Early-Life Silver Spoon Improves Survival and Breeding Performance of Adult Zebra Finches.

AbstractDevelopmental plasticity allows organisms to increase the fit between their phenotype and their early-life environment. The extent to which such plasticity also enhances adult fitness is not well understood, however, particularly when early-life and adult environments differ substantially. Using a cross-factorial design that manipulated diet at two life stages, we examined predictions of major hypotheses-silver spoon, environmental matching, and thrifty phenotype-concerning the joint impacts of early-life and adult diets on adult morphology/display traits, survival, and reproductive allocation. Overall, results aligned with the silver spoon hypothesis, which makes several predictions based on the premise that development in poor-quality environments constrains adult performance. Males reared and bred on a low-protein diet had lower adult survivorship than other male treatment groups; females' survivorship was higher than males' and not impacted by early diet. Measures of allocation to reproduction primarily reflected breeding diet, but where natal diet impacted reproduction, results supported the silver spoon. Both sexes showed reduced expression of display traits when reared on a low-protein diet. Results accord with other studies in supporting the relevance of the silver spoon hypothesis to birds and point to significant ramifications of sex differences in early-life viability selection on the applicability/strength of silver spoon effects.

The parental umwelt: Effects of parenthood on sensory processing in rodents.

An animal's umwelt, comprising its perception of the sensory environment, which is inherently subjective, can change across the lifespan in accordance with major life events. In mammals, the onset of motherhood, in particular, is associated with a neural and sensory plasticity that alters a mother's detection and use of sensory information such as infant-related sensory stimuli. Although the literature surrounding mammalian mothers is well established, very few studies have addressed the effects of parenthood on sensory plasticity in mammalian fathers. In this review, we summarize the major findings on the effects of parenthood on behavioural and neural responses to sensory stimuli from pups in rodent mothers, with a focus on the olfactory, auditory, and somatosensory systems, as well as multisensory integration. We also review the available literature on sensory plasticity in rodent fathers. Finally, we discuss the importance of sensory plasticity for effective parental care, hormonal modulation of plasticity, and an exploration of temporal, ecological, and life-history considerations of sensory plasticity associated with parenthood. The changes in processing and/or perception of sensory stimuli associated with the onset of parental care may have both transient and long-lasting effects on parental behaviour and cognition in both mothers and fathers; as such, several promising areas of study, such as on the molecular/genetic, neurochemical, and experiential underpinnings of parenthood-related sensory plasticity, as well as determinants of interspecific variation, remain potential avenues for further exploration.

Neural responses to pup calls and pup odors in California mouse fathers and virgin males.

The onset of mammalian maternal care is associated with plasticity in neural processing of infant-related sensory stimuli; however, little is known about sensory plasticity associated with fatherhood. We quantified behavioral and neural responses of virgin males and new fathers to olfactory and auditory stimuli from young, unfamiliar pups in the biparental California mouse (Peromyscus californicus). Each male was exposed for 10 min to one of four combinations of a chemosensory stimulus (pup-scented or unscented cotton [control]) and an auditory stimulus (pup vocalizations or white noise [control]). Behavior did not differ between fathers and virgins during exposure to sensory stimuli or during the following hour; however, males in both groups were more active both during and after exposure to pup-related stimuli compared to control stimuli. Fathers had lower expression of Fos in the main olfactory bulbs (MOB) but higher expression in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis medial division, ventral part (STMV) compared to virgins. Lastly, males had higher Fos expression in MPOA when exposed to pup odor compared to control stimuli, and when exposed to pup odor and pup calls compared to pup calls only or control stimuli. These findings suggest that the onset of fatherhood alters activity of MOB, MPOA and STMV and that pup odors and vocalizations have additive or synergistic effects on males' behavior and MPOA activation.

Specificity of California mouse pup vocalizations in response to olfactory stimuli.

To investigate flexibility in vocal signaling by rodent pups, we examined whether olfactory stimuli influence characteristics of pup calls and how these calls may be affected by sex and litter size in California mice (Peromyscus californicus). Pups were isolated and recorded during a 3-min baseline period followed by a 5-min exposure to bedding containing scent from their home cage, scent from the home cage of an unfamiliar family, coyote urine, or no scent (control). Latency to call, call rate, and call characteristics (duration, frequency, and amplitude) were compared between the baseline and scent-exposure periods and among olfactory conditions. Compared with the control condition, pups from two-pup litters called more quietly when exposed to odor from a predator, whereas pups from three-pup litters called more loudly. Additionally, pups showed nonsignificant tendencies to reduce call rates in response to odors from their home cage and to increase call rates when exposed to predator urine. Last, males produced higher-frequency calls and more ultrasonic vocalizations than females. These results indicate that pup calling behavior in this species can be influenced by acute olfactory stimuli as well as litter size and sex. The flexibility of pup calling in response to these three variables potentially increases the communication value of pup calls and helps shape the parents' responses.

Female differential allocation in response to extrapair offspring and social mate attractiveness.

Renewed debate over what benefits females might gain from producing extra-pair offspring emphasizes the possibility that apparent differences in quality between within-pair and extra-pair offspring are confounded by greater maternal investment in extra-pair offspring. Moreover, the attractiveness of a female's social mate can also influence contributions of both partners to a reproductive attempt. Here, we explore the complexities involved in parental investment decisions in response to extra-pair offspring and mate attractiveness with a focus on the female point of view. Adult zebra finches paired and reproduced in a colony setting. A male's early-life diet quality and his extra-pair reproductive success were used as metrics of his mating attractiveness. Females paired with males that achieved extra-pair success laid heavier eggs than other females and spent less time attending their nests than their mates or other females. Extra-pair nestlings were fed more protein-rich hen's egg than within-pair nestlings. Females producing extra-pair offspring had more surviving sons than females producing only within-pair offspring. Collectively, results show that females differentially allocate resources in response to offspring extra-pair status and their social mate's attractiveness. Females may also obtain fitness benefits through the production of extra-pair offspring.

Age at mating and male quality influence female patterns of reproductive investment and survival.

The trade-off between the allocation of resources toward somatic maintenance or reproduction is one of the fundamentals of life history theory and predicts that females invest in offspring at the expense of their longevity or vice versa. Mate quality may also affect life history trade-offs through mechanisms of sexual conflict; however, few studies have examined the interaction between mate quality and age at first mating in reproductive decisions. Using house crickets (Acheta domesticus), this study examines how survival and reproductive trade-offs change based on females' age at first reproduction and exposure to males of varying size. Females were exposed to either a large (presumably high-quality) or small male at an early (young), middle (intermediate), or advanced (old) age, and longevity and reproductive investment were subsequently tracked. Females mated at a young age had the largest number of eggs but the shortest total lifespans while females mated at older ages produced fewer eggs but had longer total lifespans. The trade-off between age at first mating and eggs laid appears to be mediated through higher egg-laying rates and shorter postmating lifespans in females mated later in life. Exposure to small males resulted in shorter lifespans and higher egg-laying rates for all females indicating that male manipulation of females, presumably through spermatophore contents, varies with male size in this species. Together, these data strongly support a trade-off between age at first reproduction and lifespan and support the role of sexual conflict in shaping patterns of reproduction.