Precocial Mammals Research Articles

Shifts in energy allocation and reproduction in response to temperature in a small precocial mammal

BackgroundSpecies adjust to changes in temperature and the accompanying reduction in resource availability during the annual cycle by shifts in energy allocation. As it gets colder, the priority of energy allocation to maintenance increases and reproduction is reduced or abandoned.ResultsWe studied whether and how young female guinea pigs (Cavia porcellus) adjust even under ad libitum food conditions growth, storage of fat reserves and reproduction when kept at 5 °C versus 15 °C, and how offspring born into these conditions compensate during development to independence. Reproducing females grew less in the cold. Their lower weight resulted largely from less fat storage whereas growth in fat free mass was about the same for both groups. The increased need for thermoregulation diminished fat storage most likely due to the development of more brown fat tissue. Reproductive activity did not differ between groups in terms of litter frequency, mass and size. However, females in 5 °C weaned pups later (around day 25) than females in 15 °C (around day 21). Later weaning did not make up for the higher energy expenditure of pups in cold conditions leading to slower growth and less fat storage. Female pups born into the cold matured later than those born in 15 °C. Investment in reproduction continued but allocation to individual pups declined.ConclusionsIn more thermally demanding conditions female guinea pigs - even under ad libitum food abundance - transfer the higher costs of maintenance and reproduction largely to offspring.

Neocortex neurogenesis and maturation in the African greater cane rat

BackgroundNeocortex development has been extensively studied in altricial rodents such as mouse and rat. Identification of alternative animal models along the “altricial-precocial” spectrum in order to better model and understand neocortex development is warranted. The Greater cane rat (GCR, Thyronomys swinderianus) is an indigenous precocial African rodent. Although basic aspects of brain development in the GCR have been documented, detailed information on neocortex development including the occurrence and abundance of the distinct types of neural progenitor cells (NPCs) in the GCR are lacking.MethodsGCR embryos and fetuses were obtained from timed pregnant dams between gestation days 50–140 and their neocortex was analyzed by immunofluorescence staining using characteristic marker proteins for NPCs, neurons and glia cells. Data were compared with existing data on closely related precocial and altricial species, i.e. guinea pig and dwarf rabbit.ResultsThe primary sequence of neuro- and gliogenesis, and neuronal maturation is preserved in the prenatal GCR neocortex. We show that the GCR exhibits a relatively long period of cortical neurogenesis of 70 days. The subventricular zone becomes the major NPC pool during mid-end stages of neurogenesis with Pax6 + NPCs constituting the major basal progenitor subtype in the GCR neocortex. Whereas dendrite formation in the GCR cortical plate appears to initiate immediately after the onset of neurogenesis, major aspects of axon formation and maturation, and astrogenesis do not begin until mid-neurogenesis. Similar to the guinea pig, the GCR neocortex exhibits a high maturation status, containing neurons with well-developed dendrites and myelinated axons and astrocytes at birth, thus providing further evidence for the notion that a great proportion of neocortex growth and maturation in precocial mammals occurs before birth.ConclusionsTogether, this work has deepened our understanding of neocortex development of the GCR, of the timing and the cellular differences that regulate brain growth and development within the altricial–precocial spectrum and its suitability as a research model for neurodevelopmental studies. The timelines of brain development provided by this study may serve as empirical reference data and foundation in future studies in order to model and better understand neurodevelopment and associated alterations.

Developmental factors influencing bone strength in precocial mammals: An infant pig model.

Most vertebrates are precocial in locomotion, able to walk and run soon after birth. Precociality requires a bony skeleton of sufficient strength to resist mechanical loading during early locomotor efforts. The aim of this study was to use an animal model-the preterm infant pig-to investigate some of the proximate factors that might determine variation in bone strength in precocial animals. Based on the prior literature, we tested the null predictions that skeletal integrity would be significantly compromised by truncated gestation (i.e., preterm birth) and reduced body mass at birth. We generated a suite of both morphometric measures (tissue mineral density and cross-sectional geometry) and performance-related metrics (ability to resist loading, deformation, and fracture during three-point bending tests) of the appendicular skeleton of preterm and full-term infant pigs. Results showed that very few measures in our ontogenetic infant pig sample significantly varied with either gestation length or birth mass. Overall, our results contribute to a growing body of literature demonstrating the early functional capacity of the precocial infant musculoskeletal system and suggest that bone strength in perinatal precocial mammals may be robust to the factors shown to compromise skeletal integrity in more altricial taxa.

