socially promiscuous with conventional sex roles in laboratory populations. We observed promiscuous courtship behaviour and sex-role reversal in high density, female-biased field populations of H. abdominalis. We hypothesize that sex roles are plastic in H. abdominalis, depending on local population density and sex ratio. Despite promiscuous courtship behaviour, all assayed male seahorses were genetically monogamous in both laboratory and wild populations. Physiological limitations associated with embryo incubation may explain the absence of multiple mating in seahorses and may have played an important role in the development of the unique reproductive behaviour typical in these species.

Social common mole-rats enhance outbreeding via extra-pair mating

Females in many species engage in matings with males that are not their social mates. These matings are predicted to increase offspring heterozygosity and fitness, and thereby prevent the deleterious effects of inbreeding. We tested this hypothesis in a cooperative breeding mammal, the common mole-rat Cryptomys hottentotus hottentotus. Laboratory-based studies suggested a system of strict social monogamy, while recent molecular studies indicate extensive extra-pair paternity despite colonies being founded by an outbred pair. Our data show that extra-pair and within-colony breeding males differed significantly in relatedness to breeding females, suggesting that females may gain genetic benefits from breeding with non-resident males. Extra-colony male mating success was not based on heterozygosity criteria at microsatellite loci; however, litters sired by extra-colony males exhibited increased heterozygosity. While we do not have the data that refute a relationship between individual levels of inbreeding (Hs) and fitness, we propose that a combination of both male and female factors most likely explain the adaptive significance of extra-pair mating whereby common mole-rats maximize offspring fitness by detecting genetic compatibility with extra-pair mates at other key loci, but it is not known which sex controls these matings.

Behavioural flexibility in the mating system buffers population extinction: lessons from the lesser spotted woodpecker Picoides minor

1. In most stochastic models addressing the persistence of small populations, environmental noise is included by imposing a synchronized effect of the environment on all individuals. However, buffer mechanisms are likely to exist that may counteract this synchronization to some degree. 2. We have studied whether the flexibility in the mating system, which has been observed in some bird species, is a potential mechanism counteracting the synchronization of environmental fluctuations. Our study organism is the lesser spotted woodpecker Picoides minor (Linnaeus), a generally monogamous species. However, facultative polyandry, where one female mates with two males with separate nests, was observed in years with male-biased sex ratio. 3. We constructed an individual-based model from data and observations of a population in Taunus, Germany. We tested the impact of three behavioural scenarios on population persistence: (1) strict monogamy; (2) polyandry without costs; and (3) polyandry assuming costs in terms of lower survival and reproductive success for secondary males. We assumed that polyandry occurs only in years with male-biased sex ratio and only for females with favourable breeding conditions. 4. Even low rates of polyandry had a strong positive effect on population persistence. The increase of persistence with carrying capacity was slower in the monogamous scenario, indicating strong environmental noise. In the polyandrous scenarios, the increase of persistence was stronger, indicating a buffer mechanism. In the polyandrous scenarios, populations had a higher mean population size, a lower variation in number of individuals, and recovered faster after a population breakdown. Presuming a realistic polyandry rate and costs for polyandry, there was still a strong effect of polyandry on persistence. 5. The results show that polyandry and in general flexibility in mating systems is a buffer mechanism that can significantly reduce the impact of environmental and demographic noise in small populations. Consequently, we suggest that even behaviour that seems to be exceptional should be considered explicitly when predicting the persistence of populations.

SEXUAL TENSION: DOES CONFLICT LEAD TO COSTLY MATE CHOICE?1

SEXUAL TENSION: DOES CONFLICT LEAD TO COSTLY MATE CHOICE?1

Heteropopulation males have a fertilization advantage during sperm competition in the yellow dung fly (Scathophaga stercoraria).

Sexual conflict occurs whenever there is not strict genetic monogamy. The sexually antagonistic coevolution that potentially occurs because of this conflict involves adaptation by one sex followed by the counter-adaptation by the other, and may be thought of as an evolutionary arms-race. As a result of these cycles of antagonistic coevolution, females from one population may be less resistant to heteropopulation males, at least after short periods of allopatry, as they will not have evolved any resistance to them. We tested this prediction in yellow dung fly (Scathophaga stercoraria) populations from the UK and Switzerland. Males from each population mated as first and second males to females from each population, and the mean numbers of offspring sired by the last male to mate in each situation were compared. We also compared the fertility and fecundity of single females mated to males from both populations, as well as the fertility and fecundity of the F(1) crosses. Both crosses produced viable and fertile offspring and the offspring sex ratios were not skewed. However, the fecundity of F(1)-cross females was greater than that of the parentals. In the sperm-competition experiment, there was a significant interaction between male and female origin influencing the proportion of offspring sired by the second male to mate, with heteropopulation males always outcompeting conpopulation males. This effect was independent of copula duration and the delay between copulations. In a separate experiment, we tested to see whether this was due to female preference for genetically dissimilar males but found no evidence for paternity biasing based on genetic similarity. Our results therefore seem to be best explained by sexually antagonistic coevolution as females appear less resistant to males with which they have not coevolved.

Genetic monogamy in burrowing parrotsCyanoliseus patagonus?

We report on a first DNA fingerprinting study of paternity in a Psittaciform bird, the burrowing parrotCyanoliseus patagonus. In two consecutive breeding seasons, a total of 49 families was sampled, of which 11 breeding pairs were investigated each of two years. Extra‐pair paternity was not encountered suggesting that burrowing parrots are socially as well as genetically monogamous. Strict genetic monogamy is comparatively rare in birds and occurs predominantly in some groups of non‐passeriformes all of which exhibit long reproductive lifespans and essential paternal care. Psittaciformes fit this pattern. We conclude that paternal care plays a crucial role in the evolution and maintenance of genetic monogamy in the study species. Cases of intraspecific brood parasitism are rarely observed.

