Sexually extravagant males age more rapidly Preston, Brian T.; Jalme, Michel Saint; Hingrat, Yves ...
Ecology letters,
October 2011, Letnik:
14, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Ecology Letters (2011) 14: 1017–1024
Evolutionary theories of ageing posit that increased reproductive investment occurs at the expense of physiological declines in later life. Males typically invest ...heavily in costly sexual ornaments and behaviour, but evidence that the expression of these traits can cause senescence is lacking. Long‐lived houbara bustards (Chlamydotis undulata) engage in extravagant sexual displays to attract mates and here we show that males investing most in these displays experience a rapid senescent deterioration of spermatogenic function at a younger age. This effect is sufficiently large that the expected links between male ‘showiness’ and fertility reverse in later life, despite ‘showy’ males continuing to display at near maximal levels. We show that our results cannot be explained by the selective disappearance of competitive phenotypes and that they are instead consistent with an early vs. late life trade‐off in male reproductive competence, highlighting the potential significance of sexual selection in explaining rates of ageing.
Theory of Mind (ToM), i.e. the ability to understand others' mental states, endows humans with highly adaptive social skills such as teaching or deceiving. Candidate evolutionary explanations have ...been proposed for the unique sophistication of human ToM among primates. For example, the Machiavellian intelligence hypothesis states that the increasing complexity of social networks may have induced a demand for sophisticated ToM. This type of scenario ignores neurocognitive constraints that may eventually be crucial limiting factors for ToM evolution. In contradistinction, the cognitive scaffolding hypothesis asserts that a species' opportunity to develop sophisticated ToM is mostly determined by its general cognitive capacity (on which ToM is scaffolded). However, the actual relationships between ToM sophistication and either brain volume (a proxy for general cognitive capacity) or social group size (a proxy for social network complexity) are unclear. Here, we let 39 individuals sampled from seven non-human primate species (lemurs, macaques, mangabeys, orangutans, gorillas and chimpanzees) engage in simple dyadic games against artificial ToM players (via a familiar human caregiver). Using computational analyses of primates' choice sequences, we found that the probability of exhibiting a ToM-compatible learning style is mainly driven by species' brain volume (rather than by social group size). Moreover, primates' social cognitive sophistication culminates in a precursor form of ToM, which still falls short of human fully-developed ToM abilities.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Offspring resulting from mating among close relatives can suffer from impaired fitness through the expression of recessive alleles with deleterious effects. Postcopulatory sperm selection (a ...prezygotic mechanism of cryptic female choice) has been suggested to be an effective way to avoid inbreeding. To investigate whether postcopulatory female choice allows the avoidance of fertilization by close kin, we performed artificial inseminations in a promiscuous bird, the houbara bustard (Chlamydotis undulata undulata). Females were inseminated with a mix of sperm from triads of males, each constituted of a male genetically unrelated to the female, a first cousin and a half‐sibling. When counting the number of eggs sired by unrelated males, cousins or half‐siblings, we found a significant deviation from the expected random distribution, with more eggs sired by unrelated males. However, offspring sired by cousins, and especially by half‐siblings suffered from high prehatching mortality, suggesting that the observed paternity skew towards unrelated males might reflect differential offspring mortality rather than sperm selection. In agreement with this hypothesis, within‐triad siring success was similar for the three parental relatedness categories, but the relationship between siring and hatching success differed across categories. In clutches with high hatching success, unrelated males had the highest success while in clutches with high failure rate, half‐siblings had the highest success. Offspring sired by half‐siblings also suffered from reduced growth rate during the first three months and higher posthatching mortality. Hence, despite substantial fitness costs associated with fertilization by close relatives, females do not seem to select sperm of unrelated males.
•We found prosocial tendencies in capybaras, using a Prosocial Choice Test.•Subjects were prosocial towards subordinate but not dominant conspecifics.•Our results also suggested that females might be ...more prosocial than males.•We found a direct reciprocity pattern between subjects.•An audience effect sometime occurred and elicited a greater prosociality.
