Multi-year lactation and its consequences in Bornean orangutans (Pongo pygmaeus wurmbii)

In most mammals, females pay for reproduction by dramatically increasing net energy intake from conception to mid- or late lactation. To do this, they time their reproductive events in relation to environmental cycles so that periods of peak food availability coincide with peak demand or are used to build energy stores. This timing is not possible in species with slow development in which lactation is prolonged over a multi-year period with fluctuating food availability. Here, mothers are expected to sustain a stable but generally lower level of nutrient transfer. In a sample of over 1,050 complete follow days of eight mother–infant pairs collected over 7 years, we document maternal effort for wild Bornean orangutans (Pongo pygmaeus wurmbii) over their average 6.5-year lactation period. As predicted, maternal feeding time was independent of the age of her growing offspring, indicating a stable sustained “plateau” effort of ≤ 25 % above baseline level, instead of a short peak lactation as seen in seasonal breeders. Infant orangutans started to regularly supplement milk with self-harvested food when they were 1–1.5 years old, indicating milk intake was insufficient from this age onwards, even though maternal effort did not decrease. We expect the same regulation of sustained maternal effort in other large and large-brained mammals with slow infant development. We also predict that mother–infant conflict over suckling may show another peak at the onset of the milk?+?solid food phase, in addition to the well-known conflict around the endpoint of lactation (weaning), which is reached after a long and gradual increase in solid food intake by the infant.     

Innate responses to male sexual harassment in female mosquitofish

Male mosquitofish are very persistent in their sexual activity and harass any female they encounter. Gravid females pay a large tribute to this intense male sexual activity in terms of reduced foraging efficiency. Previous observations have demonstrated that gravid females, when chased by a male, dilute male harassment by moving closer to other females to form shoals. They also approach other males to promote male competition, and when males differ in size, they preferentially target large males, whose harassment is less intense. In this study, we tested whether the modulation of females’ social preferences in response to male harassment is innate or learned. We tested social preference in three groups of females that differed in experience of sexual harassment and in the factors affecting it. Females of the first group were reared without any sexual experience, and pregnancy was induced through artificial insemination. The second group was composed of naive females kept singly with a male; these females experienced sexual harassment but were prevented from experiencing the effects of male–male competition and shoaling on the amount of male sexual harassment. In the third group (controls), females were reared in multi-male, multi-female groups and could experience the modulating effects of social interactions on sexual harassment. When exposed to a harassing male, females of the three groups immediately reduced their distance from another female, approached a group of males or moved toward the larger of two available males. Moreover, the results for these three groups of females were similar to those obtained in wild-caught females that were tested in the same three tests in a previous study (Dadda et al. An. Behav., 70:463–471, 2005). This suggests that the strategies adopted by females in response to male sexual harassment do not need to be learned through specific experience of the social contexts.     

The cost of sexual coercion and heterospecific sexual harassment on the fecundity of a host-specific, seed-eating insect (Neacoryphus bicrucis)

Two species of seed-eating true bugs, Neacoryphus bicrucis (Heteroptera: Lygaeidae) and Margus obscurator (Heteroptera: Coreidae) co-occur on ragwort, Senecio tomentosus, in southern Georgia, USA. Males of both species sometimes engage in chases and protracted grappling with females that flee initial mountings. Sometimes genital coupling occurs while the wriggling female is restrained in the male's grasp. Chases, grappling, and mounting attempts are misdirected toward heterospecific females, heterospecific males, or conspecific males. In a laboratory study, confinement of mated N. bicrucis females with either conspecific or heterospecific males reduced fecundity by approximately one-half relative to mated females confined only with other females. Perhaps as a consequence of this, N. bicrucis females frequently leave areas of high host plant density, where they prefer to oviposit, when males are abundant. The abundance of each species is positively correlated with host plant density but the two species rarely occur together on the same plants. This may be an effect of heterospecific courtship which induces the flight of N. bicrucis more than the flight of M. obscurator. The laboratory results suggest that copulations following chases and grappling represent sexual harassment, not a mechanism of active female choice for a vigorous mate. As sexual harassment imposes high fitness costs that favor abandonment of host plants, it may, when misdirected, incidentally limit habitat use by ecologically similar species. Received: 3 October 1998 / Received in revised form: 21 January 1999 / Accepted: 14 February 1999     

