Hermaphrodites Reproducing Without Males Have Shorter Lifespans

Hermaphrodite nematodes reproducing without the assistance of males have been shown to have shorter lifespans, says a new study published in The American Naturalist.

Colored scanning electron microscopy image of a mating pair of Pristionchus roundworms. Credit: MPI f. Developmental Biology/ Jürgen Berger Read more at: http://phys.org/news/2016-02-males-decreases-lifespan.html#jCp
Two roundworms (Pristionchus species) mating [coloured scanning electron microscopy image]. Photo credits: MPI f. Developmental Biology/ Jürgen Berger
Being a hermaphrodite might have its perks — you don’t need a mate to mate — but, it also decreases lifespan. The new study focuses on Pristionchus nematodes which include species whereby the females have the ability to use the sperm they themselves produce for fertilisation. This comes with a huge price though, argue researchers from the Max Planck Institute of Developmental Biology in Tübingen, Germany. These female hermaphrodites have shorter lifespans, sometimes 50% less than other females.

Interactions between males and females come with certain effects on the biology of a species; for instance, important characteristics pertaining to lifespan and ageing are thought to evolve as a consequence of the ways these relationships are interwoven. This is what the team of scientists are investigating: the evolutionary consequences that arise from alternative mating systems. The latter are an indicator of how life-history evolution is moulded by sexual interactions.

The main aim of the study was to determine whether self-fertilising hermaphrodites would undergo evolved longer lifespans or shorter ones. Different species of nematodes were thus analysed and compared.

The adult lifespans of females and hermaphrodites of 11 species of the Pristionchus nematode were measured. The findings show that hermaphrodites using their own sperms to fertilise their own eggs had a significantly shorter lifespan than their female relatives. Does this mean that shorter life cycles were but the price to pay to be able to reproduce? According to the researchers, it is more than that: the fact that no correlation was found between lifespan and the number of offspring suggests that these differences were not simply the product of a trade-off mediating long life and reproductive investment.

What makes the females and hermaphrodites different from each other in terms of lifespan? The researchers explain that the latter begin reproducing earlier in life since they are able to produce sperm before they reach adulthood; on the other hand, females need time to find males for mating purposes. Another factor to be considered is that females tend to be damaged during mating such that they might need to develop strength to cope with the situation, thus triggering the evolution of the capability of living longer. Another aspect the researchers have mentioned is inbreeding: this might be impeding natural selection among the hermaphrodites, causing the accumulation of disadvantageous mutations. More research is needed to find an exact answer.

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