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Heribert Hofer - One of the best experts on this subject based on the ideXlab platform.
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Siblicide in Serengeti spotted hyenas: a long-term study of maternal input and cub survival
Behavioral Ecology and Sociobiology, 2008Co-Authors: Heribert Hofer, Marion L. EastAbstract:In the Serengeti National Park, Tanzania, large fluctuations of prey abundance alters the frequency at which spotted hyena ( Crocuta crocuta ) cubs are nursed and thus the total level of maternal input available to them. Maternal input is high when mothers feed on high densities of locally available migratory herbivores and low when mothers travel up to 70 km to forage. Using data from 19 cub cohorts on the incidence of Siblicide (from monitoring the survival of 609 cubs in twin litters) and cub growth rates (from 195 cubs in twin litters) as a measure of maternal input, we demonstrate that the incidence of Siblicide increased as average cohort growth rate declined. In total, there were 37 Siblicides in 384 litters (9% of litters). When both cubs were alive, total maternal input in siblicidal litters was significantly lower than in non-siblicidal litters and the mean share of the dominant sib of 64.6% was significantly higher than the mean of 52.1% for dominant sibs of non-siblicidal litters. After Siblicide, growth rates of Siblicide victors substantially increased, demonstrating that mothers did not reduce maternal input after litter reduction. As a result, Siblicide victors achieved a long-term growth rate similar to that of singletons and thus significantly increased their expected survival. We conclude that in spotted hyenas, high maternal input in lactation has favoured the evolution of facultative Siblicide in populations inhabiting areas with low or fluctuating food resources.
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Low aggression levels and unbiased sex ratios in a prey-rich environment: no evidence of Siblicide in Ngorongoro spotted hyenas (Crocuta crocuta)
Behavioral Ecology and Sociobiology, 2002Co-Authors: Bettina Wachter, Marion L. East, Oliver P. Höner, Waltraud Golla, Heribert HoferAbstract:Avian models of facultative Siblicide predict that rates of sibling aggression and the incidence of Siblicide should be lower in prey-rich than prey-poor environments, and that Siblicide should only occur when fitness benefits outweigh costs. We tested these predictions by comparing data from spotted hyena (Crocuta crocuta) twin litters in the Ngorongoro Crater, Tanzania, a habitat with a high density of resident prey (176 animals/km2) with similar data from the adjacent Serengeti National Park where density of resident prey is low (3.3 animals/km2). As predicted, rates of sibling aggression in Crater twin litters were substantially lower than those among twin siblings in the Serengeti. There was no evidence of Siblicide in the Crater, in contrast to the Serengeti, where facultative Siblicide occurs frequently. The growth rate of Crater cubs in singleton litters was similar to that of cubs in twin litters, whereas the growth rate of Serengeti singletons was higher than that of cubs in twin litters. Thus despotic behavior by dominant Crater cubs was unlikely to provide fitness benefits, while dominant Serengeti cubs that eliminated their sibling benefited from increased growth and enhanced survival. Previous studies have demonstrated biases in the sex-composition of hyena litters due to facultative Siblicide. No such biases were apparent in Crater litters. Our results provide strong evidence that levels of sibling aggression in spotted hyenas are adjusted in an adaptive manner, and that Siblicide is facultative and resource dependent. Our results do not support the idea of pre-natal manipulation of offspring sex by female spotted hyenas in response to changes in resource abundance.
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A note on sex ratios and sex combinations in Serengeti spotted hyaenas: Siblicide and sub-binomial variance
Applied Animal Behaviour Science, 1999Co-Authors: William H. James, Heribert HoferAbstract:Abstract Hofer and East [Hofer, H., East, M.L., 1997. Appl. Anim. Behav. Sci. 51, 307–316] reported data on the sex ratio (proportion male) of Serengeti hyaenas at around 3 months of age (the earliest time that they conveniently may be sexed). Sex ratios showed variation by litter size and the authors accordingly suggested that rates of Siblicide (varying by the sex of the aggressor) may be responsible. We show here that Siblicide could only account for the sub-binomial variance of the combinations of the sexes of the surviving twin pairs, if the probability of Siblicide depended also on the sex of the victim. Data on rates of aggression in spotted hyaena twin litters during the period when Siblicide occurs are compatible with the idea that the probability of Siblicide depends on the sex of the victim. Additional hypotheses which may explain sub-binomial variance, a feature shared by a number of other mammalian species known not to commit Siblicide, invoke pre-parturition processes. Further information may be required to exclude the possibility that zygotic or embryonic processes contribute to the observed variance as they do in a variety of other mammalian species.
