Mother-offspring relations and transition to independence in the Galapagos sea lion (Zalophus Wollebaeki)
In many species of vertebrates and invertebrates parental care continues beyond the age at which the offspring are capable of independent food acquisition. This extended period of parental provisioning varies in length, and plays an important role in offspring survival during the transition to nutri...
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| Formato: | Tesis de Doctorado |
| Lenguaje: | eng |
| Publicado: |
Bielefeld / Universidad de Bielefeld / 2015
2016
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| Materias: | |
| Acceso en línea: | http://repositorio.educacionsuperior.gob.ec/handle/28000/2425 |
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| Sumario: | In many species of vertebrates and invertebrates parental care continues beyond the age at which the offspring are capable of independent food acquisition. This extended period of parental provisioning varies in length, and plays an important role in offspring survival during the transition to nutritional independence. Theoretically, parent-offspring conflict predicts that offspring are selected to prolong the length of parental feeding, whereas parents need to balance their extendend investment against a decrease in survival and reduction in lifetime reproductive success. Furthermore, in several polygynous, sexually-size dimorphic
mammals the energy requirements of male offspring are higher than that of females.
Therefore, rearing a son entail a higher cost for the nursing mother, given that in mammals parental care mostly consists of milk transfer to the young. However, in many species the offspring is capable to contribute to their own energy needs through independent foraging well before weaning. The view of juvenile self-feeding behaviour affecting demand and supply of care has received little attention.
I here examine maternal provisioning and juvenile self-feeding behaviour during the transition to independence in the Galapagos sea lion (Zalophus wollebaeki). Females can reproduce annually, but lactation may last for several years. Male offspring are larger than females from birth to beyond weaning, suggesting differences in energy needs between the two sexes. This sexual size dimorphism further suggests that mothers bias investment towards the sex with the higher fitness return, since in polygynous species, the variance in reproductive success is higher in males than in females. I investigated the attendance
behaviour, and foraging ecology through stable isotope analysis of mothers to assess the hypothesis that mothers adjust their time budget in relation to offspring sex. I show that mothers did not differ in their body condition, attendance behavior or foraging ecology in relation to yearling sex.
Alternatively, son offspring may demand more maternal investment than daughters in order to maintain fast growth. I studied the foraging behaviour of juveniles during the transition to independence to test for sex differences in diving behaviour as an important aspect of the demand fuction. I show that in the study colony, sons relied less than daughters on independent foraging during the first two years of life. This suggests that sons were apparently sustained by milk input, whereas daughters were more likely to contribute to their
energy needs through self-feeding behaviour.
In addition, I studied the influence of sea surface temperature as a proxy for food conditions on offspring survival during the first two years of life. The nearly equal survival rate of juveniles at each stage of development suggests that mothers seems able to supply the son?s higher demands. However, whether this differential demand affects a female's future reproduction requires further research. To conclude, this thesis has highlighted the role of self-feeding behaviour of juveniles in modifying some continuous and flexible maternal supply of resources. This study has further shown the influence of environmental conditions, maternal provisioning and juvenile foraging decisions on juvenile survival. |
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