Dynamic mate-searching tactic allows female satin bowerbirds Ptilonorhynchus violaceus to reduce searching

Females can maximize the benefits of mate choice by finding high-quality mates while using search tactics that limit the costs of searching for mates. Mate-searching models indicate that specific search tactics would best optimize this trade-off under different conditions. These models do not, however, consider that females may use information from previous years to improve mate searching and reduce search costs in subsequent years. We followed female satin bowerbirds Ptilonorhynchus violaceus during mate searching and reconstructed their search patterns. We found that females who chose very attractive males typically mated with the same male in the following year, resulting in these females sampling fewer males than those who switched mates. In contrast, females who mated with less attractive males typically rejected their previous mates and searched longer for more attractive mates in the following mating season. A potential cost to mate searching is suggested by the observed increase in the likelihood of force-copulation attempts from marauding males with increased searching. Our results suggest that by using past experiences to adjust their search tactics, females may obtain high-quality mates while limiting search costs. These results emphasize the need to consider historical effects in studies of sexual selection, especially for long-lived species with stable display sites.     

Complex mate searching in the satin bowerbird Ptilonorhynchus violaceus

Mate-choice studies typically focus on male traits affecting female mating decisions, but few studies seek to identify the behavioral rules females use when searching for mates. Current models suggest that females may either directly compare a set of males ("pooled comparison") or compare each male to an internal standard ("sequential-search rule") when judging the suitability of potential mates. Models also differ in other specific aspects, such as the predicted number of sampling bouts initiated and the tendency of females to return to males after previous visits. We monitored 63 female satin bowerbirds, Ptilonorhynchus violaceus, during mate sampling to reconstruct their search patterns. We found that females typically sampled several males and returned to the most attractive male for mating: a behavior consistent with the pooled-comparison tactic. Females, however, varied in the number of males sampled; some visited only one male before mating. We found that this variation can be explained by differences among females in the number of mates, the date mate searching is initiated, and long-term experience with males. Further, females were observed to initiate two distinct sampling bouts, with the rejection of most of their potential mates occurring before the start of the second sampling bout. This suggests that the choices of potential mates are narrowed prior to the second sampling bout and that the later visits may function to reconsider preliminary decisions made during the first sampling bout or to resolve decisions concerning the remaining potential mates. Our results indicate that mate searching is a complex process in which females use multiple sampling bouts to find suitable mates and in which several different factors influence their search behavior.     

Female signals enhance the efficiency of mate assessment in satin bowerbirds (Ptilonorhynchus violaceus)

Recent evidence suggests that males adjust their sexually selecteddisplay traits in response to female behaviors during courtships.Little is known, however, about whether females signal to influencemale displays and whether females benefit from this interaction.Male courtship displays in the satin bowerbird (Ptilonorhynchusviolaceus) are highly intense and aggressive. Females may usethese displays as indicators of mating benefits, but these displaysoften startle females and disrupt courtship. Previous studieshave shown that successful males decrease female startling byadjusting their display intensity according to female crouchingbehaviors, suggesting that crouching behaviors function as signals.Here we address whether female crouching is a signal by usingobservations of natural courtship behaviors. In addition, weexamine why females differ in signaling and whether femalesbenefit from signaling. First, we find that female crouchingis related to the likelihood that females will be startled bymale displays, suggesting that crouching signals the degreeof display intensity that females will tolerate from a malewithout being startled. Second, we find that female tolerancefor intense display increases during successive courtships asfemales assess potential mates, and that female tolerance mayalso be affected by age and condition. Third, we find evidencethat females that reduce startling by signaling their intensitytolerance are more efficient in mate searching. These resultssuggest that females signal to influence how males display theirsexually selected traits, and by doing so, females may increasetheir benefits in mate choice.     

