̽��ֱ�� of Cambridge - reproductive strategies

Mind Over Chatter: ̽��ֱ��future of reproduction

ns480 — Thu, 27 May 2021 12:41:58 +0000

Season 2, episode 6

Our reproductive capabilities are changing in exciting ways, altering our fundamental understanding of fertility, reproduction, and even parenthood.

In this episode of Mind Over Chatter, we ask our guests what the consequences of novel reproductive technologies are likely to be, and how they will impact the future of human reproduction.

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We cover topics ranging from egg-freezing, so-called ‘three-parent-babies, and the importance of studying the embryonic development of primates.

Historical demographer, Dr Alice Reid, who researches fertility, mortality and health in the late nineteenth and early twentieth centuries, tells us how reproduction has changed over the last 200 years and how it has been influenced by improvements in gender equality, as well as discussing the likely demographic impact of assisted reproduction.

Dr Lucy Van de Wiel, whose research focuses on the social and cultural analysis of assisted reproductive technologies such as egg freezing, introduces the important ways in which reproductive technologies must be considered in the context of wide social and political issues.

Finally, Dr Thorsten Boroviak shares his cutting-edge research on developing new reproductive technologies – the ability to generate your own egg or sperm from any cell of your body – and the importance of studying the embryonic development of primates.

Key points:

[2:10]- change of human reproduction over the last 200 years

[5:45]- egg freezing and changing meaning of what it means to be ‘fertile’

[12:05]- higher levels of gender equity can produce higher levels of fertility

[23:19]- generating eggs and sperms from any human cell

[24:02]- can a man produce an egg?

[40:37]- when should one freeze their eggs?

[64:54]- reproductive justice and reproductive equity. Ensuring reproductive autonomy while ensuring non-exploitation

[65:59]- Final question: what is the most exciting thing that will happen to humankind in the future?

Mind Over Chatter: ̽��ֱ��Cambridge ̽��ֱ�� Podcast

Calls vs. balls: monkeys with more impressive roars produce less sperm

fpjl2 — Thu, 22 Oct 2015 16:02:52 +0000

Howler monkeys are about the size of a small dog, weighing around seven kilos, yet they are among the loudest terrestrial animals on the planet, and can roar at a similar acoustic frequency to tigers.

Evolution has given these otherwise lethargic creatures a complex and powerful vocal system. For males, a critical function of the roar is for mating: to attract females and scare off rival males.

But not all male howler monkeys have been equally endowed. New research on howler species has revealed an evolutionary “trade-off” between investments in the size of the male hyoid – the bulbous, hollow throat bone that allows the howlers’ guttural roar to resonate – and in the size of reproductive organs, namely the testes.

̽��ֱ��bigger a male howler’s vocal organ, and the deeper and more imposing roar they possess, the smaller their testes and the less sperm they can produce.

Researchers found that the trade-off corresponds to the mating systems of different howler species. Males with large hyoids and deeper roars but more diminutive testes live in small social groups with often only one male dominating a number of females – a “harem” social model.

Males with bigger testes and smaller hyoids live in large groups with up to five or six males, and females mate with all males in the group. These males don’t have exclusive access to females, and the battle for reproduction is geared more towards “sperm competition”: quantity and quality of sperm.

̽��ֱ��findings, published today in the journal Current Biology, are a further example of sexual selection say the researchers – a theory first proposed by Charles Darwin in 1871 – and in particular the evolutionary trade-off between “pre- and post-copulatory reproductive strategies”: traits that help males compete for access to mates versus those that help males compete to fertilise eggs.

“In evolutionary terms, all males strive to have as many offspring as they can, but when it comes to reproduction you can’t have everything,” said Dr Jacob Dunn, from the ̽��ֱ�� of Cambridge’s Division of Biological Anthropology, who led the new study.

“There is evidence in other animals that when males invest in large bodies, bright colours, or weaponry such as horns or long canines, they are unable to also invest in reproductive traits. However, this is the first evidence in any species for a trade-off between vocal investment and sperm production,” he said.

In biology, trade-offs are said to exist when one trait cannot increase without a decrease in another. However, Dunn says that it’s not yet clear exactly how the evolutionary trade-off in male howler monkeys works.

“It may be that investment in developing a large vocal organ and roaring is so costly that there is simply not enough energy left to invest in testes. Alternatively, using a large vocal organ for roaring may be so effective at deterring rival males that there is no need to invest in large testes,” he said.

Along with collecting data on the average testes size across howler species, the researchers also used 3-D laser scans to analyse the size of over 250 hyoids – finding a ten-fold variation from the smallest to the largest howler throat bone. ̽��ֱ��team also conducted in-depth acoustic analyses of a number of howler roars.

