Early weaning in bighorn sheep, Ovis canadensis affects growth of males but not of females

Theories of parental investment and parent-offspring conflictassume that investment involves a cost to the parent and a benefitto the offspring, but for herbivorous mammals, behavioral andnutritional weaning are gradual processes that are difficultto define, and little is known about the consequences of individualvariation during weaning. To study the effects of late maternalcare on offspring fitness, we removed female bighorn sheep (Oviscanadensis) from a marked population in Alberta, Canada, andmonitored the survival, growth, and reproductive success oforphan and nonorphan lambs. Mothers were removed when lambswere 3.5–4.0 months, about 2–4 weeks before thesuspected time of nutritional weaning. Femaleorphans and nonorphanshad the same weight as yearlings, the same probability of producingtheir first lamb at 2 years of age, the same lifetime reproductivesuccess (lambs produced or lambs that survived to early autumn),and the same longevity. Male orphans from most cohorts weresmaller as yearlings compared to nonorphans from the same cohort.They were unable to compensate for this early weight differencein later life: at 4 years, orphan males had smaller horns andwere lighter than nonorphans. Small horn and body size likelylowered the reproductive success of orphaned males comparedto nonorphans from the same cohort. We suggest that in thissexually dimorphic species late maternal care is more importantfor males than for females. Because late maternal care had nomeasurable benefit for daughters, we suggest that parent-offspringconflict over the duration of maternal care may not exist formother-daughter pairs. or mother-son pairs it remains to beshown whether late maternal care involves a cost to the mother,but the assumption of a benefit to the son was met.     

Season of birth affects juvenile survival of giraffe

Variation in timing of reproduction and subsequent juvenile survival often plays an important role in population dynamics of temperate and boreal ungulates. Tropical ungulates often give birth year round, but survival effects of birth season for tropical ungulate species are unknown. We used a population of giraffe in the Tarangire Ecosystem of northern Tanzania, East Africa to determine whether calf survival varied by season of birth. Variation in juvenile survival according to season of birth was significant, with calves born during the dry season experiencing the highest survival probability. Phenological match may confer a juvenile survival advantage to offspring born during the dry season from greater accumulated maternal energy reserves in mothers who conceive in the long rainy season, high-protein browse in the late dry-early short rainy seasons supplementing maternal and calf resources, reduced predation due to decreased stalking cover, or some combination of these. Asynchrony is believed to be the ancestral state of all ungulates, and this investigation has illustrated how seasonal variation in vegetation can affect juvenile survival and may play a role in the evolution of synchronous births.     

Allonursing in Captive Guanacos,Lama guanicoe: Milk Theft or Misdirected Parental Care?

Females in several ungulates transfer milk to non-filial (NF) offspring, in a process known as allonursing. This behavior is less common in monotocous species, including most ungulates, and it has been associated with parasitic behavior of calves or mothers who have lost their own offspring. To examine whether the calves 'steal' milk from the females or whether females fail to discriminate their own calves in guanacos, allonursing behavior was observed. If milk theft drives allonursing, mothers should reject NF offspring, they should search for their own calves, and calves attempting to suckle from alien mothers should adopt parallel (as opposed to the anti-parallel) position during allonursing. Alternatively, if allonursing is caused by mothers unable to discriminate own offspring, mothers are not expected to reject NF offspring, and alien calves should use parallel and antiparallel position similarly when allonursing. Allonursing was investigated during the first 3 mo of lactation in two groups of captive guanacos composed of 15 and 14 mother-calf pairs, respectively. While 40% and 62.5% of mothers in groups 1 and 2 performed allonursing, high individual variation prevailed; some females exhibited this behavior infrequently (4.1% and 6.5 % in groups 1 and 2). The rejection rate to NF nursing attempts was threefold higher than the rejection rate to filial nursing attempts. The occurrence of nursing to NF was associated to a parallel posture by the calves. Our findings suggest that 'milk theft' is a more plausible hypothesis to explain allonursing in guanacos than 'misdirected parental care'.     

