Modeling a version of the good-genes hypothesis: female choice of locally adapted males

In addition to other potential causes, immigration into locally adapted populations has been suggested to maintain the genetic variance in fitness that is necessary for the good-genes hypothesis. Using population-genetic simulations, the present contribution shows that co-occurring local adaptation and migration can maintain genetic variance in fitness. In combination with an effect of local adaptation on condition and condition-dependent sexual signaling, such a scenario therefore enables the evolution and maintenance of female choice for locally adapted males. The simulations show that this mechanism can also work when choice is costly, and that the potential benefit is similar to that in other good-genes mechanisms. As a consequence of female choice in favor of locally adapted males, differentiation between populations can be expected to increase due to the decreased effective gene flow between populations. Based on such effects, choice of locally adapted males has the potential to play an important role in speciation and adaptive radiation.     

Female choice of sites versus mates in a coral reef fish,Thalassoma bifasciatum

To understand the dynamics of sexual selection, one needs to identify the basis of female choice in mating. Daily censuses showed that most spawns of individual female bluehead wrasses, Thalassoma bifasciatum, occurred at one of several available mating sites, either in a group-spawning aggregation of small males or with a large territorial male. Most females were not located near their principal mating site during the non-spawning period of the day. Females were thus exposed to other males and sites and should have had the opportunity for choice. When a resident territorial male disappeared or was removed experimentally from a mating site, females did not alter their fidelity to that site. Furthermore, manipulations showed that when a territorial male changed the location of his mating activity to an adjacent site, females did not follow him but continued to mate at their customary site. Thus mating sites, rather than the males occupying them, appeared to be the objects of female choice. The bright coloration and courtship behaviour of larger males may demonstrate the safety of a particular site rather than indicating some aspect of male quality.     

Parasites, male-male competition and female mate choice in the sand goby

Male sand goby Pomatoschistus minutus dominance in competition over nest sites was associated with higher body condition but not with the intensity of infection with any individual parasite of six different species, nor with an overall index combining relative levels of infection by all parasites. Body condition was not related to the intensity of infection with any individual parasite nor with the index of total relative parasite load. In trials in which females spawned, they showed a tendency to choose dominant over subordinate males as mates, but did not consistently choose less parasitized males. Variation in the relative size of the dorsal fins of males was detected, and this related to numbers of the ectoparasitic monogenean Gyrodactylus sp., suggesting that at least some infections have phenotypic effects that could allow females to detect and avoid the most heavily infected males.     

Female choice for heterozygous mates changes along successive matings in a lizard

Female mate choice and female multiple mating are major focuses of studies on sexual selection. In a multiple mating context, the benefits of mate choice can change along successive matings, and female choice would be expected to change accordingly. We investigated sequential female mate choice in the moderately polyandrous common lizard (Zootoca vivipara, synonym Lacerta vivipara). Along successive mating opportunities, we found that females were relatively unselective for the first mate, but accepted males of higher heterozygosity for subsequent mating, consistent with the trade-up choice hypothesis. We discuss the evidence of trade-up mate choice in squamates and generally trade-up for mate heterozygosity in order to motivate new studies to fill gaps on these questions.     

Patterns of fluctuating asymmetry in sexual ornaments predict female choice

Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.     

First experimental evidence for female mate choice in a nocturnal primate

Female mate choice can be hypothesised in most nocturnal primates, since females show a higher investment in their offspring than males. The aim of this experimental study was to investigate if female grey mouse lemurs perform mate choice and whether age, relatedness (to the male), or male advertisement call activity systematically influence their decisions. A two-way mate choice design was developed in which females could choose between two males. Mate choice was deduced from the time spent in proximity to the males and from mating behaviour. During oestrus 12 of 17 females participated actively in the experiment and all of them showed either a significant spatial (n=11) or behavioural (n=1) preference for one male. In four cases copulations were observed. The influence of age on female mate choice was not statistically significant. In the cases with copulations, however, females mostly preferred the older male. This might indicate a preference for older age as an indicator of experience, fitness, and/or status. The influence of relatedness on female mate choice could not be definitely clarified. However, results imply a mechanism of kin recognition on the basis of familiarity. In the majority of choices, females preferred the male with higher trill call activity. Since trill call activity correlates with the relative dominance status of males, these results suggest an importance of the male dominance status for female mate choice in grey mouse lemurs. Altogether our findings indicate that females use a complex of different cues to choose their mates.     

