Post-copulatory sexual selection processes can have important evolutionary consequences, one of which includes the maintenance of variation in nature. In Chinook salmon, red and white color morphs exist due to variation in carotenoid deposition genes. Using microscopy and in vitro competitive fertilizations, we show that post-copulatory processes, including sperm competition and CFC, play an important role in the maintenance of the red and white color morphs in salmon.
Many animals obtain fitness benefits by living and working together in groups. In some hibernating social species, huddling and exchanging heat during winter provides another benefit to sociality. However, we found that in yellow-bellied marmots, a species that may or may not interact with other members of its species, individuals with stronger amicable relationships were more likely to die overwinter. These results indicate that social bonds can be costly and further our understanding of the role of social relationships.
Observations have suggested a correlation between life-history characteristics and the prevalence of certain coalitionary behaviors. Using an analytic model, we demonstrate that dominant individuals rarely evolve to make concessions to their subordinates, even when threatened by coalitions. Consequently, under most social and ecological conditions, low-ranking individuals should evolve to form coalitions that target dominant individuals when contesting fecundity. Conversely, dominant and low-ranking individuals should form coalitions to target medium-ranked individuals when contesting social rank.
Interactive effects of yolk testosterone and carotenoid on prenatal growth and offspring physiology in a precocial bird
Mothers can influence offspring phenotype through the transmission of hormones, immune, or antioxidant compounds, but the interactive effects of these resources have never been studied. Here, we show that maternally transmitted testosterone and carotenoid interact to influence embryo growth and reactive oxygen metabolites in Japanese quail. These results provide the first experimental evidence for interactive effects of 2 maternally derived egg compounds on offspring phenotype and suggest that developmental cues are tightly coadjusted within an egg.
Evolution of elaborate parental care: phenotypic and genetic correlations between parent and offspring traits
Although the evolution of parental care is a central topic in behavioral ecology, we know relatively little about how complex forms of care evolve. We studied elaborate parental care in the burying beetle N. vespilloides. Our results suggest that females differ in their parental quality, that some parental behaviors enhance offspring growth while others enhance offspring survival, and that there is little genetic variation in parental and offspring behaviors.
Avian brood parasites should select the most profitable host species to lay their eggs. However, although the magpie guarantees better survival for great spotted cuckoo nestlings, this parasite uses mainly carrion crow nests in a population in northern Spain. We suggest that current ecological conditions can locally hinder parasitism on magpies, pushing the cuckoo to a suboptimal choice and influencing the selective pressure that the parasite exerts on different populations of its 2 main hosts.
Urbanization is commonly studied by comparing urban versus rural populations or by using urban gradients. Yet, it is not known whether specific environmental gradients like light, noise, or temperature can explain differences between urban and rural populations. In this study, we tested the effects of different quantified environmental gradients on life-history traits in great tits. We show that none of those components explain differences between populations well, implying cautiousness in interpretations of gradient studies.
Cannibalism is the process of consuming same-species individuals and is affected by hunger and high density. However, a comparison of cannibalism levels between populations has rarely been performed. We examined cannibalism levels of an insect predator from Mediterranean and desert regions. Although we expected Mediterranean populations, experiencing stronger competition, to be more cannibalistic than desert ones, this did not hold true. Cannibalism level was nevertheless higher when individuals did not originate from the immediate vicinity.
Leadership can only occur if others are willing to follow. This study revealed that within fish shoals, individuals that were experienced and motivated (by hunger) could lead groups, but that motivation also strongly affected followership. Experienced fish led moderately hungry groupmates, but fish that were either well fed or very hungry did not arrive sooner if accompanied by a trained leader. Leadership is determined by both the state of the leader and the potential followers.
An individual’s position in a social network is a behavior that is expressed as consistently as mate choice or parental care. We measured social networks in forked fungus beetle groups in artificial populations and found that individuals occupied similar network positions throughout the experiment—even if their whole population was moved to a new location. Surprisingly, this disturbance “reset” the structure of the whole network, whereas the network structure of populations that were left undisturbed changed over time.
Adjusting behavior according to changes in the environment is an important mechanism for survival. Water flow is a fundamental property of aquatic environments that shapes the behavior of freshwater fish. Here, we found that even with a weak water flow fish form less cohesive, more aggressive, and more active groups. This information suggests that even a small change in the physical environment can have a profound impact on different aspects of behavior.
Animals can exhibit personality traits that are consistent over time and across contexts. Moreover, individuals with different personalities generally differ in their propensity to modify their behavior in response to changing conditions. We conducted a laboratory experiment to test whether personality differences might be related to cognitive differences. Supporting our expectation, we found that less neophobic individuals exhibited less plasticity and were faster learners compared to more neophobic ones, but only in the less difficult learning task.
