Female choice on male quantitative traits in lizards — why is it so rare?

Female choice on the basis of male traits has been described in an array of taxa but has rarely been demonstrated in reptiles. In the sand lizard (Lacerta agilis), and possibly in other non-territorial reptiles, a male's contribution to a female's fitness is restricted to his genes. In order to choose males of high genetic quality, females have to trade the fitness gain against the costs of active choice. In a Swedish population of sand lizards, long-lived males sired offspring with higher embryonic survival compared to offspring sired by short-lived males. In spite of this female sand lizards did not mate selectively with older and/or larger males. There appeared to be mo reliable cues to male longevity; age-specific male body size was highly variable. Furthermore, estimates of male nuptial coloration did not covary with ectoparasite load and, hence, females cannot use male coloration as a cue to heritable resistance to pathogenic parasite effects. When cues to male genetic quality are poor, or inaccurate, and males make no parental investment, we predict that female choice will be rare. Sand lizard females mating with many partners lay clutches with higher hatching success. Thus, females may obtain good genes for their young by multiple mating, thereby avoiding costs associated with mate choice.     

Mate choice and the supernormality effect in female sticklebacks (Gasterosteus aculeatus)

Summary Female threespine sticklebacks Gasterosteus aculeatus from a marine population were presented simultaneously with two dummy males that differed in size. When the dummies were moved with a carousel apparatus in a way that roughly simulated a male courtship activity (circling) females responded to the dummies with following behaviour normally directed to courting males. Female sexual response was elicited more effectively by the larger (supernomal) dummy, even though it exceeded by 25% the length of the largest males in the study population. Females did not show complete preference for the larger dummy but allocated courtship effort in proportion to the sizes of the two dummies (Fig. 3). The relative projection areas of the two dummies provided the best predictor of how courtship was allocated between them, suggesting a perceptual basis on which females might select mates. This pattern of partial preference for the supernormal dummy occurred in females that exhibited either high or low amounts of following behaviour and is apparently independent of female responsiveness. Supernormality may therefore provide a mechanism whereby secondary sexual traits can be elaborated, even without evolutionary change in preference for those traits by the opposite sex.     

Mate choice and fitness in a hybrid frog: Rana esculenta females prefer Rana lessonae males over their own

Summary The evolution and maintenance of female choice based on purely genetic differences is still a controversial issue, not only for theoretical reasons, but also because of the practical difficulty of demonstrating the fitness consequences of preferences and heritability of and genetic variability in the chosen traits. We argue that hybrid systems (broadly defined) offer suitable models for studying mate choice according to genetic differences. We present such a study for European water-frogs of the hybridogenetic Rana lessonae/Rana esculenta complex (L/E complex). R. esculenta, originally a hybrid between R. lessonae and R. ridibunda, eliminates the L genome premeiotically and only produces eggs and sperm containing only the R. ridibunda (R) genome. Consequently, the hybrid will only persist when it lives and mates with R. lessonae in mixed populations where it can regain the lost L genome. In such mixed populations, there is strong selection against E x E matings. because these will produce no viable offspring. We tested whether females of the hybrid R. esculenta do indeed avoid their own R. exculenta males and choose males of the parental species R. lessonae instead. Eleven E females were offered a simultaenous choice between one L and one E male. Females exhibited a significant preference for L males that was determined by the type of male, rather than by its size or activity. This choice is in the direction predicted from genetics. The question of why L males agree to mate with E females, but L females only rarely mate with E males, is answered by a sexual asymmetry in the cost/benefit ratios of mating with the wrong type and the right size. Our results are consistent with the mating pattern found in natural populations, but further studies are needed to show that female choice really causes this pattern.Correspondence to: H.-U. Reyer     

Fighting success and attractiveness as predictors of male mating success in the black field cricket, Teleogryllus commodus: the effectiveness of no-choice tests

Females are generally assumed to prefer larger, more dominant males. However, a growing number of studies that control for male-male competition have shown no correlation between dominance and attractiveness. Aggressive males can interfere with female mate preference either by physically coercing females into mating or by driving submissive males away and restricting mate choice. The most common method of assessing female mate choice is by using simultaneous two-choice tests. These control for male-male interactions, but usually interfere with physical and chemical cues involved in mate selection or alter male behaviour. They are therefore unsuitable for many study species, especially insects. Another method is the no-choice test that measures a females latency to mating when placed with a single male as an indication of male attractiveness. No-choice tests control for male-male aggression while allowing full contact between pairs (they allow actual mating to be directly observed rather than to occur based on a correlated behaviour). So far, however, no study has confirmed that males that entice females to mate sooner actually enjoy increased longer-term mating success. As such, the accuracy of no-choice tests as a method of examining mate choice remains untested. Here, we used no-choice tests on the black field cricket, Teleogryllus commodus, to show that (1) females did not prefer males that won fights (dominant males), and (2) latency to mating predicts actual mating success. We have clearly demonstrated the usefulness of no-choice tests and, considering the advantages of this method, they should be more often considered for a wider variety of taxa.Communicated by D. Gwynne     

