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Volume 27, Issue 2
March-April 2016
ISSN 1045-2249
EISSN 1465-7279
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Invited Review

In an analysis of published studies to date, we found that physiological measures of stress were not associated with the expression of traits used to attract mates. We found, however, that stress had a detrimental effect on opposite-sex preferences, so that individuals with physiological evidence of high stress were less attractive to the opposite sex. This suggests that stress may mediate attractiveness to the opposite sex but that we do not yet know which physical or behavioral traits signal stress.

INVITED COMMENTARY

Original Article

In this article, we address the question of when males gain more extrapair paternity in relation to the fertile cycle of their social female. We find that males are more likely to sire extrapair offspring when their social female is fertile because male investment in fertilization-related behaviors during their mate’s fertile period aimed at increasing within-pair siring success will have positive “spillover” effects on their extrapair siring success.

Should I stay or should I go: in brown trout, the migration strategy of the parents interacts with the environmental conditions experienced by the offspring to potentially influence its motivation to compete for feeding territories and hence its probability of migration.

Sibling rivalry and nestling death are considered to derive from shortage of food. The aims of our study were to examine this in the Arabian babbler and to understand better the relationships between siblings. We found that lack of food was not the reason for death and that young nestlings contributed to food recruitment for the entire brood more than elder siblings. A medium extent of asymmetry between the chicks may be beneficial to all.

It is presumed that most animals reach peak foraging skill early in life in order to support the onset of reproduction. In contrast, we show that tool-using female bottlenose dolphins peak in foraging performance around midlife, well after reaching both physical and sexual maturity. The timing of this peak in foraging performance also corresponds to a peak in reproduction (the likelihood of lactating), suggesting that the two are closely linked within animal life histories.

How asexual species perceive their environment is understudied but may explain why some asexual species have survived so long. Olfaction—the ability to detect odorants—may be enhanced in asexual species of hybrid origin. We found that asexual Amazon mollies can use olfaction to detect each other and to avoid males, and that smaller Amazons were more likely to use these olfactory cues.

Numerous studies report kin grouping preferences. However, the benefits actually emerging from such behavioral preferences are less well studied. Here, we examine both shoaling preferences and their consequences in juveniles of a cichlid fish. Juveniles preferred shoaling with kin over shoaling with unrelated individuals. Growth was significantly higher in kin-only groups than in mixed groups indicating that grouping with kin yields benefits.

Differences in diet composition between immature and adult birds have been found in many species. Generally, differentiation is linked to the reduced foraging skills of younger and less-experienced immatures. However, in Cory’s shearwater and black-browed albatross, immatures of different ages are able to consume prey that occupy the same position in a food chain as do nonbreeding adults. Differences between breeding adults and nonbreeders (including immatures) likely are related to the requirements of reproduction.

Male and female bushcrickets adjust a suite of reproductive behaviors in response to acoustic experience. Male acoustic advertisement signals provide a source of information on the range and number of mates and/or competitors in the vicinity. We show that males and females adjust pre- and postmating reproductive behavior according to their prior acoustic experience. Such adjustments may impact the dynamics of sexual selection, and in turn signal diversity both within and between populations.

Sexual ornaments may signal males’ ability to produce superior offspring. In a study of Drosophila bipectinata , we showed that females mating with the most ornamented males produce offspring with higher survival and mating success. However, we also show that the mechanisms underlying effects on offspring survival and mating success are likely to be different. Knowledge of the way indirect benefits transmit to offspring will improve our understanding of “good genes” sexual selection.

We all respond to our social environment, to fit in or to become more competitive—fruitflies are no exception. Male larvae responded to their immediate and expected future competitive environments by developing larger sex accessory glands as adults. As expected, the larval competitive environment did not alter the extent to which adult males responded to their immediate sexual environment. The results show the multifaceted ways in which males respond to their sexual environments.

Cooler temperatures can cause female insects to mate more often, but genetic background still has strong control over long-term behavior. How often females mate has major impacts on conflict, cooperation, and how disease spreads within populations. We found that females mate more often when it is colder, which explains why females in northern populations mate more often than in southern ones. However, genetic background strongly determines the long-term patterns of female behavior within and across populations.

Animals have evolved a diversity of strategies to reduce predation risk. We investigated predator avoidance for the morphologically well-defended North American porcupine during a nutritional bottleneck in winter and found that movement was unrelated to nutritional state or energetic costs but driven by the risk landscape—the amount of predation risk and number of refuge trees. Even for species with advanced morphological defenses and during nutritional stress, behavior can be overwhelmed by perceived predation risk.

