The Evolution of Parental Care
... The initial prediction of the expensive son hypothesis is that producing or rearing sons is associated with short-term detrimental consequences on maternal reproduction and survival (Clutton-Brock, 1991). Whether mothers producing and rearing more sons over several reproductive events suffer from a reduced lifespan or impaired reproductive performance in the long-run remains a major area for exploration. ...
... The expensive son hypothesis posits that differences in the costs of producing and rearing sons and daughters result from sex differences in offspring behaviour (Clutton-Brock, 1991) such as a higher propensity for sons to extract milk from their mother compared to daughters (that may even lead to acute mother-offspring conflicts over food provisioning, see Haig, 2010). ...
... A complicating factor here is that the assumptions of Trivers-Willard hypothesis are more likely to hold in highly sexually dimorphic species (Hewison & Gaillard, 1999). However, while under the Trivers-Willard hypothesis the higher cost of sons should be particularly high for mothers in good condition, we may expect to observe the opposite pattern under the expensive son hypothesis (a higher cost of sons for mothers in poor condition) (Clutton-Brock, 1991). On the other hand, Myers (1978) predicted that parents with low resources (either because they are in poor condition or reproduce during poor environmental conditions) should overproduce the cheapest sex to buffer costs in terms of future reproductive success. ...
In its initial form, the expensive son hypothesis postulates that sons from male-biased sexually dimorphic species require more food during growth than daughters, which ultimately incur fitness costs for mothers predominantly producing and rearing sons. We first dissect the evolutionary framework in which the expensive son hypothesis is rooted, and we provide a critical reappraisal of its differences from other evolutionary theories proposed in the field of sex allocation. Then, we synthesize the current (and absence of) support for the costs of producing and rearing sons on maternal fitness components (future reproduction and survival). Regarding the consequences in terms of future reproduction, we highlight that species with pronounced sexual size dimorphism display a higher cost of sons than of daughters on subsequent reproductive performance, at least in mammals. However, in most studies, the relative fitness costs of producing and rearing sons and daughters can be due to sex-biased maternal allocation strategies rather than differences in energetic demands of offspring, which constitutes an alternative mechanism to the expensive son hypothesis stricto sensu. We observe that empirical studies investigating the differential costs of sons and daughters on maternal survival in non-human animals remain rare, especially for long-term survival. Indeed, most studies have investigated the influence of offspring sex (or litter sex ratio) at year T on survival at year T+1, and they rarely provide a support to the expensive son hypothesis. On the contrary, in humans, most studies have focused on the relationship between proportion of sons and maternal lifespan, but these results are inconsistent. Our study highlights new avenues for future research that should provide a comprehensive view of the expensive son hypothesis, by notably disentangling the effects of offspring behaviour from the effect of sex-specific maternal allocation. Moreover, we emphasize that future studies should also embrace the mechanistic side of the expensive son hypothesis, largely neglected so far, by deciphering the physiological pathways linking son's production to maternal health and fitness.
... The initial prediction of the expensive son hypothesis is that producing or rearing sons is associated with short-term detrimental consequences on maternal reproduction and survival (Clutton-Brock, 1991). Whether mothers producing and rearing more sons over several reproductive events suffer from a reduced lifespan or impaired reproductive performance in the long-run remains a major area for exploration. ...
... The expensive son hypothesis posits that differences in the costs of producing and rearing sons and daughters result from sex differences in offspring behaviour (Clutton-Brock, 1991) such as a higher propensity for sons to extract milk from their mother compared to daughters (that may even lead to acute mother-offspring conflicts over food provisioning, see Haig, 2010). ...
... A complicating factor here is that the assumptions of Trivers-Willard hypothesis are more likely to hold in highly sexually dimorphic species (Hewison & Gaillard, 1999). However, while under the Trivers-Willard hypothesis the higher cost of sons should be particularly high for mothers in good condition, we may expect to observe the opposite pattern under the expensive son hypothesis (a higher cost of sons for mothers in poor condition) (Clutton-Brock, 1991). On the other hand, Myers (1978) predicted that parents with low resources (either because they are in poor condition or reproduce during poor environmental conditions) should overproduce the cheapest sex to buffer costs in terms of future reproductive success. ...
In its initial form, the expensive son hypothesis postulates that sons from male‐biased sexually dimorphic species require more food during growth than daughters, which ultimately incur fitness costs for mothers predominantly producing and rearing sons.
We first dissect the evolutionary framework in which the expensive son hypothesis is rooted, and we provide a critical reappraisal of its differences from other evolutionary theories proposed in the field of sex allocation. Then, we synthesize the current (and absence of) support for the costs of producing and rearing sons on maternal fitness components (future reproduction and survival).
Regarding the consequences in terms of future reproduction, we highlight that species with pronounced sexual size dimorphism display a higher cost of sons than of daughters on subsequent reproductive performance, at least in mammals. However, in most studies, the relative fitness costs of producing and rearing sons and daughters can be due to sex‐biased maternal allocation strategies rather than differences in energetic demands of offspring, which constitutes an alternative mechanism to the expensive son hypothesis stricto sensu.
We observe that empirical studies investigating the differential costs of sons and daughters on maternal survival in non‐human animals remain rare, especially for long‐term survival. Indeed, most studies have investigated the influence of offspring sex (or litter sex ratio) at year T on survival at year T + 1, and they rarely provide a support to the expensive son hypothesis. On the contrary, in humans, most studies have focused on the relationship between proportion of sons and maternal lifespan, but these results are inconsistent.
Our study highlights new avenues for future research that should provide a comprehensive view of the expensive son hypothesis, by notably disentangling the effects of offspring behaviour from the effect of sex‐specific maternal allocation. Moreover, we emphasize that future studies should also embrace the mechanistic side of the expensive son hypothesis, largely neglected so far, by deciphering the physiological pathways linking son's production to maternal health and fitness.
... At the beginning of the active period, in early spring, individuals dig a 10-20 cm-deep tunnel which serves as a shelter before they find a partner. Paired beetles prepare a 50-90 cm-deep burrow, terminating in six to eight brood chambers, each of them serving as nest for a single developing egg 7,17,45,46 . Eggs are relatively large, laid sequentially and provisioned with green leaves the parents gather in the area surrounding the burrow (i.e. an area of about 3.5 m 2 , Frantsevich et al. 16 ). ...
Males and females generally differ in resource investment strategies in order to maximise reproductive output. These strategies involve the control of important systemic processes such as self-maintenance and immune activity, which in turn could be traded-off against aspects of reproduction in a sex-specific manner. While some aspects of this immunomodulation have been previously shown in domestic animals, sex-specific immune modulation using repeated sampling over the breeding period has rarely been tested in the wild. Here we used Lethrus apterus, a sexually dimorphic beetle with parental care, to investigate the association between sex roles (e.g. offspring provisioning) and sex-specific immune gene expression. By determining the immune gene activation of males and females at five successive moments within the active season, we found that their sex-specific immune gene expression varies substantially across the active season, alternating between male bias to female bias and vice versa. Though, when pooling all sampling dates together, there was no overall difference in the number of up-regulated immune genes between the sexes. Sex roles in this beetle are associated with energetically demanding behaviours that could potentially explain our results. We highlight the importance of successive sampling protocols to understand ecological dynamics in the wild.
