Mating effort and female receptivity: how do male guppies decide when to invest in sex?

Males vary in the degree to which they invest in mating. Several factors can explain this variation, including differences in males’ individual condition and the fact that males allocate their energy depending on the context they face in each mating attempt. Particularly, female quality affects male reproductive success. Here, we studied whether male guppies (Poecilia reticulata) strategically allocated more mating effort, in terms of mating behaviour and male–male competition, when they were matched with a receptive (R) female than a non-receptive one. In accordance with our prediction, we found that males increased their mating behaviour when they were with a receptive female. Even though male guppies can inseminate non-receptive females, we only found high levels of courtship between males that were with a receptive female rather than a non-receptive one. Although there was little affect of female receptivity on male–male competition, we found that males chased and interrupted courtships more with receptive females than with non-receptive females regardless of odour. Finally, we also studied whether the sexual pheromone produced by receptive female guppies is a cue that males use in order to increase their mating effort. We found that males were more attracted to a female when they perceived the sexual pheromone, but only increased their mating and aggressive behaviours when females showed receptive behaviour. This strategic increase in mating effort could result in higher male reproductive success because mating attempts towards receptive females are likely to be less costly and males could have a greater probability of fertilisation.     

Inhibition of cyclooxygenase-2 protects against cocaine hepatotoxicity in CF-1 mice

Gender differences in oral cocaine hepatotoxicity have been observed and lipopolysaccharide (LPS) was shown to potentiate cocaine hepatotoxicity in male CF-1 mice. Since cocaine and LPS inflict hepatocellular damage through the production of harmful reactive species, the role of cyclooxygenase-2 (COX-2) in gender-dependent cocaine hepatotoxicity was investigated. COX-2 increases nitric oxide (NO) synthesis and pro-inflammatory mediator production in response to hepatocellular insult. Male and female CF-1 mice were orally administered 20 mg kg^?1 cocaine hydrochloride once daily for 7 days. Four hours after the last cocaine administration, the mice received 12 × 10⁶ EU LPS intraperitoneally (cocaine + LPS). Mice receiving meloxicam (7.5 mg kg^?1, p.o.), a selective COX-2 inhibitor, were pretreated 1 h before each cocaine administration. Meloxicam prevented liver damage in males produced by cocaine and cocaine + LPS as evidenced by microscopic appearance and biochemical indices equivalent to saline treatment. Acetaminophen (APAP) was administered orally as a positive control which shows no gender dependency and elicited a hepatotoxic response in both males and females. Altered biochemical indices suggest that COX-2 is activated, possibly to a greater extent in females versus males in APAP-induced hepatotoxicity. Meloxicam prevented all oxidative stress changes induced in males following APAP. The results suggest that the induction of COX-2 is responsible, in part, for cocaine hepatotoxicity with and without LPS exposure in male mice.     

Effect of female molt stage and sex ratio on courtship behavior of the blue crab Callinectes sapidus

In many species, males and females actively participate in courtship, and the outcome of pre-mating interactions influences the mating success of both sexes. Female blue crabs, Callinectes sapidus, mate soon after their final molt to maturity; thus female molt stage dictates the timing of mating. In a field experiment, we manipulated female molt stage and sex ratio to test their effects on the courtship behavior of both sexes, if female behavior influences the behavior and pairing success of males, and if male courtship influences male pairing-success. Early-molt-stage females avoided males during courtship, whereas late-molt-stage females sought out males. As a result, males had to pursue and capture early-molt-stage females whereas males displayed to late-molt-stage females and more easily physically controlled them. Males sometimes abandoned late-molt-stage females, but this occurred more often when females were abundant. The rate at which females avoided males was positively correlated with that of males abandoning females, and males that were unsuccessful at pairing met with higher rates of female resistance than successful males, suggesting that female behavior influences male pairing-success. Unlike unsuccessful males, successful males more often made the transition between display and maintaining physical control of the female. At high male sex ratios, males initiated courtship more readily; thus both sexual competition and female behavior influence male courtship in this species. Received: 7 July 1996 / Accepted: 10 January 1998     

Alternative mating strategies in the water strider Gerris elongatus (Heteroptera,Gerridae)

