Lazy sons, self-sufficient daughters: are sons more demanding?

Piedrahíta, Paolo; Meise, Kristine; Werner, Christiane; Krüger, Oliver; Trillmich, Fritz

doi:10.1016/j.anbehav.2014.09.027

Cited by 23 publications

(12 citation statements)

References 61 publications

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“…This variability from year to year appears to be related to environmental influences but, during the cold season, also relates to the number of pups born in a given season, which varied strongly among years. At our colony, females lactate their offspring approximately for 2 years [ 39 ]. If females are not as likely to support a pregnancy successfully while suckling an offspring than when without a dependent offspring, this could influence pup numbers born in the following year and partly explain the approximately 2-year cycle of pup numbers observed in the majority of years.…”

Section: Discussionmentioning

confidence: 99%

On the Challenge of Interpreting Census Data: Insights from a Study of an Endangered Pinniped

et al. 2016

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Population monitoring is vital for conservation and management. However, simple counts of animals can be misleading and this problem is exacerbated in seals (pinnipeds) where individuals spend much time foraging away from colonies. We analyzed a 13-year-series of census data of Galapagos sea lions (Zalophus wollebaeki) from the colony of Caamaño, an islet in the center of the Galapagos archipelago where a large proportion of animals was individually marked. Based on regular resighting efforts during the cold, reproductive (cold-R; August to January) and the warm, non-reproductive (warm-nR; February to May) season, we document changes in numbers for different sex and age classes. During the cold-R season the number of adults increased as the number of newborn pups increased. Numbers were larger in the morning and evening than around mid-day and not significantly influenced by tide levels. More adults frequented the colony during the warm-nR season than the cold-R season. Raw counts suggested a decline in numbers over the 13 years, but Lincoln-Petersen (LP-) estimates (assuming a closed population) did not support that conclusion. Raw counts and LP estimates were not significantly correlated, demonstrating the overwhelming importance of variability in attendance patterns of individuals. The probability of observing a given adult in the colony varied between 16% (mean for cold-R season) and 23% (warm-nR season) and may be much less for independent 2 to 4 year olds. Dependent juveniles (up to the age of about 2 years) are observed much more frequently ashore (35% during the cold-R and 50% during the warm-nR seasons). Simple counts underestimate real population size by a factor of 4–6 and may lead to erroneous conclusions about trends in population size.

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Section: Discussionmentioning

confidence: 99%

On the Challenge of Interpreting Census Data: Insights from a Study of an Endangered Pinniped

et al. 2016

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“…Thus, raising sons may mean greater lactational demands on mountain gorilla mothers and less ability to adjust weaned age. Galápagos sea lion offspring (Zalophus wollebaeki) show neonatal sexual dimorphism and have varying lactational demands associated with the level of independent feeding, indicating an offspring's contribution to its own survival and growth (Piedrahita et al 2014). Thus, the mother's supply of resources and offspring's food intake through independent feeding should to be studied concurrently to understand sex-biased investment and underlying behavioral mechanism in mammals (see Royle et al 2004).…”

Section: Offspring Sex and Maternal Conditionmentioning

confidence: 99%

Weaned age variation in the Virunga mountain gorillas (Gorilla beringei beringei): influential factors

