Five factors in a winning
formula (part 1)
(EE, pp. 21-29)
Five factors contributing to insect success
- Small size
- A protective cuticle
- An efficient nervous system
- (blood-brain barrier & sensory neuromotor refinement)
- The evolution of flight
- High reproductive rate
First winning formula - small size
- Insects average 3 mm in length
- e.g., in Brunei rain forest 90% of beetles collected were
under 5 mm in length
- Size has consequences
- F = ma means that insects are not harmed when they frail
from significant heights
Why is it good to be small?
- Small animals are relatively more powerful than large animals
because the cross-sectional area of muscles is relatively large
compared to the mass they are supporting.
- Ants can lift loads many times their own weight, and earwigs
can lift objects 50 times their own weight; humans can lift
weight equal to their own
Small size
allows insects
to adapt to
more “niches”
than larger
animals
But there are limits to size
Although insects were historically large
Two key limits to size
Weight of exoskeleton, especially at moulting?
Moving oxygen to tissue?
How small can insects get?
- Smallest insects are species of parasitic wasps that are
0.2 mm or less from head to tail
- Half the size of protozoans such as Paramecium
What is the limit to small size?
Cell size - animal cells tend to be similar in size due to
internal transport and operational constraints dictated by
surface area and volume ratios. Big animals have lots of
cells, small animals relatively few cells. A minimum
number of cells are probably needed to function properly. Temperature regulation - large surface area to volume
ratio of insects can make it difficult to keep cool and
expensive to keep warm
Lots of physiological and behavioral adaptations are used
to help regulate temperature
Warming mechanisms...
Cooling
mechanisms...
Microclimate matters!
Second winning formula - the cuticle
Integument - the cuticle together
with the epidermis that produces it.
Integument is to a large degree
capable of self repair. It is replaced at each molt.
Some insects can produce new legs
to replace lost limbs! (e.g., some stick
insects)
Cuticle Function (I)
Cuticle Function (II)
What does the cuticle do?
- Integument also protects against pathogens (viruses,
bacteria, and fungi)
- Exoskeleton serves as anchor for muscles and allows
movement (apodemes - internal attachment point of
muscles)
-
Contains chemo- and mechanosensory “devices”
Provides color which can act as a signal.
Sealant to assist with water retention (terrestrial insects)
Tremendous variation in cuticle truly represents the
variation of insects
Integument structure is variable
Insect epidermal cells produce cuticle
Additional epidermal cells: 1) class 1 - involved in pheromone production, 2) class 3 - below the epidermis, they produce cement
Insect cuticle architecture
Cuticle is secretion of the epidermis that covers the whole of the
outside of the body as well as lining ectodermal invaginations
There are two major regions
Chapman (Fig 16.2)
1) inner region (200 µm thick); consists of endocuticle and exocuticle (together the procuticle)
2) outer region (1-4µm thick); consists of and inner and outer region of epicuticle
Chapman (Fig 16.17)
(A visual sequence of events)
The molting process
Examples of molting...
More about molting...
Number of molts varies from 3 or 4 to as many as 50
Danger - protective function of cuticle is lost
Controlled by hormones secreted by brain and
neuroendocrine glands which act on cells of epidermis
and nervous system
Two major processes: Apolysis & Ecdysis
Apolysis - separation of old & new cuticle
Ecdysis - last stage; sloughing of old cuticle