Increasing listening duration does not improve mate choice accuracy for females. Studying calls emitted by male tree frog during a whole night, we noticed strong modifications of call frequency during the course of the night. As a consequence, in many cases females make mistakes when evaluating male quality on this parameter. We demonstrate that increasing sampling duration was not a good strategy for females to overcome these temporary variations in male signal.
In the African widowbirds and bishops, it appears red plumage colors have convergently evolved as agonistic (threat) signals, driven by sensory biases. However, neither signal function nor receiver bias has been demonstrated in the most extravagant red bishops. An experimental super-red color patch gave red bishop males a competitive advantage over control-red or green manipulations, indicating agonistic sexual selection for red also in bishops, and the persistence of a receiver bias following extravagant color evolution.
Habitats near roads often have fewer songbirds than undisturbed locations. Noise and pollution may be responsible adjacent to busy roads, but novelty and fear may play a role along lower use roads. We found that song playback, a cue associated with habitat selection, increased songbird densities near roads. Our positive results suggest that adding cues to the environment which signal safety or high quality habitat may reduce avoidance, leading to higher establishment in underutilized habitats.
Early-life nutrition sometimes sets up sons to have greater reproductive success than daughters. Access to dietary antioxidants when young, for example, influences plumage color and territorial behavior of adult male hihi (a songbird of New Zealand). This then increases their reproductive success. Do mothers with better access to antioxidants produce more of these sexy sons? We tested this in the field by providing a population of hihi with carotenoids during breeding; however, we found that hihi mothers did not alter the sex ratio of their offspring in response.
Some pay attention to what’s going on around them and adjust their behavior accordingly, others do their own thing regardless. In superb fairy-wrens, all males seem to defend their territories aggressively regardless of the type of threat. Territories are important for both surviving and breeding, so maybe it is only big differences in the type of threat that are worth adjustments in behavior.
The distribution of resources such as food and shelter determines how animals are organized in space, influencing the nature of social and reproductive interactions between individuals. This is well established for mammals and birds, but research is lacking on other vertebrates. Using captive populations of a social lizard, we show that the distribution of shelter sites influences how many females a male regularly encounters, but not how many females males are able to mate with.
Animals in groups either experience safety in numbers or attract predators. We found that Christmas tree worms hid longer when near others. Given that hiding is the Christmas tree worm’s only form of antipredator behavior, this suggests that sessile invertebrates may generally experience greater predation risk in groups. This antipredator behavior varied in consistent ways across individuals on short time scales, suggesting that Christmas tree worms have some degree of consistency in their responses.
Males of many species push their physical capabilities to the limit as they display for females. In a Neotropical bird exhibiting “leap displays,” we show that costs of displays are higher for signalers of lower body mass, because they cannot conduct leaps that are both rapidly repeated and high in performance.
Male wood warblers preferred to set up breeding territories near conspecific males, which we experimentally simulated with song playback. Pairing rates and reproductive performance did not differ between experimental plots with and without song playback, but fewer eggs survived to produce young on song plots. Additionally, because consequences of artificial attraction for distribution and settlement of the wood warbler remain unclear, acoustic attraction as method for songbird conservation has to be further evaluated.
Using “rules of thumb” based on constant environmental cues may be the best way for squirrels to assess risk when hiding food. When squirrels assess the competing risks of theft and predation, they use fixed cues such as distance from cover, rather than using constantly changing visual cues such as number of other squirrels or predators present. Using fixed cues may save them time that might otherwise be spent constantly updating their risk assessments.
We propose a method for evaluating models explaining individual motion that can work with sparsely collected movement data. This approach can be applied to any system of moving objects. We apply our approach to the movement of a female baboon within its social group and quantify the influence of individual groupmates as well as the group as a whole on her observed motion.
Telomeres are nucleoproteins that confer stability to the eukaryotic genome, but shorten at each cell division, impairing bodily functions. We found that nestling barn swallows in experimentally enlarged broods had shorter telomeres, implying social effects on telomere dynamics. However, nestlings displaying darker plumage retained longer telomeres. Because barn swallows preferentially feed darker nestlings, our study shows that parents privilege offspring of greater phenotypic quality.
Competitive interactions may sometimes explain reproductive character displacement in contact zones. To test this hypothesis, we compared patterns of aggression during male–male encounters between isolated and adjoining populations of two house mice subspecies. A combination of between- and within-population trials allow us to show that although agonistic interference impacts mice aggressiveness in the contact zone, it probably does not contribute to signal divergence and reproductive isolation between the subspecies.
Seasonal declines in breeding performance have been found in many bird species. Generally, observed declines are linked to a progressive deterioration in food availability (“timing hypothesis”) or in parental competence (“quality hypothesis”). In the Lesser Kestrel, both individual quality and deterioration in environmental conditions seems to dictate this seasonal pattern, acting with different intensities in different breeding phases. Moreover, individual optimization rather than individual quality is likely to mitigate the fitness costs of reproduction.
