Social play does not reduce aggression in wild meerkats

Of the numerous hypotheses advanced to explain the adaptive significance of play, several assert that social play increases social harmony, cementing alliances and reducing aggression between group members or littermates. These hypotheses are frequently cited, but their validity remains unknown. We examined the relation between social play and aggression in juvenile meerkats, Suricata suricatta, living in a wild population in the southern Kalahari Desert. We tested the hypothesis that social play reduces aggression, by examining rates of play, play partner choices, the structure of social play and rates of aggressive interactions during foraging. We found no relation between frequency of play and level of aggression, either between individuals or during the course of development. Pups that played together frequently were just as aggressive towards one another as pairs of pups that played infrequently, and play interactions had no subsequent effect on the likelihood of aggression. In contrast, aggressive interactions during foraging inhibited the subsequent likelihood of play, and high levels of aggression during foraging changed the structure of social play, with victimized pups avoiding play wrestling. We conclude that social play does not reduce aggression in young meerkats. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

A simple test of vocal individual recognition in wild meerkats

Individual recognition is thought to be a crucial ability facilitating the evolution of animal societies. Given its central importance, much research has addressed the extent of this capacity across the animal kingdom. Recognition of individuals vocally has received particular attention due, in part, to the insights it provides regarding the cognitive processes that underlie this skill. While much work has focused on vocal individual recognition in primates, there is currently very little data showing comparable skills in non-primate mammals under natural conditions. This may be because non-primate mammal societies do not provide obvious contexts in which vocal individual recognition can be rigorously tested. We addressed this gap in understanding by designing an experimental paradigm to test for individual recognition in meerkats (Suricata suricatta) without having to rely on naturally occurring social contexts. Results suggest that when confronted with a physically impossible scenario-the presence of the same conspecific meerkat in two different places-subjects responded more strongly than during the control, a physically possible setup. We argue that this provides the first clear evidence for vocal individual recognition in wild non-primate mammals and hope that this novel experimental design will allow more systematic cross-species comparisons of individual recognition under natural settings.     

Maternal cardiovascular changes during pregnancy and postpartum in mice

Genetically altered mice may provide useful models for exploring cardiovascular regulation during pregnancy and postpartum if changes in mice mimic humans. We found in awake ICR (CD-1) mice at 17.5 days gestation that hematocrit was reduced 18%, and the pressor response to intravenous angiotensin II was reduced ~33%. Arterial pressure in awake mice was 12% lower in early pregnancy (3.5 days) than late pregnancy (17.5 days) and postpartum (3 and 17 days after delivery), whereas heart rate was 10-20% higher in the peripartum period (17.5 days gestation and 3 days postpartum). In late pregnancy, cardiac output under isoflurane anesthesia was 64% higher than in nonpregnant mice, due to a 37% increase in stroke volume and a 17% increase in heart rate. All changes P < 0.05. We conclude that, as in humans, mice exhibit hypotension in early pregnancy, and a blunted pressor response to angiotensin II, a decrease in hematocrit, and a marked increase in cardiac output in late pregnancy.     

Maternal investment tactics in superb fairy-wrens

In cooperatively breeding species, parents often use helper contributions to offspring care to cut their own costs of investment (i.e. load-lightening). Understanding the process of load-lightening is essential to understanding both the rules governing parental investment and the adaptive value of helping behaviour, but little experimental work has been conducted. Here we report the results of field experiments to determine maternal provisioning rules in cooperatively breeding superb fairy-wrens (Malurus cyaneus). By manipulating carer: offspring ratios, we demonstrate that helpers allow females to reduce the rate at which they provision their brood. Female reductions, however, were less than that provided by helpers, so that chicks still received food at a faster rate in the presence of helpers. Despite this, chicks fed by parents and helpers were not heavier than those provisioned by parents alone. This is because maternal load-lightening not only occurs during the chick provisioning stage, but also at the egg investment stage. Theoretically, complete load-lightening is predicted when parents value themselves more highly than their offspring. We tested this idea by 'presenting' mothers with a 'choice' between reducing their own levels of care and increasing investment in their offspring. We found that mothers preferred to cut their contributions to brood care, just as predicted. Our experiments help to explain why helper effects on offspring success have been difficult to detect in superb fairy-wrens, and suggest that the accuracy with which theoretical predictions of parental provisioning rules are matched in cooperative birds depends on measuring maternal responses to helper presence at both the egg and chick stages.     