Development of fetal Eurasian beavers (Castor fiber)

Mammals are categorized along an altricial-precocial spectrum based on degrees of neonatal development. Altricial neonates are immature at birth and dependent on care, whereas precocial neonates are relatively well developed and independent post-partum. The Eurasian beaver (Castor fiber) is a large, semiaquatic, relatively precocial mammal in the order Rodentia. However, the extended care of kits in burrows begs the question of why beavers have precocial characteristics. A study of fetal development might enable understanding of the traits that are significant for neonatal survival. The present study examined external morphological characteristics, external biometry and the development of internal organs in 80 Eurasian beaver fetuses (crown-rump length [CRL], 2.5–19.3 cm) derived from 33 wild pregnant females hunted in Norway (33 gestational age). We also created equations to predict fetal ages from biometric parameters based on a linear relationship between biometric parameters and fetal ages estimated from fetal weight. Fetal features appeared in the following chronological order; eyelid bulbs and tactile hairs (CRL ≥ 7.3 cm), outer ears, claws, skin differentiation (CRL ≥ 8.9 cm), and hair coverage and tooth eruption (CRL ≥ 9.4 cm). All biometric parameters increased linearly and positively as the CRL increased and did not tend to stabilize. Notably, slopes of hindfoot parameters were higher than those of forefeet, suggesting that the hindfeet of beavers grow faster than forefeet, as they do in other semi-aquatic mammals. Our calculations revealed that dorsal length, CRL, thoracic and abdominal circumferences were candidate predictors of fetal age due to a high coefficient of determination (≥ 0.95) and broad range (≥ 10 cm). Our findings revealed that beaver growth was precocial in terms of differentiated skin, hair coverage, and tooth eruption, but not fully completed, as none of the fetuses had open eyes. The rapid growth of the hindfoot and some precocial traits (skin and hair differentiation) may be involved with the ability of neonatal beavers to move in water.

Breathing patterns and CO2 production in adult spiny mice (Acomys cahirinus)

The spiny mouse (Acomys) is a precocial mammal with unique regenerative abilities. We used whole-body plethysmography to describe the breathing patterns and CO2 production (VCO2) of adult spiny mice (n = 10 male, 10 female) and C57BL/6 mice (n = 9 male, 11 female). During quiet breathing, female but not male spiny mice had lower tidal volumes and CO2 production vs. C57BL/6 mice. During extended hypoxia (30 min), male and female spiny mice decreased VCO2 and tidal volume to a greater degree than C57BL/6 mice. During an acute hypoxic-hypercapnic respiratory challenge (10% O2, 7% CO2), male and female spiny mice had blunted ventilatory responses as compared to C57BL/6 mice, primarily from a diminished increase in respiratory rate. These data establish a baseline for studies of respiratory physiology and neurobiology in spiny mice in the context of their remarkable regenerative capacity and their unique background of a desert dwelling species.

Morphological Characterization of the Developing Greater Cane Rat (Thryonomys swinderianus) Brain