Environmental and Physiological Influences to Isotopic Ratios of N and Protein Status in a Montane Ungulate in Winter

Winter severity can influence large herbivore populations through a reduction in maternal proteins available for reproduction. Nitrogen (N) isotopes in blood fractions can be used to track the use of body proteins in northern and montane ungulates. We studied 113 adult female caribou for 13 years throughout a series of severe winters that reduced population size and offspring mass. After these severe winters, offspring mass increased but the size of the population remained low. We devised a conceptual model for routing of isotopic N in blood in the context of the severe environmental conditions experienced by this population. We measured δ¹⁵N in three blood fractions and predicted the relative mobilization of dietary and body proteins. The δ ¹⁵N of the body protein pool varied by 4‰ and 46% of the variance was associated with year. Annual variation in δ¹⁵N of body protein likely reflected the fall/early winter diet and winter locations, yet 15% of the isotopic variation in amino acid N was due to body proteins. Consistent isotopic differences among blood N pools indicated that animals tolerated fluxes in diet and body stores. Conservation of body protein in caribou is the result of active exchange among diet and body N pools. Adult females were robust to historically severe winter conditions and prioritized body condition and survival over early investment in offspring. For a vagile ungulate residing at low densities in a predator-rich environment, protein restrictions in winter may not be the primary limiting factor for reproduction.     

Short-term benefits,but transgenerational costs of maternal loss in an insect with facultative maternal care

A lack of parental care is generally assumed to entail substantial fitness costs for offspring that ultimately select for the maintenance of family life across generations. However, it is unknown whether these costs arise when parental care is facultative, thus questioning their fundamental importance in the early evolution of family life. Here, we investigated the short-term, long-term and transgenerational effects of maternal loss in the European earwig Forficula auricularia, an insect with facultative post-hatching maternal care. We showed that maternal loss did not influence the developmental time and survival rate of juveniles, but surprisingly yielded adults of larger body and forceps size, two traits associated with fitness benefits. In a cross-breeding/cross-fostering experiment, we then demonstrated that maternal loss impaired the expression of maternal care in adult offspring. Interestingly, the resulting transgenerational costs were not only mediated by the early-life experience of tending mothers, but also by inherited, parent-of-origin-specific effects expressed in juveniles. Orphaned females abandoned their juveniles for longer and fed them less than maternally-tended females, while foster mothers defended juveniles of orphaned females less well than juveniles of maternally-tended females. Overall, these findings reveal the key importance of transgenerational effects in the early evolution of family life.     

Social Effects of Maternal Age and Experience in Bison: Pre- and Post-weaning Contact Maintenance with Daughters

Effects of maternal age and experience on long-term contact maintenance interactions with female offspring were examined in bison (Bison bison), as part of a study of factors influencing dyadic behavioural interaction. During the first five months, patterns of change in interactions varied with maternal age and parity. Young (largely primiparous) mothers and their calves steadily increased the frequency with which they maintained contact, while older mothers and their calves became increasingly independent (e.g. calves walked away from mothers more and followed them less often). Filial independence was most extreme in the (last) calves of the two oldest mothers. These age-specific patterns appeared to result largely from contrasting shifts in maternal behaviour from Month 1 to 2; differences between groups before and after this shift were opposite in direction. In the first month, older mothers maintained more frequent contact and were behaviourally more synchronized with their calves. After the first month, however, the efforts of older mothers to maintain dyadic proximity abruptly decreased, while those of young mothers and their calves gradually increased. Subsequent differences between groups were more consistent. Young mothers and their daughters maintained closer contact and continued to do so well past weaning, at least as late as the third year, when daughters reached sexual maturity. Filial behaviour played an important role in determining patterns of dyadic spatial relations; the close proximity maintained by young mothers and their offspring appeared due largely to the frequency with which these calves followed their mothers' movements. The relatively independent calves of older mothers took greater initiative in contact interactions with mothers (e.g. nosing, licking). Young mothers appeared to strengthen long-term bonds with daughters by initiating contact frequently; the closeness of post-weaning dyadic association increased with the frequency of pre-weaning maternal contact.     

Social rank,feeding and winter weight loss in red deer: any evidence of interference competition?