Eckardt

Fawcett

Fletcher

2016

Behav Ecol Sociobiol

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Weaning marks an important milestone during life history in mammals indicating nutritional independence from the mother. Age at weaning is a key measure of maternal investment and care, affecting female reproductive rates, offspring survival and ultimately the viability of a population. Factors explaining weaned age variation in the endangered mountain gorilla are not yet well understood. This study investigated the impact of group size, group type (one-male versus multi-male), offspring sex, as well as maternal age, rank, and parity on weaned age variation in the Virunga mountain gorilla population. The status of nutritional independence was established in 69 offspring using long-term suckling observations. A Cox-regression with mixed effects was applied to model weaned age and its relationship with covariates. Findings indicate that offspring in one-male groups are more likely to be weaned earlier than offspring in multi-male groups, which may reflect a female reproductive strategy to reduce higher risk of infanticide in one-male groups. Inferior milk production capacity and conflicting resource allocation between their own and offspring growth may explain later weaning in primiparous mothers compared to multiparous mothers. Sex-biased weaned age related to maternal condition defined by parity, rank, and maternal age will be discussed in the light of the Trivers-Willard hypothesis. Long-term demographic records revealed no disadvantage of early weaning for mother or offspring. Population growth and two peaks in weaned age within the Virunga population encourage future studies on the potential impact of bamboo shoots as a weaning food and other environmental factors on weaning.Female reproductive rates are key in determining the viability of endangered populations. Using suckling observations from the Virunga mountain gorilla population spanning nearly forty years, we investigated factors affecting variation in age at weaning, a principal determinant of reproductive rate. Our findings provide evidence that females in one-male groups that have higher risk of infanticide wean offspring earlier than those in multi-male groups, that there is differential investment in males depending on age and reproductive experience of the mother, and that we should focus more on the availability of easily digestible foods (here bamboo) in relation to age at weaning. Improved understanding of such influencing factors enables us to more readily predict future population dynamics of these great apes as they grow towards their carrying capacity with continued change in their environment. 1996; Quinn 2013) as it can determine both female future reproductive rates and offspring fitness in mammals (

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“…The sex‐allocation hypothesis predicts that parents should invest more in offspring of the sex with the greater variance in reproductive success; usually males in polygynous species (Trivers & Willard, ). Empirical support for the sex‐allocation hypothesis remains limited for carnivores, although Piedrahita, Meise, Werner, Krüger, and Trillmich () showed that Galapagos sea lion Zalophus wollebaeki sons demand greater levels of provisioning than daughters. Environmental conditions may also influence the duration of parental care (the resource limitation hypothesis).…”

Section: Introductionmentioning

confidence: 99%

Flexibility in the duration of parental care: Female leopards prioritise cub survival over reproductive output

Balme

Robinson

Pitman

et al. 2017

Journal of Animal Ecology

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Deciding when to terminate care of offspring is a key consideration for parents. Prolonging care may increase fitness of current offspring, but it can also reduce opportunities for future reproduction. Despite its evolutionary importance, few studies have explored the optimal duration of parental care, particularly among large carnivores. We used a 40-year dataset to assess the trade-offs associated with the length of maternal care in leopards in the Sabi Sand Game Reserve, South Africa. We compared the costs imposed by care on the survival and residual reproductive value of leopard mothers against the benefits derived from maternal care in terms of increased offspring survival, recruitment and reproduction. We also examined the demographic and ecological factors affecting the duration of care in the light of five explanatory hypotheses: litter size, sex allocation, resource limitation, timing of independence and terminal investment. Duration of care exhibited by female leopards varied markedly, from 9 to 35 months. Mothers did not appear to suffer any short- or long-term survival costs from caring for cubs, but extending care reduced the number of litters that mothers could produce during their lifetimes. Interestingly, the duration of care did not appear to affect the post-independence survival or reproductive success of offspring (although it may have indirectly affected offspring survival by influencing dispersal distance). However, results from generalised linear mixed models showed that mothers prolonged care during periods of prey scarcity, supporting the resource limitation hypothesis. Female leopards also cared for sons longer than daughters, in line with the sex-allocation hypothesis. Cub survival is an important determinant of the lifetime reproductive success in leopards. By buffering offspring against environmental perturbation without jeopardising their own survivorship, female leopards apparently "hedge their bets" with current offspring rather than gamble on future offspring which have a small probability of surviving. In many species, parents put their own needs before that of their offspring. Leopard mothers appear sensitive to their offspring's demands, and adjust levels of care accordingly.

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Lazy sons, self-sufficient daughters: are sons more demanding?

Cited by 23 publications

References 61 publications

On the Challenge of Interpreting Census Data: Insights from a Study of an Endangered Pinniped

On the Challenge of Interpreting Census Data: Insights from a Study of an Endangered Pinniped

Weaned age variation in the Virunga mountain gorillas (Gorilla beringei beringei): influential factors

Flexibility in the duration of parental care: Female leopards prioritise cub survival over reproductive output

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