Developmental mode along the altricial-precocial spectrum is well known to be influenced by brain development and maturation. The greater cane rat (GCR) is an indigenous precocial African rodent with uncommon phenotypes and life traits. This study was therefore designed to characterize and describe distinctive external developmental features in the prenatal GCR brain across the entire gestational length using the emergence and differentiation of external features of the brain vesicles. Four gross morphometric brain parameters (weight, length, width, and height) were evaluated and expressed as mean ± SEM. Relationship between all brain morphometrics and gestation length were analyzed using one-way ANOVA and linear regression. Developmental milestones in the prenatal GCR were then compared with closely related precocial mammals. The earliest time point with gross observable features in the prenatal GCR brain was at gestation day (GD) 60. The period with the most remarkable gross developmental features was noted between GD80 and GD100. Some of these gross features include differentiation of the cerebellar plate into vermis and lateral lobes, emergence of the piriform lobes, mammillary bodies, colliculi bodies, cerebral peduncles, and primordial pons. By GD130, most gross topographic neural features were already established. Cerebellar lobation and patterning at GD130 were the last recognizable gross developmental features noticed in the prenatal GCR brain. This coincided with the time of first eye opening in the GCR fetus. The developmental pattern observed in the prenatal GCR brain is similar to those noted in precocial rodent like the guinea pig. However, the onset of these milestones was delayed, and their duration was relatively shorter in the GCR. This study provides a frame of baseline reference of morphological brain features in the GCR embryos and fetuses that will be useful for fetal age estimation, for home grown neurodevelopmental and eco-toxicological studies, as this rodent is being proposed as a research model.

Development of motor control and behaviour in Asian elephants in the Kabini elephant population, southern India.

Although neonates of precocial mammals are capable of locomotory, sensory, nutritional, and thermoregulatory independence to some extent soon after birth, they attain their adult body mass more slowly than altricial mammals, allowing for an extended period of learning or perfecting skills to an adult-like degree. Asian elephants are precocial but are nutritionally dependent on the mother for at least two years and are long-lived and social. We wanted to examine the ontogeny of trunk motor control and various behaviours in Asian elephant calves and see whether the former develops faster than the latter since limb motor control is achieved soon after birth. We collected field data on trunk use, lateralisation, and behaviours from individually identified, free-ranging elephants in southern India and examined how they were affected by age and other factors. Unlike limb motor control, we found trunk motor skills and behaviours to develop gradually with age. Trunk lateralisation occurred very early on, was not highly dependent on trunk motor skills, and is probably not a developmental marker in Asian elephants. Adult-like behaviours that required low trunk usage emerged within 3 months, while some feeding behaviours emerged later. Calves spent less time resting and more time feeding as they grew, and their activity budgets resembled those of adults only after a year; hence, mother-offspring behavioural synchrony was low for young calves and increased with age. Behavioural development and trunk motor control in Asian elephants are both gradual processes, taking about a year to mature.

Comparing Adult Hippocampal Neurogenesis Across Species: Translating Time to Predict the Tempo in Humans.

Comparison of neurodevelopmental sequences between species whose initial period of brain organization may vary from 100 days to 1,000 days, and whose progress is intrinsically non-linear presents large challenges in normalization. Comparing adult timelines when lifespans stretch from 1 year to 75 years, when underlying cellular mechanisms under scrutiny do not scale similarly, presents challenges to simple detection and comparison. The question of adult hippocampal neurogenesis has generated numerous controversies regarding its simple presence or absence in humans versus rodents, whether it is best described as the tail of a distribution centered on early neural development, or is several distinct processes. In addition, adult neurogenesis may have substantially changed in evolutionary time in different taxonomic groups. Here, we extend and adapt a model of the cross-species transformation of early neurodevelopmental events which presently reaches up to the equivalent of the third human postnatal year for 18 mammalian species (www.translatingtime.net) to address questions relevant to hippocampal neurogenesis, which permit extending the database to adolescence or perhaps to the whole lifespan. We acquired quantitative data delimiting the envelope of hippocampal neurogenesis from cell cycle markers (i.e., Ki67 and DCX) and RNA sequencing data for two primates (macaque and humans) and two rodents (rat and mouse). To improve species coverage in primates, we gathered the same data from marmosets (Callithrix jacchus), but additionally gathered data on a number of developmental milestones to find equivalent developmental time points between marmosets and other species. When all species are so modeled, and represented in a common time frame, the envelopes of hippocampal neurogenesis are essentially superimposable. Early developmental events involving the olfactory and limbic system start and conclude possibly slightly early in primates than rodents, and we find a comparable early conclusion of primate hippocampal neurogenesis (as assessed by the relative number of Ki67 cells) suggesting a plateau to low levels at approximately 2 years of age in humans. Marmosets show equivalent patterns within neurodevelopment, but unlike macaque and humans may have wholesale delay in the initiation of neurodevelopment processes previously observed in some precocial mammals such as the guinea pig and multiple large ungulates.