... Mammals mainly rely on their mother during their early life stage to survive. Their mother provides critical care such as food provisioning, protection from predators, warmth, teaching, etc. [1,2]. For such care to be optimal, the mother and offspring must communicate with each other. ...
Baleen whale calves vocalize, but the behavioural context and role of their social calls in mother–calf interactions are yet to be documented further. We investigated the context of call production in humpback whale (Megaptera novaeangliae) calves using camera-equipped animal-borne multi-sensor tags. Behavioural states, including suckling sessions, were identified using accelerometer, depth and video data. Call types were categorized through clustering techniques. We found that call types and rates predict the occurrence of a given state. Milling, resting and travelling were associated with a median call rate of 0 calls min⁻¹, while surface play, tagging responses and suckling were associated with higher call rates, averaging up to a median of 0.5 calls min⁻¹ for suckling. Suckling sessions were mainly associated with two sets of low-frequency calls corresponding to previously described burping, barking and snorting sounds. Surface play sessions featured mid-frequency calls with whoop-like sounds and other call types. These results address the significance of vocal signalling in mother–calf communication and the calf’s development, including the first identification of potential begging calls. Overall, this study offers new insights into baleen whale behaviour, underscores the importance of social calls in mother–calf interactions and enhances our understanding of communication systems in aquatic mammalian mother–young pairs.
Parental care in nature can present itself in different forms and vary in intensities and strategies, being maternal care one of the widely observed patterns in animals. In spiders, parental investment is carried out mainly by females. Despite this, newly hatched eggs can still be targets of a series of natural enemies. In a remnant of Atlantic Forest in Brazil, females of the spider Eldar galadrielae sp. nov., family Anyphaenidae, build nests at the forest’s edge by folding plant leaves. However, information about the plants chosen for nest, the importance of maternal care by females in offspring survival, and predators are completely unknown. In this study, we (1) presented new information about the nest built by females of Eldar galadrielae sp. nov.; (2) compared the predation rate on eggs of the spider Eldar galadrielae in nests with and without the presence of the female; (3) provided morphological descriptions and distribution maps to the genus Eldar gen. nov. as well as presenting; and (4) the described Pseudogaurax vasconcellosi sp. nov. as the predator of the spider eggs. This is the first report on an interaction between Pseudogaurax flies and Anyphaenidae spiders. Our results support predation rates higher in female-less Eldar galadrielae sp. nov. nests. Although egg consumption was 100% in nests attacked by flies, overall nest predation rate was low, as flies were only recorded in three of the 12 nests that maintained female care, indicating that active protection of egg sacs by females can increase the offspring’s chances of survival.
Reproductive accessory glands are organs involved in reproduction that do not directly produce or release gametes but can play crucial roles in securing reproductive success. In fishes, the two leading hypotheses about why accessory glands evolved are 1) in response to sperm competition, or 2) to facilitate parental care activities. Here, we investigate the evolutionary history of accessory glands and test these hypotheses by estimating quantitative differences in evolutionary rates. We found that accessory glands are present in 116 of the 607 sampled species of ray-finned fishes, representing 26/267 families. We estimated that accessory glands have arisen independently ~20 times and that these glands were gained 5.8 times faster in lineages with male parental care, compared to those without male care, supporting the hypothesis that they evolved to facilitate care. In contrast, group spawning, used as a proxy for sperm competition risk, seemed to select against the evolution of accessory glands, as lineages exhibiting group spawning gained accessory glands 3.9 times slower than those with pair spawning (though this failed to reach statistical significance). This study provides new insights into the evolutionary history of accessory glands in fishes and highlights the importance of parental care in shaping reproductive anatomy.
Mammalian species with slow life histories invest heavily in offspring care to meet offspring nutritional and developmental requirements, typically at significant costs to mothers. While maternal care has been extensively studied, understanding the mechanisms driving variation in mother‒offspring relationships during key offspring developmental periods require more comparative data from natural populations. Using eight years of behavioral data, we analyzed mother-offspring interactions in 68 infants born to 46 mothers in wild mandrills (Mandrillus sphinx), spanning multiple birth cohorts and the entire first year of infant life, a critical period for individual social and physical development. We found that mothers dynamically adjusted caregiving behavior as infants aged, reducing physical contact while promoting spatial independence and social integration. Maternal traits, such as age, social rank, and reproductive history, shaped maternal phenotypes: high-ranking mothers promoted infant socialization while reducing carrying, and older, multiparous mothers invested more in grooming and physical contact than younger, inexperienced females. Previous infant loss predicted reduced maternal aggression, potentially due to fewer immatures to care for or behavioral adjustments aimed at improving offspring survival. Finally, mothers fostered closer bonds with their daughters while encouraging their sons’ independence, possibly resulting in more frequent tantrums observed in males. This sex-biased pattern likely reflects preparation for contrasting life histories between the sexes in this species. By combining extensive longitudinal observations with fine-scale, individual analyses, our study emphasizes the dynamic and multifaceted nature of early mother-offspring interactions and their evolutionary implications in long-lived mammals.
In this study, we present a predator-prey model that incorporates a delay in the prey’s reproduction resulting from fear induced by predators. Next, we modify our model to a fractional-order system, incorporating the effects of memory. Establishing positivity and boundedness of the solutions demonstrates the well-posedness of the system. The local and global asymptotic stability of the positive equilibria are established under certain suitable parametric conditions. Additionally, we prove the existence and uniqueness of solutions for the fractional-order system while ensuring that they remain bounded. It is observed that, depending on constraints defined by the values of the model parameters, the breeding delay in the model system has both a stabilizing and destabilizing role in the system dynamics. The maximum length of delay that preserves the stability of the limit cycle is calculated. In the presence of delay, it is noticed that the fear factor in model system dynamics plays exactly the opposite role to that of the system without delay; more preciously, when the prey species delayed their breeding, fear acts as a destabilizing factor. We also consider the modified fractional order system to reveal the impact of the forgetting process on the system dynamics. Numerical simulations capture system dynamics and reveal that the delayed model system exhibits abundant dynamics, including several stability changes and chaotic behavior. Order of fractional derivative found to be involved in changing the stability property of the system near the coexistence equilibrium state.