Summary Males of the water strider Gerris elongatus established territories which included copulation and oviposition sites (small pieces of fallen bamboo). Males were aggressive and competition for territory and females was observed frequently. Male midlegs were more developed than female midlegs and were used as weapons. Reproductive behaviour changed as the breeding season advanced. Early in the season immature females were attracted by male surface wave courtship signals, then copulated white floating on the water surface without ovipositing (type 1). In midseason, males established territories, produced calling signals and attracted females which copulated and oviposited there with male postcopulatory guarding (type 2). In late season, many females oviposited without postcopulatory guarding on pondweed mats near fallen bamboo. Non-territorial males waiter for the arrival of these females and copulated without courtship, but mating success was low (type 3). These alternative mating strategies appeared to depend on differences in male size. Larger males were superior to smaller males in many ways (establishing territory, fighting, mating etc.). The largest males defended territories and had higher mating success than small non-territorial males. Medium sized males used all three strategies according to the number of empty territories and seasonal femald distribution.     

Experimental studies on water strider mating dynamics: spatial variation in density and sex ratio

Summary We used field surveys, field experiments and experiments in artificial pools to study the effects of variation in sex ratio and density on mating dynamics of a stream water strider, Aquarius remigis. Our field survey documented the existence of hot spots, sites of higher than average total gerrid density, a male-biased sex ratio, and higher than average female mating activity. Female gerrids frequently changed sites, usually moving upstream, perhaps to spread their eggs among many sites. Male gerrids showed two movement strategies: some males frequently changed sites, while other males were stationary at hot spots. Surprisingly, smaller males tended to be stationary at hot spots. A field manipulation of the availability of refuges for females to avoid harassment by males supported the notion that males prefer hot spots because they are sites where a scarcity of refuge for females makes it relatively easy for males to intercept females. Experiments in plastic pools compared sites with 20 males: 5 females (simulating hot spots) to pools with 5 males: 5 females. The rate of male harassment of females was higher in 20:5 pools as compared to 5:5 pools. In response to increased male harassment, females reduced their activity on the water and increased their time spent out of the water and thus unable to forage. Males showed a large male mating advantage (LMMA) in 5:5 pools, but, surprisingly, not in 20: 5 pools. This pattern can explain the field observation that small males prefer hot spots. A behavioral mechanism that can explain the LMMA is as follows. Mating occurs when males overcome female resistance. Larger males have a mating advantage over smaller males if females resist heavily. Increased harassment (e.g., in 20:5 pools as compared to 5:5 pools) might result in reduced female resistance to males and thus a reduced LMMA. Females also showed some non-random mating by size that might reflect an interplay between male preference for large females and the avoidance of males by large females. Correspondence to: A. Sih     

Repeatable female preferences, mating order and mating success in the poeciliid fish, Heterandria formosa

Sexual selection via female choice can afford preferred males comparably higher mating success than those males that lack preferred traits. In addition, many models of sexual selection assume that both male traits and female preferences are heritable. In this study we test whether females of the poeciliid fish, Heterandria formosa, have repeatable pre-copulatory preferences for larger males. We also test whether female pre-copulatory preferences are always reliable indicators of male mating success. When given a choice between a large and a small male, females prefer larger males, and the repeatability of this preference is high. Although there are no overall differences in male mating success between large and small males, large males have a higher mating success when they are the first to mate than when they are the second to mate. Likewise, preferred males also have higher mating success when they are the first to mate than when they mate second. Therefore, the repeatable female preferences observed in this study only predict male mating success when the preferred male mates first. These results illustrate that even significantly repeatable female preferences do not translate into male mating success, which is an assumption of many examinations of the importance of female choice in sexual selection.     

A test of male mating and hunting success in the kestrel: the advantages of smallness?