Maternal hormone levels during Na 872 infusion in late pregnancy

In order to assess the effects of Na 872 infusion on maternal endocrinology during late pregnancy, we measured serum estradiol, estriol, progesterone, human placental lactogen, follicle simulating hormone, prolactin, cyclic adenosine monophosphate, cortisol and insulin before, during and after Na 872 infusion (bromhexine 2 mg/min for one hour) in ten mothers. As compared to six control mothers, no changes could be observed. This suggests that the claimed maturing effect of Na 872 on the fetal lungs is not mediated by the hormonal changes measurable in maternal blood.     

Radiocollars do not affect the survival or foraging behaviour of wild meerkats

The practice of radiocollaring is increasingly being used in the study of wild animal populations. However, methods of tracking and monitoring are known to affect some species negatively. On a wild population of habituated meerkats Suricata suricatta , we investigated the potential costs and consequences of carrying a radiocollar for small carnivores, focusing on detailed aspects of foraging behaviour and survival. Radiocollared individuals were no more likely to be predated than non-collared individuals in the same social group. We also found that collaring did not affect foraging efficiency, with collared individuals being equally efficient foragers (four measures) while wearing a collar compared with the pre-collaring period. To control for group-specific events, changes in foraging efficiency after collaring were compared with the behaviour of control individuals from the same group and no significant differences were found. In conclusion, we found no evidence to suggest radiocollars impact negatively on the bearer's welfare, survival or foraging ability.     

Maternal energetic investment in a monogamous mouse

Concurrent gestation and lactation is costly and rodent females may manage their reproductive effort by adjusting the length of the inter-litter latency. In this study, we attempted to build a model of this phenomenon as a function of maternal condition and energetic investment (measured as the litter size and weight) in the mound-building mouse, Mus spicilegus. We analysed the distributions of two successive inter-litter latencies using linear models. These distributions revealed a high inter-individual variability in latencies (22–38 d). Our results showed that none of the parameters reflecting female investment could explain this variability. The only link revealed by our analyses was a significant positive correlation between two successive inter-litter latencies. These results suggested that other parameters were involved in the regulation of inter-litter latencies. We propose that paternal care, which has a direct effect on inter-litter latency, may play a major role by allowing females to save energy or through differential allocation. In addition, genetic characteristics of the females and the prenatal environment of the female should also be considered.     

Maternal enrichment during pregnancy accelerates retinal development of the fetus

The influence of maternal environment on fetal development is largely unexplored, the available evidence concerns only the deleterious effects elicited by prenatal stress. Here we investigated the influence of prenatal enrichment on the early development of the visual system in the fetus. We studied the anatomical development of the rat retina, by analyzing the migration of neural progenitors and the process of retinal ganglion cell death, which exerts a key role in sculpturing the developing retinal system at perinatal ages. The number of apoptotic cells in the retinal ganglion cell layer was analyzed using two distinct methods: the presence of pyknotic nuclei stained for cresyl violet and the appearance of DNA fragmentation (Tunel method). We report that environmental enrichment of the mother during pregnancy affects the structural maturation of the retina, accelerating the migration of neural progenitors and the dynamics of natural cell death. These effects seem to be under the control of insulin-like growth factor-I: its levels, higher in enriched pregnant rats and in their milk, are increased also in their offspring, its neutralization abolishes the action of maternal enrichment on retinal development and chronic insulin-like growth factor-I injection to standard-reared females mimics the effects of enrichment in the fetuses. Thus, the development of the visual system is sensitive to environmental stimulation during prenatal life. These findings could have a bearing in orienting clinical research in the field of prenatal therapy.     