Resource limitation shapes the nuclear family, even for an ectotherm living in captivity. Mother strawberry poison frogs ( Oophaga pumilio ) lay unfertilized eggs to feed their developing tadpoles, and this provisioning is beneficial to tadpoles. However, these caring mothers forgo alternative, new, reproductive opportunities, and seem to be limited, even when resources are superabundant: Tadpoles in larger broods are fed less, develop more slowly, and in the largest broods, are less likely to survive.

We study the ontogeny of personality in red junglefowl and show that personality mainly stabilizes after independence and sexual maturation. Despite the large interest in animal personality, it is still unclear how personality develops during life. We therefore followed red junglefowl chicks to adulthood and demonstrate that different personality traits show different patterns of stability over ontogeny. Our study improves our understanding of how personality develops and the stabilizing factors underlying personality.

The condition of parents does not only influence parental behavior but also determines how their offspring interact with each other. By manipulating the nutritional state of tending females, we showed in the European earwig that maternal condition affected food transfer among their offspring and the begging behavior these juveniles toward their mother. Importantly, the body condition of mothers also influenced their own maternal behavior.

In order to enhance foraging efficiency, seabirds usually use local enhancement to locate their patchy prey, triggering the formation of multispecies feeding flocks. We studied the relevance of intrinsic factors determining the seasonal stability of multispecies feeding flock composition. In winter, taxonomic affinities are determinant, whereas in spring foraging affinities are more relevant. We suggest that information sources seasonally change from aleatory to a more structured, with highest reassociation probability during the austral winter.

Men’s optimum masculinity depends on whether they want to attract partners or compete with rivals. We found that men’s voice pitch was most attractive around 1.5 standard deviations lower than average, whereas facial hair growth did not consistently affect attractiveness. In contrast, men were perceived ever more dominant with lower voices and more facial hair. Sexual selection consists of both attracting mates and competing against rivals, but here selection pressures might oppose each other somewhat.

We present the first test of color learning and generalization in jumping spiders, a group of tiny, voracious predators. We trained spiders with different combinations of red prey (either palatable or unpalatable) and showed that spiders can learn to either prefer or avoid the color red, but their memories are short term. The ways that spiders learn and remember are different from other predators studied, adding to our understanding of evolutionary selection pressures shaping prey color patterns.

Seawater is too salty for most land animals, but many marine birds and reptiles can cope with it owing to flexible cephalic “salt” glands that excrete excess salt from the bloodstream. We show that red knots without access to freshwater prefer prey with relatively low salt content when their salt glands are small, but this preference is lost after they enlarge their salt glands and regain access to freshwater.

We carried out a simulated-predator encounter experiment in a sea-cage on a large wild-caught school of Atlantic herring. Herring collectively reacted stronger toward a predator model if previously exposed to playbacks of killer whale vocalizations. However, the fish did not modify their schooling dynamics in response to the killer whale calls alone. Therefore, our results demonstrate that risk awareness influences group-level responsiveness and how information propagates in a large pelagic school.

Predators targeting groups often select “odd” individuals. This is mediated by body size, with large individuals selected. However, this depends on a predator’s ability to detect and target particular individuals. In turbid water, predators lose their preference for large, odd individuals. This in turn alters shoaling decisions of prey, with individuals no longer shoaling with size-matched groups. Turbidity alters predator–prey interactions by altering levels of risk, and results in the formation of less uniform groups.

We demonstrate that intraspecific variation in collective behaviors can predict the outcome of contests for food and nest sites between 2 ant species. Whether a colony was successful depended not only on its own behavior but also on the opponent’s behavior. How behavioral variation within a species influences species interactions is still poorly understood. Our results suggest that intraspecific variation could help maintain species coexistence and explain how intraspecific differences in behavior are maintained.

Sociality can be measured by the frequency of encounters between specific individuals or as the social structure of a population. In wild bighorn ewes, these different levels of sociality appear affected by different ecological factors. We found that a ewe’s age and reproductive status had weak effects on her position in the social network, and almost no effects on frequency of close association. Relatedness, however, appear to have no effect on the social structure in this fission–fusion animal society.

Billions of migratory passerines encounter ecological barriers during migration that are risky in time, energy, and safety. Migrants are thought to behave differently prior to crossing to minimize these risks. We demonstrate that departure from stopover is influenced by both wind conditions and energy stores. However, this behavior did not differ pre- or post-crossing of a migratory barrier. We conclude that barriers of varying sizes are likely to have different effects on stopover departure behavior.

