Male-male competition and female choice in brown trout

In some salmonid species, the females have been assumed to choose their mates on the size of the male's adipose fin. This hypothesis was tested in a stream water aquarium, in which 19 brown trout, Salmo trutta, females were allowed to choose between two males of the same body size but with different adipose fin sizes. The two males were separated from each other in cages. After the female had started to prepare her nest close to one of them, the males were released and allowed to fight each other for the opportunity to spawn. Out of 19 females, 14 prepared a nest closest to the male with the larger adipose fin. However, only six of the 14 females spawned with this male. Males that spawned were more dominant (i.e. were more likely to win fights). When the female spawned with the male she chose, he was less aggressive towards her than when she spawned with the other male. There were no significant differences in the plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) between the chosen males and those not chosen. However, the dominant males had significantly higher plasma levels of T and 11-KT both before and after the experiment. The results support the view that female brown trout exhibit mate choice, but their choice is overruled by male-male competition. Copyright 1999 The Association for the Study of Animal Behaviour.     

Female preference for dominant males in the Mexican mojarra cichlid fish,Cichlasoma istlanum

It is widely assumed that female preference and male competition operate simultaneously during sexual selection. Dominance is likely an honest indicator of male quality, and females can identify and choose the dominant male to reproduce with individuals with greater competitive abilities, thus improving the quality and competitiveness of their offspring. In this context, few studies have investigated female preference in relation to male fighting ability. The Mexican mojarra, Cichlasoma istlanum, is a cichlid species native to the Balsas River basin. It is territorial during reproduction and provides parental care. Males commonly engage in territorial defence, whereas females care directly for offspring. This study examined whether females prefer dominant males that exhibit more aggressive behaviour. The authors conducted experiments using groups of two males and one female to test competitive ability in males and female preference. They also quantified the time during which the female associated with the dominant male and the subordinate male after observing the outcome of a fight between the two males. They found that Mexican mojarra females preferred dominant males and that the time females spent associating with males was positively related with their aggressive behaviours during competition. These results indicate that dominant males were more attractive than subordinate males to female Mexican mojarra. The relationship between female preference and male dominance in the Mexican mojarra demonstrates the importance of male competitive ability for future parental care in reproduction.     

Extrapair paternity and egg hatchability in tree swallows: evidence for the genetic compatibility hypothesis?

Tree swallows (Tachycineta bicolor) show one of the highestlevels of extrapair paternity in birds, and there is evidencethat females have control over who fathers their offspring.However, it is unclear which benefits female tree swallows obtainfrom mating with multiple males. Using microsatellite DNA fingerprinting,we studied extrapair paternity in relation to nesting successand male, female, and offspring characteristics. More than 70%of all nests contained extrapair young, and more than half ofall offspring were extrapair. Within broods, the extrapair youngwere often fathered by several males. Despite screening allresident and some floater males, we could identify the biologicalfather of only 21% of all extrapair offspring. All identifiedextrapair males were close neighbors. Extrapair males did notdiffer from within-pair males in any of the measured characteristics,except that the former had larger cloacal protuberances than thelatter. Extrapair males were equally successful in gaining paternityin their own broods as males that did not father extra young.In nests with mixed paternity, extrapair young did not differfrom within-pair young in body size or mass. However, nestswith extrapair young had higher hatching success than nestswithout extrapair young. All examined unhatched eggs were fertilizedand thus hatch failure resulted from embryo mortality. The availabledata are in accordance with the genetic diversity and the geneticcompatibility hypothesis, but not with the good genes hypothesis.     

Effect of auxiliary males on territory ownership in the oribi and the attributes of multimale groups

I observed free-ranging oribi, Ourebia ourebi, in Serengeti National Park, Tanzania, to determine whether group formation by males provides evidence for cooperative territory defence, a behaviour that is rare among male vertebrates. Socially dominant males that shared territories with subordinate auxiliary males were replaced by rivals less often than males that defended territories without auxiliary males. Auxiliary males marked territories with preorbital glands, dung and urine, and territories defended by male groups were marked more thoroughly than those defended by single males. Fifteen of 24 (62.5%) auxiliary males whose histories were known were born on territories defended by males that probably were their fathers. But 37.5% of auxiliary males probably were unrelated to dominant males, because male groups also formed when territory owners accepted adult male immigrants as subordinates, and when owners allowed young males to remain philopatric after evicting a male likely to have been the young male's father. All males in groups probably had some mating access to females, but dominant males may have minimized matings of auxiliary males by guarding fertile females. These results suggest that auxiliary male oribi aided dominant males in territory defence, and that dominants traded off the risks of losing matings to auxiliaries, or being overthrown by them, in exchange for a reduction in their chance of being evicted by rival neighbours or immigrants. Copyright 1999 The Association for the Study of Animal Behaviour.     