We tested female choice for male wing and tarsus length and body mass in the kestrel (Falco tinnunculus), a species in which males average about 10% smaller than females. We also studied how male characters are related to their hunting success. In the laboratory, females preferred lighter males with shorter tarsi as mates, if the difference in those characters between competing males was larger than average. Lighter and shorter-winged males seemed to be better hunters than heavier and longer-winged males. Field observations in a year in which voles were scarce suggested that shorter-winged males were also better food providers in courtship feeding than longer-winged males,although in good vole years such a relationship was not found. We argue that females may prefer to pair with smaller males, because they have higher flight performance and better hunting success than heavier males. By doing so, females may gain direct breeding advantages. We conclude that both female choosiness and the hunting efficiency of males well contribute to reversed sexual size dimorphism (RSD, females larger than males) in the kestrel. Received: 18 July 1995/Accepted after revision: 17 August 1996     

Female egg investment in relation to male sexual traits and the potential for transgenerational effects in sexual selection

Life-history theory predicts that individuals should increase their reproductive effort when the fitness return from reproduction is high. Females mated with high-quality males are therefore expected to have higher investment than females mated with low-quality males, which could bias estimates of paternal effects. Investigating the traits females use in their allocation decisions and the aspects of reproduction that are altered is essential for understanding how sexual selection is affected. We studied the potential for differential female allocation in a captive population of a precocial bird, the Chinese quail, Coturnix chinensis. Females paired with males with large sexual ornaments laid larger, but not more, eggs than females paired with males with small sexual ornaments. Furthermore, female egg mass was also significantly positively affected by male testis size, probably via some unknown effect of testis size on male phenotype. Testis size and ornament size were not correlated. Thus, both primary and secondary male sexual traits could be important components of female allocation decisions. Experimental manipulation of hormone levels during embryonic development showed that both male and female traits influencing female egg size were sensitive to early hormone exposure. Differences in prenatal hormone exposure as a result of maternal steroid allocation to eggs may explain some of the variation in reproductive success among individuals, with important implications for non-genetic transgenerational effects in sexual selection.Communicated by C. Brown     

Costs of courtship and mating in a sexually cannibalistic orb-web spider: female mating strategies and their consequences for males

The costs of courtship and mating may include increased risks of predation, the transmission of pathogens, and a loss of foraging opportunities. Thus, a female's decision to tolerate a courting male will depend upon how these costs offset the benefits of mating, which will depend on her reproductive and nutritional status. While these costs may be similar for mated and unmated females, the benefits of mating will be less for mated than virgin females. However, the cost of lost foraging opportunities may be higher for females with fewer nutritional reserves necessary for forming eggs. We examined how these costs and benefits influence the courtship and mating behaviour of male and female orb-web spiders, Argiope keyserlingi. In the field, females on webs that also contained a courting male intercepted fewer prey items per hour than females on webs without a male. In the laboratory, the presence of a courting male at the hub also attracted mantid predators to the web, increasing the risk of predation for both male and female. Staged mating experiments in the laboratory revealed that the frequency of female attacks and pre-copulatory cannibalism was greater among mated than virgin females. Feeding history did not affect aggression in virgin females but, among mated females, food-deprived spiders attacked and cannibalized males more frequently than sated females and only the latter ever remated. These differences in female behaviour influenced male mating strategies. Choice experiments demonstrated that males preferred to venture onto the silk threads of virgin rather than those of mated females. Similar patterns of mate selectivity were observed in the field; females with narrow abdomens attracted more males to the webs than females with broad abdomens, and copulations were observed more frequently among females with narrow abdomens. These smaller females are likely to be virgins that have recently molted. Males that preferentially mate with virgin females will not only avoid potentially fatal attacks but also obtain, on average, a higher fertilization success.     

Indicators of physiological and immunological status of <Emphasis Type="Italic">Litopenaeus setiferus</Emphasis> wild populations (Crustacea,Penaeidae)