“ ̽��ֱ��vocal folds of a howler monkey are three times longer than in a human, yet they are ten times smaller than us, with a hyoid bone uniquely adapted to resonate sound and exaggerate their size,” said Dunn.

“ ̽��ֱ��results of our acoustic analyses show that howler monkeys produce roars at a similar frequency as tigers, which is far lower than we would have predicted from their body size, yet exactly what would be predicted from measuring their giant vocal folds.”

This vocal system means that howlers give the acoustic impression of animals with much larger bodies, and can indeed roar louder and deeper than creatures ten times their size. ̽��ֱ��unnerving sound of a howler chorus ringing out across forests of Central and South America has long fascinated humans – from ancient Mayans to modern primatologists – and can carry as far as five kilometres through dense rainforest.

Charles Darwin was fascinated by the “wonderfully powerful” vocal organs of the howler monkey, despite describing their chorus as a “dreadful concert” in ̽��ֱ��Descent of Man.

̽��ֱ��new Cambridge research continues to show just how accurate Darwin was when he wrote in On the Origin of Species: “ ̽��ֱ��whole organism is so tied together that when slight variations in one part occur, and are accumulated through natural selection, other parts become modified.”

Evolutionary ‘trade-off’ between size of throat and testes discovered in howler monkeys furthers Darwin’s theory of sexual selection and corresponds to mating systems: males with larger throats but smaller testes often have exclusive access to females, while those with larger testes share mates.

In evolutionary terms, all males strive to have as many offspring as they can, but when it comes to reproduction you can’t have everything

Jacob Dunn

Calls vs. balls: An evolutionary trade-off

Mariana Raño

A black howler monkey chorus

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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̽��ֱ��importance of grandmothers in the lives of their grandchildren

bjb42 — Thu, 29 Oct 2009 00:00:00 +0000

According to the "Grandmother Hypothesis," post-menopausal women can increase their genetic contribution to future generations by increasing the survivorship of their grandchildren.

While some demographic studies have found evidence for this theory, others have found little support for it.

A team led by biological anthropologist Leslie Knapp in the Department of Biological Anthropology have discovered that a grandmother's effect on grandchildren varies according to their X-chromosome relatedness.

̽��ֱ��research was carried out by a re-evaluation of the birth and death records of seven populations in Asia, North America, Europe and Africa who had lived in different periods dating back to the 17th century.

By specifically looking at child mortality in the first three years of life it was found that a grandmothers' effect on grandchildren varies according to their X-chromosome relatedness.

It was discovered that the effect of a grandmother's presence on grandchild survivorship corresponds relatively with her X-relatedness to the grandchild, which is not equivalent in boys and girls.

Specifically, maternal grandmothers have 25% X relatedness with both grandsons and granddaughters and both grandchildren are equally likely to inherit any one of her X-linked genes.

Contrastingly, paternal grandmothers will pass on one of her X chromosomes to their granddaughters (making them 50% X-related) but she will not pass this chromosome on to her grandson (making them 0% X-related).

Molly Fox, Gates Cambridge Scholar at the Department of Biological Anthropology said : "We suggest that maternal and paternal grandmothers have different incentive to invest in grandsons and granddaughters, due to differences in genetic relatedness.

" ̽��ֱ��presence of a paternal grandmother in all seven of the populations had a harmful effect on grandsons because her presence was linked with an increase in mortality.

"Meanwhile, in six out of seven populations, the paternal grandmother's presence in her granddaughter's early life had a beneficial effect in terms of the risk of mortality. This difference between paternal grandsons and granddaughters would explain a lot of the inconsistencies in previous studies, where the sex of the grandchild was not considered.

"We've only looked at child mortality, and the mechanism itself remains mysterious. Other studies have given evidence against conscious favouritism towards one grandchild or another".

It is widely believed that women live long post-reproductive lives to help care for their grandchildren and the "Grandmother Hypothesis" is based on the fact that women are genetically related to their grandchildren. ̽��ֱ��results suggest that the nature of that genetic relatedness should not be overlooked since boys and girls differ in the percent of genes they share with maternal versus paternal grandmothers based on differences in X-chromosome inheritance.

Biologists use genetic relatedness between family members to explain the evolution of not only longevity, but also altruism, kin investment, offspring recognition, parenting strategies, and tribe formation, and so reconsidering the genetic relatedness between grandmothers and grandchildren has implications throughout the field of human evolution.

It is widely believed that women live long post-reproductive lives to help care for their grandchildren. Now research suggests that the pattern may differ depending on the relationship between grandmother and grandchild.

We suggest that maternal and paternal grandmothers have different incentives to invest in grandsons and granddaughters, due to differences in genetic relatedness.

Molly Fox

dok1 from Flickr

Korean Grandmother and Baby

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