Multiple paternity and breeding system in the gopher tortoise, Gopherus polyphemus

Little is known about the reproductive behaviors and the actual outcomes of mating attempts in the gopher tortoise (Gopherus polyphemus). We examined the mating system and reproductive behaviors of a population of gopher tortoises in central Florida. Using microsatellite markers, we assigned fathers to the offspring of seven clutches and determined that multiple fathers were present in two of the seven clutches examined. We found that gopher tortoises exhibited a promiscuous mating system with larger males fertilizing the majority of clutches. The advantage of larger males over smaller males in fertilizing females may be a result of larger males winning access to females in aggressive bouts with other males or larger males may be more attractive to females. Clutches produced by larger females tended to be sired by a single male, whereas clutches of smaller females tended to be sired by multiple males.     

Sex Change in Both Directions by Alteration of Social Dominance in Trimma okinawae (Pisces: Gobiidae)

The mating system of the gobiid fish Trimma okinawae is one of polygynous hermaphroditism, in which the largest female of a social unit changes sex following the removal of the dominant male. Histological observations of the gonads however, revealed that males have an ovarian tissue within a functional testis. The occurrence of ovarian tissue in the functional male suggests that T. okinawae males should be able to revert back into being functional females. To test this prediction, we placed females in an aquarium and allowed them to change sex. After confirming sex change from female to male, we individually placed new males into another aquarium and added a larger male to each. Our experiments revealed that females change sex and become males upon the removal of dominant males, and that those males changed sex again and became females in the presence of larger males. Sex change in both directions may be advantageous when a male is forced to become subordinate following the take over of the social unit by a larger male.     

Evaluation of Darwin's fecundity advantage hypothesis in Parthenium beetle,Zygogramma bicolorata

In the Parthenium beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), variation in body size exists between and within the sexes. The females are larger than the males. Darwin (1874) proposed the fecundity advantage hypothesis, that is, large‐sized females produce more progeny, with subsequent studies supporting, as well as, refuting the hypothesis. Thus, in order to evaluate whether this hypothesis stands in Z. bicolorata we performed experiments to investigate the role of body size in influencing: (i) assortative mating; (ii) reproductive attributes; and (iii) growth, development and survival of offspring. It is the first attempt in this beetle. We found that size influenced assortative mating, reproductive output and offspring fitness. Larger males and females were preferred as mates over smaller ones. The pairs, having larger adults as mates, had higher fecundity, while the egg viability was influenced by the male size only. The offspring of larger parents had fast development and higher survival, indicating thereby possible better nutrient allotment by the female and supply of accessory gland proteins by the male in addition to better quality of genes.     

Polyandry in dragon lizards: inbred paternal genotypes sire fewer offspring

Multiple mating in female animals is something of a paradox because it can either be risky (e.g., higher probability of disease transmission, social costs) or provide substantial fitness benefits (e.g., genetic bet hedging whereby the likelihood of reproductive failure is lowered). The genetic relatedness of parental units, particularly in lizards, has rarely been studied in the wild. Here, we examined levels of multiple paternity in Australia's largest agamid lizard, the eastern water dragon (Intellagama lesueurii), and determined whether male reproductive success is best explained by its heterozygosity coefficient or the extent to which it is related to the mother. Female polyandry was the norm: 2/22 clutches (9.2%) were sired by three or more fathers, 17/22 (77.2%) were sired by two fathers, and only 3/22 (13.6%) clutches were sired by one father. Moreover, we reconstructed the paternal genotypes for 18 known mother–offspring clutches and found no evidence that females were favoring less related males or that less related males had higher fitness. However, males with greater heterozygosity sired more offspring. While the postcopulatory mechanisms underlying this pattern are not understood, female water dragons likely represent another example of reproduction through cryptic means (sperm selection/sperm competition) in a lizard, and through which they may ameliorate the effects of male‐driven precopulatory sexual selection.     