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Skewed offspring sex ratios and sex composition of twin litters in Serengeti spotted hyaenas (Crocuta crocuta) are a consequence of Siblicide
Applied Animal Behaviour Science, 1997Co-Authors: Heribert Hofer, Marion L. EastAbstract:Long-term data on the sex ratio among offspring and sex composition of litters in a population of several hundred individually known spotted hyaenas in the Serengeti National Park, Tanzania are presented. Females produced singleton or twin litters. The overall sex ratio (proportion of males) was unbiased at 0.52 (n = 318) but masked significant deviations in opposite directions in litters of different size. Sex ratio in singleton litters was female biased at 0.43 (n = 91 individuals, p = 0.07). The sex ratio in twin litters was significantly (P < 0.05) male-biased at 0.56 (n = 228 individuals); there were significantly too many mixed-sex and too few all-female twin litters. Three hypotheses are considered that may explain these sex ratio biases: (i) the primary sex ratio may be skewed, (ii) cub mortality may be female-biased, leading to the loss of more females than males, or (iii) the biases are due to Siblicide. The first two hypotheses predicted the same sex ratio biases for both singleton and twin litters, while the third hypothesis predicted opposite trends for singleton and twin litters. The results are inconsistent with the two first hypotheses but support the third. The study suggests that the lack of all-female twin litters and the female bias amongst singletons is due to a higher incidence of Siblicide in all-female twin litters than among mixed-sex or all-male twin litters. Siblicide is the major source of post-natal sex ratio biases to the age of independence in this population.
Marion L. East - One of the best experts on this subject based on the ideXlab platform.
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Siblicide in Serengeti spotted hyenas: a long-term study of maternal input and cub survival
Behavioral Ecology and Sociobiology, 2008Co-Authors: Heribert Hofer, Marion L. EastAbstract:In the Serengeti National Park, Tanzania, large fluctuations of prey abundance alters the frequency at which spotted hyena ( Crocuta crocuta ) cubs are nursed and thus the total level of maternal input available to them. Maternal input is high when mothers feed on high densities of locally available migratory herbivores and low when mothers travel up to 70 km to forage. Using data from 19 cub cohorts on the incidence of Siblicide (from monitoring the survival of 609 cubs in twin litters) and cub growth rates (from 195 cubs in twin litters) as a measure of maternal input, we demonstrate that the incidence of Siblicide increased as average cohort growth rate declined. In total, there were 37 Siblicides in 384 litters (9% of litters). When both cubs were alive, total maternal input in siblicidal litters was significantly lower than in non-siblicidal litters and the mean share of the dominant sib of 64.6% was significantly higher than the mean of 52.1% for dominant sibs of non-siblicidal litters. After Siblicide, growth rates of Siblicide victors substantially increased, demonstrating that mothers did not reduce maternal input after litter reduction. As a result, Siblicide victors achieved a long-term growth rate similar to that of singletons and thus significantly increased their expected survival. We conclude that in spotted hyenas, high maternal input in lactation has favoured the evolution of facultative Siblicide in populations inhabiting areas with low or fluctuating food resources.