Estimation of spawning sites in the spotted flagtail, Kuhlia marginata, based on sperm motility

To estimate the spawning site of the spotted flagtail, Kuhlia marginata, sperm motility was examined under conditions of different salinities. The spermatozoa were immotile in 0 and 5 ppt test solutions and in seminal fluid but lived longer in 20–30 ppt. Sperm were most active at 25–35 ppt. Therefore, we considered that spotted flagtail spawn in 20–35 ppt salinity. Because the mean salinity of the Genka estuary is below the optimum required for spawning, the spawning site in Okinawa Island would be seawater. This evidence suggested that the spotted flagtail is a catadromous species. Received: January 26, 2001 / Revised: July 6, 2001 / Accepted: July 24, 2001     

Spawning timing of the cleaner wrasse, Labroides dimidiatus, on a warm temperate rocky shore

We observed spawning behaviors of the haremic cleaner wrasse Labroides dimidiatus at a rocky reef in southern Japan. Females released pelagic eggs daily from June to September after a spawning ascent by pairs. When the high tide occurred between noon and evening (quarter moon to new or full moon), they spawned around the time of the tide providing fast offshore currents. For the rest of the lunar cycle, spawnings occurred during late afternoon independent of the state of the tide at the time of day. This spawning pattern is quite different from that of conspecifics on coral reefs that always spawn around the high tide at all lunar stages to avoid potential egg predators. The wrasse ascended high in the water column, probably because of its predator-immune characters as a cleaner. The steep slope of the study site seemed to contribute to releasing gametes far above aggregating planktivores. Thus, gametes were not subject to heavy predation. Current direction might not always affect survival of spawned pelagic eggs on the temperate reefs so crucially as it does on coral reefs. We conclude that spawning during unfavorable tidal conditions during the daytime may be better than spawning during the best tidal condition in the crepuscular period when predation pressure on adults will be high. Intraspecific variation in the timing and location of spawning of the wrasse may result from different conditions for larval survival. Received: February 6, 2000 / Revised: June 16, 2000 / Accepted: July 17, 2000     

Delayed copulation as a means of female choice by the hermit crab Pagurus filholi

Male hermit crabs perform precopulatory mate-guarding behavior during their reproductive season. As females generally cannot reject guarding attempts by males, male guarding prevents females from inspecting and choosing other male mates. However, as guarding males are often replaced by other males through competition for females during the guarding phase, females may be able to select males by delaying their copulation. To examine the possibility of female choice by hermit crabs, we investigated whether female Pagurus filholi that were being guarded in the field were ready to copulate and spawn. We found that about 30% of females guarded in the field were ready to spawn, indicating that guarded females delayed copulation with their current male. Our results suggest that by delaying copulation females may exploit male–male competition to choose dominant males. However, delaying copulation reduced the spawning potential of females. Hence, there is a trade-off between waiting for the opportunity to mate with a dominant male and decreased spawning success if females exploit male–male competition.     

Nestmateship and body size do not influence mate choice in males and females: A laboratory study of a primitively eusocial wasp Ropalidia marginata

We investigated the effect of nestmateship and body size on mate selection through a choice based assay in the primitively eusocial wasp Ropalidia marginata. A recent study has shown that male and female R. marginata mate with their nestmates and non-nestmates with equal probability if no choice is available. That study could also not detect any influence of body size on mating probability in the absence of choice. To confirm that the same results can be obtained even when the wasps have a choice, we offered a choice of two virgin partners either to a virgin test male or to a virgin test female and measured the probability that the test individual would mate with any particular partner based on nestmateship or body size. We show here that even when a choice is available, neither male nor female test wasps base their mate choice on the nestmateship or body size of the partner. We therefore suggest that the natural mating habit of these wasps is sufficiently promiscuous and not constrained by such factors as nestmateship and body size.     