Size-mediated dominance and aggressive behavior of male Japanese fluvial sculpin Cottus pollux (Pisces: Cottidae) reduce nest-site abundance and mating success of conspecific rivals

Despite growing evidence for plasticity in the mating patterns of nest-holding animals in relation to the changes in nest abundance, the effects of aggressive interaction by dominant males on nest availability for conspecific rivals remains unclear. To quantify the effects of male–male competition on nest-site choice and mating success of the male Japanese fluvial sculpin Cottus pollux, we conducted experiments on 5 males from different 5 size classes under both sufficient and shortage nest-abundance conditions. Nest-choice experiments showed that both male size class and nest-abundance condition had significant effects on the nesting rates of males. Following the nest-choice experiments, 10 gravid females were added in the experimental tanks. Mating experiments revealed that male size, nesting rate before addition of females, and the number of courtship attempts on females were valid variables of male mating success, regardless of nest-abundance conditions. After achieving initial mating success, the largest nesting male exhibited more frequent aggressive interaction with other conspecific males than he did before obtaining eggs in his nest. Our results suggest that size-mediated dominance and aggressive behavior of males may disrupt nest acquisition of other conspecific males, and may consequently result in extreme variation in mating success among males even under sufficient nest-abundance conditions.     

Adaptive Offspring Sex Ratio Depends on Male Tail Length in the Guppy

A biased sex ratio in a brood is considered to be an adaptive strategy under certain circumstances. For example, if the expected reproductive success of one sex is greater than that of the other, parents should produce more offspring of the former sex than the latter. A previous study has documented that in the guppy, Poecilia reticulata, the female offspring of males possessing proportionally longer tails exhibit smaller body sizes and show decreased reproductive outputs than those of males having shorter tails. On the other hand, the total lengths of the male offspring of the long‐tailed males are larger because of their longer tails; consequently, they exhibit greater sexual attractiveness to females. Therefore, it has been hypothesized that this asymmetry in the expected reproductive success between the male and female offspring of long‐tailed males may result in a biased sex ratio that is dependent on the tail lengths of their fathers. This hypothesis was tested in the present study. The results showed that the females that mated with long‐tailed males produced more male offspring than those that mated with short‐tailed males. Logistic regression analysis showed that the ratio of tail length to the standard length of the fathers is a determinant factor of the sex of their offspring. These results suggest that the manipulation of the offspring sex ratios by parents enhances the overall fitness of the offspring.     

COMPLEX INTERACTIONS BETWEEN PATERNAL AND MATERNAL EFFECTS: PARENTAL EXPERIENCE AND AGE AT REPRODUCTION AFFECT FECUNDITY AND OFFSPRING PERFORMANCE IN A BUTTERFLY

Parental effects can greatly affect offspring performance and are thus expected to impact population dynamics and evolutionary trajectories. Most studies have focused on maternal effects, whereas fathers are also likely to influence offspring phenotype, for instance when males transfer nutrients to females during mating. Moreover, although the separate effects of maternal age and the environment have been documented as a source of parental effects in many species, their combined effects have not been investigated. In the present study, we analyzed the combined effects of maternal and paternal age at reproduction and a mobility treatment in stressful conditions on offspring performance in the butterfly Pieris brassicae. Both paternal and maternal effects affected progeny traits but always via interactions between age and mobility treatment. Moreover, parental effects shifted from male effects expressed at the larval stage to maternal effects at the adult stage. Indeed, egg survival until adult emergence significantly decreased with father age at mating only for fathers having experienced the mobility treatment, whereas offspring adult life span decreased with increasing mother age at laying only for females that did not experience the mobility treatment. Overall, our results demonstrate that both parents’ phenotypes influence offspring performance through nongenetic effects, their relative contribution varying over the course of progeny's life.     

Paternity cues and mating opportunities: what makes fathers good?

Human males provide facultative paternal investment to their offspring; that is, the male care is not necessary for the survival of his offspring. It is expected that the degree of male investment (1) increases with growing paternity certainty, (2) increases when investment increases the survival and later reproductive prospect of offspring and (3) declines when there are opportunities to mate with multiple females. Using a large sample of adult offspring and their fathers (n = 245), we first investigated the role of two factors possibly involved in the assessment of paternity and subsequently regulating the level of paternal investment: (a) father–child facial resemblance and (b) assortative mating for eye colour. Second, because mating opportunities are inversely related to paternal investment, we also investigated how male facial attractiveness (a cue of mate opportunities) correlates with paternal investment. In line with paternal investment theory, male investment positively correlated with offspring facial resemblance. However, paternal investment were neither higher among blue-eyed couples, nor there were preferences of blue-eyed men to marry with blue-eyed women. Moreover, father facial attractiveness was unrelated to paternal investment. These results indicate that resemblance between offspring and their fathers still plays an important role in paternal investment decision later in offspring’s life.     

