Behavioral Ecology and Sociobiology最新文献

Abstract

Insurance-based mechanisms, where surviving group-members can complete parental care after the death of a nestmate, are key to the origin of cooperative group formation in insects. Selection for group living via these models is proposed to be dependent on the life expectancy of adult carers relative to the duration of offspring dependency on parental care. Progressive provisioning, where adults feed offspring gradually as they grow, is thought to extend this period of dependency and is therefore suggested to be an important factor promoting the evolution of sociality. In contrast, mass-provisioning species provide offspring with all the food they need to reach maturity at the beginning of their development. Since offspring are then nutritionally independent, the applicability of insurance models is less clear. In this paper we experimentally demonstrate that adult presence on the nest, even after the end of provisioning, is critical for brood survival in the mass provisioning silk wasp Microstigmus rosae. After 10 days, experimentally orphaned nests contained 65% fewer healthy offspring than controls. Adult females were also recorded performing post-provisioning parental care behaviours including nest maintenance and repair, putative hygienic brood care and aggressive nest defence against both ants and parasitoid wasps. By demonstrating the potential applicability of insurance advantages our results highlight how, even in mass provisioners, insurance-based mechanisms may be part of what favours group living.

Significance statement

Extended parental care is an important precursor to the evolution of eusociality. In this context, group living can serve as a form of “life insurance”, ensuring that dependent offspring receive the care they need to reach maturity should the mother die. Such mechanisms are especially important to our understanding of social evolution as they are able to account for the origins of cooperative group formation, not just its maintenance. However, for mass-provisioning species, where all food items are provided upfront, the significance of insurance advantages remains unclear. In this study, we experimentally demonstrate that adult attendance is critical for brood survival in the mass provisioning wasp, Microstigmus rosae. Our results reveal the applicability of insurance advantages to M. rosae with important implications for our understanding of the potential adaptive value of group living in mass provisioning species.

Abstract

The estimation of heritability is a common practice in the field of ecology and evolution. Heritability of the traits is often estimated using one single measurement per individual, although many traits (especially behavioural and physiological traits) are characterized by large within-individual variance, and ideally a large number of within individual measurements can be obtained. Importantly, the effect of the within-individual variance and the rate at which this variance is sampled on the estimation of heritability has not been thoroughly tested. We fill this gap of knowledge with a simulation study, and assess the effect of within- and between-individual sample size, and the true value of the variance components on the estimation of heritability. In line with previous studies we found that the accuracy and precision of heritability estimation increased with sample size and accuracy with higher values of additive genetic variance. When the sample size was above 500 accuracy and power of heritability estimates increased in the models including repeated measurements, especially when within-individual variance was high. We thus suggest to use a sample of more than 100 individuals and to include more than two repeated measurements per individual in the models to improve estimation when investigating heritability of labile traits.

Significance statement

Heritability reflects the part of the trait’s phenotypic variation underlined by genetic variation. Despite the difficulties of heritability calculation (high number of individuals is needed with known relatedness), it is a widely used measure in evolutionary studies. However, not every factor potentially affecting the quality of heritability estimation is well understood. We thus investigated with a comprehensive simulation study how the number of repeated measurements per individuals and the amount of within-individual variation influence the goodness of heritability estimation. We found that although the previously described effect of the number of studied individuals was the most important, including repeated measurements also improved the reliability of the heritability estimates, especially when within-individual variation was high. Our results thus highlight the importance of including repeated measurements when investigating the heritability of highly plastic traits, such as behavioural or physiological traits.

Abstract

While there are many studies documenting female mating preferences across taxa, male mate choice remains relatively understudied. Male mate choice often develops when there is variation in female quality and thus the fitness benefits of mating with particular females. Specifically, males tend to prefer females with traits that confer direct fitness benefits such as large body size, which may be linked with high fecundity. Prior work has shown that females of the strawberry poison frog, Oophaga pumilio, prefer males bearing certain coloration (most often the female’s own color), and that this preference can be learned through maternal imprinting. Females have been shown to prefer larger males as well. Here we test whether similar mate preferences for color and size exist in males of this species using two-way choice tests on captive bred male O. pumilio. In each test focal males were placed in an arena with two stimulus females: either both of the same size but differing in color, or both of the same color but differing in size. We found only weak evidence for behavioral biases toward particular colors and no evidence for biases toward larger females, suggesting that males of O. pumilio do not predictably choose mates based on these female traits. Despite several aspects of their natural history that suggest males have reasons to be choosy, our findings suggest that the cost of mate rejection may outweigh any fitness benefits derived from being selective of mates. Studies of additional populations, ideally conducted on wild individuals, are needed to better understand the range of conditions under which males may exhibit mate choice and the types of traits on which they base these choices.

Significance statement

To fully understand the fitness landscapes and evolutionary trajectories that result from sexual selection, we need to understand when and how the mate preferences of the two sexes act and interact. While female mate choice has been widely studied, male mate choice remains poorly understood. To help bridge this gap, we studied male mate preferences in the strawberry poison frog Oophaga pumilio, a small brightly colored frog for which female preferences for male color and size have been well-documented. We found no evidence that male O. pumilio exhibit mate preferences based on female size and little evidence for male mate preferences based on female color. This is surprising given that larger females are often more fecund, male O. pumilio are known to exhibit color-based behavioral biases in the context of male-male competition, and both sexes provide parental care.