Sexual conflict selects for male and female reproductive characters

Background: Strict genetic monogamy leads to sexual harmony because any trait that decreases the fitness of one sex also decreases the fitness of the other. Any deviation from monogamy increases the potential for sexual conflict. Conflict is further enhanced by sperm competition, and given the ubiquity of this phenomenon, sexual conflict is rife. In support of theory, experimentally enforced monogamy leads to the evolution of sexual benevolence. In contrast, with multiple mating, males evolve traits causing massive female fitness reductions when female evolution is restrained. Theory also predicts increased investment in spermatogenesis when sperm competition risk is high. While this supposition has correlational support, cause and effect has yet to be firmly established.Results: By enforcing monogamy or polyandry in yellow-dung-fly lines, we have shown experimentally that males from polyandrous treatments evolved larger testes. Furthermore, females from this treatment evolved larger accessory sex glands. These glands produce a spermicidal secretion, so larger glands could increase female ability to influence paternity. Using molecular techniques, we have shown that, consistent with this idea, males' success as second mates is reduced in females from the polyandrous treatment. Nevertheless, males from polyandrous lines achieve higher paternity during sperm competition, and this finding further supports the testis evolution patterns.Conclusions: These results provide direct experimental support for macroevolutionary patterns of testis size evolution. Furthermore, we have shown that sperm competition selects for traits likely to be important in sexual conflicts over paternity, a result only previously demonstrated in Drosophila melanogaster.

Genetic conflicts, multiple paternity and the evolution of genomic imprinting.

We present nine diallelic models of genetic conflict in which one allele is imprintable and the other is not to examine how genomic imprinting may have evolved. Imprinting is presumed to be either maternal (i.e., the maternally derived gene is inactivated) or paternal. Females are assumed to be either completely monogamous or always bigamous, so that we may see any effect of multiple paternity. In contrast to previous verbal and quantitative genetic models, we find that genetic conflicts need not lead to paternal imprinting of growth inhibitors and maternal imprinting of growth enhancers. Indeed, in some of our models--those with strict monogamy--the dynamics of maternal and paternal imprinting are identical. Multiple paternity is not necessary for the evolution of imprinting, and in our models of maternal imprinting, multiple paternity has no effect at all. Nevertheless, multiple paternity favors the evolution of paternal imprinting of growth inhibitors and hinders that of growth enhancers. Hence, any degree of multiple paternity means that growth inhibitors are more likely to be paternally imprinted, and growth enhancers maternally so. In all of our models, stable polymorphism of imprinting status is possible and mean fitness can decrease over time. Neither of these behaviors have been predicted by previous models.

Fertility Advertisement in Birds: a Means of Inciting Male‐male Competition?

AbstractCertain loud calls made by female red junglefowl and Lapland longspurs are given most frequently immediately after egg laying, when a copulation should have the highest probability of fertilizing the next egg to be laid. In these species there is considerable male‐male interaction for access to fertilizable females, and males are attracted to or follow females making these calls. Based on our interpretation of these calls, we develop a general hypothesis to predict the pattern of occurrence of fertility advertisement both within and among bird species. We hypothesize that certain loud calls given by female birds before and during the egg‐laying period are designed to advertise fertility and thereby incite male‐male competition. This hypothesis predicts that calls advertising female fertility should most often occur soon after an egg is laid (i.e. during the period of highest fertility) but may also occur at any time during the female's fertilizable period. Such calls are unlikely to be given by females in strictly monogamous species (especially those with long‐term pair bonds) because in these species each female usually mates with only a single male and extra‐pair copulations are avoided. Although reports of loud female calls associated with copulation are rare in the literature, the 18 examples we found (including junglefowl and longspurs) were predominantly (15/18) in species adopting mating systems other than strict monogamy, and these calls were most commonly and disproportionately reported in multi‐male mating systems. This form of “estrus” in birds may be widespread because few species appear to be strictly monogamous, but it will be difficult to study because the period of high fertility for female birds is so short.

Demography of White-Crowned Sparrows (Zonotrichia Leucophrys Nuttalli)

Analysis of a White-crowned Sparrow population in coastal California resulted in es- timates of the magnitude of variation in longevity (a) among cohorts in the same breeding season, (b) between sexes, and (c) between years. Mean longevity calculated from early juvenile life averaged ;13 mo whereas mean longevity calculated from the egg stage was =6 mo. Survival of fledglings to 1 January was generally lower and more variable among cohorts than survival beyond January as adults. Reproductive information from a sample of known-age females indicated that clutch size and number of nestlings increased with female age. Age-specific longevity and clutch size were combined to calculate the net reproductive rates of two female cohorts. These were 1.042 and 1.025, respec- tively. A combination of survival information from five cohorts and information on the numbers of males and females in reproductive condition suggested an effective sex ratio of one male per 1.2 females. This departure from strict monogamy reduces the genetically effective population size by 10% .

On the minimum size of endogamous populations.

Abstract The survival of small endogamous human populations is investigated by computer simulation. It is shown that (1) populations practicing strict monogamy with no extramarital pregnancy are less likely to survive as endogamous groups than are those in which marriage is not a prerequisite for childbearing ; (2) low fertility—low mortality populations can survive with fewer individuals than can populations subject to high fertility and mortality; (3) avoidance of close consanguinity reduces the probability of population survival, but the effect is much greater when fertility and mortality are low. In addition, an attempt is made to determine which demographic characteristics are likely to be the best predictors of potential population decline or disruption.