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| Erebid Moth |
What
chronotype are you? In other words are you a lark or an owl? Personally I’m a
lark; wide awake and raring to go at sunrise and dozy as a dormouse by sunset. About
half of us, apparently, are neither. Today I thought we’d stroll down the hill
and look at things from a slightly different perspective, that of rhythm.
As
human beings we are generally diurnal creatures (active during the day) whereas
other creatures such as bushbabies, tarsiers and my twenty year old niece (who,
I am convinced, sleeps in a coffin during the hours of daylight) are nocturnal
(active at night). Many beetles and moths (such as this Erebid which was on the
terrace the other night), as well as your pet moggy, are crepuscular (active in
the hours of twilight). These circadian
or daily rhythms which are linked to the rising and setting of the sun, and to
a lesser extent the moon, are just one of the rhythms of life which governs the
existence of every living thing on the planet.
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| Four O'clock Flower |
It
is not only animals that exhibit these circadian rhythms; plants do too.
Certain baobab trees and at least one species of jasmine are night flowering in
order to be pollinated by nocturnal creatures. Some flowers such as salsify
open in the mornings and this one, the four o’clock flower (an introduced plant
to Crete), opens in the late afternoon and produces a heady scent throughout
the night. Pollination isn’t something that happens by chance, plants have evolved
to attract certain pollinators not only by size, shape, colour and scent but also by the time of day when they flower.
Back in 1751the Swedish botanist and father of modern taxonomy Carl Linnaeus even designed a flower clock by placing flowers at appropriate intervals around the face depending upon their opening times.
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| Willow Warbler |
Listen.
Do you hear that questioning “oo-whit?” call
coming from the carob tree over there? I think that’s a willow warbler. Yes,
there it is. It’s just alighted in the tamarisk trees. Willow warblers are highly migratory birds
and this one will be on his way from northern Europe to central Africa.
Migration is another one of the rhythms of life, in this case an infradian
rhythm which describes any rhythm that occurs in a time period longer than a
day.
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| Beech Marten Trails and Scat |
You
won’t be surprised to learn that if there are infradian rhythms that last
longer than a day there are also ultradian rhythms that last less than a day.
Which brings us back to the naturalists’ favourite topic – pooh. Over there on
the far bank of the gully you can see a beech marten’s den with tracks leading
down to the water (we won’t see the marten as he is a crepuscular/nocturnal
creature and won’t be out for a good few hours yet). And down here by my feet
is a scat which, by the look of the seeds embedded within it, belongs to the
owner of the den. Both eating and defecation are examples of ultradian rhythms.
Eating is stimulated by an increase in appetite which involves the release of
certain chemicals within the body and there are other chemicals which suppress
bowel movements when an animal is asleep (typically between 10.30pm and 8.30am
in us humans).
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| Moonrise |
I
see that the moon is just rising in the west. For us land animals this is of
minor importance but for sea life it is more important than the sun. There are
three lunar cycles: the lunar day which lasts for 24 hours and 50 minutes.
(Incidentally some research into human circadian rhythms suggests that most
people prefer a 25 hour day which makes you wonder if these rhythms of ours
have been in-built since we were sea creatures); the semilunar cycle which
lasts for 14.8 days; and the lunar month which is 29.5 days. If we trot down to
Ferma harbour I may be able to introduce you to a little animal that can help
to illustrate this.
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| Fireworm |
Here
we are, this little guy is a fireworm. He is a relative of the common earthworm
(they both have a body cavity, moveable bristles and bodies divided into
segments by transverse rings) and he’s called a fireworm because those white
bristles running down his side glow white when he feels threatened and, in some
species, can give a nasty sting. Research on a close cousin, the Bermuda
fireworm has revealed that he breeds about 55 minutes after sunset, for about
half an hour, only when there is no moon in the sky during the early part of
the night. So he is being governed by the lunar day with the transition from
sunlight to moonlight and also the lunar month as he chooses to mate when there
is no moon visible which occurs from two or three days after the full moon
until the new moon. Obviously a very shy creature that doesn’t like making love
with the light on – of any sort.
So
there you have it, a short introduction to chronobiology or the rhythms of
life. Yet another fascinating aspect of the natural world around us. Meanwhile
I’m still waiting for that special event that I mentioned a couple of weeks
ago. That too is chronobiological in nature but as I did not witness the
beginning of the cycle I cannot predict the next stage with any accuracy. I’ll
keep monitoring the situation and let you know when it occurs either through
the blog or in the Facebook
Naturalists Group which you are welcome to join if you
haven’t already done so. Until next week – happy hunting.
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LINKS:
Naturalists
(the facebook page that accompanies this blog)
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