Constant environmental changes in oceanic and estuarine systems due to human activity in coastal zones require different tools and strategies for their study to be able to assess the health status of aquatic ecosystems. The Gulf of Mexico has a tremendous ecological importance because of its biological diversity. Baseline levels of blood metabolites and immune components were defined for wild tropical populations of Litopenaeus setiferus, an important shrimp species of the Gulf of Mexico. Osmotic pressure, oxy hemocyanin (OxyHc), glucose, proteins, cholesterol, lactate, and triacylglycerols (TAG) were used as indicators of physiological status; pro phenoloxydase (proPO) and phenoloxydase (PO) quantification of hemocytes, as well as respiratory burst, were used to assess the immunological status. Significant differences were observed in live weight of juveniles, males, and females of L. setiferus with mean values of 10.54, 35.05, and 40.33 g, respectively. A value of 460 mOsm/kg was recorded in the water where juveniles were sampled and 1,000 mOsm/kg in adult sampling zones. Consequently, the osmotic pressure of L. setiferus juveniles (718.02 mOsm/kg) was 22% lower than in adults (925 mOsm/kg); there were no differences between sexes. A significantly lower value in juvenile OxyHc was observed. This value was 24 and 16% lower than that observed in males and females, respectively. Hemolymph glucose, cholesterol, and triacylglycerol levels were not statistically different between shrimp stages, showing median values of 0.19, 0.32, and 0.39 mg/ml of glucose, cholesterol, and triacylglycerols, respectively. Hemocyanin was distributed normally in the juvenile–male population but not in females. A proportion between 52 to 81% of OxyHc of the total protein (OxyHc/Prot) was obtained for all stages. Digestive gland glycogen showed no normal distribution in juveniles and adults. Digestive gland glycogen was significantly higher in juveniles (median value of 2.64 mg/g) than in adults (median value of 1.58 mg/g). A higher value of lactate (0.11 mg/ml) was observed in juveniles than in males (0.09 mg/ml) and females (0.04 mg/ml). Granular cells (GC) corresponded to 36, 44, and 39% of the total hemocytes (TH) observed in juveniles, males, and females. ProPO showed no normal distribution in all stages. A high proPO activity was recorded in L. setiferus females that was 95% higher than in the juvenile–male group. Respiratory burst was divided into two groups, juveniles–males and females, and was distributed normally in both. Female respiratory burst values were 40 and 45% higher than those observed in the juvenile and male groups, respectively. There was an increment in OxyHc, proteins, PO, hemocytes, and respiratory burst with an increase in body weight. In contrast, the relationship of live weight to glucose, TAG, and proPO revealed no significant regressions. A significant decrease in cholesterol, glycogen, and lactate with an increase in body weight was also observed. We now have indicators of nutritional and immune status of juveniles and adults that can reveal changes in trophic relations and health at the population level. This will serve as a basis for using L. setiferus as environmental sentinels, as non-controversial and inexpensive models to evaluate the potential changes that human activities could exert on this important marine ecosystem.Communicated by P.W. Sammarco, Chauvin     

Changes in the activity budgets of yellow baboons (Papio cynocephalus) during sexual consortships

Summary The energetic cost of guarding estrous females has been assumed to be a potentially major factor in limiting the duration of male consortships in a number of polygamous species. This issue has been examined in the present study by assessing changes in the usual activity budgets of 13 male and 20 female yellow baboons which occurred during their consortships.The percent of time adult males spent feeding was strongly related to their agonistic rank: Higher-ranking males fed proportionately more than lower-ranking males while not in consort, and they showed a relatively greater decrease in feeding time during consortships.The proportion of time females spent feeding was related to their agonistic rank and (to a lesser degree) to their parity. Higher-ranking females fed more than lower-ranking females outside of consortships, and showed a relatively greater decrease in time spent feeding while in consort. Nulliparous females tended to feed more than parous females while not in consort; during consortships, the feeding time of nulliparous females decreased, while that of parous females increased slightly.The activity of male and female consort partners was most coordinated during the fertile cycle stage of the female partner, and least coordinated once the female had passed the fertile stage.Although reductions in feeding time during consortships were generally much more pronounced in males than in females, neither males nor females appeared to attain the undisturbed optimal feeding level for their sex while in consort.     

Liver and renal lesions in mercury-contaminated narwhals (Monodon monoceros) from North West Greenland