Female preference and sexual selection for male coloration in the guppy (Poecilia reticulata)

Summary Experiments were designed to determine the effects of male pigmentation patterns on female choice in guppies. When presented with a series of variably-colored males, females of different genetic strain consistently exhibited similar preferences (Tables 1 and 2), preferring those males with the greatest development of both carotenoid and iridescent pigments (Table 3). A partial rank correlation analysis of pigments of males indicates positive correlations between the iridescent and carotenoid pigments and also between melanins and showiness (Table 4). Only when either the carotenoid or iridescent pigments were held constant was there any effect of the other pigments on the ranking order of males by the females. Other pigments appear to be relatively unimportant in influencing female choice of males. These results indicate that females discriminate among males on the basis of color and that females of different strains prefer the same male colors rather than those characteristics of males of their own strain. The results support those models of sexual selection that hold that sexually selected traits honestly advertise the phenotypic and genetic qualities of males; they do not support models of runaway selection for particular male traits, such as first proposed by Fisher (1930).     

Female house martins (Delichon urbica) reduce egg androgen deposition in response to a challenge of their immune system

Female birds deposit in the yolks of eggs substantial amounts of androgens, such as testosterone and androstenedione. These androgens have been shown to speed up nestling development, induce a fast development of ornaments and increase dominance in adults. Experiments in several species have reported that females invest greater amounts of androgens in the eggs fathered by attractive males, suggesting that yolk androgen is a costly investment for either the offspring or the mother. There is some evidence that nestling immunocompetence may be partially suppressed by high levels of yolk androgens, but it is not known whether this is also the case for females. We tested this hypothesis in the house martin by inducing an immune challenge through an injection of sheep red blood cells, a standard challenge of the humoral immune system. Experimental birds laid eggs with lower amounts of yolk androstenedione than controls, and there was a similar non-significant trend for testosterone. Furthermore, the probability of laying a replacement clutch was higher for birds that had laid a first clutch with relatively high levels of yolk testosterone. These results suggest that yolk androgen deposition is limited by immune costs in the female, and that only females in good condition may afford to invest high levels of androgen in eggs in this species.     

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     

The role of sexual harassment in cave and surface dwelling populations of the Atlantic molly, Poecilia mexicana (Poeciliidae, Teleostei)

Sexual coercion is a common behaviour for males trying to compensate for being inferior in male competition and/or female choice. We measured the cost of male sexual harassment for females as reduced feeding time in three populations of the Atlantic molly (Poecilia mexicana). Of these populations, one originated from a typical river habitat, another from a lightless cave chamber and the third one from a small, milky creek outside the cave. We gave hungry females an opportunity to feed in the presence of either another female or a male. We found the following: (1) male sexual harassment represents a cost in the river dwelling population and both small and large males significantly reduce female feeding time; and (2) sexual harassment was not detected in the other two populations (cave and cave entrance). In the cave molly, small males are at a disadvantage in female choice, but predation by an aquatic heteropteran selects against large male body size.     

Female distribution affects mate searching and sexual selection in male northern water snakes (Nerodia sipedon)

Mating systems and sexual selection are assumed to be affected by the distribution of critical resources. We use observations of 312 mating aggregations to compare mate-searching success of male northern water snakes (Nerodia sipedon) in two marshes in which differences in mating substrate availability resulted in more than fourfold differences in female dispersion. Reproductive males had significantly larger home ranges where females were dispersed than where females were clumped. The number of females encountered by males increased significantly with male home range size where females were dispersed, and decreased significantly where females were clumped. Where females were clumped, males were more likely to encounter other males when they located females. We found no evidence in either population that mate searching was energetically expensive or that males with relatively more energy had larger home ranges. However, males with greater fat reserves at the start of the season participated in more mating aggregations when females were dispersed, suggesting that fat reserves could affect a male’s willingness to attempt mating or to persist in aggregations. When females were dispersed there was weak stabilizing selection acting to maintain male body size (β=–0.14), but strong directional selection favoring larger (β=0.50) and fatter (β=0.37) males. Over 7 years, the intensity of selection favoring larger males varied substantially (β=0.14–1.15), but that variation was not related to variation in the operational sex ratio. We found no evidence of directional selection on either body size (β=0.05) or fat reserves (β=0.10) of males when females were spatially clumped. Overall, the distribution of females had a pronounced effect on male behavior, on the factors that affected male success in locating females, and probably on the extent of sperm competition once females had been located. Received: 23 November 1998 / Received in revised form: 9 August 1999 / Accepted: 18 August 1999     