Malnutrition vs calorie restriction: The effects on maternal nutrient reduction in cardiac fetal mitochondrial function

Despite the recognized beneficial effects of caloric restriction, poor maternal nutrition alters development, predisposing offspring to chronic diseases including cardiovascular disease. Mitochondrial bioenergetics are central to cardiac energy metabolism and growth. Most developmental programming studies are in polytocous altricial rodents, which show different trajectories of development and maternal nutrient burden from monotocous precocial mammals, including humans. To enable translation to human programming, we developed a primate baboon model of moderate maternal nutrient reduction (MNR) in which mothers receive 70% global nutrition eaten by controls during pregnancy and lactation and offspring often showed growth restriction. Our hypothesis is that MNR adversely impacts fetal cardiac mitochondrial metabolism and homeostasis. Our results show in the baboon model that MNR increased fetal mtDNA content and transcription of key mitochondrial genes. MNR fetal oxidative phosphorylation was decreased and mitochondria contained sparse disarranged cristae. This study provides the first association between MNR and cardiac mitochondrial remodeling in the primate fetus. Thus, disruption of cardiac mitochondrial fitness may contribute to later life cardiac dysfunction.

Life-history trade-offs: are they linked to personality in a precocial mammal ( Cavia aperea )?

Life-history trade-offs are predicted to contribute to the maintenance of personality variation. Individuals with 'fast' lifestyles should develop faster, reproduce earlier and exhibit more risky behaviours. Evidence for such predicted links, however, remains equivocal. Here, I test how growth rate, timing of maturation, litter size and maternal effort correlate with exploration, boldness, fearlessness, docility and escape latency. I found several links that were predicted by recent theory while others were against theoretical predictions, e.g. fast-growing individuals were more fearful. Thus, while I found personality to be integrated with life history, I cannot fully support recent hypotheses aiming to explain such behaviour-life-history associations.

The evolution of ontogenetic allometric trajectories in mammalian domestication.

Morphological divergence of domesticated as compared to wild forms must result from changes in the ontogenetic process. Species-specific tests for heterochrony have rejected a single explanation of domestic forms representing juveniles of their wild relatives. Ontogenetic allometric trajectories for 12 pairs of wild and domestic mammals were examined using skull growth data for 1070 specimens, including representatives from all lineages in which domestication has occurred. A suite of tests were performed to quantify allometric disparity in wild and domestic forms and assess the extent and patterning of modification to allometric trajectories. Domestication has modified postnatal ontogenetic allometric trajectories in mammals, and has generated disparity, achieved through lengthening of trajectory slopes and alteration to slope angles. Allometric disparity was similar for domestic forms compared to their wild relatives, whereas the magnitude of dispersion along allometric vectors differed between precocial mammals and altricial mammals, underscoring the importance of life history and shared evolutionary history in patterns of ontogenetic variation. The results verify the importance of scaling in the morphological changes associated with domestication. The response to domestication for all measured trajectory parameters was variable across species, suggesting multiple pathways of change.

Understanding mammary activity in red-rumped agouti and implications for management and conservation of this Neotropical game species.

The red-rumped agouti (Dasyprocta leporina) produces precocial young and is the most hunted and farmed game species in several Neotropical countries. An understanding of the reproductive biology, including the relationship between litter size and teat functionality is crucial for conservation management of this animal. In precocial mammals, as the red-rumped agouti, maintaining maternal contact to learn foraging patterns may be more important than the energy demands and nutritional constraints during lactation and suckling may not play important roles when compared to altricial mammals. Therefore, in this study we evaluated the relationship between mammary functionality with litter size, litter birth weight, and parturition number in captive red-rumped agouti. Functionality was assessed by manual palpation of teats from un-sedated females (N=43). We compared the average birth weight of all newborns, male newborns and female newborns among agoutis with different litter sizes and different parturitions by one way ANOVA's, while Pearson's Chi-squared tests were used to detect relationships between teat functionality, litter size, and parturition number. Parturition number had no effect on the mean birth weight of all young (F0.822, P > 0.05), male young (F0.80, P > 0.05) or female young (F0.66, P > 0.05) in the litters. We found (i) no significant correlations (P > 0.05) between teat functionality and litter size and (ii) no significant correlations (P > 0.05) between teat functionality and parturition number. This suggests that whilst all teat pairs were functional, functionality was a poor indicator of litter size; suggesting that female agouti young may not have a high dependency on maternal nutrition; an possible evolutionary strategy resulting in large wild populations; hence its popularity as a game species.