Narwhals (Monodon monoceros) from North West Greenland are known to bioaccumulate mercury (Hg) in tissues and internal organs. This is postulated to be a health concern and therefore studies were undertaken to conduct a screening study of Hg concentrations and histopathology of liver and renal tissues in a total of 12 specimens. The sample consisted of two sub-adults (one male, one female) and 10 adult (six males, four females) collected in Qaanaaq (Thule) 2010. In liver, Hg mean ± SD was 11.88 ± 10.47 μg/g ww (range: 0.39?31.8 μg/g ww) while the concentrations in kidneys were 1.85 ± 1.20 μg/g ww (range: 0.41?4.03 μg/g ww). There was no marked difference in Hg concentrations between males and females while sub-adults had significantly lower concentrations. The histological examinations of renal tissue showed glomerular capillary dilatation and basement membrane thickening, dilatation, and hyalinization of Bowman's space/capsule and tubular lesions with hyaline casts accompanied by interstitial fibrosis in the kidneys. In liver tissue, portal cell infiltrates and fibrosis, bile duct proliferation, lipid-filled Ito cells, and steatosis were found. There was no marked difference in histological prevalence between males and females and in Hg concentrations in individuals with or without lesions. Four of seven renal lesions and one liver lesion were found in the two sub-adult whales. Based upon these findings, as well as the nature of the lesions, evidence suggests that histopathological alterations were a result of age but that Hg might be an aggravating co-factor in development of renal lesions in particular.     

Sexual selection and female fitness in <Emphasis Type="Italic">Drosophila simulans</Emphasis>

There is a current debate over the net fitness consequences of sexual selection. Do preferred males increase female fitness or are these males manipulating females for their own benefit? The evidence is mixed. Some studies find that mating with attractive males increases female fitness components, while others show that preferred males decrease measures of female fitness. In this study, we examined some of the fitness consequences of pre-copulatory sexual selection in Drosophila simulans. Virgin females were either paired with one male and given an opportunity for one copulation or were exposed simultaneously to two males. This allowed us to compare female preference (copulation latency) and fitness (longevity, lifetime productivity and rate of offspring production) both with and without the influence of male–male competition. When females had access to a single male, neither female longevity, productivity, nor short-term rate of productivity were associated with female preference, and although females mated more quickly with larger males, male size was also not associated with any female fitness measure. Inclusion of male–male competition showed that female longevity was negatively affected by preference, while productivity and rate of productivity was unaffected. This latter experiment also indicated that females preferred larger males, but again, male size was not associated with female fitness. These results indicate that females may not benefit from mating with preferred males, but they may incur survival costs.     

Aggressive male mating behavior depends on female maturity in Octopus bimaculoides

This laboratory study examined the combined effects of male and female behaviors on the outcome of mating encounters in Octopus bimaculoides. We found that male–male competition for mating opportunities depends on female maturity; the presence of immature females elicited significantly higher levels of aggression between competing males. We conclude that males are able to assess the reproductive status of females. The study also found that immature and mature females resisted male mating attempts to a similar extent but that males that showed more aggression toward male competitors were able to spend more time in contact with females. We suggest that the lack of prominent visual displays in these mating trials indicates the importance of chemical cues in Octopus mating systems, as has been demonstrated for other cephalopods. This study contributes to the growing research on cephalopod mating systems and in particular shows that Octopus mating dynamics may be more behaviorally complex than initially assumed.     

Association patterns among male and female spotted hyenas (Crocuta crocuta) reflect male mate choice

Although female animals tend to be choosier than males in selecting mates, sexual selection theory predicts that males should also be choosy when female fecundity varies. Reproductive success among female spotted hyenas varies greatly with social rank. Our goals were therefore to determine whether male hyenas preferentially associate with high-ranking females, and whether male preferences are affected by female reproductive state. Interactions between adult males and females were observed intensively, and association indices calculated for all male-female pairs, over a 7-year period in one population of free-living hyenas. Males initiated most affiliative interactions with females, and males associated most closely with females that were likeliest to be fertile. High- and middle-ranking males associated most closely with high-ranking females, but low-ranking males associated equally closely with females in all rank categories. We used molecular markers to determine the paternity of cubs born during the study period, and found that sires associated more closely with the mothers of those cubs than did non-sires, particularly during the last months before conception. These association data indicate that male spotted hyenas do indeed exhibit selective mate choice, and that they prefer females likeliest to maximize male reproductive success.     

Uganda kob mating success does not increase on larger leks

One explanation for the movement of sexually receptive females to clusters of male territories in lek-breeding species is that larger clusters provide females with higher-quality mating partners, as would be the case if males were distributed between leks in an ideal free distribution for unequal competitors. This ideal free model of lek evolution predicts that male competitive ability and mating success will be greater on larger leks than smaller ones. I tested these predictions by comparing the mean number of males on 19 different Uganda kob leks with the sex ratio, the availability of oestrous females, mating rates, male fighting rates and male turnover rates. Contrary to the predictions of the model, numbers of females, receptive females and fights increased proportionally with lek size, but were no greater per male on larger leks. Multivariate analyses of male and female numbers on leks showed that male numbers were associated with female numbers, female numbers in the past, and a variety of habitat variables which may have related to the costs of holding a lek territory, but female numbers varied only with male numbers and female density in the area. These data do not provide evidence that females gain access to superior males by mating on larger leks, though they do support the possibility that lekking may be promoted by a tendency for larger leks to retain females longer.     