During winter at northern latitudes, large herbivores often exploit patches of concentrated, relatively high quality forage, which may lead to interference competition. The factors affecting success in contests and subsequent dominance rank, such as age and body weight, remain key issues in ungulate behavioural ecology. Maternal effects on offspring body weight are well known, but few studies have investigated if mothers social rank influence offspring rank. Moreover, no study has related dominance rank in ungulates to weight loss during winter. Outcomes of social interactions (n=7,609), feeding time and spatial position in red deer (Cervus elaphus) hinds and calves, and weight loss of calves, were registered from 1981 to 1996 at six winter-feeding sites within the county of Sør-Trøndelag in Norway. The level of aggressiveness was higher among calves than among adult hinds, and the factors determining the outcome of contests also differed. The initiator won the majority of interactions (more than 90% in both hinds and calves). Social rank was related to both age and body weight in adult hinds, and related to body weight and mother rank in calves. The relationship between feeding time and rank was non-linear. Feeding time was correlated with rank only among high ranked hinds, while there was no such relationship among low ranked hinds or calves. There was no correlation between winter weight loss and social rank in calves. Our study therefore underlines that, although frequent aggression is observed at artificial feeding sites of northern herbivores, this is not necessarily sufficient to give rise to interference competition.     

Long-term impact of orphaning on field colonies ofCoptotermes lacteus (Froggatt) (Isoptera: Rhinotermitidae)

Summary Colonies ofCoptotermes lacteus (Froggatt) from a site in coastal south-eastern Australia were experimentally orphaned in early 1989. Sample colonies were examined 3, 6, 12, 18, 24 or 30 months later for their caste composition, the presence of replacement reproductives and brood. All replacement reproductives were nymphoid neotenics. The number of functional (physogastric) females ranged from 1 to 27; this variability was maintained irrespective of the length of time between orphaning and inspection of the colonies. The average live mass of individual females stayed at 30 to 40 mg over the period of 6 to 30 months after orphaning in groups of more than five neotenic queens, but increased from 38 mg three months after orphaning to about 125 mg after 24 months in colonies headed by fewer than five neotenic females. The combined live mass of neotenic females could approach or even exceed that of primary queens. Two key features characterized experimentally and naturally orphaned, neotenic-headed colonies: (1) Nymphs differentiated in significant numbers all year round for a period of at least 30 months right from the time neotenics commenced breeding (in primary-headed colonies nymph production is strictly seasonal). (2) All or most nymphs were males (in primary-headed colonies the sex ratio of nymphs is more or less balanced). The mechanism(s) for achieving the male-biased sex ratio is (are) unknown. Even when colonies have resumed breeding with the help of neotenics, colony survival is not guaranteed. Under such circumstances the gene pool is best preserved if colonies were to raise and release large numbers of alates as potential founders of new colonies. By producing largely male nymphs orphaned colonies ensure outbreeding and may prevent competition (and its disruptive impact an breeding) between existing reproducing neotenic queens and newly differentiating female neotenics. Competition between male neotenics is unlikely to have any impact on the rate of brood production and therefore would not require a mechanism to prevent it from occurring.     

Microhabitat heterogeneity influences offspring sex allocation and spatial kin structure in possums

1. Sex allocation theory predicts that where dispersal is sex biased, the fitness consequences of producing male or female offspring are mediated by resource availability and maternal competitive ability. Females in poorer condition are expected to favour dispersing offspring to minimize resource competition with kin. Environmental heterogeneity may drive spatial variation in sex allocation through resource competition-related benefits to females and territory quality benefits to dispersing or philopatric offspring. 2. Here, we demonstrate that microhabitat heterogeneity can drive extremely fine-scale spatial heterogeneity in offspring sex allocation. Female bobucks (Trichosurus cunninghami) in temperate rainforest were more likely to produce male offspring than those in surrounding Eucalyptus forest. 3. A maternal physiological effect was identified, in that females of lower body mass were more likely to produce male offspring. This finding is consistent with resource competition predictions, in that smaller females are expected to have poorer competitive ability. 4. Genetic spatial autocorrelation analysis identified males as the more dispersing sex. Furthermore, overproduction of males by mothers in the rainforest habitat was geographically concordant with reduced philopatry, as inferred from spatial genetic analysis. This provides empirical validation of dispersal-related explanations of offspring sex allocation: that production of offspring of the dispersing sex minimizes the potential for resource competition with kin. 5. Spatial variation in dispersal via sex allocation responses to environmental heterogeneity can potentially contribute to spatial patterns in population dynamics.     