Adiposity,compared with masculinity,serves as a more valid cue to immunocompetence in human mate choice

According to the ‘good genes’ hypothesis, females choose males based on traits that indicate the male''s genetic quality in terms of disease resistance. The ‘immunocompetence handicap hypothesis’ proposed that secondary sexual traits serve as indicators of male genetic quality, because they indicate that males can contend with the immunosuppressive effects of testosterone. Masculinity is commonly assumed to serve as such a secondary sexual trait. Yet, women do not consistently prefer masculine looking men, nor is masculinity consistently related to health across studies. Here, we show that adiposity, but not masculinity, significantly mediates the relationship between a direct measure of immune response (hepatitis B antibody response) and attractiveness for both body and facial measurements. In addition, we show that circulating testosterone is more closely associated with adiposity than masculinity. These findings indicate that adiposity, compared with masculinity, serves as a more important cue to immunocompetence in female mate choice.     

Female within-nest spawning-site preference in a paternal brooding blenny and its effect on the female mate choice

Female spawning-site preference within a nest and its effect on the female mate choice in a paternal brooding blenny Rhabdoblennius ellipes , were examined in rocky intertidal pools using artificial nests. The number of eggs deposited at the nest entrance site was lower than the number deposited at the center and at deep sites. Moreover, the within-nest difference in the egg developmental stage indicated that eggs at the nest entrance site were deposited after those at the center and deep sites. These results indicated that females prefer to spawn eggs in the center and deep sites rather than at the entrance site. Owing to the higher egg mortality rate at the entrance site, females may avoid spawning at such sites. An analysis of the nests in the study area suggested that the within-nest site preference affects female mate choice that is females avoided nests where only the entrance site was available for spawning and instead spawned in nests where the center and deep sites were available.     

Male mating competition,female choice and dominance in a free ranging group of Japanese macaques

Focal and ad libitum samples of high and middle ranked males in a group of free ranging Japanese macques were taken in order to examine rank related differences in male mating strategies. Males tended to have like ranked females as consort partners, with high rank males showing more consort activity, over all, than middle rank males. High rank males tended to interfere in consorts and middle rank males tended to have their consorts disrupted. Consorts involving high rank females were most subject to interference. With one exception, proximity between partners in consorts involving high rank males was due to male actions while proximity in consorts involving middle ranked males was due to female actions. The two highest ranked males were never observed copulating. Their mating failure may have been due to avoidance by females who had known them since immaturity. High rank males were somewhat more likely than middle rank males to have consorted with females during the period of likely conception. There was some evidence that frequent consort partners joined the same subgroup during a group fission. Males appeared to use the advantage conferred by high rank mainly in competition for high rank females. Females showed some indications of preference for mates likely to retain or attain high rank in the future.     

Male morphology,performance and female mate choice of a swarming insect

1. Females of many species select mates based on important morphological and performance traits. This behaviour likely facilitates reproductive success thus exhibiting sexual selection. Most such studies have evaluated a single morphological variable, and only a minority of them studies the effects of behaviour and performance (functional capacity: Irschick et al., Evolutionary Ecology Research, 10 , 177–196, 2008) at all.
2. This study compares male morphological and performance traits differing in three variables that may correlate with fitness: condition index, flight ascent speed and resistance to torpor in relation to male mating success in the parasitoid wasp species Alabagrus texanus (Braconidae), a species where males swarm about emerging virgin females that display both choosy and non-choosy behavioural phenotypes.
3. Males that successfully mated with choosy females exhibited higher condition indices and somewhat stronger resistance to torpor than other males. Conversely, males that mated with non-choosy females did not differ in any trait from other males we measured. Early-arriving males did not have higher condition indices or greater mating success than other males.
4. Thus, both morphological and performance traits contributed to male success, which acted through female choice, indicating a role for sexual selection. Patterns of choice further differed among females, independent of male traits.