Prosocial behaviours (providing benefits to a recipient with or without cost for the donor) have been found to be highly influenced by sex and by hierarchy. Rodents, in particular, are good model for studying prosocial responses, as they were found to exhibit intentional prosocial behaviours to reward a conspecific, and are very sensitive to reciprocity. In our study, we conducted a Prosocial Choice Test (PCT) in which four capybaras (Hydrochoerus hydrochaeris) living in a social group could choose between three tokens: choosing the prosocial token rewarded simultaneously the subject and a recipient, while choosing the selfish token only rewarded the subject; and choosing the null token provided no reward to anyone. Dominance within each dyad was also studied, both before and during the PCT experiment. Our results showed an influence of hierarchy: subjects were more prosocial towards the recipient when it was a subordinate than when it was a dominant individual. These results could be interpreted as a desire of strengthening a hierarchical rank regarding the subordinate, of punishing aggressive conspecifics (usually the subject’s direct dominant), and of weakening dominant individuals in order to modify the pre-existing hierarchy. Additionally, our results highlighted a direct reciprocity phenomenon, a subject being more likely to be prosocial towards a prosocial recipient. All these findings suggest that prosociality could be well developed in other taxa than Primates and that, in long enough PCT experiments, subtle rules could influence individual prosocial strategies.
Male senescence has detrimental effects on reproductive success and offspring fitness. When females mate with multiple males during the same reproductive bout, post-copulatory sexual selection that ...operates either through sperm competition or cryptic female choice might allow females to skew fertilization success towards young males and as such limit the fitness costs incurred when eggs are fertilized by senescing males. Here, we experimentally tested this hypothesis. We artificially inseminated female North African houbara bustards with sperm from dyads of males of different (young and old) or similar ages (either young or old). Then, we assessed whether siring success was biased towards young males and we measured several life-history traits of the progeny to evaluate the fitness costs due to advanced paternal age. In agreement with the prediction, we found that siring success was biased towards young males, and offspring sired by old males had impaired hatching success, growth and post-release survival (in females). Overall, our results support the hypothesis that post-copulatory sexual selection might represent an effective mechanism allowing females to avoid the fitness costs of fertilization by senescing partners.
Ejaculate attributes are important factors driving the probability of fertilizing eggs. When females mate with several males, competition between sperm to fertilize eggs should accentuate selection ...on ejaculate attributes. We tested this hypothesis in the North African houbara bustard ( Chlamydotis undulata undulata) by comparing the strength of selection acting on two ejaculate attributes when sperm from single males or sperm from different males were used for insemination. In agreement with the prediction, we found that selection on ejaculate attributes was stronger when sperm of different males competed for egg fertilization. These findings provide the first direct comparison of the strength of selection acting on ejaculate attributes under competitive and non-competitive fertilizations, confirming that sperm competition is a major selective force driving the evolution of ejaculate characteristics.
Archaeological discoveries suggest that human interest in odd objects emerged as early as the end of the Lower Paleolithic with Homo erectus, although it is still difficult to understand why early ...humans collected these objects. Several studies show that nonhuman primates are able to appreciate the physical characteristics of their tools, but their interest in the physical properties of nonutilitarian objects has, to our knowledge, never been tested. Here, objects of different brightness, color, and shape were proposed to five orangutans to test whether odd objects intrigue orangutans (Pongo pygmaeus) and whether they induce specific and noticeable behavior. This preliminary experiment shows that orangutans are responsive to the physical properties of nonutilitarian objects, particularly visually striking, bright, and colorful objects. Our experiment shows that these are the most manipulated pieces, regardless of their respective proportions. However, unlike (early) humans, orangutans did not show any tendency to preserve objects.