During lactation, mammalian pups rely on the dam for survival and associative learning related to maternal stimuli. This study investigates how maternal preference shifts during the late lactation period in mouse pups. Pups conditioned with odorized dams during this period exhibited distinct preferences: those exposed to 4-methylthiazole (4MT) preferred it, while controls avoided it, and eugenol (EG)-conditioned pups showed no response. Interestingly, dams painted with 4MT displayed reduced maternal care compared to EG- or oil-painted dams. To separate maternal presence from odor experience, pups were exposed to 4MT or EG without the dam. Odor-preference learning occurred only when pups remained with their siblings but failed when separated from both the dam and all of their siblings. These findings suggest that dam separation in the presence of siblings facilitates odor-preference learning, indicating a developmental shift towards reduced dam reliance and preparation for independence.
Offspring predation is one of the greatest obstacles to an organism's reproductive success, but parents vary in the strength of their response to potential predators. One explanation for this variable investment is that defending current offspring has the potential to lower future reproductive success if the predator is also capable of injuring or killing the parent. Northern house wrens (Troglodytes aedon) are cavity‐nesting songbirds that defend against multiple species of nest predators including small mammals, birds of prey, and snakes. Here, we used three different predator decoys: two nest predators—an eastern chipmunk (Tamias striatus) and an eastern ratsnake (Pantherophis alleghaniensis)—as well as a predator of both offspring and adults—a juvenile Cooper's hawk (Accipiter cooperi)—to elicit nest defense and test whether females use risk assessment to modulate their antipredator behavior. We found that antipredator behaviors were not significantly different between the two nest predators, which posed a high risk to the nestlings, but lower risk to the parents, as neither species frequently captures adult wrens outside the nest box. However, female wrens never dove at or attacked the Cooper's hawk, while they frequently attacked both the snake and chipmunk decoys. Neighboring house wrens from adjacent territories were also less likely to respond to the hawk, but more heterospecifics mobbed the hawk than the snake decoy. Collectively, these results show that risk assessment and the strength of the antipredator response varies substantially both within and among species. Female house wrens exhibit plasticity in their nest defense behavior, and they respond to different types of predators in a way that could maximize lifetime fitness while risking the loss of their current offspring.
The family is the smallest unit of society, where parents invest significant time and resources in their offspring, providing parental care through defense and feeding. These parental investments, which benefit the offspring by increasing their survival rates and growth, are constantly at risk of exploitation by both conspecifics and heterospecifics. As a result, parents are known to employ various mechanisms that prevent the inclusion of unrelated young in the family unit. In this study, we investigated burying beetle Nicrophorus quadripunctatus , which exhibits elaborate parental care, and found that the rate of exclusion of heterospecific larvae varies genetically across different populations. Two populations were identified: one where competing congeners were present and one where they were absent. We bred individuals from these populations under laboratory conditions, isolated from competitors, and tested the exclusion rates of unrelated larvae. Our results revealed that parents from the population coexisting with competitors had a significantly higher exclusion rate of heterospecific larvae. In contrast, no significant differences were observed between the populations regarding the exclusion of unrelated conspecific larvae. These findings suggest that the exclusion of heterospecific larvae is genetically higher in populations where competitors are present. This study represents an important step toward understanding the genetic basis underlying parental acceptance or rejection of unrelated young, offering new insights into the evolution of family life and parental care strategies.
Unraveling the numerous factors that drive phenotypic variation in trait expression among animals has long presented a significant challenge. Whereas traits like growth and adult size are often heritable and are passed on from one generation to the next, these can be significantly affected by the quality and quantity of resources provided by one or both parents to their offspring. In many vertebrates, such as birds and mammals, parents raise their young until adult, providing food, shelter, and protection. On the other hand, in insects, there is often little or no parental care, and the young are left to fend for themselves. Despite that, some insects can enhance the growth of their offspring. In parasitoid wasps, for example, mothers inject biochemical factors, including venoms, teratocytes, and virus-like particles into the host that increase host quality by regulating the nutritional milieu. However, it is not known whether maternal size is positively correlated with host regulation. Here, we evaluate maternal and host size-related effects on the development of an asexually reproducing (= female only) secondary idiobiont ectoparasitoid, Gelis agilis on pre-pupae in cocoons of its host, the primary parasitoid, Cotesia glomerata. Females G. agilis from 2 adult size classes, “small” (mean 0.7 mg) or “large” (mean 1.2 mg), were allowed to parasitize cocoons of differing size along a continuum from ~1.2 mg to ~4.0 mg, and the body size and development time of their offspring were measured. In both body size classes of G. agilis mothers, there was a strong correlation between host size and offspring size. However, there was no effect of adult G. agilis size on this parameter: for a given host size, the size of G. agilis offspring did not differ between small and large mothers. Our results reveal that host quality is mostly pre-determined, irrespective of maternal size.
Parental care enhances reproductive success. Yet these advantages come with associated costs for the parents, including those affecting their own survival. Environmental conditions and species life history can influence which parental care strategy emerges. In birds, parental care is prevalent and often biparental, in which both males and females contribute to the same activities, although the extent varies between species. This study aimed to compare parental investment between male and female Mato Grosso Antbirds Cercomacra melanaria in the Pantanal wetlands, Brazil. Analysed behaviours included carrying material and nest shaping during nest-building; total incubation duration and incubation related to time of day (morning and afternoon) during the incubation period; and brooding, feeding offspring and faecal sac removal during the nestling stage. Nest defence events were recorded for all three periods, investigating whether this behaviour intensified with nestlings’ development. Whereas no differences between males and females were found in most analysed behaviours, males were observed to incubate more throughout day-time, specifically during the morning. This heightened provision by males may serve as compensation for the substantial costs associated with egg production and/or as a response to the elevated predation risk that females incur during nocturnal incubation. Males defended the nest more than females, but the outcomes do not suggest that Mato Grosso Antbird parents tend to show increased aggressiveness when the value of their offspring is higher, which diverges from parental investment theory. Further studies incorporating manipulative methods, such as vocalisation playbacks, are necessary to establish whether this similarity in behaviour between developmental periods holds true. If so, it raises questions regarding what motivates the pair to defend the nesting stages to a similar extent.
In the wild, stressors occur with varying likelihood throughout the day, leading animals to evolve plastic stress responses that exhibit circadian rhythmicity. In mammals, studies have revealed that the circadian plasticity of stress response may differ with age. However, such developmental effects have been largely overlooked in other vertebrate groups. In our research, we explored the presence of developmental variation in the daily pattern of behavioral stress response in a teleost fish model: the zebrafish ( Danio rerio ). We compared juvenile and adult individuals in two behavioral paradigms commonly used to analyze fish stress response, such as the open‐field test and the diving test. Our comparisons were conducted every 4 h during a 24‐h cycle to analyze daily variations. Significant daily rhythms were detected for almost all analyzed behaviors in both tests. In general, the analyses suggested a greater stress response in adults during the daytime and in juveniles during the night‐time, although not all indicators aligned in this direction. Moreover, we found average differences in zebrafish behavior, suggesting that juveniles were more sensitive to stress. Overall, these findings highlight the importance of considering developmental variation in the circadian pattern of stress response in non‐mammalian species like zebrafish.