The Retina of Asian and African Elephants: Comparison of Newborn and Adult

Elephants are precocial mammals that are relatively mature as newborns and mobile shortly after birth. To determine whether the retina of newborn elephants is capable of supporting the mobility of elephant calves, we compared the retinal structures of 2 newborn elephants (1 African and 1 Asian) and 2 adult animals of both species by immunohistochemical and morphometric methods. For the first time, we present here a comprehensive qualitative and quantitative characterization of the cellular composition of the newborn and the adult retinas of 2 elephant species. We found that the retina of elephants is relatively mature at birth. All retinal layers were well discernible, and various retinal cell types were detected in the newborns, including Müller glial cells (expressing glutamine synthetase and cellular retinal binding protein; CRALBP), cone photoreceptors (expressing S-opsin or M/L-opsin), protein kinase Cα-expressing bipolar cells, tyrosine hydroxylase-, choline acetyltransferase (ChAT)-, calbindin-, and calretinin-expressing amacrine cells, and calbindin-expressing horizontal cells. The retina of newborn elephants contains discrete horizontal cells which coexpress ChAT, calbindin, and calretinin. While the overall structure of the retina is very similar between newborn and adult elephants, various parameters change after birth. The postnatal thickening of the retinal ganglion cell axons and the increase in ganglion cell soma size are explained by the increase in body size after birth, and the decreases in the densities of neuronal and glial cells are explained by the postnatal expansion of the retinal surface area. The expression of glutamine synthetase and CRALBP in the Müller cells of newborn elephants suggests that the cells are already capable of supporting the activities of photoreceptors and neurons. As a peculiarity, the elephant retina contains both normally located and displaced giant ganglion cells, with single cells reaching a diameter of more than 50 µm in adults and therefore being almost in the range of giant retinal ganglion cells found in aquatic mammals. Some of these ganglion cells are displaced into the inner nuclear layer, a unique feature of terrestrial mammals. For the first time, we describe here the occurrence of many bistratified rod bipolar cells in the elephant retina. These bistratified bipolar cells may improve nocturnal contrast perception in elephants given their arrhythmic lifestyle.

Reproductive performance and gestational effort in relation to dietary fatty acids in guinea pigs

BackgroundDietary saturated (SFAs) and polyunsaturated (PUFAs) fatty acids can highly affect reproductive functions by providing additional energy, modulating the biochemical properties of tissues, and hormone secretions. In precocial mammals such as domestic guinea pigs the offspring is born highly developed. Gestation might be the most critical reproductive period in this species and dietary fatty acids may profoundly influence the gestational effort. We therefore determined the hormonal status at conception, the reproductive success, and body mass changes during gestation in guinea pigs maintained on diets high in PUFAs or SFAs, or a control diet.ResultsThe diets significantly affected the females’ plasma fatty acid status at conception, while cortisol and estrogen levels did not differ among groups. SFA females exhibited a significantly lower body mass and litter size, while the individual birth mass of pups did not differ among groups and a general higher pup mortality rate in larger litters was diminished by PUFAs and SFAs. The gestational effort, determined by a mother’s body mass gain during gestation, increased with total litter mass, whereas this increase was lowest in SFA and highest in PUFA individuals. The mother’s body mass after parturition did not differ among groups and was positively affected by the total litter mass in PUFA females.ConclusionsWhile SFAs reduce the litter size, but also the gestational effort as a consequence, PUFA supplementation may contribute to an adjustment of energy accumulations to the total litter mass, which may both favor a mother’s body condition at parturition and perhaps increase the offspring survival at birth.