Alternative mating tactics and the law of Diminishing Returns: The Satellite Threshold Model

Summary The mating systems of many species comprise at least 2 alternative male mating tactics — broadly termed Dominant and Satellite tactics here. But, there exists no satisfactory conceptual framework in which to explain their co-occurrence and persistence.A Dominant male's ability to copulate is a positive, but decelerating, function of either his territory's attractiveness or his own attractiveness to females. This Diminishing Returns Effect affords mating opportunities for Satellite males associated with the most attractive sites (or males). A graphical Satellite Threshold Model, analogous to the Polygyny Threshold Model (Orians 1969), is developed to predict quantitatively the presence or absence of Satellite male tactics.Five predictions of the Model are supported quantitatively by data from dragonfly and anuran social systems and, more generally, by evidence from a wide variety of species.The Model should apply both to circumstances in which males are able to alternate between tactics and the instances in which males make an irrevocable tactical decision.     

Sex ratio,monogamy and breeding success in the Midas cichlid (Cichlasoma citrinellum)

Summary The Midas cichlid (Cichlasoma citrinellum) is a large, aggressive monogamous fish from the Great Lakes of Nicaragua. It lives in an ecosystem where breeding sites are at a premium and where breeding success can be low. I tested the strength of the pair bond by manipulating the sex ratios in captive groups, using ratios of 1:1, 2:1, 4:1, 1:2 and 1:4 (:). No polygamy was seen at any of the ratios. Departure from a ratio of 1:1 decreased breeding success for those pairs that formed. Both sexes appeared to enforce the pair bond but did so in different ways: females attacked males and females equally but males attacked other males significantly more than they did females. These results, coupled with field observations, indicate the Midas cichlid is obligated to monogamy by the demands of competition for breeding sites, the need for two parents to protect the fry and by energetic constraints.     

The evolution of leks through female choice: differential clustering and space utilization in six sympatric manakins

Summary The degree to which lekking and non-lekking male manakins select display sites in order to maximise proximity to females was examined by contrasting movements of females with male dispersion. Data on female visiting patterns, male courtship disruption, and mating skew were also collected over three successive breeding seasons. For the five lek-breeding species, female home-ranges were 3–7 times larger than those of adult males. Female movements were concentrated around leks, fruiting places and stream bathing sites. None of the females monitored by radio-tracking expanded her normal range in order to visit males on leks. On the contrary, feeding bouts of females frequently preceded a visit to potential mates at neighboring leks. Despite small sample sizes, significant correlations were found between female home-range size and male clustering (distances between neighboring leks and distances between neighboring males), as predicted by the female choice model and the hotspot model. Adult and immature male home-range sizes were not significantly correlated with male dispersion or female ranges. On the other hand, males and females of the only non-lekking species exhibited similar use of space and home-range size. Male settlement at sites with high levels of female traffic showed that the hotspot model is adequate to explain differences in male dispersion among sympatric lekking species. Comparisons with other studies suggest that apparent female choice could be overidden by past and present male-male interactions or female mate-comparison tactics. In fact, both the hotspot model and the attractiveness hypothesis appear to shape male dispersion on leks: males appear to settle under hotspot conditions with despotic rules generated through bias in female choice or male-male interference. It is proposed that the evolution of leks is ecologically motivated by the spatio-temporal distribution of trophic resources, initially leading to a dispersed male-advertisement polygyny. Following this, a foraging ecology that promotes high mobility by females and the magnetic effect of mating skew in particular males may have favored clustering on exploded leks. Later, the development of male-male interference and the increasing female home-range size could have led to the evolution of classical leks.     