To maximize energy available for foraging or reproduction, optimality theory suggests individuals allocate energy toward defensive behaviors equivalent to risk of predation. In this framework, repeat encounters with humans by wildlife that do not reduce individual fitness could result in a decreased defensive response toward humans in subsequent encounters. We investigated whether individual experience influenced the defensive behaviors and frequency of site use of foraging eastern copperheads (Agkistrodon contortrix) at Koomer Ridge Campground in the Daniel Boone National Forest, Kentucky. Beginning in 2015, this site has been used for annual mark-recapture studies of copperhead foraging ecology as they predate emerging annual cicadas (Neotibicen tibicen). Using a standardized behavioral trial, we tested how copperhead defensive behavior toward humans was influenced by capture history, body size, and soil temperature. Model averaging results indicated that the overall intensity of copperhead defensive response to humans increased with capture history length, and soil temperature was positively associated with likelihood to respond when touched. Number of years recaptured was a significant, positive predictor of foraging frequency in 2022. Therefore, copperheads with longer capture histories visit the site to forage more frequently and are more willing to defend their opportunity to forage, suggesting a degree of acquired tolerance absent from naïve snakes that fled readily. Collectively, these results provide evidence that eastern copperheads at our site modulate their foraging and defensive behavior based on previous capture experience to more efficiently predate a seasonally abundant prey item.
Parental care is costly to parents because it consumes energy and reduces the available time for future reproduction. Hence, in theory, parents should not care for the eggs or offspring of unrelated individuals. However, parental care for unrelated offspring has been demonstrated for some animal species, although it has been unclear whether such animals distinguish their offspring from unrelated individuals. Here, we examined protection of non-offspring eggs by adult females of the predatory mite Gynaeseius liturivorus, which discriminate eggs laid by other females, against the predatory mite Neoseiulus californicus. Adult female G. liturivorus protect their eggs against predators. Several adult females of this species are sometimes found with clustered eggs in field; hence, G. liturivorus mothers may protect non-offspring eggs. When G. liturivorus eggs were kept with N. californicus in the presence of conspecific adult females that were not mothers of the eggs, their survival was higher than in the absence of conspecific females. Although adult female G. liturivorus oviposited during experiments, the addition of eggs did not increase the survival of non-offspring eggs. Adult females did not cannibalise newly hatched non-offspring larvae in the presence of food, suggesting that the presence of adult females did not affect larval survival. Furthermore, adult females protected their own eggs laid during experiments, suggesting that protection of non-offspring eggs was not costly to the females. Our results also suggest that adult female G. liturivorus may protect conspecific eggs when abundant food is available.
Significance statement
Parental care is observed in a wide range of taxa and commonly provided for offspring and/or kin individuals. However, some animal species take care of unrelated individuals. This might be because such species do not discriminate between their own offspring and those of conspecifics. In this study, we experimentally demonstrated that non-offspring eggs were protected from predators by adult females of the predatory mite, Gynaeseius liturivorus, which distinguish their own eggs from conspecific eggs. Newly hatched non-offspring larvae were not cannibalised by adult female mites in the presence of food. Adult females also protected their own eggs irrespective of the presence of conspecific eggs. Our results suggest that adult female predatory mites protect non-offspring when food availability is high.
Populations of large pelagic sharks are declining worldwide due to overfishing. Determining the overlap between shark populations and fishing activities is important to inform conservation measures. However, for many threatened sharks the whereabouts of particularly vulnerable life-history stages – such as pregnant females and juveniles – are poorly known. Here, we investigated the spatial distribution of size classes, energy transfer and reproductive states of pregnant females of the endangered shortfin mako, Isurus oxyrinchus, using spatially resolved catch data from a Spanish surface longline vessel (1996 − 2009) in the South-east Pacific Ocean. Our results suggest a general eastward gradient of occurrence of pregnant females of thousands of kilometers from western oceanic feeding grounds towards the eastern Pacific, where we observed an aggregation area of small juveniles. Moreover, the potential nursery likely overlapped a longline fishing hotspot, increasing the vulnerability of juveniles from fisheries. Our results suggest that limiting fishing pressure in this area could reduce mortality of early life stages and contribute to the conservation of this endangered shark species.
La etapa de crecimiento posnatal es clave en el ciclo de vida de los individuos ya que la variación en las trayectorias de crecimiento y los fenotipos juveniles resultantes pueden afectar directamente a las habilidades competitivas, la supervivencia y el éxito de apareamiento futuro, lo que se refleja en última instancia en términos de eficacia biológica. En este sentido, a pesar de que diferentes aspectos del crecimiento corporal han sido estudiados en aves en general y aves marinas en particular, los estudios realizados en aves marinas sudamericanas son escasos. Aquí, presento una síntesis de causas próximas, últimas, e implicancias de la variación en el crecimiento corporal en aves marinas, abordando además la utilidad de algunas herramientas estadísticas para su estudio. Asimismo, planteo una revisión bibliográfica de la información existente para la región, identificando aspectos de interés a ser considerados en futuros estudios.
Anthropogenically induced climate change has significantly increased the frequency of acute weather events, such as drought. As human activities amplify environmental stresses, animals may be forced to prioritize survival over behaviors less crucial to immediate fitness, such as socializing. Yet, social bonds may also enable individuals to weather the deleterious effects of environmental conditions. We investigated how the highly social plains zebra (Equus quagga) modify their activity budgets, social networks, and multimodal communication during a drought. Although animals prioritized feeding and the number of social interactions dramatically decreased in the late drought period, social associations remained robust. We observed age/sex class‐specific changes in social behavior, reflecting the nutritional needs and social niche of each individual. Stallions devoted more time to greeting behaviors, which could mitigate harassment by bachelor males and facilitate grazing time for the females of the harem. Juveniles significantly increased time spent active socializing, despite mothers showing the greatest decrease in the number of social interactions. Instead, unrelated, nonlactating females served as social partners, accommodating both juveniles' social needs and lactating mothers' nutritive requirements. Using a network‐based representation of multimodal communication, we observed a decrease in the number of signals used during the drought. Individuals used less diverse multimodal combinations, particularly in the costly context of aggression. These findings illustrate how social roles and differential responses to acute environmental stress within stable social groups may contribute to species resilience, and how communication flexibly responds to facilitate both survival and sociality under harsh environmental conditions.
Human interaction with birds has never been more positive and supported by so many private citizens and professional groups. However, direct mortality of birds from anthropogenic causes has increased and has led to significant annual losses of birds. We know of the crucial impact of habitat loss on the survival of birds and its effects on biodiversity. Direct mortality via anthropogenic causes is an additive but biologically important cause of avian decline. This is the focus of this paper. This paper synthesises and interprets the data on direct anthropogenic causes of mortality in birds, and it also discusses emerging and relatively hidden problems, including new challenges that birds may not be able to manage. This paper points out that such deaths occur indiscriminately and have negative behavioural and reproductive consequences even for survivors. All of these factors are important to address, because any functional habitat depends on birds. This paper suggests that some of this death toll can be reduced substantially and immediately, even some of the seemingly intractable problems. This paper also proposes cross-disciplinary solutions, bearing in mind that “ecosystem services” provided by birds benefit us all, and that the continued existence of avian diversity is one cornerstone for human survival.