Limitations to colour-based sexual preferences in three-spined sticklebacks (Gasterosteus aculeatus)

Female three-spined sticklebacks (Gasterosteus aculeatus) are suggested to select mates based on their red nuptial coloration, males with a redder display being more preferred. Although there are both laboratory and field data to support this view, there are also published accounts where females do not show a preference for the redder male. Here we report the results of a series of 19 trials where receptive gravid female three-spined sticklebacks were allowed to choose between two size-matched rival males. We used photographic and image analysis techniques to quantify male nuptial coloration to investigate how the magnitude of the colour difference between the two alternative males influenced female preferences. Using the amount of time a female spent oriented towards each male as a measure of his attractiveness to her, females were not always found to select the redder of the two presented males. We did, however, find that that the relative difference in coloration of the two males in each pair was important in determining the level of coloration-based preference, with females only selecting redder males consistently when the difference in coloration was sufficiently large. Received: 26 October 1999 / Received in revised form: 10 January 2000 / Accepted: 13 February 2000     

“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.     

Pursuit-deterrent communication between prey animals and timber rattlesnakes (Crotalus horridus): the response of snakes to harassment displays

A thorough understanding of communication requires an evaluation of both the signaler and receiver. Most analyses of prey–predator communication are incomplete because they examine only the behavior of the prey. Predators in these systems may be understudied because they are perceived as less tractable research subjects, due to their more cryptic hunting behaviors and secretive lifestyles. For example, research on interactions between rodents and rattlesnakes has focused on the behavior of rodent signalers, while responses of snakes have been virtually unexamined. Rattlesnakes are ambush predators, and capture rodents by waiting at foraging sites for long periods of time. In this study, I take advantage of the sedentary nature of this foraging strategy and use fixed videography to record natural encounters between timber rattlesnakes (Crotalus horridus) and their prey. Three different prey species were found to exhibit conspicuous visual displays to snakes, both when snakes were actively foraging, and when they were basking. After receiving displays, foraging snakes left their ambush sites and moved long distances before locating subsequent ambush sites, indicating that they responded to displays by abandoning attempts to ambush prey in the vicinity of signalers. This study represents the first quantitative analysis of the response of free-ranging snakes to signals from their prey, and elucidates a technique by which such quantitative data can be more easily obtained.     

An alternative mechanism to reduce intracapsular hypoxia in ovicapsules of Fusitriton oregonensis (Gastropoda)

Oxygen supply inside egg masses has been reported as a constraint of embryo development. Many species that enclose their eggs in jelly masses or ovicapsules have strategies to avoid or reduce intracapsular hypoxia. In some amphibian species, a decrease in the wall thickness of the egg capsule over time produces an increase in oxygen conductance of the wall, reducing the problem of intracapsular oxygen limitation. Previous studies of gastropods have reported a decrease in the thickness of the capsules during development. However, there are no studies relating capsule thinning to the oxygen limitation problem in this group. This study links the thinning of egg capsules with oxygen diffusion as a possible mechanism to reduce or avoid hypoxia inside the capsules of the gastropod Fusitriton oregonensis. Capsule thickness, capsule area, oxygen partial pressure inside and outside the capsule, and oxygen consumption of the embryos at early and late developmental stages were measured. The conductance and the diffusion coefficients of the capsule were estimated using these measurements. Results showed that (1) capsule thickness decreased throughout development by about 50%, (2) oxygen consumption of embryos increased from early to late stages, (3) oxygen partial pressure inside the capsule did not change during development, (4) conductance coefficient increased with time, and (5) estimation of diffusion coefficient was lower than amphibian egg jelly, shark capsules, egg fishes, and eggs of giant cuttlefish. The reduction in the thickness of the capsule wall and the associated increase in its conductance during embryonic development may reduce oxygen constraints, especially at late developmental stages.     