Patterns of painting in satin bowerbirds Ptilonorhynchus violaceus and males' responses to changes in their paint

Satin bowerbirds Ptilonorhynchus violaceus have an elaborate multi-component sexual display, some components of which have been extensively studied. We describe a relatively unstudied component of this display, bower painting, and birds' responses to manipulations of their paint. Males of this species focus their display around a stick bower constructed on the forest floor which they decorate with a variety of objects and paint. Painting involves a male masticating plant material and wiping the plant-saliva mixture onto the inside walls of the bower; during courtship visits to bowers, females nibble at this paint. We found that 93% of 53 males painted their bowers at our study site and the time males spent painting their bowers accounted for 24% of their time at the bower. We experimentally removed and added paint to bowers to test whether males respond to these changes in their paint. Males gave more advertisement calls and spent less time manipulating sticks at the bower when we added fresh wet paint to their bowers compared to older dried paint or a control treatment. They did not respond to the removal of paint from their bowers, perhaps because it was primarily older dried paint that was removed. We also found that males painted more frequently when there was measurable wind in their bowers, which could have degraded the quality of the signal. Our findings indicate that fresh wet paint is more important to males than older dried paint and, together with previous work at this site, suggest that paint may act as a signal to females. Given that females nibble bower sticks during courtship, we suggest that bower paint may function as a chemical sexual signal rather than a visual signal.     

Structural plumage colour and parasites in satin bowerbirds Ptilonorhynchus violaceus: implications for sexual selection

We investigated whether variation in structural plumage coloration in satin bowerbirds, Ptilonorhynchus violaceus , could reveal the intensity of infection from parasites, as predicted from models of parasite-mediated sexual selection (PMSS). To do this, we captured adult male, female, and juvenile male satin bowerbirds in Queensland, Australia, and objectively measured individual plumage reflectance from four body regions using a spectrometer. We quantified both ectoparasite load and the intensity of infection from blood parasites. In iridescent blue adult males, plumage reflectance is unimodal, with a single peak in the ultraviolet, while in greenish females and juveniles, plumage reflectance is bimodal, with peaks in both the ultraviolet and green portions of the spectrum. In adult males, the intensity of infection from blood parasites was best predicted by plumage brightness (total reflectance), with brighter males having fewer parasites. Similarly, juvenile males exhibiting greater UV chroma (proportion of reflectance in the UV) had fewer blood parasites. Our findings support a key prediction of PMSS models and provide the first evidence that a structural colour ornament can signal the intensity of infection from blood parasites.     

Patterns of painting in satin bowerbirds Ptilonorhynchus violaceus and males’ responses to changes in their paint

Satin bowerbirds Ptilonorhynchus violaceus have an elaborate multi‐component sexual display, some components of which have been extensively studied. We describe a relatively unstudied component of this display, bower painting, and birds’ responses to manipulations of their paint. Males of this species focus their display around a stick bower constructed on the forest floor which they decorate with a variety of objects and paint. Painting involves a male masticating plant material and wiping the plant‐saliva mixture onto the inside walls of the bower; during courtship visits to bowers, females nibble at this paint. We found that 93% of 53 males painted their bowers at our study site and the time males spent painting their bowers accounted for 24% of their time at the bower. We experimentally removed and added paint to bowers to test whether males respond to these changes in their paint. Males gave more advertisement calls and spent less time manipulating sticks at the bower when we added fresh wet paint to their bowers compared to older dried paint or a control treatment. They did not respond to the removal of paint from their bowers, perhaps because it was primarily older dried paint that was removed. We also found that males painted more frequently when there was measurable wind in their bowers, which could have degraded the quality of the signal. Our findings indicate that fresh wet paint is more important to males than older dried paint and, together with previous work at this site, suggest that paint may act as a signal to females. Given that females nibble bower sticks during courtship, we suggest that bower paint may function as a chemical sexual signal rather than a visual signal.     

Isolation of polymorphic tetranucleotide microsatellite markers in the satin bowerbird,Ptilonorhynchus violaceus

We isolated 13 polymorphic microsatellite markers from the satin bowerbird, Ptilonorhynchus violaceus from a genomic library enriched in (AAGG)_n repetitive elements and characterized them in 20 individuals. The number of alleles ranged from two to 18 per locus with the observed heterozygosity ranging from 0.15 to 1.00. These markers will be useful for analysing questions concerning parentage, population genetic structure and models of speciation.     

