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Early maternal investment in male and female African elephant calves
Abstract
The suckling behaviour of 130 freeranging elephant calves aged between birth and 4.5 years old was examined in Amboseli National Park, Kenya. Analyses of frequencies of suckling and durations of suckling bouts showed that males attempted to suckle more often, were more successful at their attempts, and as a result were estimated to have a higher milk intake than did female calves. Mothers were equally tolerant of their sons' and daughters' demands to suckle at young ages, but were less tolerant of their older sons' demands. The growth rates of males based on hind footprint length were faster than those of females from birth onwards. During drought years with low food availability, male calf survivorship in the first year was lower than that of female calves. During wet years, there was little difference between sexes in survivorship. It appeared that during dry years mothers were unable to sustain milk production at a level that met the metabolic requirements of their sons, and as result male calves were more likely to die. Females with a surviving son tended to have a longer interbirth interval than did females with a surviving daughter. We suggest that greater early maternal investment in male calves occurs because, in the highly-competitive polygynous mating system of elephants, size in adult male elephants is an important factor in mating success.
... Younger mothers tend to be smaller, with fewer energy reserves than older females [28,57]. In addition, due to greater birth weights and faster growth rates, male calves pose a larger energetic demand on their mothers than female calves [57,58]. Whilst there was no significant difference in the mean age of first parturition between the Orphans and the A&B herd ( Figure 7), there was a dramatic difference in calf sex ratios. ...
... Most private smaller reserves in South Africa preferred not to introduce many males with the founding herd, but over the years, the sex ratio has evened to reflect a more natural distribution. As most private reserves have reached their limit in the number of elephants the fenced environment can sustain, there may be a resource or density factor (or a cost-benefit effect) influencing the sex at conception [58]. ...
African elephants (Loxodonta africana) exhibit a long developmental period during which they acquire complex social and ecological knowledge through social networks. Central to this is that matriarchs and older individuals play an important role as repositories of information gained through experience. Anthropogenic interventions—including poaching, culling, translocation, and hunting—can disrupt elephants’ social networks, with implications for individual fitness and potential long-term population viability. Here, we draw on a unique long-running, individual-based dataset to examine the impacts of translocation on a population of elephants in South Africa, taking into consideration demographic rates, social dynamics, and ecological decision-making. Specifically, we compared two translocated groups: a group of unrelated culling Orphans and a family herd. We found that the Orphan group experienced accelerated reproductive rates when compared with the family herd. The Orphan group also fissioned more frequently and for longer periods of time, suggesting lower cohesiveness, and were less decisive in their large-scale movement decisions. These results add to the growing body of literature on the downstream impacts of social disruption for elephants. Whilst the translocation of culling Orphans is no longer practised in South Africa, we encourage careful consideration of any elephant translocation and the resulting social disruption.
... However, if diet influences which tooth morphotype is displayed then it does not make sense why only the adult molars correspond to the "smooth" morphotype while the deciduous premolars correspond to the "rugged" morphotype. Modern elephants start incorporating solid food in their diet by 3 months old (Lee and Moss, 1986) and show wear on their dP2/dp2 from mastication by 6 months old (Laws, 1966;Haynes, 1991). If the "smooth" or "rugged" morphotype was influenced by diet alone as stated in Saunders (1977), then the ZRFS mastodon deciduous premolars should also correspond to the "smooth" morphotype since they are in an environment dominated by spruce. ...
The Ziegler Reservoir fossil site (ZRFS) in Colorado contains over 4000 mastodon bones that date from 140,000 to 100,000 years ago. At an elevation of ~2705 meters above sea level, ZRFS represents an alpine ecosystem dated to Marine Isotope Stage (MIS) 5. Formal descriptions of cheek teeth, mandibles, crania, and femora were completed. Statistical analyses of the upper and lower third molars, including a novel measurement of interloph(id) distances, indicate significant differences between ZRFS mastodons and Mammut pacificus, while falling within the ranges for Mammut americanum. This study agrees with the taxonomic assignment of ZRFS mastodons to Mammut americanum and not Mammut pacificus. Body mass estimates of ZRFS mastodons are between 3451 and 6244 kg, and a niche model indicates elevation and water availability influenced Mammut distribution during MIS 5. Incorporating ZRFS mastodons into large comparative datasets will contribute to ongoing research into Late Pleistocene Mammut.
