Chemosensory Behavior And Development Of African Male Elephants Loxodonta Africana

Author : Jenna Marie Parker
Publisher :
ISBN 13 :
Total Pages : 213 pages
Book Rating : 4.:/5 (128 download)

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Download or read book The Physiological Condition of Orphaned African Elephants (Loxodonta Africana) written by Jenna Marie Parker and published by . This book was released on 2021 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prolonged maternal care is an energetically expensive behavior, yet it has evolved in many mammal species. This is presumably because of its benefits to offspring even after they are weaned, including defense again aggression from other individuals of the same species, protection from predation, provisioning of food, transfer of knowledge, and inherited rank for offspring of high-ranking individuals. We know these benefits matter because studies have shown that weaned orphans of some long-lived mammal species survive less than weaned nonorphans. However, we lack understanding of the physiological mechanisms leading to lowered survival for weaned orphans who are no longer dependent on their mother’s milk. Understanding physiological benefits of prolonged maternal care is valuable to understanding how it evolved, and, as some have speculated prolonged parental care was a cornerstone in the evolution of sociality, to further understanding sociality. Moreover, many long-lived species for which prolonged maternal care is fundamental are also of conservation concern, some due to practices like poaching that kill adults and leave orphans behind. Yet we were previously unaware of how orphan deaths impact population growth. African elephants (Loxodonta africana) are a highly social species, and the mother-calf bond is exceptionally important to elephant society. They are also endangered due to habitat loss and poaching, the latter of which removes adults from populations for their ivory tusks. My colleagues and I investigated the physiological consequences of losing prolonged maternal care by comparing the physiology and survival of individually known, wild African elephant orphans with those of their nonorphan peers in the Samburu and Buffalo Springs National Reserves of Kenya. We longitudinally collected dung samples to compare strongylid (gastrointestinal worm) fecal egg counts as a proxy for parasite loads and fecal glucocorticoid concentrations as a proxy for general stress. We also used 19 years of long-term demographic data to compare survival and the effect of orphaning on population growth. Chapter 1 reveals that we did not discover differences in strongylid infection between orphans and nonorphans, and surprisingly found evidence of lower strongylid infection in nonorphans who had left their natal family as compared to natal orphans and nonorphans. This may be due to social isolation; orphans who have left their family receive more aggression and are kept on the periphery of popular social hubs that contain old dung infected with strongylid larvae. In support of this idea, elephants who received more aggression as measured by behavioral focal follows had fewer strongylid eggs in their dung. Further supporting the role of social behavior in determining strongylid infection of wild elephants, we counted more strongylid eggs in the dung samples of females, who are more often in the company of family groups, than males, who spend less time in the company of family groups and more time in areas less contaminated by old dung. Agreeing with findings in other species, younger elephants were more infected with strongylids than older elephants, likely because their immune systems are still developing. Finally, using GPS radio collar data, we determined that elephants spending more time within reserves have fewer strongylid eggs in their dung compared to elephants who spend less time in reserves. This could indicate that livestock grazing outside of reserves is altering soil content so it is more conducive to strongylid larval survival. Chapter 2 concerns orphan versus nonorphan survival and the effect of orphaning on population growth. We found that even weaned African elephant orphans survive less than their nonorphan peers. Moreover, with a robust sensitivity analysis based on long-term data, we discovered that orphaning substantively decreases population growth. This demonstrates that, on top of its direct effects, adult elephant death indirectly decreases population growth through orphaning. As environmental conditions can affect sensitivity, we reran our analysis twice more using only data from years when there was less poaching in the study system, then only data from years of more poaching. Population growth rate’s sensitivity to orphan survival increased for the analysis parameterized with data from years of more poaching, indicating orphan survival is more important for population growth as orphaning increases. We concluded orphaning should not be overlooked when quantifying the impacts of poaching, and population models characterizing systems with extensive parental care benefit from explicitly incorporating orphan stages. Finally, Chapter 3 provides foundational insight into orphaning’s impact on the stress response of a wild long-lived mammal. We found no difference in baseline glucocorticoid levels of orphan and nonorphan elephants two or more years after their mother’s death. We did, however, find lower average levels in orphans who had left their natal family versus nonorphans and natal orphans. We also found lower glucocorticoid levels in individuals with more adult females and age mates in their core group. The observed lower levels in non-natal orphans were contrary to our predictions and may indicate downregulated glucocorticoid secretion following a period of sustained stress without familial support, which could be adaptive and/or negatively impact fitness. We do not think the lower glucocorticoids in non-natal orphans relate to their lower strongylid infection described in the first chapter, as strongylid egg counts did not correlate with glucocorticoids. Our third chapter findings indicate resilience in surviving orphans who remain with their family following their mother’s death, which is hopeful for the recovery of elephant populations that have been moderately poached. Although social context influenced glucocorticoid levels, they correlated most with ecological conditions. Elephants had lower levels when resources were plentiful, and higher levels during seasonal changes when resources were unevenly distributed. We therefore highlight that social context, and most of all ecological conditions, impact the stress response of wild African elephants. My dissertation indicates that maternal care is important not only to individual survival, but also to larger population dynamics. Therefore, orphaning matters for conserving African elephants and potentially other species with prolonged maternal care. Yet our findings are hopeful for orphans who manage to survive, as only elephant orphans without family showed altered physiology as compared to nonorphans. Concerning parasites, the changes we observed in non-natal orphans were advantageous because they were less infected with strongylids. Regarding the stress response, we found lower glucocorticoid levels in non-natal orphans without the support of family, which could affect their fitness and encourages similar research in heavily poached populations with more non-natal orphans. Broadly, my dissertation reveals that social behavior and social context affect the physiology of orphans, and that prolonged maternal care affects population growth.