Jun 17, 2021 11:44 PM
(This post was last modified: Jun 18, 2021 03:17 PM by C C.)
Darwin got sexual selection backwards, research suggests
https://theconversation.com/darwin-got-s...sts-162711
EXCERPTS: . . . So why do many birds species have more males, while mammals often have more females? The short answer is that we don’t know. But there are smoking guns.
Some uneven sex ratios can be partially explained by lifespan differences. Female mammals, including humans, usually outlive their male counterparts by a wide margin. In humans, females live on average about 5% longer than males. In African lions and killer whales, the female lifespan is longer by up to 50%.
Predator preferences could also play a part. African lions kill approximately seven times more male than female buffalo, because male buffalo tend to roam alone, whereas females are protected within herds. In contrast, cheetahs kill many more female Thompson’s gazelles than males, presumably because they can outrun female gazelles easier – especially the pregnant ones.
Finally, males and females often suffer differently from parasites and diseases. The COVID-19 pandemic is a striking example of this: the number of infected men and women is similar in most countries, but male patients have higher odds of death compared to female ones.
[...] It’s clear how sexual selection can sometimes create size dimorphism. Knocking out an enemy requires muscular power, while fight endurance requires stamina. So being bigger often means dominating rivals, thereby winning the evolutionary lottery of reproduction.
Analysing 462 different species of reptiles, mammals and birds, our study found a tight association between sexual size dimorphism and sex ratios, vindicating Darwin’s conjectures.
But the trend was the opposite to the one Darwin predicted with his limited evidence. It turns out the most intense sexual selection – indicated by larger males relative to females – occurred in species where there were plenty of females for males to choose from, rather than a scarcity of females as Darwin suggested.
This in no way invalidates Darwin’s theories of natural selection and sexual selection. Our finding simply shows that a different mechanism to the one Darwin proposed is driving mating competition for animals living in sex-skewed populations.
Darwin’s assumption was based on the idea that the most intense competition for mates should occur when there’s a shortage of mating partners. But more recent theories suggest this logic may not be correct, and that sexual selection is actually a system in which the winner takes all.
That means that when there are many potential partners in the population, a top male – in our study, the largest and heaviest – enjoys a disproportionately high payout, fertilising a large number of females at the expense of smaller males, who may not reproduce at all.
We need further studies to help us understand how males and females seek out new partners in male-skewed and female-skewed populations, and in what circumstances ornaments, armaments and sheer size are particularly useful. Such studies could provide us with unprecedented new insights into how nature works, building on Darwin’s original theory of sexual selection... (MORE - missing details)
Alberta now a 'hot spot' for tapeworm that can cause fatal tumours in humans
https://www.cbc.ca/news/canada/edmonton/...-1.6069818
EXCERPTS: Alberta is now a hot spot of a potentially deadly tapeworm passed from wild canines to humans, and many cases of the parasitic infection could be going undetected, warns an infectious disease specialist. "Alberta is clearly the hot spot," said Stan Houston, a University of Alberta professor in the Faculty of Medicine & Dentistry and lead author of a new study detailing a recent cluster of alveolar echinococcosis (AE) cases in Alberta.
[...] Houston's study, published in the American Journal of Tropical Medicine and Hygiene, details 17 cases diagnosed in Alberta between 2013 and 2020, including a man who died of surgical complications from the infection. ... Before the recent surge in Alberta, only two human cases of the disease had been confirmed in North America — one in Manitoba in 1928 and another in Minnesota in 1977, Houston said.
"This remains a pretty rare disease but we should be paying attention to it," Houston said. "It's been found in Saskatchewan and in B.C., but Alberta has had most of the cases."
AE is an infection caused by the European strain of a tiny intestinal tapeworm. It's believed the strain arrived in Canada through imported dogs, Houston said. The parasite is often carried by wild canines, such as coyotes, but domestic dogs can also be a carrier.
Humans can acquire the infection by ingesting food or soil contaminated with worm eggs too small to see. In humans, the disease develops slowly and causes multiplying lesions in the body, usually in the liver.