Twitter: @BryantDossman

Males transfer more than just sperm when mating and some of those transferred substances can be beneficial to females. We found that in red flour beetles, an insect that lives in dry grain storage sites and does not drink, females benefit by receiving moisture from mating. Additionally, we found that providing moisture to females reduces male life span. We suggest that these sex-specific effects of mating have influenced the evolution of other reproductive traits in this species.

Twitter: @LizDrogeYoung

The ability to invent new foraging behaviors or use pre-existing ones in novel circumstances will serve you well in a changing environment. But why is it that some individuals and some species are seen to forage innovatively so much more frequently than others? The capacity of an array of free-ranging urban bird species to forage innovatively varied substantially and innovativeness was best predicted by the capacity to vary their ongoing motor actions.

It is assumed that the sexes always face a conflict of interest over mating: each aims to benefit at the other’s expense. In the cooperatively breeding cichlid fish, Neolamprologus pulcher , no such conflict is apparent: males benefit from mating with several females, but this incurs no detectable fitness costs to their mates.

Song sparrows adjust their singing and visual displays flexibly depending on predation risk and the need to deal with an opponent. Male song sparrows stopped singing and wing waving (a visual display) in response to song playback on their territory (simulating another male intruding) when we played calls of a Cooper’s hawk. However, when the hawk calls were stopped and the song playback restarted, the males rapidly resumed signaling at previous levels.

Twitter: @caglarbakcay

Not only does city noise affect bird song but higher population densities also encourage urban birds to sing longer and faster songs than rural birds. This finding is novel because human-associated noise is generally assumed to be the primary cause of song divergence between urban and rural birds. However, we show that other ecological factors in cities contribute strongly to changes in song.

Twitter: @dlnarango

Causing energy drain is enough to fulfill a parasite’s need to change host behavior. A parasite can manipulate host behavior to its own interest either directly or indirectly through increased energy drain driving the host to be risk prone. We can distinguish experimentally between these mechanisms using a potential conflict of interest between 2 simultaneous parasites. We find support for the latter mechanism. An additional experiment with hungry and satiated hosts confirms our interpretation.

Using the plainfin midshipman fish, we tested the hypothesis that parents providing care will cannibalize their young to compensate for poor body condition. Such starvation-induced cannibalism is commonly reported among animals but has not been fully explored. We found that although parental care in this species causes individuals to lose body condition and energy reserves, those fish most in need of supplemental energy are not more likely to cannibalize offspring in their nests.

Elucidating the behavioral and physiological traits enabling species to live in urban areas might help us understand and foresee responses to increasing anthropogenic disturbance. Here, we investigated the problem-solving and discrimination learning abilities, personality, and immunocompetence of an opportunistic bird, the Barbados bullfinch, in sites with different degrees of urbanization. We found that problem solving, boldness, and immunocompetence increase significantly with urbanization. This study is the first to jointly consider all these traits along an urbanization gradient.

Parasites can manipulate their hosts to ward off predators, by making them glow, become smelly, and toxic. We show this experimentally. Odors protect young infections particularly well.

Taking it in turns to provide parental care is beneficial for bird parents and chicks. Long-tailed tit parents that alternate their visits to feed chicks provision their nestlings at a higher total feeding rate and the chicks are less likely to be depredated. Parents who take turns also tend to arrive at the nest together, which may simultaneously allow them to keep an eye on each other’s efforts and reduce predation risk.

Wood ant workers forage to other nests in their spatially dispersed colonies. Ant colonies can be dispersed between several different nests. Sharing resources between these nests is an important challenge for these dispersed colonies. We show that in dispersed colonies of the wood ant Formica lugubris , resources are redistributed between nests by workers using the same behaviors as they use to forage. Resources are therefore shared between nests using simple, pre-existing behaviors.

Twitter: @Samellisq

It is hard to make yourself heard amid the cacophony of a busy cocktail party. Here, we show that male frogs increase their voice amplitude when it gets noisy. This phenomenon is known as the Lombard effect, and our results show that at least some frogs possess this signaling trait. Males also increase amplitude in response to competition, similar to the way humans raise their voice when in a heated debate, which may provide insight into the conditions under which signaling flexibility evolved.

Unlike humans, birds are able to see ultraviolet (UV) light. This ability plays an important role in the lives of birds. In brood parasites such as common cuckoo and their hosts, it may be the question of life or death. We found that hosts can recognize and reject parasitic eggs according to the eggshell UV reflectance. Therefore, UV signals may be an important part of the evolutionary arms race between brood parasites and their hosts.

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