Nuclear family structures are often thought to be essential for the well-being of children. Divorce, the loss of either biological parent, the presence of step-parents, and the practice of polygynous marriage have all been claimed to negatively impact child well-being. However, empirical research on these topics has been limited by the routine use of cross-regional and cross-sectional databases. Cross-regional data render research vulnerable to the ecological inference fallacy, and cross-sectional data prevent assessment of age-specific impacts of time-varying family-structure variables. When longitudinal data are available, they tend to be drawn from Western/urban contexts. Detailed data on family structure and children’s well-being are rarely collected in more marginalized communities. In many rural and traditional communities, nonnuclear family structures are indeed prevalent and viewed as socially permissible—and, as such, may have different impacts on children’s well-being than in Western contexts. Here, we draw on a detailed, longitudinal dataset from a 20-y prospective study in rural Tanzania, where polygyny and serial monogamy are common. We analyze survival outcomes for 3,693 children born between 1931 and 2014, growth outcomes for 881 children born between 1976 and 2014, and educational outcomes for 1,370 children born between 1976 and 2014. Our analyses indicate that monogamous marriage is not consistently associated with better outcomes for children—contrary to some popular and public health perspectives on human family structure.
Comparative research on the evolution of parental care has followed a general trend in recent years, with researchers gathering data on clutch size or egg size and correlating these traits with ecological variables across a phylogeny. The goal of these studies is to shed light on how and why certain strategies evolve. However, results vary across studies, and we rarely have results explaining why the observed pattern occurred, leaving us with further hypotheses to test. By using a combination of comparative methods, we provide an explanation of how such patterns emerge based on the evolutionary timeline of constructing burrows and the energy invested into egg size and egg number; this combination also allowed us to pinpoint why the pattern occurred. We do so with data on freshwater crayfish, which are ideal for such investigations because they vary in their reliance on burrows, their body size, and their investment into their offspring. Specifically, we tested whether a strong dependence on burrows is related to investment in eggs (i.e., larger eggs or more eggs) given the body size of the species. Surprisingly, we found no correlation between burrowing and the size or number of eggs crayfish lay; instead, body size was the best predictor of the number of eggs (but not the size of eggs) that each species lays. Interestingly, our analysis suggests that crayfish ancestors had a small clutch size, relatively large eggs, and a weak connection to burrows. Thus, the shift to heavily relying on burrows appeared after this lineage was already investing in large eggs, which gives insights into the colonization of freshwater by an ancestral astacidean ancestor. While other studies show that the evolution of parental care strategies is not straightforward, our study provides a clear evolutionary timeline of the interplay between the evolution of burrowing behavior and shifts in the evolution of egg investment. Furthermore, our work showcases how merging multiple phylogenetically informed approaches can disentangle the origin and evolution of life history traits.
Infant adoption is an association that occurs between an adult individual and a dependent infant and occurs most often when lactating females care for a nutritionally dependent infant that is not her offspring. Adult females are often involved in adoption; while, direct infant care by males occurs in less than 5% of all mammalian species. We report the first record of adoption by wild male adults of Alouatta caraya, a platyrrhine primate species that does not typically participate in parental care. We observed two independent cases of adoption, in two different groups (G1, G2) at the Corrientes Biological Station, Argentina. After the death of two adult females with dependent infants, one adult male adopted an orphan in each group. We recorded the activity of the adoptive males and the two infants. During this period, adoptive males expressed parental care behaviors toward infants. However, after 38 days in G1 and 53 days in G2, both infants died. Based on our continuous monitoring of study groups, we suggest that adoptive males are the biological parents of the orphaned infants. As such, kin selection may explain the care of the infants. However, another explanation could be group familiarity, which refers to the social bonds and cohesion that develop among individuals within a group, even if they are not genetically related. An adult male, although not genetically related to the infants, may take care of them due to the cohesion and relationships established within the group during his period of residence. The study of these rare parental behaviors taken by A. caraya adult males provide insights into the knowledge of group social cohesion and structure.
In species where both sexes care for offspring, one parent—generally the female—typically provides more care than the other. While current theory offers broad predictions on the evolution of sex differences in parental care, it remains unclear whether ecological factors, such as short-term environmental variation and the intrinsic state of parents, also influence the size of existing asymmetries between parents. Here, I highlight how recent work on burying beetles ( Nicrophorus sp.), a now well-established taxon to study biparental care, has contributed to research on sex differences in parenting. Although female burying beetles provide more care than males, the extent of this asymmetry is context-dependent as each sex constantly readjusts care depending on the surrounding environment and own state. Nevertheless, despite variation in the magnitude of the sex differences, there are still clear patterns of care specific to each species, highlighting the importance of the evolutionary history. Finally, the presence of sex differences presumably has consequences for the efficiency of parental care and can affect offspring performance. To gain a more comprehensive understanding of the life-history and environmental conditions driving sex differences in parenting, we need more natural history research on the less commonly studied Nicrophorus species and more work examining behavioural responses to rapid environmental changes in all taxa. Addressing these gaps will contribute to our understanding of how sexual conflict over care is resolved and how biparental cooperation persists despite asymmetries between caring parents.
Why and how we age are probably two of science's oldest questions, echoing personal beliefs and concerns about our own finitude. From the earliest musings of ancient philosophers to recent pharmacological trials aimed at slowing ageing and prolonging longevity, these questions have fascinated scientists across time and fields of research. Taking advantage of the natural diversity of ageing trajectories, within and across species, this interdisciplinary volume provides a comprehensive view of the recent advances in ageing and longevity through a biodemographic approach. It includes the key facts, theories, ongoing fields of investigation, big questions, and new avenues for research in ageing and longevity, as well as considerations on how extending longevity integrates into the social and environmental challenges that our society faces. This is a useful resource for students and researchers curious to unravel the mysteries of longevity and ageing, from their origins to their consequences, across species, space and time.