... Bird and mammal species with sexual size dimorphism (SSD) illustrate the SR theory [26,27]. In this case, if available resources are limited, offspring of the larger sex may receive relatively fewer resources, thus compromising their development and survival [28][29][30][31]. Parents may respond by adjusting the production of offspring of the smaller size, which generates a bias in PSR and SSR [31][32][33][34]. ...
The primary (PSR), secondary (SSR) and adult (ASR) sex ratios of sexually reproducing organisms influence their life histories. Species exhibiting reversed sexual size dimorphism (RSD) may imply a higher cost of female production or lower female survival, thus generating biases in PSR, SSR and/or ASR towards males. The Harpy Eagle is the world's largest eagle exhibiting RSD. This species is found in the Neotropical region and is currently threatened with extinction. We used molecular markers to determine the sex of 309 Harpy Eagles spanning different life stages—eaglets, subadults and adults—from 1904 to 2021 within the Amazon Rainforest and Atlantic Forest. Sex ratios for all life stages revealed a female-biased deviation across all periods and regions. Our results suggest that the population bias towards females is an evolutionary ecological pattern of this species, and SSR and ASR likely emerged from the PSR. This natural bias towards females may be compensated by an earlier sexual maturation age of males, implying a longer reproductive lifespan and a higher proportion of sexually active males. A better understanding of the Harpy Eagle's life history can contribute to understanding sex-role evolution and enable more appropriate conservation strategies for the species.
... African elephants (Loxodonta africana) are known for their complex and close social bonds. Calves are born into stable families and cared for by their mothers, other females (allomothers), and older siblings [1][2][3]. The death of a mother during the first 24 months of life will leave the calf with almost no chances of survival in situ [4][5][6] and even in captivity [7]. ...
Simple Summary
In the wild, African elephant calves must stay close to their mothers and the family unit as the African environment holds many threats. African elephant calves in zoos are raised in a protected environment. Therefore, we hypothesize that calves ex situ hold bigger distances and behave differently than in situ. Additionally, those differences are likely to increase with further zoo generations. This study used ethological research methods to compare the mother–calf bond of African elephant calves in situ and ex situ (first and second generation). The results showed that ex situ living calves of both generations maintain greater distances to their mothers and show a wider variation (positive and negative) in behavior than in situ. The detected differences indicate that calves ex situ can behave more freely as they are in a protected environment. Therefore, they can develop faster than in the wild, which agrees with similar findings on African elephant calf development and adult African elephants. The hypothesis that differences between in situ and ex situ increase with the zoo generations could not be verified. Hence, modifications in behavior under different environmental selection pressures may be adaptive.
Abstract
African zoo elephants live in safe environments with sufficient resources, are protected from threats, and have their health and body conditions cared for. Calves ex situ undergo the same developmental stages as in situ and are raised by the whole family unit. However, due to environmental differences, there might be behavioral modifications between calves in situ and ex situ. We hypothesize that these differences increase with ongoing generations. This ethological study compares social and general behavior and the distance calves kept to their mothers’ between calves of the first (F1) and second (F2) zoo generation and the wild. Using ethological methods, data were collected for ~90 in situ calves and 16 ex situ (8 F1, 8 F2) between the ages of 0.5 to 4 years (120 observation hours per group). Results showed that in situ calves spent significantly more time close to mothers than the F1 and the F2 zoo generations (F1/in situ: p = <0.001; F2/in situ: p = 0.007). The behaviors of eating, drinking, trunk movement, washing, and affiliative behaviors showed significant differences between in situ and ex situ calves. The amount and distribution of affiliative and agonistic behavior initiated and received by calves was displayed with a greater variety ex situ. Ex situ calves not only performed affiliative but, in contrast to the in situ, also agonistic behavior (F1/in situ: initiated p = 0.002, received p = 0.010; F2/in situ: initiated p = 0.050, received p = 0.037). The comparison of zoo generations suggests that differences did not increase with the generation. The more casual binding between mothers and offspring in zoos and the age-dependent improvement of social behavior of zoo-born calves are seen as a result of elephants’ adaptation to secure zoo conditions. The results of this study agree with the faster development of ex situ African elephants, like earlier puberty and more frequent breeding patterns, as known from the literature.