Adaptations to polar life in mammals and birds.

This Review presents a broad overview of adaptations of truly Arctic and Antarctic mammals and birds to the challenges of polar life. The polar environment may be characterized by grisly cold, scarcity of food and darkness in winter, and lush conditions and continuous light in summer. Resident animals cope with these changes by behavioural, physical and physiological means. These include responses aimed at reducing exposure, such as 'balling up', huddling and shelter building; seasonal changes in insulation by fur, plumage and blubber; and circulatory adjustments aimed at preservation of core temperature, to which end the periphery and extremities are cooled to increase insulation. Newborn altricial animals have profound tolerance to hypothermia, but depend on parental care for warmth, whereas precocial mammals are well insulated and respond to cold with non-shivering thermogenesis in brown adipose tissue, and precocial birds shiver to produce heat. Most polar animals prepare themselves for shortness of food during winter by the deposition of large amounts of fat in times of plenty during autumn. These deposits are governed by a sliding set-point for body fatness throughout winter so that they last until the sun reappears in spring. Polar animals are, like most others, primarily active during the light part of the day, but when the sun never sets in summer and darkness prevails during winter, high-latitude animals become intermittently active around the clock, allowing opportunistic feeding at all times. The importance of understanding the needs of the individuals of a species to understand the responses of populations in times of climate change is emphasized.

Effects of prenatal stress and emotional reactivity of the mother on emotional and cognitive abilities in lambs.

Consequences of prenatal stress on emotional reactivity and cognitive abilities in offspring are under-documented in precocial mammals. Here, we investigated to what extent emotional reactivity, judgment bias and spatial learning abilities of lambs are affected by chronic stress during late pregnancy and by their dams' emotional reactivity. The 20 highest-responsive (HR) and 20 lowest-responsive (LR) ewes from a population of 120 Romane ewes were selected according to their pre-mating reactivity to social isolation in a new environment. Over the final third of pregnancy, 10 HR ewes and 10 LR ewes were exposed daily to various unpredictable aversive events such as restraint, mixing groups and transport while the other 20 selected ewes were not. In a human and an object test, prenatally-stressed lambs were more fearful than control lambs, but the prenatal stress effect was moderated by the reactivity of the mothers: prenatally-stressed lambs from ewes with high emotional reactivity were more affected. Prenatally-stressed lambs did not perform as well as control lambs in a maze test and showed pessimistic-like judgment in a cognitive bias test. Prenatally-stressed lambs were thus characterized by a negative affective state with increased fear reactions and impaired cognitive evaluation. The development of negative moods could have long-lasting consequences on the coping strategies of the lambs in response to their rearing conditions.

Mild effects of gestational stress and social reactivity on the onset of mother–young interactions and bonding in sheep

Consequences of prenatal stress on mother–young relationships are well-documented in altricial mammals but less so in precocial mammals. In this study, we investigated the effects of unpredictable aversive events on maternal behavior and mutual mother–young recognition in pregnant ewes while accounting for modulatory effects of ewe reactivity. From a population of 120 Romane-breed ewes, we selected 20 high-responsive (HR) and 20 low-responsive (LR) ewes according to pre-mating reactivity assessed in isolation tests. Over the final third of pregnancy, 10 HR ewes and 10 LR ewes were exposed daily to various aversive events such as social isolation, mixing and transport (stressed ewes), while the other 20 ewes were not exposed to aversive events (control ewes). Although the treatment induced chronic stress, physiologically confirmed by an increase in salivary cortisol following transport and sham shearing, maternal behavior of stressed ewes observed during the first 30 min postpartum and in the selectivity test 1 h 30 min later did not differ from controls. However, in a maternal motivation test performed 48 h postpartum, stressed ewes vocalized less than controls when separated from their lambs, and walked less readily past an unknown object to reach their lambs. Lambs of stressed ewes spent more time near their dam in a preference test performed 15 h after birth compared to control-ewe lambs. HR ewes spent more time grooming their lambs than LR ewes. We posit that domestication could have selected animals displaying robust expression of maternal behavior related to social reactivity and producing offspring that are better adapted to challenging situations.

