Experimentally elevated plasma levels of testosterone do not increase male reproductive success in blue tits

In temperate passerines, increased testosterone (T) levels during breeding mediate male aggressive and mating behaviour. If individual variability in T levels is reflected in behavioural differences during mating, males with higher T might gain higher reproductive success. This can be tested experimentally by elevating T levels. However, high exogenous T levels are known to have negative effects on male sperm production. This may reduce male fitness, particularly if sperm competition is intense. We experimentally elevated T levels in breeding blue tit males to investigate how T levels above the natural mean influence male reproductive success. Contrary to most—if not all—previous experimental manipulations of T levels in birds, we restricted the treatment with exogenous T to the time when females were fertile and T levels were naturally high in males. In blue tits, extra-pair paternity is an important component of male reproductive success, and its frequency is likely influenced by androgen-mediated behaviours such as mate attraction and aggression towards other males. Here we show that T-males were equally likely to become cuckolded and did not gain more extra-pair paternity than control males. Cuckolded T-males, however, lost more paternity than control males. We discuss the possibility that this is caused by negative effects of T treatment on sperm production.Communicated by M. Webster     

Effects of testosterone on male-male competition and male-female interactions in blue tits

In temperate-zone birds, testosterone (T) influences male behavior during the breeding season. The elevation of plasma levels of T to a breeding baseline is necessary for basic reproductive behaviors, but it is still unclear whether variation in T levels above this critical threshold influences the intensity of these behaviors. Such a relationship between T and sexually selected traits is a critical assumption of the immunocompetence handicap hypothesis. We here experimentally elevated T levels in blue-tit males above the natural mean (T-males) during the period of nest building and egg laying, without manipulating hormone levels during chick feeding. T-males neither interacted more often with other males, nor did they respond more aggressively to a dummy intruder, compared to males with control implants. T-males did not guard their social mates more closely, but they were more likely to interact with potential extra-pair mates. Females mated to T-males did not change their behavior during egg laying and the treatment did not significantly affect male and female feeding rates. Despite this, nests of T-males produced larger and heavier fledglings in one study year. Our observations suggest that T levels above the natural mean during the mating period do not increase aggressive or territorial behavior in male blue tits. However, if females perceived T-males as high-quality mating partners, superior offspring development in nests of T-males might be caused by higher maternal investment. Hence, male behaviors involved in mate attraction may have been influenced by T levels above the natural mean.Communicated by R. Gibson     

Effects of testosterone supplementation on chemical signals of male Iberian wall lizards: consequences for female mate choice

In some lizards, female mate choice is influenced by chemicals secreted by males, e.g., via the femoral glands. Secretions of the femoral glands are under direct androgenic control and vary seasonally with androgen production. However, whether increased testosterone (T) levels affect the concentration and chemical composition of secretions or their attractiveness to females is unknown. We manipulated T levels of male Iberian wall lizards, Podarcis hispanica, with silastic implants. Differential tongue-flick rates indicated that females detected and discriminated between femoral secretions of control and T-implanted males based on chemical cues alone. Females showed greater responses to secretions of T-males, which might suggest that T increased the concentration of chemical signals. Further analyses by gas chromatography–mass spectrometry indicated that T supplementation induced qualitative changes in lipid composition of femoral secretions. T-males had decreased relative proportions of cholesta-5,7-dien-3-ol in secretions, which might be related to the negative effects of T on the immune system and on lipid metabolism. However, experiments of choice of males’ scent showed that females neither preferred nor avoided the scent marks of T-males but preferred males that maintained higher proportions of cholesta-5,7-dien-3-ol in secretions, independently of the experimental manipulation. Thus, because this steroid is negatively affected by T, there might be trade-offs among increasing T levels to increase the production of chemical secretions, maintain metabolism, and attract females.     