The magnitude of many kinds of biological structures and processes scale with organismal size, often in regular ways that can be described by power functions. Traditionally, many of these “biological scaling” relationships have been explained based on internal geometric, physical, and energetic constraints according to universal natural laws, such as the “surface law” and “3/4‐power law”. However, during the last three decades it has become increasingly apparent that biological scaling relationships vary greatly in response to various external (environmental) factors. In this review, I propose and provide several lines of evidence supporting a new ecological perspective that I call the “mortality theory of ecology” (MorTE). According to this viewpoint, mortality imposes time limits on the growth, development, and reproduction of organisms. Accordingly, small, vulnerable organisms subject to high mortality due to predation and other environmental hazards have evolved faster, shorter lives than larger, more protected organisms. A MorTE also includes various corollary, size‐related internal and external causative factors (e.g. intraspecific resource competition, geometric surface area to volume effects on resource supply/transport and the protection of internal tissues from environmental hazards, internal homeostatic regulatory systems, incidence of pathogens and parasites, etc.) that impact the scaling of life. A mortality‐centred approach successfully predicts the ranges of body‐mass scaling slopes observed for many kinds of biological and ecological traits. Furthermore, I argue that mortality rate should be considered the ultimate (evolutionary) driver of the scaling of life, that is expressed in the context of other proximate (functional) drivers such as information‐based biological regulation and spatial (geometric) and energetic (metabolic) constraints.
Parents may experience a trade‐off between caring for offspring and protecting themselves from predators. The reproductive value hypothesis predicts that parents should take more risks for older, more valuable offspring, whereas the harm to offspring hypothesis predicts that parents should risk more for vulnerable offspring that would suffer most from a lack of parental care at the moment. After exposing parent mountain bluebirds ( Sialia, currucoides ) to a model predator, we recorded latency times for them to touch, to look into, and to enter their nestbox and the number of times they inspected the box across three breeding stages: nest‐building, incubation and nestling‐rearing. Females took greater risks than males during the nest‐building and incubation stages by inspecting and entering boxes sooner and more times, consistent with their role in parental care at those early breeding stages that requires them to enter the box. Risk‐taking in males was consistent with the reproductive value hypothesis, increasing across breeding stages. In contrast, females took the greatest risk during incubation, consistent with the harm to offspring hypothesis. Furthermore, the riskiest behaviours were not correlated between pair members, and both sexes assumed the risk to first inspect the nestbox approximately equally. This suggests there is not a ‘war of attrition’ between mates over risk‐taking, but neither was there cooperation by the male to facilitate the rapid resumption of parental care by his mate. The results highlight that patterns of investment in nest defense in birds may be sex‐specific.
The face is the most important area on the human body for visually differentiating between individuals. When encountering another person, humans initially gaze at and perceive the face holistically, utilizing first-order relational information and specific neural systems. Information such as identity and emotional state are then obtained from the face by distinguishing between small inter-individual differences, i.e., second-order relational information. Similar patterns and mechanisms underlying individual face recognition have been documented in primates, other social mammals, birds, and more recently in some fishes. Like humans, fish are capable of rapidly (<0.5 s) and accurately recognizing multiple familiar conspecifics by individual-specific variation in the face. Fish can also recognize faces from various distances and angles, providing evidence for mental representation of faces in this large and diverse vertebrate group. One species, the cleaner fish, has even demonstrated mirror self-recognition (MSR) via self-face recognition, strengthening the claim that non-human animals are capable of having mental images and concepts of faces. Here, we review the evidence for individual face recognition in fishes and speculate that face identification neural networks are both similar and widespread across vertebrates. Furthermore, we hypothesize that first-and second-order face recognition in vertebrates originated in bony fishes in the Paleozoic era ~450 Mya, when social systems first evolved, increasing the importance of individual recognition.
The breeding behaviour of raptors is determined by many characteristics, such as courtship and mating patterns, nest building, foraging, territorial defence activities, clutch incubation, and caring for the young. Here, we study the breeding behaviour of the Red Kite (Milvus milvus), a European native bird of prey. From a period between 2018 and 2022, we analysed data for 33 adult Red Kites (14 males and 19 females) during 70 successful breeding episodes in Austria, the Czech Republic, and Slovakia. Using satellite telemetry and in situ observations, we found differences between males and females in the size of the home range, number of nights on the nest, and maximum distances from the nest. We analysed the influence of different factors on movement activity, breeding productivity, and home range size. Females spent significantly more nights on the nest than did males, flew shorter distances from the eyrie, and occupied smaller areas. Red Kites with two or more breeding experiences arrived significantly earlier than did unexperienced Kites in their first breeding attempts. Juveniles departed from the nest sooner than did their parents. Birds with more fledged juveniles occupied smaller home ranges. Our study reveals new knowledge of substantially different breeding behaviours in male and female Central European Red Kites.
Although the effect of sperm quality is well studied in the context of sperm competition, its effect on offspring performance, especially after the embryo stages, has been less investigated. Here, we investigated whether the proportion of spermatozoa with normal morphology was associated with offspring performance during chick development in the black-legged kittiwake, a behaviorally and genetically monogamous seabird in which sperm competition is absent. First, we found that, at hatching, the difference in body condition between the first- and second-hatched siblings was higher when the father had a lower proportion of normal spermatozoa. We discuss this result in light of maternal allocation strategy to manipulate sibling competition. Second, we showed that, in first-hatched chicks, body mass growth between hatching and the age of 10 days, body condition at the age of 10 days and maximum body mass reached before fledging were positively related to the proportion of normal spermatozoa in the father’s sperm. Overall, our results support the role of sperm quality on offspring performance in the black-legged kittiwake and call for further studies investigating the importance of sperm quality in genetically monogamous species.
The existence of life‐history trade‐offs is a fundamental assumption of evolutionary biology and behavioural ecology, yet empirical studies have found mixed evidence for this. Such trade‐offs are expected when individuals vary in how they allocate their limited resource budgets between different life‐history functions (variation in resource allocation), but they may be masked when individuals vary in how many resources they have acquired that they can later allocate to life‐history functions (variation in resource acquisition). We currently lack studies on the extent to which individual differences in behaviour reflect variation between individuals in resource acquisition and resource allocation. Here, we use parental care as a case study for exploring this question. We used the burying beetle Nicrophorus vespilloides, which exhibits facultative biparental care, comprising direct care (provisioning food or interacting with larvae) and indirect care (guarding or maintaining the carcass). We found some evidence for a positive relationship between these two components of care for both male and female parents. In addition, parents that spent more time providing care 24 h after hatching also tended to provide care for longer. Lastly, parents that provided more parental care did not experience a trade‐off of reduced lifespan after the breeding attempt. On the contrary, we found a positive relationship between the duration of care provided and parents' post‐breeding lifespan. Our finding of positive relationships between parental behaviours and between parental care and lifespan suggests that variation in care was mainly driven by differences in prior resource acquisition (i.e., parental quality) among individuals rather than differences in resource allocation. Our findings thus suggest that high intraspecific variation in parental quality can potentially mask reproductive investment trade‐offs within populations.