Parental age has profound consequences for offspring’s phenotype. However, whether patrilineal age affects offspring sperm production remains unknown, despite the importance of sperm production for ...male reproductive success in species facing post‐copulatory sexual selection. Using a longitudinal dataset on ejaculate attributes of the houbara bustard, we showed that offspring sired by old fathers had different age‐dependent trajectories of sperm production compared to offspring sired by young fathers. Specifically, they produced less sperm (−48%) in their first year of life, and 14% less during their lifetime. Paternal age had the strongest effect, with weak evidence for grandpaternal or great grandpaternal age effects. These results show that paternal age can affect offspring reproductive success by reducing sperm production, establishing an intergenerational link between ageing and sexual selection.
Parental age has profound consequences for offspring’s phenotype. Number of gametes transferred during the mating is an important driver of siring success and especially so in species where females mate with several males and ejaculates compete for egg fertilization. We investigated if maternal and paternal age affect sperm production in a bird species with post‐copulatory sexual selection. We found that offspring sired by old fathers had different age‐dependent trajectories of sperm production compared to offspring sired by young fathers, producing less sperm (‐48%) in their first year of life, and 14% less during their lifetime. These results show that paternal age can affect offspring reproductive success by reducing sperm production, establishing an intergenerational link between aging and sexual selection.
1. The information content of secondary sexual traits and the benefits gathered by choosy females are at the heart of sexual selection theory. Indicator models of sexual selection assume that ...secondary sexual traits reflect the phenotypic/genetic quality of their bearers and that females gather benefits from choosing these high-quality males. 2. Here, we tested the idea that courtship display reflects the health status in a bird species with a lek-based mating system, the houbara bustard (Chlamydotis undulata undulata). A group of males was treated with the lipopolysaccharide (LPS) of the cell wall of the bacterium Escherichia coli during the seasonal peak of courtship display, while another group of males was injected with a phosphate-buffered saline solution (PBS) as a control. We then monitored the effect of the treatment on both courtship display and ejaculate quality. Finally, females were artificially inseminated with semen from LPS and PBS males, which allowed us to assess the effect of the immunological treatment on reproduction. 3. We found that the inflammatory challenge reduced courtship display and semen quality compared to controls. Interestingly, males that better resisted to the immune challenge in terms of courtship display also better resisted in terms of ejaculate quality. Early reproductive failure was increased when females were artificially inseminated with semen from immune-activated males. Failure of eggs laid by females inseminated with LPS semen was due to a reduced fertilization power of sperm of LPS males or to increased embryo mortality in the very early stage of embryo development. As a consequence, hatching rate was reduced for females inseminated with semen collected from LPS males. 4. These results show that by assessing male courtship display, females may gain insight into the current phenotypic/genetic quality of mates and gather fitness benefits in terms of reproductive success.
Abstract Certain toxic plants are beneficial for health if small amounts are ingested infrequently and in a specific context of illness. Among our closest living relatives, chimpanzees are found to ...consume plants with pharmacological properties. Providing insight on the origins of human self-medication, this study investigates the role social systems and physiology (namely gut specialization) play on learning mechanisms involved in the consumption of unusual and potentially bioactive foods by two great ape species. We collected data from a community of 41–44 wild chimpanzees in Uganda (11 months, 2008), and a group of 11–13 wild western gorillas in Central African Republic (10 months, 2008–2009). During feeding, we recorded food consumed, its availability, and social interactions (including observers watching conspecifics and the observers' subsequent activity). Unusual food consumption in chimpanzees was twice higher than in gorillas. Additionally chimpanzees relied more on social information with vertical knowledge transmission on unusual foods by continually acquiring information during their life through mostly observing the fittest (pre-senescent) adults. In contrast, in gorillas observational learning primarily occurred between related immatures, showing instead the importance of horizontal knowledge transmission. As chimpanzees' guts are physiologically less specialized than gorillas (more capable of detoxifying harmful compounds), unusual-food consumption may be more risky for chimpanzees and linked to reasons other than nutrition (like self-medication). Our results show that differences in sociality and physiology between the two species may influence mechanisms that discriminate between plants for nutrition and plants with potential therapeutic dietary components. We conclude that self-medication may have appeared in our ancestors in association with high social tolerance and lack of herbivorous gut specialization.
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