Sequential male mate choice in a fish,the Pacific blue-eye<Emphasis Type="Italic"> Pseudomugil signifer</Emphasis>

Mate choice is not just a female preoccupation. Under some circumstances, males may also be choosy. However, studies of male mate choice have generally been confined to situations where males can make direct comparisons between potential partners. In contrast, sequential male mate choice has largely been overlooked despite its biologically importance, especially if current investment in mate attraction diminishes a males future mating opportunities. Using the Pacific blue-eye fish Pseudomugil signifer, we show that males are capable of exercising sequential mate choice. When presented sequentially with large and small females, males spent more effort courting the former. However, males did not appear to modify the time spent courting a given female based on the size of the female encountered previously. We suggest that greater attention to the sequential choice problem in males may help illuminate similarities and differences between the sexes when it comes to mating decisions.Communicated by T. Czeschlik     

Linking male qualities to multiple display traits: an example in a fish with exclusive male care

Recent theoretical models predict that the relative allocation to advertisement and parental care depends on whether paternal care is necessary for offspring survival: In species with exclusive male care, male investment in attraction is expected to reliably indicate paternal care effort and male phenotypic quality. Previous research, yielding contrasting results, has considered how one trait involved in mate attraction interacts with parental care or a specific aspect of male quality. In the blenny Salaria pavo, we perform a comprehensive analysis of the interplay between overall male attractiveness and male quality, the latter in terms of fertility, condition, and parental care. In this fish, males are larger than females, exhibit two sexually dimorphic traits (head crest and anal glands), and solely care for eggs. We generated a male attractiveness index through principal component analyses of morphological traits and quantified parental effort as the total time spent in egg care. In addition, we analyzed the relationships between specific components of attractiveness and male qualities. In agreement with theory predictions, we found that male overall attractiveness is a reliable indicator of fertility, in terms of sperm number, but is unrelated to body condition and parental care effort, with males able to perform high levels of care regardless of their level of advertisement. However, the relative expression of head crest area appears positively related to sperm number but is traded-off with parental care effort. These findings underline the need, in addressing real patterns, to consider interactions between multiple aspects of male display and quality.     

Mate attraction by females in a sexually cannibalistic praying mantis

We studied mate attraction by females of the praying mantid, Tenodera aridifolia sinensis, testing honest signaling of mate availability versus deceptive signaling to attract males for sexual cannibalism. We experimentally varied female diet and mating history and measured the rate of attraction of a wild population of males to caged females. Honest signaling theory predicts that virgin females will attract males at the greatest rate whereas deceptive signaling predicts that hungry females (which are more likely to cannibalize males) will attract more males, particularly among non-virgin females. Our results show that hungry females did not attract more males than well-fed females. Indeed, the opposite was true: hungry females attracted significantly fewer males. Moreover, hungry females were no more likely than well-fed females to attract males subsequent to mating, and mated females attracted males at a lower rate than did virgin females. We also observed female T. aridifolia sinensis and male Mantis religiosa arriving at the caged females and we discuss the significance of these observations. The results refute the hypothesis of deceptive signaling and show that mate attraction signals of female T. aridifolia sinensis are honest indicators of female mate availability and a lower risk of sexual cannibalism.     

Exogenous testosterone increases female aggression in the European starling (<Emphasis Type="Italic">Sturnus vulgaris</Emphasis>)

In the European starling, Sturnus vulgaris, optimal mating systems differ between males and females. Males gain from polygyny, whereas monogamy increases female fitness. The cost of polygyny to females lead to intense female–female competition, and it has previously been shown that the intensity of female aggression during the pre-breeding period can predict the realised mating system. The physiological regulation of such female aggression in starlings is not yet known. This study examines the role of testosterone in mediating aggressive behaviours involved in intra-specific reproductive competition in female starlings. Testosterone levels were experimentally elevated with testosterone implants in females during the pre-laying period. To simulate a situation in which an additional female tried to mate with the focal female’s mate, a caged female was presented close to a nest-site to which the male could attract a secondary female. Testosterone was significantly related to several behaviours involved in female–female interactions. Females with testosterone implants spent significantly more time close to the caged female and produced more song bouts than control females. In contrast, male behaviour was unrelated to the experimental status of the mate. Females mated to males that attracted a secondary female were less aggressive towards the caged female than those that remained monogamously mated. The effect of exogenous testosterone in this study indicates that androgens may mediate social behaviours in female starlings during the breeding season.     