Many oviparous animals are selective about where to lay eggs, as this greatly affects their offspring’s survival. Theoretically, species sharing the same habitat are expected to experience similar selective pressures, leading to the prediction that they might share similar oviposition preferences. However, this hypothesis has not yet been tested. In this study, through an extensive field survey, we examined the oviposition site selection of four sympatric amphibian species (Rana uenoi, Hynobius quelpaertensis, Bombina orientalis, and Dryophytes japonicus) that reproduce in the same natural ephemeral stream. Our focus was on understanding how abiotic and biotic factors influence their reproductive choices. We primarily found that desiccation avoidance is a universal selective pressure affecting all species, with a tendency to avoid laying eggs in smaller pools prone to desiccation. Species-specific responses to leaf litter and canopy coverage were observed, but none of the species’ oviposition choices correlated with the quantity of stones in pools. We also explored biotic influences, revealing species-specific trends in the selection of pools with conspecific and heterospecific juveniles, predators, and mosquito larvae, indicating a complex ecological interplay. These findings highlight the complexity of ovipositional patterns in animals, where decisions are not driven solely by a single factor such as the avoidance of predators or competitors but also by intricate assessments of multiple factors. The study highlights that amphibian oviposition in ephemeral streams is influenced by a diverse interplay of biotic and abiotic factors, essential for understanding their reproductive strategies in dynamic environments.
Differences in brain size among homeothermic vertebrates are known to have important ecological and evolutionary consequences, involving trade-offs between the cognitive benefits of larger brains and the associated energetic costs. Nonetheless, other poikilothermic vertebrate groups have been largely overlooked in this context, challenging the broad applicability of the proposed theories for vertebrates more generally. Fish brains are highly plastic organs that adapt to environmental conditions, so we focused on local-scale validation based on comparisons of species from the undisturbed headwaters of Šumava National Park, Czech Republic. The brains of common minnows (Phoxinus phoxinus L.), brown trout (Salmo trutta m. fario L.) and European bullheads (Cottus gobio L.) were scanned via computed tomography. Our aim was to determine whether the brain size patterns of these three species, which are unrelated at the level of phylogenetic order and occur naturally in a single locality without significant anthropogenic pressures, follow general predictions. The cognitive buffer hypothesis, which suggests that large brains provide a behavioural buffer facilitating successful introduction to new environments, was confirmed, as brown trout and minnows, i.e., species with invasive potential, had larger brains than non-invasive, stationary bullheads. This confirmation provides new support for the general validity of the cognitive buffer hypothesis across vertebrates. However, our results were not in alignment with the parental brain hypothesis. The patterns of sensory areas of the brain also measured in the present study (i.e., the olfactory bulb, optic tectum and eminentia granularis) indicate that minnows invest more in the development of the sensory areas of the brain and, thus, primary sensory processing, whereas trout invest in cognitive and integrative processing. The present study emphasises that general evolutionary predictions and theories regarding brain size, especially in fish, should also be verified at a local scale with comparable ecological conditions across species.
Females of some species improve their reproductive success not only by being choosy and selecting males with certain traits, but also by sequentially mating with multiple males within one reproductive season. However, it is relatively unknown whether females also evaluate parental care during mate choice and, if they do, whether males actively communicate their care status to approaching females. We monitored a natural population of the glassfrog Hyalinobatrachium valerioi, a species with sequential polyandry and paternal care, to assess the role of parental care and advertisement calling on male mating success. Using field observations and acoustic analysis , we found that even in this species which has single-note calls, variations in call parameters allow for individual discrimination. Calling was strongly associated with mating success in H. valerioi males. Males with longer calls achieved the highest total mating success over the entire study period, indicating that females might have a preference for longer calls. Moreover, active calling and the presence of clutches were both linked to male mating success on a given night, although we cannot fully exclude that the link between presence of clutches and mating success is due to attractive call features alone. Call parameters differed between males when they were calling on top of their clutches, compared to sitting on the leaf directly, which might provide reliable cues about parental state to approaching females. These findings demonstrate the prominent role of acoustic communication and female choice in a species with male parental care and sequential polyandry.
Dispersal is a key demographic parameter that plays an important role in determining spatial population dynamic and genetic structure. Linking differences in dispersal patterns to key life-history traits is often confounded by inconsistent environmental pressures experienced by different populations. To explore the link between dispersal and life history, we focus on a site where oviparous and viviparous lineages of the common lizard (Zootoca vivipara) are found adjacent to each other. We take advantage of this shared environment to investigate parity-specific dispersal patterns using high resolution, individual-level spatial genetic autocorrelation and population genomic approaches (11,726 SNPs; 293 oviparous and 310 viviparous individuals). We found isolation-by-distance patterns to be present in both the oviparous and viviparous populations. Density was 2.5 times higher in the viviparous population than the oviparous one, though heterozygosity and genetic diversity measures were similar in the two populations. We found marked differences in the extent of genetic neighbourhoods between the lineages, with the viviparous population showing both dispersal (σ) and spatial genetic autocorrelation (Moran’s I) at two-fold greater geographic distances than the oviparous population. We found clear evidence of male-biased dispersal from genetic estimates in the viviparous population. In the oviparous population, evidence of male-biased dispersal is weak or absent. These differences are likely to be closely linked to specific requirements of the alternative reproductive strategies and may be the demographic consequences of mother-offspring interactions. Fine-scale geographic and individual-level measures are key to understanding parity mode differences at microevolutionary scales and to better identifying their ecological and evolutionary impacts.
Objectives: Allomaternal care (AMC) is suggested to be energetically beneficial to mothers and costly to allomothers. However, among primates, AMC is a heterogeneous phenomenon and its implications are less clear especially in female dispersal species. Here, we investigated infant care in a female dispersal species, Phayre's leaf monkeys (Trachypithecus phayrei crepusculus), to evaluate whether mothers were constrained by infant care and benefitted energetically from AMC, whether AMC was energetically costly for allomothers and how maternal experience was associated with AMC.
Materials and Methods: Data were collected via instantaneous focal animal sampling between 2004 and 2005 for juvenile and adult females (N = 18) from two groups at the Phu Khieo Wildlife Sanctuary, Thailand (440 h). We used generalized linear mixed models to determine how infant care during the first month after birth affected the time mothers and allomothers spent feeding, socializing, resting, and locomoting and how AMC varied.
Results: In the first month, infants spent 26% of their time with an allomother. We
found no differences in mothers' overall activity before versus after birth, although
mothers fed significantly more and rested less when without their infant. Allomothers fed and rested less when with an infant. AMC varied between 0.0% and 20.5%, with immature females being most active.
Discussion: Mothers appear to benefit energetically from AMC such that their overall
activity after birth remained unchanged. Costs and benefits for allomothers seem to
be variable. Some very active immature females may be benefitting from learning-to-mother. The overall low cost of AMC may facilitate a reciprocal social network
among unrelated females.
