Parents show bias in sibling rivalry, says study

Dec 19, 2007
Beetle
The parent beetle feeding a young grub. Credit: Allen Moore

Most parents would hotly deny favouring one child over another but new research suggests they may have little choice in the matter.

Biologists studying a unique species of beetle that raises and cares for its young have found that parents instinctively favour the oldest offspring.

The University of Manchester research – published in Ecology this month – supports the findings of studies carried out on human families but is significant in that it suggests a wholly natural tendency towards older siblings.

“The burying beetle Nicrophorus vespilloides has a similar family structure to that of a human family unit in that there are two parents, a number of offspring and interactions between parents and their young,” said Dr Per Smiseth, who led the research in the University’s Faculty of Life Sciences.

“Of course human families are more complex and parent-child relationships are much more sophisticated. However, studying this beetle can help us understand the basic biological principles of how family relationships work.

“Our study looked at how the parent beetles mediate competition between different aged offspring compared to what happens when the young were left to fend for themselves and indicates that parental decisions are important in determining the outcome of competition between offspring.”

The beetles, which are native to Britain, give birth to a batch of about 20 young in the carcass of a dead animal over a period of 30 hours. The parents feed the young grubs on regurgitated flesh from the carcass.

The young beetles are able to feed themselves but they grow more quickly and become larger when fed by their parents. By generating experimental broods comprising two sets of offspring, one set of older grubs and one younger set, the scientists were able to study their development, first with the parents present and then when left to fend for themselves.

“When both sets of grubs were left to fend for themselves they grew at the same rate and matured to an equal size,” said Dr Smiseth, whose research is funded by the Natural Environment Research Council and the Medical Research Council.

“However, when we allow the parents to remain with the offspring, there is clear favouritism towards the older siblings, which grow at a faster rate as they take the lion’s share of their parents’ offerings.”

The team believes there are two explanations for the behaviour: the first is that the parents attach more value to the older offspring as their maturity gives them a better chance of survival than their younger siblings.

The second explanation is that the older grubs, being stronger, are able to dominate their younger rivals and, in doing so, better attract the attention of the parents when begging for food.

“Even if this second theory is true, the parents are still complicit in the bias towards the older siblings,” said Dr Smiseth. “However, the true answer is probably some combination of the two explanations.

“The research tells us something about the relationships within families. We have this view that families are harmonious and that the overriding concern is to help one another. This is true to an extent but it’s not to say that families are not without conflict, especially if the resources cannot be divided equitably.”

Source: University of Manchester

Explore further: Honey bees sting Texas man about 1,000 times

add to favorites email to friend print save as pdf

Related Stories

Biologists link sexual selection and placenta formation

Jul 09, 2014

Sexual selection refers to species' selection for traits that are attractive to the opposite sex. This special type of natural selection enhances opportunities to mate, the tail of male peacocks being an ...

Who's your daddy? Researchers program computer to find out

Jun 19, 2014

A University of Central Florida research team has developed a facial recognition tool that promises to be useful in rapidly matching pictures of children with their biological parents and in potentially identifying ...

Father's age influences rate of evolution

Jun 12, 2014

The offspring of chimpanzees inherit 90% of new mutations from their father, and just 10% from their mother, a finding which demonstrates how mutation differs between humans and our closest living relatives, ...

Marketing to net mums

Apr 29, 2014

Mums on the net should be the focus of those carrying out market research as it turns out that the old word-of-mouth benefits to sales are stronger than ever now that the school gathering places, shops and mother and child ...

Recommended for you

Study indicates large raptors in Africa used for bushmeat

3 minutes ago

Bushmeat, the use of native animal species for food or commercial food sale, has been heavily documented to be a significant factor in the decline of many species of primates and other mammals. However, a new study indicates ...

The microbes make the sake brewery

59 minutes ago

A sake brewery has its own microbial terroir, meaning the microbial populations found on surfaces in the facility resemble those found in the product, creating the final flavor according to research published ahead of print ...

Fighting bacteria—with viruses

1 hour ago

Research published today in PLOS Pathogens reveals how viruses called bacteriophages destroy the bacterium Clostridium difficile (C. diff), which is becoming a serious problem in hospitals and healthcare institutes, due to its re ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

legendmoth
5 / 5 (1) Dec 19, 2007
When left to fend for themselves why does the oldest sibling's strength not play a part? If that is a factor then it would seem that the oldest would dominate his siblings even without parents around.
gopher65
not rated yet Dec 19, 2007
Good point legendmoth. They probably meant to say that the Oldest's strength acts as positive feedback to the biased nature of the parents.

IE, the parents feed the Oldest more, so it grows slightly faster, and therefore is able to out-compete its younger siblings for more parental attention, which in turn makes it grow even faster, etcetc.