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Low aggression levels and unbiased sex ratios in a prey-rich environment: no evidence of Siblicide in Ngorongoro spotted hyenas (Crocuta crocuta)
Behavioral Ecology and Sociobiology, 2002Co-Authors: Bettina Wachter, Marion L. East, Oliver P. Höner, Waltraud Golla, Heribert HoferAbstract:Avian models of facultative Siblicide predict that rates of sibling aggression and the incidence of Siblicide should be lower in prey-rich than prey-poor environments, and that Siblicide should only occur when fitness benefits outweigh costs. We tested these predictions by comparing data from spotted hyena (Crocuta crocuta) twin litters in the Ngorongoro Crater, Tanzania, a habitat with a high density of resident prey (176 animals/km2) with similar data from the adjacent Serengeti National Park where density of resident prey is low (3.3 animals/km2). As predicted, rates of sibling aggression in Crater twin litters were substantially lower than those among twin siblings in the Serengeti. There was no evidence of Siblicide in the Crater, in contrast to the Serengeti, where facultative Siblicide occurs frequently. The growth rate of Crater cubs in singleton litters was similar to that of cubs in twin litters, whereas the growth rate of Serengeti singletons was higher than that of cubs in twin litters. Thus despotic behavior by dominant Crater cubs was unlikely to provide fitness benefits, while dominant Serengeti cubs that eliminated their sibling benefited from increased growth and enhanced survival. Previous studies have demonstrated biases in the sex-composition of hyena litters due to facultative Siblicide. No such biases were apparent in Crater litters. Our results provide strong evidence that levels of sibling aggression in spotted hyenas are adjusted in an adaptive manner, and that Siblicide is facultative and resource dependent. Our results do not support the idea of pre-natal manipulation of offspring sex by female spotted hyenas in response to changes in resource abundance.
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Skewed offspring sex ratios and sex composition of twin litters in Serengeti spotted hyaenas (Crocuta crocuta) are a consequence of Siblicide
Applied Animal Behaviour Science, 1997Co-Authors: Heribert Hofer, Marion L. EastAbstract:Long-term data on the sex ratio among offspring and sex composition of litters in a population of several hundred individually known spotted hyaenas in the Serengeti National Park, Tanzania are presented. Females produced singleton or twin litters. The overall sex ratio (proportion of males) was unbiased at 0.52 (n = 318) but masked significant deviations in opposite directions in litters of different size. Sex ratio in singleton litters was female biased at 0.43 (n = 91 individuals, p = 0.07). The sex ratio in twin litters was significantly (P < 0.05) male-biased at 0.56 (n = 228 individuals); there were significantly too many mixed-sex and too few all-female twin litters. Three hypotheses are considered that may explain these sex ratio biases: (i) the primary sex ratio may be skewed, (ii) cub mortality may be female-biased, leading to the loss of more females than males, or (iii) the biases are due to Siblicide. The first two hypotheses predicted the same sex ratio biases for both singleton and twin litters, while the third hypothesis predicted opposite trends for singleton and twin litters. The results are inconsistent with the two first hypotheses but support the third. The study suggests that the lack of all-female twin litters and the female bias amongst singletons is due to a higher incidence of Siblicide in all-female twin litters than among mixed-sex or all-male twin litters. Siblicide is the major source of post-natal sex ratio biases to the age of independence in this population.
Kay E Holekamp - One of the best experts on this subject based on the ideXlab platform.
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Siblicide in the spotted hyena analysis with ultrasonic examination of wild and captive individuals
Behavioral Ecology, 2007Co-Authors: Sofia A Wahaj, Mary L. Weldele, Stephen E. Glickman, Ned J Place, Kay E HolekampAbstract:Integrated field and laboratory studies of long-lived, large-bodied mammals are rare but offer unique opportunities to elucidate the behavioral ecology of these animals. Here, we used this approach to examine whether Siblicide in spotted hyenas (Crocuta crocuta) is obligate or facultative. First, we tested predictions of obligate and facultative hypotheses by using ultrasonography to compare litter size before and after parturition and identify potential causes of litter reduction. Second, we compared litter size and composition between wild and captive hyenas to assess variation in offspring sex ratios. Third, we used demographic data to compare survivorship among litters of various sizes and compositions. Fourth, we compared sex ratios within twin litters born in the wild under conditions of high population density and intense feeding competition with those born when population density and intensity of feeding competition were reduced. Our data were inconsistent with the obligate Siblicide hypothesis. Litter reduction occurred during roughly one-third of pregnancies in both wild and captive hyenas, and all such reductions among captives were due to fetal resorptions or stillbirths. Litter sizes and compositions differed little between wild and captive hyenas. However, sex ratios in twin litters varied in the wild with intensity of feeding competition. In conjunction with captive data, long-term study of a wild hyena population under varying environmental conditions suggests facultative Siblicide is most likely to occur when feeding competition is most intense, thus offering an ecological explanation for earlier conflicting reports on Siblicide in this species. Copyright 2007, Oxford University Press.
