Asian elephants exhibit post-reproductive lifespans

Simon N Chapman,Virpi Lummaa,Win Htut,Mirkka Lahdenperä,John Jackson

doi:10.1186/s12862-019-1513-1

Simon N Chapman, Virpi Lummaa + Show 3 more

Open Access

https://doi.org/10.1186/s12862-019-1513-1

Copy DOI

Abstract

BackgroundThe existence of extended post-reproductive lifespan is an evolutionary puzzle, and its taxonomic prevalence is debated. One way of measuring post-reproductive life is with post-reproductive representation, the proportion of adult years lived by females after cessation of reproduction. Analyses of post-reproductive representation in mammals have claimed that only humans and some toothed whale species exhibit extended post-reproductive life, but there are suggestions of a post-reproductive stage for false killer whales and Asian elephants. Here, we investigate the presence of post-reproductive lifespan in Asian elephants using an extended demographic dataset collected from semi-captive timber elephants in Myanmar. Furthermore, we investigate the sensitivity of post-reproductive representation values to availability of long-term data over 50 years.ResultsWe find support for the presence of an extended post-reproductive stage in Asian elephants, and that post-reproductive representation and its underlying demographic rates depend on the length of study period in a long-lived animal.ConclusionsThe extended post-reproductive lifespan is unlikely due to physiological reproductive cessation, and may instead be driven by mating preferences or condition-dependent fertility. Our results also show that it is crucial to revisit such population measures in long-lived species as more data is collected, and if the typical lifespan of the species exceeds the initial study period.

Highlights

The existence of extended post-reproductive lifespan is an evolutionary puzzle, and its taxonomic prevalence is debated
This controversy is due to a combination of methodological differences, variation in definitions of what constitutes a post-reproductive period, and the fact that post-reproductive lifespan is mathematically constrained to be positive unless all females immediately die after reproduction
We found a slight difference between the values for captive-born only (PrR = 0.207) and the full population

Summary

Introduction

The existence of extended post-reproductive lifespan is an evolutionary puzzle, and its taxonomic prevalence is debated. The evolution of extended post-reproductive lifespan is a long-term puzzle in evolutionary biology, where extended refers to post-reproductive lifespan that is not an artefact of individual variation in somatic and reproductive senescence rates [1]. Species with extended post-reproductive lifespans are implicitly considered to be physiologically incapable of further reproduction, and though postreproductive lifespan is often considered rare [2, 3], others claim it to be a general mammalian trait [4,5,6] This controversy is due to a combination of methodological differences (reviewed in [7]), variation in definitions of what constitutes a post-reproductive period, and the fact that post-reproductive lifespan is mathematically constrained to be positive unless all females immediately die after reproduction. Individual-based measures are often correlated with overall longevity and may introduce biases through exclusion of individuals considered to have died before being able to reproduce again (see [7] for further discussion of these issues).

Methods

Results

Discussion

Conclusion