Alternative mating tactics in males of Polistes dominulus (Hymenoptera: Vespidae)

Summary In summer, males of Polistes dominulus form large aggregations at sunny landmarks. We identified two size-correlated behavioural categories: residents (R) and transient (T). R males, which constitute 20%–25% of the total population, are larger than T males, territorial, aggressive, and more site-faithful, while T males range more widely, are non-aggressive, and show little site tenacity. Field and laboratory data suggest that R males have an advantage in mating, particularly if they engage in frequent flights while on their territories. These alternative mating tactics within the same population are combined with behavioural flexibility in some individuals, which switch from one option to the other.     

Female preference for apparently symmetrical male sexual ornaments in the barn swallow Hirundo rustica

Summary The outermost tail feathers of barn swallows Hirundo rustica apparently reliably signal the quality of males, because individuals with the longest tails have the lowest degree of fluctuating asymmetry (random deviations from symmetry in the otherwise symmetrical tail trait) despite the size of their secondary sexual character. I experimentally tested whether females preferred males with symmetrical tails without altering the aerodynamic properties of birds by painting the tips of the outermost tail feathers with white or black correction fluid. Unmated males were randomly assigned to one of four treatments: (i) asymmetrical tails, where the outermost 20 mm of one tail feather was painted white and the other black; (ii) symmetrical tails where the outermost 10 mm of both tail feathers was painted white (symmetric I); (iii) symmetrical tails where the outermost 20 mm of both tail feathers was painted white (symmetric II); or (iv) controls where the outermost 20 mm of both tail feathers was painted black. The experimental treatment affected the duration of the premating period since it took longer for asymmetrical males to acquire a mate than for either group of symmetrical males or control males. This gave rise to a delayed start of laying among males with apparently asymmetrical tails. The seasonal production of fledglings therefore decreased from control males through males with either symmetrical treatment to males with the asymmetrical treatment. Females therefore pay direct attention to the level of fluctuating asymmetry in secondary sexual characters even when the asymmetry does not affect the aerodynamic properties of males.     

Lying down as a means of reducing fly harassment in red deer (Cervus elaphus)

Summary Resting time in red deer (Cervus elaphus) was shown to be more than twice as long on days when harassment by head flies (Hydrotaea irritans) was considered severe compared with days when fly harassment was estimated as low. Avoidance reactions in the deer decreased as soon as the deer reclined and became stabilized at a level corresponding to approximately 50% of the initial response frequency. The present observations do not give any clear indications as to whether it is the head flies per se or climatic factors that are the primary cause of reduced locomotory behaviour in the deer. It is concluded, however, that due to a causal relationship between the appearance of flies and certain types of weather, and because lying down has a relieving effect, inactivity may be an important part of the strategy used by red deer to cope with head fly harassment.     

Female mate choice in the non-territorial lizard Ameiva plei (Teiidae)

Mate choice by females has been documented in a variety of taxa. Female mate choice in species lacking male resource control or paternal care might occur if preferred males provide protection from harassment. Female mate choice was investigated in a natural population of the non-territorial lizard Ameiva plei (Teiidae). Consort pairs were allowed to form naturally. Consort males were significantly larger than non-consort males. After removal of consort males, the “abandoned” female's reaction to the first male who approached her was recorded. Females rejected all small males. Female preference for large males was significantly higher than preference for small males. Large males may be better equipped to guard the females from harassment and behavior of large males is less harassing than behavior of small males, thereby affording the female increased foraging time. Received: 21 June 1996 / Accepted after revision: 28 December 1996     

Female choice contributes to offspring fitness in the field cricket,Gryllus bimaculatus (De Geer)

Summary Females of the field cricket, Gryllus bimaculatus, are known to mate non-randomly with respect to male size. The reproductive output of females allowed to choose their mates was compared with that of females allocated mates. Females allowed to choose their mates laid a greater proportion of their available eggs, thereby investing more heavily in reproduction. Female choice did not appear to influence hatching success, suggesting that no short term benefits are derived from non-random mating. However, the offspring of females allowed to choose their mates developed more rapidly and began their own reproductive output before those of females who had been allocated mates. Furthermore, the faster developing offspring of females who chose their mates tended to have a consistantly higher survival rate as well as a lower variance in survival (i.e. less risk of mortality) at adult eclosion. Female choice may therefore contribute to offspring fitness and thus to long term reproductive success. Females allocated large males as mates did not equal those of females allowed to choose their mates, in terms of reproductive output and offspring fitness. This suggests that females may choose their mates with regard to a mixture of characters of which male size is only one.     

