Less Attractive

But More Successful in Attracting High Quality Males

Sexual dimorphism in which males and females differ from each other morphologically is widespread among animals and occurs in many groups, e.g., to name but a few: insects, spiders, fishes, birds and even mammals. It puzzled already Charles Darwin why, for instance, some male moths and male beetles frequently had much larger and seemingly better developed antennae (which during Darwin’s time had not been identified as the sensors for odours, but were seen merely as touch receptors).  He and many other researchers felt that the larger development of certain structures in male animals served as ‘advertisements of prowess and vitality’ and indicated to a female the presence of a superior sex partner. That enlargements and greater conspicuousness of structures increased the chances of being recognized (and preyed upon) could, of course, have been a handicap, which is why Zahavi suggested females chose males because they had survived and reached sexual maturity despite being more vulnerable and in greater danger of being attacked than cryptic ones.

What, according to Australian researchers Mark Elgar et al. had not fully been considered till 2018 in the discussion of sexual dimorphisms and attractiveness (at least with regard to insects in which female individuals release some odoriferous chemicals known as pheromones) was the role sensors play. Large and often plumose antennae in insects contain receptors that detect the presence of molecules in the air, i.e. chemicals released by plants, possible food items and, of course, females in case of moths and many beetles. Some of these sensors or so incredibly sensitive that only a few key molecules need to be present for the males to respond to. In case of some moths, a male can smell a female 10 km away. To maintain the sensitivity of sense organs, whether they be mechano-, photo- or chemoreceptors and to process the information received by them is energetically expensive as my former colleague Dr Simon Laughlin at Cambridge University has shown. Consequently, as has been argued, those males with the most highly sensitive sensors are more ‘valuable’ than males, whose sensors only respond to the most obvious and strongest stimulation. But how to eliminate the latter and favour the former?

Maybe some female moths and beetles that attract their males with pheromones have found a way. If a female sends out a strong pheromone signal, the latter will disperse widely and reach a huge number of possible male partners, including those that have rather insensitive “noses”, in other words do not exactly possess a highly developed sensory system. But they are not the males the females want to have as “fathers for their babies”; the females want those males that are alert to the slightest of stimulation and what better way to get their attention than to emit only a fraction of the pheromone that is so successful in reaching all kinds of males near and far? This is apparently a strategy that works, because young females which because of their age can afford to be choosy, use it, while older females that have not obtained a partner increase the amount of pheromone they emit.

Whether this idea of “less being more” can be applied to vertebrates as well has not been tested (yet). However, if we take an unbiased, objective look at our own species, aren’t we observing that it is those who are beautiful and attractive as young individuals that need less make-up, lipstick, and other beauty-enhancing stuff than physically less fortunate females, who want to become more noticeable to men through exaggerations? And isn’t the use of perfume, wrinkle-hiding cream, eye-catching jewellery increasing among older females? Perhaps there is indeed a parallel to female moths and beetles. But what about the males that the females attract? There, too, could be a parallel: the less sharply observant and somewhat superficial males do not see beyond the make-up on the skin, the red colour of the lips and the artificially enhanced signals of the female. It takes “sensitivity” and “smartness” (as in case of the male moths and beetles), for males to identify a quality female. And yet, it seems enhanced female signalling is there to stay  –  in moths, beetles and humans as well.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

Dogmas Are There to Be Challenged

Even those linked to Nobel Laureates

There are few events in a scientist’s life more satisfying and rewarding than to overturn a dogma, in other words a viewpoint or belief that is unreservedly accepted by almost everybody. Older dogmata in the life sciences that were proved wrong include the teachings of spontaneous generation or the Lamarckian inheritance of acquired characters; more recent ones would be the rejection that stomach ulcers could be caused by bacteria, that insects are poor food for humans, that mature cells under no circumstances can give rise to different cell types, etc. One could also include the Nobel laureate Karl v. Frisch’s conclusions on how honey bees perceive colours of the flowers they visit for pollen and nectar. The name of this Austrian scientist is inextricably connected with the theory of tri-chromatic vision in bees, used to distinguish colours with. However, unlike human colour vision based on red, green and blue, the dogma of honey bee vision involves  green, blue and ultraviolet. 

Not so, states Emeritus Professor G.A. Horridge of the Australian National University.  After having tested honey bees and their colour vision capacity under a variety of different experimental conditions and after having studied the older literature on often very carefully conducted but rarely cited bee experiments, he concluded that the dogma of the honey bee’s trichromatic vision needed to be debunked. What then are Horridge’s (for some people ‘heretic’) arguments and how does he explain the bee’s ability to distinguish flowers of different shapes and colours?