     

A theoretical study on the evolution of male parental care and female multiple mating: effects of female mate choice and male care bias

Male parental care and female multiple mating are seen in many species in spite of the cost they entail. Moreover, they even coexist in some species though polyandry, by reducing paternity confidence of caregiving males, seems to hinder the evolution of paternal care. Previous studies have investigated the coevolutionary process of paternal care and polyandry under various simplifying assumptions, including random mating and random provision of male care. We extend these models to examine possible effects of female mate choice and male care bias, assuming that (a) monandrous females mate preferentially with caregiving males while polyandrous females compromise their preference in order to mate with multiple males and (b) caregiving males tend to direct their care to offspring of monandrous females. Our models suggest that both the female preference and the male bias always favor caregiving males while they may not always facilitate the evolution of monandry.     

Heritable variation in the timing of spermatophore removal, a mechanism of post-copulatory female choice in crickets

Female crickets can exert post-copulatory mating preferences by prematurely removing a male's spermatophore after copulation, which terminates sperm transfer. Although most models of sexual selection assume that female mating preferences are heritable, there has been little work addressing genetic variation underlying post-copulatory mate choice. We used a paternal half-sib design, in which different males were randomly assigned as mates to several females to create half-sib families, to determine the heritability of spermatophore retention time in female house crickets, Acheta domesticus. There was significant additive genetic variance in the timing of spermatophore removal by females [h(2) = 0.50 +/- 0.19 (+/- SE)], suggesting that the timing of spermatophore removal is determined, in part, by the female's own genotype independent of the quality of her mate. The relatively high heritability of spermatophore retention time may be reflective of the absence of strong selection on this trait, consistent with previous work showing no difference in the fitness of females permitted to freely remove the spermatophore of their mates and those forced to accept complete ejaculates.     

The effect of cryptic female choice on sex allocation in simultaneous hermaphrodites

Sex allocation theory for simultaneous hermaphrodites has focused primarily on the effects of sperm competition, but the role of mate choice has so far been neglected. We present a model to study the coevolution of cryptic female choice and sex allocation in simultaneous hermaphrodites. We show that the mechanism of cryptic female choice has a strong effect on the evolutionary outcome: if individuals remove a fixed proportion of less-preferred sperm, the optimal sex allocation is more female biased (i.e. more biased towards egg production) than without cryptic female choice; conversely, if a fixed amount of sperm is removed, sex allocation is less female-biased than without cryptic female choice, and can easily become male biased (i.e. biased towards sperm production). Under male-biased sex allocation, hermaphroditism can become unstable and the population can split into pure males and hermaphrodites with a female-biased allocation. We discuss the idea that the evolution of sex allocation may depend on the outcome of sexual conflict over the fate of received sperm: the sperm donor may attempt to manipulate or by-pass cryptic female choice and the sperm recipient is expected to resist such manipulation. We conclude that cryptic female choice can have a strong influence on sex allocation in simultaneous hermaphrodites and strongly encourage empirical work on this question.     

Complex genital structures indicate cryptic female choice in a haplogyne spider (Arachnida,Araneae, Oonopidae,Gamasomorphinae)

Female genital structures with their allied muscles of the haplogyne spider Opopaea fosuma are described. A functional explanation of this system is given, which indicates that cryptic female choice may occur in these spiders: the anterior wall of their spermatheca is strongly sclerotized and possesses a cone-shaped hole in its upper part. A transverse sclerite that serves as muscle attachment bears a nail-like structure and lies in a chitinized area of the anterior wall of the uterus externus. Muscle contraction presses this nail into the hole of the spermatheca. In this way, the uterus externus gets both locked and fixed. Furthermore, as this occurs the copulatory orifice is enlarged and the resulting suction probably leads to previously deposited sperm being drawn from the spermatheca and dumped. This is a common mechanism used by females to influence a male's chances of fathering their offspring in a process known as cryptic female choice.