Information regarding the location of a foraging site spread most rapidly through guppy groups made up of both “friends” and “strangers.” Furthermore, the pattern in which foraging information spread through a group was influenced by their social network, defined by who was shoaling with whom. These social networks differed depending on whether groups were made up of “friends,” “strangers,” or a mixture of the two.
Fission–fusion processes weaken dominance networks of female Asian elephants in a productive habitat
Asian elephants may be more egalitarian than African savannah elephants. Assertion of dominance is much less frequent in Asian elephants than among African elephants. Although older individuals tend to win conflicts more often, there is no linear hierarchy and no clear order by social group. Asian elephants occupy more stable and productive environments than most African savannah elephants, with smaller group sizes and more dynamic social affiliations, which may inhibit formation of strong hierarchies.
Many prey species show behavioral lateralization, such as bias in escape direction and asymmetrical use of eyes for scanning, that can cause ecological disadvantages. We showed that tadpoles raised as embryos in a high predation risk environment mainly develop a lateralization phenotype that confers enhanced predator recognition learning. Learning ability can help lateralized tadpoles to survive in high predation risk environments despite behavioral asymmetries.
Ground-nesting birds employ different defensive behaviors as part of their anti-predator strategies because they nest in sites easily accessible to a wide range of predators. We analyzed defensive behavior and nest survival in the Kentish Plover. Nests in which parents invested more on defense survived longer. Females performed riskier defensive behaviors than males. Increased risk in offspring defense is advantageous in terms of individual fitness.
Animals frequently and consistently differ from one another behaviorally, a phenomenon also termed animal personalities. Not much is known about the effects of changes in social status on the expression of personalities. Using the Australian field cricket (Teleogryllus oceanicus), we show that changes in dominance status erode personalities, disrupting the consistency with which individuals differ from each other for some behaviors, but not others.
Many animals are creatures of habit and display behavioral routines, such as repeating the order of visits to known places. This may have emerged from the use of spatial memory, but the study of this behavior has been limited so far to stereotypical situations, because of a lack of concepts and methods. We here formally define routine movement behavior, provide appropriate methods for its analysis, and demonstrate their usefulness on simulated and real-world movement data.
During the rut, fights were often disrupted by the intervention of third-party males. Fight interventions were more likely to occur if the individual had a sufficiently high number of different opponents and if they experienced interventions of their own fights. The level of aggressive activity in the wider herd and mating opportunities were not associated with intervention behavior. Therefore, interventions are related to directly experienced aggression rather than monitoring the behavior of the social group.
Simultaneous occurrence of cannibalism and copulation appears critical to offspring performance. Sexual cannibalism—the consumption of males by females in a mating context—is common in spiders and often treated differently from other types of cannibalism outside of mating. We found that female Australian redback spiders that cannibalized males during mating had offspring that survived better and grew faster than females that cannibalized males outside a mating context.
In many animal species, individuals can join nearby feeding groups and can also allocate time to vigilance against predators. These 2 mechanisms can reduce the risk of predation, but they have rarely been considered together. In a model, I show that joining tendencies and vigilance levels can be influenced by the number of groups in the same area, by the spatial distribution of resources, and by predator attack tactics.
The timing and frequency of predator experience play an important role in learning to recognize risk from predators. Here, tadpoles displayed similar responses towards a predator odour after different numbers of learning opportunities within a short time period. However, when tadpoles were experienced with the predator from earlier in development, their antipredator responses were enhanced from multiple learning opportunities. Our results shed light on conflicting outcomes of previous studies and have implications for conservation programs.
Switching between tasks may incur time costs and select for the evolution of individual specialization. Individuals in animal societies often specialize on particular tasks, though the benefits of such division of labor are not always clear. We tested whether there were temporal costs of switching between types of work in a species of ant. We found that individuals are faster in starting a new bout of work when repeating the same type of work, regardless of which task workers had specialized on. Workers may therefore specialize on certain tasks to avoid this cost of switching.
How do animals decide to give up on a fight? Fighting ability is central to the answer, and we may be assuming that it increases linearly with body size, when that may not be entirely true. Here, we adapt a framework for analyzing fights to allow fighting ability to increase exponentially with body size. We show that when that assumption is considered, the answer may differ.
When the mean no longer matters: developmental diet affects behavioral variation but not population averages in the house cricket (Acheta domesticus)
Understanding behavioral differences in animals is a complex task as many factors play a strong role in shaping these differences. Here, we show that house crickets exposed to a low quality diet over development expressed stronger differences among individuals relative to within individuals when responding to predator cues, compared to individuals exposed to a high quality diet. Our research stresses the importance of variation in developmental environment when investigating factors affecting behavioral variation.
Cover ImageA female Kentish plover (Charadrius alexandrinus) starts to perform distraction behaviour, prompted by an approaching researcher. Nests in which parents invested more on defense survived longer. Image credit: Miguel Angel Gómez-Serrano. See Gómez-Serrano and López-López, p. 260–269.
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