Birthdate, mass and survival in mountain goat kids: effects of maternal characteristics and forage quality

In temperate environments, early-born ungulates may enjoy a longer growth period before winter, and so attain a higher body mass and an increased probability of survival compared to late-born ones. We assessed the effects of maternal characteristics, forage quality and population density on kid birthdate, mass and survival in a population of marked mountain goats (Oreamnos americanus) in Alberta. The duration and timing of the birth season were similar in all years. Births were highly synchronised: 80% of kids were born within 2 weeks of the first birth. Maternal age, maternal social rank and density did not affect kid birthdate or mass. Previous breeding experience was not related to kid birthdate, but kids born to pluriparous mothers were heavier during summer than kids born to primiparous mothers. Male and female kids had similar mass and accumulated mass linearly during summer. Early-born kids were heavier than late-born kids. Faecal crude protein (FCP) in late spring and maternal mass were positively related to kid mass. Survival to weaning appeared higher for males (90%) than for females (78%), but survival to 1 year was 65% for both sexes. FCP in late spring, density, birthdate and mass did not affect kid survival to weaning in either sex. Survival to 1 year increased with FCP in late spring for females, but not for males. Survival to 1 year was independent of birthdate for both sexes, but heavy females survived better than light ones. Multiple logistic regression revealed a positive effect of mass on survival to 1 year when the sexes were pooled. Our results suggest that mountain goats are constrained to give birth in a short birth season synchronised with forage productivity.     

Global climate change and reindeer: effects of winter weather on the autumn weight and growth of calves

Reindeer/caribou (Rangifer tarandus), which constitute a biological resource of vital importance for the physical and cultural survival of Arctic residents, and inhabit extremely seasonal environments, have received little attention in the global change debate. We investigated how body weight and growth rate of reindeer calves were affected by large-scale climatic variability [measured by the North Atlantic Oscillation (NAO) winter index] and density in one population in central Norway. Body weights of calves in summer and early winter, as well as their growth rate (summer to early winter), were significantly influenced by density and the NAO index when cohorts were in utero. Males were heavier and had higher absolute growth than females, but there was no evidence that preweaning condition of male and female calves were influenced differently by the NAO winter index. Increasing NAO index had a negative effect on calves' body weight and growth rate. Increasing density significantly reduced body weight and growth rate of calves, and accentuated the effect of the NAO winter index. Winters with a higher NAO index are thus severe for reindeer calves in this area and their effects are associated with nutritional stress experienced by the dams during pregnancy or immediately after calving. Moreover, increased density may enhance intra-specific competition and limits food available at the individual level within cohorts. We conclude that if the current pattern of global warming continues, with greater change occurring in northern latitudes and during winter as is predicted, reduced body weight of reindeer calves may be a consequence in areas where winters with a high NAO index are severe. This will likely have an effect on the livelihood of many northern indigenous peoples, both economically and culturally.     

Big mothers invest more in daughters – reversed sex allocation in a weakly polygynous mammal

How mothers allocate resources to offspring is central to understanding life history strategies. High quality mothers are predicted to favour investment in sons over daughters when to do so increases inclusive fitness. This is the case in ungulates with polygynous mating systems, where reproductive success is more variable among males than females, but information is scarce on sex allocation in less polygynous species. Here, for the weakly dimorphic roe deer, we show that as maternal capacity to invest increases, mothers increase allocation to daughters more than to sons, so that relative allocation to daughters increases markedly with increasing maternal quality. This cannot be explained by a between sex difference in growth priority, hence we conclude that this is evidence for active maternal discrimination. Further, we demonstrate that condition differences between offspring persist to adulthood. For high quality mothers of weakly polygynous species, daughters may be more valuable than sons.     