Treatment involves surgery or a lifelong regimen of medication to keep the lesions in check. The disease is more severe in people who are immunocompromised. Without treatment, the infection is usually fatal... (MORE - spot & diagnose)
https://theconversation.com/darwin-got-s...sts-162711
EXCERPTS: . . . So why do many birds species have more males, while mammals often have more females? The short answer is that we don’t know. But there are smoking guns.
Some uneven sex ratios can be partially explained by lifespan differences. Female mammals, including humans, usually outlive their male counterparts by a wide margin. In humans, females live on average about 5% longer than males. In African lions and killer whales, the female lifespan is longer by up to 50%.
Predator preferences could also play a part. African lions kill approximately seven times more male than female buffalo, because male buffalo tend to roam alone, whereas females are protected within herds. In contrast, cheetahs kill many more female Thompson’s gazelles than males, presumably because they can outrun female gazelles easier – especially the pregnant ones.
Finally, males and females often suffer differently from parasites and diseases. The COVID-19 pandemic is a striking example of this: the number of infected men and women is similar in most countries, but male patients have higher odds of death compared to female ones.
[...] It’s clear how sexual selection can sometimes create size dimorphism. Knocking out an enemy requires muscular power, while fight endurance requires stamina. So being bigger often means dominating rivals, thereby winning the evolutionary lottery of reproduction.
Analysing 462 different species of reptiles, mammals and birds, our study found a tight association between sexual size dimorphism and sex ratios, vindicating Darwin’s conjectures.
But the trend was the opposite to the one Darwin predicted with his limited evidence. It turns out the most intense sexual selection – indicated by larger males relative to females – occurred in species where there were plenty of females for males to choose from, rather than a scarcity of females as Darwin suggested.
This in no way invalidates Darwin’s theories of natural selection and sexual selection. Our finding simply shows that a different mechanism to the one Darwin proposed is driving mating competition for animals living in sex-skewed populations.
Darwin’s assumption was based on the idea that the most intense competition for mates should occur when there’s a shortage of mating partners. But more recent theories suggest this logic may not be correct, and that sexual selection is actually a system in which the winner takes all.
That means that when there are many potential partners in the population, a top male – in our study, the largest and heaviest – enjoys a disproportionately high payout, fertilising a large number of females at the expense of smaller males, who may not reproduce at all.
We need further studies to help us understand how males and females seek out new partners in male-skewed and female-skewed populations, and in what circumstances ornaments, armaments and sheer size are particularly useful. Such studies could provide us with unprecedented new insights into how nature works, building on Darwin’s original theory of sexual selection... (MORE - missing details)
Alberta now a 'hot spot' for tapeworm that can cause fatal tumours in humans
https://www.cbc.ca/news/canada/edmonton/...-1.6069818
EXCERPTS: Alberta is now a hot spot of a potentially deadly tapeworm passed from wild canines to humans, and many cases of the parasitic infection could be going undetected, warns an infectious disease specialist. "Alberta is clearly the hot spot," said Stan Houston, a University of Alberta professor in the Faculty of Medicine & Dentistry and lead author of a new study detailing a recent cluster of alveolar echinococcosis (AE) cases in Alberta.
[...] Houston's study, published in the American Journal of Tropical Medicine and Hygiene, details 17 cases diagnosed in Alberta between 2013 and 2020, including a man who died of surgical complications from the infection. ... Before the recent surge in Alberta, only two human cases of the disease had been confirmed in North America — one in Manitoba in 1928 and another in Minnesota in 1977, Houston said.
"This remains a pretty rare disease but we should be paying attention to it," Houston said. "It's been found in Saskatchewan and in B.C., but Alberta has had most of the cases."
AE is an infection caused by the European strain of a tiny intestinal tapeworm. It's believed the strain arrived in Canada through imported dogs, Houston said. The parasite is often carried by wild canines, such as coyotes, but domestic dogs can also be a carrier.
Humans can acquire the infection by ingesting food or soil contaminated with worm eggs too small to see. In humans, the disease develops slowly and causes multiplying lesions in the body, usually in the liver.
Treatment involves surgery or a lifelong regimen of medication to keep the lesions in check. The disease is more severe in people who are immunocompromised. Without treatment, the infection is usually fatal... (MORE - spot & diagnose)