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Siblicide revisited in the spotted hyaena: does it conform to obligate or facultative models?
Animal behaviour, 1999Co-Authors: Laura Smale, Kay E Holekamp, Paula A. WhiteAbstract:Aggression among spotted hyaena, Crocuta crocuta, siblings is often intense, and sometimes lethal. Frank et al. (1991, Science, 252, 702‐704) proposed that Siblicide routinely occurs in half of all spotted hyaena litters, namely those composed of same-sex twins. We propose an alternative to this ‘obligate’ model. In our ‘facultative’ model we suggest that Siblicide is far less common than previously supposed, and that it occurs only when resources are insufficient to sustain two cubs. According to this facultative model, intense neonatal aggression functions to establish intralitter dominance rather than to kill siblings. Furthermore, differences in litter size and composition between captive and field settings previously used to support the obligate model are assumed in the facultative model to be due to prenatal factors rather than to postnatal Siblicide. Here we tested the predictions of these two hypotheses with 10 years of field data from hyaenas inhabiting the Masai Mara National Reserve, Kenya. We found that, although sex compositions of hyaena litters averaged over the entire 10-year period did not differ from those predicted by chance, they did vary with environmental conditions. Litter sizes, by contrast, remained constant. These data are inconsistent with the widely accepted hypothesis that spotted hyaenas in same-sex litters routinely engage in Siblicide. © 1999 The Association for the Study of Animal Behaviour
Paula A. White - One of the best experts on this subject based on the ideXlab platform.
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Siblicide revisited in the spotted hyaena: does it conform to obligate or facultative models?
Animal behaviour, 1999Co-Authors: Laura Smale, Kay E Holekamp, Paula A. WhiteAbstract:Aggression among spotted hyaena, Crocuta crocuta, siblings is often intense, and sometimes lethal. Frank et al. (1991, Science, 252, 702‐704) proposed that Siblicide routinely occurs in half of all spotted hyaena litters, namely those composed of same-sex twins. We propose an alternative to this ‘obligate’ model. In our ‘facultative’ model we suggest that Siblicide is far less common than previously supposed, and that it occurs only when resources are insufficient to sustain two cubs. According to this facultative model, intense neonatal aggression functions to establish intralitter dominance rather than to kill siblings. Furthermore, differences in litter size and composition between captive and field settings previously used to support the obligate model are assumed in the facultative model to be due to prenatal factors rather than to postnatal Siblicide. Here we tested the predictions of these two hypotheses with 10 years of field data from hyaenas inhabiting the Masai Mara National Reserve, Kenya. We found that, although sex compositions of hyaena litters averaged over the entire 10-year period did not differ from those predicted by chance, they did vary with environmental conditions. Litter sizes, by contrast, remained constant. These data are inconsistent with the widely accepted hypothesis that spotted hyaenas in same-sex litters routinely engage in Siblicide. © 1999 The Association for the Study of Animal Behaviour
David J. Anderson - One of the best experts on this subject based on the ideXlab platform.
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Hormonal Correlates of Siblicide in Galapagos Nazca Boobies
Hormones and behavior, 2001Co-Authors: Elisa M Tarlow, Martin Wikelski, David J. AndersonAbstract:Nazca boobies (Sula granti) show unconditional obligate Siblicide immediately after hatching, reducing the typical two-egg clutch size to one. We studied body mass changes and levels of testosterone (T), corticosterone (CORT), and progesterone (P) for A-chicks (dominant, first hatched), B-chicks (subordinate, second hatched), and singletons, during the first 7 days after hatching, when Siblicide normally occurs. Mass increase with age was higher for A-chicks than for singletons and B-chicks. This exaggerated the existing developmental advantage of A- over B-chicks that is due to hatching asynchrony. In nests with two chicks, CORT titer was significantly higher in B-chicks than in A-chicks. During ontogenetic development, CORT decreased with age for A-chicks, but did not change for singletons. P showed qualitatively similar ontogenetic changes to CORT, remaining unchanged for A-chicks but increasing for singletons. Thus, both CORT and P levels were lower for A-chicks than for singletons, and both hormones varied inversely with body mass. Overall, T levels did not differ between different categories of chicks. However, one B-chick in the process of reversing the dominance relationship with its older, but weakened, sibling had significantly elevated T. We suggest that CORT and P are regulated to promote exaggerated mass gain in socially challenged A-chicks, facilitating Siblicide. Whether T induces aggressiveness during short time intervals of intense sibling rivalry needs further attention.