Song as an attractant for male and female European starlings,and the influence of song complexity on their response

Summary We tested the hypothesis that song attracts females and repels males in the European starling. We broadcast recorded song from speakers attached to nestboxes, while paired boxes with silent speakers served as controls. As predicted, females were attracted to the song boxes. Contrary to prediction, males were also attracted to the `song' boxes. Singing by male starlings may be costly because it attracts competitors for limited nesting sites, but the cost cannot be avoided due to the need to attract a mate. In a second experiment simple song (composed of 20 different phrase types) and complex song (40 phrase types) were played simultaneously. More males were captured at boxes where simple song was played. Song complexity may function as an indicator of male quality and be used by male starlings to assess potential competitors.     

Lack of social entrainment of free-running circadian activity rhythms in the Australian sugar glider (Petaurus breviceps: Marsupialia)

Summary Social influence on circadian activity rhythms was investigated in the nocturnal Australian marsupial Petaurus breviceps. The activity of two and two was recorded electroacoustically and observed by an IR television camera in LD 12:12 (10¹:10^-1lx) and in LL (10^-1lx) when housed isolated and in pairs (+). In LD-entrained animals the average duration of locomotion, orientation movements, grooming and total activity is influenced by social housing, and individually different activity patterns are harmonized. In constant illumination conditions, however, the members of a pair are not mutually synchronized and free-run with different circadian periodlengths. Therefore social influence on the LD-entrained activity rhythm in Petaurus should be interpreted as social masking rather than direct influence on the circadian system.     

Sexual selection and cues for female choice in leks of Jackson's widowbird Euplectes jacksoni

Summary Sexual selection through female mate choice was investigated in the lekking Jackson's widowbird by applying multivariate selection analysis to observational data from four leks. Males perform a stereotyped jump display on small display courts (dance rings) constructed by the males in open grassland. Females visit the lek solely for mating and nest on their own, away from the lek area. Few cases of interference during courtship and absence of position effects on mating success indicated that female choice within the leks was not pre-empted by male-male competition. In a set of 11 male traits with mating success as the dependent fitness measure, significant selection differentials (covariances) were found for the length of the conspicuous tail and the rate of the jump display, suggesting sexual selection of these traits. They also showed the largest selection gradients (partial effects) and thereby seem to be the cues on which females base their choice. The success of males in obtaining copulations appears to depend on two components: display rate and lek attendance affect the number of female visits, whereas tail length seems to primarily influence the chance of copulating with a visiting female. Tail length was positively related to a measure of body condition, which is of interest with regard to the suggestions that sexual ornaments may serve as indicators of male viability.     

Sexual selection and the evolutionary effects of copying mate choice

We examine the evolutionary consequences of copying mate choice using models in which the preferences of younger females are affected by the mate choices that they observe older females making. We introduce two models of copying, termed single mate copying and mass copying, corresponding to situations in which immature females imprint on the choices of only one or of a very large number of older females, respectively. Female mating preferences are assumed to evolve only through cultural evolution, while the male trait on which they act is inherited either via a haploid autosomal or a Y-linked locus. Results show that the preference and male trait can rapidly coevolve, with a positive frequencey-dependent advantage to the more common male trait allele. This process can cause a display trait that lowers male viability to increase in a population. Mass copying results in stronger frequency dependence than does single mate copying. Mass copying and, under some conditions, single mate copying lead to two alterative stable equilibria for the male trait. Neither copying model supports variation at the male trait locus, and copying makes it more difficult for a novel male trait phenotype to spread. Correspondence to: M. Kirkpatrick     

Costs and consequences of variation in the size of ruff leks

Summary We studied 13 ruff leks in a small region on the island of Gotland (Sweden) to investigate the effect of lek size on the costs and benefits of lekking for individual males. Male ruffs occur in two behaviourally and morphologically distinct forms, independents (residents plus marginals) and satellites, whose costs and benefits we have assessed separately. These ruff leks had from 1–10 resident (territory-holding) males and were visited daily by satellites, marginals and females from 5–25 May, when most copulations occurred. We used the average number of independent males, counted during censuses taken every 5 min during 2-h observation periods at each lek, as an index of mean lek size. Per independent male, the numbers of both satellites and females increased significantly with mean lek size. Female arrival rate and attendance (total female-minutes) also increased significantly with mean lek size as did the average per capita rate of mating success for resident males (that of satellites was not quite significant). Thus, the dispersion of both of these male categories did not appear to fit an ideal free distribution with respect to mating success. In addition, the number of independent-independent fights per independent and the rate of satellite-resident dyad formation per resident increased significantly with mean lek size. These results suggest that ruffs on larger leks enjoy higher mating success than those on smaller leks but also that costs increase with lek size. We suggest that independent males distribute themselves so as to maximize their own net benefits and that this factor can account for both the occurrence of ruff leks and the variation in their size. Correspondence to: J. Höglund     