Feather stealing in the satin bowerbird (Ptilonorhynchus violaceus): male competition and the quality of display

Male satin bowerbirds use feathers to decorate their bowers and often steal feathers and other decorations from the bowers of other males. Decorations are a key element in sexual display and tracking their movement between bowers provides the first detailed information about this unique pattern of sexual competition. For two field seasons the movement of marked feathers was followed. Males varied greatly in stealing activity. The most active feather thieves were often from areas where bowers were close together and they were involved in reciprocal stealing with males at adjacent bowers. The rate of stealing by males was significantly correlated with the number of feathers on their bowers. This suggests that stealing is important in determining the level of bower decoration and mating success. Patterns of stealing behaviour support models of sexual selection which suggest that male interactions are important in influencing female choice through their effect on the quality of male display.     

Phylogeography of an east Australian wet-forest bird, the satin bowerbird (Ptilonorhynchus violaceus), derived from mtDNA, and its relationship to morphology

Australian wet forests have undergone a contraction in range since the mid-Tertiary, resulting in a fragmented distribution along the east Australian coast incorporating several biogeographical barriers. Variation in mitochondrial DNA and morphology within the satin bowerbird was used to examine biogeographical structure throughout almost the entire geographical extent of these wet forest fragments. We used several genetic analysis techniques, nested clade and barrier analyses, that use patterns inherent in the data to describe the spatial structuring. We also examined the validity of the two previously described satin bowerbird subspecies that are separated by well-defined biogeographical barriers and tested existing hypotheses that propose divergence occurs within each subspecies across two other barriers, the Black Mountain corridor and the Hunter Valley. Our data showed that the two subspecies were genetically and morphologically divergent. The northern subspecies, found in the Wet Tropics region of Queensland, showed little divergence across the Black Mountain corridor, a barrier found to be significant in other Wet Tropics species. Biogeographical structure was found through southeastern Australia; three geographically isolated populations showed genetic differentiation, although minimal divergence was found across the proposed Hunter Valley barrier. A novel barrier was found separating inland and coastal populations in southern New South Wales. Little morphological divergence was observed within subspecies, bar a trend for birds to be larger in the more southerly parts of the species' range. The results from both novel and well-established genetic analyses were similar, providing greater confidence in the conclusions about spatial divergence and supporting the validity of these new techniques.     

Parasites and Bright Male Plumage in the Satin Bowerbird (Ptilonorhynchus violaceus)

Results from our field studies of the satin bowerbird (Ptilonorhynchusviolaceus) suggest that females choose males as mates basedon their level of infection with the ectoparasite (Myrsideaptilonorhynchi: Menoponidae). We evaluated predictions fromthree hypotheses for why this pattern of choice might evolve.The bright male and correlated infection models both suggestthat females choose parasite free males because these malesare more likely to sire parasite resistant offspring. The brightmale hypothesis suggests that females are able to gauge infectionbased on plumage brightness. The correlated infection hypothesisclaims that females assess resistance to endoparasites througha correlated effect on ectoparasites. In the parasite avoidancemodel female choice is shaped by the proximate benefits of avoidinginfection. Six predictions from these models were tested usinginformation on patterns of infection in satin bowerbirds. Ofthese models the parasite avoidance model was best supportedby the available data.     

The Costs of Male Display and Delayed Plumage Maturation in the Satin Bowerbird (Ptilonorhynchus violaceus)

The costs associated with the evolution of male display traits has attracted much attention in regard to the type of traits that evolve and the timing of their expression. We investigate these costs by using testosterone implants to alter the development of male display traits in the satin bowerbird (Ptilonorhynchus violaceus). Testosterone implants advanced the development of adult display traits in males with juvenile plumage. We then measured the costs of early expression of these characters in treated males. Testosterone implants caused young males to (1) become more involved in behavior normally carried out by older males when visiting bowers, (2) build bowers, and (3) molt prematurely into an adult plumage. No difference was observed between the testosterone-treated birds and controls in return rate or condition the year following treatment, suggesting that the physical costs of display are not high. We found that males in adult plumage are tolerated less, and are not displayed to as frequently as juvenile plumage males at the bowers of established bower holders. The causes of delayed plumage maturation are most consistent with the facilitated-learning hypothesis. That is, early development of adult characteristics reduces the opportunity of young males to learn display behavior critical for later reproductive success.     