Maternal thyroid hormone trajectories during pregnancy and child behavioral problems

There is ample evidence demonstrating the importance of maternal thyroid hormones, assessed at single trimesters in pregnancy, for child cognition. Less is known, however, about the course of maternal thyroid hormone concentrations during pregnancy in relation to child behavioral development. Child sex might be an important moderator, because there are sex differences in externalizing and internalizing behavioral problems. The current study examined the associations between maternal thyroid hormone trajectories versus thyroid assessments at separate trimesters of pregnancy and child behavioral problems, as well as sex differences in these associations. In 442 pregnant mothers, serum levels of TSH and free T4 (fT4) were measured at 12, 24, and 36 weeks gestation. Both mothers and fathers reported on their children's behavioral problems, between 23 and 60 months of age. Latent growth mixture modeling was used to determine the number of different thyroid hormone trajectories. Three trajectory groups were discerned: 1) highest and non-increasing TSH with lowest fT4 that decreased least of the three trajectories; 2) increasing TSH and decreasing fT4 at intermediate levels; 3) lowest and increasing TSH with highest and decreasing fT4. Children of mothers with the most flattened thyroid hormone trajectories (trajectory 1) showed the most anxiety/depression symptoms. The following trimester-specific associations were found: 1) lower first-trimester fT4 was associated with more child anxiety/depression, 2) higher first-trimester TSH levels were related to more attention problems in boys only. A flattened course of maternal thyroid hormone concentrations during pregnancy was a better predictor of child anxiety/depression than first-trimester fT4 levels.     

Maternal smoking during pregnancy affects neuroendocrine cells in the neonate hamster lung

Primigravid Syrian golden hamsters were exposed in a Walton smoking machine to the smoke from either weak or strong cigarettes for 10 minute periods, 4 times a day from the 3rd to 14th (2nd last) day of pregnancy. Control hamsters were either similarly restrained in a Walton machine equipped with an unlit cigarette, or were not placed in the machine or restrained. Examination of the progeny in the first 6 days of life showed changes in density indices of grouped pulmonary neuroendocrine (NE) cells (neuroepithelial bodies, NEB) that were related to in utero exposure to maternal smoking. Argyrophil NEB were more numerous, larger, and contained more cells at birth among neonates whose mothers smoked the strong cigarette (2.45 mg nicotine and 36.8 mg tar) during pregnancy. This suggests a dose-related effect as the weak cigarette (0.37 mg nicotine and 33.8 mg tar) group did not show such changes. However, some of the changes described did not last through 3 or 6 days of age. The stress resulting from restraint alone also appeared to increase argyrophil NEB indices. Lung tissue volume fraction was increased in the weak cigarette group over all other groups at birth and 3 days; this suggests that low nicotine has the strongest pharmacological effect on lung tissue growth. The medial thickness of pulmonary arterioles was unchanged by either treatment; this provides morphometric evidence that chronic pulmonary hypertension was not present. We could not determine whether the increased NEB indices were caused by increased stainability, by activation of resident reserve cells, or by actual mitosis.     

Maternal investment and size-specific reproductive output in carcharhinid sharks

1.  Life-history theory predicts that organisms will provide an optimal level of parental investment for offspring survival balanced against the effects on their own survival and future reproductive potential.
2.  Optimal resource allocation models also predict an increase in reproductive output with age as expected future reproductive effort decreases. To date, maternal investment in sharks has received limited attention.
3.  We found that neonatal dusky sharks ( Carcharhinus obscurus ) are not independent from maternal resource allocation at the point of parturition but instead are provisioned with energy reserves in the form of an enlarged liver that constitutes approximately 20% of total body mass.
4.  Analysis of long-term archived data sets showed that a large proportion of this enlarged liver is utilized during the first weeks or months of life suggesting that the reported weight loss of newborn sharks signifies a natural orientation process and is not necessarily related to prey abundance and/or indicative of high mortality rates.
5.  Interrogation of near-term pup mass in two carcharhinids, the dusky and spinner shark ( Carcharhinus brevipinna ), further revealed an increase in reproductive output with maternal size, with evidence for a moderate decline in the largest mothers.
6.  For the dusky shark, there was a trade-off between increasing litter size and near-term pup mass in support of optimal offspring size theory.
7.  For both the dusky and spinner shark, there was a linear increase in near-term pup mass with month, which may indicate variable parturition strategies and/or that carcharhinids are able to adjust the length of the gestation period.
8.  The identification of optimal size-specific reproductive output has direct implications for improving the reproductive potential of exploited shark populations and for structuring future management strategies.