“Alternative” mating behavior in the swordtails Xiphophorus nigrensis and Xiphophorus pygmaeus (Pisces: Poeciliidae)

Summary The swordtail Xiphophorus nigrensis exhibits three relatively discrete male body-size classes that derive from allelic variation at the Y-linked pituitary (P) locus. Previous studies have shown that larger males have greater relative reproductive success, and that females prefer large males. We describe the mating behavior utilized by males of each size class during individual encounters with females. Small males rely on chase behavior, similar to the alternative mating behavior classified as sneaker in small males of other species. Large males court and intermediate-sized males court or chase, depending on their body size. There is a strong correlation between P alleles for small size (s) and large size (L) with chasing and courting, respectively. The relationship between mating behavior of males of the genotype I is ambiguous. In the closely related species X. pygmaeus, males are of size similar to smaller X. nigrensis males. Paradoxically, these males do not show the courtship display that typifies larger male X. nigrensis and many other species of swordtails, but instead often employ chase behavior identical to the alternative mating behavior in small male X. nigrensis. We suggest that historical and genetic constraints, in addition to current selection forces, might be important factors in explaining the existence of alternative mating behavior in X. pygmaeus.     

Effects of receptive females' secretion on some male reproductive behaviors in the amphipod crustacean Microdeutopus gryllotalpa

The use of a choice test apparatus has shown that receptive females of the tube-building amphipod crustacean Microdeutopus gryllotalpa (Costa) secrete a waterborne substance which attracts males. This substance (1) increases the level of activity of males, and (2) orients the males' movements towards its source. Males do not secrete this substance. In this species, females tend to remain inside their residential tubes, and males generally travel from receptive female to receptive female. Thus, in the field, the attractant may stimulate the male to accelerate his movements toward, and guide him directly to a receptive female. On the other hand, at the concentration tested, the substance alone does not elicit intermittent pleopod beats, a male-specific behavior that only occurs in a reproductive context. The expression of intermittent pleopod beats is shown to require the presence of a female plus its tube.     

Active mate choice at cock-of-the-rock leks: tactics of sampling and comparison

Summary The importance of active mate choice as a component of sexual selection remains controversial, despite recent studies identifying traits that correlate with male mating success. We analyzed the sampling sequences of individual female Guianan cock-of-the-rock, providing quantitative documentation of active female choice in this lekbreeding species. We compared observed sampling patterns with null models of random female movement and of movement weighted by the observed distribution of male success. The courts actually visited by individual females were significantly more clumped and centrally located than predicted by computer simulations of either random or weighted movement. Contrary to simplified hypotheses of female choice, hen cock-of-the-rock were not limited either to sequential comparisons or to threshold decision rules when selecting mates. Instead, they repeatedly sampled a subset of potential mates, using the pool-comparison tactic. Within this pool, females preferentially mated with the males ranked highest in terms of total courtship visits received, and rejected low-ranking males. Our results suggest complex interactions between patterns of female sampling and male dispersion in lek mating systems, and also provide insights into the constraints on female sampling in lek species.     

The role of learning in the mating biology of a sweat bee Lasioglossum zephyrum (Hymenoptera: Halictidae)

Summary Results from experiments on the role of learning in the mating biology of a sweat bee, Lasioglossum zephyrum (Hymenoptera: Halictidae), are described in this paper. Male learning of individual female odors is important in natural populations (Table 1), as has been shown in the laboratory. Four other hypotheses are unlikely to account for the observed behavior: (1) Female odors dissipate rapidly; (2) Males learn and then avoid the study area; (3) Males or females produce repellents which are effective against other males; or (4) males recognize their own odor on previously-contacted females, which they subsequently avoid. Regarding questions of male preference and optimal outbreeding, Tables 2 and 3 show there are no consistent preferences for more novel or less novel female odors.     