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Parent blue-footed boobies suppress siblicidal behavior of offspring
Behavioral Ecology and Sociobiology, 1999Co-Authors: Lynn W. Lougheed, David J. AndersonAbstract:Behaviorally dominant nestlings routinely kill sibling nestmates in blue-footed booby (Sula nebouxii) broods during periods of food shortage. Previous work demonstrated that these dominant, first-hatching “A-chicks” regulate the lethality of their behavior towards subordinate, second-hatching “B-chicks,” showing tolerance towards B-chicks except during chronic food shortages. Siblicide by A-chicks usually occurs after the hatchling stage. Results of an interspecific cross-fostering experiment indicated that A-chicks also attempt Siblicide shortly after hatching, but parents apparently exert control over these attempts, and thwart them, when chicks are young. Theory predicts selection for such regulation in siblicidal birds that are likely to experience genetic parent-offspring conflict over the value of subordinant nestlings; our evidence of post-hatching parental regulation is consistent with that prediction.
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ORIGINAL ARTICLE
1998Co-Authors: Lynn W. Lougheed, David J. AndersonAbstract:Abstract Behaviorally dominant nestlings routinely kill sibling nestmates in blue-footed booby (Sula nebouxii) broods during periods of food shortage. Previous work demonstrated that these dominant, first-hatching ‘‘A-chicks’ ’ regulate the lethality of their behavior towards subordinate, second-hatching ‘‘B-chicks,’ ’ showing tol-erance towards B-chicks except during chronic food shortages. Siblicide by A-chicks usually occurs after the hatchling stage. Results of an interspecific cross-foster-ing experiment indicated that A-chicks also attempt Siblicide shortly after hatching, but parents apparently exert control over these attempts, and thwart them, when chicks are young. Theory predicts selection for such regulation in siblicidal birds that are likely to ex-perience genetic parent-ospring conflict over the value of subordinant nestlings; our evidence of post-hatching parental regulation is consistent with that prediction. Key words Siblicide á Brood reduction á Galápagos á Booby á Sula á Parent-ospring conflic
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The Role of Parents in Sibilicidal Brood Reduction of Two Booby Species
The Auk, 1995Co-Authors: David J. AndersonAbstract:ABSTRACr.--Parental regulation of the probability and timing of avian brood reduction is expected to exist and evolve because natural selection should favor parents that match brood size to food availability most efficiently. Since food availability varies among species, interspecific variation in this regulation is expected. Comparative study of species with different brood reduction systems is one way to test the hypothesis that these mechanisms evolve as adaptations. Previous work on obligately siblicidal Masked Boobies (Sula dactylatra) and facultatively siblicidal Blue-footed Boobies (S. nebouxii) has shown that their different hatching asynchronies cannot fully explain the qualitative difference in their brood reduction systems. In this study, I report interspecific differences in nest shape that appear to contribute to early Siblicide in Masked Boobies, but that suppress early Siblicide in Blue-footed Boobies. Bluefooted Booby nest shape is closely regulated by parents. Differences in egg sizes of nest mates do not appear to contribute to the difference in social systems. Received 19 January 1995, accepted 2 July 1995. FATAL SIBLING AGGRESSION, known as "Siblicide," often reduces the brood size of a number of bird species (Stinson 1979, Mock et al. 1990). Lack's (1954) brood-reduction hypothesis is the basis for the common evolutionary interpretation of Siblicide, and of brood reduction (Ricklefs 1965) in general. When food supply for nestlings cannot be predicted reliably at the time of laying, selection is expected to favor a strategy of hatching as many nestlings as can be raised in the best conditions, and then of eliminating nestlings after hatching, if necessary, to bring demand into line with supply (see also Temme and Charnov 1987, Forbes and Ydenberg 1992). Siblicide provides parents an optimizing tool with a notable advantage: individual nestlings are best able to gauge their own physiological condition and can use that information, in conjunction with a competitive hierarchy, to maximize efficiency of brood reduction (Mock et al. 1987a).