Sexual behavior is related to badge size in the house sparrow Passer domesticus

Summary Badge size, which functions as a signal of dominance status in male house sparrows Passer domesticus, was significantly related to their sexual behavior. Males with large badges participated in communal displays (multi-male chases directed towards single females) more often than males with small badges, irrespective of whether the female involved was the male's mate or not. Experimentally released females were more often chased if they were fertile than if they were nonfertile. Estradiol-implanted females were chased more often than control females without a hormone implant, and males with large badges chased estradiol-implanted females more often than did males with small badges. Both forced extra-pair copulations during communal displays and unforced extra-pair copulations were more often achieved by males with large than small badges. Male house sparrows with large badges also copulated with their mates at a higher rate than did males with small badges. A higher certainty of paternity therefore is hypothetized to accrue to male house sparrows with large badges.     

Phenotypic differentiation in female preference related to geographic variation in male predation risk in the Trinidad guppy (Poecilia reticulata)

Summary Populations of the Trinidad guppy range from areas with high levels of predation by other species of fish to areas with little or no piscine predation. Previous studies have shown that variation among populations in male coloration can be explained by a balance between female preference for brighter males and natural selection against bright males. High levels of male courtship activity may also increase both predation risk and mating success. Therefore, in high-predation areas, females that mate with males that court frequently as well as those that choose bright males would presumably produce male offspring with low survivorship. Consistent with this variation in natural selection, we observed that females from high-predation populations were less likely to choose bright and frequently courting males than females from low-predation populations. This result supports the hypothesis that female preference is evolving as a character genetically correlated with the preferred male character, in which case higher levels of natural selection acting against the male character should be related to lower levels of female preference.     

Male preference for large females and assortative mating for body size in the sand lizard (Lacerta agilis)

Summary Male sand lizards (Lacerta agilis) are polygynous and guard individual females for several hours to days after copulation. Even though the copulation itself only lasts 2–4 min, the total time that a male invests per female is considerably more and may constitute a substantial investment during a mating season. In such situations, when male copulation frequency is constrained, or when variation in female fecundity is high, mate choice by males may be adaptive. Large body size in female sand lizards is correlated with higher fecundity. In choice experiments performed in the laboratory, male sand lizards preferred to court large females rather than small females. In addition, when there was little difference in size between the females in the experiment, the males visited the two females more often before they started to court the preferred female. The results from a field study during 1984 and 1987–1990 showed that females are non-aggressive, have small neighboring home ranges (c. 100 m²) and may share burrows and sites for thermoregulation. This means that females can be found close together and thus gives males the opportunity to choose a mate. Assortative mating with respect to size was observed in a natural population, as well as a limited number of direct choices of females by males. These results support the results of the choice experiment.     

Sexual dimorphism and the mating ecology of polar bears (Ursus maritimus) at Svalbard

We assessed the role of size, mass, and age in mating and non-mating polar bears (Ursus maritimus) at Svalbard, Norway, during the spring breeding season. The ratio of male to female mass, in male-female pairs, ranged from 1.00 to 3.02 ([`(x)] = 1.99 \overline x = 1.99 ) indicating that mating males were larger than mating females but with substantial variation. Paired males were older than unpaired males and male mass was related to age. However, males paired with females were not significantly different in body mass from those males caught alone. Wounds and scars resulting from fights between males began at about 6 years of age and peaked at about 17 and 20 years of age, respectively. The frequency of broken canines in males, presumably due to increased male-male conflicts, increased with age but showed little increase in females. The wide range of male size in male-female pairs and the age-related signs of injury suggest that male polar bears engage in both scramble competition and contest competition for access to breeding females. The mating system of polar bears is variable but is best described as female defense polygyny or serial monogamy.