Controls over reproductive phenology among ungulates: allometry and tropical‐temperate contrasts

Ungulates inhabiting high latitudes schedule the timing of conceptions so that offspring are born during the most favourable nutritional conditions for reproductive success. The optimal period for births is less reliably predictable in tropical and subtropical savanna environments where plant growth is governed by rainfall, suggesting that reproductive phenology could be influenced more proximately by resources affecting the body condition of females around the time of conceptions. To assess how these controls operate, we compared the timing of births and conceptions among tropical and subtropical savanna ungulates with the patterns shown by ungulates in northern temperate or subarctic latitudes. The association between the timing of births and the onset of plant growth early in the growing season is less consistent among tropical savanna ungulates than among ungulates inhabiting northern temperate environments, and apparently subject to other influences affecting vegetation phenology. Nevertheless, birth peaks seem to coincide with the time of the year when forage quality is expected to be best for offspring survival and growth for most tropical or subtropical ungulates with gestation periods shorter than a year. When gestation time exceeds one year, proximal effects of nutritional conditions around the time of conceptions apparently become overriding and birth synchrony with early season plant growth is no longer effective. Proximate nutritional influences on conceptions may also govern the somewhat diffuse spread of births shown by ungulate populations in equatorial latitudes where photoperiod cues controlling oestrus and mating cannot be used to schedule the later timing of births.     

Cryptic maternal effects in Hippodamia convergens vary with maternal age and body size

Maternal effects can mold progeny phenotypes in various ways and may constitute ecological adaptations. By examining the effect of oviposition sequence on progeny produced by different size classes of female ladybird beetles (produced by controlling larval access to food), we show that maternal signals can change through adult life and alter the developmental programs of progeny, ostensibly to synchronize their life histories with predictable resource dynamics, thus maximizing maternal fitness. We also show that female body size, as determined by larval food supply, interacts with female age to influence progeny fitness. When fed ad libitum as adults, small females reared with limited food access laid fewer, smaller eggs than large females reared with ad libitum food access. Maternal body size interacted with oviposition sequence to influence progeny development, but the latter had greater impact. Eggs laid later by medium and large females hatched faster than those laid earlier, larvae fed longer in the fourth instar, their pupation period was shorter, total developmental time was reduced, and adults emerged with greater mass, most notably daughters. Oviposition sequence effects on progeny from small mothers were non‐significant for total developmental time and progeny mass. Only large mothers increased egg size over time and egg mass was not consistently correlated with developmental parameters, indicating that progeny phenotype was impacted by other, more cryptic, maternal signals. Such signals appear costly, as food limitation during development constrained not only fecundity and egg size but also maternal ability to manipulate progeny phenotype. The production of faster‐developing offspring that mature to larger sizes late in the oviposition cycle may be adaptive for exploitation of ephemeral aphid outbreaks with predictable dynamics of prey abundance and competition.     

Assured fitness returns in a social wasp with no worker caste

The theory of assured fitness returns proposes that individuals nesting in groups gain fitness benefits from effort expended in brood-rearing, even if they die before the young that they have raised reach independence. These benefits, however, require that surviving nest-mates take up the task of rearing these young. It has been suggested that assured fitness returns could have favoured group nesting even at the origin of sociality (that is, in species without a dedicated worker caste). We show that experimentally orphaned brood of the apoid wasp Microstigmus nigrophthalmus continue to be provisioned by surviving adults for at least two weeks after the orphaning. This was the case for brood of both sexes. There was no evidence that naturally orphaned offspring received less food than those that still had mothers in the nest. Assured fitness returns can therefore represent a real benefit to nesting in groups, even in species without a dedicated worker caste.     

Global climate change and phenotypic variation among red deer cohorts.

The variability of two fitness-related phenotypic traits (body weight and a mandibular skeletal ratio) was analysed among cohorts and age-classes of red deer in Norway. Phenotypic variation among cohorts was pronounced for calves, yearlings and reproductively mature adults. Fluctuations in cohort-specific mean body weights and skeletal ratios of adults correlated with global climatic variation in winter conditions influenced by the North Atlantic Oscillation while cohorts were in utero. Red deer born following warm winters were smaller than those born after cold winters, and this inter-cohort variability persisted into adulthood. Phenotypic variation among cohorts of red deer influenced by climate change may pose consequences for fitness of cohorts since body size and condition contribute to reproductive success and survival in male and female red deer. In particular, the recent trend of increasingly warm winters in northern Europe and Scandinavia may lead to reduced body size and fecundity of red deer, and perhaps other ungulates, in those areas.     