Male mate guarding in a socially monogamous mammal,the round-eared sengi: on costs and trade-offs

Mate guarding is predicted to be one of the driving forces for the evolution of monogamy, but supporting evidence in free-living mammals is rare. The goals of our study were three-pronged. First, we tested if mate guarding, measured as intrapair distance, occurs as a behavioral tactic in round-eared sengis (Macroscelides proboscideus), a socially monogamous species lacking paternal care and in which females breed asynchronously, producing 2–3 litters during an 8-month long breeding season. Second, we determined if mate guarding involves costs which we identified as changes in male body mass. Third, we investigated whether variation in individual investment in mate guarding depended on the males’ body mass and the number of neighboring males. Field data were collected in a semidesert in South Africa using radio-tracking, trapping, and direct observations during three successive breeding seasons. Mate guarding strongly depended on the females’ reproductive state, and all males started to guard their mates prior to and during estrus, as exemplified by reduced intrapair distance. Mate guarding incurred costs: overall, males lost about 5% of body mass. Male body mass loss and initial body mass were negatively related to the intensity of precopulatory mate guarding. Furthermore, during estrus intrapair distance was inversely correlated with the number of neighboring males. The results show that mate guarding is the predominant male tactic in round-eared sengis. However, since mate guarding imposed costs, males may balance benefits and costs associated with guarding by varying their effort in relation to their physical capabilities and the competitive environment.     

Effects of paternal care on reproductive success in the polygynous spotless starling Sturnus unicolor

For males of socially polygynous avian species like the spotless starling, there may exist a trade-off between investing in paternal care and controlling several nests. To determine how the intensity of paternal care affects reproductive success per brood sired or expressed as the total number of young raised in all nests controlled by the same male, it is necessary to manipulate paternal care. Testosterone (T) has been shown to depress the tendency for males to care for their young, and induces them to acquire more mates. The effects of paternal care on reproductive success were studied by treating certain male starlings with exogenous T and others with the antiandrogen cyproterone acetate (CA), and comparing the parental behavior of T- and CA-males throughout the breeding season with that of controls. CA-males fed their chicks more during the first week after hatching than T-males, with controls feeding at intermediate rates, both on a per nest basis and as total effort for all nests controlled by the same male. Paternal feeding rates during the first week of chick life had a significant positive effect on the number of fledged young. The hormone treatment significantly affected the number of chicks raised per nest, CA-males having a higher breeding success per nest than T-males, and controls showing intermediate levels of success. There was no significant effect of treatment on total reproductive success attained by males throughout the season. In the polygonous spotless starling, the intensity of paternal care of young affects reproductive success per nest positively but not on a seasonal basis. Received: 6 February 1999 / Received in revised form: 30 June 1999 / Accepted: 11 July 1999     

Female sand gobies gain direct benefits by choosing males with eggs in their nests

In some fish species with paternal care, females prefer to spawn with males whose nests already contain eggs. Several hypotheses have been put forward to explain this behaviour, such as reduced risk of predation or cannibalism (the dilution effect), increased parental investment, and mate copying. This experimental study focuses on female mate choice in the sand goby, Pomatoschistus minutus. Females were found to choose males with eggs in their nests. In addition, hatching success increased with clutch size, mainly because males with larger clutches showed less filial cannibalism. Increased egg survival in large clutches may thus be explained by a combination of the dilution effect and higher parental investment. In another experiment, females did not seem to copy the observed mate choice of other females. In conclusion, female preference for males with eggs in their nests is adaptive, and can be explained by direct benefits, as more surviving offspring are produced. Received: 23 December 1995/Accepted after revision: 11 May 1996