Digestive carbohydrases from the hepatopancreas of two Antarctic euphausiid species (Euphausia superba and E. crystallorophias)

The hepatopancreatic extracts of Euphausia superba Dana and E. crystallorophias Holt and Tattersall collected from the Antarctic. Ocean during January 1985, are most effective in hydrolysing substrates containing (13)--glucosidic linkages. Three enzymes appear to be involved in the depolymerization of (13)--D-glucans in the euphausiid diet: (1) an exo-(13)--D-glucanase, (2) an endo-(13)--D-glucanase and (3) a -D-glucosidase. The glucanases have a pH optimum of 5.4, a temperature optimum of 50°C and are optimally extracted in bistripropane buffer, pH 7.2. Levels of (13)-D-glucanase in laboratory-cultured E. superba are inversely affected by food availability, and activities double after starvation for 12 d. The increase is due mainly to higher activities of exo-acting glucanases. -Amylase and endo-(14)--D-glucanase (cellulase) activity are also present in the extracts in addition to glycosidase activity against a range of p-nitrophenyl substrates (-and -D-glocose, - and -D-galactose, -D-xylose, - and -D-mannose). Digestive activity against several acidic polysaccharides, including the acidic mucilage polysaccharide of the ice diatom Stauroneis amphioxys, is minimal and is not induced when the polysaccharide is present in the diet of E. superba. These results indicate that some, but not all, components of the algal material in the euphausiid diet can be hydrolyzed and assimilated.     

Mating system of the commensal marine isopod Jaera hopeana (Crustacea)

The commensal marine isopod Jaera hopeana Costa, 1853 was reared in the laboratory through 30 generations in the absence of its host, Sphaeroma serratum, to study its development and reproductive behaviour. It was found that adult males take virtually any opportunity to associate with a young conspecific in manca-I stage (first free-living stage) and carry it around in a characteristic position. This male-manca(I) amplexus ends during the manca's first postmarsupial molt (manca-I to manca-II) at an average age of about 9 d after hatching from the marsupium. Entry into amplexus does not alter a manca's molt timing, the duration of the amplexus thus depending exclusively on the manca's age when it joined by a male. Given a choice, males do not prefer manca-I close to molting over those just hatched. With the first postmarsupial molt, long before sexual maturity, female J. hopeana become receptive to mating. Before a female manca is released from amplexus, it is inseminated by its male partner. Sperm transferred to young immature females are stored within special sperm stores until they are needed for fertilization. The male-manca(I) amplexus seems to be a precopula, wherein males wait for their partners to molt and become sexually receptive. Nevertheless, it is inevitable that every second amplexus on average ends unsuccessfully: although manca-I have already been determined irreversibly (and probably genetically) as males and females in equal numbers, adult males are unable to predict which manca-I are potential mates and which are not. Males accept any manca-I as a precopula partner, and even when given a choice they do not prefer female over male manca-I. From the manca-II stage onward, females are continuously receptive to mating for the rest of their life, and mating can occur immediately upon contact of the partners without any significant investment in energy and time (en passant copulation).     

Reproductive biology of commercially exploited deep-water royal red prawns (Haliporoides sibogae,Solenoceridae) in south-east Australia

Deep-water royal red prawns (Haliporoides sibogae de Man, 1907; Solenoceridae: Penaeidea) were sampled from commercial catches off south-east Australia between November 1988 and May 1990. Four stages of sexual development were distinguished macroscopically for each sex. For the females, histology and analysis of oocyte size were used to validate the macroscopic staging of ovaries into undeveloped, developing, early ripe and ripe. Females were larger than males, reaching a maximum size of 46 mm carapace length (CL) compared to 32 mm CL for males. Average size at sexual maturity was 30.8 mm CL for females and 25.8 mm CL for males. Females apparently breed several times in their life, whereas males probably breed only once. Individual fecundity (ranging from about 58 000 to 140 000 oocytes) was relatively low compared with other penaeids, but oocytes were larger (mean diameter=0.41 mm). Two short breeding seasons occurred per year (February to April and July to August). There was a clear size-related latitudinal distribution of the prawns, with largr prawns (spawners) being more abundant in the northern region of the fishing area, and juveniles (CL20 mm) being more abundant in the south. Most of the spawning stock probably lies outside the main fishing ground, while the fishery targets mainly prawns below the size at maturity.     

Comparisons of the feeding activity and diets of male and female cunners Tautogolabrus adspersus (Pisces: Labridae)

The diel distribution of feeding activity during the spawning season was compared for territorial male and female cunners Tautogolabrus adspersus in Conception Bay, Newfoundland, Canada between June and August, 1978. Territorial males feed significantly less often than females and concentrate their feeding activities in the morning, whereas females feed as frequently in the afternoon as in the morning. Based on the contents of alimentary tracts, territorial males, non-territorial males, and females have different diets. Since these three groups share the same habitat, the observed dietary differences probably reflect differences in their foraging behaviour. The relevance of these findings to the concept of time minimizer and energy maximizer is discussed.