Principles of social evolution have long been used retrospectively to interpret social interactions, but have less commonly been applied predictively to inform conservation and animal husbandry strategies. We investigate whether differences in developmental environment, facilitated by divergent social conditions, can predict resilience to environmental change. Upon exposure to harsh novel environments, populations that previously experienced more benign social environments are predicted either to suffer fitness losses (the “mutation load hypothesis” and “selection filter hypothesis”) or maintain fitness (the “beneficial mutation hypothesis”). We tested these contrasting predictions using populations of burying beetles Nicrophorus vespilloides we had evolved experimentally for 45 generations under contrasting social environments by manipulating the supply of post-hatching parental care. We exposed sexually immature adults from each population to varying heat stress and measured the effect on survival and reproduction. The greater the level of parental care previously experienced by a population, the better its survival under heat stress during sexual maturation. Although this is consistent with the “beneficial mutation hypothesis”, it is also possible that populations that had evolved without post-hatching care were simply more prone to dying during maturation, regardless of their thermal environment. Overall, we suggest that stochastic genetic variation, probably due to founder effects, had a stronger influence on resilience. We discuss the implications for translocation and captive breeding programmes
The most generalized reproductive mode in anurans is the deposition of egg clutches in water that develop into exotrophic aquatic tadpoles. Yet, despite this extended distribution, cases of parental care on submerged egg clutches are poorly documented. Because of its high diversity, its aquatic habits, and reports on males of two species standing next to the clutch, the Andean genus Telmatobius Wiegmann, 1834 offers an excellent model to examine the evolution of such behavior and the factors influencing it. Here, we combine field and laboratory studies to describe the breeding biology and parental care behavior in Telmatobius culeus (Garman, 1876), Telmatobius hintoni Parker, 1940, Telmatobius intermedius Vellard, 1951, Telmatobius jelskii (Peters, 1873), and Telmatobius oxycephalus Vellard, 1946. Our findings indicate that these five species have prolonged breeding season, and use concealed underwater shelters between rocks or macrophytes for mating and egg deposition. We showed that clutches of 35–560 eggs are deposited in these shelters. Males were observed next to the egg clutch and defending it aggressively against intruders, including conspecifics. Females were, on average, larger than males supporting the hypothesis that competition among males does not drive sexual size dimorphism in the genus. Our findings provide meaningful data to use in conservation programs, given that most species of Telmatobius are considered endangered and fill a significant information gap in understanding parental care’s origin in Nobleobatrachia.
Nest defence is one component of parental investment by which individuals can increase the survival of their offspring. Aggressive behaviours and the time spent protecting nests are determining factors in the reproductive success of cichlid species. The Mexican mojarra is the only cichlid native to the Balsas River Basin in Mexico. At least four invasive cichlids have been introduced, including the convict cichlid and the spotcheek cichlid. These three species establish their nests in the River and defend them aggressively. We quantified the number of nests, aggressive behaviours and time spent in the nest by parents of the native species and these two invasive species. We expected that the invasive parents would be more aggressive during defence, spent more time protecting the eggs, and would have a higher density of nests. We also explored differences in nest defence between the sexes within each species. We found that invasive cichlids had a greater number of nests than the Mexican mojarra. In the two invasive species, there was no difference between males and females in the time spent in the nest or the number of aggressive behaviours. In contrast, male Mexican mojarras spent less time in the nest and performed fewer aggressive behaviours than their mates. The smaller number of nests and nest defence behaviour of this native species could compromise its reproductive success and population size. This differential nest defence between the Mexican mojarra and the invasive cichlids could have negative implications for the physiology, reproduction, and health of this native cichlid.
In many animal species, including most birds, parental care is performed by both parents, which has important implications for mate choice (good parent hypothesis) and parental investment strategies. Partitioning the variance in measures of parental care into heritable and non-heritable components is important to understand the evolvability of parental investment and its potential role in mate choice. We employed an automated system to monitor provisioning behavior at 817 blue tit nests over 10 years (totaling ~3 million visits). Daily provisioning rates of males and females were moderately repeatable between years (Radj = 0.16 and 0.15 respectively), which was almost entirely explained by additive genetic effects. While this degree of heritability is sufficient for parental investment to respond to selection, we argue that the modest level of repeatability provides limited potential for a ‘provisioning phenotype’ to be used as a criterion in mate choice. Daily visit rates were positively correlated between pair members, but after accounting for shared environmental factors this relationship became clearly negative, thereby providing support for models of partial compensation. Visit rates also differed substantially between years, and between days within a year. Thus, it is important to account for these variables when comparing parental investment between individuals. Our results highlight the interplay between genetic, social, and environmental influences on provisioning behavior.
There has been considerable work to test the role of organismal oxidative stress as a mediator of reproductive trade-offs. Intense research focussed on whether parental effort in offspring rearing results in oxidative stress. Many other studies carried out comparisons between non-reproducing and reproducing individuals in a narrow range of taxa. By contrast, we have a very limited number of studies that tested whether pre-breeding oxidative stress constraints reproductive decisions and quality of parental care (and reproductive success as a consequence). In this chapter, I have examined how the need to manage oxidative stress has possibly influenced the evolution of reproductive strategies, from courtship to parental care. I have also illustrated (1) the impact of oxidative stress on fertility, (2) differences between sexes in the regulation of oxidative status homeostasis, and (3) oxidative benefits and costs of cooperative breeding. Finally, I have highlighted a number of weaknesses in experimental designs that have been used to test the oxidative cost of reproduction hypothesis, calling for novel and more realistic studies.
Human-induced disturbance is perceived by avian species as a predation risk. However, the anti-predatory behaviour triggered by these non-lethal events can have negative impacts on reproduction and offspring survival. Research on breeding birds often involves visits to their nests and is likely to disrupt parental behaviour, but nest visits that do not involve direct handling of females have been overlooked as important disturbance events. This study focuses on the impacts of short visits to the nest of incubating Great tit (Parus major) females. We investigated how long they stay away from the nest (off-bout) after a disturbance, their possible compensatory behaviour once they resume incubation (on-bout), and the effects on daily incubation rhythms. We used three years of data from two breeding populations to assess the consequences of disturbances in two scenarios: when the female is present in the nest and flushed, and when the female is absent. We found that after a disturbance, the immediate off-bout was longer when the female was either present or absent, with the magnitude of the disturbance being greater when females were flushed. Females did not compensate with longer on-bouts afterwards, i.e. the research disturbance altered daily incubation behaviour by reducing the total time spent on the nest in relation to the number of daily disturbance events. Females that alter their behaviour in response to perceived predation risk would perform longer incubation periods, resulting in lower hatching rates. These effects of research on female behaviour should be considered when planning field experiments.
Significance statement
Incubating birds react to human activity near their nests by changing their behaviour. This may also apply to basic research activities, but we have no data on how a visit, e.g., to check clutch size, affects them. To find out, we classified data from routine research visits to great tit nests, which are often used for research in the wild, into long and short visits. We also considered whether a female was incubating or foraging outside the nest during the visit. We found that females tended to stay away from the nest longer after they encounter a researcher, and after longer visits. Our results show that even slight research activities in the nest alters female incubation behaviour. They flee and leave the clutch unattended for longer, changing the thermal environment of the nest, which is crucial for proper embryo development.
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