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.

Sexy Angiosperm Plants

Charles Darwin’s abominable mystery

Students are often confronted with the statement that the symbiosis between bees and flowers is a prime example of co-evolution, an evolution, which saw both groups appear and evolve together. This, however, has not happened. The origins of the flowering plants of the angiosperm lineage that subsequently began to dominate the terrestrial flora, is known to have roughly coincided with the beginning of the Cretaceous Period, i.e. approx. 130 million years ago. Social bees, however, did not appear until about 30 million years ago in the Oligocene era of the Tertiary. The discrepancy prompted Darwin to make his famous utterance of the “abominable mystery of the angiosperms” (= flowering plants) and, by extension, of the so-called co-evolution between inflorescences and honey bees.

There are, however, other difficulties to explain features of the angiosperms. Most of them possess hermaphroditic flowers with male (stamens with anthers and pollen) as well as female (pistil with stigma and ovary below) parts. Some plants possess separate male and female flowers on the same individual plant and are termed “monoecious”, while species (roughly 10% of all flowering plants) in which separate male and female individual plants are the rule, are known as “dioecious”. If male and female structures are present in the same flower, pollination by insects is not a problem and even if there are separate male and female flowers on the same plant, it’s not such a big deal. If, however, there are considerable distances between male and female plants to overcome by pollinating insects, Nature needs to have come up with some solution. Unsurprisingly, temperate dioecious species are often wind- or water pollinated, but in tropical forests with little wind, bees, beetles, flies and moths, i.e. strong fliers, are more important. Floral rewards comprise pollen, nectar, mucilage, nutritious tissues, and resins, but about one third of the species offer no reward in the female flower morphs. 

Some of the better known insect-pollinated, yet dioecious, species include, to name but a few, kiwi-fruit, wild grapes, spinach, asparagus, willow, polar, hemp, etc. For these plants to be pollinated it would make little sense if the pollinating insects would first visit female flowers and after that the pollen-bearing male flowers; the sequence needs to be male flowers first to pick up pollen followed by a visit to a female flower to deliver the pollen. To make sure of that, male inflorescences are usually somewhat larger and visually more attractive. Naïve, inexperienced foraging bees notice them easily and of course visit them to obtain sugary nectar. They pick up pollen from them and remember the flowers’ scent. And now comes the lure of the female flowers: although it’s possible to confuse them with the male flowers even though the former are smaller in size and less sightly, their smell is far more intense and alluring so that the bees hoping to find another pollen-rich nectar containing male flower visit them in error and deliver to them the pollen they had picked up earlier.

Differences between male and female plants can even affect not only the flowers but also the seeds as in the knotweed Rumex nivalus where male seeds are heavier and germinate before those of the female seeds or as in the spinach with its heavier male seeds and the White Campion (Silene latifolia) , in which male and female seeds differ with regard to dormancy and survival. In the South African Leucodendron xanthoconus male plants have more branches and smaller leaves than females and generally speaking in long-lived dioecious species (but in short-lived ones it’s the opposite) male individuals often exceed the females in vigour. Now, after all this, who would still believe that sex and reproduction in plants must be less interesting than reproduction in animals? I think this blog dispels that myth. 

© 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.

Compulsive Hoarding

A disorder with ancient roots?

I think we all know some people who are ever so ready to throw away something they no longer fancy or to discard some item if a newer version is available. But we may also know people, who behave in exactly the opposite way: they never throw away anything but keep and store and guard even things that no longer seem useful. That kind of behaviour can be compared to what is termed “hoarding” and, if compulsive, it is now considered a mental disorder of the “obsessive-compulsive” nature. But is it an atavism, a re-surfacing of an ancient trait with roots in the animal kingdom as suggested by Sandro René Pinto de Sousa Miguel, Rodrigo Ligabue-Braun of Porto Alegre in Brazil, akin to narcolepsy and quadripedalism in humans, which have also been linked to atavisms?

Hoarding, especially of food but occasionally also of material or other items, is certainly common in the animal kingdom and helps individuals survive lean periods. And immediately La Fontaine’s famous poem “La cigale et al fourmi” that I had to learn as a pupil during my High School French lesson, comes to mind. Indeed, there are several examples of invertebrates that store or cache food or, in the case of leaf cutter ants, even collect and tend inedible leaves to grow on them edible fungi. Honey bees are so successful (unlike the equally social hornets) and survive the winter, because they prepare and store food for the cold season. Although not usually overwintering, spiders, too, can often be seen in summer to keep numerous wrapped-up insect prey in their orb-webs for later use.

More obvious hoarders are found amongst our feathered friends and some of them behave seemingly intelligently when they attempt to hide food items and then firstly look around to make sure no other bird observes where they hide their treasures. A behaviour such as this has been reported from Corvus corax ravens by the Austrian researchers T. Bugnyar and K. Kotrschal and also the Eurasian jay Garrulus glandarius by the Cambridge University scientists E.W. Legg and N.S. Clayton. North American woodpeckers are less selfish and establish food stores that are accessible to other wood peckers, but whether shrikes like Lanius collurio allow other shrikes to access the insects, and even small mice and lizards, they store on thorns in the open, I do not know. However, policing food stores such as these, which are visible and in the open would be quite a task. Besides, hoarders with multiple caches (to reduce pilferage) run the risk of forgetting some of their troves, and in the case of forgotten and buried seeds, help spreading trees. A special facet of hoarding is that, which is represented by the New Caledonian crow Corvus moneduloides that bends twigs into hooks to extract grubs from wooden trunks with and then hides and hoards these precious tools.

Proverbial hoarders are the hamsters. It has been reported that European hamsters of the species Cricetus cricetus may have many kg of grain (up to 60 kg !) in their nests  – and it’s all for themselves (and their offspring). Packrats and squirrels, too, are well known hoarders and beavers establish food stores that can be used by anyone of their family. Some of the best-studied mammalian hoarders are shrews, especially a species by the name of Blarina brevicauda from the northeastern region of North America. To survive the winter they collect and cache food items in their burrows that can contain seeds and dry fruit, invertebrates and even small mice. It was this species of shrew that the Brazilian researchers, mentioned above, compared obsessive human hoarding with to suggest that the latter was an atavism going back to ancient evolutionary roots. The problem is, human hoarders more often than once, not just hoard food, but inedibles like coins, stamps, toys, clothes, buttons etc., and some are even known to hoard and guard some really weird and useless things like used underwear, smelly socks, cigarette buds, etc. Do animals do that also? Well, in the Statistical Manual of Mental Disorders, 5th edition (DSM-5) such behaviours in humans are now classified as a mental disorder. Maybe it’s risky then to mention I collect coins with animals on them.

© 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.