Third cousin couples have the most children and grandchildren

Blogging on Peer-Reviewed ResearchMarriage between closely related cousins is a heavy taboo in many cultures and its critics often cite the higher risk of genetic diseases associated with inbreeding. That risk is certainly apparent for very close relatives, but a new study from Iceland shows that very distant relatives don’t have it easy either. In the long run, they have just as few children and grandchildren as closely related ones.

Shuffling the genetic deck

Indian marriageSex chromosomes aside, every person has two copies of each gene, one inherited from their father and one by their mother. Not every gene will be in correct working order, but there’s a good chance that a faulty copy will be offset by a functional one from the other parent.

However, if two parents are closely related, there’s a higher-than-average chance that they will already share some of the same genes and a similarly increased chance that their child will receive two defective copies. That can be very bad news indeed and in cases where important genes are affected, the results can include miscarriage, birth defects or early death.

Sex, then, is a shuffling of their genetic deck and theoretically the more closely related the partners are, the greater the chance that their child will be dealt a dud hand. And yet, some studies have found that some closely related couples actually do better than distant relatives in terms of the number of children they manage to raise. This trend is certainly unexpected and the big question is whether it is the result of biology or money.

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Malawi cichlids – how aggressive males create diversity

Blogging on Peer-Reviewed ResearchCertain groups of animals show a remarkable capacity for quickly evolving into new species to seize control of unexploited niches in the environment. And among these ecological opportunists, there are few better examples than the cichlids, a group of freshwater fishes that are one of the most varied group of back-boned animals on the planet.

Malawi cichlidsIn the words of Edward O. Wilson, the entire lineage seems “poised to expand.” The Great Lakes of Africa – Tanganyika, Malawi and Victoria – swarm with a multitude of different species; Lake Malawi alone houses over 500 that live nowhere else in the world.

All of these forms arose from a common ancestor in a remarkably short span of time. Now, a new study suggests that this explosive burst of diversity has been partly fuelled by rivalry between hostile males.

Michael Pauers of the Medical College of Wisconsin found that male cichlids have no time for other males that look like them and will bite, butt and threaten those who bear the same colour scheme. In doing so, they encourage diversity in the lake since mutant males with different tints are less likely to be set upon by territorial defenders.

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Sex runs hot and cold – why does temperature control the gender of Jacky dragons?

Blogging on Peer-Reviewed ResearchAmong Jacky dragons, females are both hot and cool, while males are merely luke-warm. For this small Australian lizard, sex is a question of temperature. If its eggs are incubated at low temperatures (23-26ºC) or high ones (30-33ºC), they all hatch as females; anywhere in the idle, and both sexes are born.

Jacky dragonThis strategy – known as ‘temperature-dependent sex determination (TSD) – seems unusual to us, with our neat gender-assigning X and Y chromosomes, but it’s a fairly common one for reptiles. Crocodiles are all-male at high temperatures and all-female at low ones, while turtles flip the rules around and produce more males in cooler climes. Now, a thirty-year old idea to explain this puzzling system has finally been confirmed.

Assigning gender based on temperature is not uncommon but it is nonetheless puzzling. Gender seems like an incredibly fundamental physical trait to leave to something as variable as the temperature of your surroundings. How has such a system evolved? What possible benefits could a species receive by switching control of from chromosomes to the environment?

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The social life of our extinct relatives

Blogging on Peer-Reviewed ResearchOne of our extinct evolutionary cousins, Paranthropus robustus, may have walked like a man but it socialised like a gorilla. Using only fossils, UCL scientists have found that P.robustus males were much larger than females, competed fiercely for mates and led risky lives under heavy threat from predators.

I wrote an article about the cool new finding for Nature Network. Here’s the opening and you can read the full article here.

A single fossil can tell you about the shape, diet and movements of an extinct animal but with enough specimens, you can reconstruct their social lives too.

Charles Lockwood of University College London used an unusually large collection of fossils to peer back in time at the social structures of one of our closest extinct relatives, Paranthropus robustus, which inhabited southern Africa between 1.2 million and 2 million years ago.

Drought drives toads to mate with other species

Blogging on Peer-Reviewed Research

Spadefoot toads seek mates from other species under times of droughtWhen it comes to sex, it makes sense to stick to your own species. Even putting aside our own innate revulsion, inter-species liaisons are a bad idea because they mostly fail to produce any young. In the few instances they do, the hybrid progeny aren’t exactly racing ahead in the survival stakes and are often sterile (think mules).

But having poor unfit young is still better than having no young at all and if an animal’s options are limited, siring a generation of hybrids may be a last resort. Karin Pfennig from the University of North Carolina found that the plains spadefoot toad uses just this strategy in times of need.

Female toads breed just once a year, so it pays for them to make the right choice. According to Pfennig’s work, they take their health and their environment into account when choosing mates. If their bodies are weak and their surroundings are precarious, the benefits that another species’ genes can provide to their young are enough to outweigh the risks.

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Clock gene and moonlight help corals to co-ordinate a mass annual orgy

Every month, at the full moon, tourists and students gather on the beach at Koh Phangan, Thailand for a night of booze, dancing, and debauchery. But the moon-themed antics of these party-goers look positively tepid when compared to those of the Great Barrier Reef’s corals. With the help of two genes and a spot of moonlight, the corals synchronise one of the greatest spectacles of the natural world – a mass annual orgy.

When it comes to sex, corals play a numbers game. Encased in their rocky shells, direct contact is out of the question so they reproduce by releasing millions of eggs and sperm directly into the surrounding water.

This strategy only makes sense if all the corals release their sex cells en masse and sure enough, every individual within a third of a million square kilometres of reef does so during the days after the October full moon.

The corals’ co-ordination would put even the most organised flash-mobs to shame and until now, scientists had no idea how they did it, especially with neither eyes nor brains. Aside from the obvious contribution of moonlight, the only other available clue was that corals seem to be especially sensitive to blue light.

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Bdelloid rotifers – 80 million years without sex

Sex is, on the whole, a good thing. I know it, you know it, and natural selection knows it. But try telling it to bdelloid rotifers. These small invertebrates have survived without sex for some 80 million years.

Bdelloid rotifers under the microscopeWhile many animals, from aphids to Komodo dragons, can reproduce asexually from time to time, it’s incredibly rare to find a group that have abandoned sex altogether. The bdelloid rotifers (pronounced with a silent b) are an exception.

They live in an all-female world and since their discovery, not a single male has ever been found. Genetic studies have confirmed that they are permanently asexual, and females reproduce by spawning clone daughters that are genetically identical to them.

The bdelloids pose a problem for evolutionary biologists, who have struggled to explain how they could make do without a strategy that serves the rest of the animal kingdom very well. Now, Natalia Pouchkina-Stantcheva, Alan Tunnacliffe and colleagues from the University of Cambridge have found out how they do it.

Sexual animals have two copies of each gene that have only minimal differences between them. But the asexual bdelloid lifestyle has uncoupled the fates of each copy in a gene pair, allowing them to evolve in new directions. They get two genes for the price of one.

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