... Maternal investment plays an important role in the success of offspring (Lee and Moss 1986), and it has been shown that natural selection favors parents who invest equally in their sons or daughters (Fisher 1999). Although it is assumed that sex-ratios at birth are 50:50, sex ratios in many mammals frequently deviate from 50:50 and often the health of the mother plays a key role in dictating the sex ratio at conception in sexually dimorphic mammals (Burke and Birch 1995, Garroway and Broders 2007). ...
... Mothers were more likely to be near their juvenile daughters than to their juvenile sons. These results support previous findings that mothers associate more frequently with offspring of the philopatric sex than with those of the dispersing sex (female-philopatric species: Missakian, 1974;Fairbanks & McGuire, 1985;Lee & Moss, 1986;Nakamichi, 1989;Timme, 1995;Holekamp et al., 1997;Kulik et al., 2016;male-philopatric species: Toda et al., 2021). The observed frequent associations between mothers and their juvenile daughters may continue after maturing. ...
Females of female-philopatric species form lifelong affiliative relationships with one another. Given that adult daughters can provide benefits to mothers in the future, mothers may invest more in juvenile daughters than juvenile sons. A potential implication of this sex difference in investment is that mothers of juvenile daughters have reduced capacity to form affiliative relationships with other adult females. We tested whether the strength of female–female affiliative relationships varies depending on the sex of their juvenile offspring in free-ranging Japanese macaques (Macaca fuscata). We analyzed affiliative interactions (spatial proximity and social grooming) of 14 adult females to assess the strength of affiliative relationships between them over a 3-month period. We found that affiliative relationships between females with juvenile daughters were weaker than those between females without juvenile daughters. In contrast, the presence of juvenile sons did not significantly influence the strength of affiliative relationships between females. Mothers associated more with juvenile daughters than with juvenile sons, suggesting that mothers invested more in associating with juvenile daughters than with juvenile sons. Our data confirmed that females form strong affiliative relationships with kin, as is typical for this species. The results imply that females invest more effort in offspring with whom they can maintain affiliative relationships after maturing, which may reduce their level of affiliative relationships with non-kin. Further studies over longer time periods are required to determine whether the reduction in non-kin affiliative relationships is temporary or permanent.
... During droughts, maternal elephants struggle to maintain milk production, when the metabolic demands of young male elephants are greater, making it difficult for maternal elephants to meet their needs. Thus, young male elephants are more likely to die [8]. A major reason for the high mortality rate of elephant calves in zoos, especially in Asia, is the refusal of mothers to nurse their young, resulting in the need for manual intervention to feed the young [9,10]. ...