On the cost of searching for a mate in female pied flycatchers Ficedula hypoleuca

Female pied flycatchers, Ficedula hypoleuca, were trapped in one area and released in another a few kilometres away, where the positions of all available nest sites and males were known beforehand. Many of the females moved only a short distance before mating, settling after about 2 (0–6) days in early spring and about 1 day later on. The length of the premating period was negatively correlated with female body weight and prevailing air temperature, indicating that the females were subject to an energy constraint when searching. The premating period was longer for females that settled with an alreadymated male than for those mating with an unmated male. The significance of the results is discussed in relation to the evolution of avian mating systems, and of male behaviour and plumage colour. Competition for a mate, rather than for food, may explain the spacing of males (territoriality).     

Fitness effects of female mate choice: preferred males are detrimental for Drosophila melanogaster females

The evolution of female mate choice, broadly defined to include any female behaviour or morphology which biases matings towards certain male phenotypes, is traditionally thought to result from direct or indirect benefits which females acquire when mating with preferred males. In contrast, new models have shown that female mate choice can be generated by sexual conflict, where preferred males may cause a fitness depression in females. Several studies have shown that female Drosophila melanogaster bias matings towards large males. Here, we use male size as a proxy for male attractiveness and test how female fitness is affected by reproducing with large or small males, under two different male densities. Females housed with large males had reduced lifespan and aged at an accelerated rate compared with females housed with small males, and increased male density depressed female fitness further. These fitness differences were due to effects on several different fitness components. Female fitness covaried negatively with male courtship rate, which suggests a cost of courtship. Mating rate increased with male size, whereas female fitness peaked at an intermediate mating rate. Our results suggest that female mate choice in D. melanogaster is, at least in part, a by-product of sexual conflict over the mating rate.     

Bower quality,number of decorations and mating success of male satin bowerbirds (Ptilonorhynchus violaceus): an experimental analysis

Bowerbirds build large bowers of twigs decorated with brightly coloured objects at display sites where males court females. The bower and its decorations are hypothesized to influence female choice in these birds. However, there have been no empirical tests of this hypothesis. Data from two years of field research on the satin bowerbird (Ptilonorhynchus violaceus) show: (1) an extremely skewed distribution of matings among males, and (2) a consistent pattern of female preference for particular males, especially those with well-constructed, highly-decorated bowers. These results support the hypothesis that bower quality is important in influencing female mating preferences. In particular, they support the ‘marker’ hypothesis, which suggests that the construction of bowers evolved to provide females with information about the relative quality of males.     

Vocal discrimination of potential mates by female giant pandas (Ailuropoda melanoleuca)

In the current study, we used male giant panda (Ailuropoda melanoleuca) bleats in a habituation–discrimination paradigm to determine whether females discriminate between the vocalizations of different males. We found that females habituated to the bleats of a specific male showed a significant dishabituation when they were presented with bleats from a novel male. Further playbacks, in which we standardized the mean fundamental frequency (pitch) and amplitude modulation of male bleats, indicated that amplitude modulation is the key feature that females attend to when discriminating between male callers. Our results show that female giant pandas can discriminate between the vocalizations of potential mates and provide a platform for further studies investigating the functional role of caller identity in giant panda sexual communication.     

Olfactory conditioning in mate searching by the parasitoid Aphidius ervi (Hymenoptera: Braconidae)

Despite the fact that insect learning capacity has been broadly demonstrated, the role that this process plays during mate searching has been scarcely explored. We studied whether the sexual behaviour of a male parasitic wasp can be conditioned to the odours from two alternative host plant complexes (HPCs) present during its first copulation. The experimental subjects were newly emerged males of the aphid parasitoid, Aphidius ervi, and two alternative HPCs (alfalfa or wheat). In the training protocol, copulation experience corresponded to an unconditioning stimulus and HPC odours to the conditioning stimuli. The initial (just after eclosion) and trained responses were assessed in a glass Y-olfactometer. The results showed that neither alfalfa HPC nor wheat HPC stimuli elicited sexual-related behaviours in initial male responses. Conversely, both HPCs triggered strong attraction and wing fanning courtship behaviour in trained responses when the male was exposed to a female plus HPC during training. In males trained with females plus a given HPC but tested with the alternative HPC in the olfactometer, trained response showed a similar trend to the non-associative treatments. Hence, through learning, the olfactory stimulus context present during copulation could become a predictive cue for further mate searching. These results are discussed in terms of parasitic wasp ecology and host fidelity.     