Professor Horridge quotes the thorough more than 100 year old work by the Munich Professor of Ophthalmology Carl von Hess, who, based on many weeks of tests with trained bees, contradicted  v. Frisch’s work in 1912 and claimed that the latter’s work on how bees see colours and shapes was sloppy and that v. Frisch’s conclusions had been wrong, for honey bees do not have colour vision like humans or see objects like humans. Such criticism enraged v. Frisch, writing in 1914 “I protest against the unscholarly methods of argument, the wandering logic and underhand methods; Hess should shut up or put up.” (translated by G.A.Horridge from German into English). Hess did publish in 1918 a rebuttal, pointing out that essential evidence that bees saw shapes or colours of flowers in ways humans do was still lacking. Because of v. Frisch’s influence, it seems, further publications critical of his own results were suppressed. According to Horridge, v. Frisch made sure that research by a young woman named Mathilde Hertz and people like Lotmar, Friedlaender, Wiechert and Zerrahn, who worked on bee vision up to 1939 and cast severe doubts on the (by then) accepted “colourful ideas” of v. Frisch, did not receive the attention it deserved. Interestingly, v. Frisch himself apparently never again got involved in investigating colour vision in the honey bee. 

So, what went wrong and what is Prof. Horridge’s alternative? He concludes that trichromatic vision of hues of colour is impossible in the bee and that even though bees have three types of spectral receptors in their eyes (namely UV, blue and green), the UV-channel is used to indicate the direction of the sky, to detect escape routes, open space. He concludes that UV receptors can be ruled out as a factor in bee colour vision because UV inhibits the detection of white. The green sensitive receptors, he says he showed, do not see coloured areas or grey, but only detect, measure and learn edge directions and widths between edges. What this means is that bee vision is not trichromatic (as the dogma would have it), but monochromatic in blue and that when a bee approaches a target, it first determines, to within 5%, the total amount of blue content to compare that with another target. Green, not being detected as a colour, is measured as the total modulation of the green receptors in the bee’s eye as it scans across (especially vertical) edges. The combination of the two inputs: total blue content and green modulation, according to Horridge, is sufficient to distinguish between any two targets’ shape and colour without detecting the actual hues as we humans would see them. Would this also explain why so many flowers are red (when in fact bees do not possess a red receptor) and often possess UV-markers? It’s best to read Prof Horridge’s book or to ask the Professor himself on that! To debunk a long-held dogma, if proven, could be a great legacy of his.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2022. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

Some Animals Can Do It

Wouldn’t it be nice if we could do it too and close our ears

The daughter of one of my friend’s has recently learned to swim  –  and she loves it. But what she does not love, is having to shake out the water in her ear after a swim. So, she asked me why we can’t close our ears. Nice question, and I answered I don’t think dogs and cats can close their ears either when they swim and whales and harbour seals (so-called phocids) don’t have any ears at all  -well, at least those parts of the ear that you can see, i.e. the outer part, the so-called “pinna”. But it made me think, because in Antarctica I was surrounded by fur seals (so-called otariid seals) and they all had small, but very prominent ears. Besides, even though whales and phocids lack the pinna, they can certainly hear quite well under water and possess all the inner ear structures (like ear canal, middle ear and cochlea ) that are similar to even our own ears.

All diving animals, whether they be whales, phocids and even walruses (none of which possessing external ears) or whether they be those with ears such as otariid fur seals and sea lions or otters and hippopotamuses or the aquatic insectivores known as desmans or egg-laying platypuses: they all can hear under as well as above water. However those with visible ears have means to prevent water from entering their ears and hippopotamuses, for example, angulate their small ears backward and close the ear canal by contraction when they dive; desmans achieve the same result by glandular swellings to seal up their ears temporarily and eared seals like fur seals are capable of controlling the state of their ear canals by muscles when diving or when in air. Rising pressure expels the air that happens to be trapped in the outer ear when the fur seal dives and improves underwater hearing. 

In the aquatic mammals that lack an outer and visible ear like whales, harbour or hooded seals and walruses, adaptations to hearing under water are a little different. There is no need to close the outer ear, because there isn’t one. However, hollow structures like ear canals and the air-filled middle ear (connected via the Eustachian tube to the respiratory tract) need to be protected against a collapse during a dive owing to the increasing pressure.  During dives the tissues around the external ear canal and the middle ear fill with blood to occupy any air spaces and as the air spaces get smaller and smaller with depth, hearing under water improves. In phocid seals the middle ear bones are less separated from the skull than those of the fur seals, and that enhances sound amplification, but fur seals are better in determining the direction of a sound under water. The underwater sounds of the latter range from about 1000 to 4000 Hz, but those of whales and phocids cover ranges from 40 to 8 kHz and 100 to 15 kHz, respectively. Some species of dolphins (with very long ear canals) can even hear frequencies across the enormous range of about 100 to 150 kHz.

Other adaptations include copious amounts of earwax (especially in the ears of walruses) and elastic fibres in the walls of the Eustachian tube. An interesting adaptation to strengthen the ear canal lateral to the eardrum (the well known tympanic membrane that causes the problem in our ears when it’s blocked and we are in an aeroplane or are diving) are the so-called exostoses and the latter are thought to facilitate deep dives into very cold water. Exostoses do sometimes also occur in humans, where they are often referred to as “surfer’s ear” and involve benign, non-tumorous, firm and sessile, often bilaterally symmetric, nodular bony growths within the ear canal. Their occurrence seems to be closely connected with the amount of time a person spends surfing or diving in cold seawater. Can this similarity to phocid seals and other diving animals be used by people who champion the idea that during the evolution of humans there was an aquatic period? It’s a long shot and I doubt it very much. But what this blog has shown once again is that responding to a child’s question is something not to dodge, because it makes you think. And that can only be something positive.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2022. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.