Evidence for a trade-off between growth and body reserves in northern white-tailed deer

We contrasted patterns of growth and accumulation of body reserves in autumn between two high-density (HD) white-tailed deer populations facing winters of different severity and length. Both populations occurred in the absence of effective predators and suffered from some forage competition based on reduced body masses. A third population living at low density (LD) and confronting long and severe winters (SW) served to distinguish the influence of food competition and winter severity on growth and body reserves. We estimated body components (water, protein, fat and ash) of deer during the first half of November and compared growth patterns between sexes and regions. HD-SW males continuted growth to an older age than HD males facing short and mild winters (MW) but females of both regions reached adult body mass at the same age. LD-SW deer exhibited a growth pattern similar to that of HD-SW animals but were the heaviest and the largest, suggesting that growth patterns are related to winter harshness (or length of the growing season) and that final body size is related to forage competition in summer. Sexual dimorphism became evident at an older age in the HD-SW population than in the HD-MW population, demonstrating that winter harshness does not affect immature males and females in the same manner. Fawns from the HD-SW population had proportionally longer legs and a higher percentage of body fat. Adaptations of immature deer to long and severe winters suggest that survival during the first winter represents the most critical step in the life span of northern white-tailed deer.     

Maternal condition and offspring sex ratio in polygynous ungulates: a case study of bighorn sheep

The Trivers and Willard model (TWM) predicts that for sexuallydimorphic polygynous mammals, mothers able to provide a highlevel of care should bias offspring sex ratio in favor of sons.Contradictory results of empirical studies, however, suggestthat selective pressures for adaptive offspring sex ratio varywith species and environmental conditions. We report the resultsof a 29-year study of marked bighorn sheep (Ovis canadensis)in a population that underwent wide changes in density and wheremost females were weighed each year. Lamb sex ratio was independentof absolute ewe mass and yearly deviations from individual orpopulation average mass, but there was a nonsignificant trendtowards fewer males being born at high population density. Bighornsheep satisfy all the assumptions of the TWM but not its prediction:lamb sex ratio is independent of maternal ability to providecare. Recent hypotheses to explain the lack of relationshipbetween maternal condition and offspring sex in ungulates areunlikely to apply to bighorn sheep. We suggest that the TWMmay only apply when social rank strongly affects the abilityto provide maternal care. Those circumstances are likely tooccur for only a few species and within a narrow range of environmentalconditions.     

The effects of twinning and maternal experience on maternal-filial social relationships in confined beef cattle

The objective of this investigation was to assess the maternal-filial social relationships of Hereford beef cattle as influenced by maternal experience of the dam (primiparous vs. multiparous) and number of offspring (one vs. two calves). Calves were temporarily separated from their dams during the first week after parturition, and the behavioral responses of mother and young were noted during and following separation.Contact and contact-seeking behaviors between twins and their mothers began to decline by the 5th or 6th day post-partum. Over the same period, contact behaviors exhibited by single calves and their dams remained stable or increased in frequency. Mothers of twins were less responsive to their calves than mothers of singles both during and following separation, and twins interacted with alien females more frequently than single-born young. It is proposed that insufficient milk production by Hereford dams bearing two calves provides an incentive for twins to parasitize the milk supply of alien mothers and, thus, become less dependent on their natural mothers. Social feedback between mother and twins may be further reduced by dams dividing their maternal attentiveness between two offspring.In general, experienced cows were more responsive to separation from their offspring than inexperienced heifers. Cows and their calves exhibited more frequent contact and contact-seeking behavior than heifers and their young.     

Mother-calf relationships and maternal investment in European bison<Emphasis Type="Italic">Bison bonasus</Emphasis>

Mother-young relationships, up to the third month of the calves’ life, were investigated in European bisonBison bonasus (Linnaeus, 1758) from Białowieża National Park breeding centres (Poland). During the first week, calves spent most of their time close to their mothers and were rarely seen in the vicinity of other group members. Highest suckling rate, most frequent vocal contact and agonistic behaviour of mothers towards intruders, were other characteristics of this period. Although being a forest species, European bison exhibit a following type of strategy for offspring protection, typical for ungulates living in open areas; no hiding phase was observed. Suckling rates were similar in calves of both sexes, however, the pattern of nursing was different: male calves suckled longer, but in rarer bouts than female calves. The mothers’ condition, reflected by their social rank, did not influence the suckling rate. No sex differences were recorded in other maternal activities or mother-calf distance. The presumption of a lack of sex-biased maternal investment in European bison is confirmed by the results of other research.