Relatedness in wild chimpanzees: influence of paternity, male philopatry, and demographic factors

In chimpanzees (Pan troglodytes), high-ranking males are expected to have high reproductive success and females typically emigrate upon reaching maturity. Although high average relatedness among males in the same social groups has been assumed, previous reports have indicated that relatedness among males is not necessarily significantly higher than that among females. The paternity of 11 offspring and the relatedness of 50 individuals in the M group of chimpanzees at Mahale Mountains National Park, Tanzania, were investigated using DNA analyses. We determined the fathers of 10 offspring. Two different alpha males sired a total of five offspring, whereas the other males had low reproductive success. The proportion of paternal half-sibling pairs among the 10 offspring was 15.6%. The average relatedness among mature males was significantly higher than that among mature females. The existence of an old male and the long tenure of one alpha male may have contributed to this significant difference. The average dyadic relatedness among mature natal individuals was significantly higher than that in natal-immigrant pairs in which the individuals came from different groups. The average relatedness among immigrant females was similar to that in pairs of natal and immigrant females, suggesting that the immigrants came from various groups. Thus, female transfer acts to maintain low average relatedness within the group. A comparison of our results to those from other study sites suggests that although the average relatedness among adult males does not reach the level of half-siblings, under some circumstances it can exceed the relatedness of females.     

Multiple paternity in Littorina obtusata (Gastropoda, Littorinidae) revealed by microsatellite analyses.

Parental identity for juvenile Littorina obtusata was determined from three egg masses by means of microsatellite DNA markers. Results confirm that the attendant adult female in each case was the dam of the offspring and that at least 4-6 males contributed to each brood. This correlates with our behavioral observations that indicated multiple copulations between the female and several males in each experimental aquarium. A significant number of offspring from each brood were sired by non-sampled males (males that had copulated with females before capture) whose sperm had been stored by the female. This is the first direct evidence of multiple paternity in the Littorinidae. Results are discussed in reference to current theories of sperm competition, male precedence, and cryptic female choice.     

A female's past experience with predators affects male courtship and the care her offspring will receive from their father

Differential allocation occurs when individuals adjust their reproductive investment based on their partner''s traits. However, it remains unknown whether animals differentially allocate based on their partner''s past experiences with predation risk. If animals can detect a potential mate''s experience with predators, this might inform them about the stress level of their potential mate, the likelihood of parental effects in offspring and/or the dangers present in the environment. Using threespined stickleback (Gasterosteus aculeatus), we examined whether a female''s previous experience with being chased by a model predator while yolking eggs affects male mating effort and offspring care. Males displayed fewer conspicuous courtship behaviours towards females that had experienced predation risk in the past compared with unexposed females. This differential allocation extended to how males cared for the resulting offspring of these matings: fathers provided less parental care to offspring of females that had experienced predation risk in the past. Our results show for the first time, to our knowledge, that variation among females in their predator encounters can contribute to behavioural variation among males in courtship and parental care, even when males themselves do not encounter a predator. These results, together with previous findings, suggest that maternal predator exposure can influence offspring development both directly and indirectly, through how it affects father care.     

Signals of female reproductive quality and fertility in colony‐living baboons (Papio h. anubis) in relation to ensuring paternal investment

The fitness of a female's offspring depends cruicially on the traits, genetic and paternal, that the father contributes. As such, females may either have an interest in behaviorally choosing the highest‐quality male, or in reliably signaling their fertility status to males. Combining hormonal data on a female's ovulatory fertile window with a behavioral context, we suggest that captive female olive baboons (Papio h. anubis) provide fathers with reliable signals of their fertile period. One signal, the maximum anogenital swelling (AGA), typically coincided with a 4‐day fertile window of ovulation, which occurred 2–3 days prior to deturgescence. As expected from previous studies, AGA swelling indicated general attractiveness to males, and males attended to the relative attractiveness of females. Males approached and copulated with females significantly more often during the 4‐day window around ovulation, irrespective of the absolute swelling stage. The two adult males present in the group were both able to copulate with consistent partners as at least two cycling females were available in most months; the dominant male was more selective about the timing of his copulations close to ovulation during the maximal swelling phase. Females with ovulatory but nonconceptive cycles were less attractive to males, especially during their maximal AGA swelling phase. Am. J. Primatol. 71:529–538, 2009. © 2009 Wiley‐Liss, Inc.     