Abstract

Apex carnivores that rely primarily on predation play a central but complex role within scavenging ecology by potentially suppressing intra-guild competitors, but also facilitating them by providing a reliable supply of carrion. We investigated the competitive relationship between sympatric wolves (Canis lupus) and wolverines (Gulo gulo) in Norway across three seasons. We deployed remote cameras at fresh wolf kills (n = 29) and built Bayesian generalized linear mixed models (GLMMs) to explore the use of fresh wolf-killed prey by sympatric wolves and wolverines. Our results showed that wolves facilitated wolverines by providing scavenging opportunities. Biomass available from wolf kills was influenced by seasonal wolf prey preference and group size. Wolverines visited 100% of wolf kills in fall and winter, whereas only 18% in summer. We found that in winter, wolverines visited wolf kills 3.6 and 6.7 times more often than single wolves and wolf groups revisited their kills, and spent 10 and 25 times as much time at carcasses compared to single wolves and groups of wolves. Thus, wolverines played an important role in the depletion of wolf-killed prey, with potential effects on the scavenging behavior of other guild members. Understanding how globally threatened top predators may function as key species in scavenging processes is important to conservation as this may have community-wide cascading effects and support important ecosystem functions and services.

Significance statement

Large carnivores serve a central role within scavenging ecology through the suppression and facilitation of intraguild competitors. The wolf, as an apex obligate predator, can provide a reliable supply of carrion, that can serve as an important resource to facultative scavengers. However, while facultative behavior helps to mitigate the effects of limited prey for scavengers, it can also increase exposure to competition and intraguild predation. Across three seasons, we explored the use of fresh wolf-killed prey by sympatric wolves and wolverines. Our findings reveal that wolves facilitate wolverines by providing scavenging opportunities, where biomass available from kills is influenced by wolves’ prey preference and group size. Wolverines, like wolves, utilized kills heavily during winter, when increased access to food is important to wolverine reproductive rates. Wolverines exhibited caching behavior, possibly reducing exposure to interspecific competition, while serving an important role in the depletion of carrion biomass.

Co-occurrence of ecologically similar species can lead to direct agonistic interactions, including kleptoparasitism, where one individual consumes trophic resources acquired by another. We documented facultative kleptoparasitism in two similarly-sized raptors, the lesser kestrel (Falco naumanni) and the red-footed falcon (Falco vespertinus). These two species currently co-occur in Northern Italy due to recent range shifts influenced by climate and land-use changes. Multi-year focal observations revealed that single or multiple red-footed falcons were associated with 72% of foraging groups of lesser kestrels. Red-footed falcons initiated kleptoparasitic attacks on lesser kestrels in 46% of foraging group observations, with a success rate of 34%. Attacks were more likely when the prey capture rate (i.e. a proxy of foraging efficiency) of lesser kestrels was high. Red-footed falcons were more successful in stealing prey when the food items carried by lesser kestrels were larger, and kleptoparasitic attacks by groups of red-footed falcons had a higher success rate than attacks by singletons. Overall, we propose that such frequent kleptoparasitic events, which have never been previously documented in these two species, may have emerged as a consequence of their recently established co-occurrence. Kleptoparasitism could reduce the foraging efficiency and fitness of lesser kestrels, potentially leading to broader ecological consequences, such as population declines or range shifts. These findings highlight how species redistributions associated with global changes may lead to novel interspecific interactions with unforeseen ecological implications.

Abstract

Behavioral modifications induced by parasites have been extensively documented across multiple taxa. However, a major challenge is to experimentally determine whether such manipulations confer an adaptive advantage to the parasite. Behavioral alterations in spiders attacked by ichneumonid wasps are characterized by the construction of modified webs. These modified webs can enhance the survival chances of the parasitoid by reducing mortality due to natural enemies and environmental factors during the pupal stage. Additionally, some modified webs offer extra protection by keeping a centrally attached leaf shelter, originally used by the spider as a refuge, where parasitoids can build their cocoon. In these webs, it is possible that web modifications are not critical for the survival of parasitoid pupae. We evaluated the hypothesis that modifications made by parasitized spiders in a web with leaf shelter do not improve the survival of the parasitoid and presented details of behavioral modifications induced by the wasp Zatypota alborhombarta (Ichneumonidae) in its host spider Cryptachaea migrans (Theridiidae). We observed that modified webs built by parasitized spiders had silk thread around the web shelter, reduced vertical lines, and an increase in forked distal ends of lines. However, these changes in the host web did not improve the survival of parasitoid pupae. Our results indicate that the benefits of host behavioral modification for the parasitoids may vary across different host species. In addition, we suggested that the effects of altered web designs may depend on specific host-created web features and environmental factors like predation pressure.

Significance statement

Behavioral manipulations of hosts induced by parasites are often suggested as an adaptive trait, increasing the fitness of the parasitic organism. Still, the influence of host characteristics on the parasite’s fitness is rarely experimentally assessed, raising questions about the extent of the adaptive nature of manipulation. Here, we demonstrate for the first time that behavioral modifications induced by Ichneumonidae wasps in a cobweb spider do not increase the survival of the parasitoids. We argue that the presence of shelters in these webs, used by parasitoids in their pupal stages, provides a safe environment for development, independent of other modifications. Furthermore, we suggest that the behavioral modification reflects the maintenance of a phylogenetically conserved trait.