Alternative reproductive tactics and male-dimorphism in the horned beetle Onthophagus acuminatus (Coleoptera: Scarabaeidae)

Adult dung beetles (Onthophagus acuminatus) exhibit continuous variation in body size resulting from differential nutritional conditions experienced during larval development. Males of this species have a pair of horns that protrude from the base of the head, and the lengths of these horns are bimodally distributed in natural populations. Males growing larger than a threshold body size develop long horns, and males that do not achieve this size grow only rudimentary horns or no horns at all. Previous studies of other horned beetle species have shown that horned and hornless males often have different types of reproductive behavior. Here I describe the mating behaviors of the two male morphs of O. acuminatus during encounters with females. Females excavate tunnels beneath dung, where they feed, mate and provision eggs. Large, horned males were found to guard entrances to tunnels containing females. These males fought with all other males that attempted to enter these tunnels. In contrast, small, hornless males encountered females by sneaking into tunnels guarded by other males. In many instances, this was accomplished by digging new tunnels that intercepted the guarded tunnels below ground. Side-tunneling behavior allowed sneaking males to enter tunnels beneath the guarding male, and mate with females undetected. Both overall body size and relative horn length significantly affected the outcome of fights over tunnel ownership. These results suggest that alternative reproductive tactics may favor divergence in male horn morphology, with long horns favored in males large enough to guard tunnels, and hornlessness favored in smaller males that adopt the “sneaking” behavioral alternative. Received: 12 October 1996 / Accepted after revision: 8 August 1997     

Switching to Plan B: changes in the escape tactics of two grasshopper species (Acrididae: Orthoptera) in response to repeated predatory approaches

Most studies examining escape behaviour have considered single approaches and single fleeing responses; few have considered how organisms’ response is influenced by persistent pursuit. We explored fleeing behaviour of two grasshopper species to test whether they modified escape behaviour when approached repeatedly. Schistocerca alutacea did not increase flight initiation distance (FID) upon repeated approach but fled farther. Psinidia fenestralis increased its FID on the second approach but decreased its flight distance over successive escapes. Both species showed a bimodal pattern of flight direction, either flying directly away or flying perpendicular to the direction of the observer’s approach. Neither species showed a significant pattern of flight direction or change in flight direction with successive escapes. Most (88 %) P. fenestralis initially landed on sand, but after repeated approaches an increasing proportion landed in grass and hid. Both species therefore changed escape behaviour with persistent pursuit but used different tactics, suiting their flight ability or camouflage, and optimised habitat use. Three grasshopper species have now been examined for responses to repeated approach by predators and all show different tactics supporting escape decision theory. Our results emphasise the variety of escape responses across species and how the dynamic nature of escape responses vary according to an animal’s situation. Rather than single optimum escape options, each grasshopper species shows a range of responses, which vary with risk from persistent predators. Although grasshoppers provide an excellent model, it would be profitable to examine responses of a range of species according to levels of predation risk.     

Satellites and sneakers: opportunistic male breeding tactics in pupfish (Cyprinodon pecosensis)

Summary Manipulations of population density, availability of oviposition substrate, and size of breeding habitat affected the proportion of pupfish (Cyprinodon pecosensis) males adopting territorial and satellite breeding tactics. Satellites occupied stations above breeding substrates defended by territorial males. Both territorial and satellite males developed a bright blue breeding coloration. A third breeding tactic, sneak-spawning, was occasionally observed. Sneak-spawning males retained the cryptic female coloration and occasionally spawned on territories. The lower reproductive success of satellites and sneak-spawning males suggested that both are conditional breeding tactics adopted by competitively inferior males. Satellites were present in all treatments that favored a territorial breeding system, but were absent when the breeding system was a dominance hierarchy. Satellites were associated with territorial males that had higher reproductive success and larger territories than males without satellites. Satellites functioned as parasites rather than as mutualists, since they disrupted spawnings and stole copulations from territorial males. The occurrence and frequency of the conditional breeding behaviours in pupfish represent facultative responses of males to changes in the intensity of competition for breeding sites and females.