Evaluating the association between milk-containing diets and the microbiomes of young Asian elephants could assist establishing optimal breast milk supplementation to improve offspring survival rates. The microbiomes of young Asian elephants on different milk-containing diets (elephant milk only, elephant milk–plant mixed feed, and goat milk–plant mixed feed) were investigated using high-throughput sequencing of 16S rRNA genes and phylogenetic analysis. Microbial diversity was lower in the elephant milk-only diet group, with a high abundance of Proteobacteria compared to the mixed-feed diet groups. Firmicutes and Bacteroidetes were dominant in all groups. Spirochaetae, Lachnospiraceae, and Rikenellaceae were abundant in the elephant milk–plant mixed-feed diet group, and Prevotellaceae was abundant in the goat milk–plant mixed-feed diet group. Membrane transport and cell motility metabolic pathways were significantly enriched in the elephant milk–plant mixed-feed diet group, whereas amino acid metabolism and signal transduction pathways were significantly enriched in the goat milk–plant mixed-feed diet group. The intestinal microbial community composition and associated functions varied significantly between diets. The results suggest that goat milk is not suitable for young elephants. Furthermore, we provide new research methods and directions regarding milk source evaluation to improve elephant survival, wellbeing, and conservation.
With the escalating challenges in captive elephant management, the study of elephant reintegration emerges as a pivotal area of research, primarily addressing the enhancement of animal welfare. The term ‘reintegration’ refers to the process of rehabilitating captive elephants to a natural system, allowing them to roam freely without intensive human intervention. There is a relative paucity of research addressing the behavioural adaptations post-reintegration, despite reintegration of over 20 elephants across various fenced reserves in South Africa. Our study centres on two distinct herds of reintegrated African elephants, monitoring their movement patterns in two South African reserves over a 57-month period post-release. The primary goal of the study was to establish whether the flexibility and adaptability of movement behaviour of reintegrated elephants can be considered as one of the indicators of determining the success of such an operation. The second aim of our study was to investigate if the reintegrated elephants demonstrated an adaptability to their environment through their hourly, daily, and seasonal ranging patterns after a period of free roaming that exceeded 4 years. Our findings indicated that reintegrated elephants, much like their wild counterparts (movement based on literature), displayed notable seasonal and diurnal variations in key movement parameters, such as utilisation distribution areas and reserve utilization. These patterns changed over time, reflecting an adaptive shift in movement patterns after several years of free roaming. Notably, the trajectory of changes in movement parameters varied between herds, indicating unique adaptation responses, likely resulting from differences in the reintegration process (familiarity of reserve, season of release, presence of wild elephants). Although our study is constrained by the limited number of reintegrated herds available for analysis, it underscores the potential of captive elephants to successfully adapt to a free-living environment, emphasising the promising implications of reintegration initiatives.
Bats have undergone one of the most drastic limb innovations in vertebrate history, associated with the evolution of powered flight. Knowledge of the genetic basis of limb organogenesis in bats has increased but little has been documented regarding the differences between limb organogenesis in bats and that of other vertebrates. We conducted embryological comparisons of the timelines of limb organogenesis in 24 bat species and 72 non-bat amniotes. In bats, the time invested for forelimb organogenesis has been considerably extended and the appearance timing of the forelimb ridge has been significantly accelerated, whereas the timing of the finger and first appearance of the claw development has been delayed, facilitating the enlargement of the manus. Furthermore, we discovered that bats initiate the development of their hind limbs earlier than their forelimbs compared to other placentals. Bat neonates are known to be able to cling continuously with their well-developed foot to the maternal bodies or habitat substrates soon after birth. We suggest that this unique life history of neonates, which possibly coevolved with powered flight, has driven the accelerated development of the hind limb and precocious foot.
Weight at birth, weight at weaning, time to weaning, liter-size and adult size were recorded from 100 studies reported in the literature. These data were used to compare adaptive offspring size, offspring biomass, time to weaning, litter-size and reproductive effort among mammals and to determine the interrelationships among these parameters. Size and growth rates of offspring are relatively constant features of mammalian reproduction. These characteristics vary as the 0.69-0.73 power of adult body mass and do not appear to vary in relation to litter-size or feeding habits. Litter-size and time to weaning appear to be the adaptive variables of mammalian reproduction. Litter-size is the dominant factor determining the energy requirements of breeding females. Reproductive effort and energy limits may not always be important factors when considering the evolution of mammalian reproductive rates.