From preferred to actual mate characteristics: the case of human body shape

The way individuals pair to produce reproductive units is a major factor determining evolution. This process is complex because it is determined not only by individual mating preferences, but also by numerous other factors such as competition between mates. Consequently, preferred and actual characteristics of mates obtained should differ, but this has rarely been addressed. We simultaneously measured mating preferences for stature, body mass, and body mass index, and recorded corresponding actual partner's characteristics for 116 human couples from France. Results show that preferred and actual partner's characteristics differ for male judges, but not for females. In addition, while the correlation between all preferred and actual partner's characteristics appeared to be weak for female judges, it was strong for males: while men prefer women slimmer than their actual partner, those who prefer the slimmest women also have partners who are slimmer than average. This study therefore suggests that the influences of preferences on pair formation can be sex-specific. It also illustrates that this process can lead to unexpected results on the real influences of mating preferences: traits considered as highly influencing attractiveness do not necessarily have a strong influence on the actual pairing, the reverse being also possible.     

Temperature coupling of mate attraction signals and female mate preferences in four populations of Enchenopa treehopper (Hemiptera: Membracidae)

Variation in temperature can affect the expression of a variety of important fitness‐related behaviours, including those involved with mate attraction and selection, with consequences for the coordination of mating across variable environments. We examined how temperature influences the expression of male mating signals and female mate preferences—as well as the relationship between how male signals and female mate preferences change across temperatures (signal–preference temperature coupling)—in Enchenopa binotata treehoppers. These small plant‐feeding insects communicate using plantborne vibrations, and our field surveys indicate they experience significant natural variation in temperature during the mating season. We tested for signal–preference temperature coupling in four populations of E. binotata by manipulating temperature in a controlled laboratory environment. We measured the frequency of male signals—the trait for which females show strongest preference—and female peak preference—the signal frequency most preferred by females—across a range of biologically relevant temperatures (18°C–36°C). We found a strong effect of temperature on both male signals and female preferences, which generated signal–preference temperature coupling within each population. Even in a population in which male signals mismatched female preferences, the temperature coupling reinforces predicted directional selection across all temperatures. Additionally, we found similar thermal sensitivity in signals and preferences across populations even though populations varied in the mean frequency of male signals and female peak preference. Together, these results suggest that temperature variation should not affect the action of sexual selection via female choice, but rather should reinforce stabilizing selection in populations with signal–preference matches, and directional selection in those with signal–preference mismatches. Finally, we do not predict that thermal variation will disrupt the coordination of mating in this species by generating signal–preference mismatches at thermal extremes.     

Multiple pollinator visits to Mimulus ringens (Phrymaceae) flowers increase mate number and seed set within fruits

The timing and effectiveness of pollinator visitation to flowers is an important factor influencing mating patterns and reproductive success. Multiple pollinator probes to a flower may increase both the quantity and genetic diversity of progeny, especially if single probes deposit insufficient pollen for maximal seed set or if the interval between probes is brief. When pollen carryover is limited, sequential pollen loads may also differ markedly in sire representation. We hypothesized that these conditions help explain high levels of multiple paternity in Mimulus ringens fruits. We documented all bee visits to individual flowers, quantified resulting seed set, and determined paternity for 20 seeds per fruit. Most (76%) flowers received multiple probes, and the interval between probes was usually <30 min. Flowers probed multiple times produced 44% more seeds than flowers probed once. All fruits were multiply sired. Flowers receiving a single probe averaged 3.12 outcross sires per fruit, indicating that single probes deposit pollen from several donors. Multiple paternity was even greater after three or more probes (4.92 outcross sires), demonstrating that sequential visits bring pollen from donors not represented in the initial probe.