The development of vestibular system and related functions in mammals: impact of gravity

This chapter reviews the knowledge about the adaptation to Earth gravity during the development of mammals. The impact of early exposure to altered gravity is evaluated at the level of the functions related to the vestibular system, including postural control, homeostatic regulation, and spatial memory. The hypothesis of critical periods in the adaptation to gravity is discussed. Demonstrating a critical period requires removing the gravity stimulus during delimited time windows, what is impossible to do on Earth surface. The surgical destruction of the vestibular apparatus, and the use of mice strains with defective graviceptors have provided useful information on the consequences of missing gravity perception, and the possible compensatory mechanisms, but transitory suppression of the stimulus can only be operated during spatial flight. The rare studies on rat pups housed on board of space shuttle significantly contributed to this problem, but the use of hypergravity environment, produced by means of chronic centrifugation, is the only available tool when repeated experiments must be carried out on Earth. Even though hypergravity is sometimes considered as a mirror situation to microgravity, the two situations cannot be confused because a gravitational force is still present. The theoretical considerations that validate the paradigm of hypergravity to evaluate critical periods are discussed. The question of adaption of graviceptor is questioned from an evolutionary point of view. It is possible that graviception is hardwired, because life on Earth has evolved under the constant pressure of gravity. The rapid acquisition of motor programming by precocial mammals in minutes after birth is consistent with this hypothesis, but the slow development of motor skills in altricial species and the plasticity of vestibular perception in adults suggest that gravity experience is required for the tuning of graviceptors. The possible reasons for this dichotomy are discussed.

Age at weaning, immunocompetence and ectoparasite performance in a precocial desert rodent.

We studied the effects of early weaning on immunocompetence and parasite resistance in a precocial rodent Acomys cahirinus. We hypothesized that if parasite resistance is energetically expensive and nutritional and immunological support from mothers are necessary for the long-term health of offspring, then early weaned animals would be immunologically weaker and less able to defend themselves against parasites than later weaned animals. We weaned pups at 14, 21 or 28 days after birth and assessed their immunocompetence and resistance against fleas Parapulex chephrenis when they attained adulthood. Immunocompetence was assessed using leukocyte concentration (LC) and a phytohaemagglutinin injection assay (PHA test). To estimate resistance against fleas, we measured performance of fleas via the number of produced eggs and duration of development and resistance to starvation of the flea offspring. We found a significant positive effect of weaning age on the PHA response but not on LC. The effect of age at weaning on flea egg production was manifested in male but not female hosts, with egg production being higher if a host was weaned at 14 than at 28 days. Weaning age of the host did not affect either duration of development or resistance to starvation of fleas produced by mothers fed on these hosts. We conclude that even in relatively precocial mammals, weaning age is an important indicator of future immunological responses and the ability of an animal to resist parasite infestations. Hosts weaned at an earlier age make easier, less-resistant targets for parasite infestations than hosts weaned later in life.

Brain size in neonatal and adult Weddell seals: Costs and consequences of having a large brain

AbstractLittle is known about the ontogeny of brain size in pinnipeds despite potential functional implications of brain substrate (glucose, oxygen) requirements for diving, fasting, growth, and lactation strategies. We measured brain mass (brM) and cranial capacity (CC) in newborn and adult Weddell seals. Neonatal Weddell seals had brM that represented ~70% of adult brM. Weddell seals have the largest neonatal brain, proportional to adult brain, reported for any mammal to date, which is remarkable considering the relatively small size of Weddell seal pups at birth (6%–7% of maternal body mass) compared to neonates of other highly precocial mammals. Provision of sufficient glucose to maintain the large, well‐developed brain of the neonatal Weddell seal has a nontrivial metabolic cost to both pup and mother. We therefore hypothesize that this phenomenon must have functional significance, such as allowing pups to acquire complex under‐ice navigation skills during the period of maternal attendance.