Male dominance determines female egg laying rate in crickets

A key prediction of theories of differential allocation and sexual conflict is that male phenotype will affect resource allocation by females. Females may adaptively increase investment in offspring when mated to high quality males to enhance the quality of their offspring, or males may vary in their ability to manipulate female investment post-mating. Males are known to be able to influence female reproductive investment, but the male traits underlying this ability have been little studied in taxa other than birds. We investigated the relationship between male dominance and female oviposition rate in two separate experiments using the field cricket, Gryllus bimaculatus. In both experiments, females mated to more dominant (but not larger) males laid more eggs. This reveals that either females allocate more effort to reproduction after mating with a dominant male or that dominance status is associated with male ability to manipulate their mates. This is the first evidence that dominance, rather than male attractiveness, has a post-copulatory effect on reproductive investment by females.     

Social Dominance among Male Meadow Voles is Inversely Related to Reproductive Success

Intrasexual selection can occur through direct aggressive interactions between males for access to females. We tested the relationship between social dominance and male reproductive success among meadow voles, Microtus pennsylvanicus. Dominance ranks of wild‐caught males were determined using neutral arena trials, with the winner of two of three trials considered dominant. These males were then released into field enclosures and allowed to visit females housed in nestboxes for 8 wk, and males’ home range sizes were determined using weekly grid trapping. Male reproductive success was determined using molecular paternity analysis (six microsatellite primers) for all pups born during the field experiment. Males with higher dominance ranks had larger home ranges. However, male dominance rank was not predictive of the number of total visits to females’ nestboxes or the number of visits to each male's most frequently visited nestbox. Males that made more visits to nestboxes sired more litters. Males that had higher dominance ranks sired fewer litters. These results suggest that there is a reproductive disadvantage to having higher dominance rank among male meadow voles.     

High frequency of multiple paternity in the largest rookery of Mediterranean loggerhead sea turtles

Mating systems are a central component in the evolution of animal life histories and in conservation genetics. The patterns of male reproductive skew and of paternal shares in batches of offspring, for example, affect genetic effective population size. A prominent characteristic of mating systems of sea turtles seem to be a considerable intra- and interspecific variability in the degree of polyandry. Because of the difficulty of observing the mating behaviour of sea turtles directly in the open sea, genetic paternity analysis is particularly useful for gaining insights into this aspect of their reproductive behaviour. We investigated patterns of multiple paternity in clutches of loggerhead sea turtles in the largest Mediterranean rookery using four highly variable microsatellite loci. Furthermore, we tested for a relationship between the number of fathers detected in clutches and body size of females. More than one father was detected in the clutches of 14 out of 15 females, with two clutches revealing the contribution of at least five males. In more than half the cases, the contributions of different fathers to a clutch did not depart from equality. The number of detected fathers significantly increased with increasing female body size. This relationship indicates that males may prefer to mate with large, and therefore productive, females. Our results suggest that polyandry is likely to increase effective population size compared to a population in which females would mate with only one male; male reproductive contributions being equal.     

Reduction of maternal care: a new benefit of multiple mating?

Cost/benefit analyses have been used to understand the evolutionof mating by females with multiple males, as in extrapair copulations(EPCs), which are now known to occur commonly in socially monogamousand polygynous birds. Indirect (genetic) benefits have beeninvoked to explain such mating patterns in some cases, butdirect benefits have received less attention. We report a studyof direct benefits in the communally rearing Mexican jay (Aphelocoma ultramarina). The social mate of the mother (putative father)is the most reliable feeder of the young in his nest, regardlessof cuckoldry. Feedings provided by social fathers are not reducedin relation to their paternity loss. In contrast, mothers havingnestlings sired by a second male tend to have lower feedingrates than those without such young. Secondary fathers provideda significantly higher level of feeding to the brood of theirfemale than did (1) random nonbreeders of all ages and bothsexes, (2) random male nonbreeders of all ages, and (3) older(2+ years), male nonbreeders. Surprisingly, however, broodswith two fathers did not receive a higher level of total feeding,despite our observation that two-father broods had two more helpers, on average, compared to broods without extra fathers.Regardless of age or breeding status, males were more frequentfeeders than females. This study provides the first evidencethat one of the major costs of reproduction, maternal careof nestlings, is reduced for females that have young sired by secondary males.