„Großmütter sind wichtig für die Familie. Das ist nicht nur bei Menschen so, sondern auch bei Elefanten, wie Biologen während einer Langzeitbeobachtung von mehr als 800 weiblichen Tieren im Amboseli-Nationalpark in Kenia festgestellt haben. So haben Elefantenbabys, die eine Mutter wie auch eine Großmutter haben, größere Überlebenschancen als andere Kälber. Auch auf ihre erwachsenen Töchter haben Elefanten-Omas starken Einfluss: „Weibliche Elefanten, deren Mutter lange lebte, bekamen mehr Nachwuchs“, schreiben die Wissenschaftler in der Fachzeitschrift Behavioral Ecology and Sociobiology.“
in: Süddeutsche Zeitung, 19.1.2016
Artikel zur Studie „The reproductive advantages of a long life: longevity and senescence in wild female African elephants“ von Phyllis C. Lee, Victoria Fishlock, C. Elizabeth Webber und Cynthia J. MossBehavioral Ecology and Sociobiology,
Summary: „Long-lived species such as elephants, whales and primates exhibit extended post-fertile survival compared to species with shorter lifespans but data on age-related fecundity and survival are limited to few species or populations. We assess relationships between longevity, reproductive onset, reproductive rate and age for 834 longitudinally monitored wild female African elephants in Amboseli, Kenya. The mean known age at first reproduction was 13.8 years; only 5 % commenced reproduction by 10 years. Early reproducers (<12.5 years) had higher age-specific fertility rates than did females who commenced reproduction late (15+ years) with no differences in survival between these groups. Age-specific reproductive rates of females dying before 40 years were reduced by comparison to same-aged survivors, illustrating a mortality filter and reproductive advantages of a long life. Overall, 95 % of fertility was completed before 50, and 95 % of mortality experienced by age 65, with a mean life expectancy of 41 years for females who survived to the minimum age at first birth (9 years). Elephant females have a relatively long period (c. 16 years) of viability after 95 % completed fertility, although reproduction does not entirely cease until they are over 65. We found no evidence of increased investment among females aged over 40 in terms of delay to next birth or calf mortality. The presence of a mother reproducing simultaneously with her daughter was associated with higher rates of daughter reproduction suggesting advantages from maternal (and grandmaternal) co-residence during reproduction.“
Ähnliche Studie bezogen auf Asiatische Elefanten: „Nearby grandmother enhances calf survival and reproduction in Asian elephants“ von Mirkka Lahdenperä, Khyne U. Mar und Virpi Lummaa, in: Scientific Reports 6, Juni 2016.
Summary: „Usually animals reproduce into old age, but a few species such as humans and killer whales can live decades after their last reproduction. The grandmother hypothesis proposes that such life-history evolved through older females switching to invest in their existing (grand)offspring, thereby increasing their inclusive fitness and selection for post-reproductive lifespan. However, positive grandmother effects are also found in non-menopausal taxa, but evidence of their associated fitness effects is rare and only a few tests of the hypothesis in such species exist. Here we investigate the grandmother effects in Asian elephants. Using a multigenerational demographic dataset on semi-captive elephants in Myanmar, we found that grandcalves from young mothers (<20 years) had 8 times lower mortality risk if the grandmother resided with her grandcalf compared to grandmothers residing elsewhere. Resident grandmothers also decreased their daughters’ inter-birth intervals by one year. In contrast to the hypothesis predictions, the grandmother’s own reproductive status did not modify such grandmother benefits. That elephant grandmothers increased their inclusive fitness by enhancing their daughter’s reproductive rate and success irrespective of their own reproductive status suggests that fitness-enhancing grandmaternal effects are widespread, and challenge the view that grandmother effects alone select for menopause coupled with long post-reproductive lifespan.“
Bildnachweis (Titel): Chen Hu / Unsplash